Comment on esurf-2022-21

Abstract

How deadwood mitigates rockfall hazard in mountain forests is a key scientific question to understand the influence of climate induced disturbances on the protective capacity of mountain forests. To address this question both experimental quantification combined with numerical process modelling are needed. Modelling provides detailed insights into the rock-deadwood interaction and therefore can be used to develop effective forest management strategies. Here, we introduce an automatic deadwood generator (ADG) to assess the impact of fresh woody storm debris on the protective capacity of a forest stand against rockfall. The creation of deadwood scenarios allows us to directly quantify their mitigation potential. To demonstrate the functionality of the proposed ADG method, we compare genuine deadwood log patterns, their effective height, and ruggedness at two natural windthrow areas at Lake Klöntal, Switzerland, to their generated counterparts. We perform rockfall simulations for the time a) before, b) directly after and c) 10 years after the storm. The results are compared to scenario d) a complete clearing of the thrown wood, in other words a no forest scenario. We showcase an integration of deadwood in rockfall simulations with realistic, deadwood configurations alongside with a DBH- and rot fungi dependent maximal deadwood breaking energy. Our results confirm the mitigation effect of deadwood significantly reducing the jump heights and velocities for 400 kg rocks. Our modelling results suggest that even after a decade, deadwood has a stronger protective effect against rockfall compared to standing trees. An ADG can contribute to the decision making in forest and deadwood management after disturbances.