Global impacts of edge effects on species richness

Abstract

Almost all world's forest areas are predicted to be near edges by 2100, making the detection and prediction of biodiversity responses to edges an urgent need. Yet, idiosyncratic observations across studies have hampered general inferences on the main drivers of edge effects. We provide a global meta-analysis on 674 forest edge-interior comparisons of plant and animal communities, considering both global and local drivers as well as their interactions, to predict the direction and magnitude of edge effects on species richness. We found a clear latitudinal gradient in both the direction and magnitude of edge effects, with edges in temperate regions having more species than interior forests, while tropical communities generally had fewer species at edges. Unexpectedly, communities near high-contrast edges had higher richness at edges more frequently than near low-contrast edges. In addition, richness decreases at edges were weaker in regions subjected to historical disturbance than regions without historical disturbance. These patterns were modulated by distance from the edge and became clearer when comparing more distant sampling locations. Our results provide possible explanations for the variable impacts of edge effects and thereby forest fragmentation on biodiversity, showing that a combination of local and global predictors are able to partially predict variation in edge effects.