Eupatorium rugosum (Asteraceae) flowering as an indicator of edge effect from clearcutting in mixed-mesophytic forest

Abstract

We analyzed flowering of white snakeroot ( Eupatorium rugosum) as an indicator of edge effect from recent silvicultural clearcutting in mixed-mesophytic forest in northcentral West Virginia. Edge effect estimated by a common, widespread, easily identified perennial herb could permit an estimate of the spatial extent of edge habitat for other understory plant species, an important consideration in forest ecosystem management. The study had two objectives: (1) to analyze flower production and reproductive stem density across existing south- and west-facing edges of similar age and forest type; and (2) to analyze flower production under controlled shading conditions designed to simulate the light environment across the forest edge. The effect of distance from clearcuts and edge aspect on flower production was examined using a two-way factorial model I analysis of variance. Flower biomass did not differ between aspects but decreased significantly with distance, indicating an effect of clearcutting on flower production in adjacent edges. Using regression, independent analyses of the number of flower heads per stem and reproductive stem density were found to decline significantly over distance from clearcuts. Slopes and y-intercepts were similar within and between south- and west-facing edges, indicating a consistent flowering response to adjacent clearcuts. In a greenhouse experiment analyzed as a Latin Square analysis of variance, flower biomass per individual did not differ between no shade ‘clearcut’ and intermediate shade ‘intermediate edge’, but flower biomass in heavy shade ‘far edge’ was significantly different from both of these treatments and in general support of the dramatic decline in flower production beyond 30 m from clearcuts. Consistency in flower production under controlled shading and consistency in flower production as a function of distance from clearcuts demonstrates that white snakeroot is a sensitive, consistent indicator of edge effect. These characteristics, in combination with the species’ widespread distribution, suggest that white snakeroot flowering might prove useful as a phytometer to assay edge effects in mixed-mesophytic forests from even-aged timber harvests, forest road corridors, wildlife openings, or other activities that create large openings in the forest canopy. This idea should be tested in these and similar types of edge environments, as well as in other eastern deciduous forest types where white snakeroot is an abundant component of the herbaceous flora.