Classification and environmental relationships of plant communities in the southern Appalachian Mountains of North and South Carolina

Background/Question/Methods In his classic research on vegetation in Great Smoky Mountains National Park, published a half-century ago, Robert H. Whittaker established the importance of complex-gradients of elevation and topographic moisture in controlling distributions of plant species and communities. Whittaker’s model has been widely adopted to account for variation in vegetation and environment throughout the southern Appalachians. With data on vegetation and environment now available from a much wider geographical extent in the southern Appalachians, vegetation scientists have become increasingly aware of the importance of other gradients influencing regional vegetation patterns, particularly soil chemistry. To explore vegetation-environment relationships across the region, we took advantage of the large database of southern Appalachian vegetation and environment compiled by the Carolina Vegetation Survey. We selected observations from 3,032 plots representing 85 forest, woodland, and shrubland associations of the National Vegetation Classification. We included in our analysis associations occurring in the mountains of North and South Carolina, although we also included plots from other states falling within these associations.

Results/Conclusions Principal components analysis of environmental data identified soil fertility as the first component, accounting for 45% of total variation. The second component (22% of total variation) was associated with elevation, and the third component (10% of total variation) was associated with a simple index of topographic moisture. This analysis underscores the substantial variation in soil fertility across the region, reflecting variation in bedrock chemistry, and the need to recognize this important environmental gradient as we interpret vegetation patterns in the southern Appalachians. As anticipated, elevation and its correlates (increasing organic matter, cation exchange capacity, and slope) represent a second major suite of environmental variables. Variation in aspect, affecting topographic moisture through differences in interception of solar irradiation, is a third important direction of environmental variation independent of the others. We discuss trends in compositional variation and community properties related to these principal gradients of physical environment in the southern Appalachian Mountains.