Exploring the phenological responses of European beech forests to summer extreme weather events from remotely sensed data

Extreme summer heatwaves are emerging as a major threat to forest ecosystems under climate change, disrupting physiological processes and altering vegetation phenology. Remote sensing offers a unique opportunity to detect phenological responses to climate extremes, capturing changes in canopy greenness, senescence timing, and vegetation condition with temporal continuity and spatial scalability. In this context, the thesis investigates how European beech (Fagus sylvatica) forests respond to such thermal stress, using satellite remote sensing to monitor phenological dynamics across large spatial-temporal scales. The research is structured into three studies, each addressing a specific objective: (i) evaluating the capacity of satellite products to characterize forest distribution across Europe; (ii) comparing satellite-derived and ground-based observations of autumn phenology in beech forests to understand the meaning of their discrepancies and the environmental drivers; and (iii) quantifying the spatial extent and phenological impacts of summer heatwaves, identifying both immediate and delayed responses across biogeographical gradients in beech distribution. The main results reveals that heatwaves suppress summer canopy greenness and accelerate autumn senescence, with region-specific patterns ranging from graded, intensitydependent declines in cooler and mesic areas to threshold-type responses in Mediterranean zones. By integrating multi-temporal satellite data with climatic indicators, this thesis demonstrates the potential of phenology as a valuable remote sensing indicator for monitoring forest vulnerability at continental scale. The findings contribute to support decision-making and to guide future research for the development of adaptive forest management, reinforcing the role of Earth observation in tracking ecosystem resilience under intensifying climate extremes.