A CLEAN SLATE? EFFECTS OF THE VAIA STORM AND SALVAGE LOGGING ON FOREST VEGETATION

Natural and anthropogenic disturbances are key factors in forest vegetation dynamics. Forest disturbance regimes are rapidly changing, with increasing magnitude and frequency of extreme events such as pathogen invasions, wildfires and windstorms, possibly as a consequence of climate change [1]. In October 2018, the “Vaia” storm hit the Eastern Italian Alps and destroyed or intensely damaged ca. 42.500 ha of forest with a volume estimation of 8.5 millions m3 of fallen trees [2]. These montane and subalpine forests, which have been managed for hundreds of years, are usually dominated by Picea abies, often derived from old plantations. In summer 2021, the field workshop of the “Gruppo di lavoro per l’Ecologia della Società Botanica Italiana (SBI)” collected data about the vegetation succession and the effects of management practices on forest vegetation after the Vaia storm in the Trento province (IT). We selected four sites, including three treatments at each site: undisturbed forest, storm-disturbed forest with salvage logging and storm-disturbed forest without salvage logging. For each treatment, we randomly selected and sampled three plots of 50 m2 , obtaining a total of 36 georeferenced sampling units (4 sites × 3 treatments × 3 plots). Topographic variables (aspect, slope and altitude) were recorded along with information on the cover of rocks, bare soil, deadwood and different components of vegetation such as shrubs, forbs, grasses, ferns and mosses. We assessed forest structure by measuring standing trees and deadwood. We recorded all the vascular plant species occurring in the sampling units. For each species the percentage cover was assessed. Seedlings and juveniles of woody species were also counted. We compared the rarefaction curves of the three treatments at all sites by means of the iNEXT package using the Hill number framework. We also compared the number of seedlings and juveniles as well as their species richness. Overall, we found 191 species (on average 26 in undisturbed forest, 33 in storm-disturbed forest with salvage logging, and 30 in storm-disturbed forest without salvage logging). An attempt was also made to interpret the evidence relating to the distance between actual and potential vegetation. Our preliminary results show that plant diversity increased in the disturbed areas, with a greater increase in salvaged areas. The number of seedlings and juveniles do not differ among treatments, while weak differences exist in terms of the number of tree species occurring in the regeneration. Our approach contributes to elucidating the short-term effects of the Vaia storm on forest vegetation and will feed the debate on management practices, for example the usefulness of salvage logging for forest vegetation recovery, to be applied in future extreme windstorms