Morphological and topographic profile analysis of shallow landslides inside and outside of forests with a semi-automatic mapping approach and bi-temporal airborne laser scanning data

Abstract. Investigating the effects of forest land cover on shallow landslide characteristics such as their morphology (e.g., area and mean depth) and topographic profiles could provide a better understanding of how forest affect landslide processes. Landslides located under the forest canopy, which are often overlooked by conventional landslide mapping methods (e.g., using aerial imagery), can be captured using airborne laser scanning (ALS). In this study we investigated forest effects on landslides by developing a well-performing semi-automated workflow for mapping landslide scars and analysing their characteristics in relation to the forest canopy cover, using terrain models from ALS data. The mapped landslide scars were analysed with a forest canopy cover mask and forest structure parameters, such as the closest tree distance and the number of trees surrounding the scar. The investigated scars within the forest have significantly larger depths, thicknesses and higher pre-failure slope values than scars located outside the forests. Additionally, the differences are clearer when forest structure parameters are considered, of which the closest tree distance showed the strongest relation to the landslide characteristics. The evidence aids better understanding of how forests affect landslide processes and how they serve their protective function.