Windstorms represent one of the main large-scale disturbances that shape the European landscape and influence its forest structure, so post-event restoration activities start to gain a major role in mountainous forest management. After a disturbance event, biological legacies may enhance or maintain multiple ecosystem services of mountain forests such as protection against natural hazards, biodiversity conservation, or erosion mitigation. However, the conservation of all these ecosystem services after stand-replacing events could go against traditional management practices, such as salvage logging. Thus far, the impact of salvage logging and removal of biological legacies on the protective function of mountain stands has been poorly studied. Structural biological legacies may provide protection for natural regeneration and may also increase the terrain roughness providing a shielding effect against gravitational hazards like rockfall. The aim of this project is to understand the dynamics of post-windthrow recovery processes and to investigate how biological legacies affect the multifunctionality of mountain forests, in particular the protective function. To observe the role of biological legacies we performed 3000 simulations of rockfall activity on windthrown areas. Results show the active role of biological legacies in preventing gravitational hazards, providing a barrier effect and an energy reduction effect on rockfall activity. To conclude, we underline how forest management should take into consideration the protective function of structural legacies. A suggestion is to avoid salvage logging in order to maintain the multifunctionality of damaged stands during the recovery process.

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<p>Shallow landslides are one of the most frequent gravitative natural hazards in the Alpine region that could affect human infrastructures. Forests can play a direct protective function, preventing the triggering of such events thanks to the role they play in water regulation and mechanical effects, in particular with root reinforcement. Few studies, however, report empirical assessments, based on after-events shallow landslides inventory, of the protective effects given by the presence of the forest on this natural hazard. With this study, an attempt was made to assess the possible influence of the presence of the forest on the topographic triggering conditions and the magnitude of the landslides respect to those triggered in open lands. A comparison was then developed between the structural characteristics of forest stands, in which landslides were recorded, and the reference parameters of the protection forests guidelines. In addition, it has been evaluated how root reinforcement can have an influence at a local scale on the location of shallow landslide triggering. Finally, a subsample of the forest landslides was selected for field surveys, in order to analyze the influence of stand structure on the magnitude of landslides. The study area corresponds to the territory of upper Agordino valley (405 km<sup>2</sup>), in the Veneto Region (Italy), which was severely affected by storm Vaia in October 2018 that caused widely the trigger of numerous shallow landslides and large windthrows. Through the analysis of the orthophotos pre and post-event and the Dem of Difference of DTMs, overall 469 (116 triggered in the forest) shallow landslides were identified with median values of area of 177 m<sup>2</sup> and volume of 163 m<sup>3</sup>. In terms of density, forest landslides are less frequent than those in open lands and are triggered on slopes with higher inclination. Forest stands where landslides were recorded show median values of coverage of 60%, gap area of 551 m<sup>2</sup>, gap length of 18 m, and gap width of 16 m. It turned out that comparing to the silvicultural guidelines on the management of protection forests, the most important parameter appears to be the gap length. Such gaps represent the weakest zone in terms of root reinforcement where the landslides can be triggered more easily. This has been confirmed by the application, at the plot scale, of the SOSlope model (Cohen and Schwarz, 2017) which results that most of the landslide scarps (42 out of 53) were located in the zones with the lowest lateral root reinforcement. A multivariate analysis carried out on data collected in the field on a subsample of 20 forest landslides highlights that landslides with higher volume and area were recorded mostly in young forests with high density. A stand with a good amount of large trees and an uneven-aged structure seems to be the most effective in these terms. These results emphasize the protective effects of forests against shallow landslides and suggest the need for their optimal silviculture management, taking also into account the increasing susceptibility to other natural disturbances which could compromise the protective function.</p>