Ecologically sustainable retention forestry supports spider biodiversity in the Lower Morava UNESCO Biosphere Reserve

Floodplain forests are among the most endangered ecosystems worldwide, even though they are hotspots for numerous taxa. The abandonment of traditional management and large‐scale timber extraction, such as clear‐cutting, has led to a decline in floodplain forest biodiversity. Retention forestry has the potential to facilitate the implementation of an ecologically sustainable forest management approach. Despite the increasing popularity of this method, its potential for spider diversity conservation, especially its comparison with the widespread practice of clear‐cutting, is still poorly studied. We studied the short‐term effect of forestry treatments (dispersed retention with 60% retained trees and clear‐cutting) on the diversity of ground‐dwelling spiders in the floodplain forests along the Lower Morava (March) and Dyje (Thaya) rivers in the Czech Republic. Spiders were sampled using pitfall traps during 2021 (pre‐harvest year) and 2022 (post‐harvest year). A total of 10,005 specimens from 167 species were recorded. Both forestry treatments simplified habitat structure compared with pre‐harvest conditions, resulting in lower beta‐diversity within sites. However, dispersed retention had higher alpha‐ and beta‐diversity than clear‐cuts, indicating that retention provided a more complex‐structured habitat. Dispersed retention and clear‐cuts hosted distinct spider assemblages with characteristic indicator species. Species typical of open and significantly disturbed habitats preferred clear‐cuts, while species typical of forests and (semi‐) open habitats, including threatened species, showed a preference for dispersed retention. Our results demonstrated, for the first time, that dispersed retention forestry could serve as an effective management tool for conserving the ground‐dwelling assemblages of spiders in floodplain forests.