Vegetation of Virginia

Vegetation refers to the general plant cover of  a region.Virginia's natural vegetation is forest, specifically a type referred to as Temperate Broadleaf Deciduous Forest. Such forests are associated with humid subtropical climates in the northern hemisphere and, in western Europe, with the marine west coast climate.For general information on this vegetation beyond Virginia, visit my Biomes of the World site.

The Temperate Broadleaf Deciduous Forest in North America consists of a group of plant communities that cover the eastern US. Some 2200 species of vascular plants can be found in Virginia: more than in West Virginia but markedly fewer than the 3600 known from North Carolina. Generally the number of species in any class of organisms increases as one goes toward the equator, and the comparison between North Carolina and Virginia fits this trend.

In part because the forest is deciduous (looses its foliage during the non-growing season), it contains a mix of canopy trees, subcanopy or smaller trees, shrubs, and herbs. With no leaves on the trees in early spring, the sun warms the forest floor and an array of wildflowers bloom and set seed before the tree canopy casts its shade. Members of the shrub and subcanopy layers are usually the next to bloom: species like spicebush, Allegheny serviceberry, redbud, and dogwood, the state flower. As spring progress, the buds on the tallest trees of the canopy layer swell and, in a matter of a few weeks, leaves prevent most of the sun’s energy from penetrating to the forest floor. The most common canopy trees are oaks and hickories, although this was not always the case. Until the 1930s, when an introduced blight killed off nearly all mature specimens, the American Chestnut was an important component of eastern forests.

Not all species occur everywhere in the state, so it is possible to recognize within the general forest type, four variations (see map below.)

Figure 1. Vegetation of Virginia. Main subdivisions of the Temperate Broadleaf Deciduous Forest
(as delineated by Braun 1950) are shown. Triangles identify stands of relict red spruce.

The forest type with the largest number of plant goes by the name of mixed mesophytic forest. The "mix" refers to the co-occurrence of northern, southern, Appalachian, and western species. "Mesophytic" refers to plants preferring cool, moist conditions, just the conditions found on the unglaciated Cumberland Plateau. More than 20 species of trees share dominance in this forest. They include american beech, sugar maple, northern red oak, eastern hemlock, white basswood, tulip poplar, yellow buckeye, various hickories, and several magnolias. (Similar assemblages of species occur in deep, cool valleys in the Alleghenies and Blue Ridge, where they are referred to as cove forests.)

An oak-chestnut forest characterized the Blue Ridge, Valley and Ridge, and northern Piedmont before the demise of the chestnut. The oaks of this forest include the northern red oak, white oak and chestnut oak. Nutrient-rich soils developed under this forest type, especially in areas with underlying limestone bedrock. Much of the valley areas were cleared for agriculture in the 18th and 19th centuries; the mountain slopes were timbered for lumber, charcoal, and tanning bark as well as for opening pastureland. Therefore, what we see in all but the most inaccessible areas today is second growth.

An oak-pine forest dominated the southern Piedmont and northern Coastal Plain. Black oak replaces the red oak of the mountains, but white continue to be prevalent. Common pines are the short-needled Virginia pine and short leaf pine. They are probably more abundant today than in pre-colonial times due to old farming practices associated primarily with tobacco growing that robbed the soils of their nutrients. Pines in general do better than broad-leaved trees on poor soils.

On the Coastal Plain south of the James River one finds the northern limits of the southeastern evergreen forest, a forest dominated by long-needled pines that stretches from Virginia along the Gulf-Atlantic Coastal Plain to Texas. On sandy soils the common pines include longleaf pine and loblolly. Much of this forest today is managed as a commercial crop by lumber and paper companies. The trees grow in straight lines and fire is used as a tool to prevent the growth of understory plants.

Along the rivers that flow in the region covered by southeastern evergreen forest and in Great Dismal Swamp are heavy alluvial soils on which pines do not usually thrive. The forest that has developed on these soils include bald cypress, black gum, tupelo and red maple. A commercially important species of the past, Atlantic white cedar, once occurred in pure stands on deep peat in Dismal Swamp, but 200 years of logging have changed that, and today it is a rare species.

In addition to these four main forest types there are several specialized plant communities that reflect localized conditions of climate or bedrock. Two will be mentioned here, the high-elevation or boreal evergreen forests and the shale barrens.

Boreal means northern. At elevations above 4,500 feet in Virginia, temperatures are cool enough to resemble northern climates; and on such restricted and isolated sites one encounters a forest more typical of Canada, a boreal evergreen forest. The trees are short-needled and evergreen, like Christmas trees.

Figure 2. Boreal vegetation on the uplands near Mt. Rogers. This scene
gives an idea of what Pleistocene Virginia must have looked like.

A boreal forest of red spruce and Fraser fir is best developed on the summit of Mt Rogers; red spruce also occurs on Whitetop, both Beartown mountains a few other peaks in the Alleghenies and Blue Ride Mountains. Red spruce is widespread and common in the northeastern US/southeastern Canada forest, and its distribution extends down the Appalachians to the Carolinas. Fraser fir on the other hand, is a Southern Appalachian endemic, found only on the higher peaks of the southern Blue Ridge and Great Smoky Mountains of western North Carolina and eastern Tennessee, and on Mt Rogers in Virginia. Both species are considered Pleistocene relicts—living fossils from the ice ages, when a Canadian-type forest was widespread across Virginia and, much of North America south of the great ice sheets. A die-off these trees is occurring today, perhaps a result of climate change and air pollution.

Another unique vegetation type has developed on steep, south-facing slopes developed on shale. Outcropping shale tends to weather into thin flakes that shed rainwater like roof-shingles. Rainwater quickly flows downhill rather than infiltrating the soils and thus the ground is exceptionally dry even in a humid climate, Furthermore, on steep slopes the flakes move themselves move downhill due to the force of gravity. This creates a very unstable surface which discourages the growth of trees that need to sink their roots into solid ground for support. The lack of trees means no shade; and this, combined with the more direct rays of sunlight striking the south facing slopes, means a very hot site in summer. Most plant species of the Temperature Broadleaf Deciduous Forest cannot tolerate these hot, dry conditions and so the exposures of shale are barren of tall trees, hence the name shale barrens. A sparse scrub pine/scrub oak vegetation with a number of highly specialized smaller plants is characteristic on shale barrens. These smaller species are often most closely related to plants growing in the semiarid western states, and some are found nowhere else but on the few shale barrens that dot the Valley and Ridge from Virginia and West Virginia north to western Maryland and south-central Pennsylvania. Several rare shale barrens endemics are on Virginia’s list of endangered species.

Sources:

Braun, E. Lucy 1950. Deciduous Forests of Eastern North America (New York: Hafner Publishing Company).

Porter, Duncan M. and Thomas F. Wieboldt 1991. "Vascular Plants," pp. 51–59 in Virginia’s Endangered Species, coordinated by Karen Terwilliger (Blacksburg: The McDonald and Woodward Publishing Company).

Woodward, Susan L. and Richard L. Hoffman 1991. "The Nature of Virginia," pp. 23–48 in Virginia’s Endangered Species, coordinated by Karen Terwilliger (Blacksburg: The McDonald and Woodward Publishing Company).

For information on possible causes of the die-off of boreal tree species and threats to the broadleaf species of Virginia as well, see An Appalachian Tragedy, Air Pollution and Tree Death in the Eastern Forests of North America, edited by Harvard Ayres, Jenny Hager, and Charles E. Little, 1998 (San Francisco: Sierra Club Books).

Posted by slw, March 14, 2000