Biological legacies as nature-based solutions for maintaining the protective effect of alpine mountain forests against rockfall

Protective forests are of critical importance in mountainous regions to ensure the security of human life, infrastructure and stability of ecosystems. In the face of the challenges posed by natural disturbances, particularly in the Alps, forests are increasingly vulnerable to the effects of climate change, compounded by deficiencies in stand structures and their capacity to provide essential ecosystem services. Consequently, the estimation of the residual protection provided by biological legacies has become a priority.

This research adopts a multiscale methodology, ranging from individual trees to regional analysis, employing diverse techniques and data sources such as field studies, lidar, satellite imagery, and UAV data. The primary objective of this study is to enhance comprehension regarding the impact, capabilities, and real-time service life of natural disturbance legacies within protective forests, particularly in mitigating rockfall risks. Additionally, the research aims to contribute to implement a more ecologically sound and effective post-disturbance forest management approach. The study zones are located all over the Western-and Eastern Alps and include areas impacted by windthrow, bark-beetle as well as forest fire sites.

Between one to ten years post-event, ongoing field assessments aim to comprehensively evaluate the degradation status of existing deadwood. This analysis takes into account specific conditions, including altitude, tree species, and disturbance event. This comprehensive analysis involves the deployment of sensors for prolonged monitoring of moisture levels, water content in logs, climate data collection, and sampling for dry-matter content and decay assessment of deadwood. The ultimate objective of this research is to enhance scientific insights into decay conditions, contributing to a substantiated, application-oriented understanding of the "service lifetime" of biological legacies following a disturbance event in protective forests, particularly in their role against rockfall.