Species richness and exotic species invasion in middle Tennessee cedar glades in relation to abiotic and biotic factors

COFER. M. S., J. L. WALCK, AND S. N. HIDAYATI (Department of Biology, Middle Tennessee State University, Murfreesboro, TN 37132). Species richness and exotic species invasion in middle Tennessee cedar glades in relation to abiotic and biotic factors. J. Torrey Bot. Soc. 135: 540-553. 2008.-Abiotic factors, particularly area, and biotic factors play important roles in determining species richness of continental islands Such as cedar glades. We examined the relationship between environmental parameters and species richness on glades and the influence of native species richness on exotic invasion. Field surveys of vascular plants on 40 cedar glades in Rutherford County, Tennessee were conducted during the 2001-2003 growing seasons. Glades were geo-referenced to obtain area, perimeter, distance from autotour road, and degree of isolation. Amount of disturbance also was recorded. Two-hundred thirty two taxa were found with Andropogon virginicus, Croton monanthogynus. Juniperus virginiana, Panicum flexile, and Ulmus alata present on all glades. The exotics Ligustrum sinense, Leucanthemum vulgare, and Taraxacum officinale occurred on the majority of glades. Lobelia appendiculata var. gattingeri, Leavenworthia stylosa, and Pediomelum subacaule were the most frequent endemics. Richness of native. exotic and endemic species increased with increasing area and perimeter and decreased with increasing isolation (P <= 0.03); richness was unrelated to distance to road (P >= 0.20). Perimeter explained a greater amount of variation than area for native and exotic species, whereas area accounted For greater variation for endemic species. Slope of the relationship between area and total richness (0.17) was within the range reported for continental islands. Disturbed glades contained a higher number of exotic and native species than nondisturbed ones. but they were larger (P <= 0.03). Invasion of exotic species was unrelated to native species richness when glade size was statistically controlled (P = 0.88). Absence of a relationship is probably due to a lack of substantial competitive interactions. Most endemics occurred over a broad range of glade sizes emphasizing the point that glades of all sizes are worthy of protection.