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Live oak forests, woodlands and savannas in southeastern North America- There are various species (and lower taxa) of Quercus across North America that retain their leaves more-or-less yearlong (or through the cool-season) so as to be described as "evergreen" or "live" oaks. Evergreen or live oaks of one species or another range from the Atlantic Coast at Virginia southward, then along the Gulf Coast, and sporadically westward to the Coast Range of California and Oregon. The evergreen oak of eastern (southeastern) and Gulf coastal North American is the eastern live oak, Virginia live oak, or, simply, live oak (Quercus virginiana). Various forms and varieties of Q. virginiana have been recognized in the region of the Eastern Deciduous Forest of North America. The most distinctive of these varieties of the Eastern Deciduous Forest is Q. virginiana var. maritima, dwarf live oak, which often exist more as a shrub and thus forms shrubland or scrub rather than forest.
The live oak of eastern North America growing farther west along the Gulf Coast, and often extending inland for considerable distance, has had (still has) a confusing if not arbitrary taxonomic treatment. Traditionally the live oak species ranging from Virginia and the Carolinas westward to eastern and central Texas and northward to localized pockets in Oklahoma and Arkansas was regarded as Q. virginiana including the more western and northward live oaks designated as Q. virginiana var. fusiformis (Muller, 1951). Later, Muller (1961, p. 27) revised his previous work and concluded that all Texas plants except for a small portion of those in southeast were of the species, Q. fusiformis. More recent taxonomists in Texas (Correll and Johnston, 1979; Diggs et al, 1999) followed Muller (1961) and other treatments and elevated Q. virginiana var fusiformis to the species status as Q. fusiformis accompanied by such common names as plateau live oak, escarpment live oak, scrub live oak, and west Texas live oak. Q. fusiformis (= Q. virginiana var. fusiformis) varies in size from shrubs to large trees and in morphology from arboreus (true tree) to scrub form. Typically this taxon spreads by rhizomes and/or root sprouts (often these asexual reproductive organs are referred to as root stocks). Diggs et al. (1999, p.716) stated that it was possible that Q. fusiformis was… "only a more xeric and cold tolerant subsepecies of the more widespreat Q. virginiana". That has been the traditional interpretation of this taxon, and it was the one followed herein. Forest and range ecologists have been much more reluctant to distinguis between Q. virginiana and Q. fusiformis than have taxonomists.
The following treatment of live oak (either the classic mesic, eastern Q. virginiana or the xeric [less mesic], western Q. virginiana var. fusiformis) dealt with the tree form of this species either as woodland (= open forest) made up of individual trees (genetic individuals; different genotypes) or as smaller mottes (Texan usage for "grove") in which many to most tree trunks were shoots of the same tree. In the latter case single or distinct tree trunks are individual or separate shoots of the same genetic plant originating from a common rootstock derived from one acorn (single trunks are modules of the same tree distinguished as the same genotype or genetic individual). It is nigh on to impossible to determine if live oak trunks in a motte or closely spaced live oaks in a larger forest or woodland community are several different trees (unique genotypes; each tree from an embryo) or different tree trunks of the same tree (tree trunks from the same embryo; all shoots derived from one acorn). Usually there are some of both sources, but it is generally accepted by ecologists and plant physiologists that most trunks in a live oak motte are of the same tree meaning that a live oak motte is a clonal plant as in the case of quaking aspen (Populus tremuloides). Also, it must be assumed that trees and shrubs in mottes and many of those in the larger woodland tracts have root-grafted so that the local community does have some features of the Clementsian "super organism".
The term woodland rather than forest was used for live oak-dominated range communities because this designation seemed more appropriate (a more apt description) for the more open canopy and, im most instances, only slightly interlocking crowns of mature trees coupled with well-developed herbaceous and shrub-small tree layers in understories. Woodland more than forest seemed to the author to connote more clearly this idea, but at the same time it was possible that the converse was true and that forest was the more relevant or accurate descriptive term. The designation of forest was used by Brown et al. (1998. p. 41) for the Floridian Evergreen (Hammock) Forest biotic community (see below). The Live Oak forest cover (89) of the Society of American Foresters (Eyre, 1980) was described as bottomland forest, but the description for this type clearly included a denser and more species-diverse plant community than the more open vegetational architecture of the Florida hammock and western Gulf of Mexico live oak motte and larger woody communities dominated by live oak.
1. Live oak hammock (hammock is Indian for "shady place")- This is a unique land form and range vegetation type restricted to the southeastern portion of North America, especially Florida. Hammocks are characterized by being fairly level to gently rolling and higher than surrounding land. Yet they are poorly drained and fertile (soils are high in humus) with hardwood communities that are typically dominated by live oak canopy and an understory of cabbage palm (Sabal palmetto), skunk cabbage (Symplocarpus foetidus), carpetgrass (Axonopus affinis), and panicgrasses (Panicum spp.). FRES No. 16 (Oak-Gum-Cypress Ecosystem). There is no Kuchler equivalent for communities this small; the Kuchler system lumped this type in with some other larger unit of which K-81 (Live Oak-Sea Oats) seemed most fitting. SRM 817 (Oak Hammocks). Mixed Hardwood Series 124.1j1 of Floridian Evergreen (Hammock) Forest biotic community 124,1j of Brown et al. (1998). Southern Coastal Plain- Central Florida Ridges and Uplands Ecoregion, 75c (Griffith et al., undated).
2. Interior of a Florida live oak hammock with tell-tale raised yet wet ground—Mid-canopy shrubs include wax myrtle (Myrica cerifera) and American beautyberry (Callicarpa americana) with sparsely scattered saw palmetto (Serenoa repens).FRES No. 16 (Oak-Gum-Cypress Ecosystem). Subunit of K-81 (LiveOak-Sea Oats). SRM 817 Oak Hammocks). Mixed Hardwood Series 124.1j1 in Floridian Evergreen (Hammock) Forest biotic community 124.1j of Brown et al. (1998). Southern Coastal Plain- Central Florida Ridges and Uplands Ecoregion, 75c (Griffith et al., undated).
3. A woodland on the coastal sand prairie- A live oak woodland had developed on the Kenedy sand prairie (Johnston, 1963, p. 460), one form or subtype of Gulf coastal tallgrass prairie inland from the coast but within the Texas Coastal Prairies and Marshes Area. Seen from perspective of Landscape Ecology this range vegetation (these units of hardwood evergreen woodland), ecosystems, and/or landscape elements could be interpreted as patches of live oak woodland in a matrix of seacoast bluestem (Andropogon littoralis= Schizachyrium scoparium var. littorale)- sacahuiste or Gulf cordgrass (Spartina spartae) coastal prairie. From the classical viewpoint of savanna as put forth by Dyksterhuis (1957) this overall grassland-woodland landscape could be seen as a savanna in which units or assemblies of woody vegetation ranging from smaller mottes (Texan for "groves") to extensive "woods" of several hundred acres are the physiogonomic equivalent of vegetation consisting of individual to "a few" trees and/or shrubs isolated on grassland. In other words, this would be a savannah in which the woody elements are larger and include more woody plants (eg. groves) rather than the typical situation of scattered individual trees and/or shrubs. This would not necessarily imply that such a structural or physiogonomic savannah was a successional or genetic (as to origin) savanna, this latter of which is the usual definition or, at least, connotation of an ecotone (a transition) from herbaceous to woody vegetation.
Interpretation of the woody vegetational units perhaps would hinge on whether mottes or woodlands were actually one up to "just a few" genetic plants whose individual stems (trunks or boles) were repeating clonal units or, alternatively, if these groves or woodlands were composed of many genetic individuals (each or most trees as denoted by a single tree trunks were derived from one embryo, that is, one acorn).
Range vegetation shown here was part of what has long been known as the Wild Horse Desert part of the Rio Grande Plains. This native grazing land is a slightly rolling or hummock aeolian plain of sand entitled the "Kenedy loose sand prairie" that consist of different range plant communities as "a tight mosaic of vegetation types..." (Johnston, 1963, p. 460). The uncertain successional status of large live oak mottes like the one shown here that develop on loose sand uplands was mentioned briefly in the caption of the immediately succeeding slide. The present photograph illustrated the spatial arrangement of sandy sachuiste prairie and mottes dominated by live oak that attest to the "very complex mosaic of vegetation types" (Johnston, 1963, p. 460) of the Wild Horse Desert on the Rio Grande Plains.
Norias Division, King Ranch, Kenedy County, Texas. February, late hibernal or early vernal aspect.
4. Live oak motte turned woodland- Exterior view of a live oak woodland or forest (larger than typical live oak motte) situated within seacoast-sacahuista tallgrass coastal prairie. The dominant herbaceous plant growing at perimeter of live oak woodland was Gulf cordgrass or sacahuista. Other tree species present--at rare to trace amounts of canopy cover--werehoney mesquite (Prosopis glandulosa) and common hackberry or sugarberry (Celtis laevigata). Even though crowns of trees produced a fairly closed canopy with considerable interlocking of branches there was a well-developed (e) herbaceous understorey (often consisting of two to three layers) as well as a second (lower) woody layer or understorey of shrubs and small (immature) trees.
Areal extent (acreage) of this live oak-dominated range community was considerably larger than typical live oak mottes and therefore was viewed more as a live oak woodland or forest rather than as a grove of trees within or on a prairie. Perhaps this distinction was arbitrary or even incorrect but, as in the case for fire behavior, at some point size (spatial scale) becomes an ecologically critical feature. Impacts and role of fire would be a case in point. Prairie fires could easily burn under or scorch crowns of small mottes whereas with expansive woodland areas there would places where fire could not reach (ie. as size of live oak-dominated stands increase in area there is increased probability that larger proportions of stands will be unaffected by fire). The situation would be similar for dispersal of plant propagules from outside live oak-dominated stands as well as for penetration of light from edges (vs. through canopy) of live oak stands.
Successional status of mottes on coastal (and sone iinterior tallgrass and mixed) prairies apparently has not been completely established. Johnston (1963) described, quantified, and discussed changes in range vegetation in the much of the area of the Rio Grande Plains, including that part known as the Wild Horse Desert. Based on personal accounts, including that of a longtime ranchman on the Norias Division of King Ranch, Johnston (1963, p. 464) concluded that live oak had so increased on the sandy seacoast bluestem-sacahuiste coastal prairie that previously separate live oak mottes had coalesced and become interconnected. Causes of the shift from more herbaceous to woody vegetation included the "usual suspects" of overgrazing, seed dispersion by livestock, and reduction or cessation of fire were proposed for the increased in woody vegetation, including that of live oak mottes. Notwithstanding brush invasion due to influences of white man, live oak mottes (of much smaller acreage) are native, potential natural, or climax range vegetation.
The range vegetation of both live oak mottes and surrounding Gulf cordgrass or sacahuista sand prairie were samples of two climax (= potential natural) plant communities. Live oak mottes had expanded into range that was formerly "Kenedy loose sand prairie" (Johnston, 1963, p. 460) so that the overall vegetation of this natural grazing ground had departed from climax conditions of the virgin range. Yet species composition, structure, etc. of the two range communities was representative of that of each climax community. A description and discussion of the general or overall range vegetation over much of the Rio Grande Plains was provided by Fulbright in Shiflet (1994) as SRM 719 (Mesquite-Live Oak-Seacoast Bluestem). The Society for Range Management did not offer a separate designation or treatment of live oak motte as a distinct range type. Likewise, the Live Oak forest cover type of the Society of American Foresters (Eyre, 1980) did not include the live oak motte form of the Gulf Coast prairies.
Norias Division, King Ranch, Kenedy County, Texas. February, later hibernal or early vernal aspect. FRES No. 16 (Oak-Gum-Cypress Forest and Woodland Ecosystem). Variant of K- 81 (Live Oak-Sea Oats), Variant of SAF 89 (Live Oak). Alternatively and based on geographic location: FRES No. 32 (Texas Savanna), K-55 (Mesquite-Live Oak Savanna). Live Oak variant of SRM 719 (Mesquite-Live Oak-Seacoast Bluestem). Western Gulf Coastal Plain- Coastal Sand Plain Ecoregion 34d (Griffith et al, 2004).
5. Into the woods we go- Inside a live oak motte with a well-developed (and heavily utilized) herbaceous understorey and a shrub/immature tree layer. Almost all tree trunks where those of live oak (clonal trunks or those of individual genotypes was not determined), but there were a few honey mesquite and sugarberry trees (at least nine out of ten trunks were live oak). There were immature trees of three of these species. Most common (abundant) shrubs were Hercules club that also "goes by" tickle-tongue, pricklyash, pepperbark, and toothache tree (Zanthoxylum clava-herculis), lime pricklyash or colima (Z. fagara), and mustang grape (Vitis mustangensis). The herbaceous layer was made up almost exclusively of numerous grasses including: Gulf cordgrass or sacahuista, seacoast bluestem, tumble windmill grass (Chloris verticillata), and hooded windmillgrass (C. cucullata), red lovegrass (Eragrostis secundiflora ssp. oxylepis),Gulf dune paspalum (Paspalum monostachyum), Canada wildrye (Elymus canadensis), white tridens (Tridens albescens), Texas tridens (T. texanus), redtop panicgrass or thatchgrass (Panicum rigidulum), and Ghiesbreght panicgrass (P. ghiesbreghtii) as well as naturalized King Ranch bluestem (Andropogon ischaemum= Bothriochlor ischaemum) and Guineagrass (Panicum maximum). There were no obvious or conspicuous forbs other than an Aster sp ("go figure").
Norias Division, King Ranch, Kenedy County, Texas. February, late hibernal or early vernal aspect. FRES No. 16 (Oak-Gum-Cypress Woodland and Forest Ecosystem). Variant of K-81 (Live Oak-Sea Oats). Variant of SAF 89 (Live Oak). Alternatively and based on geographic location: FRES No. 32 (Texas Savanna), K-55 (Mesquite-Live Oak Savanna). Live Oak variant of SRM 719 (Mesquite-Live Oak-Seacoast Bluestem). Western Gulf Coastal Plain-Coastal Sand Plain Ecoregion 34d (Griffith et al., 2004).
6. Inside the live oaks- Another view of the interior of an upland (loose sand) live oak woodland or an extensive motte dominated by live oak. Tree cover and density was almost exclusively live oak (of both mature and immature tree trunks), but there were occasional honey mesquite, sugarberry or common hackberry, and least abuncant huisache (Acacia farnesiana= A. smallii). These three species were also of both mature and immature ages. Most abundant shrubs were Hercules-club or tickle-tongue (all leafless short shrubs in foreground), lime pricklyash, and mustang grape. Grasses included the dominants, Gulf cordgrass or sacahuiste and seacoast bluestem plus tumble windmillgrass, hooded windmillgrass, red lovegrass, Gulf dune paspalum, white tridens, Texas tridens, Canada wildrye, redtop pancigrass or thatchgrass, and Ghiesbreght panicgrass plus the naturalized King Ranch bluestem and Guineagrass. Strangely, no forbs other than a species of Aster were obvious.
Norias Division, King Ranch, Kenedy County, Texas. February, late hibernal or early venal aspect. FRES No. 16 (Oak-Gum-Cypress Forest and Woodland Ecosytem). Variant of K-81 (Live Oak-Sea Oats). Variant of SAF 89 (Live Oak). Alternatively and based on geographic location: FRES No. 32 (Texas Savanna), K-55 (Mesquite-Live Oak Savanna). Live Oak variant of SRM 719 (Mesquite- Live Oak-Seacoast Bluestem). Western Gulf Coastal Plain- Coastal Sand Plain Ecorgeion 34d (Griffith et al., 2004).
7. King Ranch? Ya gotta be kiddin'!- Interior of live oak woodland that developed on a surrounding Western Gulf Coast tallgrass prairie. Morphology of trees, including features of branches and crowns, and general architecture (structure and arrangement of vegetation) of a live oak motte of such area (relative spatial scale) and development as to be a woodland. Trees were exclusively live oak except for occasional (rare) mesquite, Texas hackberry or sugarberry, and, least of all, huisache. There was a prominent herbaceous layer composed of coastal prairie grasses and a woody understorey of shrubs like Hercules club, lime pricklyash, and mustang grape. Grass species included isolated individuals of the dominants, Gulf cordgrass and seacoast bluestem, as well as common and hooded windmillgrasses, Gulf dune paspalum, red lovegrass, white and Texas tridens, Canada wildrye, redtop panicgrass or thatchgrass, and Ghiesbreght panicgrass, plus naturalized King Ranch bluestem and Guineagrass. A quick search for forbs was fruitless.
The woodland range shown here does not purport with images of ranches in the popular imagination or perception or as shown in Hollywood Westerns, but there are numerous such live oak mottes and woodlands on large ranches in south Texas,especially those along the Gulf Coast. This scene was on the Norias Division of King Ranch. Live oak woodland range like this furnishes outstanding habitat for the Rio Grande turkey (Meleagris gallopavo intermedia) as well as providing shade for cattle and horses like the renowed Santa Gertrudis and sorrel Quarter Horses of the famous King Ranch. Live oak mottes such as that presented here are frequently the major roosts for Rio Grande wild turkey. This habitat in relation to wild turkey production, especially on King Ranch, has been studied intensively by numerous wildlife scientists at the Caesar Kleberg Wildlife Research Institute Texas A&M University, Kingsville, Texas.
Kenedy County, Texas. February, later hibernal or early vernal aspect. FRES No. (Oak-Gum-Cypress Woodland and Forest Ecosystem). Variant of K-89 (Live Oak). Variant of SAF 89 (Live Oak). Alternatively and based on geographic location: FRES No. 32 (Texas Savanna), K-55 (Mesquite-Live Oak Savanna). Live Oak variant of SRM 719 (Mesquite-Live Oak-Seacoast Bluestem). Western Gulf Coastal Plain-Coastal Sand Plain Ecoregion 34d (Griffith et al, 2004).
8. Crowding an ole patriarch- An old-growth speciment live oak with a unnaturally high (man-caused increase in) cover of understorey trees and shrubs. The well-developed lower tree and shrub layer was clearly a recent (hence almost assuredly anthropogenic) woody invasion. Great spreading limbs of the "big momma" or "gran'paw" live oak were undeniable proof that this ancient tree developed in the open (ie. in absence of crowding). The small-sized (relatively young) understorey trees and shrubs attested to recent establishment of these individuals suggesting absence of fire (at least low fire frequency), perhaps combined with overgrazing or periodic overuse that reduced grass cover. Most of the leafed-out shrubs were honey mesquite (eg. larger shrubs at far-right foreground with trunks inclined to the right) but there were also some huisache. Texas sugarberry or common hackberry was also present though largely dormant.
The multi-stemmed shrub with smooth, light-grey bark was lime pricklyash with an accompaning and readily identified mustang grape with its serpentine single-stem covered by dark, deeply furrowed bark. These shrubs were the subject of the next photograph.
Norias Division, King Ranch, Kenedy County, Texas. February, later hibernal or early vernal aspect. FRES No.16 (Oak-Gum-Cypress). K-89 (Live Oak). Variant of SAF 89 (Live Oak). Alternatively and based on geographic location: FRES No. 32 (Texas Savanna), K-55 (Mesquite-Live Oak Savanna). Live Oak variant of SRM 719 (Mesquite-Live Oak-Seacoast Bluestem). Western Gulf Coastal Plain-Coastal Sand Plain Ecoregion 34d (Griffith et al., 2004).
9. Prickly and twisted invaders- Close-up of lime pricklyash and mustang grape that had invaded the undersrtorey of a live oak motte on the sandy plains of the Wild Horse Desert in Rio Grande Plains. Age of these shrubs was not determined, but they were relatively young having not yet grown to height of first horizonal limb of an old live oak under the canopy of which these plants were growing. (This was presented clearly in the immediately preceding photograph.)
Successional status of these invading shrubs was unclear, but their relative youth in comparison to the obvious age of the large live oak indicated that lime pricklyash, mustang grape (as well as mesquite and huisache) had established after the live oak had reached adult size. The terms invasion, invaders, and invading shrubs could have one or two meanings in this usage, only one of which was certain. The certain meaning or usage of invasion referred to movement of plants from one area into another and subsequent successful establishment of these new plants in their environment. This is the classic original meaning of invasion in the Clementsian usage (Weaver and Clements, 1938, ps. 131-132144, 148, 166) and, hence, as used by most foresters and rangemen (at least those of the Anglo-American school of "dynamic plant ecology"). From this original meaning a star student of Weaver, E.J. Dyksterhuis adapted invasion and, especially, invader to a second meaning (an extension or outgrowth of the original meaning of Clements). This second usage was applied to plant species that continued to invade (Clementsian meaning) on habitats that had been disturbed (denuded was Clements' term) or that were continuing to be disturbed, especially by overgrazing (Dyksterhuis, 1949).
As applied to this live oak woodland Gulf cordgrass has to re-establish itself on (ie. to invade) a previously denuded (as by overgrazing, plowing, drought) range. Gulf cordgrass has to invade (ie. complete or effect an invasion) but because this species declines with disturbances (specifically abusive or improper grazing) it is a decreaser not an invader in usage as applied to plant succession and range condition/trend (Dyksterhuis, 1949). Decreaser corresponds to member of the climax plant community. On the live oak-dominated range type/site featured here lime pricklyash, mesquite, and huisache also invaded when they successfully established. Up to this point invasion has the same meaning as successful establishment of a decreaser such as Gulf cordgrass, but because these particular woody range plants have continuing or on-going invasion under disturbances such as overgrazing or, as is also likely, underburning these shrub species are invaders in contrast to decreasers like Gulf cordgrass.
The prevailing judgment of rangemen with regard to such abundant establishment (invasion) of these woody species on the live oak woodland and sacahuista sand prairie range types is that this unnatural excessive invasion is symptomatic of disturbance (perhaps cessation of fire, improper grazing management, or drought) so that these shrubs are invaders in the meaning of Dyksterhuis, 1949). This is an invasion of brush, of woody invaders as per the Dykstehuis (1949) model and therefore noxious range plants. This brush invasion is different from the general (the Clementsian) invasion. Invasion by Dyksterhuis (1949) invaders is range deterioration through the process of retrogression (retrograde movement from climax vegetation).
Continuing invasion by species like lime pricklyash, honey mesquite, huisache, and, probably, mustang grape resulting in development of a lower woody understorey constituted brush invasion (changes in the plant community by retrogression) and commensurate loss of economically valuable and ecologically natural forage.
The real question is, "How much of the cover of live oak is brush invasion"? Or same thing with reversed emphasis, "How much of the uniting (the coalescing) of live oak mottes into extensive live oak woodland is climax (potential natural) vegetation"?
Norias Division, King Ranch, Kenedy County, Texas. February.
10. Ranchman's touch- Naturalized Guineagrass (Panicum maximum) formed the complete understorey of a motte of mature live oak. On this large live oak motte or woodland on the King Ranch, the understorey was such an exclusive single species- stand of Guineagrass that woody species as well as other grasses were absent. This isolated tract was subject only to infrequent defoliation.
There are various "versions" of how the introduced Gunieagrass (native of Central and South America) naturalized and spread throughout the Coastal Prairies and Marshes and eastern parts of the Rio Grande Plains. One of the more popular explanations is that Guineagrass was spread by Hurricane Beluah from seed nurseries and experimental plantings at branch stations of the Texas Agricultural Experiment Station. Others insist that Gunieagrass spread from some of the larger ranches in the region, especially King Ranch, that had planted it as the latest "miracle grass". Cypher (1995, ps. 77, 92, 94, 107, 183) described planting of Guineagrass on King Ranch under direction of Bob Kleberg. However most of these plantings and established pasturess of Guineagrass described by Cypher (1995) were King Ranch holdings in Cuba and South America.
As late as the early 1970s Guineagrass was probably not established in any part of Texas (Gould, 1975, p. 469). This introduced forage grass is a "new comer" compared to Johnsongrass, bermudagrass, King Ranch bluestem, and buffelgrass.
Norias Division, King Ranch, Kenedy County, Texas. February, later hibernal or early vernal aspect. Understorey so modified that FRES, Kuchler, SAF, and SRM designations would be meaningless. Western Gulf Coastal Plain-Coastal Sand Plain Ecoregion 34d (Griffith et al., 2004).
11. Leader of the western taxon of eastern or southern or, most precisely, plateau live oak (Quercus virginiana var. fusiformis= Q. fusiformis)- Catkins and new leaves have emerged on this live oak on the Cross Timbers/Grand Prairie ecotone of northcentral Texas. Shedding of last year's leaves and emergence of this year's leaves typically occurs synchronously causing some lay observers to state that "the new leaves are phushing off the old leaves". "Leaving out" usually also occurs with flowering. It's a busy (and critical) time in the life of a live oak.
Erath County, Texas. March, immediate pre-anthesis to anthesis stage.
12. Flushing in eastern or southern live oak- The synchronous emergence of new leaves (from preformed buds of previous season) and shedding of old or current year's leaves in trees (such as the plateau form of southern live oak shown here) is known as flushing. These two views of a leader of southern live oak illustrated this phenological phenomenon.
Erath County, Texas. March.
13. Off with the old on with the new- Tip of branch in plateau form of southern live oak on which current season's or old leaves (large leaves of dark green color) persisted even as new leaves emerge accompanied by catkins. This phenomenon is designated as flushing.
Erath County, Texas. March, early catkin (pre-anthesis) stage of phenology.
14. A live oak's life in the fall- Summer-hardened leaves provided a backdrop for this southern live oak acorn. Southern (eastern) live oak is a white oak (Leucobalanus subgenus), the species of which produce an annual (vs. a biennial) acorn crop. Acorns are a rich and major carbonaceous (energy) concentrate on numerous ranges and range types. Acorns are often extremely important components of the diets of many species of range animals ranging from insects through birds and mammals, the latter often including man (American Indians especially relied heavily on various kinds of acorns.). Excessive intake of acorns (as well as buds, catkins, and leaders) can result in toxicity. Older leaves are not toxic. The poisonous principle is a group of tannins known as gallotannins. Energy stores of acorns generally offset adverse impacts of poisoning for wildlife such as upland game birds, especially wild turkey and white-tailed deer (Odocoileus virginianus).
Grand Prairie, Erath County, Texas. October, fruit-ripe.
15. Doubleheader or twins- Two cotyledons emerging from a single acorn while still on the tree exemplified the phenomenon of vivipary in plants. Vivipary is the condition in which seeds germinate and emerge from fruit or seed while they are still attached to the parent plant. Under certain conditions live oak has viviparous germination as shown here. "Plant species in which the embryo grows sufficiently to emerge visibly from within the seed tissues before dispersal are termed viviparous" (Farnsworth, 2000). Bonner and Vozzo (1987) reported that vivipary was common in southern live oak (as well as white oak [Q. alba]) when wet weather occurred during acorn maturation. That was exactly growing conditions that existed when this acorn (and those in a pile shown in the succeeding photograph) had two cotyledons emergent from one acorn in the Grand Prairie of northcentral Texas.
Emergence of two embryos (and hence potentially two trunks) of southern live oak complicated the understanding of distinct shoots (trunks) of this species in live oak mottes. Not only is there the question as to whether trunks are asexual shoots from roots of existing trees (= shoots or trunks) or derived from acorns (such sexual shoots would be unique genotypes), but also as to if more than one trunk arose from a single fruit and a single fertilized ovule. In other words, are most of the "trees" (trunks or shoots) in a motte of southern live oak clones (= such offshoots are ramets) or are they distinct (genetic) plants that are genets?
Erath County, Texas. Late October.
16. Ready to grow- Numerous viviparous acorns off of the same young southern oak presented in the preceding slide. All these acorns had germinated while still attached to this tree. Theses viviparous acorns subsequently fell to ground from which they were gathered and arranged by the author for viewing purposes. All of these viviparous acorns had a single embryo (cotyledon) emerging from the nut. Almost all acorns of southern live oak are shed from a cup that persist much longer on the tree. An ecception to this pattern was included in this pile. Predation on nutrient-rich acorns is universal and by many species.
The acorn at lower left had been bored into and fed upon by some larval insect. The rest had been spared (so far) and were ready to grow in soil beneath the parent live oak. This situation illustrated how sexual reproduction contributed to formation of mottes.
Erath County, Texas. Late October.
17. A big ole good 'un or a good ole big 'un- Trunk and inner crown of an immense and, by extrapolation, very old plateau live oak. This magnificant specimen of Q. virginiana var. fusiformis or Q. fusiformis was growing at the outer edge of the floodplain of Bosque River. It epitomized the size and shape of which this taxon is capable of achieving under ideal habitat. The pattern of huge trunk ( frequently with forks) from which arise tremendous limbs explains much of the beauty and adoration attributed to southern and/or plateau live oak.
This tree had just shed last year's leaves and grown the current year's foliage to adult size. Hence the bright, light-green color. Most of the foliage in the background were new leaves of cedar elm and sugarberry which had emerged before synchronous emergence of new leaves and shedding of last year's leaves, the physiological phenomenon knonw as flushing (recall from above).
Erath County, Texas. April.
Herald of spring, and of live oak mottes- Leaders (shoots, limbs, branches) of spring herald, herald-of-spring, elbow-bush, Devil's elbow, stretch-berry (Forestiera pubescens) is the shrub most commonly associated with mottes of clonal and/or seedling clumps (small groves) of plateau live oak in northcentral Texas. Examples presented here were of the smooth forestieria or smooth-leaved elbow-bush (F. pubescens var. glabrifolia) according to the distinction offered by Diggs et al (1999, p. 848).
As implied by the common name of spring herald or herald-of-spring, F. pubescens is one of the earliest, in not the earliest, shrubs to bloom in a northcentral Texas spring. The fruits of elbow-bush (drupe) are a valuable feed source for birds and small mammals, although these drupes are usually not very abundant. The author has observed that hen turkeys are fond of using the cover of elbow bush as nesting spots. It forms dense thickets though the shoots of elbow-bush are unarmed. Dillard et al. (2005, p. 39) reported that elbow-bush "is a moderately preferred bowse species in the Cross Timbers and Prairies Region" with the drupes serving as mast for white-tailed deer (Odocoileus virginianus).
Elbow-bush is a member of the olive or ash family (Oleaceae) and, like most of the ash species, this shrub is dioecious with separate male and female plants.
Tarleton State University, Hunewell Ranch, Erath County, Texas. Mid-April; post-bloom phenological stage.
Heralding leaves- Young (still a spring-green color) leaves of elbow-bush or spring herald associated with plateau live oak mottes in northern Texas.
Tarleton State University, Hunewell Ranch, Erath County, Texas. Mid-April; post-bloom phenological stage.
Fire-intolerant eastern red cedar (Juniperus virginiana) forms climax forests or, more accurately, woodlands of sparse understorey on higher-elevation lands having shallow, rocky soils that are fairly unassailable by fire due to insufficient ground fuel. The relative sparcity of fine fuels results in a forest range cover type largely impervious to most fires with such obvious exceptions as which can be started when lightening makes direct contact with a cedar canopy of winter-desiccated needles. The Society of American Foresters (Eyre, 1954, ps, 20-21; Eyre, 19890, ps. 50-51) recognized the forest cover type of Eastern Redcedar (SAF 46), The earlier version of SAF forest cover types (Eyre, 1954, ps, 20-21) also included Eastern Redcedar-Pine (Type 47) and Eastern Redcedar-Hardwood (Type 48). These were dropped from the second edition (Eyre, 19890, p. 50) which was expanded to trake in tallgrass prairie (including the Kansas Flint Hills) invaded by eastern redcedar and periodically burnt to control the invasive conifer.
Although treatment in Eyre (1980, p. 50) recognized a "cedar glade" variant of SAF Type 46--including listing of the four major tallgrass species--they incorrectly (at least in this author's interpretation) failed to see this as a savanna (or maybe even grassland) and instead grouped it as a forest type. This was the cedar glades (Juniperus-Quercus-Sporobolus) potential natural vegetation of Kuchler (1964, p. 83) and shown as unit 74 in the Forest Service Forest and Rangelands Ecosystems map (Garrison et al., 1977). Cedar glades noted, the descriptions in Eyre (1954, 1980) still did not recognize (at least did not describe) the true climatic forest or woodland vegetation dominated by eastern red cedar that develops on land least apt to carry fire and having relatively infertile soils (extremely stoney and shallow such as rock outcrop forest/range sites).
There are such sites (although they are admittedly relatively restricted) and such climax eastern redcedar-dominated plant communities. Such soil-vegetation units are most commonly found on tops of bluffs above streams and similar stone outcroppings. In fact, these are widespread (although or comparatively small acerage) throughout the Ozark Plateau and associted areas of other old mountains such as the Arbuckles and Applachians. On such habitats, eastern red cedar often attains to comparatively large size and quite likely lives to extreme old age. This form of eastern red cedar-dominated vegetation--and it is the natural (climax) plant community--is true forest or, at least, woodland and not glades which by definition are climax communities dominated and defined by herbaceous species, especially grasses.
An example of this climax eastern red cedar-dominated vegetation was presented below. (Cedar glades were covered in Range Types of North America under Miscellaneous Grasslands.)
18. Atop the bluffs- A local consociation of eastern red cedar on the pinacle of limestone bluffs in the western Ozark (Springfield) Plateau. These were relatively large (and, almost assuredly, very old) trees. There was limited--though undoubtedly adequate--regeneration of eastern red cedar. There was a sparse understorey and this was limited to herbaceous vegetation, including a moss-lichen lichen on surface rock. Vascular plants included poverty oatgrass (Danthonia spicata); Japanese chess or brome (Bromus japonicus) a naturalized Eurasian annual; and a few stunted-appearing plants of big bluestem (Andropogon gerardii). At this very early stage of spring most plants had not emerged from dormancy.
Leafless hardwood trees in the foreground were black oak (Quercus velutina) that were at the edge of a black oak-post oak (Q. stellata)-black hickory (Carya texana) forest which was a separate plant community from the narrow strip of cedar woodland that had developed on even shallower and stonier soil than that of the oak-hickory forest.
Bluffs above Lost Creek. Ottawa County, Oklahoma..March. No FRES or Kuchler unit for this forest or woodland range community. SAF 46. No units in Brown et al.(1998). Variant of Dry Limestone/Dolomite Woodland (Nelson, 2005). Ozark Highlands- Springfield Plateau Ecoregion, 39a (Woods et al., 2005).
19. Oldests ones on the highest ground- Old and fairly large trees of eastern red cedar dominated and defined a forest or woodland range community that had developed along the very edge and on the north slope just below the top of limestone bluffs in the Springfield Plateau of the Ozark Region. These were obviously old-growth trees as indicated by the form of twisted and gnarled trunks and broken crowns.There were a few smaller saplings of eastern red cedar as well. A lower layer of woody plants was lacking otherwise. Instead the understorey consisted of two herbaceous layers: 1) a moss-lichen zone on exposed rock surfaces and trunks of junipers and 2) vascular plant zone consisting primarily of poverty oatgrass with a few patches of Japanese chess or brome and runt-sized plants of big bluestem that were still dormant in this early spring (nearly late winter) season.
Trunks and crowns of leafless trees were those of a few black oak at the edge of an adjoining black oak-post oak-black hickory forest that had developed farther away from the bluffs and on soil that was somewhat deeper and less rocky.
The paucity of herbaceous plants assured low fuel load so that any surface fires (any such would likely originate or be started from the adjacent oak-hickory forest or on grasslands, farm fields, house yards, etc. farther below these upland forests. It is because of this nearly assured protection from fires--lightening-set, prescribed, or accidental--that eastern red cedar was able to live to such comparatively great age and size and continue to dominate this range vegetation. Otherwise, eastern red cedar is as specified in Eyre (1980, ps. 50-51) a seral cover type. Clearly Juniperus virginiana does not need shallow or mineral soil for germination and seedling establsihmene as attested to by the all-too-plentiful presence of this horrid invading conifer on tallgrass prairie and oak-hickory forest.
On this forest site, eastern red cedar woodland is the potential natural (climax) plant community. It is a restricted range cover type that occupies small, isolated, patchy, areas adding mostly diversity providing an interesting natural community albeit one of low productivity and even less economic importance.
Bluffs above Lost Creek. Ottawa County, Oklahoma..March. No FRES or Kuchler unit for this forest or woodland range community. SAF 46. No units in Brown et al.(1998). Variant of Dry Limestone/Dolomite Woodland (Nelson, 2005). Ozark Highlands- Springfield Plateau Ecoregion, 39a (Woods et al., 2005).
20. Female essentials- Close-up views of needles and fleshy ovuliferous cones of eastern red cedar (Juniperus virginaina). Both the fleshy seeds and needles of estern red cedar have somewhat pointed extensions that have a "sharp" feel. This is especially the case for leaves which easily cause shallow scratches on humn skin. Vines (1960, p. 27) explained that there were two forms of leaves on eastern red cedar: 1) small,, scalelike needles and 2) longer needles that are "awl-shaped, sharp-pointed"
Ottawa County, Oklahoma. Late June.
21. Two distinct plant communities comprising locally restricted vegetation types: 1) a swamp of water oak with bald cypress as an associate and 2) a maidencane (Panicum hemitomon) marsh designated as a lowlands range site. These two types together constitute a flat woods pond. FRES No. 16 (Oak-Gum-Cypress Ecosystem) and corresponding K-101 (Southern Flood-Plain Forest) and FRES No.41 (Wet Grasslands Ecosystem) with with no Kuchler units small enough to pick up the maidencane type. Maidencane would be included with Kuchler-83 (Everglades) in Florida. The maidencane marsh type is SRM 819. Mixed Hardwood Series in Southeastern Swamp and Riparian Forest biotic community and Maidencane Series (if and when such is recognized) Series in Southeastern Interior Marshland biotic community, respectively, of Brown et al. (1998). South Central Plains- Flatwoods Ecoregion, 35f (Griffith et al., 2004).
22. Edge of two wetland range communities- Boundary between the water oak-bald cypress swamp and maidencane swamp introduced in the preceding slide. The swamp portion of this flatwoods pond was FRES No. 16 (Oak-Gum-Cypress Ecosystem) and corresponding K-101 (Southern Flood-Plain Forest) while maidencane marsh was FRES No.41 (Wet Grasslands Ecosystem) with with no Kuchler units small enough for this region so that instead maidencane would be included with Kuchler-83 (Everglades) in Florida. Maidencane rangeland cover type was SRM 819 (Freshwater Marsh and Ponds). Swamp with water oak dominant and bald cypress the associate species comprised a combination or "hybrid" of SAF ted
23. Maidencane in the spring- Hardin County, Texas. May, late vernal aspect. Maidencane Series (if and when such is recognized) in Southeastern Marshland biotic community, respectively, of Brown et al. (1998). South Central Plains- Flatwoods Ecoregion, 35f (Griffith et al., 2004).
24. Bay-Gall Bog or Titi in the Texas Big Thicket- This vegetation is the most impenetrable “jungle” or “tangle’ in the Big Thicket. The local mound-and-intermound relief creates a bog ecosystem. The soil series of the mound microrelief (on the mound) has the spodosol soil series Babco. This is currently the only spodosol mapped in Texas. The dominant plants are red bay (Persea borbonia) and sweet bay or swamp bay (Magnolia virginiana) among the hardwood trees and shortleaf and loblolly pine from the conifers. Gall, swamp cyrilla or, by the Indian name, titi (Cyrilla raecmiflora) is the dominant species of the shrub layer along with gallberry (Ilex coriacea; not to be confused with the preceding gall), bull-briar (Smilax bona-nox), saw-brier (S. glauca), buttonbush (Cephalanthus occidentalis), and wax myrtle (Myrica cerifera) dominate the shrub layer. Completing this “tangle” is the herbaceous understory often dominated by rather rank-growing ferns.
The largest trunk (in center) is a loblolly pine, the trunk immediately behind and to the right of it is a water oak, the two trees immediately behind and to the right of the water oak are sweet bay magnolias, and the left foreground tree is a red bay. Most of the shrubs in the foreground understory are swamp cyrilla or titi. Hardin County, Texas. May. There is no specific FRES or Kuchler for this local community that grows within the FRES No. 13 (Loblolly Pine-Shortleaf Pine forest Ecosystem). Mixed Hardwood Series in Southeastern Swamp anbd Riparian Forest biotic community of Brown et al. (1998). South Central Plains- Flatwoods Ecoregion, 35f (Griffith et al., 2004).
25. Interior of a Texas Big Thicket Bay-Gall Bog- Detail of the shrub layer described in the preceding slide caption. Note the seedling or young tree stage of loblolly pine in the foreground and the adult loblolly pines in background indicating that this is the dominant conifer for this unique local community. Hardin County, Texas. May.
26. The floor or herbaceous layer of a Bay-Gall Bog dominated by ferns. Over 20 species of ferns are native to the Big Thicket and there are another four or five species that may have naturalized here. The ferns are growing on a mound of Babco soil. Hardin County, Texas. May.
27. Profile of Babco soil (the only spodosol mapped in Texas)- Spodosols comprise the soil order characterized by having a light gray eluvial horizon over a reddish aluminum- and/or iorn-enriched horizon. They typically occur in humid areas. The Babco pH ranges from 3.1 to 3.6. Hardin County, Texas. May.
28. Sandjack= bluejack oak (Quercus incana)-sandhill bluestem scrub type— The bluestem is a taxonomic complex of little bluestem, including the taxa often shown as Andropogon divergens or Schizachyrium scoparium var. divergens, and slender bluestem (Andropogon tener= Schizachyriumtenerum). A few post oaks are associates of bluejack oak. Composites and various prickly pears (Opunia spp.) are scattered throughout the bunchgrass sward. An aeolian ("blowsand") ridge community.
Beech Creek Unit, Big Thicket National Preserve, Hardin County, Texas. May. FRES No. 14 (Oak-Hickory Forest Ecosystem). A variant of K-72 (Oak Savanna). One of the many forms of Southern Scrub Oak, a variant of SAF 72 (Southern Scrub Oak). A Scrub Oak Series of Brown et al. (1998), but one was not shown for this region. Sandy upland variant of South Central Plains- Flatwoods Ecoregion, 35f (Griffith et al., 2004).
29. Jack pine (Pinus banksiana) Forest- This small stand of jack pine is on the sand dune complex along the southern shore of Lake Michigan where it is clearly seral to the climax or subclimax basswood and climax beech-sugar maple forests. Here it grows on more mesic northern slopes of the dunes, often with eastern white pine (Pinus strobus) and the local black oak (a subspecies or variety of Quercus velutina). Jack pine is seen here as a pure form in the upperstory with invasion of young trees into a grass understory dominated by little bluestem with the associated Gramineae species of Canada or nodding wildrye, bluejoint, and, as remnants from the colonizing seral stage, Merramgrass or American beachgrass.
Indiana Dunes State Park, Porter County, Indiana. Hibernal aspect. FRES No. 10 (White-Red-jack Pine Forest Ecosystem), K-86 (Great Lakes Pine Forest), SAF 1 (Jack Pine).
30. Jack Pine Forest on dunes of Lake Michigan shore- This seral plant community grows on more moist and protected north slopes and is clearly seral to climax norther hardwood forest of either Basswood or American Beech-Sugar Maple-Eastern Hemlock Forest Cover Types. The jack pine seen here are near the southern extreme of the species’ range and they are not associated with the more typical assemblage of species in communities they dominate. Specifically, this jack pine stand is not any of the five subtypes described by the Society of American Foresters (Eyre, 1980, ps. 8-9). It does, however, fit into the SAF jack pine forest cover type. That includes as seral to such hardwood species as sugar maple and basswood as it is here on the Lake Michigan dunes. In fact, Eyre (1980, p. 8) indicated that the main distribution of jack pine is in the Lake States.
This view is inside the “dune complex” which is a patchwork of communities representing the various seral stages of vegetation development. The foreground is the second seral stage after colonization with Merramgrass or American beachgrass and sand cherry. The foreground community is dominated by little bluestem which succeeds the colonizers. Associates are Canada wildrye and bluejoint. This grass understory extends under the jack pines but with reduced cover.
Indiana Dunes State Park, Porter County, Indiana. Hibernal aspect. FRES No. 10 (White-Red-Jack Pine Forest Ecosystem), K-86 (Great Lakes Pine Forest), SAF 1 (Jack Pine).
A climax range plant community dominated by sand post oak (Quercus margarettiae= Q. margarettae= Q. Margaretta= Quercus stellata var. margarettiae), a stoloniferous/rhizomatous of large shrub to small tree dimensions was included in both Miscellaneous Scrubland= Miscellaneous Shrubland and Miscellaneous Forest chapters herein because this potential natural vegetation could rationally be regarded as either a range cover type of either 1) shrubland or 2) scrub (=dwarf= pygmy) forest.
31. Sandy exterior- Part of perimeter of a climax hardwood scrub or scrub forest known by local folk as "sandrough" or "sandtangle". Ths predominantly woody range vegettion develops on deep, sandy soil. Sandrough is a classic example of the concept of postclimax vegetation proposed by F.E. Clements. This shrubland occurrs in patches--both large and small--in the vegetational mosaic of Grand Prairie and West Cross Timbers. It is probably most correctly interpreted as a scrub forest form of Cross Timbers.
The defining species of sandtangle is a species of scrub oak (some individuals grow to size of small or, rarely, medium-sized trees) known by such common names as sand post oak, dwarf post oak, scrub post oak, Drumond's oak, runner oak, or Margarette oak. Oaks in this group are currently given their own species, Quercus margarettiae.In this regard see taxonomic note immediately below. Most of the trees, including largest ones, seen in this "photographic forest bisect" were sand post oak or scrub post oak (or, sometimes, M[m]argarete oak).
Other woody species in this photograph included blackjack oak (Q. marilandica) and sugarberry (Celtus laevigata), although only a few trees of these two species (especially of blackjack oak) were present, common or saw greenbriar (Smilax bona-nox), lime prickly-ash or tickle-tongue (Zanthoxylum hirsutmm), rusty or southern blackhaw (Virburnum rufidulum), Drummond's or roughleaf dogwood (Cornus drummondii), and eastern or devil's-tongue pricklypear (Opuntia humifusa). Herbaceous plants included sand lovegrass (Eragrostis trichoides), heart-sepal wild buckwheat (Eriogonum multiflorum), and slender flat-sedge or slender umbrella-sedge (Cyperus lupulinus). Obviously, herbaceous species were not visible at this camera distance, but they were present.
Sand or dwarf post oak sometimes grows to small (or, more rarely, meium)-tree size, but this species is strongly rhizomatious (or, less frequently, stoloniferous) so that the individual trunks or boles are, in reality, shoots (clonal units) of genetically distinct individuals. The source or orgin of most of these various shoots or trunks ("trees") cannot be determined with any degree of accuracy in the field. Furthermore, the size of these clonal shoots is most commonly that of large shrubs and not "regular trees"; specifically, most are under 12 to 15 feet in height. A large "plant" (clonal unit) of over 20 feet was rare. This height along with the clonal feature and formation of colonies) appeared to this worker to better fit the definition of shrub rather than tree as proviced by the Society of American Foresters (Helms, 1998) which specified a minimum height of 15 feet and the Society for Range Management (Bedell, 1998) which explained that shrubs produced "several basal shoots instead of a single bole". Admittedly, however, this distinction is open to interpretation and has a degree of unavoidable ambiguity.
Nonetheless in the judgment of this author native vegetation dominated and defined by dwarf or scrub post oak was better regarded as scrub or shrubland than as a form of pygmy forest or a grove of midget trees.
Erath County, Texas. Mid-October, autumnal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem), K-75 (Cross Timbers), but it is a shrub form of it. No SRM type description; an edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
Taxonomic note translated to community classification: Sand post oak, dwarf post oak, scrub post oak, Drumond's oak, runner oak or M(m)argarete oak has been treated variously as Quercus stellata var. margarettiae (Sargent 1933, p.295; Vines, 1960, p. 155), Q. margarettiae (Small, 1933, p. 424; Muller, 1951, ps. 49-51; Correll and Johnston, 1979, p. 477; Diggs et al., 1999, p. 716). At one time, sand or scrub post oak was even lumped in with Q. drummondii (Diggs et al., 1999, p. 716). Dwarf post oak, or runner oak is quite likely the most complex and confusing Querus species in Texas where Q. margarettiae resembles Q. drummondii and there are Q. margaretta X Q. stellata hybrids as well as all manner of intergrades between these.
Muller (1951, p. 52) stated: "No greater taxonomic and nomenclatorial puzzles were encountered in this study than those centering about Quercus stellata, Q. Margaretta, and Q. drummondii. Between the easily separated extremes of Q. stellata and Q. Margaretta there exist a greater number of intermediate forms representing fairly frequent hybridization. In spite of this the two species have maintained themselves abundantly distinct by virtue of the close confinement of Q. Margaretta to deep sands and of Q. stellata to rocky or sandy soils containing clay."
There is even confusion and controversy over the correct spelling of the specific epithet of this species. Muller (1951) remains the encyclopedic authority on the Quercus species of Texas, and he (Mueller, 1951, ps. 49-51) spelled the epithetic epithet, Margaretta. By contrast (and way of confusion) Diggs et al. (1999, p.716), the floral authority for northcentral Texas, spelled the specific epithet, margarettiae.
32. Sandy and scrubby- Exterior (outer edge) of a "sandrough" or "sandtangle" shrubland on deep sand in northcentral Texas. This was a "closer-up-to-it" view of the same perimeter of the tract of scrubland featured immediately above and below this slide-caption set. Species visible in this slide (at least when projected) were both sand post oak and blackjack oak, saw or common greenbriar, lime prickly-ash or tooth-ache bush, devil's-tongue pricklypear, Ashe or post juniper (Juniperus ashei) and heart-sepal wild buckwheat.
Presence of Ashe or post juniper and devil's-tongue pricklypear was probably explained by absence of fire from this scrubland range for at least a half century (and almost assurredly much longer).
Erath County, Texas. Mid-October, autumnal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem), K-75 (Cross Timbers), but it is a shrub form of it. SAF 72 (Southern Scrub Oak, Sand Post Oak variant). No SRM type description; an edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site.. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
33. More of a sandy, scrubby exterior- Outer edge of a "sandtangle" or "sandrough" scrub climax community on deep sand in northecentral Texas. In addition to the major shrublands of coastal and mountain chaparral and deserts there are numerous local kinds of vegetation dominated by and made up largely of shrubs due to unique habitat features like soil, topography, water table, and so on. Riparian vegetation falls into this category as does that of deep sand or water drainage like seeps that support vegetation more mesic than that of the region in which it occurs. Ecologists like Fredric Clements labeled such vegetation as postclimax. An example of a local postclimax range vegetation type in the Texas Cross Timbers is sandrough or sandtangle, stunted, or dwarf forms of post oak, blackjack oak, sugarberry with such associates as common or saw greenbriar and lime prickly ash, tickletongue, or toothache-tree.
There were a few, rather large individuals of sand lovegrass.
The dominant--in fact, the defining species species is sand or scrub post oak, runner oak, or Margarete oak. See again, taxonomic note.
Here sandrough is growing on a Deep Sand range site. Erath County, Texas. October, autumnal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem), K-75 (Cross Timbers), but it is a shrub form of it. SAF 72 (Southern Scrub Oak, Sand Post Oak variant). No SRM type description; an edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
34. Sanded "purty bad"- Exterior of a sandtangle range in the West Cross Timbers of northcentral Texas. The local dominant on the outer edge of the climax scrubland range community was mustang grape (Vitis mustangensis) with saw or common greenbriar being the associate liana. Sand or scrub post oak was also present (foreground of upper right corner and background of upper left corner) as was roughleaf dogwood, this latter species being intermixed with mustang grape. Leaves of mustang grape, saw greenbriar, and roughleaf dogwood were all tattered by blowing sand in an Extreme Drought at end of the warm growing season.
As a general rule, mustang grape and roughleaf dogwood occur as part of the sandrough range vegetation only along the exterior. This phenomenon appeared to be light-related. In the sandrough interior there is generally rather dense shade and limited light penetration through to lower levels of range vegetation. Leaves are much more apt to get "sand-blasted" on the perimeter of sandrough range.
Erath County, Texas. October, autumnal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem), K-75 (Cross Timbers), but it is a shrub form of it. SAF 72 (Southern Scrub Oak, Sand Post Oak variant). No SRM type description; an edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
35. Climax not brush- Although frequently misinterpreted as a woody invasion of deteriorated range, sandrough or sandtangle is an edaphic climax. Thus while it is a minor range type it provides an example of the variation in vegetation that exist within regional or zonal scale climaxes. It is but one example of the sort of plant community that fueled the debate between monoclimax and polyclimax theories of vegetation. Of the few herbaceous understory species in sandrough, sand lovegrass is dominant.
Erath County, Texas. October, autumnal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak) Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
36. Sandy stand- Satand of sandy post oak, scrub post oak, or Margarete oak at endge of a sandrough scrub range in the West Cross Timbers of northcentral Texas. It was likely tht the formost (center foreground) three shoots belonged to the same genetic individual (genotype). The clonal nature of this species was explained below. There was almost no understorey or herbceous species in the view seen here, but saw greenbriar was everywhere.
Erath County, Texas. October, autumnal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
37. Inside sandrough or sandtangle- Interior of a sandrough dominated by post with some blackjack oak as minor associate. Even deep in interior of this edphic climax scrubland there are frequently herbaceous species including sand lovegrass (Eragrostis trichoides), and little bluestem. A dominant forb was spiderwort (Tradescantia subacaulis). Also present, especially on primeter, were mustang grape and rough-leaf dogwood.
Erath County, Texas. April, vernal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub vriant of K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut PlainCross Timbers Ecoregion 29 e (Griffith et al., 2004).
38. Impenetrable core- Deep interior of a sandrough scrubland range in West Cross Timbers. This "photplot" featured a woody species that is fairly uncommon to the West Cross Timbers: American beautyberry (Callicarpa amricana), "stitched completely up" as it were with the ever-present saw or common greenbriar. American beautyberry is much more at home in the sandy forests of the Pineywoods of east Texas, but in the mesic, deep sand habitat of the postclimax sandtangle vegetation American beautyberry frequently finds a home.
Erath County, Texas. April, vernal aspect. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub vriant of K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site (Soil Conservation Service, 1973). Edaphic variant of Limestone Cut PlainCross Timbers Ecoregion 29 e (Griffith et al., 2004).
39. Herbaceous spot- At the outer edge of a sandtange scrubland range community numerous large plants of sand lovegrass formed a local herbaceous community, a consociation (or, perhaps more precisely, a population) with only a few plants of heart-sepal wild buckwheat. Shade in the background of this "photoplot" was typical of sandtangle scrub range. There was typically only limited development of of lower layers--herbaceous or woody--in sandrough shrubland (other than lower shoots of saw greenbriar of course).
Erath County, Texas. October, autumnal aspect. Grain-ripe phenological stage of sand lovegrass. Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak) Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
40. A study in clumps- Two clumps of sand, scrub, or dwarf post oak or Margarete oak that appeared to be two modules or clonal units each of one genetic individual (ie. units of offshoots or ramets of a genet; two genets, one in each photograph). It was explained above that this taxonomic variety, Quercus stellata var. margarettiae (Sargent 1933, p.295; Vines, 1960, p. 155), or species, Q. margarettiae (Small, 1933, p. 424; Muller, 1951, ps. 49-51; Correll and Johnston, 1979, p. 477; Diggs et al., 1999, p. 716) had been little studied (barely described as matter of fact) yet possessed diverse morphology and a predominant asexual mode of reproduction.
Both of these clonal clumps of shoots had seedling-sized, new offshoots or clonal shoots arising from adult horizontal shoots or or, more commonly, immediately beneath the soil surface. (Examples of some aboveground or surficial shoots were presented ahortly below.) Thus, asexual reproduction was on-going. Saw greenbriar, which also had active asexual reproduction, was the associate species in this sandrough scrubland and was also present in these two "photoplots".
Erath County, Texas. Late and Mid-October; first and second slide, respectively Entering early stage of annual dormancy.
41. Old-growth scrub- Two large (comparatively speaking) shoots of sand, dwarf, or scrub post oak growing on a Quercus margarettiae-Smilax bona-nox habitat type known by local folk as a sandrough or sandtangle in the West cross Timbers of northcentral Texas. These tree-sized individuals, which were as large as this photographer encountered, were senescing (ie. slowly dying as they neared completion of their life cycle).
It was not known whether these two trunks of about the same size were two trees (two genotypes) or two shoots of the same tree (one genotype). The light-shaded brown on the right trunk was dead lichen (live lichen was below the dead) and not a fungal disease.
Erath County, Texas. Late October; entering early stage of annual dormancy.
42. Modular units- Two groups of shoots (lower trunks thereof) of sand, scrub, or dwarf post oak or Margarete oak that were comprised of or modules, offshoots, or clones (each shoot a clone or offshoot) of the same genetic individual (genotype). Each shoot in both of these modular or clonal units was a ramet of the original genetic (the genotype). This is the typical growth or asexual regeneration pattern of this species.
Offshoots or clonal shoots arise from horizontal rootstocks most of which are subterranean while others lie partially exposed or raised above the upper soil (ground) surface. This was visible in the first of these two slides (and numerous other photographs presented immediately below). It could not be determined if the exposed horizontal shoots had naturally grown upward from the soil ("pushed" above ground level) or if these rootstocks had been exposed due to soil loss by erosion.
Shoots of these two modules (ramets of a single genet or genotype) were accompanied by even more clonal shoots of saw greenbriar which arise from globular rhizomes or slender subterranean shoots coming off of these roughly spherical rhizomes. Asexual reproduction is the" order of the day" in this scrub post oak-saw greenbriar habitat type known locally as sandtangle or sandrough.
It was not known if the proper designation of these horizontal shoots was rhizome (belowground shoots) or stolon (aboveground horizontl shoots), but the former seemed most appropriate gievn that most such rootstocks remained belowground or subterranean. (See immediately below, and no pun intended.)
Early November; entering initial stage of annual dormancy (onset of leaf fall).
43. Stolen identity- Four specimens (four distinct plants) of sand, scrub, or dwarf post oak or Margarete oak with horizontal shoots that were growing (protruded) above ground level (higher than the soil surface). It was explained in the immediately preceding slide-caption set that it could not be determined if these horizontal shoots were woody rootstocks (rhizomes) or, alternatively, stolons which are aboveground. While the four examples presented here were aboveground it could not be determined if this was the result of rhizomes (subterrnean horizsontal shoots) growing partly above the soil surface (or if soil loss by erosion--if any such occurred--resulted in exposure of rhizomes) or, alternatively, if these were aboveground horizontal shoots that would, by definition, be stolons.
Sargent (1933, p. 295), in what (though dated) is still the definitive encyclopedia of North American trees, described this shrub formof post oak as Quercus stellata var. Margaretta f. stolonifera which forms "broad thickets by stoloniferous shoots". Gleason and Cronquist (1991, p. 85) described Q. margaretta as "spreading underground and becoming colonial". Muller (1951, p. 50) did not describe the stoloniferous or rhizomatous morphology of Q. margaretta, but he showed the vernacular name as "runner oak".
Whatever the technical designation of such horizontal shoots the relevant fact is that many, if not most, shoots (trunks plus crowns) of sand, scrub, or dwarf post oak are clones, offshoots, or modules in the same fashion as such bettter known woody species as quaking aspen (Populus tremuloides), black locust (Robinia pseudoacacia), some plums (Prunus spp.), certain willows (Salix.spp.).
In this context, sand post oak stands are to a some extent clonal groves. Likewise, saw greenbriar is a highly clonal woody vine. Sandrough or sandtangle scrub is a range plant community that developed around a "botanical nucleus" of asexually regenerating shrubs or, in a few instances, small to even medium-sized trees. Finally, students were reminded that roughleaf or Drummond's dogwood was also a thicket-forming (from rhizomes or woody rootstocks). Sandrough is to a large degree a shrubland of modular species.
Erath County, Texas.Early November (first and second slides), late October (third and fourth slides) Phenology: early stages of annual dormancy with onset of leaf shedding in first two slides.
44. Springtime in sandrough- Young, immediate pre-bloom catkins and "fox ear"-sized new leaves of sand post or margaretta oak on deep sand in the Western Cross Timbers. The climax renge vegetation that was dominated by sand post oak was called "sandrough" or "sandtangle" by local folks.
Erath County, Texas. Early April; developing catkins and this year's leaves.
45. Growing and sexually active- Early growth (extension of internode) of a new leader and developing female catkins of sand post or margaretta oak in the West Cross Timbers.
Erath County, Texas. Early April.
46. Sand Gents- Male catkins of sand post or margaretta oak on a deep sand habitat in the West Cross Timbers.
Erath County, Texas. Early April; fullly developed catkins.
47. Sand Ladies- Female catkins of sand post or margaretta oak on a deep sand habitat in the West Cross Timbers.
Erath County, Texas. Early April; fullly developed catkins.
48. Still not green- Developing new leaves and senescing catkins of sand post oak or margaretta oak in a dwarf forest or shrubland (depending on interpretation) of deep sand-soil in the West Cross Timbers of northcentral Texas. These still-baby leaves had not yet attained their fully grown, mature dark green color, but had the yellowish-green characteristic of this stage or point of leaf development. The youngest and smallest leaves are a dark pink or reddish color while the living catkins are a mixture of green, yellow and tan coloration (see immediately preceding four slide/caption sets). As leaves get older they progress through a series of color shade changes until they achieve a dark, almost burnished, green cast. Then it autumn leaves turnvarious light yellow or orange color (see above photographs).
Catkins in the first of these two shots were senescing (dying having "finished their business" while catkins in the second or lower slide were still alive with the "living green" coloration.
Erath County, Texas. Early April; fullly developed to dying catkins and still young (immature) leaves.
49. A parting composite shot- New leaves and catkins on young twigs coming off of a lower limb of sand post or margaretta oak on a sandtangle dwarf forest in the West Cross Timbers of northcentral Texas.
Erath County, Texas. Mid-April, peak anthesis.
50. It even looks tough- Synopsis view of portion of a leader of sand post or margaretta oak showing a cluster of three acorns and a representative leaf of this scrub tree or shrub growing in a "sandrough" dwarf forest in the West Cross Timbers of northcentral Texas. This was a typical specimen of a short shoot (Sosebee, 1977, p. 272-275) in this species.
Erath County, Texas. Early September.
51. Corned clusters- Short shoots of sand or scrub post oak or, also, Margarete oak that was the dominant species of a scrub range type known as sandrough. Short shoots of scrub post oak have a whorled cluster of leaves at their "tip" (the terminal end). If these short shoots develop into sexual short shoots, acorns are borne at this tip (although these nuts can sometimes fail to develop into mature fruit). Acorns can be borne singly or in groups. A terminal bud or, even, several terminal buds sometimes also form at the terminus or apex ("tip")of a short shoot, but leaves and fruit formation are the characteristic features at apex of short shoots. By contrast, long shoots terminate ("end") in a terminal bud typically without fruit or developed leaves during the season (year) of terminal bud formation.
A detailed, readily read explanation of long and short shoots of woody plants was provided by Dahl and Hyder (in Sosebee, 1977, ps. 272-276).
Erath County, Texas. Mid-October; fruit-ripe stage of phenology.
52. More sand than scrub- Three examples of acorns produced and borne at apex of short shoots of sand or scrub post oak (known also as Margarete oak), the dominant species of a shrubland range type known as sandrough or sandtangle. Several buds were on the tips of the three sexual short shoots shown here, but these were not the typical preformed terminal bud of long shoots (Dahl and Hyder in Sosebee [1977, ps. 272-275]).
The sandpaper-like pubescent surface of leaves of sand, scrub, or dwarf post oak was visible in the first two of these slides as well as the three slides of the immediately preceding slide-caption set and in the single slide in the immediately following slide. This pubescent leaf surfaace was noted in such standard taxonomic treatments as Small (1933, p. 424), Sargent (1933, p. 295), Muller (1951, p.50), and Diggs et al. (1999, p.712). Gleason and Cronquist (1991, p. 84) described this pubescence as consiting of "stipitate, few-branched hairs" There is considerable varition in leaves of A. margaretta (also spelled Q. margarettiae) though not generally as much as in Q. stellata even when many of the forms of Q. stellata are elevated to their own species as, for example, Q. margaretta (see Muller, 1951, passim for Texas specimens).
Erath County, Texas. Mid-October; fruit-ripe stage of phenology.
53. Nothin' scrub with this mast- Several acorns of sand or scrub post oak with the actual nut separated from the cup that enclosed part of the attachment end of the nut. Sand post oak or M(m)argarete oak is in the white oak group (subgenus Leucobalanus of genus Quercus). Acorns of white oaks mature in one year in contrast to the two period of acorn development in the red oaks. Thus, white oak species like sand post oak produce more regular crops of mast than the red oak species.
This mast crop is one of the important dietary components of range animals including wild turkeys, coons, and cattle (and, unfortunately, feral hogs).
Erath County, Texas. Mid-October; fruit-ripe stage of phenology.
54. Inflorescence of the defining liana- Three views at progressively closer camera distance of the flower cluster of fiddleleaf or saw greenbrier (Smilax bona-nox) Fiddleleaf greenbrier is one of five Smilax species native to northcentral Texas and one of two abundant Smilax species in this region (Diggs et al., ps. 1344-1348). In many regards, fiddleleaf or saw greenbrier is the most characteristic shrub (and certainly the major woody vine or liana) in the West Cross Timbers of Texas and Oklahoma. Fiddleleaf greenbrier is the most characteristic woody vine of the sugarberry-cedar elm-pecan floodplain forest characteristic of bottomland forests in the Cross Timbers and Prairies vegetational area of Texas. Saw or fiddleleaf greenbrier is the co-dominant range plant species of the pygmy or dwarf sand post oak (Quercus margarettiae= Q. stellata var. margarettiae) forest of the West Cross Timbers. In these various range types, fiddleleaf greenbrier edges out out mustang grape (Vitis mustangensis), poison ivy (Rhus radicans= Toxicodendron radicans), and trumpet creeper (Campsis radicans).
Some taxonomists such as Smith (1977, ps. ) placed Smilax species in a "super-large" lily family (Liliaceae) as part of subfamily, Smilacoideae. Other authors such as Diggs et al. (1999, p. 1344) put Smilax in a small family, Smilaceae, of three genera (or, in effect, for northcentral Texas, in its own family).
Young spring shoots of fiddleleaf greenbrier (of all Smilax species for that matter) are extrmely palatable for most species of range animals. In fact, the tender spring shoots make a nice "native green" for human sandwiches. These shoots are not strongly flavored but they do add a certail "zest" to a ham or turkey sandwhich being eaten at dinner time in the woods. Shoots of fiddleleaf greenbrier (including the young thorns) are extremely tender and crisp. The freshly cropped shoot (by beef cattle or white-tailed deer) shown in all three of these slides bespoke to the palatability of spring shoots of saw greenbrier.
The fruit of saw greenbrier ( a one to three-seeded berry) is an important concentrate for wildlife, especially birds, and, for their part, these vertebrates likewise provide the srvice of zoochory (dispersal of plant propagules or germules by animals).
While there are several references that treat fiddle or saw greenbrier, Vines (1960, ps. 72-73) probably provided about as much detail as any.
Erath County, Texas.
55. Bad belowground, too- Rhizomes of fiddleleaf or saw greenbrier that had been growing on a "sandrough", depending on interpretation either a scrub forest or scrubland (shrubland), a Deep Sand range site (Soil Conservation Service, 1973) and, by Daubenmire (1952, 1968) plant community classification, a sand post oak-saw greenbrier habitat type. Such rhizomes of shrubs and trees have been best known as woody rootstocks. These woody rhizomes and aboveground woody vines are shoots. Fiddleleaf greenbrier grows a vast network of woody rhizomes that aven surpass those of sand post oak.
The second image showed green regrowth (left part of upper unit of rhizome) following browsing to ground level by white-tailed deer (Odocoileus virginianus). Saw or fiddleleaf greebrier appears to be extremely well-adapted to defoliation, including that by fire.
Erath County, Texas. Early April.
56. Sand lovegrass (Eragrostis trichoides) on a Cross Timbers sand rough- This is the climax dominant grass on the deep sandy soils that support the scrub oak form of Cross Timbers or, more precisely,. the deep sand oak shrubland of the Texas Cross Timbers and Prairies vegetational area. As is typical for plants adapted to harsh habitats, sand lovegrass is actually a delicate species. It can thrive in severe environments, but is very susceptible to abnormal stress such as improper defoliation (overuse or even heavy use during early growth).
Erath County, Texas. October. Deep Sand range site (sand rough).
57. Flowering shoots of sand lovegrass- The large, showy inflorescence of a climax understorey species on sites of deeper sands such as sand rough. Sand lovegrass grows most abundantly in well-lite natural openings in the oak scrub. It is a satisfactory sand-binding species but is quickly grazed out under excessive stocking rates. Sand lovegrass is an "ice cream species" on range habitats like this sand rough (Deep Sand range site). Erath County, Texas. October.
58. Panicles of of sand lovegrass- The flower clusters of sand lovegrass often make up over half of it's total shoot length. Sand lovegrass is one of the most showy plants that can be used as an ornamental when landscaping with native species. To the point of this discussion, sand lovegrass is quite sensitive to improper grazing (namely overuse) and it's common occurrence on ranges such as those of Cross Timbers vegetation indicates careful management and concerned husbancry (or protection from grazing).
Tarleton State University Hunewell Ranch. Erath County, Texas. October (at anthesis stage).
59. Spikelets on sandstone- Tiny spikelets of sand lovegrass lying against the parent material of Cross Timbers soils. Sand lovegrass usually has four to 18 florets (Gould, 1975, p. 185). These spikelets were gathered from the plants shown in the preceding slide.
Bosque River, Erath County, Texas. October, grain-ripe stage.
60. Rosetted and fascicled foliage on the floor- Two plants (one in each of two photographs) of white-haired panicgrass, white-haired rosettegrass, white-haired rosette panicgrass (Panicum villosum= P. acuminatum var. villosum= Dichenthium acuminatum subsp. villosissimum= D. villosissimum) on the floor of a Quercus margarettiae-Smilax bona nox habitat type, a scrubland known locally as sandrough or sandtangle. Foliar clusters of these plants at this season were both the basal rosette and autumnal-phase fascicles. The basal rosette was visible clearly at right of the second slide (and in the first slide of the next or immediately following slide-caption set).
The rosette panicgrasses are quite distinctive from the non-rosette Panicum species. The rosette Panicum species are cool-season species that have the C3 photosynthetic pathway. Based on the rosette morphological feature Hitchcock and Chase (1950, ps. 627, 638-642) recognized and distinguished the rosette panicums as a subgenus designated Dichanthelium. Subsequently, various agrostologists--largely led by Gould (1975, ps. 477-498) and, later, bolstered by cladistic studies--elevated subgenus Dichanthelium to genus Dichanthelium. Such treatments included the cladistic-crazed Barkworth et al. (2003, ps. 406-450) and Gould's protégé, Shaw (2012, ps. 390-418). Other agrostologists including Texas-based workers (Diggs et al., 1999, ps. 1291-1302) and the widely respected Gleason and Cronquist (1991, ps. 796-806) retained Dichanthelium as a subgenus (meaning they rejected Dichanthelium as a genus-level taxon, and as being part of the binominal) thereby leaving Panicum as the nomenclatural unit.
To further complicate the matter of the Dichanthelium taxon (genus or subgenus), according to Barkworth et al. (2003.p. 358) not all species included in the Dichanthelium genus have the rosette of basal leaves. In the key provided by Barkworth et al. (2003, p. 358) some Dichantheliumnot species do not have differing morphology between basal leaves and those produced on upper shoots (cauline leaves). Instead, some Dichanthelium species had to be distinguished from Panicum species based on whether panicles appeared by late spring (Dichanthelium) or by mid-summer (Panicum). Such a distinction could be readily regarded as arbitrarry and based on taxonomic arguments grounded on flimsy--if not fabricated (prejudically selected to justify a pre-determined distinction)--botanical facts (general dates of flowering were correct). Arguments for or against elevating Dichanthelium to a separate genus (rather than retention as subgenus) depend on "cherry picked"-criteria used as evidence for phylogeny (phylogenetic relatedness; systematics as to evolutionary origins).
The author of Range Types rejected cladistics and retained the traditional genus, Panicum for the rosette panicgrasses, but did offer a discussion and cited the most rleevant references.
There may well always be controvesy regarding nomenclature and taxonomy of the rosette panicgrass species of which there are as many as there are imaginative ways to 'split hairs" (in cases of some pubescence features almost literally) among taxonomic splitters. In Flora of Northcentral Texas Diggs et al.(1999, ps.1293-1294) recognized (listed and described) fifteen species of rosette panicgrasses and three varieties of P. acuminatum. These latter varieties have been interpreted as separate species by various taxonomists.
Erath County, Texas. Early November; complete vegetative development of these shoot units.
61. Rosettes and fascicles or upper and lower shoot-outs- Entire shoot (first slide) and upper shoot only (second slide) of Lindheimer's rosettegrass, white-haired panicgrass, or white-haired rosette panicgrass growing on the floor of a sand post oak-saw greenbriar shrubland ("sandrough" or "sandtangle") in the West Cross Timbers. The example presented in the first slide both the tuft or rosette of basal leaves (left) and the upper cluster of leaves known as a fascicle (right) whereas the upper shoot in the second slide had two fascicles.
White-haired rosette panicgrass is one of many species of panicoid grass (subfamily, Panicoideae; tribe, Paniceae) the shoots of which consist of 1) a rosette of basal leaves that develop during the cool-growing season and 2) an upper shoot with clusters of short leaves out which develops the panicle this unit knonw as a fascicle. Most rosette panicgrasses produce both vernal and autumnal phases of fascicles which have different morphological features. Some dichotomous keys to the rosettegrasses or rosette panicgrasses include both spring and autumn phases while others include only one phase. The flora of northcentral Texas (Diggs et al. 1999, ps. 1291-1302) included only spring fascicles (vernal phase).
Even without differences between spring and fall fascicles the rosette panicgrass are very problematic and their taxonomic treatment controversial. The rosette-grasses (as these rosette-producing panicgrasses are sometimes called) were included in the Dichanthelium subgenus of Panicum by Hitchcock and Chase (1950, ps. 627, 638-642). Later, Gould (1975, ps. ps. 477-498) elevated Dichanthelium to genus status and his intrepretation was adopted in some agrostologiscal treatments including the cladistic-based arrangement in Barkworth et al. (2003, ps. 406-450) and by Gould's student, Shaw (2012, ps. 390-418).
White-haired panic, the native grass and the herbaceous species with greatest cover in these dwarf forest tracts, apparently has a pattern or condition of genetic, morphological, and taxonomic variation that is similar to that of sand post oak and dwarf conifer species found on harsh, infertile soils. Taxonomic interpretation of white-haired panic has varied among agrostological authorities (Silveus, 1933; Correll and Johnston, 1979, Gould, 1975; Hignight et al., 1988; Diggs et al., 1999; Feckman and Lelong, 2003, Shaw, 2012) at levels of genus, species, subspecies, and variety. White-haired panic was designated by numerous scientific names including Panicum acuminatum var. villosum, P. villosissimum, P. lanuginosum in part, P. ovale var. villosissimum, Dichanthelium villosum, D. acuminatum var. villosum, and D. lanuginosum var. villosissimum. Intergradation and hybridization among subspecies and varieties is widespread within the Panicum or Dichanthelium taxon resulting in morphological diversity and taxonomic difficulty (Gould and Clark, 1978; Feckman and Lelong, 2003; Shaw, 2012). Lelong (1984) described eight taxonomic varieties within the polymorphic Panicum acuminatum complex which he described as the "most troublesome" species in the Panicum genus. Even with such varietal diversity in P. acuminatum, Lelong (1984) departed from the treatment by Gould and Clark (1978) and interpreted P. acuminatum var. villosum as a variety of the morphologically similar P. ovale (= P. ovale var. villosum) which had been recognized by Hitchcock and Chase (1950) at the species level as P. villosissimum as was P. ovale which Gould and Clark (1978) recognized as Dichanthelium ovale. For this taxon in the Cross Timbers of Texas (Diggs et al., 1999) used P. acuminatum var.villosissimum while Shaw (2012) gave D. ovale var. villosissimum.
Shaw (2012, p. 394) cited work stating that Dichenthium acuminatum was the most problematic species in the Dichenthium genus due to extreme polymorphic variability. Smaller plants of Lindheimer's rosettegrass often produce only one shoot whereas larger individuals have been found to produce from three to seven shoots arising from the basal rosette (R.E. Rosiere, personal observation).
Erath County, Texas. Early November; complete vegetative development of these shoot units.
62. A fascicle of fascicles- Three progressively closer-in and more detailed views of an autumn phase fascicle of white-haired rosette panicgrass that grew on a sandrough shrubland, a sand or scrub post oak-saw green briar habitat type, in the West Cross Timbers of northcentral Texas. Fascicle was defined generally by Diggs et al. (1999, p. 1436) as "a condensed or close bundle or cluster", but Hitchcock and Chase (1950, p.990) after providing the generic "little bundle or cluster" went on to specify "clustered leaves, branches of a panicle, and spikes or racemes on an axis".
The typical fascicle of Lindheimer's rosettegrass is actually a fascicles of fascicles. There are several clusters each of which bears a panicle so that the entire unit is a collection of small fascicles (most are complete with a panicle) forming a larger, denser, collective bundle (ie. a "bundle of bundles" or "cluster of clusters"). This specimen had three fascicles within the overall fascicle or three sub-fascicular units with the entire bundle or cluster. Eaach of these three units or smaller sub-fascicular parts had a panicle (so a "panicle of panicles" as well as "a fascicle orf fascicles". Hence, a repeating pattern of shoot, including inflorescence, development. Furthermore, there were frequently two to four such "fascicles of fascicles" on a single shoot of Lindheimer's rosette panicgrass, and three or more shoots per individual plant of this rosette-forming Panicum species. Net result was quite a number of grains (caryopses) produced per small plant of Lindheimer's rosette panicgrass.
Erath County, Texas. Early November; complete vegetative development of these shoot units.
63. Dwellers of deep sand- Purple sandgrass, Texas bullnettle (Cniolus texanus), slender snakecotton (Froelichia gracilis), and heart-sepal wild-buckwheat (Eriogonum multiflorum) as local members of the herbaceous understorey at edge of a "sand roughscrubland dominated by sand post oakin the Western Cross Timbers.
Eastland County, Texas. Mid-October; early autumnal aspect.
64. Sand-adapted annual- Purple sand grass (Triplasis purpurea) is a native, annual, warm-season (tribe, Eragrostiteae) grass that, as implied by its common name, is best adapted to deep-sand habitats and locally disturbed areas. This smallish, cespitose (tufted or bunched) grass prefers deep sand, especially along margins of forest or in forests of relatively open composition. It is also adapted to disturbed areas of the Cross Timbers and is generally uncommon, other than locally. The dwarf forest or shrubland of "sandrough" is ideal habitat for this tufted yet sprawing species. In fact, purple sand grass is a good indicator species--though not exclusively so by any means--of sand post oak-dominated vegetation.
The first of these two photographs showed six rather distinct plants on the recent clearing of a powerline corridor. The second slide presented a single plant on the new clearing. Both images were top-down photographs of purple sand grass to show its rather prostrate and sprawing habit.
Erath County, Texas. Early October; mature plants with ripening grain and approaching end of their life cycle.
65. Stand-alone sandy characters- Two large specimens of purple sand grass growing on a power line corridor at edge of a sandrough range community in the West Cross Timbers. The first slide ws taken in mid-morning under fairly heavy cloud cover whereas the second slide was taken in mid-afternoon under a cloudless sky. The second slide includes a tiny though mature plant of purple sand grass to immediate left of the regular-sized mature plant.
Purple sand grass is not particularly palatable, but this species is extremely valuable in providing protection against accelerated soil erosion, both of wind- and water-induced forms.
Erath County, Texas. Early October; mature plants with ripening grain and approaching end of their life cycle.
66. Up close and personal- Two mature plants of the native, tufted, annual grass called purple sand grass growing in a "sandtangle" dwarf forest of sand shrubland in the West Cross Timbers of northcentral Texas.
Eastland County, Texas. Early October; approaching final stages of plant maturity with ripening grain.
67. Almost as red as purple- A close-in, side view of purple sand grass to show the high density of tillers, a characteristic of this native, annual species. Plant base and basal parts of shoots of a robust plant. This specimen was growing at edges of a power line adjoining a climax sand post oak.
Erath County, Texas. Early October; mature plants with ripening grain and approaching end of their life cycle.
68. Showy shoots- Details, including unique coloration of shoots and their prostrate and ascending habit, of purple sand grass. The upper of these slides was a top-down view into the center of the tufted dense congregation of tillers. The lower photograph included portions of several shoots so as to present leaf blade, leaf sheath, loeaf axils, and portions of culm.
This was another plant that grew at adjoining edge of a power line clearing and a climax range plant community dominated by sand post oak and fiddleleaf or sawtooth greenbrier, potential natural vegetation known locally as "sandrough" or "sandtangle".
Erath County, Texas. Early October; mature plants approaching end of their life cycle.
69. Get the general picture- Spikelets of sand grass, a native annual adapted to deep sand and growing on the sandrough scrubland or dwarf forest dominated by sand post oak.
Erath County, Texas. Mid-October; sort- to hard-dough phenological stage.
70. Arrow-feathered- Inflorescences of arrowfeather threeawn (Aristida purpurascens) lying on decomposing, downed trunk of sand post or margarette oak in a deep-sand scrub forest or shrubland dominated by this woody species. Arrowfeather threeawn was very sparse in the understorey of this range plant community, but it served as an indicator species of a more-or-less closed woody canopy. (Arrowfeather threeawn is one of the few Aristida species in the Cross Timbers and Prairie area of northcentral Texas and southcentral Oklahoma that inhabits forests and dense scrub vegetation.)
Erath County, Texas. Mid-October; grain-ripe to grain-shatter phenological stage.
71. A clammy one in the sand- Single, large (perhaps not for this species) plant of big clammyweed or big crestpetal (Polanisia erosa) growing in a stand of purple sandgrass on "sandrough", a dwarf forest or shrubland dominated by sand post oak, in the Western Cross Timbers in northcentral Texas. Big clammyweed is a member of the caper family (Capparaceae= Cappardaceae) many members of which are, like P. erosa featured here, xerophytes (Smith, 1977, p. 129). Another feature of several caper family members growing on North American ranges is the annual life cycle pattern. This is an evolutionary adaptation to xeric habitats such as the deep-sand, infertile soil of "sandrough" vegetation.
Eastland County, Texas. Mid-October; late-bloom/early fruit stage.
72. Deep sandy flowers and fruits- Fruit (capsule) and flowers (first slide) and the unique flowers (second slide) of big crestpetal or big clamyweed on the deep-sand habitat of a dwarf forest or shrubland dominated by sand post oak in the West Cross Timbers of northcentral Texas. These organs were growing on the specimen introduced in the immediately preceding slide. Basis of the common name, crestpetal, was obvious in the second slide.Big crestpetal is a xerophyte that is well adapted to the xeric, edapnic environment of the "sandtangle" pygmy forest that so fascinated this author.
The "crest" of these petals was described by Diggs et al. (1999, p. 506) as a "long claw".
Eastland County, Texas. Mid-October; late-bloom/early fruit stage.
73. Two humble ones- Two plants of Texas spiderwort (Tradescantia humilis) growing on a locally disturbed spot of deep sand on which a dwarf forest or scrubland dominated by sand post oak had developed. This is one of several Tradescantia species within the Cross Timbers and Prairies area of northcentral Texas and southcentral Oklahoma. T. humilis is one of the smaller of this speciesand is a characteristic species in bare-soil spots in "sandrough" as these dwarf forest or scrublands are known by ranchers, dairymen, and farmers in this general area.
Erath County, Texas. Mid-April; peak-bloom stage (was there any doubt?).
74. Ahumble one seen up close- Two views of a plant of Texas spiderwort growing on a disturbed microhabitat in "sandtangle", a scrub forest or shrubland dominated by sand post oak.This is one of the smaller, even dimutitive, Tradescantia species in the Cross Timbers-Prairies vegetational area of Texas.
Erath County, Texas. Mid-April; peak-bloom stage (and a nice showing).
75. Drummonded in the sand- Drummmond's phlox or pride-of-Texas (Phlox drummondii), a dainty annual that thrives in the spring-moist sand of "sandrough", the dwarf forest or oak scrubland dominated by sand post or margaretta oak. In small openings and at the edge of sand post oak-dominated vegetation this member of the phlox family (Ploemoniaceae) thrives for a brief period.
Erath County, Texas. Early April; full-bloom phe3nological stage.
76. Texas-proud- Drummond's phlox or pride-of-Texas growing in a local disturbance (a natural opening or gap; a so-called "clearing") in the interior of a "sandrough" or "sandtangle" community, a dwarf or scrub forest or, alternatively (depending on perspective), a shrubland dominated by sand post oak. In a ratio of shoot to inflorescence size this annual forb may well be without peer in North America. Few other native dicotyledons allocate as a great a proportion of their resources to sexual reproductive effort (at least from the standpoint of flower size and growth) as does this pride-of-Texas phlox. What? You thought the pride of Texas was a yellow rose? Shows what you know about Texas.
The annual life cycle is an (= one) adaptation of plants to extremely harsh ("sterile", "barren") habitats or living conditions be that determined by soil, light, moisture, wind, flooding, temperatures, etc.; variations in these; or interactions among them that make for extremely rigerous conditions for life. The opportunistic feature of annuals with their capacity for "boom or bust" populations is one survival mechanism or "foraging strategy" for living in "feast or famine" environments. Therophyte (Raunkiaer, 1934) is the name for the life or growth form of annuals (and of some biennials) characterized by high allocation of resources to seed production as the means for survival during dormancy or from one generation to the next. Drummond's phlox epitomizes this annual life cycle adaptation, this approach or means to natural selection or fitness (perpetuation of the species through successful reproduction).
The deep--and characteristically dry--sand beds of the sand post oak range type and ecosystem is a "hostile" habitat to which the annual life cycle is a "good fit" for species fitness.
Erath County, Texas. Mid-April; full-bloom stage.
77. A mean one- Plant of Texas bull-nettle, spurge-nettle, or tread-softly (Chidoscolus texanus) growing in a small opening of sandrough or sandtangle (Margarette oak, sand post oak or scrub post oak scrubland) in the West Cross Timbers-Grand Prairie vegetational mosaic in northcentral Texas. This member of the spurge or croton family (Euphorbiaceae) is a perennial with an extremely large taproot and an extraordinary drought tolerance. (The large root is edible, by the way.) The most distinguishing or sometimes and, unfortunately, memorable feature of this range plant if one brushes up against it (or cluelessly touches it) is the long-lasting stings imparted by numerous of trichomes (large, needle-like, poisonous or toxic hairs) with which this monster is armed. This physiological condition is known as contact urticaria, from Urticaceae, the sting-nettle family (Diggs et al., 1999, p. 598). Early chemical analysis of extracts from the trichomes showed presence of serotonin and perhaps as-yet unknown compounds (Lookadoo and Pollard, 1991).
The standard euphorb-type inflorescence of the Crotonoideae or Euphorboideae subfamily with opened and unopened flowers was presented in the second slide. Texas bull-nettle is monecious with separate male and female flowers in the flower cluster (Diggs et al., 1999, p. 598). Open flowers seen here were staminate (anthers still down deep in corolla).
For all of its remarkable (sometimes, sensational) feature Texas bullnettle has apparently received little study. Brief botanical descriptions such as that in Diggs et al. (1999, ps. 596, 598) are about the extent of thorough treatment. Another brief description was that of Johnston and Warnock (1963, ps. 124-126) as was that in the "bible" of Texas plant species, Manual of the Vascular Plants of Texas (Correll and Johnston, 1979, ps. 954-955).
Texas bull-nettle is generally observed to do best on disturbed habitats such as old fields (abandoned farmland), road cuts, and overgrazed pastures. The open, (often bare sand) habitat of dwarf post oak shrubland afforded similar environments, especially at microsite scale, for Texas bull-nettle. The pink flowers around the Texas bull-nettle seen here were on the annual Phlox drummondii, another species doing well on disturbed land and especially common on scrub post oak shrubland.
Erath County, Texas. Mid-April, and both slides taken under overcast sky); peak bloom stageof phenology.
78. An infrequent community member- Three early shoots of Queen's delight (Stillingia sylvatica) at early bloom stage in a small opening inside a dwarf forest dominated by sand post or margaretta oak in the West Cross Timbers of northcentral Texas. Queen's delight was one of the least common plants in this pygmy forest or scrub oak shrubland (depending on one's perspective), but it was present in local microsites. Interestingly, this Stillingia species has deep sand as its prime habitat whereas S. texana, the other Stillingia species in this area, is a plant of shallow, calcareous soils of the adjoining Grand Prairie. Both of these Stillingia species are perennial forbs arising from a woody root.
Queen's delight is a member of the spurge family (Euphorbiaceae) like Texas bull-nettle, but this plant does not bear any epidermal weapons.
Erath County, Texas. Early May, early bloom stage of phenology.
79. Succulent in the scrub- Comparatively large sprawling colony of Devil's tongue or eastern pricklypear (Opuntia humifusa or, based on some authorities, O. compressa) growing in an opening of "sandrough", a scrub forest or scrubland (depending on interprettion), in the Western Cross Timbers.
Eastland County, Texas. Early October.
80. Scrawny fruit- Three berries, the fruit type of the Cactaceae, on cladophylls of Devil's tongue or eastern pricklypear growing in a sand post-oak dominated range community. The two gray-colored "sticks" running horizontally through the cladophylls were shoots of the ever-present fiddleleaf greenbrier.
Erath County, Texas. Late October.
81. Grapes on perimeter- Mustang grape (Vitis mustangensis= V. candicans) growing on deep sand on outer edge of a sandrough (tanglerough) community. This Vitis species is adapted to a wide array of habitats. This particular specimen was in full-bloom. Erath County, Texas. April.
82. Blooming on the rough (sandrough that is)- Photograph of mustang grape showing arrangement of inflorescences and leaves along shoots. Deep sand has high infiltration capacity but harsh overall edaphic moisture relations so that remarkably low quantities of soil moisture are often available which makes for a hard-scramble habitat.
Erath County, Texas. April, full-bloom phenological stage.
83. Details of mustang grape- Leaves and flower clusters of mustang grape growing on sandrough scrub or dwarf forest range.
Erath County, Texas. April; immediate pre-bloom opening phenological stage.
84. Now wer're open for business- Clusters of opened flowers of mustang grape on the same "sandrough" scrub or dwarf forest dominated by sand post oak as in the preceeding slides of unopened flowers of mustang grape.
Erath County, Texas. Mid-April; peak-bloom phenological stage.
85. Plentiful (and sandy) harvest- Fruit-laden shoots of mustang grape growing on the edge of a sandrough or sandtangle scrubland on deep sand in the West Cross Timbers of northcentral Texas. Fruit crops in mustang grape are less common than no crop (crop failure), and bumper crops like the one displayed in these and subsequent slides are quite infrequent. This was the heaviest yeild of mustang grape on sandrough seen by this field observer so it was promptly shared.
Erath County Texas. Late October; fruit-ripe to mostly over-ripe phenological stage.
86. Abundant crop; reluctant harvest- Details of berry bearing shoots of mustang grape on edge of a sandtangle scrub range in the West Cross Timbers of northcentral Texas. Most leaves had already been shed and those still on the shoots were mostly senesced (more dead than alive having completed the life cycle of these annual organs).
The author did not know when these berries had ripened, but their mostly over-ripe state of maturity yet presence "still on the vine" attested to the general lack of palatability to most aniimals, inculding to humans in a raw state (see captions below).
Erath County Texas. Late October; fruit-ripe to mostly over-ripe phenological stage.
87. Fit for wild horses (or hogs, and that's about all)- Over-ripe berries and senesced (more dead than alive) leaves of mustang grape on the perimeter of a sandrough scrub range (beef cattle, white-tailed deer, Rio Grande wild turkey) in the West Cross Timbers of northcentral Texas. Fruit type of grapes (Vitis spp.) is a berry, "a multiseeded, indehsicent fruit in which the pericarp is fleshy throughout (Smith, 1977, p. 290). In case of mustang grape, these berries are extrmely tart not uncommonly imparting a burning sensation to the human mouth. In fact, apparently this characteristic "taste" (chemical sensation to taste and associated organs) also obtains in many other animals given that these fruits are usually left uneaten as, for example, on this range where even wild turkeys and numerous individuals of northern mockingbird (Mimus polyglottos) had elected to leave these tart fruits untouched.
The deltoid leaves of mustang crape characteristically have a dished adaxial ("upper") surface with leaf margins turned upward (as if to hold water). "On the other leaf" it is common to see leaves of mustang grape with upper leaf margins projecting downward. Examples of both inclinations were visible in the examples seen in photographs included in this section.
Details of the grape berry was provided in the immediately succeeding caption.
Erath County Texas. Late October; fruit-ripe to mostly over-ripe phenological stage.
88. Sand-covered and pert 'nar juiceless- Berries of mustang grape produced on the margins of a sandtangle scrubland that developed on deep, loose sand in the West Cross Timbers of northcentral Texas. This author did not know when these fruits reached peak ripeness, but obviously most of these berries were past that stage having progressed to the point of being primarily a semi-moist pulp covered with a leathery skin. If that stage of maturity had not been enough to reduce palatability of these organs a covering of sand and caliche (calicum carbonate) further added to reluctance of animals (including white-teiled deer, wild turkeys, mockingbirds) to consume these berries.
The fleshy fruit of Vitis species is a true fruit in which the entire pericarp is soft (Smith (1977, p. 69). Cronquist (1971, p. 626) described a berry generally as being a flsehy fruit with fleshy pericarp or with a hard or leathery rind and specifically the berry of grape was a typical berry with a fleshy pericarp and having an exocarp being a thin skin. The exocarp is the outermost layer of a the pericarp which is the ovary wall of ripe fruit (Cronquist, 1971, p. 625).
Erath County Texas. Late October; fruit-ripe to mostly over-ripe phenological stage.
89. Deceiving fruit- Detailed views of berries (berry being the fruit type of grape species) of mustang grape growing on the outer contact of sandrough, a scrubland range type dominated by sand or dwarf post oak, in the West Cross Timbers of northcentral Texas. Berries shown here were in various stages of maturity ranging from early ripeness to overripeness. Most had progressed to the post-ripeness stage of matuirty so that most "juice" was gone and the inner pericarp had turned to a semi-moist pulp.These berries had been "dusted" with blown sand and caliche (calcium carbonate) particles so that their palatability (mostly lack thereof) to animals, including man, on this range had been further reduced.
At their "very best" mustang grapes have a shrp tartness or "tangy" taste. Vines (1960, p. 716) described this fruit as "possessed of a fiery pungency which, unless the skin is carefully removed, irritates the mouth". Mustang grapes are best when made into jam or jelly or, if one is not a teetotlaer, wine. This latter form of consumption would not quite be up to standards for domesticated "fruit of the vine" in France, California, or even viticultural newcomer Texas. It should be noted tht resident whit-tailed edeer, wild turkey, mockingbird, and bluejay (Cyanocitta cristata) chose to leave this fruit of the vine still on the vine. Even free-ranging feral hogs in this area had somehow missed these tangy morsels.
Description and specifics of the grape berry were given in the immediately preceding caption.
Erath County Texas. Late Octobe ; fruit-ripe to mostly over-ripe phenological stage.
90. Rusty on a sandrough- Inflorescences and leaves of rusty or southern blackhaw (Virburnum rufidulum) growing on outside edge of a sandrough or tanglerough range. The deep sand of this range site has high water infiltration capacity so that a lot of soil moisture is available to plants, at least for short periods of time. This versatile shrub that is often at home on river bottoms was taking full advantage of recent spring rains.
Erath County, Texas. April, full-bloom phenological stage.
91. Roughleaf dogwood blooms- Two views of flower clusters of rusty blackhaw thriving on a sandrough range shortly after heavy rains, almost all water of which quickly went into the soil profile of this otherwise tough country. Erath County, Texas. April.
92. Doggone study- Bunch or cluster of drupes and leaves of roughleaf or Drummond's dogwood (Cornus drummondii). These two examples had been produced on the large, spread-crowned specimen introduced in the immediately preceding photograph. This individual was growing on Richardson's Creek, a small stream running through a landscape patchwork of Grand Prairie and West Cross Timbers in northcentral Texas.
The fruit type of dogwood (Cornus) species is a drupe, "a fleshy fruit with a firm endocarp that permanently encloses the usually solitary seed, or with a portion of the endocarp separately encloseing each of two or more seeds" (Gleason and Cronquist, 1991, p. 872). In the specific instance of Cornus species the drupe has one stone which has one to five locules each of which has a single ovule developing into a seed (Gleason and Cronquist, 1991, p.323).
Tarleton State University Hunewell Ranch, Erath County, Texas. Late October; fruit-ripe stage.
93. Drupped in the Cross Timbers- Ripe and over-ripe (dried) drupes of roughleaf or Drummond's dogwood on a large plant growing on the bank of a small stream (Richardson's Creek) in northcentral Texas in a landscape mosaic of Grand Prairie and West Cross Timbers. Drupes of roughleaf dogwood are borne in groups or clusters that are typically widely spaced on red-pigmented branchlets or pedicels.
Roughleaf dogwood is a characteristic shrub of tallgrass prairie and adjacent savannahs like those of the Cross Timbers and Prairie Peninsula.
Tarleton State University Hunewell Ranch, Erath County, Texas. Late October; fruit-ripe stage.
94. Doggone fruit- Immature (first or top slide) and mature fruit (second or lower slide) of roughleaf dogwood. The former was in the Texas Blackland (also Waxyland) Prairie (Fannin County, Texas; July). Example of mature fruit was in West Cross Timbers (Erath County, Texas; October). The fruit type of dogwood is a drupe.
95. Study of sandrough scrub range- Physiogonomy and structure of a climax sandtangle or sandrough shrubland in the West Cross Timbers. At the exterior of this potential natural (postclimax in the Clementsian model) vegetation of deep-sand soil the architecture typical of this range community was readily seen. The two trees at right were blackjack oak, a woody species much less abundant than the dominant sand, scrub, or dwarf post oak (known also as Margarete oak).
Almost all of the lower vegetative cover in this perimeter view was that of common or saw greenbriar, which is consistently the associate to co-dominant plant species of this unique rangeland cover type.
Erath County, Texas. October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
96. Bare interior- Inside a sandrough shrubland that was dominated almost exclusively by sand, scrub, or dwarf post oak or Margarete oak and with common or saw greembriar as the associate species. This stand of dwarf post oak afforded a typical example of: the more open form of this range type showing 1) the habit of sand post oak, 2) interior structure of this range vegetation when dominated almost exclusively by sand post oak, 3) simple structure largely devoid of lower vegetational layers (except for greenbriar), and 3) nearly complete coverage of soil surface by oak leaves yearlong. Note that current year's leaves are still on trees (ie. were not yet shed) so that ground cover consisted of leaves from previous years.
The first of these two photographs was taken from a small opening in the canopy cover. A few upper shoots of mare'stail or horseweed (Conyza canadensis) were visible in foreground (along with planty of saw greenbriar of course). Horseweed is typically a pioneer or colonizing species of disturbed or very marginal areas.
Erath County, Texas. October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
97. More of a bare inside- Set of three progressively closer-up views within the interior of the more open or "bare" understorey form of a sand, scrub, or dwarf post oak-dominated shrubland in West Cross Timbers. The vegetational expression (or form) of more open understorey (fewer layers of vegetation and/or less lower cover) of sandrough scrubland provided almost no range feed other than the mast of acorns in autumn and grazable lower leaves and tender shoots of saw greenbriar in spring.
Attention was drawn to the almost complete ground cover of oak leaves shed from previous years. All current year's leaves were still alive on oak branches.Some plants of various herbaceous species had emerged through the shallow cover of leaf litter. Any mulching effect of leaves was limited to moisture conservation and not plant exclusion. Conversely, it seemed obvious that the sparse ground cover was due--to some degree at least--to shade or, rephrased, to exclusion by canopy cover of adequate light for survival of plants that were limited to lower levels of the vegetation structure. Common or saw greenbriar, the associate and, rarely, co-dominant plant species obviously gathered adequate light for robust growth (including reproduction) by climbing to top of tree crowns.
It must also, however, be allowed that grazing by cattle and white-tailed deer on this range was almost assuredly another important factor for scarcity of herbaceous species like the grasses. Then again, as will be discussed below, the species of grasses present in this understorey were usually decreaser species such as sand lovegrass and little bluestem (Andropogon scoparius= Schizachyrium scoparium). Invader species of grass such as annuals like crabgrass (Digitaria spp.) and grassbur (Cenchrus insertus= C. longispinus) were absent. This observer did not encounter a single plant of crabgrass or grassbur in this range plant community in two and a half days of sampling this vegetation (Rosiere, unpublished data).
Important hint to sandrough visitors: the appearance of "openness" and thus relative ease in moving through the range vegetation seen in this section is most deceiving. Spaces between oak shoots (boles, trunks, or whatever term is appropriate) were almost inevitably spaces occupied by shoots of saw greenbriar such that there was so much cover--such a living barrier--of thorn-fitted vertical "strands" that movement of larger animals, including humans and livestock, was greatly impeded. It was "woody hell" getting through this mess. Recommendation: wear strong, durable clothing and move slowly and carefully when passing through sandtangle scrub.
Erath County, Texas. October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
98. Woody all around- Interior of a more open form of a shrubland on deep sand dominated by sand, scrub, or dwarf post oak with common greenbriar as associate species and almost no understorey other than basal shoots (with some leaves) of the common or saw greenbriar. This pair of "nested photoplots" fetured a comparatively large plant of mustang grape (center midground of first slide and right most trunk of second slide). Mustang grape typically occurs almost exclusively along the more sunlite perimeter of sandrough range, but it does rarely become established and apparently thrives in the more open areas in the interior of sandrough as seen in these two "nested" photographs.
Several thorn-fitted shoots of saw greenbriar--visible as basal green leaves near the ground surface--were in the range vegetation of these two slides. Even though this wooded vegetation appears to be relatively "open" it was so full of greenbriar stalks that movement through it was severely hampered.
Erath County, Texas. October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
99. Still all woody- Another plant of mustang grape (different from the mustang grape shown in the preceding two slide-caption set) with sand or scrub post oak in a tract of sandtangle, a shrubland dominated by dwarf post oak with saw greebriar as associate on a deep sand environment in the West Cross Timbers of northcentral Texas.
Erath County, Texas. October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
100. Oak shoots and briar- Local stand of sand or dwarf post oak and blackjack oak (right-most tree with "pins", dead limbs, hanging down) with a lot of saw greenbriar shoots climbing into crowns of oaks. Greenbriar shoots are not conspicuous in this photograph or even when one is in this vegetation until right upon them. This is the problem in trying to move through this mess. While this range plant community appears to be "open" it is actually so filled with greenbriar shoots that movement by humans, livestock, and deer is difficult and time-consuming. Greenbriar also impeds utilization of any herbaceous growth in the understorey. In this way, greenbriar offers considerable protection from grazing/browsing animals.
This would be a Quercus margarettiae-Smilax bona nox habitat type using Daubenmire (1952, 1968A) classification.
Erath County, Texas. October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
Interpretation of morphology and, therefore, plant community: The small tree-size of stature and trunk-diamter of scrub or dwarf post oak was such that these woody plants could be interpreted as trees (albeit them of "substandard" size) and hence this woody vegettion interpreted as a forest. Perhaps the concept of a forest of midget trees: something like the so-clled pygmy forest of northern California as, for instance, the Jug Handle State Natural Reserve in Mendocino County, California. (This latter example was covered in Range Types in the chapter, Pacific Northwest Forests under the section in turn titled Scrub Forests of the Pacific Coast Region.)
Such a conceptual view of sandrough scrub as a "pygmy forest" would, in this worker's view, be less descriptive than scrub oak shrubland because the oak plants sare generally (though arbitrarily) the size of large shrubs than of small trees. Perhaps more importantly is the fact that many of the shoots--that appear as individual trees--of sand or scrub post oak are various offshoots (clones, modules, ramets) of rhizomatous genotypes (genets), trees with generally belowground rootstocks. This was recognized by Sargent (1933, p. 295) when he described Q. stellata var. Margaretta f. stolonifer that formed "broad thickets with stoloniferous shoots". (These horizontal shoots could be interpreted as either woody stolons or rhizomes but most of these structures are belowground.)
Conversely, these oaks could be interpreted as trees in the same fashion as other colony-forming tree species with spreading rootstocks such as quaking aspen (Populus tremuloides) and black locust (Robinia pseudoacacia) or New Mexico locust (R. neomexicana). New Mexico locust has generally been viewed as a shrub whereas black locust is clearly of tree-size.
Thus there seemed to be no way to avoid some arbitrary interpretation of dwarf, scrub, or sand post oak. Many plants (shoots) of this species in northcentral Texas seemed to be larger than some scrub oak plants described elsewhere. (Perhaps this larger size was appropriate for the Lone Star State.)
One thing for certain: this woody plant community had a closed canopy (ie. interlocking crowns) so that it was not woodland or savanna.
101. Internal structure and makeup- Two examples of the sand or scrub post oak-saw greenbriar (Quercus stellata var. margarettiae= Q. margarettiae-Smilax bona nox) habitat type system of Daubenmire (1952, 1968A) was applied to this sandtangle scrub plant community. Interior of this range cover type was presented in these two views. A number of basal shoots of greenbriar were on the floor of this scrubland which had a more-or-less completely closed canopy. This range vegetation had been grazed by cattle and white-tailed deer. It was not known what, if any impact, this had on the understorey layer. Plant cover of lower layers was sparse, but much of this apparently was due to extremely limited sunlight penetrating through the canopy to the lower layers.This scrub plant community was in the West Cross Timbers of northcentral Texas.
For all of its simplicity from a plant species composition standpoint this is the potential natural (climax) vegetation for this deep sand environment. In the monoclimax theory of F.E. Clements this is postclimax vegetation (Clements, 1936, ps. 266-267, 269; Weaver and Clements, 1938, ps. 82-83, 85-86). This phenomenon of deep sand furnishing a more favorable habitat tthan the adjacent environments explains to large extent such postclimax plant communities as the Nebraska Sandhills and the Cross Timbers of which of this sandyland scrub is a part. Such shrubland is known locally as sandrough or sandtangle.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
102. Less bare interior- In the deep interior of a cattle and white-tailed deer range of sandrough--a sand post oak-saw greenbriar woody community--the density of greenbriar shoots and and lower leaves of scrub post oak were of greater density than is other parts of this same range. At this density, human penetration of the lower vegetational layers was nearly--though not quite--impossible.
There were sapling- and seedling-sized shoots of dwarf post oak. Most of these smaller, younger were clonal offshoots from rootstocks (woody rhizomes) of adult oaks. There was almost no herbaceous growth in the range vegetation seen here. Note heavy and nearly complete cover of the land surface by oak leaves.shed the previous year(s). This comparatively simple (from a plant species composition standpoint) range plant community is the climax vegetation for this deep sand habitat. Such sandyland shrubland is postclimax vegetation in the Clementsian monoclimax theory.
This vegetation was being sampled for quantiative description. Sampling included diameter breast height (DBH) and density of oak boles as well as recording density and size ctegories of greenbriar shoots.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
103. Only thing bare is "booger bear"- Interior of a nearly inpenetrable "thicket" comprised of scrub post oak or margarette oak and saw greenbriar known as sandrough or sandtangle that developed on deep sand in the West Cross Timbers of northcentral Texas. The Daubenmire (1952, 1968A) unit of habitat type could be applied readily to this range vegetation: Quercus stellata var. margarettiae= Q. margarettiae-Smilax bona nox habitat type.
There was--for all intents and purposes--zero herbaceous layer in most of this climax plant community including in the two "photoplots" presented here. The only lower woody layer was that composed of basal leaves and stems of common or saw greenbriar. Given that this liana extended from the ground to oak crowns perhaps it made no more sense to describe those lower greenbriar shoots as a layer than to regard the lower boles of dwarf post oak as part of a lower woody layer. Conversely, there were seedlings and/or small, young offshoots of runner or sand post oak that could be regarded as a lower woody layer. (Some of this lower sand post oak leafy layer was shown shortly below.)
One fact that nobody whoever traversed (or tried to) this "sandtangle" could deny that it was nearly impassable.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
104. Livin' up to its name- Interior of a shrubland known as sandtangle, a range plant community dominated by sand or scrub post oak (sometimes known as runner oak or Margarete oak) with saw or common greenbriar, a monocotyledonous liana, as the associate species. The habitat type concept of Daubenmire (1952, 1968A) could be applied handily to this simple climax vegetation: dwarf or Margarete oak-saw greenbriar or the Quercus stellata var. margarettiae= Q. margarettiae- Smilax bona nox habitat type.
In the vernacular of Winston Churchill this was a "briar curtain". Nothing but small animals can pass through the dense local stands of greenbriar such as those seen here. Larger animals like deer, cattle, and humans are compelled to go aroung such "briar curtains or "braids of briar" and usually there are abundant "vertical strands" of greenbriar along such edges. This range was being grazed by white-tailed deer and beef cattle. Both of these animal species did graze and travel throughout this scrub vegetation, or at least around patches of 'briar curtain".
Given that 1) there is very limited herbaceous plant life in such local stands of saw greembriar and 2) limited foliar cover of herbaceous species is predominately that of climax species such as little bluestem and sand lovegrass, it was not likely that grazing by cattle and deer had substantially shifted the species composition of the sporadic or widely scattered herbaceous portion of this range.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
105. Lower parts of "bearcat" vegetation- Deep interior of a cattle and white-teailed deer range of sandrough or sandtangle, a shrubland of sand post oak or Margarete oak (dominant species) and saw greenbriar (associate species) on deep sand in West Cross Timbers of northcentral Texas. By the Daubenmire (1952, 1968) habitat type system this range vegetation would be the dwarf or sand post oak-saw greenbriar or the Quercus stellata var. margarettiae= Q. margarettiae- Smilax bona nox habitat type.
It was explained in introduction of this section devoted to sandrough that dwarf or scrub post oak is a clonal species some shoots of which reach the size of small- or, rarely, medium-sized trees with most shoots being the general size of shrubs. For this reason, this range plant community, known also as sandtangle, has been interpreted herein as a shrubland, scrubland, or scrub rathern than a pygmy forest or forest of midget trees. Likewise, the shoots of this colony forming oak are of such density that a closed canopy (intertwined or interlocking crowns of the closely spaced shoots) is characteristic of this scrub so that it could not qualify as either woodland or svanna.
The clonal or modular feature of Margarete oak or scrub post oak was particularily in these two "photoplots" which featured seedling-sized offshoots (clonal or vegetatively produced shoots) forming what could be interpreted as a lower woody layer. This interpretation would be an arbitrary call as shcu shoots would not differ in orgin from leaf-bearing lower branches coming directly off the lower bole of adult-sized boles or trunks. Still, these two slides presented the predominant mode of asexual reproduction of Margarete oak. It was possible that some of these seedling-resembling shoots were, in fact, seedlings from an abundant crop of acorns produced the preceding year. Actual seedlings--instead of small or seedling-sized clonal shoots--would constitute a component of a lower woody layer in this scrub range vegetation.
There were also some shoots of saw greenbriar in the shrubland vegetation seen in these two shorter camera-distance slides of sandtangle, the appropriateness of this local, descriptive name being only all too evident. It is extremely for any large animal (eg. man, deer, cow, turkey) to move through sandtangle having this density of scrub post oak and greenbriar shoots. Density of saw greenbriar shoots seen here can be compared to the lower density and cover of greenbriar shoots in the more open understorey form of this same range that was featured earlier in this section (see again above).
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub .variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
106. Shoots, aboveground and below- Good example of the woody horizontal shoots of Margarete oak or scrub, sand, or dwarf post oak (Quercus margarettiae= Q. stellata var. margarettiae f. stolonifer) along with shoots of saw greenbriar (Smilax bona nox), the dominant and associate, respectively, of a shrubland known as sandtangle or sandrough in the West Cross Timbers of northcentral Texas.
It was not known whether these woody horizontal shoots of sand post oak were rhizomes or stolons, but most of them are below the soil surface suggesting to this worker that they were rhizomes commonly known as woody rootstocks.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub .variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
107. Something besides dead leaves- Two "photosamples" of the very limited understorey of a dwarf post oak-saw greenbriar scrubland, known as sandrough, in the West Cross Timbers of northcentral Texas. The first slide included shoots of saw greenbriar, scrub post oak or Margarete oak, and white-haired panicgrass or white-haired rosette panicgrass (Panicum acuminatum var villosum= P. villosium or P. villosissimum= Dichanthelium villosissimum) while the second slide had shoots of saw greenbriar and Lindheimer's rosette panicgrass or taper-leaf panicgrass.
Lindheimer's rosette panicgrass was the most common (or, more precisely, the least uncommon or the least infrequent) native, cool-season, perennial grass in this range plant community.
Note the essentially complete cover of soil surface by shed leaves of dwarf or scrub post oak that were shed in previous years (all oak leaves of the current year were still alive on shoots).
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub .variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
108. Sundry shoots- Lower layer of range vegetation of sandrough, a scrubland of Margarete oak or sand or scrub post oak and saw greenbriar, in the West Cross Timbers. Shoots of greenbriar, offshoots or seedlings of Margarete oak, and culm with autumnal fascicles of white-haired rosette panicgrass or white-leaf panicgrass.
Ground surface completely covered by oak leaves, almost all of which had been shed the previous year(s) with current year's leaves still on oaks.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub .variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
109. Oversanded in sandrough- Two pair of cespitose plants (two genotypes) of sand lovegrass that had been overused by beef cattle on a sandrough or sandtangle sxcrub range in the West Cross Timbers. The two sets of two genotypic plants were roughly 80 yards distant from each other, but the four plants had basically the same degree of overuse.
Two other individual plants of sand lovegrass with the same degree of extreme overuse were presented in the next two slide-caption set.
All six of these extremely overused plants would have been in the immature caryopsis phenological stage had they not been grazed to the ground. Accurate determination of phenological stage was readily determined from ungrazed plants of sand lovegrass in ungrazed outside fencerows of this and one other sandrough range. (This was shown in a photograph presented above of ungrazed sand lovegrass taken at the same time as these "mangled" plants.)
Erath County, Texas. Late October, autumnal aspect; would-have-been soft dough stage of phenology barring excessive defoliation.. Extreme Drought (Palmer Scale).
110. Sanded too rough- Two cespitose plants (two genetically distinct individuals) of sand lovegrass that had been overused by beef cattle on the sandrough range featured herein. Four other individual plants (featured as two sets of paired plants) of sand lovegrass on this sane sandtangle range were the subject of the immediately preceding slide-caption set.
Erath County, Texas. Late October, autumnal aspect; would-have-been soft dough stage of phenology barring excessive defoliation.. Extreme Drought (Palmer Scale).
Note regarding decreasers: All plants of sand lovegrass found on this sandrough range other than two small ones growing in a dense stand of saw greenbriar had received the same degree of use as the plants shown here (ie. as close a chins of cattle would permit them to crop the plants). Sand lovegrass, the climax dominant (or co-dominant species with little bluestem) for this scrubland on a Deep Sand range site, was the most widely distributed herbaceous species on this range. In local, open spots ("natural clearings") in this sandrough vegetation little bluestem was the most abundant grass and mare'stail or horseweed was the most abundant forb. Overall, however, throughout this scrub or sand post oak-saw greenbriar range sand lovegrass was the dominant and most abundant herbaceous species (afgain, such as its population was).
In spite of overuse, a climax decreaser grass was still the major grass, the major herb, on this range. Nor was this the first year that such overuse had taken place, the same grazing abuse having occurred for a number of years. It could not be determined if these few plants of sand lovergrass were the last survivors of overgrazing or, alternatively, if in spite of consistent, yearly overuse these sand lovegrass plants had persisted and were the natural or potential density of sand lovegrass on this Deep Sand range site though, unquestionably, at much lower foliar cover and apparently lower vigor. Plus this was a year of Extreme Drought (Palmer Drought Severity Index).
An ecological mystery was presented in these "photolots".
Meanwhile back at the sandrough- The slides presented in the following portion of this Sandrough section were taken ten days after the autumn scenes presented immediately above. In that brief intrum leaves of Margarete oak or dwarf post oak had commenced being shed resulting in a more distinct autumnal aspect and improved quality of photographs (even if this was not as apparent following scanning in an Epson Perfection V700 scanner).
Quality of photographs was distinctly improved by presence of a light overcast sky which prevented shadows (in contrast to slides presented immediately above taken under a full-sun sky). Periodically throughout this on-line publication the author has shown and discussed comparisons of photographs taken under overcast versus sunny skies. Qualtiy of photographs has varied depending on the photographic subject matter, sometimes being better under full-sun, well-lite atmospheres and sometimes being superior with overcast sky. In this instance, overcast clearly (no pun intended) won out, "lens-down", for most features. It should be emphasized however that the above photographs taken under a full-sun sky gave an accurate indication as to extent of canopy cover and, thus, of degree or extent of shading on the floor of this shrubland range.
111. Shedding in the sandrough- Onset (early phases) of leaf abscission and fall in Margarete oak or scrub post oak in a sandtangle shrubland in the West Crosss Timbers of northcentral Texas, These two (and subsequent) views of the interior of this sandrough range were of a more open (less dense or fewer shoots) portion of this dwarf post oak-saw greeenbriar community.
Groups of lower green leaves (those immediately to roughly a foot above the soil surface) were of saw greenbriar indicating the density and foliar cover of this travel-impeding monocotyledonous shrub, a well-armed liana. Denser stands of greenbriar and/or oak shoots were near4ly to completely impenetrable to man and larger animals including cattle and white-tailed deer, both of which fed and sheltered in this scrub plant commuity.
Absence (or, at least, near-absence) of herbaceous plant life in range vegetation was even more obvious at this point in the annual cycle of this climax plant community.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
112. Sandtangle in autumn- Interior of a shrubland range plant community, known to local folk as sandrough or sandtangle, in early stages (phases) of leaf shedding. The habitat type classification of Daubenmire (1952, 1968) could be readily applied to this native vegetation: Margarete oak-saw greenbriar (Quercus margarettiae- Smilax bona nox) habitat type. These two photographs were a "nested" set of "photoquadrants" with the second slide being a subplot of the larger "photolot" presented in the first slide.
Autumn coloration of leaves of both of these woody species was evident.
Leaf litter on the soil surface was a mixture of leaves shed in previous year(s) as well as some shed during on-going current leaf fall. Leaves from previous year(s) comprised the bulk of ground cover at this stage or phase of autumn.
Absence (or, at least, near-absence) of herbaceous plant life in range vegetation was even more obvious at this point in the annual cycle of this climax shrubland or scrub community.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
113. Autumn tangle- Interior of a sandrough or sandtangle range (grazed/browsed by cattle and white-tailed deer) with autumn-colored leaves being shed from Margarete oak or dwarf post oak and saw greenbriar. These "nested photoplots" (the second slide being a portion or subplot of the first slide) provided a good composite of interior structure and species composition of climax vegetation that could handily be described by the Daubenmire (1952, 1968) habitat type method as a (Quercus margarettiae- Smilax bona nox) habitat type in which sand post oak was the dominant and saw greenbrir the associate species.
Absence (or, at least, near-absence) of herbaceous plant life in this climax natural scrubland was obvious at this point in the annual cycle of this range plant community that was a postclimax (Clements, 1936, Weaver and Clements, 1938, ps. 85-86) on deep, loose sand in the West Cross Timbers of northcentral Texas.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
114. Tall and tangled shoots- Shoots of Margarete oak or sand, scrub, or dwarf post oak with ascending saw greenbriar climbing into oak crowns deep in the interior of a scrubland (known locally as sandtangle) in which these two woody species were the dominant and associate, respectively. These two "photoplots" were of the more open (lower shoot density) form of this postclimax range plant community.
While vegetation of this scrub range type as seen here might appear to be free or, at least, relatively clear of lower layers of vegetation this was definitely not the true situation. Saw greenbriar, though not conspicuous, was abundant enough that movement of larger animals, incluidng humans and cattle, through this range was seriously impeded. Literally every oak shoot had a number of shoots of saw greenbriar at its base and climbing to top of its crown. Furthermore, this strongly rhizomatous species of greenbriar had shoots twinning throughout "open" areas among oak shoots such that inter-trunk spaces were deceptively entangled with the thorny lianas. Even in these interspaces with lower density and cover of greenbriar there were remarkably few herbaceous plants. It was not known if near-absence of herbaceous plants was due to feeding by beef cattle and white-tailed deer or a result of fairly dense shade due to the closed canopy of Margarete or sand post oak and tree crown-occupying saw greenbriar.
This climax range vegetation was handily described as a sand or scrub post oak-saw greenbriar habitat type by the method developed by Daubenmire (1952, 1968).
Leaves of both scrub post oak and saw greenbriar had achieved autumn coloration. A good proportion of these leaves had been shed and added to the already nearly complete litter cover of the soil surface. Newly fallen leaves added a distinctive color to the ground leaf layer that, at time of these photograpahs, was still comprised primarily of leaves from the previous year(s).
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
115. Live trunks lying low- Examples of clonal Margarete oak or sand, scrub, or dwarf post oak with horizontal shoots aboveground (above the soil surface). It was not known if these horizontal shoots had actually grown above the land surface or if these woody shoots actually (initially) grew belowground and had been exposed by erosion of the sandy soil. The true situation would be relevant in determining if the shoots were stolons (aboveground) or rhizomes (belowground). Sargent (1933, p.295) apparently interpreted such shoots as stolons because he provided the nomenclatural designation and description of Quercus stellata var. margaretta f. stolonifera for the thicket-forming taxon that spread by "stoloniferous shoots". In contrast, Gleason and Cronquist (1991. p. 85) described Q. margaretta as "spreading underground and becoming colonial" thereby implying that most horizontal shoots were subterranean and, hence, rhizomes.
Shoots of sand post oak in the sandrough range featured here were more (at least appeared to be more) below- than aboveground. Actually, most shoots seemed to arise from a structure more like a large rootcrown than "running rootstocks" typical of saw greenbriar or roughleaf dogwood that also grew in openings and edges of sandrough scrubland.
The first and second slides displayed in this three-slide set were of the same shoots taken from opposite directions.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
116. Interior revealed- Two views deep inside a sand or scrub post oak-saw greenbriar (dominant and associate species, respectively) shrubland knonw as sandtangle or sandrough in the West Cross Timbers of northcentral Texas at an early phase of autumnal leaf fall. The first of these two slides was a local stand of shoots (trunks or boles) of sand or scrub post oak that was probably one or, at the most, two plants (two genotypes of Q. margaretta). Each shoot (bole plus crown) was a ramet or module of the genet (genotype).
The second slide was of one plant of blackjack oak (leftmost tree or shoot) and two quite large trunks and one small, sapling-size trunk or shoot of sand or dwarf post oak. To the immediate left of this bentover (and seemingly dead) sapling-sized shoot was amulti-shooted plant of sqw greenbriar with yellowed, autumn-coloration leaves. Dead, low-hanging limbs on these oaks (especially prominent on the blackjack oak) are known as "pins".
The nearly complete ground cover of shed oak leaves was comprised of leaves from the previous year(s) as well as some of the earliest-to-fall leaves of the current year.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
117. Still a tangle- Set of "nested" views of a stand of scrub, sand, or dwarf post oak or Margarete oak in a scrubland dominated by this species on a habitat of deep, loose sand in the West Cross Timbers of northcentral Texas. This oak species is clonal with belowground (and, less commonly, aboveground) shoots from which vertical shoots (trunks or boles with crowns) arise. It is extremely difficult to determine--even with superficial excavation--the origin of such shoots or, in other words, actual clonal units or modules and, likewise, to ascertain to which genetically distinct plants (genotypes) this offshoots belong. From the first slide it appeared that there were three modular units or, expressed differently, three genetically distinct plants with two or three shoots (modules or clones) each. Two of these genetically distinct plants or units of clonal shoots (one with two and the other with three such shoots) were presented in the second slide which was a subplot "nested" within the larger plot of the first slide.
It was also possible, however, that all shoots ("trees") seen here were clones of one genotype (ie. one plant). With this latter possibility, the groups of two or three shoots that were physically disjunct aboveground might be modular units of two or three shoots that arose from one woody rootstock or rhizome. Given the length of horizontal shoots visible aboveground as shown in preceding photographs this growth pattern or spatial arrangement of shoots was quite likely.
Genetic examination such as with DNA analysis would be the only definitive method by which parentage of individual oak shoots could be determined. Even careful tracing of underground shoots through deep excavation would not be definitive (probably not much more definitive than surmise based on trunk clumps).
Some recently shed oak leaves joined those of previous years to add further to the already nearly complete ground coverage by leaves. Although not clearly discernable, therre were numerous shoots of saw greenbriar growing beside trunks and up into crowns of dwarf post oak There were also two small plants of devil's-tongue pricklypear (Opuntia humifusa) growing at base of sand post oak.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
118. Fall in the sandrough- Species composition and architecture (structure) of a shrubland dominated by scrub oaks (with saw greembriar as associate specdies) known locally as sandrough or sandtangle in the West Cross Timbers of northcentral Texas. This scrubland is the climax range vegetation for this Deep Sand range site. In the monoclimax theory of Clements (1916, 1936) this range plant community that developed on deep, loose sand was postclimax. The more mesic edaphic habitat supported natural vegetation that was a stage or two beyond the average regional or zonal climax, the monoclimax. In polyclimax theory of plant ecologists like Sir Arthur Tansley and in the climax pattern theory of Robert Whittaker (1953) this potential natural vegetation was an edaphic climax. Net conclusion as to the potential natural plant community was the same regardless of sematics.
These two views were "nested" images with the second slide being a closeer-in view of the three-trunked small tree or large shrub at left in the first slide. This plant was a blackjack oak, an overall minor member of the sandrough plant community. The other trees--probably a total of two genetically distinct plants, two genotypes, each with at least two shoots (as in case of center plant) up to at least four shoots (as with clump of trunks at right)--were scrub or sand post oak or Margarete oak.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
119. Another mess of shoots- Two views of a local stand of Margarete oak or sand, scrub, or dwarf post oak with a plant of mustang grape as well as numerous shoots of saw greenbriar in a shrubland, known locally as sandrough, in a deep sand habitat within the West Cross Timbers of northcentral Texas. This was an example of the Quercus margaretta- Smilax bona nox habitat type if the Daubenmire (1952, 1968) was applied.
Mustang grape is considerably more abundant along edges of sandrough than inside this postclimax range vegetation, but for reasons unknown to this author plants of mustang grape sometimes occurred within local stands of scrub post oak as was the case in the example shown here.
Early phases of leaf fall with nearly complete ground cover by oak leaves of previous year(s) getting deeper with this year's addition.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
120. A "clearing" in sandrough- A local opening in the deep interior of a sand or scrub post oak-saw greenbriar (dominant and associate species, respectively) shrubland known by local folk as sandrough or sandtangle. Natural openings like this one exist infrequently though consistently throughout sandrough scrub. The opening featured here was photographed at two camera lengths to show the general extent and physiogonomy of "Mother Nature's clearing" (first slide; at greater distance) and, then, details at edge of opening (second slide; closer or shorter distance).
Biological basis of such openings were unknown, but all openings encountered in this scrubland range had small stands of short-statured, extremely scrubby dwarf post oak, especially at margins of openings, such as the one featured in the second slide. It was not known if these scrubby or "runt" shoots would grow to dimensions of mature shoots that surrounded the opening. In open spaces (those free of scrub post oak) within the larger opening (the natural "clearing") dominant plants (dominance varied at local scale or, even, microscale) included little bluestem, sand lovegrass, and mare'stail or horseweed along with the ever-present saw greenbriar.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
121. Softer ones in an opening- A natural opening within the deep interior of a sand post oak-saw greenbriar shrubland (called sandrough or sandtangle by "natives") on deep, loose sand in the West Cross Timbers of northcentral Texas. Dolminance by herbaceous species varied locally among horseweed or mare'stail, little bluestem, and sand lovegrass.
Horseweed is an annual, rank-growing, comparatively large composite that is a widespread pioneering or colonizing species. Horseweed is particularily common and abundant on disturbed ground such as roadcuts, old fields, cutover forests, and overgrazed ranges. It is a classic r-selected species and a ruderal in resource allocation (= life "straetgy"). Horseweed was the most abundant forb and provided the most foliar cover of any non-grass species. Little bluestem and sand lovegrass are native, perennial bunchgrasses classified as decreasers and the potential herbaceous dominants for this Deep Sand range site.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
122. Herbaceous and woody in the sand- Edge of a natural opening in a sand post oak-saw greenbriar shrubland called sandtangle in the West Cross Timbers of northcentral Texas. These two slides made up a set of "nested photoplots" that featured a local stand of oak shoots (probably a clonal unit of one oak plant) with numerous plants of mare'stail or horseweed, the most abundant forb, and little bluestem, a co-dominant native perennial grass (sand lovegrass being the other dominant grass), was locally the most common and had the most cover of any herbaceous perennial. Another sporadically important grass was tapered-leaf panicgrass or Lindheimer's rosette panicgrass. Two small plants of Lindheimer's rosettegrass were growing to the immediate right of a conspicuous though heavily grazed plant of sand lovegrass. There were also two small plants of hogwort or hog croton (Croton capitatus) joining these native, perennial grasses.
Range vegetation seen here was late enough (mid-autumn) that a sizeable proportion of the current year's oak leaves had been shed and added to the existing layer of previously fallen leaves that completely covered (nearly so anyway) the soil surface. Shoots of saw greenbriar, though indistinct in these photographs, was ever-present making travel through this postclimax vegetation unpleasant as well as challenging.
The deep, sandy osil of sandrough was such that this edaphic habitat was considerably more mesic and favorable in hot, dry weather so that the potential natural range vegetation was itself more mesic than the regional average. In terminology of the Clementsian monoclimax thoery this range plant community was postclimax.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub .ariant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
123. Seedlings for sure- Local stand of seedlings (definitely not offshoots or clonal shoots) of sand, scrub, or dwarf post or Margarete oak in understorey of a range of sandrough or sandtangle, a shrubland dominated by scrub post oak with saw greenbriar as associate species. Most of the young shoots of Margarete oak presented in this "photoplot" of sandtangle understorey were clearly seedlings though a few of these small shoots might have been clonal offshoots arising from woody rootstocks of adult sand posst oak.
In this sandrough range it was obvious that many shoots of Margarete oak were vegetative shoots (clonal offshoots= modules= ramets) of existing genetic shoots (genotypes= genets). Perhaps a majority to most scrub post oak trunks or boles and crowns in this sandrough community were clonal shoots. This local or "mini-stand" of dwarf post oak shoots was clearly comprised mostly of seedlings as was determined by finding well-rotted shells of acorns next to shoot/root crowns of most of these small oak shoots. Other young shoots appeared to have originated much deeper in this sandy soil thus most likely having originated from underground horizontal oak shoots.
This local group of "baby" shoots of sand post oak was a relatively unique phenomenon or developmental stage in this sandtangle range that was--and historically had been--grazed by both cattle and white-tailed deer.
Some of the oak leaves that littered the ground were recently shed leaves of the current growing season. Other leaves that formed a complete ground cover throughout this shrubland vegettion were from previous years. Two consecutive years of Extreme Drought (Palmer Scale) might have contributed to accumulation of leaves due to reduced leaf decay in absence of plentiful precipitation.
Erath County, Texas. Early November, autumnal aspect.
124. Crooked and armed- Horizontal basal shoots of scrub, sand, or sand post oak with prominent shoot of saw greenbrir (first slide) and with devil's-tongue pricklypear as well as saw greembriar (second slide) in the lower zone of range vegetation known as sandrough, a shrubland dominated by scrup post oak with saw greenbriar as associate species. This potential natural polant community is postclimax in monoclimax theory of Clements (1916, 1936) and an edaphic climax in the polyclimax theory (Tansley, 1926, 1935) and climax pattern theory (Whittaker, 1953).
Note two vertical shoots arising from a larger basal horizontal shoot in a sand post oak in the second slide. Imagine this horizontal shoot being below ground so that the two upright trunks would appear side-by-side. Then project this arrangement to clumps of two, three, four, etc. trunks of scrub post oak as seen above and the clonal nature of these clumps--including the clumps themselves being only a module of a long woody rootstock--becomes apparent in one's mind.
Most of the plentiful oak leaves were those shed in the previous year although some were of the current year's crop that were presently being shed at end of the current growing year in th endless cycle of life in the sandrough.
Erath County, Texas. Early November, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
125. Rough passage- A cow's eye view of the range of a shrubland dominated by scrub post oak with saw greenbriar as the associate on deep sand in the West Cross Timbers of northcentral Texas. Devil's-tongue pricklypear was the center of attention in this "photoplot" taken on a bright autumn afternoon under a full-sun sky. This was an unusually large specimen of a species that is more limited in distribution (it prefers an edaphic environment of deep loose sand) than most other Opuntia species in the Cross Timbers-Grand Prairie Region.
Attention was drawn to the heavy cover of oak leaves, all of which at this point in time were from previous years the current year's leaves still being on the sand post oaks. A few of the leaves were, of course those of saw greenbriar. Although not visible in this slide there were also plants of two Cyperaceae species which were presented in the immediately following slide-caption set.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
126. Grasslikes in the sandrough- Slender flat-sedge or slender umbrella-sedge (Cyperus lupulinus) and bracted oak caric-sedge (Carex cephalophora) left and right, respectively, in the very limited understorey of a sand post oak-dominated scrub (known locally as sandrough) in the West Cross Timbers of northcentral Texas. Saw greenbriar was the associate species of this postclimax or edaphic climax (monoclimax and polyclimax/climax pattern theories, respectively) range vegetation that developed on deep sand.
In striking contrast to almost all other areas of soil surface in this sandrough range this localized spot was relatively free of shed oak leaves. It was not known if the relatively thick cover of oak leaves (see almost all photographs in this section) had a mulching effect on herbaceous species. Such did not seem likely however as there were some grasses and even plants of the annual composite, horseweed, that came up through comparatively dense leaf cover in some locations of this scrubland range. Likewise, it was not known if grazing/browsing by beef cattle and white-tailed deer had eliminated some herbaceous plants.
Erath County, Texas. Late October, autumnal aspect. Extreme Drought (Palmer Scale). Sandrough fits in FRES No. 15 (Oak-Hickory Ecosystem). Scrub variant in K-75 (Cross Timbers). SAF 72 (Southern Scrub Oak, Sand Post Oak variant). Edaphic variant of SRM 732 (Cross Timbers, Texas; Little Bluestem-Post Oak). Deep Sand range site. Edaphic variant of Limestone Cut Plain Cross Timbers Ecoregion, 29e (Griffith et al., 2004).
127. Wetland plant? Not me!- Two typical specimens of slender or Great Plains flat-sedge or umbrella sedge (Cyperus lupulinus) growing on dry, sandy soil in the West Cross Timbers of northcentral Texas. Great Plains umbrella- or flat-sedge is one of the Cyperus species best adapted to relatively xeric habitats in this region. Most Cyprus species are best adapted to moist up to wet soil environments such that many are wetland plants. Great Plains flat-sedge has more nearly the opposite adaptations.
Slender flat-sedge is a member of range plant communities of the Cross Timbers ranging from post oak-blackjack oak-tallgrass savannahs and, even, mixed oak-pecan forests to drier, shallower grasslands to sand post (margaretta) oak dwarf forests.
It was observed by this photographer that individual plants of Great Plains flat-sedge grew to larger sizes in the savanna than in the margaretta oak- pygmy forest communities. In some localities this relative difference was drastically (ie. dramatically smaller on the margaretta oak-dominatee "sandrough".
Erath County, Texas. Early September, immature-fruit stage of phenology.
128. One for the dry sands- A third specimen (counting the preceding two plants) of slender of Great Plains umbrella-sedge (first slide) and a detailed view of some of thhat plant's sexual shoots (second slide) produced on dry, sandy soil during a relatively dry and characteristically hot summer in the West Cross Timbers. This is one of the Cyprus species that is best adapted to more xeric microsites in the Western Cross Timbers.
Erath County, Texas. Early September, immature-fruit phenological stage.
129. Flat out on sandy soil- Two inflorescences (panicles) with prominent spikelets on shoots of slender of Great Plains flat- (= umbrella-) sedge. This fruit was produced by plants growing on dry, sandy soil during a relatively dry and (always) hot summer in the Western Cross Timbers of northcentral Texas.
Erath County, Texas. Early September, immature-fruit phenological stage.
130. Another sand-lover- Bracted carid-sedge (Carex cephalophora) in the herbaceous layer of "sandrough", a dwarf forest dominated by sand post or margaretta oak in the Western Cross Timbers of northcentral Texas. This species has a morphology (at least in this climax range vegetation) of comparatively few, tall, slender shoots that emerge sparsely (versus densely) from a cespitose base. Bracted caric-sedge is so sparse and small and, along with being so widely dispersed in this pygmy forest, that it provides very little forage except maybe for rabbits (which are about the only vertebrate that can mover freely through this "sandtangle"anyway).
Erath County, Texas. Early May, late anthesis stage of phenology.
131. About as descriptive as the next description- Bracted caric-sedge shown as two sexual shoots and parts of five leaves (first slide) and an inflorescence of tightly bunched spikelets (second slide) in the understorey of a margaretta or sand post oak dwarf forest in the West Cross Timbers of northcentral Texas.
Bracted careic-sedge is in subgenus Vignea characterized by flowers having two stigmas (a forked pistil) and a two-sided achene (Steyermark, 1963, p. 313). This species is widely distributed over eastern North America generally in relatively dry habitats (Steyermark, 1963, p. 331).
Erath County, Texas. Early May, late anthesis stage of phenology.
132. A wierd one even by rangeman standards- Inland, hairy, Drummond's, Carolina fimbry (Fimbristylis interior= F. puberula= F. drummondii= F. caroliana) shown at scale of entire aboveground plant, upper sexual shoots, and inflorescence in first, second, and thierd slide, respectively. This member of the flat or umbrella sedge subfamily (Cyperoideae) of the sedge family (Cyperaceae) is a relatively uncommon species in the Western Cross Timbers. This one was growing in a seep microsite at edge of a stand of typical West Cross Timbers oak-tallgrass savanna and a sand post oak (Quercus margarettiae)-fiddleleaf green-brier dwarf forest. (For this reason, this species was included in both the Tallgrass Savanna and Miscellaneous Forests-II chapters herein.)
Inland or hairy fimbry was nowhere abundant enough to be a major range plant specie--for anything be it forage, soil conservation, nesting cover, etc. Hairy fimbry was an indicator plant for generally wet habitats. This grasslike plant increased plant species diversity and it certainly was an "attention-getter". Inland fimbry earned its place in this publication.
Erath County, Texas. Early November; mature fruit (achene) phenological stage.
133. Fimbrily missed (almost)- Two units of an infloresscence or two sexual shoots with their spike (depending on one's perspective and terminology) and a spike on end of sexual shoot (or branch of inflorescence) in first and second slide, respecitvely. These organs were on the plant introduced in the immediately preceding slide/caption set. This plant was growing on a local seep (a microhabitat) at an "intersection" or union of a post oak-American elm-tallgrass savanna and a sand post oak-fiddleleaf green-brier pygmy forest in the West Cross Timbers of northcentral Texas.
This grasslike plant is pretty much a wetland species. Diggs et al. (1999,
p. 1150) recognized and provided a detailed dichotomous key for F. puberula
var. interior and F. puberula var puberula. The latter is much more common in
the Texas Cross Timbers and Prairies area. Based on description of bulbous culms
(Diggs et al., 1999, p. 1150) the plant shown here was a specimen of F. puberula
var. puberula.
Erath County, Texas. Early November; mature fruit (achene) phenological stage.
134. Not false to itself- Entire shoots (first slide) and upper shoot (second slide) of plant of false boneset (Kuhnia eupatorioides var. corymbulosa) growing at edge of a sand post oak-fiddleleaf gerrn-brier dwarf forest in the West Cross Timbers of northcentral Texas. The specific epithet, eupatorioides, was in reference to the genus Eupatorium and/or the tribe Eupatorieae known by such common names as boneset, thoroughwort, Joe Pye weed, and several others. K. eupatorioides is in the Eupatorieae and, in addition to tribal features, presumedly or supposedly bore enough resemblance to Eupatorium species to get the specific epithet, eupatorioides.
Some taxonomic treatments included Kuhnia in genus Brickellia as in Brickellia eupatoroides (Diggs et al., 1999, ps. 328-329), but Kuhnia eupatorioides is the traditional binominal (Coulter, 1891-1894, p. 180; Fernald, 1950, ps. 1370-1371; Steyermark, 1963, ps. 1468-1469; Great Plains Flora Association, 1986, ps. 966-967).
Erath County, Texas. Early November; peak flowering phenological stage.
135. Not falsely blooming- Upper shoots and flower clusters (first slide) and
details of individual heads (second slide) of false boneset growing at the outer
edge of a sand post or margarettia oak-fiddleleaf green-brier dwarf forest in
the West Cross Timbers.
This species is just another one among "jillions" of composites growing on ranges in northcentral Texas. Falseboneset has a biological (species) range that extends from Florida to Texas in the south northward to New Jersey and Pennsylvania and then westward to Illinois and Missouri. There was sufficient morphological variability in this species to recognize three varieties in the greater Great Plains Region (Great Plains Flora Association, 1986, ps. 966-967).
Relative palatability of false boneset is apparently not known, but it is doubtful that grazing animals have much preference for it.
Erath County, Texas. Early November; peak flowering phenological stage.
136. One of a big genus- Upper shoots showing overall habit and inflorescence (first slide) and more detailed views of stem and leaves (second and third slide) of annual wild-buckwheat (Eriogonum annuum) growing on a sandy loam soil in the West Cross Timbers in northcentral Texas.
Annual wild-buckwheat is usually most abuncant on disturbed environments (Diggs et al., 1999, p. 899). That was the case for the specimen presented here which was growing on an overgrazed old-field range.
Best reference for annual wild-buckwheat this author could find Tyrl et al. (2008, ps. 314-315) which, by the way, is one of the finest treatments for numerous, major range plants in Oklahoma, southern Kansas and north Texas.
Hunewell Ranch, Erath Couhty, Texas. Late September; peak-flowering stage of phenology.
137. "Hey, Buckwheat" (from Our Gang or The Little Rascals)- Infloresceence (first slide) and groups of flowers of annual wild-buckwheat growing in the West Cross Timbers of northcentral Texas. Apparently, the exact origin or literal meaning (if any) for the common name of wild-buckwheat was not well-determined, but it is known that North American Indians used parts of Eriogonum species for food (eg. seeds used as mash) and a tea-like beverage (Moerman, 2010). Eriogonum species, including E. annuum, were used medicinally by North Amereican Indians (Tyrl et al., 2008, p. 315).
There are many Eriogonum species in North America, especially in the Intermountain West. Correll and Johnston (1979, ps. 511) reported roughly 225 Eriogonum species in North America. By contrast, Correll and Johnston (1979, ps. 510-516) gave a key for and descriptions of only 19 Eriogonum species in Texas. Three of these 19 Eriogonum species are found in northcentral Texas.
On Hunewell Ranch of Tarleton State University this author has found all three of these Eriogonum species. One of these species is a perennial, one is typically biennial or annual, and one is an annual. Heartsepal wild-buckwheat (E. mulitflorum), the biennial was treated immediately below beause both heartsepal and annual wild-buckwheats are more characteristically Cross Timbers species. The perennial E. longifolium grows on calcareous soils and is tyopically a prairie plant rather than a Cross Timbers species.
Location note: E. longifolium was included the chapter on Tallgrass Prairie Plants in Range Types of North America.
138. Broad-topped forb in Cross Timbers- Manyflowered or heart-sepal wild buckwheat (Eriogoum multiflorum) in an ecotone between a stand of post and blackjack oak in West Cross Timbers and a virgin, mima mound prairie in northcentral Texas. This annual (rarely biennial) lacks the brilliance of some forbs like standing cypress (but then what doesn't?), but it is showy in its own way-- and it certainly is prolific. This specimen was growing in deep sand.
West Cross Timbers, Erath County, Texas. October.
139. Plain but eye-catching- Details of upper shoot (first slide) and then of flower cluster (second slide) of manyflowered wild buckwheat. This was the same plant introduced in the preceding slide.
West Cross Timbers, Erath County, Texas. October.
Moerman, D. E. 2010. Native American Food Plants: An Ethnobotanical Dictionary. Timber Press.
140. Not exactly camouflaged- A green lynx spider (Peucetia viridans), a common spider in the Cross Timbers and Prairies vegetational area of Texas, on a flower cluster of heartsepal wild-buckwheat. Why this bright-green and early stage-pregnant female was bringing Christmas color (and attention to herself) at the edge of a sand post oak (Quercus margarettae)-fiddleleaf green-brier (Smilax bona-nox) dwarf forest in the West Cross Timbers was known only to her. Perhaps she did not know (was cluelessly unaware) of her vulnerablity. Maybe she had some misplaced instinct that she was invinicible. Or perhaps she felt her beauty and "charm" would carry her through anything. Kind of reminded this ole professor of a lot of college students encountered over course of a career in the classroom. Some of these self-styled, attractive personalities apparently thought or instinctively felt that their beauty, charm, excuses, and past experiences with gutless instructors made them invinicible and immune to stated expectations in courses taught by this photographer professor.
Hope the spider fares better. At least she passed this Range Ecology course with "crawling colors". Still, she needs to realize that every living thing--including an eye-catching predator--is something's prey. Just takes one serious "professor" to spoil your record.
Erath County, Texas. Early November; peak flowering phenological stage.
141. Jacked to the gills- Jack O'Latern gilled mushroom (Omphalotus illudens= Clitocybe illudens= Omphalotus olearius), saprophyte, growing on snag of blackjack oak in a sand post oak-saw greenbrier scrubland or dwarf forest in the West Cross Timbers. This fungus is in family Tricholomataceae, order Agaricales. class Basidomycotina.
The unique feature and namesake of Jack O'Latern is derived from the biolumesence of the fruiting bodies, in particular the gills or lamella. This is noted in most mushroom field guides. For example, Metzler and Metzler (1992, p. 143) described this glow or charactristic luminescence as "an eery greenish light". Hence, the descriptive and evocative common name of ghost mushroom. This phenomenon has been much discussed in the scientific literature including (Murrill, 1915; Weitz and Weitz, 2004; Desjardin et al, 2008).
This fungus is poisonous. In a classic study Clark and Smith (1913) determined that the poisonous principle in ghost mushroom was muscarin.
Erath County, Texas. Late October; full-development of fruiting body.
142. Reducers and ghosts in the sandrough- Sporeocarps (fruiting bodies) of Jack O'Latern gilled mushroom or ghost mushroom growing on decaying roots of dead sand post oak and blackjack oak. The common name of ghost mushroom is derived from the glow or bioluminescence emitted from gills of the fruiting bodies of this unusual fungus.
Fungi (interpreted by some botanists as being in their own kingdom, Fungi) comprise one of the larger groups of decomposers or reducers in range ecosystems. These fungus species are saprophytes; in other words, heterotrophs (other nourishing) in contrast to other fungal species that are autotrophs (= free-living or self-nourishing organisms). Some species of bacteria and algae are also decomposers.
Ecologists like Eugene Odum (1971) regarded reducers or decomposers as being the most important or the most critical of the biotic components of range ecosystems. This view seemed hard to reconcile with the fact that photosynthesizing plants are the producers at base of food chains. Nonetheless decomposeres like this saprophytic speciescomprise the detritis food chain that is pivotal to ecosystem function.
Erath County, Texas. Late October; full-development of fruiting body.
COMPOSITION, STRUCTURE, AND DEVELOPMENTAL DETERMINANTS OF A SCRUB OAK FOREST IN THE WEST CROSS TIMBERS OF NORTH CENTRAL TEXAS Our study areas had been grazed by cattle for over a century without other direct human impact including chemical or mechanical treatment of vegetation and with exclusion of fire for at least 60 years (landowners, personal communication). Droughts that varied from moderate to severe had occurred periodically for five years preceding our study. In the decade prior to the five-year drought precipitation had ben typical in quantity and pattern.
Randall E. Rosiere, Allan D. Nelson, Donald G. McGahan, and Kalee R. Smith
Department of Agribusiness, Agronomy, Horticulture, and Range
Management, Tarleton State University, Stephenville, TX 76402 (RER, DGM)
Department of Biological Sciences, Tarleton State University, Stephenville,
TX 76402 (ADN, KS)
*Correspondent: nelson@tarleton.edu
ABSTRACT- We evaluated composition, structure, and community determinative
factors of a scrub forest that developed on a deep-sand habitat in the West
Cross Timbers of north-central Texas. Species composition and vegetation structure
were analyzed based on 1) dominance, density, and importance values of woody
plants and 2) foliar cover (absolute and relative) of herbaceous species and
woody seedlings or offshoots in the understory. These community features were
determined on two old-growth forest stands following exploratory reconnaissance
on a total of eight separate stands. We concluded that this dwarf forest was
the potential natural vegetation for this deep-sand site with the sandy soil
being the principal determining factor in development and stability of this
natural community (i.e., an edaphic climax). We designated this as a sand post
oak-saw greenbrier (Quercus margarettiae-Smilax bona-nox) habitat type
based on the dominant tree and shrub species of the natural plant community.
The scrub forest consisted of three layers: 1) a closed canopy of sand post
oak and blackjack oak (Q. marilandica); 2) a shrub layer of six
species, including saw greenbrier, a liana that extended into the tree canopy;
and 3) an irregular understory of herbaceous plants plus seedlings and clonal
shoots of oaks and greenbrier. Herbaceous plants were all native species and
included six species of grasses, two of grasslike plants, and five of forbs
when composition was determined at autumnal peak standing crop. Most of the
herbaceous cover developed in natural openings within the overall forest community.
Comparatively low quantity of available soil water in the deep sandbeds of this
dwarf forest was the primary phenomenon that permitted domination of this site
by sand post oak. This was the only known habitat in the West Cross Timbers
on which sand post oak can outcompete other plant species, especially post oak
(Q. stellata) and blackjack oak. Apparently this West Cross Timbers scrub
forest is the only plant community reported to be dominated by sand post oak.
Various natural communities on sandyland sites in the Gulf and Atlantic Coast
regions have been described in which sand post oak and other species of this
Cross Timbers scrub forest are important constituents. This indicated the ecological
affinity among these natural communities that develop on sandy soils. This climax
scrub forest is an integral part of the landscape mosaic and natural environment
of the West Cross Timbers the same as other hardwood forests, savannas, and
grasslands of this region. Given appreciable losses of this native vegetation
to agronomic and horticultural agriculture, home sites, and various industrial
uses, we advised that land-owners be informed of the distinctive nature and
value of this forest community for such purposes as wildlife production, livestock
shelter, carbon sequestration, climate moderation, aesthetics, and historic
interest. Any land acquisitions for purposes of preserving the natural Cross
Timbers should include some relict tracts of the sand post oak-saw greenbrier
scrub forest.
RESUMEN - Durante la investigación evaluamos la composición,
estructura, y factores comunes determinantes de matorrales de robles y su desarrollo
en un ambiente de arena-profunda en en la sección oeste de Cross Timbers
en el norcento de Texas. La composición de las especies y vegetación
fue analizada basada en el predominio, densidad, e importancia de plantas leñosas
con cubiertas foliares (absolutas y relativas) de especias herbáceas
y retoños leñosos localizados en el sotobosque. Estos factores
comunes fueron determinados basados en dos bases boscosas de edad matura y los
reconocimientos en el proceso exploratorio en un total de ocho bases distintas.
Concluimos que la composición este pequeño bosque es la posible
vegetación natural del tal sitio basándose en su suelo arenoso
profundo, y tal suelo fue el factor determinante en la estabilidad de este ambiente
natural (ex. climax ecológico).
Designamos tal suelo como un ambiente de roble arenoso (Quercus margerettiae-Smilax
bona-nox) basado en el árbol predominante y especies de arbusto de
la comunidad natural de plantas. El bosque de matorrales consistía de
tres capas: 1) un pabellón cerrado de roble arenoso (Quercus margerettiae-Smilax
bona-nox) y rojo (Q. marilandica); 2) una capa de matorrales de seis especies,
incluyendo zarzaparrilla (Smilax bona-nox) que se extendía dentro del
pabellón del árbol, y 3) un sotobosque irregular de plantas herbáceas
más los retoños y brotes clonales de robles y zarzaparrila. Las
plantas herbáceas eran especies natales e incluían seis especies
de pastos, dos plantas de base pastosa, y cinco herbáceas cuando la composición
fue determinada en la cumbre otoñal del cultivo en pie. La mayor parte
de la cubierta herbácea se desarrollo en aberturas naturales dentro de
la comunidad forestal. Comparativamente la poca cantidad de agua en el suelo
arenoso de este pequeño bosque fue el factor principal que permitió
el dominio de este sitio por el roble arenoso. Este es el unico habitat conocido
en el cual el roble arenoso conquisto a otras especies de plantas, especialmente
el roble colorado (Quercus stellata) y el roble rojo (Quercus marilandica).
Aparentemente en el Oeste de Cross Timbers, este tipo de matorral boscoso es
la única comunidad de plantas en la que se ha reportado el roble arenoso
como especie dominante.
Varias comunidades naturales en sitios arenosos en zonas del Golfo y el Atlantico
han sido descritas como lugares en los cuales el roble arenoso y otras especies
de esta parte de Crón ecológica entre estas comunidades naturales
que se desarrollan en suelos arenosos. Este climax ecológico en los matorrales
boscosos es una parte integral en el mosaico del paisaje que se encuentra en
el ambiente natural de la sección oeste de la region Cross Timbers, al
igual que otros bosques de leños duros, savanas, y pastizales de esta
región. Dada la perdida considerable de la vegetación natural
a causas de la agricultura agronómica y horticultural, lotes residenciales
y otros sectores de producción industrial fueron aconsejados en que los
dueños sean instruidos sobre la distinta importancia de la zona boscosa,
equivalente en propósitos de producción animal, refugio naturales
de ganado, captura de carbono, moderación del clima, estética,
e intereses históricos. Cualquier adquisición de tierras con el
propósito de preservar el paisaje natural de Cross Timbers debería
incluir matorrales con intervalos de robles arenosos zarzaparrila.
The Cross Timbers is a comparatively large natural ecological unit distinguished by vegetation composed of hardwood trees, especially oak (Quercus) species, and shrubs with associated herbaceous plants, particularly panicoid and eragrostoid grasses (Kuchler, 1964; Garrison et al., 1977; Diggs et al., 1999; Sims and Risser, 2000), that developed on soils derived from sands, sandstone, and other parent materials including shales (Byers et al., 1938; Hoagland et al., 1999; Francaviglia, 2000). Cross Timbers soils were historically interpreted as being in the Red and Yellow Podzolic great groups that developed with deciduous forests (Dyksterhuis, 1948; Francaviglia, 2000). They correspond to the Alfisol order in the newer soil taxonomic system (Soil Conservation Service, 1990).
The Cross Timbers-a title used since frontier times (Foreman, 1947; Hollon, 1955; Dale, 1966; Francaviglia, 2000)-has long been recognized as distinctive climax or potential natural vegetation (Weaver and Clements, 1929) that forms physiogonomic patterns ranging from dense forest and woodland through savanna to grassland that has patches or groves of trees (Bruner, 1931; Dyksterhuis, 1948; Braun, 1950; Dyksterhuis, 1957; Diggs et al., 1999; Hoagland et al., 1999). Tharp (1939) provided one of the first vegetational descriptions of the Cross Timbers and distinguished the Western Cross Timbers from the Eastern Cross Timbers. ("West" and "Western" have been used interchangeably in some proper names whereas in other formal designations, such as for subunits of vegetational-land resource areas or ecoregions, only one or the other adjective is part of the published name.) Historically, the two forms of East and West Cross Timbers have been designated also as Lower and Upper Cross Timbers, respectively (Foreman, 1947; Diggs et al., 1999). Numerous workers (Dyksterhuis, 1948; Braun, 1950; Diggs et al., 1999; Hoagland et al., 1999) interpreted the Cross Timbers as a vegetational mosaic having primarily a savanna form that exist as a comparatively broad transition (ecotone) from the main or more eastern body of the oak-hickory (Carya) forest extending west to the tallgrass and true prairies. Francaviglia (2000) treated the Cross Timbers as more of a geographic region delineated by its vegetation much as did frontiersmen such as prominent author Washington Irving (1835), historian William Kennedy (1841), and freighter Josiah Gregg (1844).
Fenneman (1931) regarded the Cross Timbers as important in delineating physiographic units in the Great Plains and, later, Fenneman (1938) used Eastern and Western Cross Timbers as names of units of the Coastal Plain province. Maps of the vegetational or land resource areas of Texas have traditionally included the unit (region five) designated as Cross Timbers and Prairies (Gould, 1962; Correll and Johnston, 1979; Diggs et al., 1999). In classifying and mapping ecoregions (Bailey, 1995, 1996, 1998) the name Cross Timbers was incorporated into and used as titles and descriptions for level four ecoregions in Texas (G. E. Griffith et al., in litt.), Oklahoma (A. J. Woods et al., in litt.), and Kansas (S. S. Chapman et al., in litt.), the three US states in which Cross Timbers is potential natural vegetation (Kuchler, 1964; Hoagland et al., 1999).
Apparently all workers who studied the Cross Timbers, regardless of their emphasis or interpretation, recognized the floristic diversity along with physiogonomic and structural variation of Cross Timbers vegetation. The Cross Timbers has been studied from perspectives of human history and culture (Dale, 1966; Richardson, 1963; Francaviglia, 2000), geology, including physiography (Fenneman, 1931, 1938), as well as vegetation (Dyksterhuis, 1948; Diggs et al., 1999; Hoagland et al., 1999). Foreman (1947) related geology and vegetation of the Cross Timbers to early history, especially of exploration, commerce, and military expeditions. Reports concerning vegetation and community ecology of the Cross Timbers have included brief descriptions (Bruner, 1931; Braun, 1950), summary reviews (Diggs et al., 1999; Hoagland et al., 1999), and a detailed monograph (Dyksterhuis, 1948). Even with this long-standing study of the Cross Timbers most of the diverse forms of this regional natural community have received remarkably little evaluation.
This dearth of vegetational evaluation for most native plant communities in Texas and areas adjacent to it was recognized by L. Elliott (in litt.). We recently conducted a quantitative study of a mixed hardwood floodplain-riparian forest in the West Cross Timbers (Rosiere et al. 2012) that had been indicated (L. Elliott, in litt.) as in need of quantification. We next directed our efforts toward analysis of a scrub oak forest on deep sand in the West Cross Timbers that L. Elliott (in litt.) designated as "Crosstimbers: Sandyland Oak Woodland". In his brief description, L. Elliott (in litt.) specified that this sandyland plant community was in need of vegetational verification in anticipation of it being "sufficiently distinct to require a separate vegetation type". It was emphasized (L. Elliott, in litt.) that field data was "largely lacking" for this distinctive form of Cross Timbers vegetation. In a later version of these vegetation descriptions L. Elliott (in litt.) had not amended his previous brief treatment of the sandyland oak woodland. Apparently the type still had not been verified.
Indeed, we could find almost no description, let alone quantitative evaluation, of this native plant community. In his classic monograph, Bruner (1931) alluded to a "chaparral" community of sand or scrub post (Quercus stellata [var.] margaretta) and dwarf plants of blackjack oak (Q. marilandica) in the transition zone between oak-hickory forest and prairie in Oklahoma. Little (1939) briefly described a dwarf woodland of blackjack oak and post oak in southwestern Oklahoma comprised of trees having heights of 3 to 4.5 meters and diameters (diameter breast height) of 10 to 15 centimeters. The shrubland mentioned by Bruner (1931) and the dwarf woodland of Little (1939) was consistent with the Cross Timbers sandyland oak woodland that L. Elliott (in litt.) described as dominated by post oak and blackjack oak with characteristic presence of sand post oak, which is also known as dwarf post oak, margaretta oak, and runner oak, (Q. margarettae= Q. margarettiae= Q. margaretta). The closest specific descriptions of scrub oak communities in the Cross Timbers were brief and mostly conjectural notes on range sites associated with descriptions of soil series in county soil surveys (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1980).
Descriptions of major North American shrublands as rangeland cover types by the Society for Range Management (Shiflet, 1994) did not include sand post oak-dominated scrub types or make reference to this species under description of the two Cross Timbers cover types (SRM 731, SRM 732). Forest cover types recognized by the Society of American Foresters (Eyre, 1954; 1980) did not include sand post oak in descriptions of post oak-blackjack oak upland forest (SAF 40) though sand post oak was named as one of the scrub oak species in an oak-pine type (SAF 71).
Vegetation in which sand post oak is a dominant or, at least, major species in south-central North America is not limited to the Cross Timbers as there are similar natural plant communities with sand post oak in the Texas Post Oak Savanna (Texas vegetational area three) that occurs east of the West Cross Timbers (Gould, 1962; Correll and Johnston, 1979), including the Xeric Sandylands or Deep Sands Ecosystem (Diggs et al., 2006). Sand post oak has a species range extending from southeastern Virginia across the length of the Gulf Coastal Plain into central Texas and south-central Oklahoma (Sargent, 1933; Small, 1933; Correll and Johnston, 1979; McGregor et al., 1986; Burns and Honkala, 1991) so as to occur in various native plant communities including Coastal Plain pine savannas in Florida (Rebertus et al., 1989, 1993), an oak-pine cover type (Eyre, 1980), and western sandhill xeric woodland in Louisiana (Louisiana Natural Heritage Program, 2009). Such tree-defined vegetation notwithstanding, sand post oak-dominated dwarf forest that develops on deep sands in the West Cross Timbers is distinctly different from other plant communities. Thus, this distinctive vegetation warrants analysis and description necessary for its recognition as a natural community type.
Sandyland scrub oak vegetation is one of the most widely dispersed and distinctive-though least described-natural plant communities in the Cross Timbers. It is also one of the variants (subtypes) of Cross Timbers vegetation that is relatively limited in total area and that has been and continues to be lost in conversion to home sites; row crops, especially peanuts (Arachis hypogaea); orchards, and, most frequently, introduced forage species, especially agronomic forage crops like Coastal bermudagrass (Cynodon dactylodon Pers. 'Coastal') and exotic range grasses such as weeping lovegrass (Eragrostis curvula).
On its deep-sand environment this native scrub oak community develops into such dense vegetation that it is nearly impenetrable to humans and livestock. This sandyland vegetation supports only limited herbaceous understory, much of which is inaccessible as forage for grazing animals. In Commerce of the Prairies, Josiah Gregg (1844:361) described such Cross Timbers vegetation as "almost impenetrable 'roughs'". Farmers and ranchers know this woody vegetation as "sandrough" or "sandtangle" and, cost-permitting, replace areas of this native sandyland community with crop monocultures (type conversions) capable of producing greater yields of commodities or, more commonly, forage for hay and pasture. Most remaining tracts of "sandrough" are used as loafing areas by cattle (Bos taurus, B. indicus) that graze conterminous type conversions of introduced grasses. Smaller, remaining remnants and the perimeters of larger tracts of "sandtangle" become overgrazed, often to the extent that the surface of the sandy soil is severely disturbed, commonly resulting in elimination of the limited herbaceous layer.
The following investigation on the quantitative composition, structure, and successional status of this deep-sand, native scrub oak community in the West Cross Timbers was an initial effort to provide field data that was deemed essential to classification and mapping of natural plant communities (L. Elliot, in litt.). Ultimately, such analysis should aid in preservation and management of remaining parcels of this distinctive natural vegetation.
MATERIALS AND METHODS- The area under investigation was in the Western Cross Timbers portion of the Cross Timbers unit of potential natural vegetation (Kuchler, 1964; Diggs et al., 1999; Hoagland et al., 1999). It was in the West Cross Timbers ecoregion (29c on the ecoregion map of G.E. Griffith et al., in litt.) and Cross Timbers and Prairies vegetational area (Correll and Johnston, 1979). The study area was in the Texan biotic province of Dice (1943). The Western Cross Timbers developed at the borders of two physiographic units: 1) Coastal Plains and Piedmont and 2) Comanche Plateau of the Great Plains (Fenneman, 1931, 1938; Thornbury, 1965). Climate was classified by the modified Koppen system as mesothermal in all years, dry season in winter, with occasional desert years (Russell, 1945).
We conducted preliminary explorations of eight tracts (varying from approximately 0.1 to 36 hectares) of natural vegetation in north-central Texas (Erath and Eastland Counties, Texas) that was dominated by sand post oak with a shrub layer made up overwhelmingly of saw or greenbrier (Smilax bona-nox) which extended into crowns of oaks. Plant communities in these tracts included an herbaceous layer of varying development that was made up of perennial, cespitose grasses; grasslike plants, and miscellaneous forbs.
All eight tracts had developed on deep-sand soils that were included in the Nimrod-Arenosa-Patilo complex, Patilo-Nimrod, or Patilo mapping units (Soil Conservation Service, 1973, 1977b). The Patilo soil series consist of loamy, siliceous, thermic grossarenic Paleustalfs whereas the Nimrod series consist of loamy, siliceous, thermic aquic arenic Paleustalfs and the Arenosa series consist of thermic, uncoated ustic Quartzipsamments (Soil Conservation Service, 1990a). The range site was Deep Sand or Deep Sandy (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1980).
Physiochemical properties of soils were determined from Soil Survey Geographic data retrieved from the Web Soil Survey, National Cooperative Soil Survey (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). Soil data was retrieved for each component of the representative map units underlaying the study area. The available water-holding capacity (Dane and Topp, 2002) was hand calculated for each soil in the map unit using soil textural class, reported coarse fragment content, and modal soil description depths (maximum depth of 152 cm). Cation exchange capacity (Soil Science Society of America, 2001) was used as an indication of soil fertility (Lal, 2006; Brady and Weil, 2008).
All but the smallest tract of vegetation, a remnant parcel near a highway intersection, had been grazed continually for years by cattle and white-tailed deer (Odocoileus virginianus). Wild turkey (Meleagris gallopavo) were also commonly observed to use these deep-sand habitats. None of these tracts had burned in the last half century. These parcels had never been treated with mechanical or chemical brush control.
We selected two of these tracts (approximately 3 and 8 hectares; both in Erath
County, Texas) that appeared to have the most advanced state of vegetation development
on which we performed vegetational analyses. These two tracts had the largest
trees (maximum height of about 10 meters. maximum trunk diameter at breast height
of approximately 0.3 meter), the largest clumps of trees (those with greatest
number of boles per clonal tree; as many five to nine shoots in one modular
plant), the greatest frequency of natural canopy openings that were populated
primarily by herbaceous plants, and the most species diversity (which was related
to occurrence of openings under gaps in the tree canopy).
Vegetation of study tracts consisted of a mostly closed canopy of sand post
oak with a few blackjack oaks. Plants of both oak species were small trees or
large shrubs that had an aggregated dispersion in which oak shoots, especially
those of sand post oak, grew in clumps. There was a seemingly open (i.e. sparse
cover) understory except for saw greenbrier with occasional plants of other
shrub species and localized areas of herbaceous cover. Difficult entry and passage
beneath and among oak clumps revealed not an openness, but instead fence-like
barriers of numerous and largely leafless shoots of saw greenbrier that inflicted
shallow lacerations and puncture wounds and restricted through travel by larger
animals to established trails or paths. Grazing and browsing by large mammals
like ruminants was limited to edges of these trails and the natural openings
in the canopy.
Our study areas had been grazed by cattle for over a century without other direct human impact including chemical or mechanical treatment of vegetation and with exclusion of fire for at least 60 years (landowners, personal communication). Droughts that varied from moderate to severe had occurred periodically for five years preceding our study. In the decade prior to the five-year drought precipitation had ben typical in quantity and pattern.
An herbaceous layer consisting of native, perennial bunchgrasses; grasslike plants; and forbs had developed sporadically. This herbaceous layer was better developed in well-lite microsites and absent in areas where shade from the closed canopy was most dense. The natural opening or gaps in the otherwise closed-canopy community supported smaller plants of saw greenbrier along with the herbaceous plants. These openings or natural "clearings", which were often found on low mounds or hummocks, appeared to be randomly distributed throughout the vegetation. The soil surface was covered almost exclusively by a layer of oak leaves with minor components of leaves from other plant species. This leaf cover consisted of an upper portion of raw or undecayed leaves, a middle portion of partly decayed leaves , and a bottom layer of more-or-less fully decomposed leaves (the L, F, and H layers, respectively) laying on O horizons of the soil. It was a characteristic forest floor of organic matter (Spurr and Barnes; 1980; Kimmins, 1987; Perry et al., 2008).
We determined species composition of the herbaceous-low woody layer from measurements of foliar cover using the step-point method (Costello and Schwan, 1946; Brown, 1954; Evans and Love, 1957; Cook 1962; Cook and Stubbendieck, 1986; Bonhan, 1989). A sharp-tipped pin was used to randomly sample all plants, detritus, and bare ground occurring within the layer of vegetation delineated by the tallest grass species which was generally little bluestem (Schizachyrium scoparium) or sand lovegrass (Eragrostis trichoides). We recorded total number of hits for each herbaceous species, shoots of woody plants (both seedlings and vegetative offshoots), dead plant material, and exposed soil surface in the grass-defined layer of vegetation. A total of 5172 points was recorded.
Absolute and relative cover was derived from the total number of point hits. Relative composition of herbaceous species was expressed as both 1) percentage of all plants (including woody species) within the herbaceous zone and 2) of only herbaceous plants.
For woody vegetation, we placed four transects through the study sites and
sampled 30 randomly chosen quadrats, (5 by 5 m) along the transects for woody
vegetation >1.0 cm in diameter. For herbaceous vegetation and woody vegetation
<1.0 cm in diameter, we sampled 30 random quadrats (2 by 5 m). Species of
plants were identified and classified using Diggs et al. (1999), which also
served as the reference for common and scientific names. We deposited voucher
specimens in the herbarium at Tarleton State University in Stephenville, Texas.
We identified all woody plants in each quadrant and measured diameter at breast
height (dbh) of all that were >1.0 cm. The dbh was used to calculate basal
area. We calculated density (plants/ha), dominance (basal area/ha), and relative-importance
values as described in Rosiere et al. (2012). Vegetational analysis was done
at annual peak standing crop and fruit-ripening stage of warm-season species
(i.e. early autumn).
RESULTS- The composition and structure of this deep-sand vegetation (Tables
1 and 2) consisted of 1) a canopy made up of crowns of scrubby adult trees of
sand post and blackjack oak along with upper shoots of saw greenbrier; 2) an
intermediate woody layer of various shrub species and shorter shoots of the
two oak species; 3) a lower layer consisting of an herbaceous component of native
grasses, grasslike plants, and forbs along with a woody component (mostly seedlings
and offshoots of saw greenbrier and the two oak species) that formed a mixed
understory of sporadic cover. From perspectives of physiogonomy and dominance
this West Cross Timbers vegetation was a forest community.
This forest vegetation was made up overwhelmingly of sand post oak and saw greenbrier (Table 1) with miscellaneous scattered shrubs and an erratic, sparse cover of herbaceous species (Table 2). Herbaceous cover occurred primarily in natural openings found irregularly within the forest vegetation. We observed that these openings typically existed on low mounds or hummocks that were a characteristic feature of such deep-sand habitats as described for these soil series, especially the Patilo (Soil Conservation Service, 1990).
Plant communities of these tracts consisted primarily of closed canopies from mature plants of scrub oaks (overwhelmingly, sand post oak) the interlocking crowns of which had considerable cover of saw greenbrier. The interrupted or erratic understories consisted of both herbaceous species as well as immature, woody plants such as seedlings-saplings of oaks and smaller shoots of saw greenbrier. The intermediate woody layer was composed primarily of adults of various shrub species. Shrubs were of diverse heights and growth forms. These forms included scraggly bushes; small, single shoots such as those of chittamwood (Sideroxylon lanuginosum subsp. oblongifolium); and cladophylls of eastern prickly-pear (Opuntia humifusa).
Some sand post oaks grew as single or paired shoots, but more commonly scrub trees of this species existed in clumps of at least three, though typically, four or five up to nine boles. In most cases we could not determine if these shoots were of individual plants (different genotypes) or if they were clonal offshoots of the same tree. In a few instances we observed boles arising from horizontal shoots on or just below the soil surface. Berg and Hamrick (1994) reported that clustering in sand post oak was from both asexual reproduction (shoot proliferation or "suckering") and sexual reproduction from acorns. We observed acorn production by sand post oak on both of our sample locations. Given that most trunks of sand post oak grew in clumps or clusters it seemed likely that asexual reproduction was the predominant mode of regeneration at these locations, but it was likely that some trunks in clusters had originated from seed. New shoots of sand post oak growing in a power line clearing adjoining one of our study tracts were all from low stumps or rootstocks immediately below the soil surface (i.e. re-establishment was by coppicing and not seedling establishment).
Blackjack oak was the third-most important woody species based on dominance, but blackjack oak had lower density (plants/ha) than eastern prickly-pear. These two species had the same importance value, but given the larger size and greater cover of individual plants we interpreted blackjack oak as the associate woody species of this plant community. Trees of blackjack oak in this deep-sand community almost always consisted of a single trunk although infrequently paired trunks and, rarely, three shoots were encountered. Otherwise, blackjack oak did not form clumps or clusters of shoots in the examined tracts.
Cover and density of the woody species other than adult oaks were at size and habit of shrubs with the more common species, aside from eastern prickly-pear and saw greenbrier, being southern blackhaw (Viburnum rufidulum), lime prickly-ash (Zanthoxylum hirsutum), immature plants of the conifer, Ashe's juniper (Juniperus ashei), and chittamwood. All of these shrubs or shrub-like plants except saw greenbrier were minor compared to oak species, but they comprised a second or intermediate woody layer. Saw greenbrier, growing as seedlings and young clonal shoots up to adult age-size plants, extended from the soil surface to the crowns of oaks so as to be present in all layers of the plant community. These shrub species, except for eastern prickly-pear in the Cross Timbers, have wide distribution, adaptation to diverse habitats and, perhaps most importantly, are not restricted to deep sand. Two woody species were recorded only as seedlings or asexual shoots in the herbaceous layer: sugarberry (Celtis laevigata), a tree species, and mustang grape (Vitis mustangensis), a liana. Adults of these two species were seen infrequently on all eight forest tracts, mostly on outer edges of the scrub forest.
White-haired panic (Panicum acuminatum var. villosum), little bluestem, and sand lovegrass were the major grasses. Little bluestem and sand lovegrass were of approximately the same relative cover (Table 2). White-haired panic had greater cover than that of little bluestem and sand lovegrass combined. Bracted caric-sedge (Carex cephalophora) measured slightly greater cover than little bluestem or sand lovegrass and considerably less than white-haired panic. Bracted caric-sedge and slender flat sedge (Cyperus lupulinus) together had somewhat less measured cover than white-haired panic, but more than little bluestem and sand lovegrass combined.
Grasses made up 46% of the relative cover of the herbaceous-small woody plant layer (the understory) of the forest vegetation. This exceeded the relative cover of forbs which was 32% of the understory. Cover of horseweed (Conyza canadensis) varied sporadically throughout the understory, but it was the forb with greatest cover. Cover of horseweed exceeded than that of any herbaceous species except for white-haired panic. Grasslike plants comprised slightly over 20% of the understory cover.
Some herbaceous species occurred at extremely low cover and density. These included such forbs as frostweed (Verbesina virginica) and Texas bullnettle (Cnidoscolus texanus) and the native annual grass, purple sandgrass (Triplaisis purpurea). It could be argued that presence at trace amounts versus absence amounted to small differences, but of equal validity is the argument that presence at any amount was important from an indicator plant standpoint. For example, although Texas bullnettle and purple sandgrass are widely distributed their preferred natural habitat is open forests and woodlands that develop on sandy soils. Even trace amounts of cover (i.e. mere presence) of additional species increased biological diversity of the forest community.
Most of the herbaceous cover of this plant community was in natural openings,
but plants of all herbaceous species also grew erratically in less shaded spots
under the scrub oak-saw greenbrier canopy. Several species of herbaceous species
frequently grew together especially where greenbrier shoots and closely spaced
oak trunks appeared to offer protection from grazing by cattle and white-tailed
deer.
DISCUSSION- We organized discussion of our findings about vegetation of a West
Cross Timbers scrub oak forest into five major topics: 1) community characterization
and successional status, 2) possible factors involved in determining community
development, 3) soil and plant relations, 4) affinity with other natural communities,
and 5) conclusions with management applications.
Community characterization and Successional Status- Categorization of this Cross Timbers vegetation was problematic. Physiogonomy and species composition of this plant community were subject to interpretation, if not perception. Both sand post oak and blackjack oak typically had the shrub feature of small shoots and, in case of sand post oak, of multiple (generally, four to nine) boles per plant yet with heights up to approximately 10 or more meters and breast height diameters of 20-25 centimeters. With these dimensions the terms "shrub" or "tree" were alternatively appropriate based on criteria of Society of American Foresters (Helms, 1998). The term "brush or scrub tree" was seemingly more descriptive, so that "scrub forest" (Helms, 1998) was the most consistent term for this woody plant-dominated vegetation. The potential natural plant community for the Patilo soil series was described by the Soil Conservation Service (1978) as "scrub forest".
Reich and Hinckley (1980) applied the designation of "pygmy forest" to woody vegetation dominated by blackjack oaks that were naturally dwarfed or stunted on sandstone bluffs in the Ozark Plateau. These blackjack oaks were stunted so as to have a distorted habit or growth form (Reich and Hinckley, 1980) much like elfin-wood or krumholtz vegetation (Barbour et al, 1999). The label of "pygmy forest" was first applied to coniferous forests of stunted, sometimes distorted, and, in general, small-sized trees on infertile soils in the Coast Range of northern California (McMillan, 1956; Jenny et al, 1969; Westman, 1975). The concept of pygmy forest was later expanded to include climax vegetation dominated by coast live oak (Quercus agrifolia) that develops on deeper sand dunes as described by McBride and Stone (1976). Habit of sand post oak and physiogonomy of vegetation it dominated on deep-sand sites in the West Cross Timbers were consistent with those of pygmy forests. Blackjack oak, the associate tree species, also had a scrubby, stunted appearance on deep-sand sites in contrast to larger trees of more typical arborescent form on other Cross Timbers habitats. Perceptions of Cross Timbers trees as recorded in various frontier-era journals and military reports included such descriptions as "stunted trees", "small, gnarled", "dwarfish", "short stunted oak" , and "low, shrubby timber" (Foreman, 1947, pp. 49, 62, 81, 103, 113).
Although many plants of pygmy forest species have gnarled, twisted, or otherwise grotesque habits this morphology is not a consistent feature. Many plants are just smaller versions of regular-sized and -shaped plants as, for example, conifers in the pygmy forest of the California Coast Range studied by Jenny et al. (1969) and Westman (1975). This was consistent with the meaning of "pygmy" or the synonym, "dwarf" (Merriam-Webster, 2003). The twisted and gnarled habits of normal-sized trees is a notable feature of Cross Timbers oaks (Diggs et al., 1999; Hoagland et al., 1999; Francaviglia, 2000) such that this characteristic is not a morphological form that designates a scrub or dwarf tree. Shoots of sand post oak were typically twisted, crooked, and knotty as well as being of diminutive size at maturity. Blackjack oak, with either single or multiple shoots, on deep sand exhibited this habit though less consistently.
It would be appropriate to interpret the scrub blackjack and sand post oaks growing on deep sand in the Western Cross Timbers as dwarf trees, and the woody plant community they form as a pygmy, dwarf, or scrub forest. This scrub tree-dominated vegetation with its closed canopy was not "woodland" as labeled by L. Elliott (in litt.) because by definition (Helms, 1998) woodland is a tree-dominated community with an open canopy (even though it may consist of small, short-trunked trees). As with previous studies of pygmy forests (Jenny et. al, 1969; McBride and Stone, 1976; Reich and Hinckley, 1980), we concluded that woody vegetation dominated by sand post oak in the Western Cross Timbers constituted a scrub or pygmy forest, the adult oak trees of which were dwarfs.
According to the native vegetation classification system developed by Daubenmire (1952, 1959, 1966, 1984) the Cross Timbers scrub forest dominated by sand post oak and with saw greenbrier as the dominant shrub would be a Sand Post Oak-Saw Greenbrier habitat type. As a cover or dominance type in the system used by the two leading US scientific societies dealing with management of natural vegetation this dwarf forest would be a variant of the Cross Timbers types (SRM 731, SRM 732) recognized by the Society for Range Management (Shiflet, 1994) while it would have to have a new designation, a title, of Sand Post Oak followed by an SAF number for inclusion in the forest types described by the Society of American Foresters (Eyre, 1954, 1980). For the natural plant communities of Texas proposed by Elliott (in litt.) this vegetation would be Sandyland Scrub Oak Forest for the West Cross Timbers.
We proposed (and explained below) that this dwarf forest is the potential natural vegetation for certain deep-sand habitats. Further, we concluded that the soils of such environments were the principal determining factor in development of this forest community. These sand post oak-dominated dwarf forests comprise an edaphic climax. Below we reviewed possible determinative habitat variables and elaborated on our designation of soil-based climax vegetation.
Consistent with climax community is the concept that each climax is part of a fully evolved, mature, and dynamically stable ecosystem (Odum, 1969; Orians, 1975). The limited species richness and comparatively consistent composition and structure of this deep-sand scrub oak forest suggested a low level of biodiversity and, perhaps, by extension incomplete ecosystem function and maturity. Madritch and Hunter (2002) studied nutrient fluxes in tree litter relative to phenotypic diversity in a turkey oak (Quercus laevis)-dominated sandhills community which had comparatively low species diversity. They concluded that high species diversity might not be as important to ecosystem function as was diversity at various levels, including intraspecific variation, relative to natural diversity at those levels (Madritch and Hunter, 2002).
Turkey oak is a scrubby species that is often associated with sand post oak
on sandy soils (Schafale and Weakley, 1990; Berg and Hamrick, 1994; Espeleta
et al, 2002, 2004, 2009). It seemed reasonable that principles regarding ecosystem
functions of a turkey oak-dominated forest might apply also to a sand post oak-dominated
scrub forest. Madritch and Hunter (2002) proposed that intraspecific diversity
was more important in a community composed of a low number of species (such
as scrub oak-dominated forests) than in relatively species-rich forests. Hiers
et al. (2014) specified that clones of sand post oak provided habitat heterogeneity
on poor sites of longleaf pine-oak forests. Considerable genotypic and phenotypic
variation was to be assumed in the scrub oak forest community of the West Cross
Timbers which had numerous and obviously distinct trees of sand post oak, almost
all having multiple trunks. In addition, this same form of variation could be
expected with the clonal, many stemmed saw greenbrier, the dominant shrub of
the Cross Timbers deep-sand dwarf forest. Simpler natural communities comprised
of a few species can have considerable biodiversity and stability so as to perform
as fully functional ecosystems.
Factors determining development of Cross Timbers scrub oak forest- We considered the most likely major factors responsible for development of pygmy or scrub forests on deep-sand sites in the Western Cross Timbers. Possible factors include fire, grazing, local disturbance, and soil.
Fire as a factor- Fire has long been considered to be an important factor in development and maintenance of Cross Timbers vegetation, especially of the savanna form, This was shown in early personal accounts like that by Irving (1835) and through reviews by Hoagland et al. (1999) and Francaviglia (2000). Savanna physiogonomy was alluded to in some range site descriptions for the Patilo soil series (Soil Conservation Service, 1980) and for similar soils and the Deep Sand Savanna range site in Oklahoma (Soil Conservation Service, 1960, 1966, 1979) where oaks were of lower density and less cover (i.e. more widely spaced) and with relatively well-developed herbaceous understories. Such Cross Timbers savanna communities that may have existed to considerable degree as fire-maintained or, at least, fire-influenced communities were in contrast to vegetation of deep-sand habitats (and in absence of recent fire) in which large shrubs to small trees along with saw greenbrier developed into scrub forests with closed canopies and soil surfaces covered with oak leaves.
Stambaugh et al. (2011) hypothesized that absence of fire contributed to increased tree density and canopy closure in a relict post oak-sand post oak woodland in the transition between the Post Oak and Blackland Prairie vegetational areas described by Correll and Johnston (1979).
Stanbaugh et al. (2011) reported a sparse cover of herbaceous species in an old-growth relict stand of post and sand post oak in northern Texas. Rice and Penfound (1959) concluded that dense disturbed stands of oak-hickory forests in western Oklahoma resulted from heavy grazing and absence of fire. These two factors are interrelated as, for instance, when overgrazing eliminates herbage that is the source of fuel. Continued overgrazing and underburning creates a cycle of ever increasing tree canopy and on-going reduction of any herbaceous layers. The end result was a closed tree canopy and absence of herbaceous cover (Rice and Penfound, 1959). In contrast, Anderson and Brown (1986) reported varying responses to fire in closed canopy oak-hickory forest, blackjack oak savanna, and forest-prairie edge plant communities in which sand lovegrass and little bluestem were major grasses. Anderson and Brown (1986) reported that when there was adequate accumulation of fuel, fire had destabilizing impacts on forests resulting in savannas and forests with more open canopies. Yet fire did not result in secondary succession or apparent changes in species composition. In some instances there were greater numbers of young tree shoots (seedling and sapling) following fire. Response of grass to fire was not reported by Anderson and Brown (1986) though they implied that fire stabilized grasslands dominated by species such as little bluestem and sand lovegrass. Overall, fire has had an array of impacts on oak and oak-hickory forests in the greater Cross Timbers Region.
Peet (2006) listed several associations of fire-maintained longleaf pine (Pinus palustris) ecosystems in which sand post oak was a major component. Glitzenstein et al. (1995) found that sand post oak was a major fire-adapted species in sandhills longleaf pine types. Based on studies in north-central Florida, Cavender-Bares et al. (2004) placed each of 17 oak species in one of five groups of fire return intervals. Sand post oak was included in the group of three oak species with the greatest fire frequency (Cavender-Bares et al., 2004). Greenberg and Simons (1999) analyzed fire effects on old-growth oaks in the sandhill oak-pine ecosystem of peninsular Florida and found that oaks of several species, including sand post oak, were important components of this "fire type" forest community. Sometimes topkill of sandhill oaks, particularly smaller plants, occurred depending on fire intensity, season, etc., but such trees or shrubs resprouted. Likewise, most adult oaks were "fire-resistant" with over 80% of sand post oaks having fire scars at some locations (Greenberg and Simons, 1999). Hiers et al. (2014) explained that the prolifically resprouting sand post oak developed a "clonal dome" that afforded fire protection and prevented topkilling of shoots inside asexual clumps. Sand post oak was reported as living to ages of over 200 years on fire-maintained forests (Greenberg and Simons, 1999) and up to 300 years on regularly burned forests in Florida (Knight, 2004; Varner and Pederson, 2004). In reporting these ages, Hiers et al. (2014) emphasized that such longevity and persistence with frequent fire indicated that sand post oak was a pyrophytic species.
It could be expected that sand post oak would have a similar response to fire in the sandyland Cross Timbers scrub forest where most oak shoots were adult size and fine fuels were limited almost exclusively to shoots of saw greenbrier. Studies have shown consistently that sand post oak is a fire-adapted species. Kreye et al. (2013) designated it as a pyrophytic oak. Fire adaptations of sand post oak include vigorous resprouting and even protection against topkill of shoots by development of clonal clumps (Hiers et al., 2014). In some of the earliest writing concerning fire in the Cross Timbers, Gregg (1844) described the adaptation of post and blackjack oaks to annual burning. Sand post oak might be even better adapted to fire. (Hiers et al., 2104) reported that sand post oak burned as intensely as post oak.
The rhizomatous or, according to some authors, stoloniferous habit of sand post oak was found to be a growth form and a means of asexual reproduction of this species that takes place irrespective of disturbances like fire, felling, or land-clearing (Townsend, 2005). The formation of large rhizomes among boles of sand post oak on our study locations was consistent with the finding of Townsend (2005) because there was no record, landowner memory, or conclusive fire scar evidence that the scrub oak forests in our study had undergone fire during the lifetimes of existing sand post or blackjack oak boles. In the scrub forests that we studied, fire-alone or in concert with other variables-cannot be ruled out as a factor in initiation or maintenance of sand post oak populations present at seedling and early clonal shoot stage (or both) prior to existing records or that bore no fire scars.
Sand post oak also reproduces sexually, with acorns being dispersed by animal vectors up to distances of tens of meters (Berg and Hamrick, 1994). These workers determined that clumps of the highly clonal sand post oak could consist of more than one genetic individual, but that most shoots in clusters of sand post oak were clonal units (Berg and Hamrick, 1994). After remarking that burning in the Cross Timbers scorched lower branches of trees, Washington Irving (1835: 220) described scrub oaks "some not above a foot high, yet bearing abundance of small acorns". Such frontier observations suggested that frequent burning of Cross Timbers vegetation by Indians did not did not prevent acorn production even on the smallest oaks. We noted acorn production on both tracts of scrub forest that we sampled as well as on other observed forest stands in the Western Cross Timbers, and this was over multiple years.
Given the strongly rhizomatous nature of sand post oak (with or without disturbance), its resprouting feature, the lack of fine fuels in closed canopy scrub forest dominated by this species, and production of acorns it was unlikely that absence of fire was a major factor in determining this plant community. We found empirical evidence for this conclusion based on incidence of land-clearing and wild fire on two areas of sand post oak-dominated forest adjoining the two forest tracts we sampled.
A portion of the larger tract of dwarf forest that we sampled had been mechanically cleared (combination of sawing and bulldozing) for a power line corridor immediately prior to sampling of the intact portion. The following year almost all of the sand post and blackjack oaks, nearly all of which had been adult trees, had resprouted from stumps and/or rhizomes. This indicated that even if fire did topkill adult trees (an unlikely event due to limited availability of fine, flammable fuels for initial ignition) these same plants would have resprouted.
Part of the other tract of sand post oak scrub forest that we evaluated had a lightening-ignited wild fire in August during Severe Drought (Palmer Index). Less than 0.25 ha burned before it was extinguished by fire suppression crews. Fire-suppression activity severely disturbed the soil surface so that this small area was not representative of either natural or prescribed fire. Nonetheless, we observed that 15 months after the hot fire (during prolonged drought) none of the sand post or blackjack oak shoots that ranged from sapling up to adult trees had any apparent damage from the fire. All shoots of saw greenbrier had been topkilled, but this species had resprouted profusely resulting in greater apparent foliar cover in the understory of the burned than in the adjoining unburned and sampled part of this forest tract.
These observations were consistent with statements that fire results in increases of woody plants on the Deep Sand Savannah range site of southern Oklahoma (Soil Conservation Service, 1960, 1966) which was similar to the deep-sand scrub forest site in the Western Cross Timbers. Kreye et al. (2013) classified post oak and sand post oak as pyrophytes and explained that these flammable pyrophytic species were being replaced by fire-sensitive mesophytic species as a result of fire exclusion in much of the southeastern forest region. Hiers et al. (2014) reached the same conclusion describing sand post oak as an old-growth component in frequently burned upland forests.
Tyrl et al. (2008) stated that control of saw greenbrier was difficult unless it was burned frequently. Frequency of fire needed for control of saw greenbrier was not given, but it was remarked that even with periodic burning or mowing saw greenbrier became more shrub-like (Tyrl et al., 2008). In a brief literature review of the impacts of fire on saw greenbrier, Gucker (2011) concluded that this species was tolerant of periodic fire due to its ability to resprout from rhizomes when topkilled. Gucker (2011) also concluded that saw greenbrier was not dependent on fire for maintenance or reproduction. Saw greenbrier is a member of fire-tolerant communities that develop with periodic fire, yet also of other plant communities developing with low fire frequency (Gucker, 2011).
Saw greenbrier exhibited little difference in cover following a July fire that burned through vegetation on the eastern margin of the Eastern Cross Timbers in south-central Oklahoma (Adams et al., 1982). Hutcheson et al., (1989) reported that following a winter fire in the Texas Edwards Plateau, saw greenbrier had by July of that year already developed greater dominance and shoot frequency than before prescribed burning. In southeastern North America, saw greenbrier is an abundant member of various forms of pine forests, especially those of longleaf pine (Pinus palustris), a climax forest type that can only persist with periodic fire. Numerous studies have shown this as, for instance, those of Beckett and Golden (1982) and Gilliam et al. (1986) and as summarized in the review by Wright and Bailey (1982).
Tyrl et al. (2008) specified that rhizomes or, perhaps more correctly, lignotubers of saw greenbrier were storage organs growing up to the size of basketballs. Coker (1944) and Holmes (2002) described use of the starchy lignotubers of Smilax species as a food source of Indians. Storage organs of the woodier saw greenbrier were probably less utilized (Coker, 1944), but general use of Smilax rhizomes and tubers for human food attests to their considerable capacity to store food in organs safe from fire and heavy grazing of aboveground shoots.
It seemed unlikely that this scrub forest vegetation would accumulate quantities of fuel sufficient for fire frequency or intensity adequate to have other than minimal impact on cover of saw greenbrier, especially given its tremendous capacity to store food in subterranean organs. In fact, trials by Hutcheson et al., (1989) and those reported by Gucker (2011) showed that fire resulted in increased cover and density of saw greenbrier.
Successional status of saw greenbrier has not been established. Status of saw greenbrier in vegetation development is perhaps as variable as this widespread species itself. Tyrl et al. (2008) wrote that saw greenbrier was a species of mid to late succession though it formed densest thickets following recent disturbance (e.g. old fields). Gucker (2011) concluded that saw greenbrier was a facultative seral species citing several studies in which saw greenbrier had increased with disturbance. On bottomland forests in the Texas Blackland Prairie, Nixon (1975) studied secondary plant succession on gravel quarries of different ages subsequent to abandonment. Overall (across successional stages) Nixon (1975) found that saw greenbrier was the most important liana species though it declined with advancing age of the sere (time since quarry abandonment) until it was second in importance to poison ivy (Toxicodendron radicans) on oldest quarries. Saw greenbrier was also the shrub species with the second-highest importance value on unquarried forests (Nixon, 1975). Saw greenbrier defied a simple successional status across north-central Texas. This was consistent with it being a common species in various plant communities and habitats in this general area (Diggs et al., 1999; Tyrl et al., 2008).
Nixon (1975) emphasized that Dyksterhuis (1948) had recognized a Quercus-Smilax community as one of four major topographic or edaphic climax communities of the Western Cross Timbers. In his classification, Dyksterhuis (1948) unequivocally indicated that saw greenbrier was a dominant climax species; though certainly there were implied limits to cover of saw greenbrier beyond which this species exceeded that of the climax vegetation. Nonetheless, Dyksterhuis (1948: 333) specified that "dense thickets of saw greenbrier" commonly found on "deep sands" were representative of some Western Cross Timbers vegetation that existed in frontier times. These conclusions were consistent with our interpretation that the deep-sand dwarf forest type comprised climax vegetation of a Sand Post Oak-Saw Greenbrier habitat type based on the widely used Daubenmire (1952, 1959, 1966, 1984) method of community inventory.
Sand post and blackjack oaks on the eight tracts of scrub oak forest we observed were almost all adult trees. Tree heights and trunk diameters of several trees were noticeably greater for oaks growing on the two tracts on which we conducted vegetational analyses. Nonetheless, oak trees were of similar size and morphology on the eight tracts, all of which had developed on some combination of the general Nimrod-Arenosa-Patilo soil mapping unit (Soil Conservation Service, 1973, 1977b). If there had been recurrent fires on the tracts we observed, trees might have been immature (sub-adult age classes) and of corresponding smaller sizes (depending on frequency of fire). In such cases, fire would have retarded tree development or progression to life-cycle maturity. In such hypothetical circumstances, fire would have overridden the genetic potential of oak growth on the deep-sand habitat. Such arrested tree development would have been in concert with other climatic variables such as precipitation and ambient temperature. For that matter, fire is an atmospheric or climatic variable.
Retardation of tree development by recurrent fire would have changed age-size structure, though not necessarily species composition, of the vegetation. Assuming (for sake of argument) that fuel was adequate for topkilling of adult and younger oaks, fire could have changed forest structure and physiogonomy, though not likely species composition. Even under this extreme (and unlikely) condition there might have been no reduction in number of trees at a genotypic level yet an increase in number of clonal oak shoots (as well as of saw greenbrier shoots like that described above).
Unless there was annual or very frequent fire, some of these clonal oak sprouts would continue to growth and produce increasingly greater foliar cover so that in a few to several growing seasons crowns of juvenile trees would probably have formed a closed canopy, though of immature rather than adult oaks. This was the condition described by Gregg (1844) for post oak and blackjack oak in the Cross Timbers due to annual burning. A closed canopy of oak regrowth would be closer to the soil surface which might be even less conducive to development of herbaceous species like the climax grasses. Such a phenomenon has been documented with regrowth of various woody species in this region (Hamilton et al., 1981). With prescribed fire on mixed prairie supporting honey mesquite (Prosopis glandulosa) in north-central Texas, Ansley and Jacoby (1998) found greater grass cover and biomass produced under larger, taller mesquite trees with higher crowns than beneath and interspersed among smaller, bushier, and shrub-sized mesquites that had developed with hotter, topkilling fires. It was possible that with frequent fire and smaller oaks there would have even less herbaceous cover than in dwarf forests with larger, taller oaks.
A more fundamental consideration is flammability of this scrub oak type. While saw greenbrier shoots readily burn, fuel of these shoots is apparently inadequate to generate fires intense enough to cause much lasting damage to this woody vine, let along to adults or even saplings of the two oak species. Francaviglia (2000) concluded that even fires set by Indians died out for lack of fuel in certain parts of the Cross Timbers. Such conditions might form the sand post oak-saw greenbrier community, especially at the most advanced stage with a sporadic herbaceous understory and approximately 80% of the soil surface covered by a densely packed layer of partly decomposed oak leaves ((i.e. low-flammability leaf mulch). Obviously herbaceous material growing in natural openings would burn readily, but fuel in the oak-greenbrier vegetation surrounding these openings might not be adequate to carry fire to the grass-dominated herbage. Besides, these local microsites already supported climax grasses without recent fire. The one plant species that most likely would have been eliminated or, at least, reduced by fire in the scrub forest was Ashe juniper, a nonsprouting conifer (Diggs et al., 1999).
We concluded that scrub forests dominated by sand post oak in the Western Cross Timbers could not be interpreted as a fire community type or pyric climax. Neither, however, should these plant communities be seen as vegetation existing due to absence of periodic fire given the demonstrated ability of the dominant species to survive or even thrive with recurrent fire. Rather, fire is a largely irrelevant factor in influencing species composition of what we regarded as the potential natural vegetation. The possible role of fire in retarding tree growth and preventing development of sand post and blackjack oaks to their mature size in some stands cannot be ruled out (periodic fire could result in stands of sub-adult trees), but evidence in this study and reports from previous observations and investigations led to the conclusion that fire does not play a defining role in development of this scrub oak-saw greenbrier forest community.
Grazing and browsing as a factor- We next considered the possibility that heavy grazing and browsing by ungulates, especially grass-preferring cattle (Holechek et al., 2004), could have been a factor-though not necessarily a determining factor-in species composition of the grazable-browsable understory of this scrub forest. This possibility was considered given the obviously heavy defoliation, high degree of use (Bedell, 1998), of the dominant grasses.
Ultimately, we ruled out heavy defoliation as a variable that was responsible for the sparse, sporadic herbaceous cover because the major herbaceous species, especially the perennial grasses, in the understory of our sampled scrub forests were the same species that were reported (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1979) to be the climax herbaceous species for this range site (named variously as Deep Sand, Deep Sandy, or Sandy for the Nimrod and Patilo soil series). Little bluestem and sand lovegrass, the native tall-and mid-grass species, respectively, with most cover and greatest density on the two forest tracts we sampled, were interpreted as the two major potential grass species for this range site (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1979). White-haired panic, the grass species with greatest cover on our sampled tracts, was not named in these reports, but it was included under the name of Scribner panicgrass, the general common name in these soil surveys for all the rosette-forming Panicum species.
Little bluestem was recognized as the dominant climax herbaceous species of the Cross Timbers (Shiflet, 1994). Little bluestem and sand lovegrass are readily eaten by cattle and generally categorized as decreaser or even ice cream species (Leithead et al., 1976; Nicholson, 2006; Tyrl et al., 2008), meaning they are some of the first species to decline under overgrazing (i.e. they are most sensitive to heavy, or, especially, excessive defoliation by animals (Soil Conservation Service, 1967; Stoddard et al., 1975). Dyksterhuis (1948) emphasized that sand lovegrass was a species that was virtually absent under overgrazing in the Western Cross Timbers. Sand lovegrass was named as the principal decreaser on the Deep Sandy range site in Erath County, Texas (Soil Conservation Service, 1973).
The fact that white-haired panic, little bluestem, and sand lovegrass remained the principal grasses (though limited in their cover and density) on heavily grazed sand post oak-saw greenbrier scrub oak forests indicated that grazing was not solely responsible for the limited herbaceous layer in this range plant community. The Deep Sandy range site description for Erath County, Texas (Soil Conservation Service, 1973) explained that typically "small post oak trees" [i.e. sand post oak] shade 60 to 90% of the soil surface and restrict grass growth. Our findings were consistent with this conclusion.
Furthermore, when we sampled at peak standing crop (in early autumn) there were none of the naturalized, cool-season, Eurasian, annual grasses and forbs that are widespread throughout this region and that invade overgrazed range and domestic pasture often to point of dominance. Remarkably, we did not any encounter any of these exotic herbaceous species (at any stage of growth or decomposition) in any of the sand post oak-saw greenbrier stands we observed.
In summary, there was no evidence that grazing by livestock or wildlife had changed species composition of the understory of this deep-sand range plant community. The potential for greater numbers of grass plants, increased grass cover, and higher vigor of dominant grasses under lighter utilization (Bedell, 1998) cannot be ruled out given these commonly observed responses of high-successional species to lighter degree of use (Stoddard et a., 1975; Butler et al., 2003; Holechek et al., 2004). Heavier degree of use did not, however, result in elimination of climax grasses, increased numbers and cover of invasive annual species, or partial replacement of native species by exotic grasses or forbs, which is the usual pattern of range degradation (plant community retrogression) on these range sites (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1979, 1980).
Local disturbance as a factor- Another possible cause of limited herbaceous understory and, with exception of scattered openings, development of a closed canopy forest was competition between expansive root systems of established trees and smaller herbaceous plants, perhaps in conjunction with mulching and alleopathic impacts as reported by McPherson and Thompson (1972) with post oak and blackjack oak leaves in the Cross Timbers of northern Oklahoma. The tree leaf layer on the soil surface of the sand post oak-dominated forest undoubtedly had a mulching influence, but it was not determined if this was responsible for the limited herbaceous cover. Nor was it known if oak leaf cover (and possible alleopathic affects) acted in concert with shade, potential root competition, etc. to restrict cover and density of herbaceous species. Alternatively, it was not known if this leaf mulch functioned to conserve soil moisture so as to benefit the few plants of herbaceous species.
Gaps in vegetation, especially those in forests, have been the focus of some recent vegetation studies as summarized by Keddy (2007). Patch dynamics (Pickett and White, 1985) is concerned with more or less local disturbances in established (usually high-seral or climax) vegetation. Windthrow, lightening strike, ice breakage, spot fires, disease, and local zootic disturbances ranging from insects to rodents have been considered as variables in vegetation dynamics or plant disturbance ecology (Johnson and Miyanishi, 2007). We found no basis for such spatially restricted factors or processes to explain the occurrence of scrub oak-greenbrier forests in the Western Cross Timbers or for natural openings (canopy gaps) in this vegetation. Even if future studies in this pygmy forest revealed allelopathic and mulching affects of oak leaves such interactions would be manifest, to large degree, through the soil component of this dwarf forest ecosystem.
Soil- an edaphic climax- The key distinguishing features of the Cross Timbers scrub forest community were its deep-sand habitat, dominance by sand post oak, and high shoot density of saw greenbrier. The earliest ecological studies of the Cross Timbers such as that by Tharp (1939) recognized that this mosaic of natural vegetation was primarily attributable to soils, especially sandy soils such as the Trinity sands of the Western Cross Timbers (Sellards et al., 1932; Braun, 1950). Dyksterhuis (1948:334) stated definitively: "The very existence of the Cross Timbers is largely traceable to certain geologic units from which the sandy soils are derived". The Western Cross Timbers formed along an extremely sandy outcropping of the Lower Cretaceous (Fenneman, 1931). The greater moisture availability of Cross Timbers soils is so much more favorable than that of surrounding soils in this drought-prone region that the Cross Timbers was used as a textbook example of postclimax vegetation, a natural plant community with composition and structure characteristic of vegetation that develops under wetter, more moderate climates than climatic conditions leading to development of the regional climax (Weaver and Clements, 1929, 1938).
The sandyland or deep sand aspect of the Patilo-Nimrod-Arenosa soil unit that underlaid the sand post oak-dominated scrub forest differs from the general sandy soil characteristic of the Cross Timbers. The soils of the scrub forest have both greater depth of profile and higher proportion of sand than most other Western Cross Timbers soils (Soil Survey Staff, 2014). Given the traditional explanation for development of Cross Timbers vegetation (especially of trees being dominant and defining components) attributable to more mesic edaphic habitats (Weaver and Clements, 1938; Dyksterhuis, 1948; Braun, 1950; Francaviglia, 2000), our initial hypothesis for forests dominated by sand post oak was that deeper sand was even more mesic. The reverse condition proved to be the case.
The Patilo, Nimrod, and Arenosa soils that comprised the composite mapping unit of the sand post oak scrub forest were shown to have physical and chemical properties different from those of neighboring Cross Timbers soils(http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). While no physical limitations were recorded for these three soil series each was shown to demonstrate redoximorphic features that indicated waterlogged conditions for adequate periods of time so that anaerobic conditions prevailed. This absence of molecular oxygen limits root development, especially when such anaerobic environments coincide with rapid root elongation and respiration (Pezeshki, 1991).
Depths of redoximorphic features of these soils were related to the landscape positions on which the soils form (Ruhe, 1975). Nimrod is typically found on broad upland summit landscape positions. Patilo is found on moderately steep shoulder and backslope portions of the landscape. Arenosa typically occurs on more strongly sloping backslope portions of the landscape (https://soilseries.sc.egov.usda.gov/OSD_Docs/P/PATILO.html). The relief of these landscape positions impacts water movement through the soils and leaves a legacy in the morphology of the soils (Ruhe, 1975).
Timing of anaerobic condition occurrence was not measured, but it can be assumed it followed precipitation events. Precipitation events occur predominantly in spring and autumn. The soils differed in depths to the redoximorphic features with Nimrod showing the shallowest depths (102 cm), followed by Patilo (127 cm) at an intermediate depth, and Arenosa with the greatest depth of 165 cm (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm).
The Arenosa soil is poorly developed consisting of a thin A horizon over several C horizons. This is likely do to the steeper landscape position where erosion exceeds soil development. Lateral translocation of soil weathering products are probably more pronounced than vertical translocation as evidenced by a distinct lack of subsurface accumulation of soil weathering products. Arenosa soil is not devoid of vertical movement, however, and shows a markedly lower reactivity at greater depth (pH 4.5 to 5) than Nimrod or Patilo (pH 5.1 to 5.5). This is likely due to a relatively higher fulvic acid fraction (derived from vegetative humus) moving through the Arenosa profile (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). Fulvic acids are very efficient at chelating and translocating mineral weathering products, probably out of the solum into the unconsolidated parent material below (Joffe, 1949; Greenland and Hayes, 1978; Brady and Weil, 2008). Fulvic acids enhance growth of shoots and roots as well as stimulate root initiation and elongation (Chen and Avaid, 1978). Thus, limited root development due to anaerobic conditions resulting from waterlogged conditions of these deep-sand soils (Pezeshki, 1991) could conceivably be partially offset by role of fulvic acids in stimulating roots.
Arenosa soil has less than 5% weatherable minerals in the solum (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). Consequently, the ability to hold nutrients in the Arenosa is lower than either the Patilo or Nimrod. Cation exchange capacity of Arenosa, Patilo, and Nimrod series was 1 to 4, 1 to 25, and 7 to 15 centemoles of charge per kg, respectively. By comparison, cation exchange capacity of five associated, sometimes contiguous, soil series was: 1 to 20, 1 to 25, 2 to 20, 2 to 25, and 2 to 30 centemoles of charge per kg for Selden, Windthorst, Duffau, Demona, and Chaney soils, respectively (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm).
With the conspicuous exception of the lowest cation exchange capacity values for the Arenosa and the highest low end of cation exchange capacity for the Nimrod soil, fertility did not appear to vary substantively between soils of the scrub forest and those of associated soils which did not support sand post oak-dominated forest communities. Certainly there was not enough difference in fertility between soils of the scrub forest and those of more typical West Cross Timbers vegetation to explain the contrast of a closed canopy scrub forest that was comprised almost exclusively of sand post oak with more open woodland or savanna vegetation devoid of sand post oak and populated by post and blackjack oaks.
The subsoil accumulation of soil weathering products such as secondary phylliosilicate clay along with oxides and oxihydroxides of metals in the Nimrod and Patilo is the source of nutrient-holding capacity (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). These subsoil accumulations also impact the soil's available water-holding capacity, the water status between field capacity and permanent wilting point (Soil Science Society of America, 2001).
Available water-holding capacity of Nimrod, Patilo, and Arenosa were shown to vary, depending upon exact texture and soil compaction (or bulk density), from 11.4 to18.5, 9.7 to 16.3, and 4.8 to 10.4 cm of available water-holding capacity, respectively (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). These values compared to available water-holding capacities of the following associated soil series: Chaney, 15.7 to 21.1; Windthorst, 15.7 to 22.9; 15.7 to 22.9; Demona, 16.3 to 22.1; Daffau, 16.5 to 27.4; and Selden, 26.9 to 41.7 cm of available soil water, respectively (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). Available water-holding capacities of the three soils of sand post oak-dominated scrub forests were considerably lower than those of five associated Cross Timbers soils. This phenomenon was most pronounced for the Arenosa series. Droughty (xeric) conditions of the three scrub forest soil series likely produced a harsher habitat that had a major influence on colonization and establishment of sand post oak, which again, is a species restricted to deep sands (Nixon and Muller, 1997; Diggs et al., 1999; Simpson, 1999). It is likely that this xeric edaphic habitat largely excluded post oak and blackjack oak from this Deep Sand range site resulting in a forest stand comprised almost exclusively of sand post oak.
The complex relationship between retention of water in soil and its subsequent absorption by roots (Black 1968; Russell, 1973) would be quite similar among the related species of sand post, post, and blackjack oaks. Perhaps sand post oak had a competitive advantage in water absorption on beds of deep sand. Regardless of effectiveness of soil water uptake by sand post oak, this species via natural selection was better adapted to the more limited soil moisture conditions (and, secondly, to lower soil fertility) of the three deep-sand soils of the dwarf forest ecosystem.
Rates of water infiltration into mineral portions of sola of sandy soils were likely influenced by their O horizons as well as the mulching feature of the oak leaf layer present on soil surfaces. It could be assumed that leaf litter on soil surfaces reduced evaporation of soil water (i.e. a mulching affect). Although details of the soil-water-plant complex were not studied, it was determined that lower quantity of available soil water was the operative phenomenon which permitted establishment and persistence of sand post oak. Deep sandbeds of the three soils of the dwarf forest had less water available for plant growth in their profiles. The lower water-holding capacities of these West Cross Timbers soils (in spite of their considerable depths) limited tree domination of this scrub forest to a single species, sand post oak. Likewise, sand post oak was restricted to a habitat characterized by xeric or droughty (and comparatively infertile) soils. Said another way, it was only on these extremely water-limited soils that sand post oak could outcompete post oak and blackjack oak, co-dominant trees of the Cross Timbers.
While numerous workers (Muller, 1951; Tucker and Muller, 1958, Vines, 1960; Correll and Johnston, 1979; Gleason and Cronquist, 1991; Diggs et al., 1999; Simpson, 1999) specified that sand post oak was restricted to soils comprised of deep sand, Lenix (2014: 276) was the only reference we found that specifically stated this edaphic habitat was "too droughty for many other trees to survive". Lenix (2014) provided no data or sources as basis for his empirical conclusion, but it was supported by our assessment derived from published characteristics of these sandbed soils (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm).
With limited water-holding capacity (low quantities of available soil water) and low to moderate buffering capacity of cationic nutrients, plants would need larger root systems (or larger roots relative to shoot biomass and crown cover) in order to explore a greater volume of soil to meet their mineral and water demands (i.e. greater surface areas of roots would be needed on drier, less fertile soils to obtain plant nutrients). Individual plants of comparatively small or diminutive size and plant species that grow to smaller size at maturity might be adaptations to harsh soil environments that explained domination of sandbed soils by the shrublike sand post oak. Soil, specifically soil water, is the principal environmental variable responsible for development of a dwarf forest with a single dominant tree species. The sand post oak-dominated scrub forest is the potential natural vegetation for this forest site in the West Cross Timbers. It constitutes a sand post oak cover or dominance type that is an edaphic climax.
Our quantitative findings of this dwarf forest corroborated qualitative descriptions of the natural vegetation as defined for the Deep Sand or Deep Sandy range site (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1980). Site descriptions and our inventory consistently showed that for this deep-sand habitat the native plant community was scrub forest dominated by sand post oak with saw greenbrier comprising the major shrub component and with a sporadic, poorly developed herbaceous layer that was limited primarily to natural forest openings on mounds or hummocks.
Unlike sand post oak, saw greenbrier is not restricted to sandy environments and instead is widely distributed and adapted to diverse environments, including a variety of soil and light conditions (McGregor et al., 1986; Gleason and Cronquist, 1991; Holmes, 2002; Tyrl et al., 2008). Likewise, blackjack oak is adapted to a number of habitats though these are generally on sites of comparatively low production potential (Sargent, 1933; Correll and Johnston, 1979; McGregor et al., 1986; Burns and Honkala, 1990). None of the herbaceous species growing on the scrub forest are limited to deep-sand environments even though sand lovegrass is more abundant on sandy soils (Diggs et al., 1999; Shaw, 2012). The widespread Texas bullnettle is generally more common in sandy soils, especially partially wooded areas, but it is also abundant on disturbed locales such as abandoned fields (Diggs et al., 1999).
Sand post oak was the only plant species of this forest community that is restricted to deep-sand soils. Presence of sand post oak was the defining feature of this dwarf forest and its edaphically determined environment. This feature was elaborated on below in discussion of affinities of this sandyland forest with other deep-sand forest communities.
In final analysis, we concluded that the scrub oak-greenbrier forest was the potential natural vegetation that was described as an edaphic climax. Sand post oak-saw greenbrier was a subtype, a deep-sand variant, of the Quercus-Smilax type of Dyksterhuis (1948) who, in his seminal ecological survey, did not offer details for specific forms of the general climax types he described.
This woody plant-dominated vegetation was not a brush invasion or a disturbance climax. Some range site descriptions for Deep Sand range sites in the Western Cross Timbers implied that sandyland vegetation dominated by scrub oak and associated woody species was degraded savanna or grassland converted into a brush field by disturbances like overgrazing (Soil Conservation Service, 1966, 1990). These implications were inconsistent with this agency's description of potential vegetation for these soils, especially the Patilo (https://soilseries.sc.egov.usda.gov/OSD_Docs/P/PATILO.html). Such conclusions also ignored initial reports by this same agency (Smith et al, 1917; Bushnell, 1923) as well as descriptions by pioneers. For example, in a journal entry of 1843 (when fires still frequently burned through the pre-European vegetation) an Army captain described some Cross Timbers vegetation as consisting "of dwarfish looking scrub oaks, whose branches extending down and interlacing render it almost impenetrable" (quoted by Foreman, 1947, p. 68).
We concluded that interpretation of the sand post oak-saw greenbrier vegetation as a degraded savanna converted to brush by human disturbance was incorrect. Instead, these dense, closed-canopy dwarf oak forests on deep-sand habitats are the potential natural plant community as shown in other site descriptions (Soil Conservation Service, 1973, 1977a, 1977b, 1978, 1980), journal entries by early explorers, cursory surveys like that of Dyksterhuis (1948), and the preliminary classification by L. Elliott (in litt.).
The natural vegetation for the Deep Sandy range site in Erath County, Texas was described by the Soil Conservation Service (1973) as producing "mostly post oak trees with little grass". One of the most apt descriptions of this climax dwarf forest was in the original soil survey of Erath County Texas (Bushnell et al., 1923:393): "This land was originally heavily forested with blackjack oak and some post oak, with a tangled undergrowth of vines and bushes…" This description was for the original and general Nimrod soil series including the deep-sand phase which is now recognized as the separate Patilo series. Hence, the emphasis on blackjack oak was for a less restricted soil. Furthermore, this was when sand post oak was regarded as being restricted much farther to the east (Small, 1933) and before it was recognized as occurring in the Cross Timbers region (Muller, 1951; Francaviglia, 2000). Instead, sand post oak was commonly included as a variety or scrub form of the broader, generic post oak as, for example, in Sargent (1933) and Fernald (1950). In the early soil survey of Eastland County, Texas this deep-sand vegetation was described as "a growth of scrub oak, shin oak, brush, and grasses" (Smith et al., 1917: 24). Gregg (1844: 361) described "a very diminutive dwarf oak" in the Cross Timbers that was called "shin-oak" by hunters.
We could not find any scientific name applied to "shin oak" in the Cross Timbers literature including range site descriptions by the leading federal conservation agency in this area as, for instance, reference to "shin oak" in Shackelford County, Texas (Soil Conservation Service, 1990b). It is possible that "shin oak" as applied in early accounts and some current technical applications was a general term for any low-growing oak and did not refer to any species (i.e. did not correspond to a specific epithet). In this usage "shin oak" could have referred to younger or resprout shoots of post, sand post, or blackjack oaks as these were the only Quercus species common on sandy soils in the Western Cross Timbers. Residents in this area apply "shin oak" to scrubby oaks of any Quercus species.
It is also probable that "shin oak" was used as a species-specific common name for sand post oak. Although they did not use scientific names, accomplished frontier authors like Irving (1835) and Gregg (1844) distinguished between post oak and blackjack oak as well as their habitats. It followed that early authors such as Gregg (1844) regarded "shin oak" as a distinct species rather than a general term for any small or immature oaks. Richardson (1963: 140) used accepted common names for several native plants of the Cross Timbers and referred to "masts of the post oak, blackjack and shinnery".
Confusion and misunderstanding in use of common names was another possibility with regard to "shin oak". Foreman (1947) confused "shin oak" in early Cross Timbers literature with sand shinnery oak (Quercus haravrdii), a highly rhizomatous shrub of the Rolling Red Plains and High Plains of Texas and Oklahoma. In citing and using the words of Van Dersal (1939: 216) as her source and description for "shinnery oak" (Foreman, 1947) obviously misapplied the species Q. harvardii, which does not grow in the Cross Timbers (Turner et al., 2003), rather than Q. margaretta (Van Dersal,1939: 218). Van Dersal (1939: 216, 218) described both of these species as well as Q. mohriana, which also is not found in the Cross Timbers (Turner et al., 2003), as forming thickets.
In categorizing and describing natural vegetation of Oklahoma, Hoagland (2000) did not recognize a dwarf or scrub forest dominated by sand post oak, but plant communities of the sand post oak-blackjack oak-saw greenbrier type occur on deep-sand habitats in the East Cross Timbers in south-central Oklahoma. We observed several tracts of such forest vegetation in Love County, Oklahoma where black hickory (Carya texana) was present as an apparent associate tree species such that this East Cross Timbers scrub forest corresponded to the Cross Timbers sandyland oak vegetation described briefly by L. Elliott (in litt.). Black hickory has not been reported in the drier West Cross Timbers (Turner et al., 2003). White-haired panic and eastern prickly-pear were common to both the East and West Cross Timbers forms of scrub oak forest. Exact data on land area in this East Cross Timbers form of scrub oak-saw greenbrier forest is not available, but this forest community covers considerable area as, for example, in Love County, Oklahoma (W. R. Sanders, district conservationist, Natural Resources Conservation Service, personal communication).
The East Cross Timbers scrub oak-saw greenbrier forest was especially well-developed on the Eufaula soil series which was described as sandy, siliceous, thermic, psammentic Paleudults. Eufaula soil is associated with the Arenosa series, thermic, uncoated ustic Quartzipsamments, and is similar to the Patilo series described as loamy siliceous, thermic grossarenic Paleustalfs (Soil Conservation Service, 1990a). The Eufaula series has an available water holding capacity ranging from 9.3 to 12.5 cm, cation exchange capacity varying from 2 to 8 centermoles of charge per kg, and a pH of 5.1 (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). This compares to an available water-holding capacity ranging from 4.8 to 10.4 cm, cation exchange capacity of 1 to 4 centermoles of charge per kg, and a pH of 4.5 to 5 for the Arenosa series (http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm). Eufaula soil obviously has low water-holding capacity along with low nutrient concentrations and poor nutrient retention due to high leaching rates. The Eufaula series consist of xeric, relatively infertile soils, a nearly ideal edaphic habitat for sand post oak that is restricted to deep-sand environments (Muller, 1951; Tucker and Muller, 1958, Vines, 1960; Correll and Johnston, 1979; Gleason and Cronquist, 1991; Diggs et al., 1999; Simpson, 1999).
Apparently the Eufaula series (at least in part) was previously included in and mapped as a more general Nimrod series that extended into the Cross Timbers of central Oklahoma (Hoagland et al., 1999: Figure 14.1), as in Okfuskee County (Agricultural Research Administration, 1952) where Nimrod was replaced by the Eufaula series (Natural Resources Conservation Service, 2007). Natural vegetation of Eufaula fine sand was described as "thickets of dwarf oak" used as "woods pasture" even though there was limited cover of tall and mid grasses beneath oak canopies (Soil Conservation Service, 1966:15, 84).
Natural Resource Conservation Service official series descriptions explained that Patilo, Nimrod, and Arenosa soils formed in sandbeds, sands, and sandy loams to sandy clay loams, respectively, that were apparently reworked by wind (https://soilseries.sc.egov.usda.gov/OSD_Docs/P/PATILO.html) whereas, Eufaula soil formed in sand sediments reworked by stream action (https://soilseries.sc.egov.usda.gov/OSD_Docs/E/EUFAULA.html). Nimrod, Patilo, and Arenosa result in concave/convex land surfaces (Soil Conservation Service, 1966; Soil Conservation Service, 1973) seen as hummocky or mounded microtopography. Official descriptions of Patilo, Nimrod, and Arenosa recognized the potential natural vegetation as a scrub forest of post oak and blackjack oaks with greenbrier plus an herbaceous component of perennial and annual forbs and grasses, including little bluestem. The official description for natural vegetation of the Eufaula series was post and blackjack oaks with an herbaceous understory of tall grass species.
The pygmy forest dominated by blackjack oaks in Missouri (Reich and Hinckley, 1980) developed on the Bolivar soil series, fine-loamy mixed, thermic ultic hapludalfs. The Patilo and Nimrod soils of the sand post oak forest we evaluated, the Eufaula soil of the Red River Valley on which sand post oak forests develop, and the Bolivar soil of the scrub blackjack oak are Alfisols. The Arenosa series of our study forests was an Entisol.
Development of similar scrub forests dominated by post oak, sand post oak, and blackjack oak as the potential natural vegetation took place on soils that developed from deposits of deep sand. Edaphic and micro-topographic features were comparatively consistent among dwarf forests communities. Likewise, brief and strictly qualitative descriptions of potential natural vegetation for these soils, especially those in official series descriptions by Natural Resources Conservation Service (available online at https://soilseriessc.egov.usda.gov/OSD_Docs/_/series name html) were consistent with our quantitative report. These descriptions and the study by Reich and Hinckley (1980) corroborated our overall observations that a scrub oak-saw greenbrier community that developed on deep-sand habitats in the Western Cross Timbers constituted a unique edaphic climax.
In the earliest description of Oklahoma vegetation Bruner (1931) included in his chaparral communities dense stands of sand post oak and dwarf plants of blackjack oak that established rapidly in cleared areas and on some grasslands. Bruner (1931) presented his seminal description of native vegetation in the hierarchy of the then-dominant Clementsian monoclimax theory (Clements, 1916, 1920, 1936; Weaver and Clements, 1938) such that his chaparral communities comprised associes, vegetation that was pre- or postclimax to climatic climax. By contrast, in polyclimax theory (Tansley, 1926, 1935) or climax pattern theory (Whittaker, 1951, 1953) many of the chaparral communities described by Bruner (1931) were edaphic or topographic climaxes that would correspond to associations, climatic climaxes in monoclimax theory.
Range and ecological site descriptions such as those used in conjunction with soil series and published in soil surveys, as for the general Cross Timbers region (Soil Conservation Service, 1966, 1973, 1977a, 1977b, 1978, 1980), are, in effect, vegetational units historically viewed from polyclimax or climax pattern perspectives (Dyksterhuis, 1949; Soil Conservation Service, 1967, 1976; Butler et al., 2003). Interpretation of scrub or dwarf oak forests as climax or potential natural vegetation is consistent with historic and current soil and vegetation mapping units that were based on the smaller spatial (and shorter temporal) scales of polyclimax or climax pattern perspectives (Tansley, 1926, 1935; Whittaker, 1951, 1953) More recently, state-and-transition models of vegetation development (Lauenroth and Laycock, 1989; Westoby et al., 1989; Friedel, 1991; Briske et al., 2005), along with traditional theories of climax vegetation, were incorporated into current ecological site descriptions of natural vegetation (Butler et al., 2003). Interpretation of dwarf forests that develop on deep sand in the Western Cross Timbers as the potential natural vegetation determined primarily by soil features (an edaphic climax) is in line with all of these successional-climax models.
Soil and plant relations- Cross Timbers vegetation has traditionally been interpreted as having developed and persisted due to edaphic environments characterized by water-holding clays overlaid by sands that permit rapid infiltration of precipitation (Dyksterhuis, 1948; Braun, 1950; Tharp, 1952). Together, these soil layers make for habitats more mesic than would otherwise exist in this subhumid area (Weaver and Clements, 1938; Dyksterhuis, 1948; Hoagland et al, 1999; Francaviglia, 2000). This general Cross Timbers phenomenon of greater soil water availability is, however, less pronounced for the deeper sands such as that of the Arenosa or Patillo soil series (known in earlier works as Nimrod fine sand, deep phase).
In the early soil survey of Erath County, Texas (Bushnell et al, 1923) soil scientists explained how most rainfall was quickly absorbed by the porous deep sand which was underlaid by an "impervious clay subsoil". The result was that the Nimrod fine sand, deep phase (currently the Patilo series) stayed wet (and cold) late in the spring resulting in scrub oak forests. (Waterlogged soil profiles and consequent anaerobic soil conditions of the Cross Timbers scrub forest were discussed above.) The first soil survey of Eastland County, Texas (Smith et al., 1917) described this deep phase of Nimrod soil in virgin condition as having a surface layer of fine sand extending to depths of one to two meters with a densely structured clay layer beneath. Scrub oaks, cactus, and miscellaneous grasses constituted the natural plant community of this deep, loose soil known locally as "blow sand" (Smith et al., 1917). From the onset of soil and vegetation descriptions like those of Smith et al. (1917) and Bushnell et al. (1923) it was recognized that edaphic features played a major role in the relatively greater tree canopy cover of this scrub forest. The dwarf forest developed in contrast to the savanna physiogonomy that was more typical of the Western Cross Timbers vegetation (Dyksterhuis, 1949, 1957).
Features of this deep sand-clay soil permitted establishment and dominance of the vegetation by sand post oak. Whether this was due to less water-holding capacity, lower water availability, periodically waterlogged soils, poor soil fertility, ease of shoot and root growth-development, or other factors was not known. The importance of porous sandy soil was obvious regardless of whatever edaphic features were responsible. Muller (1951), Tucker and Muller (1958), Simpson (1999), and Linex (2014) explained that the distribution of sand post oak was determined by beds of deep sand, an environmental feature to which this dwarf species is an "obligate inhabitant" and on which it develops into "pure stands" (Muller (1951). Restriction of sand post oak to sandy soils has been reported consistently in standard treatments whether this taxon was treated as a variety of post oak as by Sargent (1933) and Vines (1960) or as a separate species (Small, 1933; Correll and Johnston, 1979; Gleason and Cronquist, 1991; Diggs et al., 1999; Simpson, 1999).
Deep sand was the key feature traditionally used to distinguish the habitat of sand post from post oak, this latter of which has a much greater species range and broader ecological niche including adaptation to shallow, rocky soils (Diggs et al., 1999; Simpson, 1999; Tyrl et al., 2008). Even though sand post oak is limited in its edaphic adaptation, Sargent (1933) specified that it was the most common and widely distributed of what he interpreted as varieties of post oak, although post oak (which he treated as Q. minor), was the major oak of the Texas Cross Timbers (Sargent, 1933).
On seven of the eight forest tracts that we observed, plant communities dominated by sand post oak were conterminous with Cross Timbers vegetation that developed on less sandy soils and in which post oak was a major species. On the boundaries between these two West Cross Timbers communities we found trees with morphological features characteristic of sand post oak yet that were considerably larger than typical sand post oak growing on deep sand. It was conceivable that these were hybrids of Quercus margarettiae X Q. stellata as described by Muller (1952), Correll and Johnston (1979), and Diggs et al. (1999). If such was the case, this was further evidence of the strict affinity of sand post oak (whether a distinct species or variety of post oak) for sandbeds.
Ecophysiological phenomena which restrict sand post oak to deep-sand sites have received limited investigation. Some plausible factors for this restriction were suggested by a few studies and reviews. Donovan et al. (2000) evaluated distribution of turkey oak, bluejack oak (Q. incana), and sand post oak along gradients of soil water and mineral nutrients on a longleaf pine-scrub oak forest in the sandhills of South Carolina. Sand post oak had the lowest overall water-use efficiency, the most negative midday water potential, highest stomatal conductance, and lowest instantaneous water use efficiency (Donovan et al., 2000). These workers suggested that poor stomatal response to drought in sand post oak could result in rapid depletion of available water to its roots.
Another investigation in the pine-oak forest of the South Carolina sandhills (Espeleta et al., 2004) involved evaluation of hydraulic lift (redistribution of soil water from dry to wet and from deep to shallow soil) among major species. Longleaf pine, turkey oak, bluejack oak, and pineland threeawn (Aristida stricta) exhibited hydraulic lift whereas sand post oak and little bluestem did not. Espeleta et al. (2004) reported that the former four species were dominant in xeric sandhill environments while the latter two species were rarely found in the xeric habitats. The different capacities of species to redistribute soil water from deep to shallow soil layers affected water balance of sandhills vegetation and, presumably, reflected species distributions along gradients of soil variables, especially soil moisture.
Lack of hydraulic lift in sand post oak and little bluestem was thought to be due, first, to death of fine roots in dry surface soil thereby resulting in loss of soil-root interaction and, secondly, in case of little bluestem, shallower roots that did not extend to deeper, more moist soil. In a companion study, at the same location as that of Espeleta et al. (2004), West et al. (2004) concluded that the typical pattern of species distribution was of turkey oak being dominant on deep sands whereas mixtures of turkey, bluejack, and sand post oaks developed on soils of intermediate depth while blackjack oak was dominant on the shallowest soils.
In a study of root demography, Espeleta and Donovan (2002) reported parallel results for blackjack oak and concluded that it was a mesic (versus xeric and subxeric) species in sandhills sites. There was greater death and turnover of fine roots in blackjack oak. Espeleta et al. (2009) conducted a further study of tree root demography at this location and found that sand post oak, which grew on subxeric sites, had higher fine-root production yet also higher root mortality and turnover rates with shorter root life span than was the case for turkey and bluejack oaks, species that grew on drier sites. In a partially compensatory or equilibration response, sand post oak exhibited some production of fine roots during the leafless, dormant season when the other deciduous oak species did not (Espeleta et al., 2009).
Espeleta et al. (2009) concluded that fine-root demography of turkey and bluejack oaks (members of Erythrobalanus, the red oak subgenus) was characteristic of the "low-resource syndrome" whereas demography of fine roots in sand post oak (Leucobalanus, white oak subgenus) was characteristic of "high resource syndrome"species. The higher turnover-death rate of blackjack oak (Espeleta and Donovan, 2002) would place this member of the red oak subgenus with sand post oak as a "high resource" species. In the southeastern Coastal Plain both oak species of the West Cross Timbers deep-sand scrub forest had more vulnerable fine roots and grew on the less xeric sites.
West et al. (2003) studied root demographics of pineland threeawn and little bluestem at the same location as that of Espeleta et al. (2004) and Espeleta et al. (2009). These two native perennial grasses had root turnover and longevity features that were consistent with those of hydraulic lift found by Espeleta et al. (2004). Roots of little bluestem had pronouncedly shorter life spans because little bluestem underwent winter dormancy in contrast to pineland threeawn which did not undergo seasonal dormancy.
Sand post oak was reported by Cavender-Burns and Holabrook (2001) to grow on habitats with the lowest soil moisture (volume water/volume of soil) of 17 oak species although there appeared to be little or no difference between sand post and turkey oak. Abrams (1990) reviewed drought adaptations in various oak species (of which sand post oak was not one) and concluded that post and blackjack oaks were well-adapted to xeric sites in the central plains and southeastern regions of North America. Sand post oak is better adapted to dry environments than are post and blackjack oaks (Espeleta and Donovan, 2002; Espeleta et al., 2004; Espeleta et al., 2009).
In essence, these various investigations suggested that sand post oak, the dominant tree species, and little bluestem, one of two major warm-season grasses, in deep-sand scrub forests of the West Cross Timbers are comparatively mesic species (perhaps even drought avoiders). Sand post oak is, however, more tolerant of drought than some native tree species such as post oak and blackjack oak (Espeleta et al., 2009). Likewise, little bluestem, the dominant grass of the Texas Cross Timbers (Shiflet, 1994), was not excluded from this deep-sand habitat. Nonetheless, the Nimrod-Arenosa-Patilo soil complex comprised a comparatively harsh habitat with relatively low water-holding capacity and low soil fertility as compared to soils of other upland sites within the West Cross Timbers.
Soil-plant adaptation and variation- Depauperate or dwarf forms of plant species growing on harsh, infertile habitats have historically posed problems for plant systematists. Under such environmental situations it cannot be determined conclusively whether (how much) morphological differences are genetic or phenotypic variations in response to growing conditions and, hence, whether or not morphologically different plants represent distinct taxa. This phenomenon was discussed by Stuessy (2009). Woody species of pygmy or scrub forests that develop on podzol, podzolic, and deep-sand soils reflect this conundrum.
In the pygmy forest of northern California (Jenny et al., 1969; Westman, 1975) there were four parapatric subspecies of Pinus contorta that corresponded to different edaphic environments along a chronosequence of podzolic soils (Aitkken and Libby, 1994; Eckert et al., 2012) thereby constituting edaphic subspecies. Mendocino or pygmy cypress (Cupressus pigmaea = a subspecies or variety of C. goveniana ) was another dwarf or scrub conifer in this pygmy forest that was a contested taxon. Two genetic races (varieties) of sand pine (Pinus clausa) were recognized as occurring on scrub forests that developed on infertile, sandy soils in Florida (Christensen, 2000).
Similar genetic and taxonomic phenomena (with accompanying ecological implications)
apparently exist for sand post oak, a dwarf taxon closely related to post oak,
that is restricted to deep sands (Muller, 1951; Diggs et al., 1999; Simpson,
1999). Sand post oak has most frequently been designated as a distinct species,
with three variations of spelling for the specific epithet: Q. margaretta=
Q. margarettae= Q. margarettiae (Small, 1933; Muller, 1951; Correll
and Johnston, 1979; Gleason and Cronquist, 1991; Nixon and Muller, 1997; Diggs
et al., 1999) Other authors (Sargent, 1933; McGregor et al., 1986; Burns and
Honkala, 1991) treated sand post oak as a taxonomic variety of post oak (Q.
stellata var. margaretta). Muller (1951:52) explained that in the
Western Cross Timbers there was a "heterogeneous assemblage of intermediates
between Q. margaretta and Q. stellata". In addition, there
were populations that have been interpreted as Q. drummondii,
but these are not stable and have such sporadic distribution that they were
treated as a nothospecies, Q. x drummondii (Nixon and Muller, 1997).
Cavender-Bares et al. (2004) evaluated commonly shared phenotypic traits and
the phylogenetic clustering of 17 Quercus species along gradients of soil variables.
They found that although Q. margarettiae and Q. stellata were
the species most closely related to each other, their current biological distributions
did not overlap along a soil moisture gradient.
Regardless of hierarchial rank, sand post oak was distinguished from the more common and more typical post oak in all floras and field guides. Sand post oak has been separated from post oak based on restriction of the former to deep sands of podzol soils whereas the latter is adapted to a wide range of soils (Muller, 1952; Diggs et al., 1999; Simpson, 1999).
Blackjack oak apparently does not have a similar array of confusing taxonomic forms, but it does form numerous hybrids with other oak species (Muller, 1952; Nixon and Muller, 1997). Blackjack oak has a much wider adaptation to different habitats than does sand post oak which is restricted to deep sands (Nixon and Muller, 1997; Diggs et al., 1999; Simpson, 1999).
White-haired panic, the native grass and the herbaceous species with greatest cover in these dwarf forest tracts, apparently has a pattern or condition of genetic, morphological, and taxonomic variation that is similar to that of sand post oak and dwarf conifer species found on harsh, infertile soils. Taxonomic interpretation of white-haired panic has varied among agrostological authorities (Silveus, 1933; Correll and Johnston, 1979, Gould, 1975; Hignight et al., 1988; Diggs et al., 1999; Feckman and Lelong, 2003, Shaw, 2012) at levels of genus, species, subspecies, and variety. White-haired panic was designated by numerous scientific names including Panicum acuminatum var. villosum, P. villosissimum, P. lanuginosum in part, P. ovale var. villosissimum, Dichanthelium villosum, D. acuminatum var. villosum, and D. lanuginosum var. villosissimum. Intergradation and hybridization among subspecies and varieties is widespread within the Panicum or Dichanthelium taxon resulting in morphological diversity and taxonomic difficulty (Gould and Clark, 1978; Feckman and Lelong, 2003; Shaw, 2012). Lelong (1984) described eight taxonomic varieties within the polymorphic Panicum acuminatum complex which he described as the "most troublesome" species in the Panicum genus. Even with such varietal diversity in P. acuminatum, Lelong (1984) departed from the treatment by Gould and Clark (1978) and interpreted P. acuminatum var. villosum as a variety of the morphologically similar P. ovale (= P. ovale var. villosum) which had been recognized by Hitchcock and Chase (1950) at the species level as P. villosissimum as was P. ovale which Gould and Clark (1978) recognized as Dichanthelium ovale. For this taxon in the Cross Timbers of Texas (Diggs et al., 1999) used P. acuminatum var. villosum while Shaw (2012) gave D. ovale var. villiosissimum.
The widely distributed and morphologically variable saw greenbrier (Fernald, 1950; Correll and Johnston, 1979; Gleason and Cronquist, 1991; Tyrl et al, 2008) shares with sand post oak and hairy rosette panicgrass diverse taxonomic treatments by various workers (Fernald, 1950; Vines, 1960; Diggs et al, 1999; Holmes, 2002). This variation is seen as an array of varieties rather than as species or subspecies. Unlike sand post oak, saw greenbrier (and most species of the West Cross Timbers scrub forest) grows on a diverse range of habitats.
Little bluestem and sand lovegrass, dominant warm-season grasses of this forest understory, are also adapted to various habitats and are not restricted to deep-sand environments. Little bluestem is widely recognized as the dominant climax plant of the Texas Cross Timbers (Shiflet, 1994). Sand lovegrass is commonly found to be the most locally abundant grass species in relict tracts of Western Cross Timbers vegetation, especially on its preferred habitats of sandy grasslands and open forests (Gould, 1975; Tyrl et al., 2008; Shaw 2012), but sand lovegrass is clearly not restricted to deep-sand sites to the degree found in sand post oak.
Sand post oak is the only major species of the "sandrough" vegetation that is confined to the distinctive deep-sand habitat of the dwarf forest that it dominates. Sand post oak is both the dominant and the defining species of scrub forests that develop on deep-sand sites in the West Cross Timbers.
In addition to its edaphic habitat, sand post oak has been distinguished by numerous morphological features of leaves, twigs, fruit, etc. (Muller, 1951; Nixon and Muller, 1997; Diggs et al, 1999). The clonal feature of sand post oak, characterized by large, often pronounced horizontal trunks that develop both above and below the soil surface, is another prominent characteristic that distinguishes sand post oak from the similar and closely related post oak. Development of horizontal shoots was recognized by Sargent (1933) in his designation, Q. stellata var. margarettiae form stolonifer. This characteristic was also recognized for Q. margaretta by Muller (1951) who applied the vernacular name, runner oak. Gleason and Cronquist (1991:85) described sand post oak as "spreading underground and becoming colonial (forming colonies)". Berg and Hamrick (1994) found as many as 30 shoots in clumps of sand post oak. They concluded that although sand post oak reproduced both sexually and asexually, most shoots in clusters were ramets of the same genetic individual there being a 71% probability that boles less than a meter apart were clonal shoots (Berg and Hamrick, 1994).
Modular growth form was largely responsible for the high density of sand post oak shoots that characterized its dwarf tree morphology along with the internal structure and physiogonomy of a pygmy forest. The scrub forest type contrasted dramatically with the more open structure of Cross Timbers savanna or woodland communities dominated by post oak and blackjack oak.
Like sand post oak, saw greenbrier is highly clonal. It produces abundant numbers of circular, knotlike, woody modules at intervals along rhizomes which are morphologically similar to aboveground vertical shoots. Under the canopy of sand post oak aboveground shoots (both as individuals and in groups) of saw greenbrier grew into the crowns of oak trees. Fewer numbers of saw greenbrier shoots were found in the natural openings that existed on the slightly higher mounds within this dwarf forest.
Saw greenbrier is common throughout the Cross Timbers where it grows in association with other woody vines such as poison ivy, trumpet creeper (Campsis radicans), Virginia creeper (Parthenocissus quinquefolia), and mustang grape (Dyksterhuis, 1948; Diggs et al., 1999; Francaviglia, 2000). This relationship between saw greenbrier and other lianas was especially prominent in mesic habitats like bottomland forests (Nixon et al., 1990, 1991; Rosiere et al., 2013). The distinctive aspect of saw greenbrier in sandyland oak scrub was its extremely high density of shoots. The combination of high density of saw greenbrier shoots with frequent clumps of sand post oak boles typically formed a nearly impenetrable barrier to humans as well as beef cattle and white-tailed deer. Both ruminant species traversed throughout stands of "sandtangle" forest and fed primarily in natural openings and along established trails or paths. Francaviglia (2000) noted that while most of the Cross Timbers was a savanna with a parklike physiogonomy, there were sizable portions of this ecotonal vegetation with a tangled understory so dense in woody species, especially vines, that human travel had been deterred. Gregg (1844:361) wrote that in parts of the Cross Timbers "[t]he underwood is so matted in many places with grape-vines, green-briars, etc., as to form almost impenetrable 'roughs'…". The first Erath County, Texas soil survey (Bushnell et al, 1923:393) described this "heavily forested" oak community as having "a tangled undergrowth of vines and bushes".
In fact, much of the pre-European Cross Timbers appears not to have been a fire-maintained savanna or open woodland as often described in later ecological treatments. From careful rereading of early accounts of travel through the Cross Timbers it seems that vegetation of the earliest frontier-era Cross Timbers was far from a consistent savanna structure. After study of records kept by General Randolph B. Marcy while traveling through the Cross Timbers in 1849, especially in conjunction with the classic account of Gregg (1844), Hollon (1955:63) concluded that much of the Cross Timbers was "dense thorny brush" that "provided an effective barrier to commerce" and that was "the dread of every traveler". Irving (1835:144, 186) gave similar descriptions of arduous journeys through various forms of Cross Timbers vegetation including those dominated by post and blackjack oaks that varied from "oak barrens" on "quicksand" (loose sand) to "forests of cast iron" on land that had been frequently burned over by Indians. Kendall (1845:118, 119) described his troublesome travels through and "escape from" the Texas Cross Timbers with such descriptions as a "toilsome journey", "dreaded passage", "toilsome and tedious passage". This was in pre-settlement vegetation that frequently consisted of "small gnarled post oaks and black jacks" with "an almost impenetrable undergrowth of brier and other thorny bushes" which in some places was "impenetrable even by mules" (Kendall, 1845:110,115).
Dyksterhuis (1948) reviewed accounts such as these and concluded that while much of the Western Cross Timbers permitted of wagon movement during the early freighting period there was also vegetation characterized as "dense woods" that developed on Nimrod sands extending into parts of Oklahoma (Dyksterhuis, 1948:333). Restricted movement of humans and ungulates through the barrier-forming vegetational structure of the scrub oak forest (a result of multiple-shoot sand post oaks and dense saw greenbrier) that we described in this study was consistent with earliest descriptions of difficult passage through portions of the Cross Timbers. Presence of thorn-bearing shrubs like chittamwood, lime prickly ash, and devil's tongue pricklypear along with saw greenbrier corroborated descriptions of dense thorny brush recorded in the earliest accounts of travel through the Cross Timbers.
Other woody vines that are common in the West Cross Timbers were absent in the sand post oak-saw greenbrier forest with exception of mustang grape that grew along outer margins and infrequently in openings of this dwarf oak forest. This was in marked contrast to occurrence of several liana species growing with saw greenbrier in other Cross Timbers plant communities such as in bottomland forests (Nixon et al. 1990; Nixon et al.1991; Rosiere et al., 2013). Also in contrast to other Cross Timbers vegetation was infrequent occurrence (near absence) of non-oak tree species and presence of fewer shrub species in this deep sand forest. For example, Drummond's or rough-leaf dogwood (Cornus drummondii) is a widespread shrub throughout the Cross Timbers (Diggs et al, 1999), but it was limited to the perimeter and missing from the interior of sandyland dwarf oak forests that we characterized.
Domination, sometimes exclusively so, of the shrub or smaller woody plant component by saw greenbrier with its dense, curtain-like growth of prickle-armed, hard shoots was a key feature of this woody plant community. If the habitat type classification system of Daubenmire (1952, 1959, 1966, 1984), which is used by conservation agencies like the US Forest Service, was applied to this natural plant community it would clearly be the Quercus margarettiae-Smilax bona-nox habitat type.
Eastern prickly-pear was a distinguishing woody species of the sand post oak-saw greenbrier community. Although this succulent was a minor species from cover and density perspectives it proved to be an important indicator species. Eastern prickly-pear was listed as a component in the understory of a pygmy blackjack oak forest that developed on a sandstone bluff in the Ozark Plateau (Reich and Hinckley, 1980). It was also a member of native pine-oak communities on sandhill habitats in Virginia (Fleming and Patterson, 2012), North Carolina (Schafale and Weakley, 1990; Schafale, 2012), and Louisiana (Louisiana Natural Heritage Program, 2009). In our observations eastern prickly-pear was more commonly found in sand post oak scrub forest than in other plant communities of the Western Cross Timbers where such species as O. engelmannii, O. phaeacantha, O. macrorhiza, and O. leptocaulis predominate yet which were absent from the dwarf oak forest community. Furthermore, eastern prickly-pear was associated more with this Cross Timbers scrub forest (as it is with forests of sandy habitats along the Atlantic and Gulf Coasts) than with other natural communities of the West Cross Timbers.
White-haired panic was another diagnostic species though perhaps less so than the more highly reported eastern prickly-pear. Gould (1975), Hignight et al. (1988), and Shaw (2012) recognized from nine to 12 species of white-haired panic (either as Panicum subgenus Dichanthelium or genus Dichanthelium) for the Cross Timbers Region in Texas. Problems of nomenclature remain within this group of C3, cool-season, panicoid grasses yet presence of hairy rosette panicgrass as the major herbaceous species of this West Cross Timbers dwarf forest served as an indicator of its deep-sand habitat and the distinctiveness of this native plant community. We also noted that hairy rosette panicgrass was the apparent herbaceous dominant in East Cross Timbers scrub forests that developed on deep-sand soil in south-central Oklahoma.
Affinity with other natural communities- The sand post oak-saw greenbrier plant community appeared to be unique and limited to the Cross Timbers yet to have a botanical affinity with various natural plant communities that develop on sandyland environments of the Coastal Plain and Piedmont physiographic provinces. We found no descriptions or even titles of sand post oak-dominated vegetation, but similar natural communities on deep-sand sites in which sand post oak was an important component have been categorized and described in the literature. For example, a pine-scrub oak sandhill and a xeric sandhill scrub community were described for North Carolina (Schafale and Weakley, 1990; Schafale, 2012). In these two sandhill communities sand post oak was a frequent important member of the understory beneath an open canopy of longleaf pine. The herbaceous layer in these two communities (Schafale and Weakley, 1990) was dominated by Aristida stricta, but little bluestem was common and spurge bullnettle (Cnidoscolus stimulosus) was a counterpart species to Texas bullnettle that grew on the Cross Timbers sand post oak-dominated dwarf forests. Smilax species were not reported for the two North Carolina communities (Schafale and Weakley, 1990; Schafale, 2012), and these communities were characterized by more species of oaks and dominated by a conifer. Devil's tongue pricklypear was found on the two sandhill plant communities as well as the sand post oak-saw greenbrier plant community. The edaphic environment of the North Carolina communities was typically deep sand to loamy sand and included some soil series classified as Paleudults (Schafale and Weakley, 1990). These were similar to the Paleudults of the sand post oak-dominated scrub forests of the West Cross Timbers. Christensen (2000) summarized community composition and structure, including presence of sand post oak, of subxeric longleaf pine woodlands in the southeastern coastal plain.
Another similar plant community was the western xeric sandhill woodland or oak-farkleberry (Vaccinium species) sandy lands reported in Louisiana (Louisiana Natural Heritage Program, 2009). This community that developed on deep, sandy soils consisted of an overstory of pine (Pinus species) and oaks, including post, blackjack, and sand post oaks. This vegetation was more variable and diverse than the Cross Timbers scrub oak forest, but the affinity of the two deep-sand communities was evident from genera and species held in common including such herbaceous species as bluestems (Andropogon and Schizachyriun species), wild buckwheats, bullnettles, and purple sandgrass as well as such shrub species as chittamwood, and eastern or devil's tongue pricklypear. The greenbrier of the Louisiana sandhill oak forest was sarsaparilla vine (Smilax pumila).
Two pine and scrub oak sandhills woodland communities and one fluvial terrace woodland community in which sand post oak was a component were listed for Virginia (Fleming and Patterson, 2012). In these brief descriptions no greenbrier species were listed, but eastern prickly-pear and spurge bullnettle were given. These two species again showed similarity and affinity of natural woody vegetation that develops on soils of deep sands and undulating microtopography.
Such descriptions of natural plant communities along with various flora extending from eastern North America (Fernald, 1950; Gleason and Cronquest, 1991; Weakley et al., 2012) across to the Great Plains (McGregor et al., 1986) showed that sand post oak is limited to sandy soils, and primarily in the Coastal Plains and Piedmont physiographic provinces with the most westward and interior extension of its species range being the Western Cross Timbers. Fenneman (1931) regarded the Western Cross Timbers as being the western edge of the Comanche Plateau of the Great Plains physiographic province, but Fenneman (1938) also included the Western Cross Timbers as a subdivision of the Coastal Plain physiographic province.
Treatments in the definitive works on North American physiography (Fenneman, 1931, 1938; Thornbury, 1965) and comparisons of the sand post oak-saw greenbrier community with natural vegetation in southeastern North America indicated the close geologic association of the Cross Timbers with the physiographic provinces of Atlantic and Gulf Coasts, and hence the botanical affiliation of the natural vegetation of these vast regions.
This relatedness was clear from the presence of little bluestem, bullnettle, and devil's tongue pricklypear in all of the above sandyland natural communities as well as in the sand post oak-saw greenbrier scrub forest in the Western Cross Timbers. Blackjack oak was reported for all sandhill communities except those in Virginia.
Interestingly, sand post oak was a dominant species of natural vegetation only at the margin of its biological range in the West Cross Timbers. Also interesting was the fact that greenbrier was not a major species of the natural communities described for any of the other deep-sand or sandhill environments even though there are numerous Smilax species throughout the Coastal Plains and Piedmont provinces. Saw greenbrier is native to an area extending from Massachusetts through Maryland to Texas and north to Kansas and Missouri where it has various varieties and commonly forms dense thickets (Fernald, 1950; Vines, 1960; Gleason and Cronquist, 1991; Diggs et al., 1999; Tyrl et al, 2008; Weakley et al., 2012). As was the case for sand post oak, saw greenbrier was a dominant woody species at the more western (and less mesic) margin of its biological range.
This climax vegetation shares an obvious floristic affinity with other natural plant communities of deep-sand habitats. It is also a distinctively different native community and one whose dominants achieve dominance only at the interior- and westernmost extensions of their species ranges. We designated this West Cross Timbers scrub forest as the Sand Post Oak-Saw Greenbrier habitat type following the method of Daubenmire (1959, 1984). We also showed that this forest community was a variant of the Cross Timbers rangeland cover type described by the Society for Range Management (Shiflet, 1994) and proposed it as the Sand Post Oak forest cover type for recognition by the Society of American Foresters as in descriptions by Eyre (1954, 1980). This natural vegetation would be designated as Cross Timbers: Sandyland Dwarf (Scrub) Oak Forest in the Ecological Systems Classification and Mapping Project for Texas vegetation types compiled by Elliott (in litt.). Using the method of Diamond et al. (1987) and as applied to Texas (Diamond, in litt.) this natural vegetation would be Quercus margarettiae- (Q. marlandica, Opuntia humilis) / Smilax bona-nox Scrub Forest with the translated name of Sand Post Oak - (Blackjack Oak, Devil's tongue pricklypear) / saw greenbrier Scrub Forest to appear in NatureServe Explorer (http://explorer.natureserve.org).
Conclusions and Application- In summary, we regarded the closed-canopy scrub forest dominated by sand post oak and saw greenbrier as the climax or potential natural vegetation on some deep-sand sites in the Western Cross Timbers. We designated this forest community as a Quercus margarettiae-Smilax bona-nox habitat type. Although the agricultural productivity of this native vegetation is extremely low we feel that the uniqueness and comparatively small acreage remaining of this natural vegetation warrants its conservation.
The uniqueness of the dwarf oak forest that develops on deep sand in the West Cross Timbers adds to the diversity, distinctiveness, and historic chronicle of the Cross Timbers Region. Land acquisition by conservation organizations for the purpose of preserving, to the extent possible, representative natural communities of the Western Cross Timbers should include examples of the sand post oak-saw greenbrier scrub forest. This natural vegetation is an integral part of the Cross Timbers landscape mosaic. Although this pygmy forest is a climax community of the patchwork of natural vegetation that comprises the Cross Timbers, the sand post oak scrub forest has been largely ignored or received brief mention in vegetational investigations, including classic ecological surveys and summary descriptions.
Ironically, the combination of scrub physiogonomy, species composition, and community structure of this deep-sand dwarf forest encapsulates the nature of the Cross Timbers as a large ecotone between forest and grassland. The sparsely dispersed, tangled, and nearly impenetrable patches of sandyland dwarf forest have also been less readily available for commercial purposes than the more accessible surrounding prairies, savannas, and open woodlands. At the same time, it appears that a higher proportion of this Cross Timbers scrub forest has been more drastically altered than has vegetation of larger, more widespread Cross Timbers communities.
With availability of powerful land-clearing machinery much of this scrub forest was converted into cropland during the 1960s and 1970s. At the end of World War I, Smith et al. (1917) estimated that although 80 to 90% of the Nimrod soil in Eastland County, Texas was being farmed, only five percent of the deep phase of Nimrod fine sand (presently mapped as the Patilo series) was under cultivation. The deep phase continued to support "a growth of scrub oak, shin oak, brush, cacti, and various grasses" (Smith et al., 1917:24). Thereafter, much of the remaining sand post oak forests were converted to peanut fields, pecan (Carya illinoinensis) orchards, home sites, and pasture, especially of introduced forage grasses.
For example, in the 1960s-1970s intensive management era sizable acreages of these "sandrough" forests were cleared and seeded to the introduced species, weeping lovegrass. This was largely through cost-sharing incentives paid through the Great Plains Conservation Program administered by the Soil Conservation Service. Much, if not most, of this weeping lovegrass died out (perhaps due to poor adaptation to the harsh edaphic environment, pasture mismanagement, or a combination of these conditions). Currently, many of these old fields seeded to weeping lovegrass remain in a degraded state with sparse cover of exotic annual grasses such as Japanese chess (Bromus japonicus) and rescuegrass (Bromus catharticus). At the same time, removal of natural vegetation, including sand post oak-dominated scrub forest, has influenced local environments by increasing wind currents and decreasing areas of shade due to loss of taller, denser plant growth (i.e. a reduction in moderation of local climate).
A half century after many of these sand post oak forests had been converted to short-lived weeping lovegrass pasture members of the Natural Resources Conservation Service, the agency that previously sponsored these type conversions, recognized the questionable value of such practice. Lenix (2014: 276) concluded that disturbance to sand post oak forests should be approached with caution due to "… the difficulty of getting other desirable vegetation to survive the droughty conditions" under which this natural plant community developed.
Given the relatively small area remaining in sand post oak-dominated scrub forests it would seem more appropriate that public conservation agencies explain the nature of this natural vegetation to private land owners, including its value for wildlife, shelter for livestock, and aesthetics. This would be especially the situation for privately owned land used for fee hunting and where wildlife production is accorded the same tax allowance as that for other agricultural uses. It might be a greater good for stockmen, sportsmen, and society in general if government agencies would refrain from using tax monies to establish introduced pasture that does not persist while losing a uniquely distinctive part of the West Cross Timbers.
Original insight for this study came from the late H.W. Turney.
Essential advice and technical assistance was provided by R. Petit, B. Hoagland,
J. B. Deal, B. J. Bone, W.R. Sanders, and C. Figueroa. We are indebted to R.
Hammit and S. Vanderpool for permission to conduct portions of this study on
their land.
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TABLE 1-Density, dominance, and relative-importance values for woody vegetation
>1 cm diameter at breast height and saw greenbrier stems in Erath County,
Texas.
Taxon Density (plants/ha) Dominance (plants/ha) Importance Value (%)
Trees
Sand post oak (Quercus margarettiae) 2810 48,744.1 54.1
Blackjack oak (Quercus marilandica) 70 90.7 0.2
Shrubs
Saw greenbrier (Smilax bona-nox) 28,425 299.1 45.4
Eastern prickly-pear (Opuntia humifusa) 80 8.5 0.2
Ashe's juniper (Juniperus ashei) 50 15.4 0.1
Southern blackhaw (Viburnum rufidulum) 50 0.5 0.1
Chittamwood (Sideroxylon lanuginosu) 10 0.3 0.02
Prickly-ash (Zanthoxylum hirsutum) 10 0.3 0.02
Total 31,505 49,158.9 100.1
TABLE 2- Species Composition (absolute and relative foliar cover) of herbaceous
and woody plants (below 1 cm diameter) in herbaceous/low woody layer of scrub
oak forests (including natural openings) at peak standing crop in the Western
Cross Timbers, Erath County, Texas as determined by step-point method in mid-October
2012. The letter "T" represents trace amounts of plants.
Category Hits (number of) Relative Cover (of herbaceous spp. only; %) Absolute
Cover (all spp. in herbaceous layer; %)
Grasses
Sand lovegrass (Eragrostis trichoides) 13 9.1 3.3
Little bluestem (Schizachyrium scoparium) 15 10.6 3.8
White-hair panic (Panicum acuminatium var. villosun) 32 22.5 8.1
Arrow-feather threeawn (Aristida purpurascens) 1 0.7 T
Thinseed paspalum (Paspalum setaceum) 3 2.1 0.8
Purple sandgrass (Triplaisis purpurea) 2 1.4 0.5
Total 66 46.5 16.8
?
Grasslike
Bracted caric-sedge (Carex cephalophora) 21 14.8 5.3
Slender flatsedge (Cyperus lupulinus) 9 6.3 2.3
Total 30 21.1 7.6
Forbs
Horseweed (Conyza canadensis) 22 15.5 5.6
Heart-sepal wild buckwheat (Eriogonum multiflorum) 7 4.9 1.8
Texas bullnettle (Cnidoscolus texanus) 2 1.4 0.5
Frostweed (Verbesina virginica) 1 0.7 T
Spotted beebalm (Monarda punctata) 14 9.9 3.6
Total 46 32.4 11.7
Herbaceous Total 142 36.0 (% of total cover of herbaceous layer)
Trees and Shrubs (seedlings & shoots)
Sand post oak (Quercus margarettiae) 41 10.4
Saw greenbrier (Smilax bona-nox) 192 48.7
Eastern pricklypear (Opuntia humifusa) 6 1.5
Mustang grape (Vitis mustangensis) 1 T
Chittamwood (Sideroxylon lanuginosu) 4 1.0
Ashe's juniper (Juniperus ashei) 4 1.0
Sugarberry (Celtis laevigata) 4 1.0
Total 252 64.0 (% of cover of herbaceous layer)
Total plant cover in herbaceous layer 394 7.6 (% of total hits)
Litter
Leaf litter 4,241 82.0 (% of total hits)
Downed tree trunks/crowns 99 1.9 (% of total hits)
Total 4,340
Bare ground 438 8.5 (% of total hits)
Total 5172
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