Tree‐base microsites contribute to physical heterogeneity and herb community structure in a temperate deciduous forest

Abstract

AbstractQuestionFine‐scale environmental heterogeneity supports floristic diversity in forest ecosystems by increasing the variety of niches available for specialist species. Although recognized in concept, the niche function of microsites has not been well documented. This study tests whether microsites at the base of large trees are physically or edaphically distinct from the forest floor in general, and whether forest herb composition responds to this form of heterogeneity.LocationLong‐established deciduous forest in the unglaciated section of southeastern Ohio, USA.MethodsWe measured fourteen herb‐relevant environmental variables and censused the herb flora at the bases of large trees and in control plots away from trees.ResultsMoss cover, exposed root cover, and canopy openness were significantly greater at large‐tree bases than in control plots, while leaf litter cover was significantly lower at tree bases. Species richness and stem density were higher in tree‐base plots, and multivariate species composition differed significantly between tree bases and controls. Two species, Eurybia divaricata and Cardamine douglassii, were significantly more abundant at tree bases. Gradients of litter cover and root exposure accounted for the compositional difference between tree bases and controls. Coarse woody debris, moss cover, and soil root fraction accounted for differences orthogonal to the tree‐base/control axis indicating heterogeneity within tree‐base microsites.ConclusionsTree bases are physically distinct microsites which support diversity by providing niches to some forest herb species. Because availability of such microsites is linked to tree size, this aspect of community diversity appears to be controlled by stand development.