Oak decline: pest outbreak threat or opportunity for saproxylic beetles? A case study from the Czech Republic

Abstract Commercially managed forests are often poor in terms of biodiversity. Saproxylic beetle species could be a useful bioindicating group for the conservation of forest stands. In recent decades, oak stands have been affected by a wide range of factors that have intensified stand decline. Saproxylic beetle richness was investigated in declining oak stands that have been consequently targeted for clearcutting due to concerns about insect pest outbreaks. The research was conducted at six managed oak forests, where we compared beetle occurrences in declining stands and in healthy stands that did not show any symptoms of decline. Beetles were collected using window traps placed on the basal and mid-trunk sections of trees. A total of 2925 adults belonging to 239 saproxylic beetle species were captured, of which 56 species are on the IUCN Red List. The results show that declining stands were richer in saproxylic species, and that the diversity of beetle species was greater in these stands. Approximately 1.4 times more species were caught within declining stands than in healthy ones (1.6 times for Red List species). Declining stands hosted more pest species (e.g., cambiophagous and xylophagous species). However, only low numbers of these species were recorded in these stands. In summary, results of this study suggest that decline of managed oak stands is creating a wide spectrum of habitats for many saproxylic species. Thus, salvage logging of declining oak trees can represent a natural trap and reduce local beetle biodiversity, mainly for saproxylic, endangered or low-mobility species that would be attracted by new suitable habitats.