Why is the hermit beetle so rare in Central European managed forests? Habitat requirements of the forest population of Osmoderma barnabita

Abstract

In Europe, more than 95% of forests are managed and only 2.2% of forests are undisturbed by man. Therefore, appropriate forest management strategies are crucial to the survival of all forest-dwelling species. Among them are saproxylic beetles, one of the most sensitive to forest management organisms, often treated as important indicators of the degree of transformation of forest ecosystems. The object of our study was the hermit beetle Osmoderma barnabita, so-called primeval forest relict, used as an umbrella species for forest conservation in Central Europe. However, most studies of habitat preferences of this species have been conducted in anthropogenic habitats, and it is not known to what extent they correspond to the habitat requirements of forest populations. The aim of this research was to fill this knowledge gap, as well as to assess differences in characteristics of hollow trees preferred by the hermit beetle between managed and unmanaged forests. Our results indicate that five predictors affect the occurrence of O. barnabita in Central European forests: trunk diameter, tree health, number of entrance holes per tree, size of the entrance hole, and their height above ground, all having positive effect on its presence. The most important predictors were tree health, size of the entrance hole and their height above the ground, while trunk diameter was the least informative variable. Managed and unmanaged forests differed significantly in three out of five characteristics of hollow trees preferred by the species. Unmanaged forests had a greater share of trees with higher trunk diameter, larger hole entrances and poorer health. Therefore, the protection of the species should be based not only on the preservation of hollow trees, but also on maintaining their diversity, ensuring availability of optimal conditions for the local habitat.