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.
Protection forests can be severely affected by natural disturbances, whose consequences could greatly alter the fundamental ecosystem services they are providing. Assessing and monitoring the status of the protective effects, particularly within disturbed stands, is therefore of vital importance, with timing being a critical issue. Remote sensing technologies (e.g., satellite imagery, LiDAR, UAV) are widely available nowadays and can be effectively applied to quantify and monitor the protective effects of Alpine forests. This is especially important after abrupt changes in forest cover and structure following the occurrence of a disturbance event. In this contribution, we present a brief introduction on remote sensing technologies and their potential contribution to protection forest management, followed by two case studies. In particular, we focus on research areas within protection forests against rockfall affected by windthrow (i.e., the 2018 storm Vaia in the Eastern Italian Alps, where LiDAR and UAV data were used), and forest fires (i.e., the 2017 fall fires in the Western Italian Alps, involving Sentinel-2 image analyses).
<p>The risk of wind damage to European forests is expected to increase due to the changed climate. Therefore, research efforts in forestry have been focussing on the development of analytical and modelling tools to improve the prediction of forests' susceptibility to wind damage, and ultimately to support forest management decisions in increasing wind resistance in forest stands. Recent catastrophic wind damage to European forests has shown that wind damage risk applies also to montane forests. Some of them are of particular importance for the various ecosystem services they provide, including protection from gravitational hazards and defence against soil erosion. At present, the available forest wind risk models have been tested and used mainly on production or planted forests in different countries, but never in the complexity of mountainous terrains. The aim of this study is to introduce a methodology for the validation of a new parametrization of ForestGALES wind risk model for the alpine environment. The parameterisation was developed through field tests (e.g., pulling tests on trees) and validated based on the observed wind damage caused by the storm Vaia, which occurred in northern Italy in October 2018, and the pre-disturbance forest characteristics. The use of this parameterisation can allow the construction of wind vulnerability maps starting from LiDAR data. Mapping vulnerability to natural disturbances, in this case, wind, is an essential tool for forest planning and management. The frequency of natural disturbances is expected to increase, as is their severity and forest management needs to target interventions to obtain more resistant and resilient forest stands. Management should aim to apply strategies to prevent future damage in a way that ensures continued protective effectiveness, guaranteeing the preservation of local communities and infrastructures.</p>
<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>
<p>Forests provide many important ecosystem services. Natural disturbances, such as wildfires, pest outbreaks and windrows, are the main phenomena shaping forest ecosystems. Due to both climate and global changes, extreme events are increasing in frequency and forests are thus increasingly being affected by stand replacing disturbances. Mountain forest dynamics and ecosystems services are critically influenced by disturbances, in particular storm. In this framework, is crucial to understand these environmental modifications, finding the best management strategies to restore or maintain ecosystem services provided by forests. After large disturbance, there are two different issues to deal with: the large amount of deadwood on the ground, and the needs of&#160; regeneration in order to re-establish the forest cover. To face these problems different management strategies can be adopted. Salvage logging (total or partial) and no-intervention are the two opposite approaches to handle the large amount of deadwood. Natural regeneration or reforestation, instead, are the main strategies to consider to re-establish forest cover. In this study we focused on post-windstorm conditions, in particular concerning large windthrows caused by the Vaia storm, occurred in October 2018 on Eastern Italian Alps. After such large-scale event, natural regeneration is the most convenient strategy to regenerate forest. This process should take place in an area with a high amount of coarse wood debris (CWD). For this reason is crucial to understand the interaction between windthrown timber and regeneration dynamics. In this study we analyzed how CWD is able to create a favorable regeneration microsite enhancing seedling establishment probability. In particular, we focused on two different facilitative mechanisms provided by CWD: microsite amelioration and seedling protection. The former has been analyzed measuring temperature and SWC in the proximity of seedling planted in the surrounding of deadwood elements, the latter by recording browsing evidence at the end of the season. &#160;In order to infer the CWD contribution, control sites have been established in empty sites (no CWD presence in the surrounding). Our results showed that in southern slopes, microsite with significative lower temperature are found northern to the logs, decreasing water stress for saplings. The ameliorative function of logs and CWD in general contribute to decrease the transplanting shock, increasing the probability to establish for saplings. Moreover, the presence of lying deadwood decreased significantly the browsing on saplings. The result of our study highlighted the importance of favorable regeneration microsites provided by deadwood, both for natural regeneration dynamics and for increasing the survival probability for planted saplings. Favorable microsites and nurse biological legacies should be considered in defining post-disturbance management strategies, promoting only a partial salvage logging or non-intervention &#160;approaches as much as possible.</p>
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