Sensitivity of Eurasian Rear-Edge Birch Populations to Regional Climate and Local Hydrological Conditions

South rear-edge populations of widely distributed temperate and boreal tree species such as birches (Betula pubescens Betula pendula) are considered particularly vulnerable to climate warming, at the same time, they constitute genetic reservoirs drought-adapted ecotypes. Here, we compared radial growth patterns responses climate, river, or reservoir flows a drought index (southernmost) (Toledo Mountains, central-southern Spain) with located in northern Spain B. pendula. Then, performed comparative analysis across Europe pendula populations. The main climatic constraint birch was high summer water deficit, although effect local hydrological conditions important We found declining trends stands dating from early 21st century, related decreasing availability increasing aridity. Our results also suggested distinct climate-growth associations that show how further south warmer locations were more sensitive stress. Drought-induced decline can be exacerbated by human land uses, leading reduced river inflow, thus endangering their southern distribution limit. Protection threatened requires adequate management resources.