Community composition in relation to substrate, elevation, and topography in the Salt Pond Mountain area in Giles County, Virginia

Vegetation-environment relationships in the Salt Pond Mountain area of western Virginia were analyzed with techniques of indirect gradient analysis. Quantitative data on the composition of the tree, sapling, seedling, shrub, and herb strata were collected from 25 forest stands. Environmental variables measured or determined at each site included elevation, aspect, slope inclination, underlying geological formation, and soil physical and chemical characteristics. In addition, exposure-induced differences in vegetation, soils, and microclimate were analyzed in two stands on adjacent north- and south-facing slopes. Measurements of microclimate were made at weekly intervals for one entire growing season.

Results of Bray-Curtis ordination indicate that environmental factors related to three major complex-gradients exert a controlling influence on the pattern of vegetation. Factors related to a moisture complex-gradient were considered to have the greatest influence on community composition, whereas factors related to elevation and soil parent materials seem to have a secondary effect. Measured environmental factors corresponded well with complex-gradients inferred from ordination analysis.

Composition gradients in the several strata of vegetation corresponded rather closely, although this was more apparent among strata of woody plants than between any of these and the herb stratum. This was interpreted as the result of generally similar responses of these strata to the major complex-gradients. There were no discernible relationships in species diversity and other community attributes among the various strata.

It was possible to classify the 25 stands into ten intergrading community types based on dominant trees. These community types were imperfectly segregated in the various ordinations. They tended to occupy particular environmental regimes along the three major complex-gradients.

Species other than dominants were distributed in an individualistic manner in relation to community types and complex-gradients. Distribution patterns were determined for 219 species of vascular plants, and several ecological groups were evident. Groups consisting of species with distributions clearly centered in xeric or mesic sites were most apparent. Quercus prinus, Sassafras albidum, and Vaccinium vacillans are the most important species of tree, sapling-seedling, and shrub on xeric sites, whereas Q. rubra, Acer pensylvanicum, and V. erythrocarpum are the most important species of these strata on mesic sites. Species with distributions centered in sites with soils derived largely from calcareous parent materials also form a relatively distinct group, with Acer saccharum and Taenidia integerrima its most conspicuous members.

The results of the present study are consistent with other published descriptions of the forest vegetation of western Virginia.