Influence of butt rot on beetle diversity in artificially created high-stumps of Norway spruce

The making of high-stumps to benefit wood living organisms is a common practice in Scandinavian forestry. To minimise the cost of this action trees of low quality, e.g. rotten trees, are chosen if possible. In this study we investigated if the wood decay fungi Heterobasidion spp. affects saproxylic beetles assemblages in Norway spruce (Picea abies) high-stumps. In total we caught 43 species of saproxylic beetles (Coleoptera) of which one was red-listed. Associations with the fungi were tested on 13 beetle species and three of them showed negative associations with the occurrence of Heterobasidion, while none of the tested species showed a positive association with Heterobasidion. Species richness did not differ between infected (30) and non-infected (33) stumps, but the beetle assemblages differed to some extent. Two additional bracket fungi species were found on some of the high-stumps, Fomitopsis pinicola and Trichaptum spp. Both these fungi had beetle species significantly associated with them. Interestingly, we found that F. pinicola and Trichaptum spp. never occurred together in the same stumps. None of them, however, seemed to be affected by presence of Heterobasidion spp. In conclusion, Heterobasidion spp. infections influence the beetle fauna by disfavouring some beetle species but we did not find any species positively associated with Heterobasidion spp. This suggests that increasing the proportion of pre-rotten high-stumps could have a negative effect on beetle diversity on clear-cuts.