Differenze di habitat e comunità ornitiche fra valanghe e piste da sci: un caso studio nelle Alpi Italiane

The Alps, thanks to their complex topography and history, represent today one of the largest wild areas in Europe. Mountain abandonment by man and following rewilding played a part in this process, but human activities still exist, even if in different forms and with different consequences on the environment. In particular, it has been shown how the presence of ski-pistes can have high local importance, but generally entails negative consequences on soil, vegetation and animal communities. Avalanche tracks can be considered the natural counterpart of ski-pistes due to the similar vertical aspect. However, the degree of disturbance generated by ski-pistes realization is greater, having even long-lasting consequences. The aim of this thesis is precisely to compare these vertical open environments in an area of coexistence: the Cottian Alps. Point counts to study the bird assemblage and habitat surveys were carried out between 2021 and 2022 on avalanche tracks (n = 130), ski slopes (n = 180) and control areas (n = 130), for a total of 440 points. Habitat was found to differ significantly among plot types: avalanche tracks (A), being richer in rocks, shrubs and small trees, generally supported a greater structural diversity than ski-pistes (S); these were constituted instead by a prevalence of grass, followed by a diffused bare ground cover attributable to machine-grading. In the alpine zone the whole bird community presented the lowest bird abundance and diversity values in correspondence of ski-pistes, in agreement with previous studies. For grassland/ecotone (GE) species, the main discrepancies regarded open habitats (i.e. ski-pistes and avalances) in relation to control points due to the macroscopically different vegetation in the two lower belts, but ski-pistes still had a high negative impact in the alpine grasslands. Despite the general trend, pure grassland specialists were not penalized in high-elevation pistes, probably because grasslands have now recovered after mechanization and the absence of higher vegetation simulates a treeline lowering; on the other side species needing a more structured habitat were impacted. In the forest belt the two open habitats were widely favoured by semi-open habitat taxa, with some species being more abundant on avalanche tracks and others on ski-runs. Natural and -to some degree- artificial vertical open habitats result to be important as colonizable land for both lowland and high-elevation open-habitat species in the forest belt. In conclusion, it is necessary to account for a more sustainable management of ski-pistes so they can be inhabited and operate as refugia for threatened open-habitat species in the lowest belt; at high altitudes, even if some species can recolonize grasslands, the realization and maintenance of pistes should be done keeping habitat structural diversity, in order to favour also an overall thriving bird community.