Negative effects of forest edges and canopy opening on moth communities

Forest loss and fragmentation are major threats to biodiversity and associated ecosystem services worldwide. Forest fragmentation leads to the creation of forest edges, which experience contrasting environmental conditions compared to forest interiors, inducing a strong change in biological communities. In addition, forest management interventions, such as thinning influence canopy opening, microclimate and strongly alter the structural environment of vegetation. Moths are a species-rich and functionally important taxonomic group because of their role in plant pollination and as bulk food for other species. Here we studied the effects of canopy structure and edge-to-interior gradients on macro-moth communities using light traps in Belgium and northern France. We found that forest edges had lower abundance of moths (a modeled reduction of 46 %) and lower species richness (-29 %) than forest interiors. Open stands had an overall lower abundance of moths compared to more closed stands (-17 %). Moreover, the interaction between forest structure and edge effect was significant, indicating stronger reductions of moth abundance towards the edge in open forest (-57 % vs −37 % in dense forest). Both local environmental variables and landscape variables explained the observed patterns, e.g., nighttime temperature of the plot and forest cover in the surrounding landscape both had a positive effect on moth activity density and species richness. We found limited evidence that moth species traits explained the observed edge-to-interior disparities, although species with larvae feeding on shrubs and trees tended to be more associated with forest cores than grass and herb feeders. Our results indicate the importance of functional forest interior habitat and relatively undisturbed forests with a high structural complexity for moth conservation.