The importance of substrate type, shading and scorching for the attractiveness of dead wood to saproxylic beetles

Modern forestry management has reduced the amount of dead wood in forest ecosystems and this has become a serious threat to flora and fauna. Efforts are therefore being made to reverse this trend but one problem is that we still lack detailed knowledge regarding the substrate requirements of many saproxylic species. In a field experiment, conducted in three forest types (forest reserve, mature managed forest and clear-cut), we evaluated the value, from a conservation perspective, of different substrate types (logs, snags and tops) of Norway Spruce, Picea abies, and if the quality of spruce logs as saproxylic habitats can be improved by simple log treatments (scorching and shading). We collected 9982 individuals representing 262 saproxylic beetle species in window traps. Both substrate type and, to a lesser extent, log treatment had a significant effect on the abundance and species richness of saproxylic beetles attracted to the different dead wood substrates. However, more importantly, the composition of the beetle assemblages differed significantly between both substrates and log treatments. Snags, logs and tops all attracted significantly different beetle assemblages and scorched logs differed from untreated control logs. Sixteen red listed species were trapped, with the highest number (11 species) being found on scorched logs. We found strong evidence that some species preferred a specific substrate type, mainly logs, in some cases treated logs (scorched or shaded), but not snags, the substrate commonly provided for conservation purposes on e.g. clear-cuts. This stresses the importance of conducting forestry in such a way that a multitude of both forest habitats and dead wood substrates are available continuously in the forest landscape to maintain biodiversity.     

Saproxylic beetles in artificially created high-stumps of spruce and birch within and outside hotspot areas

Artificially created high-stumps (snags) are created regularly during forest felling operations in Swedish coniferous production forests. The saproxylic beetle fauna in high-stumps of spruce and birch, on 20 clearcuts in Southern Sweden, were sampled by bark sieving. Ten of the clearcuts were located in hotspot areas with documented occurrence of many red-listed saproxylic beetle species. The other ten clearcuts were located in a typical production forest landscape (i.e. the matrix). Our aim was to investigate whether the benefit of creating high-stumps differs if the clearcuts is located in a hotspot area or in the matrix. In total 4,179 saproxylic beetles were found, belonging to 66 species, 9 of which were red-listed. Birch high-stumps hosted more species, on average, than spruce high-stumps. In an ordination analysis, tree species had the strongest explanatory effect among the environmental variables. No difference in beetle fauna could be found between the hotspot and matrix clearcuts, for neither birch nor spruce, according to all parameters: species numbers, species composition and red-listed species. The study does not indicate that conservation efforts in coniferous production forests should be concentrated to hotspot areas.