Habitat availability in forests and clearcuts for saproxylic beetles associated with aspen

To maintain biodiversity in managed, boreal forest in Scandinavia, aspen trees (Populus tremula) are often retained at clearcutting. In this study, the habitat availability for beetles associated with aspen coarse woody debris (CWD) was predicted for forests and clearcuts with a model of CWD dynamics. Habitat requirements of eight beetle species (Agathidium bicolor, Cerylon ferrugineum, Cyphaea curtula, Endomychus coccineus, Homalota plana, Mycetophagus fulvicollis, Ptilinus fuscus and Xylotrechus rusticus) were obtained from their occurrence patterns in relation to characteristics of CWD objects in forest and on clearcuts in a study landscape in central Sweden. Three species were more frequent in forest and three at clearcuts. Five species increased with increasing girth of the CWD. Three were more frequent on standing CWD, and two on lying CWD. From the same study area, we also obtained field data on the recruitment of CWD (i.e., tree mortality) and amounts of different types of CWD. Annual tree mortality of aspen was higher for recent clearcuts (6.3%) compared with older clearcuts (1.1%). For all species, the habitat availability was higher on clearcuts, because enhanced tree mortality increased the amount of recently dead CWD. As a conclusion, green-tree retention of aspen is a conservation effort that is beneficial for species associated with aspen CWD.