HERBACEOUS-LAYER AND OVERSTORY SPECIES IN CLEAR-CUT AND MATURE CENTRAL APPALACHIAN HARDWOOD FORESTS

The current interest among resource managers in ecosystem management necessitates a better understanding of the response of plant species diversity to forest management practices. This study attempted to assess the effects of one forest management practice-clear-cutting-on plant biodiversity in a mid-Appalachian hardwood forest by comparing species composition and diversity between two young (approximate to 20 yr following clearcutting) and two ''mature'' (>70 yr following selective cutting) watersheds. Sampling was confined to the herbaceous layer (vascular plants less than or equal to 1-m in height) and woody overstory (stems greater than or equal to 2.5 cm diameter at 1.5-m height). The important tree species occurred on all watersheds, but the relative importance of these species varied greatly with stand age. Less shade-tolerant species, such as black cherry (Prunus serotina) and tulip poplar (Liriodendron tulipifera), are replaced by more-tolerant species, such as northern red oak (Quercus rubra) and sugar maple (Acer saccharum), as the stand matures. Analysis of tree species richness per plot suggests that the competitive thinning process decreases species evenness as the stand develops. Important herb-layer species included stinging nettle (Laportea canadensis), violets (Viola spp.), seedlings of striped maple (A. pensylvanicum), and several fern species. In sharp contrast with the trees, these species appeared to vary little with stand age. Species diversity (H') did not vary with stand age for either the overstory or the herbaceous layer. Detrended correspondence analysis showed a significant correlation between species composition of the two strata for the mature watersheds, but not the young, clear-cut watersheds. Thus, we suggest a temporal shift in processes influencing species composition following disturbance from allogenic factors (e.g., soil characteristics) to autogenic factors (e.g., stand characteristics), which lead to a linkage between forest strata later in succession. The degree to which forest management alters species composition in these central Appalachian forest ecosystems may be tied to the degree of alteration of the link between strata.