Forest Management and the Colonization of Artificial Tree Holes by Aquatic Insect Larvae

Human activities in forests lead to alteration or even destruction of habitats for numerous organisms, often resulting in a decline of biodiversity. Insects inhabiting water-filled tree holes may be especially sensitive to human impact as they require these microhabitats for at least part of their life cycle, with larvae mainly feeding on plant and animal debris accumulating in the water until they actively disperse in their adult stage. The processes leading to successful colonization of these microhabitats are not well understood, and it is unclear how forest management could influence them. We used sequential collection and recording of larval communities in artificial tree-hole analogues to study the process of colonization by aquatic tree-hole insects. We focused on the effects of parameters related to forest management as well as microhabitat properties on abundance, species richness, and community composition during colonization of artificial tree holes by aquatic tree-hole insects. We observed complex, and partly species-specific, temporal patterns of colonization of these new microhabitats. We found that the forest management intensity index ForMI, tree composition of forests as well as distance to natural water-filled tree holes and debris type were important in shaping community composition of insect larvae inhabiting tree holes across the entire colonization process. Larval abundance was negatively affected by increased distance to natural microhabitats and by changes in microclimate. Our results suggest that forest management significantly impacts microhabitat colonization dynamics of tree-hole insects, emphasizing the need for less-intensively managed forests to support natural tree-hole communities. We recommend the protection, creation, and maintenance of tree-related microhabitats, for example, through the promotion of habitat trees in managed forests, to sustain higher abundances of tree-hole inhabitants. Our findings underline the ecological value of water-filled tree holes and support their integration into forest conservation strategies as both essential habitats and valuable indicators of environmental change.