Exploring the autumn phenology of European beech forests: a comparative analysis of ground-based and satellite observations

Vegetation phenology is closely linked to the functioning of multiple aspects of forest ecosystems and is regulated by a complex interaction between climatic and environmental factors. In particular, the end of the growing season has proven to be very sensitive to extreme weather events, leading to alterations in the regular physiological behaviour of forests. Autumn phenology represents a little-explored season due to the highly variable response of forests to environmental factors. This work aims to investigate late-season dynamics by comparing ground-based and satellite observations in European beech forests. The objectives of this research are: (i) quantify the temporal discrepancy between phenology obtained from ground-based observations (PEP725 stations) and satellite-derived data (MODIS EVI time series); (ii) assess the influence of the main biophysical factors, i.e. latitude, elevation, total annual precipitation and mean annual temperature, on the mismatch. The results identified key end-of-season metrics, distinguishing different stages during the season that were affected differently by biophysical factors, such as temperature and precipitations. This study highlights the complexity of late-season phenology, emphasizing the crucial role of remotely sensed phenometric analysis compared to ground-based observations, revealing a fundamental contribution to understanding of late-season phenology in the context of climate change.