Epsilon Open Archive

Abstract

In Fennoscandia, most of the forests have been under production management since the 19th or 20th century, which has resulted in decreasing amounts of dead wood (coarse woody debris, cwd). Populations of many saproxylic (wood–dependent)species have declined because of the reduction of cwd. Forestry is currently trying to increase cwd amounts on clearcuts by green–tree retention. As a result of increased mortality of retained trees this can be expected to enhance cwd amounts on clearcuts. This thesis evaluates whether this practice increases diversity of saproxylic beetles inhabiting aspen. One study compares the habitat availability of aspen–associated beetles (beetles preferring aspen cwd over cwd from other tree species) in clearcuts and forests. A second study focuses on how occupancy (proportion of occupied habitat patches) and density of aspen–associated beetles is influenced by habitat patch size and habitat connectivity. A third study evaluates the contribution aspen cwd on clearcuts makes to total beetle diversity. The results demonstrate that retention of living aspen at clearcutting favours aspen–associated species. Increased tree mortality of retained trees generates more cwd on clearcuts compared with in forests. Thus, a significant part of the beetle populations can be expected to occur on clearcuts. The spatial distribution of the cwd influenced beetle occurrence. Both occupancy and density of aspen–associated beetles was generally higher in larger than in smaller habitat patches. Thus, priority should be given to retain large patches of living and dead aspen. A majority (93 %) of the saproxylic beetle species recorded from aspen cwd in this study was not aspen–associated, i.e. they prefer other tree species than aspen. Also when considering all of these species, clearcuts provide a valuable contribution for maintaining the biodiversity in managed forest landscapes. Species richness was as high in clearcut as in forest sites. In addition, species composition differed between the two stand types which mean that they to some extent are complimentary. The thesis also includes two methodological studies. In one study the efficiency of three different beetle sampling methods (bark sieving, emergence trapping and window trapping) were compared. In another study the aim was to find an efficient odour bait for sampling of flying saproxylic aspen–associated beetles.