Unmanaged forest swamps benefit saproxylic and soil‐inhabiting crane fly communities

Abstract European forest wetlands have experienced long‐term declines due to drainage and other human disturbances. Despite their ecological importance, these habitats remain underrepresented in biodiversity assessments, and there is limited empirical evidence to guide effective conservation and rewetting efforts. In a paired design, we investigated how managed versus unmanaged forests affected saproxylic and soil‐inhabiting crane fly communities across three forest habitat types in Denmark: swamps, drainage ditches and dry patches. We collected 6842 crane fly specimens, representing 104 species, across 110 forest plots. Species richness was consistently higher in unmanaged forests, with significant positive effects observed for both saproxylic and soil‐inhabiting species across all habitat types. Soil‐inhabiting species richness was highest in swamps, intermediate in ditches and lowest in dry forest, but not for saproxylic species. Across habitats, saproxylic richness was positively associated with low light availability, and soil‐inhabiting richness with higher soil pH. Soil moisture generally had a positive influence on richness in both groups. Unmanaged swamps also supported distinct species assemblages, including several indicator species and habitat specialists. Our results highlight abandonment of forest management as a key strategy for enhancing biodiversity in temperate broadleaf forest swamps. Conservation efforts should prioritize restoring natural hydrology and protecting old‐growth swamp habitats, in combination with passive management approaches.