An Assessment of Canopy Stratification and Tree Species Diversity Following Clearcutting in Central Appalachian Hardwoods

Abstract

On high quality growing sites in West Virginia, shade intolerant tree species have increased in importance in third-generation forests following clearcutting. We investigated the effect of tree species canopy position on the Shannon-Weiner Diversity Index (H), Pielou's evenness index (E), and species richness (S) using a chronosequence of 13 clearcuts. Two to 26 yr after clearcutting, tree species diversity significantly decreased from 2.07 to 1.83, and evenness decreased from 0.80 to 0.71 while species richness was maintained. As the number of years since harvesting increased, the importance value of oaks (Quercus L.), hickories (Carya Nutt.), American beech (Fagus grandifolia Ehrh.), sugar maple (Acersaccha-rum Marsh.), and black birch (Betula lenta L.) decreased whilethe importance of yellow-poplar (Liriodendron tulipifera L) increased. In these mixed-species stands with stratified canopies, species importance in overstory versus understory canopy layers was the best indicator of competitive success during stem exclusion. Second-generation forests that had almost equal representation of overstory sugar maple and yellow-poplar prior to harvesting had 43% yellow-poplar and 13% sugar maple overstory importance 22-26 yr after harvest. Forty-five percent of the dominant crown class stems and 54% of the codominant class were yellow-poplar. While sugar maple was also an important (13%) overstory species overall, it had no dominant and few codominant stems and over 30% importance as overtopped trees and in the understory. As these stands progress through the stem exclusion stage, richness and measures of diversity may continue declining as yellow-poplar basal area increases.