Pruning for biodiversity: Drivers of cavity formation and use in Mediterranean holm oak woodlands

Abstract A critical aspect of effective forest policies is the promotion of tree‐related microhabitats, such as tree cavities, which serve as keystone structures for biodiversity. However, our understanding of the factors driving cavity formation and their use by vertebrates remains limited, particularly in holm oak Quercus ilex woodlands, which cover large areas of the Mediterranean region. We examined 22 holm oak stands that varied widely in experienced pruning intensity and tree age within two national parks in central Spain. We also recorded likely cavity origin, position (whether on a branch or on the trunk), volume and use by vertebrates. We found that pruning is the primary trigger of cavity initiation. However, cavity development from pruning wounds was uncommon, and the transition to a cavity suitable for a vertebrate occurred slowly. The relationship between pruning intensity and cavity occurrence was steeper in small trees than in large ones. In addition, trunk width was more strongly related to cavity volume in trunk cavities than in branch cavities, leading to a wider range of cavity sizes in large trees. Vertebrate occupancy was low, and cavity volume was the primary predictor of cavity use. Synthesis and applications . Our study emphasizes the role of both tree and cavity age in the long‐term establishment of cavity‐dependent vertebrates in holm oak woodlands. In the context of climate change—where holm oak trees are expected to replace more mesic, soft‐wooded tree species in the Mediterranean region—the persistence of cavity‐dependent vertebrate biodiversity will rely on the formation of cavities through appropriate pruning management, which creates the structural conditions necessary for cavity development.