Conserving woodland butterflies in managed forests: Both local and landscape factors matter

Abstract

The conservation of forest biodiversity is increasingly relying on forest landscapes managed for timber production. A precondition for successful biodiversity conservation in intensively managed landscapes is a good understanding of habitat- and landscape-level drivers of species diversity. In this study, we investigated the effects of habitat characteristics and landscape context on the species richness and composition of butterflies in temperate forest landscapes routinely managed by clear-cutting. Our focus was on forest-dependent species. Even though about a quarter of the entire butterfly fauna in Europe are associated with forest habitats, the drivers of their diversity are poorly known. We used data from an unprecedentedly extensive butterfly survey, conducted in more than 400 sites distributed across all major forest types in Estonia (Northern Europe). Our data indicate that, generally, forests harvested for timber production remain suitable as habitats for forest butterflies: across the study sites, we recorded almost the full complement of their total regional species richness. By far the most influential driver of local butterfly species richness in such forests appears to be the proportion of forest cover in the surrounding landscape. The species richness of forest butterflies starts to show signs of decline at remarkably high levels of forest cover in the landscape. Surprisingly, landscape-scale forest heterogeneity around study sites had no discernible effect on local species richness, the pattern plausibly resulting from low mobility of forest butterflies. The most important habitat-scale predictor of butterfly species richness was soil moisture, with butterfly communities being most species-rich in forests on soils of intermediate moisture. Different forest types contribute to the regional species pool of forest butterflies in a complementary manner. No single forest type alone provides habitat for the entire species pool: peaks of abundance of different species are distributed across multiple forest types. Accordingly, a substantial part of the variation in species assemblages could be attributed to characteristic soil conditions (moisture and pH) of different forest types. Our findings imply that both the extent and heterogeneity of forest landscapes are important for maintaining the diversity of forest butterflies at the landscape scale.