Invertebrate Community of Scots’ pine Coarse Woody Debris in the Southwestern Pyrenees under different thinning intensities and tree species

Thinning and tree species alter microclimate by modifying canopy cover, radiation, wind and humidity in the forest floor. Thus, forest management can directly influence edaphic microfauna responsible for decomposing coarse woody debris (CWD). This research was carried out in the southwestern Pyrenees mountains (northern Spain), and aimed to determine the influence of forest thinning and canopy type (pure Pinus sylvetris L. or mixed of P. sylvestris - Fagus sylvatica L.) on CWD colonization by edaphic fauna. CWD samples were in intermediate and advanced decomposition stages, approximately 10 cm long and 5 cm in diameter were collected. Using a design of three thinning intensities (0%, 20% and 40% of basal area removed), with three replications per treatment (nine plots in total), four samples were taken per plot (two per canopy type), to reach 36 samples in total. Microfauna was extracted from CWD samples with Tullgren-Berlese funnels, and individuals were counted and identified. Nineteen taxonomic groups were recorded, being the most abundant the microinvertebrates (mites and Collembola). Canopy type had a significant influence on richness, whereas decay class had a significant influence on total abundance and richness. In addition, there were non-significant decreasing trends in richness and abundance with increasing thinning intensity. However, interactions among thinning intensity, canopy type and decay class significantly affected microfauna. Furthermore, some taxonomic groups showed differential responses to canopy type. CWD water content was correlated with total invertebrate abundance and some taxonomic groups. Our results suggest that stand composition has the potential to directly affect invertebrate communities in CWD, whereas stand density influence is indirect and mostly realized through changes in CWD moisture. As microfauna is related to CWD decomposition rates, these effects should be accounted for when planning forest management transition from pure to mixed forests.