Tree hollow parameters and their effects on saproxylic arthropod diversity : A multi-taxon approach

Tree hollows are keystone structures for biodiversity in forest ecosystems, promoting diverse saproxylic communities. However, intensive forest management in central Europe has made them rare. Consequently, saproxylic arthropods inhabiting tree hollows are among the most endangered invertebrates. Most studies on arthropod diversity in tree hollows have focused on beetles. 2. To understand this complex habitat, non-beetle arthropod groups and their habitat requirements must also be investigated. We collected arthropods emerging from 40 tree hollows in beech trees in 2014 and a subset of 23 in 2015 in a managed forest in southern Germany using emergence traps. DNA metabarcoding identified non-beetle arthropods, assessing the influence of tree hollow parameters and forest structure on α- and β-diversity of the most species-rich taxa. 3. Parameters influencing α- and β-diversity differed by year and taxa. The most important factors positively affecting α-diversity were tree hollow volume, tree circumference and entrance area/lateral surface, while entrance area and decomposition negatively affected α-diversity. Beta-diversity was influenced by tree circumference, tree hollow volume, entrance area and forest structure (dipterans: dead wood amount, spiders: nearby tree hollows). 4. These results highlight the importance of heterogeneous tree hollows and forest structures, emphasising the need for their conservation to support highly diverse saproxylic communities.