High-stumps and wood living beetles in the Swedish production forest landscape

摘要

The amount of dead wood in Swedish production forests is low compared to natural forests. This has resulted in a high proportion of red-listed and threatened wood living beetle species. Different actions are taken to increase the amount of dead wood and one such action is to artificially create high-stumps (snags), i.e. living trees cut between 3 and 5 meters height. This thesis focuses on whether high-stumps on clearcuts in southern Sweden increase beetle diversity. One study focus on whether a high-stump offers a different substrate compared to ordinary low-stumps. Another study investigates if beetle species are affected if the high-stumps are pre-rotten or not. Finally, the beetle species number and composition between high-stumps of spruce and birch in biodiversity hotspots and production forest (matrix), respectively. High-stumps have a somewhat different beetle species composition compared to low-stumps (normal cutting stumps), and several species were primarily associated with high-stumps. This justifies the making of high-stumps even though the amount of dead wood they add to a clearcut is low. The pre-rotten spruce high-stumps (infected by Heterobasidion spp.) had a negative effect on some beetle species and none of the analyzed species showed positive associations with Heterobasidion spp. This suggests that increasing the proportion of rotten spruce high-stumps could have a small but negative effect on beetle diversity. The number of beetle species did not differ between high-stumps on hotspot and matrix clearcuts, suggesting that concentrating high-stumps to hotspot areas will not benefit more beetle species. However, the amount of broadleaved forest in the surroundings of clearcuts was important for explaining species composition on high-stumps. The amount of coniferous forest only explained a small part of the beetle species composition, possibly because coniferous forests are dominating the entire forested landscape in southern Sweden. The high-stumps in these studies were four years old at most. This means that, as the wood decay progress, the properties of high-stumps change and potentially they become even more important.