Hur påverkar naturvårdsåtgärder mängden av vedlevande insekter : Manuellt dödade träd vs självdöda

Sammanfattning: Today’s forest managers implement a large number of methods to increase the amount of dead wood in Swedish forests. They use everything from high cutting of trees to girdling trees and burning forests. However, implementation of these measures without proper knowledge of their consequences is a common problem. This study has been performed to increase knowledge about two of these measures, girdling and high cutting, and how these actions affect the number of wood-living insects living on dead trees. A total of 72 trees were randomly selected in four different locations in the municipality of Säffle. The trees, which were birch and alder, were all dead or dying and selected by three criteria, snags (as the reference tree type), girdling and high cut. A total of 15 trees of each type and measure were chosen. The trees which were either ring debarked or high cut were compared with snags to see if there were any differences in the number of wood-living insects. The collections of insects were made with so-called appropriate window traps. The traps were tied to the trees and left out for one week before emptying. The traps 2 were deployed on two separate occasions during June and July 2011. A total of 876 beetle individuals were captured during the study, including 13 longhorn beetles. There was a significantly smaller amount of families in high cut birch compared to the birch snags for the first period, but none for the second period. There were also a significantly smaller amount of families in the girdled birch than in the snags for the second period. There were no differences between the different types of dead trees when comparing insect species. There were no significant differences between the girdled alder and the alder snags, which indicate that girdling does not have a strong effect, although catches were greater for the girdled alder. High cut alder does not exist and therefore only girdled alder could be compared with the alder snags and no differences in insect catches were found. There were differences in sizes of the trees, with birch snags being larger than high cut and girdled birch and alder snags being smaller than debarked alder. There was also a significant difference in degradation rate of birch, with natural birch snags being less decayed than the high cut and girdled birch. There was no difference in the degree of decay for alder. 69 % of the trapped longhorn beetles were found in birch, 31 % on the alder, but this difference was not significant. The conclusion of the study was that high cutting birch leads to a smaller number of tree-living insects than found on natural snags and that the same applies to girdling. Alder requires further study.