We examined herb-layer plant communities in three microsites in each of 28 treefall pit and mound complexes in 1988 and again in 1992 in an old-growth forest in northwest Pennsylvania. Plant communities differed significantly between microsites in both years. Mounds and areas of adjacent undisturbed soil had greater total cover, seedling density, and species richness than did pits. Species richness was negatively correlated with depth of litter, possibly explaining community differences among microsites.
Over the four years, herb-layer communities changed only slightly within the three microsites. While total plant cover decreased in the mounds, it increased in the pits and areas of undisturbed soil. Prunus serotina seedling density increased dramatically from 1988 to 1992, while that of other tree species changed only slightly. Percent cover of all other tree species except Fagus grandifolia remained relatively stable. Many of these changes were small relative to the 1988 mean, demonstrating that while a few species may fluctuate in abundance over time scales of several growing seasons, these plant communities appear to be comparatively stable assemblages.