Canopy openness as the main driver of aculeate Hymenoptera and saproxylic beetle diversity following natural disturbances and salvage logging

Abstract

Forests are increasingly affected by natural disturbances like fires, insect outbreaks, and windstorms. Such disturbances are commonly followed by salvage logging. Disturbance and salvage logging affect biodiversity by altering microclimate, habitat structure, and deadwood amount. To mitigate possible negative effects of salvage logging on biodiversity, ecologists often recommend the retention of disturbance-created structures. However, the mechanisms through which retained structures affect biodiversity remain largely unknown. We analysed 9,602 individuals of saproxylic beetles belonging to 268 species and 3,172 individuals of aculeate Hymenoptera belonging to 68 species of cavity-nesters and 126 species of non-cavity-nesters over two years in a wind-disturbed beech forests with various intensity of salvage logging. We quantified the relative importance of canopy openness and deadwood amount. Our final dataset consisted of 268 saproxylic beetle species and 194 species of aculeate Hymenoptera out of which 68 were cavity-nesters and 126 non cavity-nesters. Generalized linear mixed effect models showed the lowest number of Hymenoptera and beetle species in undisturbed forest. Permutational analysis of variance revealed that treatment and canopy openness drive community composition of both taxa. Increased canopy openness was the main factor positively affecting numbers of species of aculeate Hymenoptera and saproxylic beetles in the first two years after the disturbance. Deadwood amount only affected community composition of saproxylic beetles. However, gamma diversity and community composition of saproxylic beetles indicated that disturbed and extensively logged plots resembled disturbed unlogged plots rather than disturbed and intensively logged plots. Our findings suggest that at least some timber might be extracted from disturbed areas, without major losses of biodiversity of saproxylic beetles and aculeate Hymenoptera.