Felled or standing retained wood—it makes a difference for saproxylic beetles

Abstract

High stumps are often retained at clear cuttings to increase the abundance of habitat patches for saproxylic (wood living) insects. However, these high stumps constitutes a very uniform dead wood habitat which probably supports only a part of the saproxylic fauna. Therefore, we compared the saproxylic fauna of high spruce stumps with the fauna of long and short felled boles of spruce. We also investigated the associations between insect species and polypore fungi growing in the wood. All wood units were created at the same occasion on a clear cut in SW Sweden. The dominating species of bark beetles and longhorn beetles were surveyed in the first year after the cutting. Four years later, the fauna was sampled again by sifting bark samples and all species found were determined. In total we recorded six species early in the succession and 43 four years later. Two species were red-listed. Three out of five statistically tested early successional species had significant associations with some of the wood types, while the corresponding figures later in the succession were six of 15. Three of the 15 species in the late succession were also significantly associated with the presence of fruiting bodies of the polypore fungus Fomitopsis pinicola. We concluded that retaining felled wood in addition to high stumps may provide an important means of diversifying the dead wood substrates, which may in turn increase the number of saproxylic species on a site.