Growth responses to climate in a tree-ring network of European beech (Fagus sylvatica L.) from the eastern limit of its natural distribution area

The first dendrochronological network of European beech (Fagus sylvatica L.) from eastern limit of its distribution was established covering the species' altitudinal range (210-1160 m a.s.l.) and three eco-regions. Statistical analysis revealed spatial trends among the 14 chronologies, with increasing tree-ring variability and synchronicity towards the east, particularly expressed by rBAR (mean interseries correlation). By means of HCA (Hierarchical Cluster Analysis) and PCA (Principal Component Analysis), the chronologies were divided into three main groups: a Mountain, Plateau and Eastern class. These correspond to the Alpine South, Continental and Pannonian bioclimatological zones. Dendroclimatological analysis revealed a general climate response pattern, with summer temperatures, April-May precipitation and April-June drought being the main limiting factors in the study area. The intensity of the correlations increases towards the eastern distribution limits and decreases towards the upper treeline of European beech. Similarly, the length of the climate-sensitive period changes, with the precipitation window increasing from April in the Mountains region to March-May in the East region and the scPDSI (self-calibrated Palmer drought severity index) window increasing from April-June in the Mountains to the previous July to the current September in the East. The western and uppermost site shows signs of being limited by low July temperatures. This chronology network represents a sensitive monitoring instrument to quantify the impact and adaptability of European beech to actual and future climatic change.