Dead wood and saproxylic beetles in set-aside and non set-aside forests in a boreal region

Abstract

The availability of habitat for wood-dependent species has been greatly reduced in Fennoscandian boreal forests and hence the setting aside of forest land for conservation purposes is a common strategy. Here, we explore the biodiversity quality and conservation relevance of three categories of set-asides dominated by Norway spruce (nature reserves, woodland key habitats and retention patches, i.e. groups of living trees left on clear-cut areas) and a non set-aside forest category (old managed spruce forests) in a boreal forest region in central Sweden. The comparisons are based on surveys of (1) dead wood volumes, (2) diversity of dead wood types in terms of tree species, decomposition stage, diameter and presence of bark and (3) occurrence of saproxylic (i.e. wood dependent) beetles in Norway spruce, Picea abies. For saproxylic beetles, species richness, species composition and occurrence of red-listed species were compared. In total 180 dead wood types and 129 beetle species were found, 12 of which were red-listed. We found no significant difference between the forest categories in terms of total dead wood volume. However, the rarefied number of dead wood types was significantly greater in reserves and key habitats compared to retention patches. Woodland key habitats had significantly more beetle species than retention patches and old managed forests, as well as significantly more red-listed species than the retention patches. The species composition of retention patches, differed significantly from that of old managed forests and reserves, probably due to higher degrees of sun-exposure. We conclude that the conservation strategies explored in this study, provide valuable habitats and contribute differently to the preservation of old forests and saproxylic beetles. We would add that inventories, to identify conservation values, should be carried out prior to harvest of old stands and that measures should be taken accordingly to set-aside the parts of forest stands with the highest biodiversity values.