Protective Effects of Forests against Gravitational Natural Hazards

In this chapter, we give a short overview of the protective effects of forests against snow avalanches, landslides and rockfall hazards in mountain areas. The overview is based on the protective mechanisms provided by forest and connects them to the effect-related indicators of forest structure from literature and European protective forest management guidelines. The thresholds of the effect-related indicators are hazard-related silvicultural targets for forest management and critical values for hazard risk assessment. The assessment of the protective effects of forests is a central part of natural hazard risk analysis and requires information on different spatial levels from single tree to slope-scale attributes. Forests are efficient in preventing snow avalanche and landslide initiation; however, they are usually unable to stop large masses of snow, soil and rock in motion. Therefore, guidelines on silvicultural targets and practices must focus on the mitigation of hazard onset probabilities at the stand-scale; however, existing guidelines under- or overestimate the protective effects of forests. Effects of forests on hazard propagation are difficult to implement in forest and risk management practice. Hence, the European protective forest management guidelines do not contain any or only general specifications that simplify the determining factors and their relationships.