Linking forest edge structure to edge function: mediation of herbivore damage

1 Forest edges, which are prominent features in the north-eastern United St ates landscape, may control the flux of organisms between forest and non-fo rest habitats. Previous studies have described edge structure rather than f unction, as determined by interaction with such fluxes. 2 The function of the forest edge may be linked to the structure of its veg etation. We tested this hypothesis by experimentally altering the structure of the vegetation at two deciduous forest edges in Millbrook, New York, US A. Intact and thinned plots were established at each edge and we determined whether the structure of the edges influenced the flux of herbivores, as m easured by herbivore damage to transplanted tree seedlings. 3 Herbivore damage to seedlings at site 1 was affected by edge vegetation s tructure and by distance from the edge. The edge structure effect was due t o herbivory by voles, which was significantly greater in the intact than in the thinned treatment. Regardless of treatment, voles damaged seedlings on ly on the edge and 30-40 m from the edge and did no damage in the forest in terior (90-100 m), whereas deer damaged significantly more seedlings in the forest interior than on the edge. At site 2, where vole damage was concent rated on the edge, damage to seedlings was affected only by distance from t he edge, not edge structure. 4 The two dominant herbivores, white-tailed deer and meadow voles, preferen tially damaged different seedling species. In addition, tree seedlings brow sed by deer resprouted more frequently than those clipped by voles. Our res ults suggest that both edge structure and distance from the edge influence herbivore activity and, as a result, influence the spatial arrangement, den sity and composition of populations of tree seedlings during regeneration i n forest fragments.