Forest dynamics and shallow landslides: a large-scale GIS-analysis Through continuous and abrupt changes in the forest and particularly in its root area, the disposition for shallow landslides also changes. The aim of this article is to learn more about the relationships between long-term forest dynamics and the risk of landslides with the help of large spatial data sets. A total of 6670 shallow landslides were selected from the natural event register StorMe, the event register of the Canton of Obwalden and the WSL database for shallow landslides and slope debris flows and overlaid with GIS data on the current and former forest situation (Siegfried maps of approx. 1880) and with windthrow areas (Vivian and Lothar). Shallow landslides occurred less frequently in the forest than outside of it at inclinations of less than 35 degrees. Higher landslide densities occurred in coniferous and mixed forests (compared to deciduous forests) and in relatively young forests (ingrown after 1880). Landslides in younger forests occurred on slopes less steep than in older forests. More shallow landslides occurred on former windthrow areas during the first 3 to 17 years after the event, however these landslides occurred on comparatively steep slopes. The analyses show that the disposition towards shallow landslides defined by slope inclination and subsoil can change strongly due to reforestation processes and natural disturbances. Silvicultural interventions may contribute to an improvement of the protective effect in the long term if they are carried out carefully and if they contribute to an increased adaptability to natural disturbances.
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