Forest structure is the distribution of trees by species and size (diameter class). Structure is the result of several factors: the growth habit of tree species, especially the degree of shade tolerance; ecological conditions; and the history of disturbance and management. The forests of Western North Carolina have over 100 tree species. Species such as oak, ash, poplar, hickory, and some pines do not tolerate shade well and are normally found in the overstory. Other species, such as beech, maple, dogwood, red bud, and black gum, survive well in shade and make up the understory of the forest canopy. Ecological conditions are highly correlated with elevation and forest types change dramatically with increases in elevation. Harvesting practices in Western North Carolina, particularly in the early 1900's, have led to a predominately even-aged forest that is reaching maturity.
Various size classes within a forest are important because they provide different goods, services, and values. In Western North Carolina, volume of growing stock is accumulating in all diameter classes 10 inches and larger. In 16-inch and larger classes, volume rises exponentially and more than doubles beyond 20 inches. The volume of 6-8 inch classes has declined; however, the decline is by less than 10 percent.
What are the implications of size class distribution? Presently, volume is accumulating in trees of a size suitable for high-value products such as veneer, barrel staves, and the better grades of factory lumber. Much of the behavior of lumber production can be related to changes in lumber prices. With a currently depressed housing market, consumption has dropped and numerous mills have cut production.
Regionally, indigenous wildlife populations depend on early, mid and late successional forests. Succession is the natural replacement of plant or plant communities in an area over time. The larger size classes (mid- to late-successional vegetation) provide habitat for turkey, bear, squirrel, fox, and bobcat, to name a few. Small den trees might house chickadees, woodpeckers, screech owls, or flying squirrels. Large den trees are used by squirrels, raccoons, wood ducks, and, occasionally, even a bear. Older, mast-producing trees produce fruits and nuts used by wildlife for food. Hickory, oak, beech, persimmon, serviceberry, black gum, holly, hawthorn, dogwood, grapevine, and many other species found in mid- to late-successional forests are valuable to wildlife.
Early-successional forests, characterized by dense growth of shrubs and saplings, are very different from that of mid- to late-successional forests, and provide distinctly different habitats. Some wildlife (breeding birds such as certain warblers, ruffed grouse, cottontails, wild turkey, American woodcock, and white-tailed deer) are either closely associated with younger forests or tend to have higher populations in them. Without an increase in management activities that create openings in a mature forest, it is likely there will be decline from current levels and potential loss of species associated with young stands.
As private timberlands account for most of the region’s patchwork landscape of abandoned fields, young forest, and small, older forest fragments, private lands may become the locus of most early-successional habitat. The maintenance and restoration of older, late-successional habitat are provided on public land, where there is potential for maintaining and creating large tracts of unfragmented forest.