Stretching over 750 km (450 mi) east to west from the Atlantic Ocean to the Appalachian mountains, the Commonwealth of Virginia spans five of the more than 20 major physiographic provinces found in North America (Fenneman 1938), making it one of the most diverse landscapes – both topographically and floristically – in the East. Because of its location between the glaciated, mountainous regions of the north and the coastal lowlands of the south, Virginia is also uniquely positioned to capture species at or near the southern limit of their range, as well as southern species reaching the northern limits of their distributions, adding to the biotic richness of the state. This combination of landscape diversity and biotic richness leads to the wealth of ecological communities found throughout the state – from the maritime forests of the coastal barrier islands to the spruce forests and shale barrens of the mountains. To better understand the distribution of ecological communities across Virginia, it may be helpful to briefly examine the characteristics of the state’s major topographic regions. This is by no means intended to be a comprehensive overview, but a “broad-brush” look to assist in understanding major vegetation patterns. For more comprehensive treatments of Virginia geology, physiography, and climate readers are referred to Woodward and Hoffman (1991) and the Geology of Virginia website at the College of William and Mary (http://www.wm.edu/geology/virginia/).
Virginia covers 109,624 sq km (42,326 sq mi), including 2,590 sq km (1,000 sq mi) of inland water and 4,475 sq km (1,728 sq mi) of coastal waters over which the state has jurisdiction. Roughly triangular in shape, it extends 755 km (469 mi) east to west and 323 km (201 mi) north to south at its widest points. Maximum elevation is reached on the adjacent southern Blue Ridge peaks of Mount Rogers (1,746 m / 5,729 ft) and Whitetop (1,682 m / 5,520 ft) , while its minimum relief is found on the Eastern Shore and Embayed Region of southeastern Virginia (0 m/ft or sea level). Virginia is bounded on the east by the Atlantic Ocean, on the north and east by Maryland and the District of Columbia, on the west by West Virginia and Kentucky, and on the south by Tennessee and North Carolina.
The physiographic provinces that intersect Virginia are generally defined by their relative elevation, relief, geologic structure, and lithology (Fig. 1). Beginning at sea level at the eastern edge of the state, the surface of Virginia rises gradually in elevation and increases in irregularity, until it reaches maximum elevation and ruggedness in the western part of the state. The major physiographic divisions of this surface, from east to west, are the Coastal Plain, the Piedmont Plateau, the Blue Ridge, the Ridge and Valley, and the Appalachian Plateaus. Each province, in turn, is divisible into subregions using geologic and topographic features, climate, biota, or some combination of these factors. Geologists, physiographers, and biogeographers often differ slightly in their delineations of subregions. We will attempt to explain the subregional divisions (indicated in bold italics) that are most commonly employed.Differences in climate, soils, and overall habitat conditions in each province greatly influence the distribution of individual plant species and the assemblages of plants that represent natural communities. Although there are many species that have wide distributions in the state, differences in the overall vegetation of the Coastal Plain, Piedmont, and Appalachian provinces are pronounced and apparent. To a great extent, these variations reflect the influences of two larger biogeographic floras: that of the northern North America and Appalachian region, and that of the southeastern Atlantic and Gulf slopes and coastal plains. Plants and vegetation characteristic of each biogeographic region are well represented in Virginia, which is situated at latitudes where these great floras intermingle. The patterns of distribution, however, are not simplistic. Gradations in species distributions and larger-scale vegetation patterns are evident on both a north-south axis related primarily to regional climate and the past history of climatic change and plant migrations, and on an east-west axis related primarily to topography and local climatic factors. Figure 1. The physiographic provinces and subregions of Virginia. Modified from Woodward and Hoffman (1991), with copyright permission. (Click on map or here for larger view that will open in a separate window.)
The present-day climate of Virginia is generally classified as humid subtropical (Woodward and Hoffman 1991) but within-state variation of temperatures, precipitation, and length of growing season is dramatic. Much of the temperature gradient is related to elevation and distance from the coast, with oceanic influences greatly moderating the climate of near-coastal areas. The relatively warm climate of eastern and southeastern Virginia is closely correlated with a concentration of southern plant species, some of which reach their northern range limits in the state. A regionally cooler climate and pronounced microclimatic variation is present in the Appalachian provinces, where local relief is greatest. Sub-boreal or boreal microclimates prevail at many sites > 1,200 m (4,000 ft) elevation, providing suitable habitat for a large number of plants whose ranges are centered to the north of Virginia.
It is important to note that the contemporary vegetation of Virginia is not static and has developed only recently on the geological time scale. Eighteen thousand years ago, at the peak of the last continental glaciation, the climate in much of Virginia was boreal due to the s