Effects of harvest intensity and aspect on a boreal transition tolerant hardwood forest. I. Initial postharvest understory composition

Disturbance effects on plant communities largely reflect the degree of overstory removal, soil disturbance, and attendant vegetation destruction. We examined initial harvest-related impacts of partial and complete canopy removal, with and without soil disturbance, on north- and south-facing aspects of an older, relatively undisturbed, boreal transition tolerant hardwood forest at Turkey Lakes, Ontario. We recorded vascular plant cover in 180 25 m(2) plots in the 3rd postharvest year and analyzed community response using unconstrained (nonmetric multidimensional scaling) and constrained (distance-based (partial) redundancy analysis) ordination, multivariate ANOVA, indicator species analysis and diversity measures. Community composition and diversity measures were related primarily to gradients in soil disturbance and, particularly for herbaceous species, aspect-related radiative exposure. Canopy opening generally played a lesser role. There were, however, notable canopy opening - soil disturbance x aspect interaction effects on both woody and herbaceous composition. In contrast with herbs, proportionately more woody species had indicator value for south- than for north-facing aspects and for disturbed than for undisturbed soils. Understory community response and diversity measures were affected more by logging-related soil disturbance than by the amount of canopy opening associated with the silvicultural system used. Aspect-related effects, however, suggest silvicultural impacts will be both site- and species (functional group) specific.