Phenological trends of European beech stands along the Carpathian arc: a 20-year MOD13Q1/MYD13Q1 based analysis

European forests are severely threatened by rapid global climate change. Predicting the effects of climate change on the future performance of tree species can be enhanced by using geographical gradients as space-time proxies. This study focuses on analysing seasonal and inter-annual phenological trends for eight sites of European beech (Fagus sylvatica L.) in the Carpathians along such geographical gradient. Using time series of the Enhanced Vegetation Index (EVI) from 2003 to 2022, derived from 16-day MODIS Terra and Aqua vegetation products, combined with meteorological parameters (temperature and precipitation) interpolated for a grid and Land Surface Temperature (LST) data from Landsat, we compared annual forest development at the study sites and extracted key phenological metrics (start, length, and end of the growing season) using the phenofit software package for R. Our results show varied responses of the studied forest sites to climate change. The end of season extended significantly at Soveja (slope = 0.50, p = 0.023). Spring temperatures had negative correlations with the start of season (r = -0.37) and autumn temperatures positive correlation with the end of season (r = 0.43). Understanding these patterns is crucial for developing adaptive forest management strategies in Carpathians.