Range Type

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Range Type: Defined and Described
Description and Designation of Vegetation vs. Biotic Communities:
The Nature Conservancy and the United Nations Systems of Vegetation Classification vs. Brown et al. Biotic Community Classification
Associations and Consociations
Cover Types are Dominance Types
Origin of the term 'Type'
Historical Note: "Founding Fathers" of Range Management
Role of Habitat
The "lost" legacy of George Nichols
Conclusion

Range Type: Defined and Described Range Type

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The term "type"-- as a unit of vegetation classification (often interpreted as a taxonomic unit that attempts to show ecological relatedness)-- as noted above has had long and widespread usage. As used by range, pasture, forest, and wildlife specialists type has often been accompanied by adjectives that denote specific uses and/or the basic kind of vegetation. Examples commonly encountered in Range Management and Forestry literature include: range type, forest type, cover type, range cover type, forest cover type, range vegetation type, vegetational type, grazing type, dominance type, dominance community type, rangeland type, rangeland cover type (Zon, 1906; Clements, 1909; Clements, 1920; Stoddart and Smith, 1943, 1955; Society of American Foresters, 1950, Wegner, 1984; Baker, 1950; U.S. Forest Service, 1964; Westveld, 1939; Weaver and Clements, 1929, 1938; Polunin, 1960; Spurr and Barnes, 1980; Mueller-Dombois and Ellenberg, 1974; Whittaker, 1975; Holechek et al., 1998). All of those in this list are, roughly speaking, basically synonyms.

There has been no standard or universally accepted definition of "type" even though it has a long and useful history in Range Management and Forestry. The term as a unit and concept of vegetation has been used rather consistently given the numerous systems of vegetation classification (generally used synonymously unless one is an extreme taxonomic "splitter"). There remains, however, considerable confusion as to where forest and range (= grazing= vegetation= cover= dominance) type fits into the hierarchy or organization of vegetation. "The terms grazing type or vegetation type are not distinct in their usage" (Stoddart and Smith, 1943, p. 66; 1955, p. 46). This situation has not changed in the half century hence.

The current Society of American Foresters Forestry Handbook (Wenger, 1984), the standard reference for foresters in the United States and Canada, still list for range classification the "eighteen broad standardized range types" first adopted by the Western Range Survey Conference on 24 April, 1937. These range types are named based on "[t]he apparent dominant vegetation lending the type its 'aspect' or general appearance" (Wenger, 1984, ps. 751-752). Though referred to in Wenger (1984) as range types these vegetation units are also called standard forage types and grazing types. They are designated as to aspect as determined by the dominant species and "have no ecological basis" (ie. they are not designated, at least not consistently, on the basis of "potential natural vegetation" nor "the successional state of the vegetation").

Most importantly, it should be emphasized that these U.S. Forest Service range (= grazing) types are not the same as forest cover types or other related but distinct classification units used in the Society of American Foresters Forest Cover Type Classification. Nor are they in the United Nations Education, Scientific and Cultural Organization classification based on physiognomy and structure of vegetation; the Potential Natural Vegetation Classification of A.W. Kuchler; the Habitat-Type Classification of R. Daubenmire; or Ecosystem Classification as, for example, by the U.S. Forest Service. These latter classification systems were described briefly by Wenger (1984, ps. 12-16).

Likewise, not all forest types are the same. Terms in the above list are roughly synonymous, but there are various categories of forest type and these kinds of forest types differ specifically and substantially from each other. The kind or category of forest type of concern herein is forest cover type, the one most commonly used to describe existing or present forest vegetation. Forest cover type may or may not coincide or overlap with other kinds of forest types discussed below. Apparently all types of rangeland vegetation are of the same category: rangeland cover types (the equivalent of forest cover types according to Shiflet [1994, p. ix, xi]). There are not parallel or equivalent units of rangeland vegetation comparable to the other forest types, but only to cover types.

The Nature Conservancy and the United Nations Systems of Vegetation Classification

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The fundamental concept of vegetation type as either 1) a broad and large unit or 2) a general term for vegetation has been widely accepted, but the precise placement of this unit within the structure or organization of vegetation and the hierarchy of various vegetation classification systems has not been agreed upon. An example is the recent comprehesive vegetation system in the United States, The National Vegetation Classification System, under aegis of the The Nature Conservancy in cooperation with several other organizations including the Ecological Society of America's Vegetation Classification Panel, US Forest Service, Natural Heritage Programs, and Conservation Data Centers. The National Vegetation Classification System apparently used "vegetation type" as the generic catch-all term for all hierarchial units (= levels) within its scheme and yet not as the formal designation for any specific unit unit ov vegetation (Grossman et al., 1998, Volume 1. ps. 12, 18, 37, 46, and 48).

The Nature Conservancy hierarchy of vegetation classification system (NVCS) for terrestrial ecological communities is:

1. Formation Class
2. Formation Subclass
3. Formation Group
4. Formation Subgroup
5. Formation
6. Alliance.

The first four units are physiognomic levels and the last two units are floristic levels.

Vegetation type and/or cover type units are obviously absent.

A "working draft (do not cite)" of "An Initiative for a Standardized Classification of Vegetation in the United States" by the Ecological Society of America (ESA) Vegetation Classification Panel (1997) stated unequivocally that there is a lack of agreement on terms used in describing and classifying vegetation:

"Vegetation science has had neither consensus nor national direction for its basic vocabulary" (p. 9).

The Panel working draft further commented:

"Agreement on terms often is not possible without agreement on the concept to be used, or at least respect for alternative perspectives on concepts" (p. 15)

The working draft of  "An Initiative" included six lists of terms used for units or levels of vegetation as found in Vegetation Science literature. For terms and definitions used at level of "specific upper-level floristic type" there were seven listings of terms and/or definitions for terms. Four of these were for cover type and these four were among the bottom five "in order of preference expressed by Terminology Work Group Members" (ESA Vegetation Classification Panel, 1997, ps. 11-13). Listed last (least preferred) was the definition proposed in 1989 which according to the Panel was the National Terminology Project of the Society for Range Management (incorrectly cited by the Panel under the former society name of American Society of Range Management which was changed almost 30 years ago). The only preferred term by the Panel for the upper level floristic type was alliance for which there were five proposed definitions which were ranked.

Likewise for "specific lower-level floristic type" the term and definition least preferred and listed last in the Initiative working draft by the Terminology Working Group of the ESA Vegetation Classification Panel (1997, p. 14) was vegetation type as defined by the "(ASRM 1989)"

In the introduction to terminology standards in the Initiative working draft, the ESA Vegetation Classification Panel (1997, p. 9) observed that the Society of American Foresters and Society for Range Management "used vegetation classification systems". "These two societies ask their members to use their official published terminology (SAF 1977, ASRM 1989), which raises related questions for the ESA." [The 1989 citation was for the National Terminology Project, Preliminary Draft, and not the 1989 SRM third edition of A Glossary of Terms Used in Range Management.]

The twenty members of the ESA Vegetation Classification Panel were listed as from universities (nine members) and federal agencies like the Bureau of Land Management, US Geologic Survey, US Forest Service, and Agricultural Research Service. Scientific/ professional societies such as the SAF, SRM, and The Wildlife Society were not represented directly or per se (at least these organizations were not listed or associated with Panel members).

With introduction of the U.S. National Vegetation Classification (USNVC) System The Nature Conservancy did compare or relate (briefly) their system to the Society of American Foresters (SAF) cover types:

"SAF cover types are 'a descriptive classification of forest land based on present occupancy of an area by tree species' (Eyre 1980). By contrast the USNVC uses all vascular plant species present in a community to help define vegetation units. Where dominant tree species are also diagnostic for a community type, similar, though not identical, units are identified by SAF cover type and USNVC alliance. Examples include the Jack Pine Forest Cover Type and the Pinus banksiana Forest Alliance, and the Post Oak-Blackjack Oak Forest Cover Type and the Quercus stellata-Quercus marilandica Forest Alliance. In other cases, the SAF cover types are more broad-ranging over both structural and environmental gradients than are the alliances recognized in the USNVC. For example, the Black Spruce Cover Type is separated by the USNVC into an upland Picea mariana Forest Alliance, a Picea mariana Saturated Forest Alliance, and a Picea mariana Saturated Woodland Alliance. The primary difference between these systems is that the SAF cover types are defined exclusively for forest vegetation, whereas the USNVC classifies all terrestrial vegetation." (Grossman et al., 1998, p. 44).

No reference was made by The Nature Conservancy (Grossman et al., 1998) to the SRM rangeland cover types. Given that publication of descriptions of rangeland cover types as, noted by Shiflet (1994, p. ix), was intended to serve as a "companion" to the SAF forest cover types published in Eyre (1980) it would seem that both rangeland and forest cover types (range types) would correspond roughly to one or more USNVC alliances. This is not a "perfect match" because, as noted by Grossman et al. (1998, p. 44), the SAF forest cover types were "based on existing tree cover", "…forests as they are today—what the land manager finds on the ground and must deal with" (Eyre, 1980, p. 1). By contrast a higher proportion of the rangeland cover types, while described as "existing" and "today", are climax or potential natural vegetation. Quick glance at the range vegetation types described in Shiflet (1994) reveals that most of these are what seem to be, to best existing knowledge, the highest expression of vegetation development possible under existing environments. This includes human-induced "new climaxes" (disclimaxes) that have thoroughly naturalized such as the California annual range type. The SRM rangeland cover types would likely correspond somewhat less closely to the USNVC alliances because The Nature Conservancy classification scheme is applied to existing vegetation: "The focus of the USNVC is on existing, rather than potential, vegetation" (Grossman et al., 1998, p. 16). Yet this was not all that clear or specific because later on Grossman et al. (1998, p. 16) also stated: "…efforts have been primarily focused on mid- to late-seral, natural/near natural vegetation".

Both The Nature Conservancy (Grossman et al., 1998, ps. 7-8) and the Society for Range Management (Shiflet, 1994, p. xii) cited classification systems of potential natural vegetation, noting especially the well-known maps of A.W. Kuchler, and clarified that their units of vegetation sometimes coincided with climax or potential natural vegetation. Shiflet (1994, p. xii) was explicit:

"Some of the cover types included here may bear some resemblance to those of Kuchler, but most do not since they are, for the most part, the result of human influence since the mid-1880's. If plant succession were allowed to take place unimpeded, in time the vegetation of these should approximate those communities described by Kuchler".

The Society of American Foresters offered a similar assessment for the forest cover types it described:

"Without disturbance, the present forest would tend to move toward the Kuchler potential and some SAF descriptions of climax types strongly resemble Kuchler's phytocenoces" (Eyre, 1980, p. 3).

In conclusion, the range cover types (both SRM rangeland and those SAF forest cover types useful or usable as range) correspond to the USNVC alliances with the main difference being that the alliances are more specific or restrictive than cover types (ie. cover types would often include several alliances as noted by USNVC authors).

The USNVC System was offered as an International Classification of Ecological Communities (though it was restricted to vegetation— included no fauna— and limited to the United States). It obviously had its origin in the United Nations Educational, Scientific and Cultural Organization (UNECSO, 1973). Grossman et al (1998, p. 43) also cited Driscoll et al. (1984), but the USNVC System is that of UNESCO with modifications as described below.

The UNESCO system in turn was a direct application of the Physiognomic- Ecological Classification of Plant Formations developed by Ellenberg and Mueller-Dombois in 1967 and shown in detailed revised form in Mueller-Dombois and Ellenberg (1974, ps. 466-488). The vegetation hierarchy of the Ellenberg and Mueller-Dombois scheme is:

1. Formation Class
2. Formation Subclass
3. Formation Group
4. Formation
5. Subformation
6. Further Subdivisions.

The Nature Conservancy USNVC System retained the first three vegetation units of UNESCO/Mueller-Dombois and Ellenberg, inserted Formation Subgroup between Formation Group and Formation, and deleted Subformation while specifying Alliance and Association as the first two of Further Subdivisions (see above listing of USNVC hierarchy)

The USNVC System also differs from the Mueller-Dombois and Ellenberg Physiognomic-Ecological System in that the former is based almost solely on the single factor of vegetation:

"A pivotal decision made by Conservancy ecologists was to develop a terrestrial classification system that was based primarily on vegetation" (Grossman et al. 1998, p. 14).

After reviewing single-factor vs. multi-factor classification systems The Nature Conservancy cited Mueller-Dombois and Ellenberg (1974) and decided upon a single-factor system based on vegetation "because it generally integrates the ecological processes operating on a site or landscape more measurably than any other factor or set of factors".

The UNESCO Structural-Ecological Formation System is also based primarily on vegetation but "some environmental-geographic information" is incorporated. It's hierarchial levels "are real vegetation units" but the system is "artificial" (Mueller-Dombois and Ellenberg, 1974, ps. 163-164). Mueller-Dombois and Ellenberg (1974, ps. 157-168) reviewed structural vegetation units and systems like UNESCO. In this context vegetation structure refers to "physiognomic criteria" such as plant life (=growth) form (which is the most important), plant size or height, deciduousness vs. evergreenness, and leaf features (eg. shape, size, and texture). These are essentially the same features of vegetation physiognomy given by Warming (1909, ps. 137-140 passim). They have traditionally formed the basis of distinguishing formations:

"Plant communities that are dominated by one particular life form, and which recur on similar habitats, are called formations [in the physiognomic-ecological sense]" (Mueller-Dombois and Ellenberg, 1974, p. 157).

This has been the European tradition of defining formations physiognomically. By comparison the American— actually Anglo-American— perspective "has been to define the same concept [formation] geographically and climatically". This is the classic Clementsian interpretation in which several physiognomic units occurred within the same formation (eg. units of forest within grassland). The European view of this scale of vegetation, the Clementsian formation, was "…not a formation, but a vegetation region". "A vegetation region usually contains a mosaic of actual vegetation types" (Muelller-Dombois and Ellen, 1974, p. 157). The "zonal or regional vegetation mosaic" was recognized by Clements, but in the European view he confounded their use of formation by interpreting some physiognomic units as successional (seral) stages of what he interpreted as the regional or climatic climax, the monoclimax, (or as preclimax or postclimax to the prevailing climatic climax).

A longer historical examination suggests that the dichotomy between European and Anglo-American views of formation and physiognomy is not as clear as Muller-Dombois and Ellenberg (1974) suggested. Warming (1909, p. 139) credited Grisebach with the introduction of the term "formation" or "vegetative formation" in 1838 "in the form of 'phytogeographical formation'". The original coinage and usage by Grisebach with the adjective of "geographical" is clearly consistent with the interpretation of Clements suggesting that it was the European and not the American (Clementsian) school that took formation away from it's seminal usage. This is further suggested by the definition by Warming (1909, p. 140):

"A formation may then be defined as a community of species, all belonging to definite growth-forms, which have become associated together by definite external (edaphic or climatic) characters of the habitat to which they are adapted".

The inclusion of both soil and climate as a basis for formation is consistent with both the Tansley polyclimax and Clements monoclimax views. Either way, Warming (1909, p. 140) used "the chief types of growth-forms as the prime basis of classification" for formations. Again, physiognomy is the basis of formations and life (= growth) forms are the primal criteria for physiognomy.

In continuing their review of vegetation classification Mueller-Dombois and Ellenberg (1974, p. 165) concluded that 'most investigators consider floristically defined vegetation units as more useful than structurally defined ones". Thus species composition, the floristic component, cannot be ignored in "any detailed study of vegetation". The structural (= physiognomic) component of vegetation by itself is not adequate.

The Nature Conservancy (USNVC) team reviewed vegetation classification systems as three groups: 1) physiognomic systems (eg. UNESCO), 2) floristic systems (eg. Zurich-Montpellier or Braun-Blanquet and Daubenmire association/habitat type systems), and 3) physiognomic-floristic systems (eg. Dick-Peddie, [1993, ps. 35-45]). The USNVC System is a combination system that "uses both physiognomic and total floristic composition criteria", "a hierarchial taxonomic structure with physiognomic criteria used at coarsest levels of the hierarchy and floristic criteria used at the finest" (Grossman et al., 1998, p. 17; USNVCS vegetation hierarchy shown above). The first (highest) five hierarchial vegetation units are physiognomic levels and the Alliance and Association are floristic levels (Grossman et al., 1998, ps. 20-26).

Hierarchial Classification of North American Biotic Communities- The System and Map of Brown, Reichenbacher, and Franson

Currently (and probably for the forseeable future) the system of classification for North American vegetation that is both comprehensive and most consistent with the traditional biome-association-dominance type model used in Range Management and Forestry (eg. SRM and SAF cover types) is that of Brown et al. (1998). These workers specified that their classification was "a biotic-community approach" in contrast to "purely vegetative classification systems", but their seven-level system published as A Clsssification of North American Biotic Communities included examples only of the biotic community (fourth level) and the series (fifth level) for most communities and to the association (sixth level) for some communities (Tables 4 and 5, ps. 36-48). All of these were designated by dominant plant species. Association was defined consistent with it's usage traceable to the International Botanical Congress in 1910, but spatial scale of association was "more or less local" (Brown et al., 1998, p. 35) and thus not consistent with the Clementsian-Tansylian association that was by and large the scale, interpretation, and usage of association adopted by the professions of Range Management and Forestry. Brown et al. (1998, p. 35) specified that the sixth level refered to "a distinctive association" with such associations "generally equivalent" to the Daubenmire habitat type. The few examples of the association (sixth level) were "plant associations". Nonetheless, the series (fifth level) corresponded very closely with the SRM and SAF cover types. Brown et al. (1998, p. 14) stated that their "general series of actual or potential plant dominants" were referred to as cover types by the Society of American Foresters (and alliances by The Nature Conservancy).

As was explained above, cover types and alliances are not synonyms and are not really interchangeable or completely convertible/translatable from one to the other. Many (probably most) of the Brown et al. (1998) series were very similar and often essentially synonymous with SRM and SAF cover types. These two units of vegetation are far rmore similar to each other than is either to The Nature Conservancy alliance because Brown et al. (1998) series and cover (= dominance) types both are essentially Clementsian in origin and outlook while The Nature Conservancy classification system is fundamentally based on the Braun-Blanquet model (Zurich-Montpellier School of Phytosociology). Brown et al. (1998, ps. 9-12) briefly reviewed the approaches to vegetatation classification more commonly used in the United States (including that of The Nature Conservancy). They also explained how and why A Classification of North American Boiotic Communities had adopted the Clementsian biome and the terms/concepts of disclimax and subclimax.. They then explained "advantages of a biotic-community approach over purely vegetative classification systems" (Brown et al., 1998, ps. 12-14).

Brown et al. (1998, p. 12) stated that "Clements was a great ecologist" and "… many of his contributions remain valid in modified form". (This conclusion was enthusiastically shared by your current author as was made evident throughout this publication.)

The Brown et al. (1998) hierarchial classification system was highly recommended and extremely useful. The earlier publication, Biotic Communities- Southwestern United States and Northwestern Mexico (Brown, 1994), was even more utilitarian and applicable in classifying and describing flora-fauna communities and, especially, vegetation in that region of the continent.

Unfortunately, A Classification of North American Biotic Communities (Brown et al., 1998) did not include enough series to correspond with all SRM and SAF cover types. This limitation was especially noticable and problematic for North American grasslands. The Brown et al. (1998) classification however did include (without major emphasis) subclimax and disclimax plant associations as well as climax vegetation (Brown et al., 1998, p. 35-36). This was particularily useful for Range Management as the biotic community system included such important disturbance climaxes as the California annual grassland (Annual Disclimax Series) and former climax bunchgrass-shrub steppe depleted to cheatgrass range (Cheatgrass Disclimax Series). Here again, though, Brown et al. (1998) omitted the climax Stipa bunchgrass prairie of the Central Valley, Coast Range, and Sierra Nevada foothills. This omission was consistent with omissions in the published SRM cover types (Shiftlet, 1994) and U.S. Forest Service forest and range ecosystems (Garrison et al, 1977) and inconsistent with the potential natural vegetation mapped and described by Kuchler (1964). Interestingly, for the Kuchler manual describing the climax California bunchgrass prairie, California steppe, there was apparently not even a readily available photograph of this pre-Columbian grassland so that a U.S. Forest Service photograph of California foothill annual grassland was used (Kuchler, 1964, p. 48). This was the same photograph used to accurately illustrate annual grassland disclimax in the manual by Brown et al. (1998, Plate 62, p. 88)! This rather comic situation was symptomatic (and symbolic) of the fact that the disclimax grassland designation was a more correct one for practical management than the designation of the pristine-- and essentially "extinct"-- virgin range.

Brown et al. (1998) series and associations were also quite limited for conifer forests of western North America. This was especially obvious (and bothersome) for SAF cover types of the Northern Rocky Mountains. This situation may have been partly a result of the Brown et al. (1998) emphasis on climax vegetation whereas several SAF cover types were "based on existing tree cover", "... forests as they are today...", such that some of these types are transitory or temporary (ie. seral) to climax forest communities (Eyre, 1980, p. 1). That partial explanation was largely unsatisfactory however because: 1) Brown et al. (1998) classification did encompass units of disclimax and subclimax forest vegetation and 2) Brown et al (1998) omitted several distinct forest communities long recognized as climax by workers like the "great ecologist" Clements. For example, Brown et al. (1998, ps. 36- 38) omitted series and associations in the Rocky Mountains that applied to SAF cover types 212 (western larch), western white pine (215), western redcedar- western hemlock (227), and western redcedar (228) that are all parts of the larch-pine forest association (thus climax) recognized by Wesver and Clements (1938, ps. 503-504).

Overall, the Brown (1994) and Brown et al. (1998) classification appeared to be more relevant-- more applied and more similar-- to range and forest cover types as both a hierarchial system and designations/descriptions of plant communities (= vegetation) than those of The Nature Conservancy and United Nations. In some respects, the Brown et al. classification of biotic communities was also more comparable to the Kuchler (1964) map and manual of Potential Natural Vegetation (disclimax and subclimax of the former being exceptions). Kuchler units of vegetation served as the basis for Forest Service forest and range ecosystems (Garrison et al., 1977, ps. 1-3) and for comparisons with SAF (Eyre, 1980, p. 3) and SRM (Shiflet, 1994, p.xii) cover types.

Associations and Consociations

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Mueller-Dombois and Ellenberg (1974, ps. 171-176) also reviewed floristic vegetation units and systems. Their format and brief historic analysis of floristic concepts allowed further comparison of the SRM and SAF range cover types to The Nature Conservancy USNVC vegetation units, and to pivotal perspectives leading to the development of vegetation type as used as a restrictive and specific unit in Range Management and Forestry. According to the brief review of Mueller-Dombois and Ellenberg (1974) there have been two fundamental floristic units and concepts in vegetation classification and description. These two "species dominance community-type concepts" are: 1) the sociation and consociation generally and 2) in specific usage by the Clementsian school, the association.

On the European mainland sociation was seen as a basic unit of vegetation classification where a sociation was any plant community that essentially had a "homogenous species composition with at least certain dominant species in each layer". Sociation was one of the lower units in the Clementsian hierarchy of climax vegetation largely based on or describing seasonal sequence or phenological aspects (hence "aspect") (Clements, 1936, ps. 276-277, 281).

Consociation was a major unit of vegetation in both European thought and in the Anglo-American (Tansley-Clements) school of dynamic vegetation (Clements 1916a, p. 120; Tansley, 1926, ps. 34-36; Clements, 1936, p. 274). In the Clementsian model consociation was "the unit of the association" (Clements, 1916a, p. 120) though the association "is to be regarded as divided into definite groupings of dominants or faciations" where faciation "is the concrete subdivision of the association" (Weaver and Clements, 1938, ps. 94-95). The distinguishing or defining characteristic of consociation was presence of a single dominant, one dominant species, or at least a single major dominant if several domiants were present. In an abstract sense each major dominant of an association was a consociation (Weaver and Clements, 1938, p. 94). Tansley (1926, p. 34) explained that an association usually had "more than one dominant species" or co-dominants. The community (the unit or level of vegetation) within an association formed by a single dominant species was the consociation. Pinus ponderosa in the montane forest formation and Stipa spartea or Agropyron smithii within true prairie were used as examples of consociations in Weaver and Clements (1938, p. 94-95).

Mueller-Dombois and Ellenberg (1974, ps. 172-173) concluded that as a unit consociation had "no universal applicability". Consociation was difficult to use in communities having high species richness or, conversely, a single species "may become dominant under different habitat conditions" (ie. when a single dominant species is used to define or delineate a community type "very different habitats" may get grouped together). The first difficulty is self-evident and an obvious limitation. The second condition of lumping together different habitats is a ridiculous criticism, at least at larger spatial scale (within the same or similar climate). Yes, it is a true statement of the actual situation but: 1) vegetation and not habitats are being classified, described, mapped etc. and 2) at that large scale (the first subdivision of a formation) "jillions" of habitats are included and these habitats, in turn, will be subdivided out at progressively lower, more specific levels. In other words with regard to 2) no unit of vegetation is site-specific unless it also includes habitat criteria, but progressively smaller units of vegetation have progressively less heterogeneous habitats. Incidentially, recall from discussions in the Range Site section that this same sort of grouping together (inclusion) of different habitats in the same taxonomic unit of vegetation is typical of the habitat type approach.

The obvious difficulty with consociation was the confusion in the different ways in which association was applied. As with— actually originating with— formation, the vegetation unit of association was applied differently in Continental schools of vegetation than in the Anglo-American school (the predominate Anglo-American perspective). As a concept and vegetation unit, association has been second to none or only to formation (or climax and, later, biome in Clementsian Ecology). Association has been a— perhaps the— major unit and unifying concept in description, classification, and mapping of vegetation. Association is traceable to the early days of Plant Geography. Warming (1909, ps. 137, 144) credited the origin of plant association (plantes associees) back to Humboldt (1807). Warming's Oecology of Plants (1909, English translation) has often been regarded as the world's first textbook in Plant Ecology. In it Warming listed several other plant geographers and ecologists who employed association (or its concept by other names). He defined association as "a community of definite floristic composition within a formation; it is, so to speak, a floristic species of a formation which is an oecological genus" (Warming, 1909, p. 145). Associations were "smaller, often more-localized subdivisions or kinds of the formation" (p. 144). As was species to genus so was association to formation. To Daubenmire (1968, p. 29) "the association serves the same purpose in synecology as the species does in taxonomy". Daubenmire stated that there was a long-standing analogy of association to species and that while "[n]either is susceptible to rigorous definition…" both remain equally essential to their fields. Tansley (1926, p. 30) succinctly put the association is perspective by describing it as "the fundamental unit of vegetation".

In 1910 in Brussels the Third International Botanical Congress adopted by official resolution the following definition of plant association:

"…a plant community of definite floristic composition, presenting a uniform physiognomy and growing [or 'when occurring'] in uniform habitat conditions" (Daubenmire, 1968, p. 27; Mueller-Dombois and Ellenberg 1974, ps. 173-174).

After a five page review of association Daubenmire (1968, p. 32) concluded that association was "a type of climax phytocoenosis". He then remarked that "very little" climax vegetation remained (due largely to human-induced disturbance) yet "each climax can normally regenerate itself repeatedly following destruction" so it was the area belonging to each association that is of ecological importance. This area of one plant association or that had been in one association or that had potential to regenerate that association was Daubenmire's habitat type (synonym, homoece).

***Note: if habitat type is equal to plant association (or previous or potential plant association) and association is a subdivision of a formation, the largest unit of vegetation in the original usage of the term, then there is absolutely no way whatsoever that habitat type could be the equivalent of or a synonym for range site, the smallest unit, the most distinctive kind, of native grazing land. Given the historic definitions of these vegetation units, the attempt to rationalize the equivalency of habitat type to range site (discussed in the Range Site section) seemed ludicrous to the present author. [It will be explained below that the Daubenmire association was generally closer to a subassociation of the Clementsian association, a unit more similar to a cover type.]

Unfortunately, the 1910 Botanical Congress definition, which was nearly verbatim (with an addition or two) that of Warming, did not specify the basis for delineating an association and the term/concept came to mean two different things to the Continental and Anglo-American views of vegetation (Mueller-Dombois and Ellenberg, 1974, ps. 174-175). In his last major paper on the climax Clements (1936, p. 273) noted this difference between the two schools of thought in defining association:

"Under the climax concept this represents the primary division of the biome or formation, and hence differs entirely from the generalized unit of the plant sociologists, for which the term community is to be preferred. Each biome consist regularly of two or more associations…".

The Clementsian school retained the meaning of association specified by Warming (1909, ps. 144-145) as a subdivision of the formation or as species of the formation genus.

Mueller-Dombois and Ellenberg (1974, p. 175) described the Clementsian association as "the general plant cover in a given macroclimatic region (ie. a vegetation mosaic)" or "more or less a climatic subregion". The latter description is apt because the formation was based on, determined by, regional climate; the former description was not of an association but of a formation which includes several associations. Mueller-Dombois and Ellenberg (1974, p. 175) were correct, and specifically so, in a synopsis statement:

"Each climax was subdivided into a few 'formations' (regions) and each 'formation' was subdivided into two or more 'associations' … Clements defined an association floristically by joining the names of two regionally dominant species and then implied that an association was a grouping of two or more consociations".

As Clements (1916a, p. 128) first used association it was a floristic subunit of the physiognomically-developmentally derived formation. Fundamental development and life-forms were the same for all associations in a formation (these two features unified or served as basis for formation); differences in dominant species distinguished the various associations. In Plant Ecology Weaver and Clements (1938, p. 93) introduced the association with this description:

"Every climax formation consist of two or more major subdivisions known as associations. These are climax communities associated regionally to constitute the formation. The number of associations in a particular formation is naturally determined by the number of subclimates within the general climate of the formation. Each association is marked by one or more dominants peculiar to it".

One of the most explicit descriptions of plant association was in Plant Indicators:

"Each climax formation falls readily into two or more major subdivisions known as associations. Toward their edges these blend into each other more or less, making a transition area or ecotone. The latter is broad in the case of relatively level regions, and narrow in that of the climax zones of mountain ranges. The associations have one or more dominants in common, or at least belonging to the same genus, and there is a certain degree of similarity as to subdominants also. Each association consist of several dominants as a rule, though there may sometimes be as many as eight or ten or more, as in scrub and chaparral. Each dominant constitutes a consociation. It may occur alone, though as a rule it mixes and alternates with the other dominants of the same association This is the direct outcome of the similar requirements of the dominants, and hence it is a guiding principle that two or more consociations are regularly associated in the larger unit" (Clements, 1920, p. 107).

This view expressed by Clements came to be the interpretation of most British, American, and Canadian ecologists as well as those in nations with ties back to "mother countries" (eg. South African ecologists like J.F.V. Phillips were largely of the Anglo-American school). The various "schools" of ecological thought were defined largely by geographic location. These were reviewed exhaustively by Whittaker (1962). Shimwell (1971, ps. 44-62) also discussed the different Schools or Traditions and drew pedigrees or lineages of them. The English Tradition (Shimwell, 1971, ps. 47, 54) which dominated Range Ecology and Forest Ecology during their formative years and formed the foundation of modern Range Science and Forest Science can be traced back through Clements (and to a lesser degree Tansley, C.E. Moss, and H.C. Cowles) to Warming, Oscar Drude, and finally to the fountainhead of August Grisebach, an oft under-rated plant geographer who described vegetation types physiognomically and in relation to climate and who was the first to use the term formation (Clements, 1916a, p. 116).

The English-American-South African Tradition came to be known as the holistic or organismic school of vegetation. It was clearly the "dominant species" of ecological thought in its day and probably, though in less pure form, today. A smaller, less influential school was the individualistic or continuum school begun by the American ecologist Henry A. Gleason and more or less perpetuated— at least experiment-wise— by Robert H. Whittaker. Whittaker actually defied pigeon-hole categorization being somewhat of a hybrid. He did expand the Gleasonian individualistic concept through gradient analysis but as discussed above (Biome section) he successfully reconciled Clements' monoclimax and Tansley's polyclimax. This, plus his views on communities (Whittaker made much use of biomes), would place him squarely in the Anglo-American "pedigree" (Shimwell, 1971, p. 54).

The Gleasonian branch of the English Tradition (Shimwell, 1971, p. 54) became known for its "individualistic concept of the plant association" (Gleason, 1917; 1926). Allen (1998) contrasted the Clementsian and Gleasonian associations by remarking that Clements used association as an abstraction for a unit of climax vegetation while ignoring seral stages leading to climax (as a subdivision of formation or climax, association was not a seral unit). By contrast Gleason used association as a concrete unit of vegetation based on species composition at an instant of time and at a site while ignoring climax. Allen (1998, p. 320) overlooked or ignored the fact that in his elaborate scheme of vegetation units Clements (1936, ps. 278, 281) included as the equivalent of associations the seral unit, the associes, which was "the major unit of every sere". (Clements was always one jump ahead of potential criticism and covered about every conceivable weakness in his pet theories.) Nonetheless, Allen's observation on Clements' association being an abstraction was partly correct because Clements (1916a, p. 126) stated that association was used "in both abstract and a concrete sense". "The general use of association in the concrete has fixed it definitely in ecological terminology". On the other hand, Allen's interpretation of the Clementsian association as an abstraction seems to have been a view either anticipated by Clements or made to him, and he seems to have denied it:

"…the formation is necessarily an organic entity, covering a definite area marked by a climatic climax. It consist of associations, but these are actual parts of the area with distinct spatial relations. The climax formation is not an abstraction, bearing the same relation to its component associations that a genus does to its species" (Clements, 1916a, p. 127).

Shimwell (1971, p. 53) commented on these words and concluded that Clements "conceived the formation not as an abstraction".

Baker (1950, p. 44) concluded that Clements (1928) used association "in a somewhat abstract sense to cover a section of a formation occupying a subclimatic zone and therefore having climax dominants dictated by that subclimate…". Nichols (1923, ps. 15-17, 172) discussed the abstract vs. concrete concept of plant association. He cited a resolution routed by letter to 85 ecologists ("mostly botanists and foresters and mostly members of the Ecological Society of America") in 1921 which read in part: "That the term Plant Association be recognized as applicable both to the abstract vegetation concept and to the concrete individual pieces of vegetation on which this concept is based". Of the 76 respondents, 67 favored adoption of the recommendation (Nichols, 1923, p. 15).

For his part, Clements (1916a, p. 117) concluded that the formation of Grisebach and the association of Humboldt "meant practically the same thing by their respective terms". Clements (1916a, p. 118) quoted Moss (1910) as dividing formations into associations following "many previous authors" but these were traced back to Warming as being the first to publish this subdivision (Clements 1916a, p. 121).

Obviously association so defined and perceived would be of immense size, considerable environmental heterogeneity (as noted earlier), and of a mosaic pattern among other associations of the same formation. Warming (1909, p. 145) specified: "Associations may occur irregularly as patches in the formation; or may exhibit a zonal arrangement". Tansley (1926, p. 31) stated it thusly: "Associations are, on the whole, large units, with wide extension, though this may be, and practically always is, interrupted by the occurrence of other associations". Daubenmire (1952, p. 302) described this same pattern when he identified associations in coniferous forests.

It seems that Warming, Tansley, and Clements shared a similar interpretation of association. For example, all used the example of "reed swamp" which was a community dominated by Phragmites communis, Scirpus lacustris or S.validus, and Typa spp. Though Warming (1909, p. 145) referred to "reed-formation" he used these individual species as examples of associations within that formation which would thus be consociations in Clementsian terms. Tansley (1926, p. 31) referred to the "reed swamp association" but did not specify single species units (= consociations) as a form of association. Clements (1936, p. 264, 278) noted that "reed swamp" was "the universal example" of a "serclimax" and Weaver and Clements (1938, ps. 62-63, 100) treated the "reed swamp stage" as a seral stage and not climax so that each unit of vegetation dominated by a single one of these "reed swamp" species was a consocies, the seral equivalent of the climax consociation.

The difference between association vs. associes (or consociation vs. consocies) between Tansley and Clements was the difference between Clements' monoclimax (where meso-, mesic, level would theoretically be the terminal regional climax) and Tansley's polyclimax (where hydric-, mesic-, xeric-levels could all lead to local, say, edaphic climaxes). The important point is that all of these ecologists of the English Tradition saw associations (associes) at the same spatial scale. Since then a younger "descendent" of the Anglo-American school cited this same example of a consocies (Polunin, 1960, p. 334, 505). Likewise, Polunin (1960, p. 333-335) gave the classic Clementsian units of vegetation verbatim from Clements (1936) climax paper illustrating the vast profusion of the Clementsian view of vegetation and its dynamic development and the persistence of the Anglo-American Tradition of Vegetation Science.

Critical note: the important sweeping— and inevitable— conclusion is not that one ecologist or school (= tradition) was "right" or "more nearly correct" and some other school or model was "wrong" but rather which one(s) formed the basis and had most impact on current applied ecological thought. The fact is that the paradigm (some would say "philosophy") of the Clements-Tansley group going clear back to Warming and Grisbach was the view that dominated American, British, Canadian, and South African ecological thought. And this domination— almost an exclusion of counter thought— was profoundly influential on the fledging disciplines and professions dealing with management of native vegetation and, for that matter, natural resources in general (eg. Soil Science, Wildlife Management).

To understand current systems treating of range and forest vegetation, students of these resources must understand the basis of this Vegetation Science upon which Range Management and Forestry are built. That basis is overwhelmingly Clementsian.

Range types (both rangeland and forest cover types) are one of the best examples of this lasting Clementsian influence. As with range site, there is no specific level or unit of vegetation in any classification or vegetation mapping system that corresponds exactly and consistently to range type (rangeland and forest cover type). It was shown previously in this review that range site is a unit of vegetation and certain environmental or habitat factors, especially soil (Range Site section). By definition, range site cannot be "retrofitted" into any system or classification scheme that is devoted solely to vegetation and that ignores habitat. By contrast, both plant formation (climax vegetation at regional or zonal scale) and plant association (the Anglo-American association at any and all scales) are both units strictly, solely, of vegetation with no environmental factors (except the biotic interactions of the vegetation) directly included. As explained earlier, this is the exact situation with the Daubenmire habitat type which is the equivalent of the Daubenmire association. Vegetation cover types are also strictly, exclusively, units of vegetation and therefore could theoretically match exactly one or more units of vegetation in the numerous schemes or hierarchies of vegetation classification, description, or mapping. At present none do match. Range cover types do not correspond directly and equivalently to any unit of vegetation in existing vegetation classification systems. For example, The Nature Conservancy unit of alliance in the USNVC System corresponds but approximately to the SAF forest cover types.

Where do rangeland and forest cover types fit into vegetation classification? To which—if any— units of vegetation do they correspond? From which— if any —did they arise?

Once again it was the genius of Whittaker (1975) to synthesize and clarify the various uses of concepts in context of vegetation types or cover types and to suggest the origin of forest and range types. In making more sense than most out of plant community classification Whittaker (1975, p. 128, 135) stated that the biome or formation is a major kind of community classified or defined, in principle, solely by physiognomy but, in practice, a combination of physiognomy and environment is required. "The physiognomic approach classifies communities by structure—generally by the dominant growth-form or the uppermost stratum or the stratum of highest coverage in the community". Further:

"Structural or physiognomic classification is the usual approach to description of the communities of a continent, or of the world, and it is widely used by geographers, climatologists, and soil scientists as well as ecologists" (Whittaker, 1975, p. 128).

Consistent with the preceding discussion, Whittaker (1975, p. 135) explained that "on a given continent" biome (or formation) is the broadest possible classification level or structural/organizational unit of plant and animal community (or of plant community, vegetation, only). He then went one unit of scale larger and one organization level of community higher to define biome-type or formation-type as "[t]he still broader [thus the broadest of all] grouping of convergent biomes or formations of different continents".

Obviously the biome-type or formation-type is the broadest unit or most general kind of vegetation (eg. "grassland biome type" and "desert biome type" include all grasslands and deserts on Earth). This is not to be confused with vegetation or cover type which is the major subdivision of biome or formation. But the use of the term "type" at different levels of organization and scale for the grouping of several units at these respective levels is consistent. Type is the all-inclusive word for the unit that encompasses all forms or kinds of plants and animals or of vegetation at a given taxonomic level (taxon) of organization.

Cover Types are Dominance Types

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Whittaker (1975, p. 128) followed the biome and formation unit with the unit he labeled as dominance-type:

"Classification by dominant species is a natural and widely used approach. Community-types defined by their dominant species can be termed dominance-types, but often they are called simply 'types'".

Whittaker noted that plant communities are usually dominated by more than one species "and subjective decisions on what combinations of major species ought to be recognized as dominance types are necessary to make the classification work". The subjectivity (and considerable experience and familiarity with the vegetation involved) notwithstanding, dominance types are "quite workable … and physiognomy and dominance can be used together, with dominance-types subordinate units within formations".

In this last phrase Whittaker described the typical arrangement or organizational pattern of the major units of vegetation as commonly used by foresters and rangemen, at least in North America. Whittaker (1975, p. 128-129) pointed out that ecologists like Clements and Braun used "as units very broadly defined dominance-types, or groups of dominance-types". Their term for these broad dominance-types was, of course, the association as defined by dominant species or genera such as the oak-hickory, beech-maple, maple-basswood, and oak pine associations or, as they are synonymously known, "types". This usage was also noted by Shimwell (1971, p. 62). In other words, type is often at the association level as the largest or broadest unit or subdivision of a given formation (eg. the preceding associations within the deciduous forest formation of eastern North America). This is the exact usage or organization (community hierarchy) of Braun (1950, p. 10-11). As quoted previously, association was explained in considerable detail in Plant Ecology (Weaver and Clements, 1938, p. 478-482) after having first defined association on pages 93-94:

"Every climax formation consists of two or more major subdivisions known as associations. These are climax communities associated regionally to constitute the formation. The number of associations in a particular formation is naturally determined by the number of subclimates within the general climate of the formation. Each association is marked by one or more dominants peculiar to it…An association is similar throughout its extent in physiognomy or outward appearance, in its ecological structure, and in general floristic composition [the mixed-prairie association was one example used; likewise Stipa spartea and Sporobolus heterolepis were two dominants of the true prairie association]".

This was requoted at extended length to show the key roles of physiognomy and floristic compostion which Clements retained from the association of Warming (1909, p. 145).

In turn:

"The visible unity of the climax is due primarily to the dominants or controlling species. All of these belong to the same life form. … Each formation is named after two of its most widely spread and important dominants" (Weaver and Clements, 1938, p. 91).

A concise summary by Shimwell (1971, p. 53) explained this arrangement and the entire Clementsian hierarchial organization (complete with seral units and climax units mentioned above):

"Formations were subdivided into associations which could be characterized by their codominant species. Within the association, if a single species was the physiographic dominant then the term consociation was used, while these were further subdivided into societies each characterized by subordinate species. However, these terms were restricted to the considered climax vegetation type. All other developmental units leading up to a climax, all seral stages, were given parallel terms such as associes, consocies and socies".

From this passage it is the association that is the vegetation unit relevant to the current discussion. The Clementsian association (or consociation where there was a sole dominant) was the unit of the "climax vegetation type" which was determined by dominant or co-dominant species. This description showed that vegetation type corresponded to association which was defined or identified by its physiographic dominant(s). Ergo, the unit Whittaker (1975, p. 128) identified as dominance-type.

Whittaker (1975, p.129) was careful to specify that "the American association of Clements and Braun" was distinct from the floristic association of Josias Braun-Blanquet or the Zurich-Montpellier School of Phytosocioloy (= Releve Method). Shimwell (1971, ps. 57, 59) drew the same distinction. Use of the terms association and alliance for the lowest and second lowest units of vegetation in The Nature Conservancy USNVC System followed in similar format the hierarchy of the Braun-Blanquet Zurich-Montpellier (Shimwell, 1971, ps. 56-62).

The association in the USNVC System is the Braun-Blanquet association and not the American association which Clements adopted from Warming. It is the Warming-Clements association (often subunits thereof) that is the basis of the cover or dominance types of range and forestry practitioners.

The Nature Conservancy United States National Vegetation Classification System is primarily an application of the Zurich-Montpellier Tradition (elaborated by Shimwell, 1971, ps. 45-47, 50-53, 56-62) to the vegetation of North America (specifically the United States of America).The USNVCS is largely an adaptation of the Ellenberg and Mueller-Dombois (UNESCO) classification from which the former is modified at upper levels (Grossman et al., 1998, p. 20). It follows that the SRM and SAF cover types, which are essentially dominance-types derived primarily from the Anglo-American Tradition of Clements and Tansley (Shimwell, 1971, ps. 45-62 passim), will inherently correspond poorly to the The Nature Conservancy System. This was bound to be the case because the SAF/SRM cover types and The Nature Conservancy USNVCS alliances are units derived from vegetation classification systems of two schools or traditions of plant community ecology that have been distinct and separate for 90 to 100 years (again, Shimwell [1971]). This was shown even before The Nature Conservancy USNVC System was developed when (as discussed above) the Ecological Society of America Vegetation Classification Panel (1997) in its initial report rated, as a level or unit of vegetation, the SRM cover type dead last.

This rating was understandable given that vegetation units are from two distinct traditions. TNC and ECA rated cover type relative to their tradition and found it to be unacceptable or least acceptable. SAF and SRM with their units derived from another tradition should— for purposes of clarity and consistency— reciprocate toward the USNVC System and rate the USNVCS association and alliance at the bottom of their lists.

In a review of its initial report (ie. its second report) on an initiative for a classification of United States vegetation the Ecological Society of America Vegetation Classification Panel (1999, p. 11-12) concluded that the SAF and SRM cover types and dominance types were close approximations of each other: dominance types "are very similar in concept to 'cover types' for simple, efficient inventory and mapping purposes". Community-layer dominance types "are simply a convenient, descriptive subdivision of Cover Types or Domanance Types based on the dominant species in a lower, conspicuous layer of vegetation". In this second report the ESA Vegetation Classification Panel did not relate or equate cover or dominance types to any units of vegetation in The Nature Conservancy USNVC System. The Vegetation Classification Panel did discuss briefly the unit of plant association, but only from the standpoint of "[t]he two major association classification approaches in North America that are based predominantly on composition of the entire plant community" which are the 1) Braun-Blanquet and 2) Daubenmire systems. Specification of "entire plant community" automatically eliminated any of the systems based on dominance (distinction based on dominant species) such as that of Weaver and Clements (1929, 1938). Yet these dominance-based systems are the systems or classifications which have dominated vegetation schemes and hierarchies used almost exclusively in Range Management and Forestry in North America. In the USNVC System both cover and dominance types were disregarded or ignored as was plant association as defined and designated by the Anglo-American Tradition (ie.the association as developed over the Grisebach-Warming-Moss-Nichols-Tansley-Clements-Weaver-Phillips lineage).

In other words, The Nature Conservancy USNVC System made no use of any of the units of forest and range vegetation traditionally used by American workers except that of the habitat type as defined by Daubenmire which includes all layers of vegetation and not just the layer of dominants. Furthermore, given that "the USNVC is of existing, not potential, vegetation" (Ecological Society of America Vegetation Classification Panel, 1999, ps. 8, 14) even the Daubenmire association and habitat type was irrelevant for the USNVC System because the Daubenmire association is a "type of climax phytocoenosis" and "based on samples restricted to 'near-climax' vegetation" [ie. potential natural vegetation] (Ecological Society of America Vegetation Classification Panel, 1999, p. 12). Thus, the USNVC System is a modification of and based on the Braun-Blanquet releve phytosociological system (the Zuric-Montpellier Tradition or School of Phytosociology) of continental Europe and in final effect totally ignored the entire heritage of American research on classification and description of range and forest vegetation. As asserted by the Ecological Society of America Vegetation Classification Panel (1999, p. 13), a partial exception to the preceding fact were studies of vegetation "sampled with releves from late successional stands …". Yet, examination of the investigations cited by the panel revealed that this sampling too was related back to "potential climax vegetation". The USNVC System also differs from such vegetation maps as those by Kuchler which are of potential natural vegetation and not existing vegetation.

Beyond doubt or debate, the United States National Vegetation Classification System is a system separate from such units as range cover types and the Anglo-American unit of plant association on which range and forest cover types are based. "Classification of existing vegetation and classification of potential natural vegetation are complimentary and of equal importance in synecology" (Ecological Society of America Vegetation Classification Panel, 1999, p. 14). So said and homage given to classification systems for climax vegetation, the obvious fact is that they are two separate though complimentary systems.

As recorded above, both the SAF and SRM cover types are of "existing vegetation", but also as noted previously most of the rangeland cover types described are, upon close reading, closer to climax or potential natural vegetation than to seral communities (any disclaimer-like statements made by Shiflet [1994, p. xii] notwithstanding). By way of example, compare how many rangeland cover type names begin with and list as dominants "Bluebunch Wheatgrass" or "Idaho Fescue" versus how many begin with or list as the dominant species "Cheatgrass". Point made. Likewise, certain SAF forest cover types are climax types and correspond closely to potential natural vegetation such as that mapped by Kuchler (Eyre, 1980, p. 3). Undoubtedly some of the USNVC units will be of climax vegetation, but this new classification scheme offers little to Range Management professionals that is not in existing range literature.

Conclusion: the unit(s) or level(s) of vegetation traditionally used in North America that most closely correspond to cover (= dominance= vegetation= grazing= range) type as applied in Forestry and Range Management is the association or, its seral counterpart, the associes. Cover type and association remain the basic descriptive units of vegetation intermediate between biome or formation and range site. These hierarchial levels are still in use and of great value because much of the most important and detailed reports of range and forest vegetation used these units and these studies remain cornerstones of Range and Forest Ecology.

Origin of the term 'Type'

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The actual connection of the forest and range types to the Clementsian association (or the seral unit associes in cases where the forest or range vegetation is seral not climax) is obscure and seems not to have been documented other than indirectly. Neither Eyre (1980) nor Shiflet (1994) included even a brief review of the type concept.

Toumey and Korstian (1947, ps. 356-397) and Baker (1950, ps. 22-47) reviewed units and systems of forest vegetation at a time when such approaches were as utilitarian as they were academic and when the history of their development was fresh in the "collective mind" of Forestry. These silviculturalists discussed such forests or forest vegetation units as the various kinds of formations (eg. climatic vs. physiognomic), forest regions or forest vegetational areas, associations, and forest types. There were different kinds of all units and hierarchial levels depending on purpose and author or mapper even at this relatively early stage or mid-age of American Forestry literature. (The American Society of Range Management was just "germinating".) Both Toumey and Korstian (1947) and Baker (1950) distinguished forest cover type from the other kinds of forest types: 1) management, 2) permanent, 3) temporary, 4) physical, and 5) indicator. It is interesting from a historical perspective that then, as now, forest cover type was of the present vegetation (could be seral or climax) and had the current meaning (Toumey and Korstian, 1947, ps. 382-383; Baker, 1950, ps. 34-35; Munns, 1950, p. 88). At this time the Society of American Foresters (Baker, 1945) and Eyre (1954) published its revised descriptions of forest cover types in North America, a project begun in 1929 (Eyre, 1980, p. v).

According to Clements (1920, p. 337) and Toumey and Korstian (1947, p. 379 in a portion that is essentially the review from Clements [1920]) the term forest type was used first by Graves (1899) of the United States Department of Agriculture Division of Forestry to mean a dominance (= cover) type of natural forest vegetation. Baker (1950, ps. 31-33) determined that the Society of American Foresters decided upon this concept for forest cover types at a special symposium (Dana et al., 1913) in the beginning days of their profession.

Even though the current concept and usage of forest cover type was established at the onset of Forestry and Forest Science in North America and while this coincided with the dawn of Ecology and the emergence of Clementsian Ecology (compare 1913 to the publication of Clements' Plant Succession and Plant Indicators in 1916 and 1920), cover type was not an ecological unit or an equivalent to any ecological unit. Toumey and Korstian (1947, ps. 383-384) wrote:

"Cover type, as at present recognized and based on floristics and economics, has no equivalent in ecology. It takes no account of site factors, consequently temporary and permanent forest communities with unlike site factors may fall into the same cover types so long as the dominant species are the same".

Also recall that cover types are based on present vegetation and not necessarily on climax or potential natural vegetation. In contrast, permanent forest type is the equivalent of climax forest vegetation so its synonym is climax type (Toumey and Korstian, 1947, ps. 380-384; Baker, 1950, ps. 44-46). Forest cover type can include both permanent and temporary forest types. Examples of the latter include subclimax forest types or ecologically transitional forest types like those of Pinus strobus of the Great Lakes forest region and Pseudotsuga menziesii of the Pacific Northwest Coastal forests. Thus even where species like eastern white pine and Douglas fir are clearly seral to the climax forest vegetation they are regarded as forest cover types because they are so valuable economically even though they are, when classified as to ecological forest type, temporary forest types and not permanent (= climax) forest types.

Apparently it was through the correspondence or equivalence of permanent (= climax) forest types to the Clementsian associations (and temporary [= subclimax] forest types to the Clementsian associes) that eventually led to the close approximation for forest cover types to a generic, nonspecific, "more-or-less" Clementsian association with both terms used in less restrictive, less precise meanings than originally intended (Toumey and Korstian, 1947, ps. 382-384; Baker, 1950, ps. 44-46). Both of these Silviculture textbooks noted that the term association had different meanings to different ecologists or foresters (Toumey and Korstian, 1947, p. 377; Baker, 1950, p. 44). "Forest types as conceived by one writer are not the same as those of another" (Toumey and Korstian, 1947, p. 379).

Toumey and Korstian (1947, p. 382) noted that there appeared "wide divergence in opinion as to what constitutes a forest type", but they interpreted Clements (1920) in Plant Indicators as having concluded "that the classification of forest into associations by ecologists and into forest types by foresters differs more in emphasis than in fact" (Toumey and Korstian, 1947, p. 382). Technically Clements did not relate or equate associations to forest types. The section of Plant Indicators referred to and interpreted by Toumey and Korstian (1947) was entitled "Forest Types" (ps. 337-345) and when Clements (p. 342) wrote "…they differ more in emphasis than in fact" he referred to the first part of that same sentence which was "…of the opinions just summarized". These were opinions of numerous foresters all discussing various versions of forest types including cover, management, permanent, temporary, physical types. There was no reference whatsoever to associations. However, a sizable portion of Plant Indicators (ps. 105-235) was devoted to description of actual (not abstract) vegetation and this was organized on the basis of formations and associations. Most importantly, both Toumey and Korstian (1947) and Baker (1950) concluded that the plant association as defined or interpreted in the Clementsian concept (including being the main subdivision of the formation) was the rough equivalent and theoretical basis of forest cover types. This seems to have been a widespread perception during the formative years of the Clementsian concept of association and the invention and adoption of vegetation cover type. This is indicated by the fact that forest cover type corresponded to plant association in the common textbooks of the day.

A better "indicator" that vegetation types as used in America corresponded to Clementsian units of vegetation is to be found in the "Grazing Types" subsection of the "Grazing Indicators" section of Plant Indicators (Clements, 1920, ps. 270-283). Clements grew up on the central continental grasslands when virgin sod was still widespread and he was educated at the great prairie land-grant University of Nebraska which became the nucleus of the "founding school of American plant ecology" (Tobey, 1981). As such Clements was much more a rangeman than a forester. Predictably he dealt with grasslands in more detail than forests. (This was also the case in Bio-Ecology co-authored with Shelford from the adjoining prairie state and land grant University of Illinois.) In Plant Indicators Clements did relate grazing types to formations and associations in the portion that preceded forest types. It is logical that foresters like Baker, Korstian, and Toumey drew conclusions from the preceding and more detailed section and applied it to forest types. Thus while Clements did not relate forest types to associations and formations, foresters could have made this rational adjustment as a logical and consistent extension of Clements' more comprehensive treatment of grazing types.

It is obvious from the "Grazing Types" portion of Plant Indicators that Clements' grazing types were of different scales and that his grazing types corresponded to both formations and associations (Clements, 1920, ps. 273-275) as well as at the smaller scale (s) of "local grazing types" or "practical grazing types". This was written so as to leave no doubt:

"Local grazing types.--While the main grazing types, such as the formation and association, indicate the comparative value of great regions, as well as the groupings possible in any one, it is the local groupings which determine the carrying capacity of a particular ranch and the proper system of management to be employed upon it. For this reason, they may well be termed practical grazing types. In areas relatively uniform, a single grazing type composed of the two or three major dominants of the association may cover a wide extent."

Clements ended this portion discussing the faciation and the facies, the subunits of the association and the associes or consociation and consocies, respectively. It is clear that Clements used grazing types as he did vegetation types in a generic, multi-level/multi-unit sense. The careful reader can also detect in the local grazing types the forerunner or germ of the smallest unit or kind of range, the range site. Clements was always ahead of his time and his influence can be found in almost all major concepts dealing with units and analysis of range and forest vegetation.

Historical Note: "Founding Fathers" of Range Management

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[NOTE: Arthur W. Sampson is traditionally and deservedly regarded as the "Father of Range Management" based on 1) his early range research, including studies of vegetation and plant succession, (his investigations actually involved experiments that used grazing trials, reseeding, etc.), 2) his teaching of university courses in Range Management and Plant Ecology, and 3) authorship of what is usually thought of as the first actual textbook in the subject, Range and Pasture Management (1923, John Wiley & Sons). In 1919 James Jardine and Mark Anderson of the U.S. Forest Service wrote USDA Bulletin 790, Range Management on the National Forests, a 98-page professional paper that became known as the "bible" of Range Management (Wasser, 1977) and that is often regarded as the first full-fledged "book" on the subject. This "range bible" came 20 years after Jared Smith (1899) authored the 47 page, pamphlet-size USDA Bulletin 16, Grazing Problems in the Southwest and How To Meet Them. Bulletin 16 was arguably the first Range Management manual though it was more of a report, with recommendations on range deterioration in Texas and New Mexico.The previous year two publications (again, more in the nature of reports) on the problems of range depletion in Texas had been authored by Bentley (1898a, 1898b). It was in 1899 that H.C. Cowles published his pioneering— no pun intended— study of plant succession on lake sand dunes from which Clements (1916a) took his model of vegetation development published in Plant Succession. It could be argued that neither Sampson (1923) nor Jardine and Anderson (1919) wrote the first textbook, but that it was Will C. Barnes (Inspector of Grazing, U.S. Forest Service) who wrote the first textbook and range "bible" in his Western Grazing Grounds and Forest Ranges published by The Breeder's Gazette in 1913. Wasser (1977) stated that Barnes (1913) was "the earliest semitechnical book about Range Management". Western Grazing Grounds placed a decidedly heavy emphasis on range livestock management and production (including poisonous plants, livestock diseases, and livestock predators) and laid relatively less importance on the range itself. Yet, it began with range plants (including photographs and line drawings) and was a text and reference for range magnagers and operators. Sampson's Range and Pasture Management followed closely the format used by Barnes including devoting three out of 29 chapters to poisonous plants. In Livestock Husbandry on Range and Pasture, Sampson (1928, also John Wiley & Sons) followed more closely Barnes' format including chapters on livestock diseases and depradation. Barnes (1926) followed Grazing Grounds with The Story of the Range, a 59 page (but small print) USDA publication, that dealt more with range use in a historical context and featured public range policy, including the "keen but friendly rivalry" between the US Departments of Agriculture and Interior.

All these titles indicated that they dealt with range, grazing, pasture, or livestock and that they were practical and industry oriented in their contents. Of these early range authors only Sampson took management of range beyond practice, craft, husbandry, policy, history, etc. to put the nascent profession of Range Management on a scientific basis. "Sammy" had a Ph.D., was a range researcher, and became a university professor early in his career. He was the scientist, an ecologist, and contributed concepts and theories as well as practices to the emerging discipline of Range Science (ie. as a rangeman, Sampson was range scientist as well as range manager).

In this period when Range Management was emerging as a profession built on the infant discipline of Range Science, Frederic Clements was most active as an author. Like Sampson, Clements was an ecologist and a researcher (an "escaped professor" as he dubbed himself). Clements and Sampson had nearly identical, as it were, backgrounds and academic "pedigrees". Both men were born in Nebraska (Clements 10 years earlier) and both were products of the Botany program directed by Dr. Charles E. Bessey at the University of Nebraska. Clements received his Ph. D. from Nebraska in 1898; Sampson earned his MS from Nebraska in 1907 and his Ph. D. from Johns Hopkins and George Washington University in 1917 (Tobey, 1981, ps. 238-239; Casamajor, 1965, p.115).

As an author of ecological monographs and scientific papers for prestigious journals Clements' titles did not readily emulate the land grant ideal of "practical education" (from the Morrill Act) or an industry orientation. Such appearance was misleading. For all of Clements' elaborate, sweeping concepts and classification of vegetation, he always sought to apply theory to on-the-ground practice. "It is believed that succession and indicators constitute the most essential and useful form into which the results of research can be put for practical use" (Clements, 1920, p. iii). Clements (1920) wrote Plant Indicators- The Relation of Plant Communities to Process and Practice, his second monumental monograph as "a companion volume to 'Plant Succession'", aimed at application of the science of Plant Ecology to the arts of farming, lumbering, and range-based ranching. The "indicator concept" was application of the ecological viewpoint that species of plants (and formations, associations, consociations, primary seres, and secondary seres) indicated certain conditions of climate, soil, etc. as well as human modifications such that there were "agricultural indicators", "forest indicators", and "grazing indicators". In Plant Indicators, for example, is to be found the genesis of the Dyksterhuis (1949) categories of decreasers, increasers, and invaders in the concept of seral types as grazing indicators:

"In the grassland climax, where the effects of overgrazing have been most studied, it is possible to recognize three or four stages. The first is marked by the decrease or disappearance of Stipa or Agropyron, or of both of them, and the corresponding increase of the short-grasses wherever these are associated; the second stage is characterized by the greater vigor and abundance of the normal societies, as well as by the increased importance of some; the third stage begins with the replacement of the grasses by annuals, while the fourth is marked by the spread of annuals and of introduced weeds generally over the area…These four stages indicate so many primary degrees of overgrazing, while minor degrees are denoted by the dropping out of particular dominants or subdominants…Palatability is the chief factor in determining the sucessive disappearance of species, and hence the indicators of the corresponding degrees of overgrazing, though the sequence is often disturbed by the vigor of certain dominants. Since there are few species that are wholly unpalatable or inedible, it becomes possible to construct for a particular community a complete sequence of indicators, reflecting each appreciable degree in the process of overgrazing" (p. 298). [Note here even the importance of "vigor" as a factor in considering the ecological status of plant communities.]

Clements (1920, ps. 298-308) then followed this with discussions of changes in range plant communities with overgrazing and lists of species indicating degrees of overgrazing (departure from climax). He discussed subshrubs, cacti, shrubs, and annuals as indicators (eg. "Annuals are typically indicators of serious disturbance, and hence serve to mark the existence of serious overgrazing when abundant. They are the universal pioneers of secondary succession." [Clements, 1920, p. 301]).

Section VI. (Grazing Indicators) of Plant Indicators (ps. 270-335) was a mini-textbook in Range Management. It included subsections on "proper stocking", "range improvement", "eradication of brush", "water development" "rotation grazing", "herd management", and even a line diagram showing arrangement of corrals and sheds. This section is as much a manual or "bible" on Range Management as was Jardine and Anderson (1919) or Barnes (1913), but it was within a massive scientific volume of Plant Ecology or what could most precisely be termed Vegetation Science.

Like Sampson, Clements combined science with practice to form the framework of practical science-based professional Range Management. With this combination, these two proto-type range scientists stood out as unique among their contemporary authors and range brethren. They were the founders of Range Management as an applied science as well as an agricultural art. This was largely through teaching and textbook writing in the case of Sampson and publication of strictly structured vegetation theories by Clements. In latter years Sampson published some work in demanding journals like Plant Physiology, but he primarily produced publications for the California Agricultural Experiment Station and Extension Service (Casamajor, 1965, 115-116). Textbooks by Sampson bespoke their applied orientation and were written for undergraduate students and the better educated stockmen, lumbermen, forest rangers, etc. of the day. Clements' tomes had high-sounding formal titles and appeared as if written for other scientists and specialists (they could be read by Sammy's crowd but less easily). Even the personal lives and personalities of these two prominent ecologists were different. Sampson had a great sense of humor, loved sports, and generally enjoyed being around people (Casamajor, 1965; Parker et al., 1967). According to Clements' close friend, Arthur Tansley (1947), Clements was kind and considerate but apparently all-business so to speak. "He was decidedly puritan, even ascetic" and while able to laugh at himself "his manner was apt to be tinged with a certain arrogance".

It was to be expected that of the two men most responsible for scientific development of Range Managaement, Sampson would be the one most associated in the public mind with creation of this new agricultural field and the increasing appreciation of range as an important renewable natural resource.

The appearance of almost all of the major seminal works on Range Management within such a brief period is of historical importance. Although Forestry had a somewhat earlier beginning than Range Managaement in North America and the latter grew out of the former, Range Management was always a "red-haired stepchild" to the "board foot timber beasts". Even though grazing feees on National Forests were a sizable portion of revenue generated from the Forests, "grazing" was not accorded much respect or consideration. By way of evidence, even the immortal Gifford Pinchot (1903) in his famous two part A Primer of Forestry, Bulletin 24, devoted but seven pages out of a total of 177 to "grazing", "trampling" and "browsing" with the discussion on ways "in which grazing animals injure the forest". (This outlook by foresters has not changed much in the ensuing 97 years.) Thus, the chronology of Jardine and Anderson (1919), Clements (1920), and Sampson (1923), the first three major works dealing with actual management of range, was of paramount importance.

While the range livestock industry and some management of ranges— to the extent of moving animals— traces to antiquity (Genesis 13: 1-12 recorded a range war everted between Abraham and Lot), the beginning of management of native grazing land as something besides an activity traces to a relatively small cadre of men. The historical review by Wasser (1977) is probably the best discussion of the development of Range Management as a profession ("technical Range Management" was Wasser's usage). C.C. Georgeson, H.L. Bentley, and Jared G. Smith (all associated with the Texas range problem) and Will Barnes (and probably a few non-publishing contemporaries) with the "core"of Jardine, Anderson, Clements, and Sampson constitute the "founding fathers of Range Management". Although all these men brought the best existing knowledge to an embryonic profession (eg. Georgeson was a professor) Sampson and Clements provided the most obvious leadership in the application of science (scientific theory and experimentation) to husbandry of natural pasture.

Sampson was propelled to prominence as "Father of Range Management" as a result of the combination of: 1) his set of three textbooks published by 1928, 2) some of the earliest experimental range research reported beginning in 1913, 3) continuous teaching of Range Management courses in a prominent university school of Forestry, and 4) sustained research output on both practical and theoretical subjects. This is well-known. What is not as well-known (at least not "well-remembered"), and what has been overlooked by many workers, is that Frederic Clements would logically be "first runner-up" for the distinction rightly held by Sampson.

The combination of easily read textbooks and university teaching along with experimental research put Sampson, to use a cliché, "in a league by himself". The "founding father" most similar to Sampson was Clements. In fact, it was Clements as Sampson's senior and the main member of the "founding school" at Nebraska who served as Sampson's teacher in most matters ecological. This is obvious in Range and Pasture Management (Sampson, 1923) which followed closely in content and organization a combination of Western Grazing Grounds (Barnes, 1913) and Section VI. of Plant Indicators (Clements, 1920). For example, Sampson (1923, ps.107-119, 127-130) followed Clements' indicator plants method and used as an illustration the four stages in depletion of Agropyron-Stipa climax grassland quoted above from Indicators (p. 298). Sampson (1923, p. 128-130) gave examples of species in these stages and at beginning of this part (p. 108) Sampson cited Plant Indicators (ps. 270-335: the entire Section VI). As remarked in the Introduction of this review, Sampson also included agronomic pastures in his 1923 text and portions pertaining to tame pasture did not trace to Clements. Sampson retained his reliance on Clementsian Ecology in his last textbook (Sampson, 1952) in which he drew heavily from Plant Ecology (Weaver and Clements, 1938). It was commonly known among his faculty colleagues that Sampson admired the work of Weaver and Clements (Casamajor, 1965, p. 116).

It is revealing that upon Sampson's retirement, H.F. Heady (Ph.D, Nebraska and one of the most active range scientists in creation of the American Society of Range Management) was recuited and hired away from Texas Agricultural & Mechanical College. Heady remained a master of Clementsian theory and its application to Range Management, including grazing methods. Readers desiring an outstanding explanation of the basic Clementsian model, with appropriate inclusion of polyclimax and climax pattern views, can find none better than "Structure and Function of climax" (Heady, 1973). Application of the Clementsian model to Range Management and in context of contemporary issues (eg. climatic change) was also discussed in Heady and Child (1994, ps. 123-145).

In Plant Indicators (Grazing Indicators) Clements did not limit his consideration of Range Management strictly to ecological aspects. He not only had sections on livestock management but also included some tables of nutrient content (proximate analysis) of forage species (Clements, 1920, ps. 286-292). Clements realized the key function of range vegetation in providing feed for livestock and wildlife. Sampson was also aware of the central role that the field of Animal Nutrition had in the grazing industries and the emerging fields of grazing land management. This was shown in Sampson's second textbook, Native American Forage Plants, which was "intended to be a companion volume to 'Range and Pasture Management'" (Sampson, 1924, p. vii) and in which Chapter I was "Pasture Forage and Animal Nutrition". In Clements' abridged range textbook inside of Plant Indicators and in Sampson's second textbook that was devoted to range forage and browse plants is evidence that both of these "founding fathers" anticipated the hybrid specialty of Range Animal Nutrition. Range Nutrition was an important part of range research in a "golden age" of grazing trials and animal diet studies before it shrunk in emphasis (C. Wayne Cook, personal communication) in the succeeding vulgar age of a "numbers game" of competititve grants, lowest publishable units, and an infatuation with research design for scientists over practical results and applications for stock raisers.

The direct contributions of Clements to Range Management and, secondly, to Forestry seem to have been lost from the collective mind and currently underestimated. These contributions were most likely overshadowed by Clements' theories of plant succession, monoclimax, biome, and vegetation classification with its proliferation of terms. Apparently Clements is remembered as a theorist of vegetation and author of "big books on Plant Ecology" while his direct and equally lasting contributions to actual vegetation management were largely forgotten.

In the Organicism section of this paper the author challenged a conclusion reached by Tobey (1981) that Clementsian Ecology as a paradigm and the "founding school of American Plant Ecology" "failed". The present writer concluded that the Tobey (1981, p. 8) claim of "breakup of the Clementsian microparagadigm" was incorrect because Tobey failed to appreciate the central role that Clements had in helping found the field of Range Management. Tobey (1981) failed to see that when the Clementsian paradigm moved from Grassland Ecology to Range Management it was not a paradigm shift but an expansion of applied Plant Ecology from primarily grassland to all range biomes and that it lead to Range Ecology with greater emphasis on grazing which led to the profession of Range Management. Also, but less importantly, the Clementsian paradigm moved into Forestry as for example in the monographic work by Braun (1950) on the eastern deciduous forests.

As discussed shortly, the appearance of Clements' monographs, a vegetation classifiction system by Nichols, and development of the forest cover type concept coincided with appearance of books, agency manuals, reports, etc. in Range Management. This was clearly a phase in the developmental era of natural resource professions. Plant Indicators with its enclosed Range Management "textbook" was a major work in the development of Range Management and the recognition of range as a major natural resource the same as forests, soils, and wildlife. Plant Indicators was also influencial in settling on the vegetation unit of forest cover type as detailed above.]

Role of Habitat

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In the Range Site and Biome sections the point was made explicit that range site, the most distinctive kind of range (the smallest taxon of natural pasture) is a unit of habitat and not of vegetation per se. Each range site is characterized by a unique plant community (a "one-of-a-kind" vegetation) but this is due to or reflective of its causal habitat which is typically defined more in terms of abiotic (edaphic, microclimatic, etc.) than of biotic environmental factors. This does not deny the obvious fact that organisms modify their physical-chemical environment (the classic soil formation formula immediately comes to mind). Pioneer ecologists were aware of the phenomena of organism-induced modifications to their habitat. This was the basis of the Cowles-Clements "dynamic vegetation". Each stage of the plant community that developed along a sere "improved" (modified to a more moderate, mesic, mature, etc. degree) the seral habitat for the next seral stage of vegetation until the habitat reached a dynamic equilibrium with the habitat-forming factors which marked terminus of the sere, the climax. This was Clements "vegetation development" and his term for that particular process of plant succession that denoted "the collective effect of organisms upon the habitat" was reaction (Weaver and Clements, 1938, ps. 4-5, 234-238).

While early ecologists recognized the role of habitat in development of plant and animal communities and the reaction of organisms in modifying habitat there was much debate in the seminal literature over what emphasis should be placed on habitat in naming, classifying, and mapping native vegetation. Eventually habitat came to have more importance, at least prominence, at some levels or units of vegetation than at others. Again, range site is basically a habitat unit delineated first by abiotic factors (eg. soil, aspect, microclimate) and distinguished secondly by unique vegetation. The larger community units such as biome-type or formation-type, biome or formation, association, and—misleading name notwithstanding— the Daubenmire habitat type are all defined, named, mapped, etc. exclusively by the plant or plant and animal community. Adoption of the ecosystem concept, foundation of the Tansley paradigm, established the role of habitat for certain things in Ecology (eg. community function) but not for others.What, if any, role habitat should play in vegetation classification remains one of the most enduring questions and persistent problems in Vegetation Science.

In discussing the relation of forest types to ecological units of forest vegetation Toumey and Korstian (1947, ps. 383-384) noted that within a region, the scale or area of a climatic forest formation (Toumey and Korstian, 1947, p. 374, 383-384), parallel series of associations formed due to existence of parallel series of habitats. These series that form habitats (which are equivalent to one another) constitute a common habitat type. "Associations that are correlated with habitats which form a habitat type" can be grouped into association types so that "it is possible to group the many associations in a given plant formation into a comparatively small number of association types" (Toumey and Korstian, 1947, ps. 383-384). These authors drew this synopsis from a paper by Nichols (1917) dealing with ecological classification of plant communities.

Observe again the close timing of the SAF cover type symposium, Clement's epic ecological monographs, and, now, the Nichols' vegetation classification paper. Nichols (1917) organized plant associations inside of association-types where the latter were roughly the subdivisions of plant formations. This suggested that association-types were the equivalent units, or at least equivalent scale, of Clementsian associations. The relevant point is: in an early vegetation classification system, units of vegetation at the level or scale of association came to be equated to vegetation types.

Here is the perspective, the concept, that formations (later biomes) are subdivided into forest vegetation types (ie. forest types as ecological units are the foresters' equivalent of associations and these forest types are the major subdivisions or the most general units within forest formations). It was explained earlier that Toumey and Korstian (1947, p. 384) specified that forest cover type (and physical forest type) had "no equivalent in ecology". Therefore the equating of of a permanent (= climax) forest type to forest association would not automatically equate forest cover type to association. It was also explained, however, that Clements (1920, p. 342) found these different kinds of forest types to "differ more in emphasis than in fact". As such, the general equating of plant association to forest cover type was a rational conclusion. Given that there was no such distinction of different range types, but that range cover type "embodies both" "cover type" and "vegetation type" (Shiflet, 1994, p. xi) the net outcome was: Anglo-American plant association= forest and rangeland cover types; range cover type corresponds, at least approximately, to plant association.

Relative sizes of plant associations also was an important feature. Clements had previously equated grazing types as units of management to units of vegetation at scales going down through the three largest or highest levels of his vegetation hierarchy (the formation to association to faciation, or the equivalent seral units). Size— scale (size of one unit of vegetation or level of hierarchy in comparison to another)— was (is) a point of confusion.

An interesting (and persistent) conceptual relationship among vegetation units is that of habitat-type corresponding to a commensurate group of associations identified as association-type (or, perhaps, association). This connection can be traced back at least as far as Nichols (1917, ps. 309, 310) to whom habitat-type was even "capable of algebraic expression" (Nichols, 1917, p. 317-318). To Nichols habitat-type was the habitat, the environment and not the vegetation, but his habitat-type and association-types usually corresponded to each other at the same level of organization and classification. Nichols' association-type apparently corresponded to the formation of other ecologists (Nichols, 1923, p. 157). Therefore, habitat-type was obviously much closer in spatial scale to the association as defined by Clements and Tansley than to smaller units.

This use of the term habitat-type and at the level of associations or groups of associations took place decades before synecologists like Daubenmire reintroduced the term and repeated the equivalency (at least rough correspondance) to the scale of association while later redirecting the emphasis of habitat type away from environment and making it a unit of vegetation or, most precisely, as the potential area covered by an association. All this was done without referring to or citing the work of Nichols. The term habitat type was not given in SAF Forest Terminology, the then-current glossary of terms, (Munns, 1950). Nor could it be found in Baker (1950). Nichols (1917, 1923) did not develop fully the habitat-type concept (and he certainly did not use it as a unit of vegetation in his system of plant community classification), but he did use the term and the concept at scale of association, or association-type. Again, this was years before Daubenmire (1952) first used it as a unit of land corresponding to climax association and later (Daubenmire, 1968) as a vegetation unit in his classification system. Still later, the U.S. Forest Service adopted the Daubenmire version of habitat type and expanded it to include actual habitat criteria (ie. returned the unit closer to that of Nichols [1917]). (The contributions— largely forgotten— of Nichols were the subject of the next section.)

In the context of rangeland and forest cover types it is stressed again that the habitat type of Daubenmire vegetation classification was at the scale of association, the climax association and seral stages having potential to reach that climax. In the original application of his vegetation classification Daubenmire (1952) made little use of habitat type instead using association as "the basic unit". Daubenmire's system was covered above in the Range Site section where it was shown that habitat type and association were the same size- or scale-wise (being of the same land area). The pertinent point for the cover type unit is what the Daubenmire plant association was (eg. what its size was) relative to the association(s) of Clements, Tansley, Nichols, etc.

As with most vegetation units of the various systems this was not— probably could not—be determined with precision (or accuracy). The area described by Daubenmire (1952) in developing his system of vegetation classification (which metamorphosed into the habitat type designation/description method) had been described as seral to the "Thuja-Tsuga association" in a previous vegetation study by John Weaver. (Like his colleague Clements, Weaver seemed always to have "already been there".) In Weaver and Clements (1938, ps. 481, 503-504) this unit of coniferous forest in northern Idaho and adjacent parts of neighboring states and Canada seemed most likely to have been in the region of the "larch-pine forest: Lariax-Pinus association of the Thuja-Tsuga Formation". Daubenmire divided this unit into: 1) Pinus ponderosa zone, 2) Pseudotsuga taxifolia var. glauca zone, 3) Thuja plicata-Tsuga heterophylla zone, and 4) Picea engelmanni-Abies lasiocarpa zone. Each of these was divided into four associations except for 2) which had two associations.

Obviously the Daubenmire associations were smaller than the traditional association as interpreted by the Grisebach-Warming-Clements lineage (the English Tradition). It seemed reasonable to characterize the Daubenmire association as a subdivision of the Clementsian association. This is consistent with Daubenmire's adoption of the Tansley polyclimax instead of the Clements monoclimax view and his recognition of edaphic and topographic as well as climatic climaxes within the region. "Most of the associations considered in the present study play different climax roles in different parts of their areas, eg., climatic climax in one place, and topographic climax in another" (Daubenmire, 1952, p. 303). This perspective and inclusion of the understory species in association designations was responsible for the smaller size of these Daubenmire associations.

In his association designations Daubenmire used scientific names of the one, sometimes two, dominant species of the upperstory and the dominant species of the understory (eg."Pinus ponderosa/Agropyron spicatum association"). This association nomenclature followed the format of Clements (Weaver and Clements, 1938; Mueller-Dombois and Ellenberg, 1974, ps. 173, 175) except that Daubenmire included understory dominants.

Daubenmire's four zones corresponded closely to the Clementsian consociation as described/defined above.

Likewise, associations of Daubenmire (1952, ps. 306-319) were smaller, more specific units than traditional forest cover types in having associations differentiated within zones primarily on basis of dominant understory species. Comparison of Daubenmire zones to current SAF cover types revealed a reasonable degree of correspondence. Daubenmire (1952, ps. 324-327 passim) discussed the fact that forest cover types typically were based largely— usually exclusively— on tree species that dominated the canopy. In the United States such cover types "show only the kinds of commercially valuable species now dominating the land" (p. 324). As these existing canopy dominants may not be climax or the potential native vegetation, cover types mix seral with terminal vegetation. This approach may omit the "benchmark" of the potential (= climax) forest vegetation and create confusion when trying to base forest management on objective criteria. Forest cover types are a form of mapped inventory and when the current forest vegetation is eliminated by disturbances cover types "have only historic value" (p. 324). Daubenmire combined the dominant understory (the "subordinate union", described in the Range Site section) with the canopy dominant (the "dominant union") to represent the climax or potential forest vegetation throughout the major layers of the forest. This served as a realistic guide to scientific management. Inclusion of the understory was used to eliminate some of the problems associated with forest cover types.

Daubenmire (1952, p. 325) explained the practical basis for his combination climax association. For instance with regard to Range and Wildlife Management he concluded:

"In classifying the land as to its forage productivity attention must be directed at least as much to the subordinate unions of the forest associations as to the trees" (Daubenmire, 1952, p. 325).

In summary, the climax plant association that somehow finally became the habitat type of Daubenmire, and then the Forest Service, was a subdivision of the traditional association and, as such, was a smaller, less heterogenous unit. This resulted from dividing traditional associations into more communities based on understory dominants. Daubenmire associations were also smaller than forest cover types because the latter are based only on dominant canopy trees. Overall, the associations of Daubenmire were consistent in size with cover types when allowance was made for division of these types into subtypes as distinguished by the greater number of understory dominants (ie. area or size of community designated only by upperstory dominants is greater or more zonal than size of communities that are designated, differentiated, within the zonal vegetation by inclusion of both understory dominants and the climax canopy species). Also adoption of the polyclimax perspective and inclusion of topoedaphic climaxes as well as climatic climaxes increased the number of and decreased the size of Daubenmire's climax associations in comparison to the Clementsian associations. As such, the Daubenmire habitat type corresponded more closely with size of the Tansley association than with the association of Clements and Weaver.

Even given discrepancy between size of British and American associations, the size relative to size of formations and the association as a community concept remained consistent and compatable within the English Tradition. The most obvious difference between the original Daubenmire (1952) association (later to become habitat type) and the vegetation cover types as they came to be applied by the Anglo-American Tradition was that associations were climax vegetation while cover types could be either seral or climax communities.

Daubenmire (1968, ps. 259-263) described briefly his Landscape Hierarchy. This is an ecosystem classification that, as was pointed out above, is actually a vegetation hierarchy being based solely on vegetation. It has four levels which lowest to highest are: 1) habitat type, 2) vegetation zone, 3) vegetation province and 4) vegetation region.

Close examination of the use of habitat type by Daubenmire strongly suggest that "his" habitat type-- which it will be recalled was the association (Daubenmire, 1968, p. 32)-- was in spatial scale smaller yet roughly similar to that of the Clementsian association. Daubenmire did not state this, but he used "climax vegetation" at scale of "landscape mosaic". Daubenmire (1968, p. 29-30) stated: "The term association may be applied to any distinctive type of climax vegetation, whether large or small, simple or complex. Some workers, however, consider it desirable to recognize broadly defined associations, these being subdivided into subassociations or phases…". He also noted: "Ordinarily one habitat type is highly discontinuous, with intervening areas occupied by other habitat types differentiated by either soil or microclimate" (Daubenmire, 1968, p. 260). Comparison of this description to those of Warming and Tansley quoted above suggest that the scale of the association (= habitat type) described by Daubenmire was the same (or very similar) scale of Warming, Clements, and Tansley. Daubenmire associations actually were smaller than the traditional Clementsian association but that was not necessarily inconsistent given that Daubenmire associations could be "large or small". This difference was again reflective of the adoption of polyclimax (vs. monoclimac) perspective. Phases as subdivisions of associations determined by soil or microclimate could be interpreted as the scale of range site. In other words, associations are range cover types that are subdivided into subassociations or phases which in turn correspond to range sites.

In concluding his discussion of habitat type Daubenmire (1968, p. 261) used the instance where "pure stands of Pinus ponderosa that are climax always occur in environments that are slightly drier than those in which Psudeotsuga menziesii is a climax dominant" over a region stretching from Canada to Mexico and Wyoming to California. Throughout this interrupted, regional coniferous forest the understory layer(s) vary greatly in species composition such that Daubenmire (1968, p. 261) asked: "Should the P. ponderosa stands in British Columbia be grouped with the wetter Pseudotsuga forests there on the basis of close similarity of undergrowth, rather than with P. ponderosa stands in remote places where there are no undergrowth species in common?" Daubenmire discussed both possibilities noting that the first grouping "… would embrace a broad spectrum of variation in climate, soil, and overstory dominants" while the second approach would result in "recognition of all climax stands of P. ponderosa as a basic group…" that is determined by climate "…as a master factor…". For purposes of ascertaining the relative scale of the Daubenmire habitat type (= association), the forgoing discussion clearly implied that the association could be of a size determined by climate (ie. regional or climatic climax) or, if the first alternative, each habitat type (= association) would be of such size as to encompass a diversity of climates, soil, etc. Either way, habitat type fits the size description of the British-American association: habitat type most closely corresponds to the range cover type and not the range site. This is consistent with what appeared to be the original usage of habitat type at the spatial scale and community organization level of association-type, a supra-group of associations that were described by the original definition as the subgroups of a formation (Nichols, 1917, p. 309).

Weaver and Clements (1938, ps. 94, 481, 505) also used Pinus ponderosa and Pseudotsuga menziesii as an example of an association in Rocky Mountain forests where each species was a consociation (ie. a forest cover type or range cover type). A difference between the traditional Clementsian plant association and the Daubenmire habitat type (ie. originally the Daubenmire [1952] climax association) was that Daubenmire (1952, 1968) placed more emphasis on understory layers than did Weaver and Clements (1938) who classified more simplistically on dominant species of the upperstory. General usage by Weaver and Clements and Daubenmire is consistent: habitat type = association = forest cover type (and, in this case, also permanent [= climatic] forest type because both associations were climax vegetation).

In discussing vegetation zone which was the next highest (next most general, next largest) unit in his vegetation hierarchy, Daubenmire (1968, p. 261) wrote: "All the area over which one association is climatic climax represents a vegetation zone of essentially uniform macroclimate insofar as vegetation is concerned". This is not only Clementsian regional (= climatic = zonal = mono-) climax but it is also consistent with the climatic zone basis of Ecosystem Geography devised by Bailey (1996, 1998) whose system, as noted above, is Clements and Tansley down the line. Clements (1904, ps. 147-162) reviewed studies of vegetation zones and traced recognition of vegetation zones back to the early 1700s. Bailey (1996, ps. 47- 49) discussed systems that mapped Earth into ecological regions based on climate-vegetation zones and gave much credit for development of this concept to the Russian soil scientist V.V. Dokuchaev (1846-1903) who traditionally has been regarded as the "Father of Pedology" (Joffe, 1949, ps. ix, 2, 8-9; Fanning and Fanning, 1987, p. 3).

Daubenmire's vegetation province was based on the "historic aspect of vegetation", the geologic flora or paleobotany, with a vegetation province including those vegetation zones "which have had a somewhat common and distinctive geologic history, which form a distinctive geographic unit at present, and which exhibit strong threads of taxonomic homogeneity…" (Daubenmire, 1968, p. 262). Dominant species were the basis for "a common historic background for a group of climatic climaxes". This emphasis on climatic climaxes over geologic time scale and inclusion of prehistoric flora in evaluation of present vegetation was an original part of the Clementsian model of dynamic vegetation that encompassed plant succession and evolution over scale of geologic time (Clements, 1916a, ps. 279-422). In fact, with reference to Plant Succession (Cooper, 1926, p. 393) wrote: "The greatest contribution of all, however, is the extension of the field of study to cover all time from the present moment back to the very beginnings of vegetation upon our planet…Clements was the first to organize the field of dynamic ecology as a unified science covering the entire history of the plant population of the earth".

Vegetation province is another echo of Frederic Clements. It is part of Clements' phylogenetic system of seres as outlined in Plant Succession (Clements, 1916a, ps. 183, 344-351). Daubenmire's vegetation province appeared to correspond to Clements' clisere: "The clisere is the series of climax formations or zones which follow each other in a particular climatic region in consequence of a distinct change of climate" (Clements, 1916a, p. 347).

The broadest (largest, most general) of Daubenmire's vegetation hierarchy is the vegetation region which is parallel to Baileys ecoregion or macroecosystem, the equivalent of the biome plus its abiotic environment as remarked previously. "The vegetation region as defined above differs from the plant formation of Clements and certain others chiefly in that a geographic area is emphasized, rather than a kind of vegetation" (Daubenmire, 1968, p. 263). Clearly Daubernmire vegetation region equals Bailey ecoregion and both equal essentially Clements' biome with its physical/chemical habitat (the Tansley ecosystem at scale of Clements biome).

There appears to be some overlap of the Daubenmire units of vegetation zone and vegetation region with Bailey Ecosystem Geography units, and the vegetation province appeared to be as much a temporal unit as a spatial unit, but the closeness of units from these two systems is consistent with the Clementsian association and the SAF/SRM cover types that developed and correspond closely to the American concept of plant association and its subunit, the consociation.

The "lost" legacy of George Nichols

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To some degree this ambiguity also existed in the ecological classification system of plant communities proposed by Nichols (1923) when he used the term association-type or, the full term, ecological association-type (ps. 156-160). The association type was Nichols' umbrella term that encompassed "all associations which resemble one another in physiognomy and ecological structure, regardless of their floristic composition". To Nichols the association-type, like association itself, was an abstract concept but the former was represented by individual concrete associations. This was, however, problematical: "Where to draw the line between the association, considered in the abstract, and the association-type is a question which can no more be answered dogmatically than the question of where to draw the corresponding line between genus and species" (Nichols, 1923, p. 158). In fact it was possible to apply the term association in the abstract and the term association-type to the exact same unit of vegetation at the regional scale (eg. beech-sugar maple of the deciduous forest of eastern North America). Thus the tendency for individual concrete associations to be referred to as association- types. Overall though, abstract associations were the floristic subunits of the association-type: "… an association-type commonly embraces several to many floristically defined abstract associations".

Given that the Clementsian association— a unit or level of vegetation in the conceptual model that came to dominate, even define, Anglo-American or English Tradition plant ecology— was both abstract and concrete depending upon context, it is not clear if the association-type was more or less synonymous with the predominate American interpretation of association or if association-type was some unit intermediate between formation or biome and Clementsian association. Nichols' use of "reed swamp type" (Nichols, 1923, p. 157) as an association-type clearly placed it as synonymous with the association level or unit of Weaver and Clements (1938), Tansley (1923), and Polunin (1960) as detailed above. Nichols (1917, ps. 307, 318) previously made reference to "the Scirpus-Typha association". Likewise Nichols' beech-sugar maple association-type was completely synonymous with the maple-beech association of Weaver and Clements (1938, ps. 481, 510-512). His oak-hickory association-type (Nichols, 1917, p. 310) was synonymous with the oak-hickory association of Weaver and Clements (1938, ps. 481, 514-516). Conversely, Nichols' xerophytic conifer forest association-type was a larger, more general unit of vegetation than the Clementsian association when the former encompassed the Clementsian jack pine (Pinus banksiana) consocies (the seral equivalent of consociation, hence a seral association) of the Canadian and Great Lakes forests and the pitch pine (P. rigida) type of the Atlantic (Nichols, 1923, ps. 156, 157; Weaver and Clements, 1938, ps. 481, 499). Also, Nichols (1923, p. 156) mentioned the "Chamaecyparis association of swamps" whereas Weaver and Clements (1938, p. 497-498) observed that the white cedar (Chamaecyparis thyoides) was but a minor member of the lake forest eastern white pine (Pinus strobus)-red pine (P. resinosa)-eastern hemlock (Tsuga canadensis) association.

Nichols (1923, p. 157) stated that the ecological association-type was identical with the ecological forest-type, but he noted that foresters made little use of the association. Ecological forest type was not defined or even noted in any of the standard Forestry texts or any of the Society of American Foresters term glossaries except the most recent by Helms (1998) as ecological type defined as:

"a category of land having a unique combination of potential natural (climax) community, soil, landscape features, climate, and differing from other ecological types in its capacity to produce vegetation and respond to management".

This sounded more similar to the definition/description of range or forest site and indeed was listed by Helms (1998) as a synonym for habitat type which, as discussed in detail above, the Society for Range Management (Bedell, 1998) defined as "similar in concept to" range site. However, the emphasis on climax is similar to the traditional permanent forest type which is the equivalent of a climax forest association (Toumey and Korstian, 1947, ps. 384, 392).

The key difference between Nichols association-type and the traditional American (=Clementsian) association was that the former was "not limited in it's application to the vegetation of regions which are floristically continuous". For instance, the associations of California chaparral and Mediterranean coastal scrub have no common flora but are regionally parallel due to "similarity in climatic conditions" and "similar in their physiognomy and ecological structure" and thus constitute "a common association-type" (Nichols, 1923, 159). This seemed synonymous with the biome-type or formation-type described by Whittaker (1975, p. 128). It appeared similar to the Bailey unit of ecological region and thus the classic Clementsian formation or regional climax or biome, all synonyms. Association- type is not identical to these Clementsian units however as the equivalent Nichols unit to those spatially delimited ecological units was the geographically defined association-complex. When Nichols (1923, p. 161) considered geographical distribution of plant associations (associations of a naturally defined area like a climatic region at largest scale or physiographically delineated at smaller scale) he used the term association-complex (vs. association-type).This too was ambiguous because in "unrestricted usage" association-complex corresponded to the general term of "community". In more specific usage Nichols (1923, ps. 162-165) distinguished between "climatically and physiographically determined association-complexes".

Nichols (1923) formulated his ecological classification scheme of plant communities on concepts and terms he had previously introduced (Nichols, 1917). These principles (Nichols, 1917) were based largely on the work of Henry Chandler Cowles and the successional theories advanced in the just-released Plant Succession (Clements, 1916a). (Clements drew many of his fundamentals from the slightly earlier work of Cowles, including Clements' signature concept of "dynamic ecology".) In his foundation paper Nichols (1917, p. 312) distinguished between permanent and temporary plant associations. Nichols' permanent associations were limited to what he designated as the regional climax association-type, the vegetation that has attained "the highest degree of mesophytism which the climate of the region permits". Nichols (1917, p. 312) explained that "it is commonly stated or implied in ecological literature that in every region, as the logical consummation of progressive successional changes, the vegetation of all soils and all types of typography is destined eventually to acquire the same degree of mesophytism that characterizes the regional climax association-type…". Here again is the Clementsian monoclimax theory which Nichols then abandoned (or, perhaps more precisely, modified) by introducing into the regional climax association-type ("in edaphically unfavorable situations") the plant community unit of edaphic climax association which was also a permanent association (Nichols, 1917, p. 314-317). Nichols went on to introduce and describe such units of plant communities as the edaphic formation, primary and secondary edaphic formations, the edaphic formation-type, the climatic formation, and the climatic formation-type (Nichols, 1917, ps. 341-348). He also had community complexes (eg. climatic formation-complex, edaphic formation-complex, association-complex) and even presented an example scheme (Nichols, 1917, 350-352).

It is historically important that Nichols and Clements simultaneously published views of climax vegetation that ran counter to each other: from the beginning there were the opposing— at least partially so— interpretations of monoclimax vs. polyclimax formations. This took place 18 years before Tansley (1935) brought this to the lasting attention of synecologists. In other words, contrary to the prevailing and popularized "personality story" of Clements and Tansley behind the two counter-views of climax, it was Nichols and not Tansley who first presented what came to be known as the polyclimax theory.

As elaborated above, Nichols (1917, ps. 317-318) introduced the unit of habitat-type. (For whatever reasons, Nichols did not receive the credit for being the first to publish ideas and major contributions that enhanced reputations of subsequent authors.) Along with habitat-type Nichols had the unit of habitat-complex that was "intimately associated with" the association-complex.

Nichols seems to have been the synecologist who first devised a vegetation classification in which there were parallel— corresponding —units of habitat equivalent to units of vegetation (eg. habitat-type with association-type, habitat-complex with association-complex).

The most relevant point in this detailed explanation is that the regional climax association-type corresponds to— and only to— the Clementsian association (Nichols, 1917, p. 312, citing Clements [1916a, p. 128]). It is at this point that the word "type" was affiliated with the word "association" irrespective of how these terms were specifically applied or how precisely they matched each other.

What for Nichols distinguished associations within his unit of ecological association-type was habitat: "… different associations belonging to the same association-type will be approximately parallel in their habitat relations; ie., the nature of the habitat will be approximately identical wherever these associations occur" (Nichols, 1923, p. 159). Thirty years later Daubenmire (1952) introduced his vegetation classification in which habitat type was basis of and commensurate to climax association.The association-complex was Nichols' vegetation unit that was determined geographically by climate or physiography. While these categories are major parts or components of the abiotic environment (= physical habitat) they do not comprise the total of habitat. Rather, climate and physiographic features relate vegetation respectively to Clements' monoclimax and Nichols' (later Tansley's) polyclimax theories.

By including the physiographic component within the larger climatic component Nichols aligned his classification of plant communities more closely to that which came to be attributed to Tansley than to that of Clements (Baker, 1950, p. 40). To be historically accurate, Tansley followed more closely the vegetational view of Nichols than that of his close friend Clements. The situation is not that simple however because Nichols (1917, p. 346) cited Tansley in his published review of Plant Succession (Tansley, 1916, p. 203) as objecting to the exclusive use of climate while failing to account for "edaphic conditions". Nonetheless, it was Nichols who apparently first published a classification of plant communities that openly broke with the climatic climax (monoclimax) theory. It apparently was also Nichols who first aligned units of habitat with units of vegetation (at least within the English or Anglo-American Tradition). These units were based on and arranged according to the polyclimax view of vegetation. This clearly predated the same arrangement (even same unit of habitat-type) of the Daubenmire (1952) classification.

Whereas the association-type and its associations amounted to community classification based on physiognomy and ecological structure, the association-complex and its associations constituted classification based on geographical relations. Nichols subdivided his geographically defined association-complexes into climatic unit-areas (climatic regions) and into physiographic unit-areas. These in turn were subdivided into climatic plant formations and physiographic plant formations, respectively. All of his units were "capable of both concrete and abstract interpretation" (Nichols, 1923, p. 161-165).

The importance of the term and concept of habitat-type by Nichols (1917, ps. 309, 310) was discussed above. Nichols included in habitat or environment the three general categories of: 1) climatic, 2) edaphic, and 3) biotic elements (Nichols, 1917, p. 306) and designated a series of habitats that occur within the association-complex as a habitat-complex (Nichols, 1917, p. 317). Nichols (1923, ps. 17-23 passim) incorporated habitat in his plant community classification system to a greater extent than Clements did in his community hierarchy. In Nichols' previous paper which laid the foundation for his plant community classification Nichols (1917, p. 305) specified that his system was a modification "of the classification originally devised by Cowles (1901)". In reviewing the genesis of climax units of vegetation and proposing his own interpretation Clements (1916a, ps. 117-128) noted repeatedly the importance of habitat. Yet Clements stated frequently that physiognomy and floristics were of more immediate usefulness than was habitat in delineating vegetation units like formations and associations though all were seen as "complementary and not antagonistic" (Clements, 1916a, p. 122). It was development of vegetation that was the bedrock of the Clementsian paradigm:

"It is for these reasons that development is taken as the basis for the analysis of vegetation. It is not a single process, but a composite of all the relations of community and habitat. It not only includes physiognomy, floristic, and habitat, but it also and necessarily includes them in just the degree to which they play a part, whatever that may be" (Clements, 1916a, p. 123). The formation "is delimited chiefly by development, but this can be traced and analyzed only by means of physiognomy, floristic, and habitat. In a natural formation, development, physiognomy, and floristic are readily seen to be in accord, but this often appears not to be true of habitat." Habitat is "the causal unit", but "… the habitat can only be used in a general way for recognizing formations" until there is "…a much clearer understanding of the climatic and edaphic factors and the essential balance between them" (Clements, 1916a, ps.126-127).

This is the same philosophy or perspective that Clements maintained when he adamently refused to include habitat in the biome (Biome section above).

By contrast, in reviewing such bases of associations as physiognomy, structure, climate, and succession, Nichols (1923, p. 172) followed more closely Gleason (1917) whom he cited twice. Nichols (1923, p. 174) concluded:

"Taken it its entirety, an association is characterized throughout by essential homogeneity or constancy of habitat, but subordinate variations of habitat within the association make it necessary to distinguish between the general habitat relations of the association as a whole and the specific habitat relations or its constituent elements".

Yet Nichols' very next point was that the plant association was a vegetation unit that was defined "by its inherent characteristics of vegetative form and structure" (notably physiognomy). Thus Nichols' ecological association-type was similar to formation and therefore "habitat uniformity is not specified as a criterion" (Nichols, 1923, p. 174).

As discussed under the Organicism section below Nichols was the Tansley rather than the Clements variety of organicist and, as shown previously in this section of the paper, it was Nichols, not Tansley, who first put forth a view of vegetation based on what became known as the polyclimax theory. In applying, at least partially, the Gleason continuum view of plant communities and the polyclimax theory Nichols' interpretation of vegetation was similar yet distinct from that of Clements and yet also different from Gleason's individualistic interpretation. Plus, and perhaps most importantly, Nichols anticipitated by a quarter century the blending of mono- and polyclimax theories that became Whittaker's climax pattern theory.

Nichols placed relatively more stress upon edaphic and physiographic features than on climatic criteria which resulted in use of lower spatial and shorter temporal scales in analysis of vegetation. In Nichols (1917) earlier paper, which laid the basis for his plant community classification, Nichols discussed Clements "developmental concept of the climatic formation" complete with quotations from Plant Succession (Clements, 1916a, ps. 3, 124-127) on vegetation "as an organism" and "an organic entity" and the formation as "the final stage of vegetational development in a climatic unit", "the highest life-form possible in the climate concerned". Immediately thereafter Nichols (1917, p. 346) departed from Clementsian monoclimax (= regional or climatic climax) and adopted what was later designated the polyclimax model with edaphic and physiographic climaxes within the climatic climax:

"It will be seen from the foregoing quotation that Clements regards the climatic formation what from the writer's point of view would be termed the regional climax association-complex (or association-type). It is the opinion of the writer that the climax association-complex should not be so regarded, but that the entire edaphic formation-complex of the region, or, as before stated, the vegetation of the region in its entirety, should be considered as constituting a unit from the standpoint of regional physiographic ecology. It seems more logical to regard the climax communitites of the region, like other ecologically parallel series of communities, as belonging to a common association-type. As the most mesophytic type of vegetation attainable under the existing climatic conditions, the climax association-type may be looked upon as the climatic indicator, but not as the climatic formation. To sum up, the vegetation of any region having an essentally uniform climate throughout, taken in its entirety, constitutes a climatic formation, the general ecological aspect of which is determined by that of the climax association-type of the region".

This is a pivotal passage for several reasons including:

1. It expanded the climatic climax from the mesophytic or most mesic form of vegetation of a climatic region to the whole vegetation of a climatic region (ie. the climax mesophytic vegetation of gently sloping uplands is no more climax than climax vegetation of such habitats as xeric south slopes or hydric bottomlands),
2. It unified monoclimax and polyclimax views even before thay had that designation and were seen later as opposing theories, and it set the stage for Whittaker (1953) to bring these interpretations together using the continuum view of Gleason (1926); interestingly, Whittaker (1953, p. 42) credited Nichols (1917, 1923) with edaphic and physiographic climaxes but he did not remark that in these same papers Nichols initiated the combining of mono- and polyclimax in classification of plant communites,
3. It indicated that soil and landform could be the basis for climax vegetation,
4. It anticipated by 60-70 years what Bailey (1996, 1998) developed as Ecosystem Geography and the ecoregion concept; it is interesting here that Bailey made no reference to the earlier hierarchial system which arranged nested units and distinctions based on climate, topography, and soils (it was remarked previously that Nichols' work has not been given it's due credit), and
5. (and most importantly for this discussion of range and forest cover types) it aligned closely the term and vegetation unit of association with the term and generic unit of type and it continued the traditional affiliation of the units of plant formation with plant association in a hierarchial relationship with association being a unit within formation (an arrangement going back to Warming [1909]).

The units and details of Nichols' classification (other than brief description of units that paralleled or anticipated contemporary units like ecoregions) is not the relevant point pertaining to origin of the concept/term of plant assocaition. The key fact is: for all its varied definitions, the hierarchial unit of vegetation or the level of plant community organization designated as plant association is the one that became most closely aligned with what foresters and range managers developed as forest and range cover types. There may have been other plant community or formation (= climax) systems besides that of Nelson, but clearly Nichols' classification format arranged formations (eg. climatic formation, edaphic formation), types (eg. association-type, edaphic formation-type, habitat type), and associations (eg. edaphic climax association, association-complex) relative to (nested within) one another.

Conclusion:

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Apparently there was no defining system or point at which the Anglo-American unit of plant association became more or less synonymous (or at least closely resembling) cover type. In fact, this relationship is obtuse and its origin obscure so as to require familiarity with the historic literature in such related but distinct fields as Plant Geopraphy, Plant Ecology, Forestry, Range Management, and Soil Science. In some cases it appeared that the relation of association to cover (= dominance= vegetation) type and these as units within formation was an automatic (or nearly so) arrangement. For example, this pattern was followed in the California Vegetation-Soil Survey (California Forest and Range Experiment Station, 1954; Kuchler, 1967). California Vegetation-Soil Survey classified and mapped vegetation at two levels: 1) vegetation cover classes which were major kinds of vegetation and 2) species types which were based on dominant plant species (Kuchler, 1967, p. 277). The species type is obviously the dominance (= cover) type which is synonymous with vegetation type:

Apparently there was no defining system or point at which the Anglo-American unit of plant association became more or less synonymous (or at least closely resembling) cover type. In fact, this relationship is obtuse and its origin obscure so as to require familiarity with the historic literature in such related but distinct fields as Plant Geopraphy, Plant Ecology, Forestry, Range Management, and Soil Science. In some cases it appeared that the relation of association to cover (= dominance= vegetation) type and these as units within formation was an automatic (or nearly so) arrangement. For example, this pattern was followed in the California Vegetation-Soil Survey (California Forest and Range Experiment Station, 1954; Kuchler, 1967). California Vegetation-Soil Survey classified and mapped vegetation at two levels: 1) vegetation cover classes which were major kinds of vegetation and 2) species types which were based on dominant plant species (Kuchler, 1967, p. 277). The species type is obviously the dominance (= cover) type which is synonymous with vegetation type:

"Vegetation types by species composition (refered to as 'species-types') are natural bodies of vegetation classified according to the dominant species growing together in an ecological association" (Kuchler, 1967, p. 282).

There was no obvious author or published system that can be pointed to as the instant at which association became established as the unit of vegetation most closely corresponding to dominance type, range vegetation type, or cover type, but that was the apparent relationship that come to be accepted within the American-British Tradition in such applied brances of Ecology or Vegetation Science as Forestry and Range Management. It was obvious that the various contemporary systems from which the American concepts of plant association and cover type emerged were not completely inter-convertible. The above historical review did indicate (at least strongly suggested) that cover type and its numerous synonyms as used by ecological practitioners grew out of, and thus is roughtly equivalent to, the term plant association as developed and applied by the Anglo-American Tradition. This was largely through the profoundly influencial writings of F.E. Clements and his colleagues and co-authors.

George E. Nichols developed a vegetation classification system simultaneously with that of Clements. Like that of Clements, Nichols' system grew out of the work of H.C. Cowles. Both systems were sophisticated, elaborate, precisely defined, (and confusing). Nichols' classification aligned the specific term and vegetation unit of association with the generic term and unit of type more directly than did Clements, but applied ecologists (especially foresters)"associated" association and type as rough equivalents more through the writings of Clements. (Nichols did not apply his work as directly to the practical management of vegetation.) Nichols adopted the view of polyclimax theory, and years before Arthur Tansley popularized it. Nichols' view of climax ultimately prevailed over Clements monoclimax view, but Nichols who published no epic ecological monographs never gained the recognition or reputation (or the wrath) reserved for Clements. The original contributions of Nichols remained largely unknown though some of his concepts like habitat-type appeared to have been adopted by later ecologists.

It was apparent from this review of the type concept that origin of the term is somewhat obscure. The tortuous path of the development of "type" resembles in its obscurity the development of the vegetation it seeks to describe. With confusion typical of much of Clementsian theory and vocabulary the term "type" was also used synonymously with biome or formation: "… three great types of vegetation, viz., forest, scrub, and grassland" and "[e]ach formation is the highest type of vegetation …" (Weaver and Clements, 1938, p. 478). In other words, Clements & Company used "vegetation type" as a general term for vegetation much as the Ecological Society of America Vegetation Classification Panel used it as a generic term. Most other authors seem to have followed this same format when using the specific words "vegetation type" as the catch-all collective term for any or all units of vegetation. Most commonly a combination of the words "vegetation" and "type" was a generic usage much like "plants", "cattle", or "dogs". Oosting (1956), Eyre (1971), Shimwell (1971), and among prominent range scientists, Holechek et al. (1998) followed this common use of "vegetation type". Other renowned range authorities ignored the terms "vegetation type", "range type", or "cover type" altogether (eg. Sampson, 1952; Stoddart et al., 1975). Sampson (1952, ps. 99-102) used the term association for units of grassland vegetation including tall-grass prairie, short-grass plains, Pacific bunchgrass, etc. He used the Clementsian definition and unit of association including consociation (Sampson, 1952, ps. 63-64). That the "Father of Range Managaement" in his last published textbook used the same (or similar) plant asociations as Clements (1920) in Plant Indicators and Weaver and Clements (1938) in Plant Ecology attest to the relatedness of associations to range types.

Based on historical usage as just described it would seem advisable to avoid the words "vegetation type" or "types of vegetation" because these terms or word arrangements have been used variously or as the generic term for units or kinds of vegetation. This is consistent with the recommendation of the Terminology Working Group of the ESA Vegetation Classification Panel (1997, p.14) which regarded the SRM (1989) term of vegetation type as the least preferred designation for a unit of vegetation. Likewise it would be advisable for authors to avoid using "vegetation types" as the generic equivalent for kinds of plant communities or hierarchial levels of vegetation. Given the numerous terms of long-standing use it would avoid confusion to stay with "range types", "range cover types", "range dominance types", "rangeland cover types", and "forest cover types". As there are various kinds of "forest types" (eg. "forest cover type", "permanent forest type", "climax forest type", "temporarty forest type") as discussed earlier, "forest type" should best be avoided except as the all-inclusive term for all kinds of forests.

In summary, the cover type concept and the specific recognition/description of cover types as used in Range Management and Forestry is well-founded and traceable back to the earliest, most influencial, and longest lasting literature on the ecology of North American native vegetation. Range (both rangeland and forest) cover types and detailed descriptions of them are current and of considerable value to scientists and professional practitioners. Range cover types are readily distinguishable to students of natural vegetation, and probably also to those such as observant stockmen, lumbermen, sportsmen, wilderness enthusiasts, etc. who are interested in vegetation even if not well-read in the subject.

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