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 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.