Analysis of the impacts of geomorphological disturbance on alpine and polar vegetation.

Under a context of climate change, polar and alpine regions have been demonstrated to be highly susceptible to climatic factors in various scientific fields. One aspect of susceptibility is treated in this thesis in terms of biogeomorphology, in particular for those geomorphic processes that couple the surficial displacements with the vegetation distribution. For these reasons, 3 study areas have been selected in polar (Svalbard and Antarctica) and alpine (Central Alps) regions to carry out this project. The methods used are different depending on the scale and the location of the target. On the Alps, at large scale, surface and climatic data have been used to produce thematic maps useful for a surface dynamic prediction model, while at landform scale, various system have been chosen to observe surface displacements (e.g., painted lines, height-o-meter) in relation to the vegetation distribution (vegetational relevé, line intercept). To quantify small-scale processes, a close-range photogrammetric application has been developed to produce detailed digital elevation models (DEMs) at a millimetric resolution. In the Arctic, ground thermistors and a time-lapse camera were set on a circumpolar active layer monitoring (CALM) grid to assess relationships among ground surface temperature (GST), snow distribution and active layer thickness (ALT) at a sub-metric scale. For understanding the effect of thaw depth on the CO2 fluxes on an arctic tundra environment, an infra-red gas analyzer (IRGA) system was coupled with a frost probing survey on different vegetation communities. In Antarctica, ground penetrating radar (GPR) with electrical resistivity tomography (ERT) have been utilized to detect ice content in 2 rock glaciers and an ice-core stratigraphy validated the digital findings. The results of this project demonstrate that a novel prediction model that take in consideration both surface and climatic data (in particular snow distribution/persistence) to quantify mountainous surface displacement is possible. In addition, the annual surface velocities of 3 alpine rock glaciers were calculated and associated to different geomorphic processes that, in turn, create specific niches for alpine tundra species, able to tolerate specific substrate rates. Further, for small processes like needle ice, new minima of soil water content and cooling rate have been defined to initiate its formation, as well as the importance of minimum air temperature for the length of ice needles. Needle ice dynamic has been quantified and coupled with a high spatial variability as well as the absence of relation between frost heave and frost creep. In the Arctic we have demonstrated how small-scale spatial distribution of snow cover affects GST, leading in turn to a high spatial variability of ALT. This is majorly driven by the microtopography of the surface in terms of slope and convexity. ALT is also the best driver of net ecosystem exchange (NEE) in arctic tundra and, coupled with the importance of soil temperature for ecosystem respiration (ER), it is a novel key of interpretation of the arctic carbon cycle. In Continental Antarctica 2 active rock glaciers have been demonstrated to be ice-cored, differently than thought in the past. This led consequences for their proved glacial origin and also for the type of creep occurring within their bodies. The strength of this project could be considered as the dependence of geomorphic processes (that induce surface displacements) on climatic factors, thus being able to be extrapolated under the future climate change scenarios. In addition, despite considerable differences in vegetation composition and functioning, the 3 distant study areas account for similar geomorphic processes that could be compared in future research to have a global understanding of surficial dynamics.