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Technically speaking, the distinction between these two groupings of range and/or forest cover types is that forests are dominated by trees whose crowns interlock, or at least touch, thereby forming a more or less closed canopy (a "solid" upperstory) whereas woodlands are dominated by trees that aredispersed widely enough that the crowns do not usually contact each other.Thus, woodlands are characterized as having an understory of herbaceous and/or shrubby layers at climax (as persistent layers in the potential natural vegetation) while forests may or may not have layers of understory plants atclimax. Numerous forest (= timber) cover types are forest range types only until the canopy becomes "closed", after which the shade-tolerant understories— if present at all— do no provide adequate forage or browse to be regarded as range (= grazing) types. These latter forest cover types are designated as transitory forest range. Other forest vegetation types have more "open" (less dense) canopies and have understory layers even at climax which furnish considerable grazable/browseable vegetation. These forest cover types are permanent forest range. They may even have a "park-like" appearance. Both permanent and transitory forest range cover types can be either even-age or uneven-age communities, though one or the other may tend to predominate either naturally due to silvics of tree species or silviculturally because of forest management practices.
Within most woodland and forest cover types there exists a continuum of plant densities of which mature tree spacing is the most important feature, and tree dispersions (hence, understory development) vary from widely scattered trees to "dog-hair" stands. Thus, some tree-dominated cover types can vary from savannas to closed-canopy forest. For example, ponderosa pine types vary fromscattered trees on tallgrass prairie to dense forests devoid of any understory.Pinyon pine and juniper occur as scattered, infrequent trees on mixed prairie and also as juniper-pinyon pine woodland to closed-canopy juniper-pinyon pine forest with zero understory. The latter form is usually interpreted as unnatural vegetation (ie. a deteriorated range plant community) due to human-induced disturbances varying from overgrazing to fire suppression, but clear lines of distinction often seem to be arbitrary and certainly are site-specific. Site descriptions themselves are often arbitrary or at least biased by the author's background, experiences, and value judgments.
The forests of North America have been viewed conventionally and conveniently as two broad groups based on taxonomy of dominant tree species (and the corresponding features of their wood):
1. Coniferous Forests- dominants are of the Gymnospermae (or Pinophyta), order Coniferales; called conifers, and
2. Deciduous Forests- dominants are in the Angiospermae.
Most gymnosperms are "evergreen", shedding their needle leaves less frequently and less pronounced. Their wood is, in general, relatively soft. The conifers are thus called "evergreens" or "softwoods" and coniferous or "evergreen" forests.
Most angiosperms, by contrast, shed their leaves annually in autumn (hence "fall") and have generally relatively hard wood. Angiosperms are called "hardwoods" and deciduous trees (deciduous= L. deciduus< decidere, to fall off> de-, off, down + cadere, to fall according to "Webster"; thus, horns such as antlers in the Cervidae that are shed or fall off annually are deciduous horns). By extension, forest dominated by deciduous or hardwood trees are deciduous or "hardwood" forests.
There are conspicuous exceptions. Bald cypress of the redwood family is an autumn-deciduous conifer. Numerous species of "live oaks" and members of the Ericaceae (heath family) in the Angiospermae are "evergreen". The woods of some angiosperms like American sycamore, basswood, and yellow poplar or tulip tree are softer than the woods of the hard pines (eg. the southern pines, ponderosa pine, jack pine). Students should remember from their Botany course that "hardwood" versus "softwood" refers to distinguishing anatomical features of the wood and not the actual physical hardness of wood (Panshim and de Zeeuw, 1970, p. 20). For example, hardwoods (angiosperms) have vessel elements called pores and they are described as porous woods; softwoods (gymnosperms) lack vessels and have nonporous wood (Panshin and deZeeuw, 1970, p. 150-151).
To add further confusion to the beginning student of forest vegetation, many if not most forests types have dominant angiosperm and gymnosperm species with relative abundance or dominance determined by the forester, natural fire regimes, other natural disasters (eg. wind or ice storms), and past human abuse. Again, some of the conifers may be deciduous (eg. bald cypress) while the angiosperms are evergreen (eg. southern live oak and magnolia). The examples just given are in the pineywoods of the Southeast which is an example of mixed forests. The mixed evergreen forest type of the Pacific Coast Range is composed of both evergreen angiosperms and gymnosperms.
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