The role of canopy tree diversity on understory plant richness and tree seedling abundance in a Pinus strobus forest in the southeastern U.S.

Abstract

The goal of my project was to determine whether diversity in the canopy layer of a Pinus strobus dominated, mixed mesic forest in the piedmont of North Carolina showed a relationship to 1) understory richness and 2) tree seedling abundance. Forty plots were randomly selected at White Pines Nature Preserve, in Sanford, North Carolina for the study. For each plot, understory, species and tree seedling richness and density were recorded. Explanatory variables included canopy tree species richness, density and cover, total diameter at breast height (dbh) and environmental data including soil type, distance to nearest trail, and elevation. Diversity was calculated using the Simpson Index of Diversity (1-D) to show the effect of dominance in the canopy. Understory richness showed a decreasing pattern with increasing canopy diversity (p= 0.0783), suggesting a negative effect of canopy diversity on understory richness. Likewise, tree seedling abundance showed a significant negative response to canopy richness (p= 0.0146) and to all soils types (both positive and negative response). Total canopy tree basal area (diameter of tree at breast height) showed a positive relationship (p= 0.0514) to canopy species diversity (with functional similarity), which supports research showing complementarity between functionally-similar canopy tree species. Overall, results for this study suggest that, in a historically Pinus strobus-dominated forest, although greater canopy tree basal area is related to higher canopy diversity, understory richness is negatively affected by higher canopy diversity, and tree seedling abundance is negatively affected by higher canopy species richness.