Forest Vegetation and Boulder Streams in the Central Appalachian Valley and Ridge Province, Southwestern Virginia

Abstract

MILLS, H. H. (Department of Earth Sciences, Tennessee Technological University, Cookeville, TN 38505) AND S. L. STEPHENSON (Department of Biology, Fairmont State College, Fairmont, WV 26554). Forest vegetation and boulder streams in the central Appalachian Valley and Ridge province, southwestern Virginia. J. Torrey Bot. Soc. 126:188-196. 1999.-The pattern and structure of forest vegetation in small boulder-floored streamless hollows vary as a function of the type of surficial deposit and topographic position on a scale of tens of meters. Data collected for a 50 m long belt transect across a 20 m wide boulder stream showed that tree species characteristic of mesic sites were most abundant near the center of the boulder stream. In addition, the lowest values of absolute tree den$ity were recorded near the center. Some tree species were found to display noticeable differences in distribution. For example, black birch was much more abundant on the boulder stream than along its margins, whereas chestnut oak, although abundant at the margins, rarely occurred on the stream. Because boulder size reached a maximum in the lowest part of the hollow cross section (i.e., the center), it was not possible to decide whether the main effect was the nature of the substrate or the topographic position (i.e., higher levels of moisture in the lower part of the cross section and lower levels of moisture in the higher parts). To distinguish these effects, a second transect was established across one side of a much wider boulder stream that showed large lateral variation in boulder size. Data collected for this transect showed that for several tree species the main factor affecting distribution was topographic position (i.e., near to or distant from the lowest part of the hollow cross section). However, black birch showed an affinity for areas underlain by large boulders, regardless of their topographic position.