Classifying patterns of understory vegetation in mixed-oak forests in two ecoregions of Pennsylvania

Understory plots in mixed-oak stands in the Ridge and Valley and Allegheny Plateau ecoregions of Pennsylvania were classified to summarize the range of understory conditions common to the region and to evaluate relationships between understory vegetation, overstory conditions, and advance tree regeneration. Factor analysis and cluster analysis were used to identify understory (lasses. Vegetation cover data including 15 variables (plant species, bare ground, and rocky ground cover) and 4 composite variables (plant species groups) were observed on 1,208 204-m(2) P lots. The eight vegetation classes resulting from the analyses were associated with different overstory compositions and advance regeneration densities. The understory classes identified in this study may provide insight on the distribution and diversity of problematic and nonproblematic vegetation types.