Manipulation experiments for the assessment and monitoring of climate change impacts on vegetation of alpine and polar ecosystems.

This thesis focused on the impacts of climate change on terrestrial ecosystems of alpine (Central Italian Alps) and Polar (Maritime Antarctica) tundra habitats, two of the three areas of the world where had been recorded the greatest air temperature warming since 1950. The alpine site is located at the Stelvio Pass where since the 2014 in-situ manipulation experiments started to assess the possible future responses of tundra vegetation to changes of: a) air and soil warming, b) water availability and soil moisture, c) snow-depth and snowmelt time. The PhD project confirmed and assessed the influence of these manipulation experiments, on environmental data, vegetation composition and structure and plant phenology, stressing how responses to the environmental drivers had species-specific differences, but also with influences from plant communities, species ecology and local conditions (topography). The Antarctic site is located at Signy Island (northern maritime Antarctica) where were installed manipulation experiments, comparable to those set up in the Alps, those will allow to compare in the next years the biotic and abiotic responses of different polar and alpine tundra ecosystems. The assessment of any vegetation changes was not possible, because of the logistical constrain and of the short period of manipulation (2 years); however, were presented the experiment design and the preliminary environmental data after the first year of deployment. Finally, through a paleo-climate investigation, that involved the analyses of organic sediment and moribund mosses collected at Rothera Point (southern maritime Antarctica), evidences were provided on how the climate system changed through time.