EFFECTS OF LANDSCAPE PATTERNS ON BIOTIC COMMUNITIES

A comparative evaluation was performed using descriptors of landscape and land cover patterns as to how they relate to varying levels of ant hropogenic disturbance and the structure of biotic communities. A spat ial analysis program (a modified version of SPAN) was used to compute measures of land cover diversity, dominance, contagion, scaled dominan ce and contagion, fractal dimension of land cover patches, mean forest -wetland patch size, amount of forest edge, clustering of selected for est types, and the largest cover patches within two 100-km(2) watershe ds of the Ridge and Valley province of central Pennsylvania. Landscape pattern analysis was conducted on a subwatershed basis, emphasizing d ifferent levels of residential-agricultural versus forest land cover, the major difference between the two watersheds. Bird and vascular pla nt guilds were chosen to represent the overall biotic community. The g eneral descriptors of diversity, contagion, mean forest-wetland patch size, proportion of forest cover, and the amount of forest edge were m ost effective in reflecting the disturbance levels within the watershe ds and changes in guild composition for both birds and plants.