Edges effects on seed predation by rodents in deciduous forests of northern Switzerland

Seed predation by rodents affects plant population dynamics and it may respond to changes in vegetation structure at forest edges. This study investigates the magnitude and direction of a potential edge effect in temperate deciduous forests, and it seeks possible explanations based on predator abundance and vegetation structure. The study was conducted at twelve forest edges in northern Switzerland; in six sites all shrubs at the forest edge were removed, whereas the other sites maintained a structurally rich shrub layer. In each site three transects were laid out from the edge towards the forest interior. In six plots along these transects (at 1, 3, 6, 12, 25, 50 m) we studied seed removal from experimental dishes, rodent abundance in live-traps and four characteristics of the vegetation structure. For both woody seed species (Prunus avium, Viburnum lantana) predation was significantly higher near the forest edge in the structurally rich sites; in the other sites no such gradient was found. Selectively accessible dishes revealed that rodents were the main predators, whereas predation by insects or molluscs was not observed. Abundance of rodents (Apodemus flavicollis, A. sylvaticus, Clethrionomys glareolus) was highest under dense shrubs close to the forest edge. In the structurally rich sites there was a clear gradient of decreasing shrub cover from the edge towards the forest interior; a weaker gradient was observed in the structurally poor sites. We conclude that high shrub cover near the forest edge is the main determinant for edge effects in seed predation, and edges without a shrub belt show no such effect.