Ecologically similar saproxylic beetles depend on diversified deadwood resources: From habitat requirements to management implications

Abstract

Organisms dependent on dead wood (i.e., saproxylic) are some of the most threatened by changes in the forest environment. Aside from anthropogenic disturbances resulting in forest fragmentation and a decrease in dead wood, the expansion of homogenous closed-canopy forests due to successional changes is identified as the main threat for many saproxylic organisms. It is especially important in major conservation areas in Europe. Thus, studies combining knowledge about the habitat requirements of saproxylic species with the impacts of different types of forest management on populations of these organisms are essential to identify effective conservation strategies.In this study, we focused on three threatened saproxylic beetles with similar ecology, i.e., Cucujus cinnaberinus, C. haematodes and Boros schneideri, in a close-to-natural forest. The study was conducted in the stronghold of these species in temperate Europe, the Białowieża Forest in Poland, based on a field survey of more than 11,000 dead wood pieces. We investigated the habitat requirements of these species and their relationships with the environment at the tree and landscape levels. We further analysed the distribution of these beetles in forests under various levels of management intensity. Based on the results of the present study and published data on compositional changes in the forests in the study area, we attempt to formulate implications related to the conservation of the studied beetles.Cucujus cinnaberinus was the most widespread and frequent species, with a preference for high-diameter dead aspens in managed forests with high dead wood amounts. The second most abundant species, C. haematodes, preferred downed ashes and alders with rather fragmented bark. Its distribution was spatially aggregated in unmanaged forests. The rarest beetle in this study, B. schneideri, was associated with forests with large dead pines.Our results confirm the importance of the Białowieża Forest for the three threatened saproxylic beetles. The study also revealed the highly diversified demands of these beetles, which may not be met in the future if the abundance of the preferred habitat tree species is declining. We recommend a conservation strategy that combines non-intervention towards naturally developed deadwood with monitoring of tree recruitment and if necessary, measures to assure recruitment of particular tree species, e.g., pine and aspen. Future studies should investigate the role of natural disturbances for recruitment of these tree species and thus, the long-term persistence of associated saproxylic beetle species.