Influence of natural disturbances on the protective effect of mountain forests against natural hazards and thereof derived risks
Abstract ID: 3.13100 | Accepted as Talk | Talk | TBA | TBA
Adrian Ringenbach (1, 2, 3)
Leon J. Bührle (2, 3, 4), Kevin Helzel (2,3), Alessandra Bottero (2,3), Tobias Kalt (5), Martina L. Hobi (5), Yves Bühler (2,3), Michaela Teich (4), Peter Bebi (2,3)
(2) WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
(3) Climate Change, Extremes and Natural Hazards in Alpine Regions Research Centre CERC, Davos, Switzerland
(4) Department of Natural Hazards, Austrian Research Centre for Forests (BFW), Innsbruck, Austria
(5) Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
Mountain forests play a crucial role in mitigating natural hazards and reducing risks in Alpine regions. However, legacies of former land use often result in increasing stand homogeneity and instability in these landscapes. Especially when compounded by climate change, both the frequency and impacts of extreme disturbances such as bark beetle infestations and windthrow are expected to increase. This study examines (a) which forest stands within the 1’700 km² study area in Eastern Switzerland are particularly susceptible to natural disturbances, and (b) how these potential large-scale disturbances would alter the protective function of the forests against rockfall and snow avalanches. To spatially map the susceptibility of the forests, we used the Nationwide Airborne Laser Scanning data and stand maps to derive high-resolution forest structure parameters and site factors. An expert-based approach was then applied to classify these forest structures and site conditions based on their resistance to windthrow and bark beetle infestations. We simulated three large-scale extreme disturbance scenarios affecting areas with predisposition above the 50% quantile: (1) windthrow, (2) bark beetle infestations, and (3) snagfall, a snag–lying deadwood combination. The disturbed stands were then incorporated into large-scale avalanche and rockfall simulations. The simulations assessed the spatial effects of lying and standing deadwood on hazard occurrence and intensity. For rockfall, a decreasing energy absorption capacity of snags and lying deadwood compared to the undisturbed forest was considered. For avalanches, we considered the changing likelihood of avalanche release in disturbed forests. In case of windthrow and snagfall, the increasing roughness caused by the lying stems was taken into account. For the snags, we considered the decreasing canopy cover and the increasing forest gap size following the decomposition of the crown. The modelling results were then integrated into a risk analysis to quantify the remaining protective function. This approach supports risk-based prioritization of active management strategies before and after large-scale disturbance events. This represents a crucial step toward developing a decision-support system (DSS) for effective and sustainable management of protective forests in Alpine regions.
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