Uneven-aged silviculture as a management tool to mitigate biodiversity loss

Intensive forest management for wood production has altered ecosystem structures and processes, and led to habitat loss and species extinctions. Subsequently, interest in alternative management methods, such as uneven-aged silviculture, has increased. Uneven-aged silviculture maintains a stratified forest with continuous cover and a stable microclimate by low level and more frequent harvesting. Due to preserved forest structures and retained habitat heterogeneity, uneven-aged silviculture may maintain species associated with old growth forest better than current forest management practices. In a large-scale field experiment, I investigated how different silvicultural approaches affected forest beetles, a group of species severely disfavoured by current forest practise. I compared the species richness, abundance and community structure of beetles in an experimental system comprising of five treatments: clear-cutting, thinning (both representing even-aged silviculture), selective felling (representing uneven-aged silviculture), reference, and old growth forest (both representing unmanaged controls). Selective felling maintained beetle assemblages similar to the reference stands with the exception of cambium consumers. The assemblage of cambium consumers was instead similar to old-growth forests, which suggest that selective felling may add conservation value. In contrast, even-aged silviculture altered the beetle assemblages. Clear-cuts differed from all other stand types, while thinning had beetle assemblages that approached the assemblages of uneven-aged stands, indicating a partial recovery after clear-cutting. However, thinned stands still differed from reference stands. Harvest trails within a selectively felled forest increased openness, resulting in higher temperatures and lower humidity. Beetle assemblages differed between the trails and the retention strips. Both open habitat species and old-growth specialists were among the species associated to harvest trails, which potentially could explain why species assemblage in selective felling did not differ from reference stands or thinned stands. My results support the hypothesis that uneven-aged silviculture better maintains beetles assemblages associated with semi-natural mature forest than even-aged silviculture. Selectively felled stands could benefit species that are dependent on mature or old growth forest since some of the needed habitat qualities persist. Uneven-aged silviculture might therefore be a better management tool when the conservation of biodiversity is of concern