HIGH-ELEVATION ROCK OUTCROP VEGETATION OF THE SOUTHERN APPALACHIAN MOUNTAINS

Species composition patterns and vegetation-environment relationships were quantified for high-elevation rock outcrops of the Southern Appal achian Mountains, an infrequent and insular habitat in a forested land scape. Outcrops occur over a wide geographic range encompassing extens ive variation in both geology and climate. Geographic-scale factors in teract with site-scale factors to produce variation in vegetation amon g outcrops. Similarly, site-scale factors interact with micro-scale fa ctors to produce variation in vegetation within outcrops. To provide a quantitatively-based classification of outcrop vegetation we used a T WINSPAN analysis of 154 100-m(2) plots. We recognized nine communities that primarily correspond to different combinations of elevation, bed rock type, geography, and moisture. Within outcrops of a single bedroc k type, vegetation composition of 100-m(2) plots was consistently corr elated with elevation and solar radiation, but relationships to soil n utrients varied with bedrock type. Both site-scale (100 m(2)) factors (e.g. elevation, slope, aspect, and bedrock type) and plot-scale (1-m( 2)) microsite factors (e.g. soil depth, vegetation height, soil nutrie nts) were strongly correlated with species composition at the 1-m(2) l evel. Environment can be used to predict composition more effectively for 100-m(2) plots on a single bedrock type than either across bedrock types or at a 1-m(2) scale. Composition-environment relationships res emble those described for outcrop systems from other regions with pron ounced topographic relief more than they do those described for the ne arby but flatter and lower-elevation outcrops of the Southeastern Pied mont. There is strong spatial autocorrelation in this community, perha ps owing to dispersal limitation. Consequently, a comprehensive conser vation strategy must include reservation of both a range of geologic t ypes and a range of geographic locations.