The positive effects of canopy openness across post-disturbance management on insect diversity

Kurzfassung

Forests across Europe are experiencing higher rates of tree mortality while many insect populations are declining, but the links between these two ecological changes are not well understood. While pulses of tree mortality from natural disturbances can enhance structural complexity through canopy openings and deadwood accumulation - both key elements for high value insect habitats - post-disturbance tree removal may reduce habitat quality. We systematically investigated the impact of natural disturbances and post-disturbance logging on total insect diversity across major European forest types, comparing triplets of undisturbed, disturbed, and cleared forest patches. Using metabarcoding and a newly developed phylogeny, we quantified taxonomic and phylogenetic diversity (standardized by sample coverage along Hill numbers) for 21,218 insect OTUs from 347 families and 19 orders. Disturbances and post-disturbance clearing increased taxonomic diversity by up to 12 % in disturbed and 26 % in cleared patches compared to undisturbed patches. However, phylogenetic diversity increased only for rare species. Spaceborne data identified canopy openness as the primary driver of this increase, but responses varied by feeding guilds, with parasitoids and fungivores showing the strongest diversity increase. Overall, our findings show that current post-disturbance logging of small-scale disturbances in Central Europe amplifies canopy openings created by natural disturbances. This leads to a positive response of insect diversity shortly after disturbance, yet effects vary among feeding guilds and phylogenetic lineages. Our combination of innovative spaceborne and metabarcoding information provides new insights into the complex impacts of increasing tree mortality on insect diversity in Central European forests.