Regional Mountain Conference

Forests of the European Alps have been strongly shaped by past human activities, which have influenced their structure and composition. Assessing the natural tree-species composition of current forest landscapes is essential for evaluating their biodiversity potential and for informing management prioritization. High levels of compositional naturalness are often associated with greater ecosystem functioning, but it remains unclear whether forest landscapes that are closer to their potential forest composition are also less vulnerable to future climate change and natural disturbances. Using the process-based landscape model iLand, we quantified the naturalness and the vulnerability to natural disturbances across a large forest landscape in South Tyrol, Italy. We developed a spatially-explicit index to evaluate how closely current tree species composition matches potential forest composition. We then simulated future forest dynamics under multiple climate change and disturbance scenarios (wind and bark beetle), using two different initial vegetation conditions on the same landscape – potential vs. current forest – and compared their future vulnerability based on changes in species dominance, vegetation structure, and height heterogeneity.

Results indicate that current forests exhibit generally low naturalness compared with their potential forest composition, reflecting historical management practices. The naturalness score varied depending on elevation across the landscape, with low- and high-elevation forests showing low naturalness, while mid-elevation forests medium to high naturalness. Vulnerability to natural disturbances under climate change differed between the two initial vegetation conditions. Current forest was more susceptible to bark beetle outbreaks, driven by past promotion of Norway spruce and further amplified by warming. In contrast, the potential forest was more vulnerable to wind disturbance, likely due to old-growth characteristics, such as greater height heterogeneity and canopy roughness, that increase blowdown susceptibility. Given the projected intensification of natural disturbances under future climates, our findings suggest that promoting more natural forest conditions alone may not guarantee higher resilience to climate-induced disturbances. Instead, management approaches should aim at increasing landscape-level structural and compositional heterogeneity in a balanced manner to minimizing future disturbance vulnerability.