RELICTUAL BOTANICAL COMMUNITIES PRESERVED AT HIGH ELEVATIONS IN THE VIRGINIA BLUE RIDGE: GEOLOGICAL RELATIONSHIPS AND IMPLICATIONS FOR GLOBAL CLIMATE CHANGE

Increased temperatures associated with global climate change have been documented worldwide, but attribution of specific effects on non-agricultural plant populations remains a matter of debate among researchers. The occurrence in the Blue Ridge mountains of Virginia of diverse communities of vascular plants that typically occur in boreal (high latitude) environments and are otherwise rare in the region presents a unique opportunity to monitor changes in climate-sensitive plants existing at the limit of their survival range. These communities, which include over a dozen species adapted to cooler climates, may provide considerable insight into environmental factors influencing plant distribution and local effects of global climate change. To date, boreal communities have been recognized at elevations of about 4,000 feet and above at Stony Man and Hawksbill Mountains in Shenandoah National Park in areas underlain by greenstone of the Late Neoproterozoic Catoctin Formation. Both sites are characterized by rugged, asymmetric slopes that provide diverse local environments ranging from relatively dry exposed cliffs to relatively wet sheltered coves. Communities at both sites include seven extremely rare species (including Abies balsamea and Juncus trifidus, among others), seven very rare species (including Lycopodium selago, Muhlenbergia glomerata, Potentilla tridentata, and Solidago simplex var. randii, among others), and several rare to infrequent species such as Picea rubens, Taxus canadensis, and Saxifraga michauxii). These plants collectively constitute relictual communities likely remaining from cooler climates of the Pleistocene Epoch. Individual species have adapted to local variations in bedrock-controlled factors such as water availablility, soil development, fracture orientation, slope aspect, and exposure to prevailing westerly winds. The environmentally fragile nature of these relictual communities provides a sensitive baseline on which to monitor local responses to broad-scale changes in climate. However, because the influence of local factors may modify externally-driven climatic effects, it is important to document and understand site-specific geobotanical interactions that define the limits of plant survival so that the effects of globally-induced changes can be identified.