Windthrown elements: a key point improving microsite amelioration and browsing protection to transplanted seedlings

Mountain forest dynamics and ecosystems services are critically influenced by disturbances, in particular storm events. After extensive disturbance, the large amount of deadwood lying on ground and the necessity for restoring the forest cover with natural regeneration are two critical issues to be dealt with. Salvage logging is the most common post-disturbance management strategy, but it does not consider the strategic role of coarse woody debris (CWD) in favoring regeneration establishment and survival. The aim of this study is to analyze how CWD contributes to creating favorable microsites for regeneration, increasing seedling establishment probability, after a large windthrow in the eastern Italian Alps. We focused on two different facilitative mechanisms provided by CWD, microsite amelioration and seedling protection, by planting a set of seedlings in the surroundings of deadwood elements. The former mechanism was analyzed by measuring temperature and SWC (Soil Water Content) locally, while for the latter we recorded evidence of browsing at the end of the season. For each trial, we established control sites in empty areas nearby with no CWD presence in order to infer its contribution. The results show that north-facing microsites on south-exposed slopes offer significantly lower temperature and fewer water stress for saplings, in comparison to south-facing microsites. More in general, saplings on deadwood-mitigated microsites are less exposed to desiccation, which mitigates the transplanting shock and facilitates the establishment. Moreover, the presence of lying deadwood increases roughness and, as a consequence, the cost for browsers to reach the seedlings. Using a coefficient expressing this increment, we underline the significant protective effect of CWD against deer browsing. The results of our study highlight the importance of deadwood in providing favorable regeneration microsites, enhancing the probability of sapling establishment and survival, protecting them from deer browsing.