Response of saproxylic insect communities to forestry

• Main Author: Stenbacka, Fredrik
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2009
• Subjects: Fennoscandia
• Online Access: https://pub.epsilon.slu.se/2117/; https://pub.epsilon.slu.se/2117/1/Stenbacka_F_090922.pdf

In boreal Fennoscandia clear-cutting practices and fire suppression have drastically reduced dead wood amount and diversity, deteriorating the sapoxylic fauna (species associated with dead wood). More effective conservation measures are urgently needed, which requires more empirical data on many saproxylics in managed forest landscapes. In this thesis I have studied both the immediate and more long-term effects of clear-cutting on saproxylic insect communities (beetles, parasitic wasps and flat bugs), by comparing species richness, abundance and assemblage composition in the whole successional range of existing spruce dominated forests. My thesis also provides data on substrate requirements of red-listed beetles, response of flat bugs to forest fires, and complementarity of sampling methods for assessing data on rare and threatened species. Old-growth forests supported the most intact communities and the highest densities of saproxylic insects and are probably very important as source habitats, especially for red-listed species. Mature managed forests were very similar in assemblage composition, strongly suggesting a high conservation value of these forests. Surprisingly, many saproxylic beetles adapted to late successional stages were present in thinned middle-aged forests, suggesting a significant conservation potential of these forests, provided that sufficient amounts and qualities of dead wood are retained. In contrast, unthinned forests held assemblages more similar to clear-cuts, which both were low in occurrence of red-listed beetles. Re-growth forests had a sparse dead wood supply compared to the older forests, especially reserves, and my results suggest that dead wood retention should include both snags and logs as these support different saproxylic assemblages. Finally, prescribed burnings are necessary for the survival of pyrophilus flat bugs. Window and eclector traps collected different assemblages of both red-listed saproxylic beetles and parasitoids. Window traps gave a better measure of the local species pool, while eclector traps provided more detailed information on substrate requirements, host choice and hatching periods. For more precise parasitoid-host relationships, debarking of logs can be a useful method. Thus, the trap types used should be carefully selected depending on the specific questions addressed in each study.