The Conservation of Saproxylic Beetles in Boreal Forest: Importance of Forest Management and Dead Wood Characteristics

Johansson, T. 2006. The conservation of saproxylic beetles in boreal forest: importance of forest management and dead wood characteristics Doctoral dissertation ISSN 1652-6880, ISBN 91-576-7115-X Forest management has altered the age structure, tree species composition and dead wood availability of Swedish boreal forests. As a consequence, many saproxylic (wood living) insect species have decreased in abundance and many species are threatened. New conservation-oriented forestry uses management measures to favour saproxylic species in managed forests. In my thesis, I evaluated the importance of these measures for saproxylic beetles and possible improvements by using a large-scale field experiment at ten sites in northern Sweden. The substrate types used in the experiment included burned and shaded logs, logs inoculated with two species of wood-decaying fungi, untreated control logs, created snags and the tops of the snags. The experiment was performed in three stand types: clear-cuts, mature managed stands and old-growth stands. Additionally, I performed attraction experiments to examine the attraction of saproxylic beetles to sporocarps and mycelia-infected wood of wood-decaying fungi in landscapes with different proportions of old spruce forest. Saproxylic beetles were affected by both forest management and dead wood characteristics. Snags differed from lying untreated logs and tops and supported different assemblages of saproxylic beetles and significantly higher numbers of several bark beetle and predator species. Tops attracted different assemblages from both snags and untreated logs. Burned logs supported a lower abundance of saproxylic beetles, particularly fire-favoured species and cambium consumers (especially Dryocoetes autographus, Hylurgops palliatus, Hylurgops glabratus and Hylastes cunicularius) and different assemblages of fire-favoured beetles, cambium consumers and predators from the untreated logs, probably because burning makes the cambium less suitable as food for bark beetles. However, some species were attracted to the burned logs. Log exposure proved to be important, especially on clearcuts where shaded logs supported different assemblages of saproxylic beetles, particularly predators, from untreated logs. Shaded logs on clear-cuts also hosted different saproxylic beetle assemblages from untreated logs in mature managed and old-growth stands, suggesting that shaded logs on clear-cuts do not provide suitable substrate for all shadedemanding species. Sporocarps and mycelia-infected wood attracted some beetle species; Lordithon lunulatus was attracted to Fomitopsis pinicola sporocarps and D. autographus to Fomitopsis rosea mycelium-infected wood. Forest management affected the saproxylic beetle fauna and landscapes with lower proportions of old spruce forest supported depauperate saproxylic beetle assemblages compared with landscapes with higher proportions of old spruce forest. Clear-cuts supported different assemblages of saproxylic beetles, and all functional groups, compared with mature managed and old-growth stands. The assemblages of saproxylic beetles and predators also differed between old-growth and managed stands. Properties of the substrate are important for saproxylic insects and many species have specific substrate demands. To conserve functionally intact beetle assemblages in an area with intense forestry, both old-growth forest reserves and measures in the managed forest, such as the creation of a variety of dead wood substrates, is needed.