A simulation framework for scenario-based quantification of natural hazard protection provided by mountain forests

Mountain forests often provide important protection against gravitational natural hazards. For this reason, developing management strategies that help maintain resilient forests withstanding climate change impacts is crucial. Existing approaches to quantify the protection against natural hazards provided by forests are often extensions of either forest or natural hazard simulation models. In both cases they tend to suffer from a rather coarse, static representation of their secondary component. Simulation results thus lack the temporally integrated perspective needed when modeling the outcome of interacting, partly stochastic processes. We present a simulation framework that allows for quantitative natural hazard assessment over time as a function of forest management and climate scenarios. By linking a process-based forest landscape model with a mass movement hazard simulation model on an annual basis throughout the simulation period, we integrate the effects of climate change and capture the complex interactions of forest growth, forest disturbances and natural hazards in mountain regions in unprecedented detail. This repeated coupling allows annual changes in forest structure to directly affect rockfall dynamics, while rockfall-induced tree mortality feeds back into subsequent forest development. We tested the framework in a case study area in the Swiss Alps and calculated the expected development of rockfall hazard beneath a currently spruce-dominated forest slope considering different forest management intensities. The residual rockfall hazard varied between 20% and 30% depending on the forest management scenario. Rock size and forest basal area had the strongest influence on protection efficiency. We deem the modeling framework suitable for scenario analysis in quantitative risk assessment, especially after disturbance events, as well as for identifying strategies to increase forest resilience in times of climate change. In conjunction with economic data on forest and infrastructure, the modeling framework even allows for integrated economic cost-benefit analysis of forest and natural hazard management.