TREES AS INDICATORS OF CLIMATE CHANGE, GEOMORPHOLOGICAL PROCESSES AND ANTHROPOGENIC IMPACT IN NORTHERN ITALY

Climate is changing due to both natural and anthropogenic causes. Among the several natural “sentinels” of climate change, trees potentially represent excellent indicators for reconstructing the changing climatic conditions in the recent and remote past and for monitoring the impacts of the current global warming and the related environmental conditions. Trees respond to changes in climate (air temperature, precipitation rate, water availability, etc.) and environment (soil nutrients, pathogen infections, mechanical wounding, etc.) both rapidly, modifying their tree-ring growth rate and physiological processes, and slowly, modifying their distribution. Chemical elements and pollutants deriving from human activity can mask the climatic signal but, at the same time, trees become precious collectors of data that can be used for multidisciplinary research. In this Ph.D. project, I aimed at testing the potential use of trees as indicators of climate, environmental and human impacts in different morphoclimatic conditions, and to investigate if natural and anthropogenic conditions can mask the climatic signal recorded in trees. For this purpose, I selected different key sites in northern Italy. I applied remote sensing techniques, dendrochronological and dendroisotopical approach and the investigation of Volatile Organic Compounds both in tree leaves and in tree rings at the Miage Glacier (AO), the widest debris-covered glacier in Italy. This site has been chosen because of its uniqueness: the Miage Glacier is the only glacier, in the southern side of the Alps, characterized by the presence of abundant supraglacial vegetation that confers an important ecological value to the site. The Miage Glacier has been recognised as a geomorphosite for its scientific, scenic, cultural, economic and educational values. The results show that high-resolution satellite images allow the rapid detection of supraglacial trees whenever their density is high and that tree establishment is driven by supraglacial slope, debris thickness, glacier thickness and surface velocity. Supraglacial trees are characterized by tree-ring width, stable carbon and oxygen isotopes and needle volatile organic compounds that are significantly different compared to trees located outside the glacier. The dendrochronological approach also resulted to be successful for defining areas affected by glacial melting water and, as a consequence, for assessing geomorphological hazards in glacial environments. Tree-ring width and terpenes in annual tree rings were found to be valuable indicators of fungal infection in mountain environments. I also performed magnetic and mineralogical analyses of tree bark samples both at the head of a sample Alpine valley, in Santa Caterina Valfurva (SO), near one of the widest Alpine glacier, the Forni Glacier, and in an urban polluted context, the city of Milan, in order to identify the accumulation rate of magnetic particles and compare different morphoclimatic environments. The results show that outer tree bark can be useful for monitoring the distribution of pollutants with magnetic properties and suggest the role of trees as PM sinks in urban areas. Overall, the results presented in this thesis represent a contribution for a better understanding of the potential use of trees both in high mountain environments and in urban areas for monitoring the impacts of the current climatic and environmental changes. Some of the proposed approaches represent scientific novelties because were never applied in extreme environments or were never considered in the context of the current climate change.