Effect of bark beetle outbreak and salvage logging on tree-related microhabitats in Białowieża Forest

Tree related microhabitats (TreMs) are key resources for forest biodiversity. Natural disturbances, such as bark beetle outbreaks, can influence forest structure and stand properties, potentially altering the composition of TreM communities. The removal of dead and damaged trees, often conducted after forest disturbances (salvage logging), further modifies the forest structure with potential consequences for TreMs. However, the effect of both disturbance and post-disturbance management on TreM communities in temperate lowland forests remains poorly understood. We assessed TreMs in 44 plots across three habitat types in a bark beetle-disturbed landscape of Białowieża Forest, NE Poland: unaffected areas, disturbed areas left unmanaged, and disturbed areas subjected to salvage logging with partial tree retention. Bark beetle disturbance increased the richness of three TreM groups (i.e., cavities, tree injuries, and fungi/slime moulds) as well as the abundance of seven individual TreMs, most of which were associated with tree injuries. Despite the significant retention (i.e., all living trees and 10 % of dead trees), salvage logging led to a decline in TreMs at the stand level compared to both unsalvaged disturbed and unaffected stands. In summary, the bark beetle outbreak positively impacted TreM communities at the stand level, while salvage logging reversed this effect. Based on our findings, we recommend limiting (excluding, if possible) salvage logging operations in forests managed primarily for biodiversity to enhance their provision of tree-related microhabitats for a diverse range of species. We also recommend including TreM surveys in the tree selection process during salvage logging operations.