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

The current interest among resource managers in ecosystem management n ecessitates a better understanding of the response of plant species di versity 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 fol lowing clearcutting) and two ''mature'' (>70 yr following selective cu tting) watersheds. Sampling was confined to the herbaceous layer (vasc ular 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 i mportant tree species occurred on all watersheds, but the relative imp ortance of these species varied greatly with stand age. Less shade-tol erant species, such as black cherry (Prunus serotina) and tulip poplar (Liriodendron tulipifera), are replaced by more-tolerant species, suc h as northern red oak (Quercus rubra) and sugar maple (Acer saccharum) , as the stand matures. Analysis of tree species richness per plot sug gests 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 stri ped maple (A. pensylvanicum), and several fern species. In sharp contr ast with the trees, these species appeared to vary little with stand a ge. Species diversity (H') did not vary with stand age for either the overstory or the herbaceous layer. Detrended correspondence analysis s howed a significant correlation between species composition of the two strata for the mature watersheds, but not the young, clear-cut waters heds. Thus, we suggest a temporal shift in processes influencing speci es composition following disturbance from allogenic factors (e.g., soi l characteristics) to autogenic factors (e.g., stand characteristics), which lead to a linkage between forest strata later in succession. Th e degree to which forest management alters species composition in thes e central Appalachian forest ecosystems may be tied to the degree of a lteration of the link between strata.