Drought Responses in Mature European Beech Forests Vary Along Regional Environmental Gradients and Differ Among Admixed Tree Species.

Climate change is increasing drought frequency and intensity, yet the drivers of variability in tree drought responses remain incompletely understood. We analyzed drought responses of Fagus sylvatica and seven admixed tree species across 62 forest stands in the Vienna Woods (Austria) using tree-ring width, stable carbon isotopes (δ13C), and tree-ring calcium concentrations. Drought resistance and resilience of Fagus sylvatica stands increased along a regional climate gradient, indicating smaller growth reductions and a return to pre-drought growth levels at warmer, drier sites, whereas stands at cooler, moister sites frequently remained below pre-drought growth levels. In addition, drought resistance decreased with increasing stand productivity and foliar nutrient status, indicating greater growth reductions in productive, nutrient-rich stands. Tree-ring δ13C and calcium concentrations increased during drought, indicating physiological stress; however, neither parameter explained spatial variation in growth reductions, consistent with a potential decoupling between short-term physiological responses and longer-term growth dynamics. Admixed species exhibited contrasting drought-response strategies. Quercus petraea and Quercus cerris showed stronger growth reductions but returned more rapidly to pre-drought levels than Fagus sylvatica. Pinus nigra and Larix decidua returned to or exceeded pre-drought growth levels, with Larix decidua showing post-drought overcompensation. These findings suggest that mixed forests comprising species with contrasting drought-response strategies may enhance resilience under future drought regimes.