Patterns of native and exotic vascular plant richness along an elevational gradient from sea level to the summit of the Appalachian Mountains, U.S.A

DENSLOW M. W. (Department of Biology, Appalachian State University, Boone, NC 28608), M. W. PALMER (Department of Botany, Oklahoma State University, Stillwater, OK 74078), AND Z. E. MURRELL (Department of Biology, Appalachian State University, Boone, NC 28608). Patterns of native and exotic vascular plant richness along an elevational gradient from sea level to the summit of the Appalachian Mountains, U.S.A. J. Torrey Bot. Soc. 137: 67–80. 2010.—We used floristic studies from the state of North Carolina to compare the patterns of total, native and exotic plant species richness from sea level (Atlantic coast) to the summit of the Appalachian Mountains. Few studies have investigated how patterns of native and exotic species richness differ along environmental gradients, and these studies have yielded contrasting results. We compare our results with those few published studies, and demonstrate that there is a need for future studies examining exotic richness along gradients. We modeled the effects of size of study area, year of study, and elevation on species richness using a dataset of sixty-eight floristic studies. Native and exotic species richness showed a positive relationship with area and year. Exotic species showed a steeper slope than native species for the species-area relationship. Richness of both groups was positively but weakly related to year of study. After accounting for area and year, native species displayed a hump-shaped pattern along the elevational gradient. Exotic species richness was weakly related to elevation, which was not a significant variable in the model. This contrasts with the few previous studies that have examined exotic richness patterns along elevational gradients that have found either a strong linear decline, or a strong hump-shaped pattern. Both native and exotic species showed high variation in richness at elevations below 400 m. We conclude that different processes may govern native and exotic plant richness patterns and that exotic richness patterns along gradients may in fact be idiosyncratic due to factors such as disturbance history.