A probabilistic 3-D slope stability analysis for forest management

A 3-D physical-based approach to slope stability has been proven to be very promising in order to provide reliable spatially distributed landslides maps. Over large areas, however, such an approach still presents some limitations, mainly related to the variability and the uncertainty of the input parameters. By combining a 3-D physical-based model with a Monte Carlo technique, such constraints can be overcome, improving the performance and the applicability of the method. Whereas uncertainties of geotechnical, morphological and hydrological parameters have been widely investigated, few studies have been focused on the variability of root reinforcement, which plays a crucial role in preventing shallow landslides in forested areas. To contribute to define the effect of different forest management strategies on slope stability, we developed a 3-D model able to properly take into account for the effect of the root systems into the soil. The main objectives of our study are: (i) to define a probability distribution function for the root reinforcement according to the forest stands characteristics (tree density, mean diameter at breast height, minimum distance between trees), (ii) to obtain a probability distribution of the Factor of Safety through the combination between a 3-D slope stability model and a Monte Carlo simulation technique, and (iii) to evaluate the difference between several forest management scenarios in terms of shallow landslide risk. The model has been applied to a small Alpine area, mainly covered by coniferous forest and characterized by steep slopes and a high landslide hazard. Our findings contribute to provide forest managers with useful information for understanding the consequences of different forestry strategies.