The indicator side of tree microhabitats: a multi-taxon approach based on bats, birds and saproxylic beetles

1. National and international forest biodiversity assessments largely rely on indirect indicators, based on elements of forest structure that are used as surrogates for species diversity. These proxies are reputedly easier and cheaper to assess than biodiversity. Tree microhabitats – tree-borne singularities such as cavities, conks of fungi or bark characteristics – have gained attention as potential forest biodiversity indicators. However, as with most biodiversity indicators, there is a lack of scientific evidence documenting their quantitative link with the biodiversity they are supposed to assess.
2. We explored the link between microhabitat indices and the richness and abundance of three taxonomic groups: bats, birds, and saproxylic beetles. Using a nation-wide multi-taxon sampling design in France, we compared 213 plots located inside and outside strict forest reserves. We hypothesized that the positive effect setting aside forest reserves has on biodiversity conservation is indi...