Response of saproxylic beetles to tree species composition in a secondary urban forest area

Urban secondary forest areas are still not in the focus of studies of forest biodiversity. Beetles (Coleoptera) are one of the key groups for assessing biodiversity. I studied beetle fauna and its response to tree species composition using flying interception traps placed on the trunks of dead and withered trees. This study was carried out in Landek, a forest area in an urban agglomeration of one of the largest central European cities, Ostrava (Czech Republic). My results show that species composition and richness and population densities of beetles in this urban forest area may be rather high. Beech (Fagus sylvatica), as the main tree species present, was more species rich and supported more individuals than admixed tree species (oak, hornbeam and ash). I obtained the same results for a group of obligate saproxylic beetles and two of their guilds (old and rotten dead wood, and wood-decaying fungi and mycelia). The beeches also maintained a higher diversity (or were close to being significantly different) than admixed tree species for several functional groups (fungivores, predators and phloeoxylophages), red-listed beetles and indicators, which prefer close-to-natural forests. Thus, beech trees as the main tree species seem to have the function of large habitat islands, which are more species rich than admixed tree species as smaller ones. The admixed tree species hosted fewer species with lower population densities. Forest managers are often confronted by the opinion that real nature cannot be found in cities. My results may be useful during their search for reasons to maintain biodiversity in urban forest areas.