Vegetative Structure of an Appalachian Oak Forest in Southwestern Virginia

Abstract

Structural parameters were used to assess differences among major vegeta- tion types in an Appalachian oak forest in southwestern Virginia. Cluster analysis re- sulted in ordering stands along a moisture gradient determined from site topographic features. Position along the moisture gradient from mesic to xeric was reflected in a number of vegetative structural variables. For the overstory these included decreased canopy coverage, decreased stand height and decreased stem basal area. Trends in the shrub stratum (l-5m) tended to be the reverse of those in the overstory. The results indicate that vegetative structure is strongly influenced by site relationships reflecting differences in moisture regime. A number of investigators have demonstrated the importance of stand structure to analysis of forest ecosystems. Horn (1971, 1975) examined the relationship be- tween structural development and succession. Whittaker (1956), Mowbray and Oosting (1968) and Whittaker and Woodwell (1969) noted structural and com- positional changes in vegetation along a moisture gradient. Whittaker (1966) demonstrated a relationship between stand structure and forest production in the Great Smoky Mountains of Tennessee. MacArthur and MacArthur (1961), James and Shugart (1970) and Morse (1976) described the importance of vegetation structure in defining certain niche requirements of bird species. The present study attempts to add to existing knowledge of forest ecosystems by structural analysis of major vegetation types in the Appalachian Oak Forest Region of southwestern Virginia. A cluster analysis of vegetative structural attributes is employed to determine interstand distances associated with a topographically de- rived moisture gradient. The relationship between the vertical stratification of foliage in forest stands and the more traditional measures of stand structure is evaluated. Methods Nine sample areas were selected on the SE slope of Potts Mountain in Craig Co., Virginia, to represent a large area of forested land in the Ridge and Valley Province. The areas are noncontiguous and extend across 5.2 km of midslope at approximately 730 m elevation. Slopes vary from 8-45%, while aspect varies from E to SW. Soils are derived mainly from ortho-quartzite sandstone with some interbedded shale outcroppings. Sites range from dry to infertile on main slopes and spur ridges to relatively fertile and mesic in coves. According to Braun (1950), the site falls within the Ridge and Valley Section