Anatomical traits and climate associations in Fagus sylvatica along the eastern edge of its distribution

European beech (Fagus sylvatica) is the most ecologically and economically important broadleaf tree species in Europe, yet it is likely to decline in growth across its native range because of climate change, which threatens to increase temperatures by 1.5° C this century together with drought frequency and intensity (IPCC 2019). While tree-ring analyses have typically been employed to understand how trees interact with climatic factors such as temperature and drought, burgeoning dendroanatomical methods can provide more in-depth illustrations of how trees react to such environmental conditions. This thesis investigates the anatomical features in samples of European beech from two sites at the eastern edge of its native range, in Poland and Ukraine. A two-step analysis of beech samples was conducted; first, a typical dendrochronology aided selection of the most synchronized samples in relation to climatic conditions. Then, the selected samples were analyzed anatomically selecting the following xylem traits: mean ring width (MRW), mean lumen area (MLA), cell number (CNo), cell density (CD), hydraulic conductivity (Kh), and mean hydraulic diameter (Dh). This anatomical analysis elucidates how xylem traits in beech change in relation to climate. It was found that precipitation and temperature both affect xylem anatomical features. We found that higher water availability tends to increase MLA and Dh while drought decreases CD. Additionally, temperature is negatively associated with Dh and positively associated with MRW and CNo. Future warming and more intense drought events could reduce beech growth across its native range, whereas the expansion of a beech dendroclimatic network across its native range could help forecast the growth of this vital species in the uncertain future of climate change.