Bird response to forest disturbance size in mountain spruce forests in Central Europe

Abstract

Although natural disturbances are likely to occur more frequently and be more severe in future as a result of climate change, we have little evidence concerning the effect of disturbance size and severity on species diversity. We aimed to compare effects of varying size and severity of natural disturbances on bird species composition in the non-intervention area of Šumava National Park, Czech Republic. For this purpose, we surveyed bird communities in 1) small- and 2) large-scale disturbance, 3) enclaves of live trees in large-scale disturbance areas, and 4) non-disturbed forests. Furthermore, we used habitat characteristics to identify structural factors affecting species composition of bird communities. Birds were sampled by the point count method during the 2021 breeding season and analysed using linear models. Additionally, we use principal component analysis (PCA) to characterize four defined disturbance classes using habitat characteristics. The most important habitat characteristics for bird communities are structural complexity, live tree density, and understorey cover. Small-scale disturbances increased structural complexity of a forest and had a generally positive effect on birds. Both small- and large-scale disturbances supported species nesting on the ground and shrub layer. In contrast, large-scale disturbances negatively affected canopy nesting and specialist species. This likely was due to a reduction of small-scale habitat heterogeneity with increasing disturbance severity. High-severity disturbance changes structurally rich forests to rather uniform, open-canopy habitats that are temporally unsuitable for closed-canopy birds. On the other hand, low-severity disturbance enhances large-scale habitat heterogeneity and maintains suitable habitat for species of closed-canopy forest, including some specialist species.