Natural forests of European beech represent important forest ecosystems in Croatia, considering it is our most widespread forest tree species. Growing awareness of climate change, especially of predicted drought events during vegetation AB (Abstract) period, increases the need for research and finding solutions that would contribute to conservation of genetic resources of the species in Croatia. Conservation of genetic resources of this dominant tree species is the prerequisite for conservation of overall biodiversity of its forest ecosystems. One of the research goals was to determine the level of intrapopulation and interpopulation genetic variability of Croatian beech provenances in order to gain insight into the potential of this species for survival in the predicted climate changes. Drought is cited as one of the main consequences of climate changes that could lead to the gradual extinction of European beech. The second goal of the study was to identify provenances III more resistant to drought stress and to determine whether differences in resilience are related to prevailing climatic conditions in different areas of origin. The research was conducted on the offspring of 10 Croatian beech provenances of different geographical origin. During the first year of the experiment, quantitative phenotypic traits (heights, leaf phenology, and the degree of plant damage by late spring frost) were assessed. The plants were divided into two treatments, one represented drought stress and the second control. Plant material (leaves, stems, roots) was sampled at certain time intervals and biomass was measured, followed by physiological parameters (amount of δ13C isotope, ratio and the total amount of carbon and nitrogen, amount of ascorbic acid and amount of phosphorus in leaves and roots). The results of the research indicate a statistically significant intrapopulation genetic variability concerning the analyzed quantitative phenotypic traits and also a significant level of genetic differentiation of the provenances. The most important climatic parameters of the determined genetic differentiation were those that indicate the harshness of the habitat, followed by the parameters that describe the heat and humidity of the habitat. Provenances have shown two different strategies for mitigating the effects of drought stress: 1) increasing root mass, and increasing the amount of nitrogen and ascorbic acid in the redox state, 2) more efficient use of phosphorus from the soil. Finally, beech provenances growing at higher altitudes have shown a wider range of responses to drought stress, and it can be said that in this study such provenances have emerged as a very valuable forest genetic resource in light of climate change.