Threatened saproxylic beetle species in tree hollows react more sensitively to surrounding landscape composition in central European managed forests than total species richness

Abstract

1. Veteran deciduous trees are a rare element in today’s central European managed forests due to intensive forest management over the last 200 years, resulting in a loss of dead wood habitats like tree hollows. Saproxylic beetle species depend on dead wood, and habitat specialists, such as species relying on tree hollows, are largely threatened. 2. To better understand how to protect saproxylic beetle assemblages in tree hollows at a landscape scale we collected beetles from tree hollows in three forest regions in Bavaria using emergence traps. We related landscape composition at spatial scales of 300–5000 m around the tree hollows to beetle diversity in the hollows using CORINE satellite data. We also modelled four dispersal-associated morphological traits as well as functional diversity indices of the beetles in relation to landscape composition. 3. The proportion of deciduous forest surrounding the tree hollows had positive effects on species richness of saproxylic beetles in two of the three study regions. Positive effects on threatened species were more pronounced than effects on total species richness at all spatial scales. Relationships between functional diversity and landscape composition only partly confirmed our expectations regarding better dispersal ability of beetles in isolated habitat patches. 4. Our study indicates that threatened saproxylic beetles react more sensitively to landscape compositional changes than common species. In the light of ongoing habitat fragmentation, efforts to protect threatened saproxylic beetle species should not only include single forest stands but focus on a landscape scale and support connectivity of forest patches.