Séminaire EPOC "Tree species vulnerability to fire in mountain ecosystems of the western Alps" Thibaut Fréjaville (Doctorant Irstea, Aix-en-Provence)

European mountain ecosystems are facing an increasing fire risk due to ongoing climate change and fuel build-up following land abandonment. In the western Alps, post-fire observation data remains too scarce that prevents a direct assessment of forest vulnerability to fire in response to global changes. I will present a modelling framework based on fuel structural traits at the community level and on fire resistance traits of dominant trees to quantify mortality rates in these forests. In south-eastern France, analyses of fire-climate relationships over the past decades show that Mediterranean ecosystems have experienced a decrease in fire occurrence and burned areas despite of warmer and drier conditions. On the contrary, an increase in fire activity over French mountain ecosystems was mainly controlled by the climate variability. Simulations of fire intensity and tree mortality within western Alps forest ecosystems were thus performed under locally-extreme weather conditions. National forest inventory of France was used to measure surface fuel parameters within the main forest ecosystems types, and to extrapolate with the help of climate data the fire simulation outputs. A comparison of the relative trends in flammability and vulnerability to fire between forest ecosystems and dominant tree species may help to anticipate the impacts of future fires in these newly-fire prone regions.