HydroBeech

Climate refugia are expected to act as important reservoirs of biodiversity under future global warming. Great efforts have recently been made to identify refugia in the landscape using fine-scale meteorological data and models. However, predicting the viability of refugial plant populations in a future warmer and drier climate requires an in-depth understanding of the diverse processes related to their water use. In trees, stable isotope techniques are often used to quantify water use, taking advantage of the distinct isotopic composition of each water pool (i.e., rainfall, fog water, soil water or groundwater) and the partial preservation of this signal in the isotopic composition of tree-ring cellulose. HydroBeech will investigate the ecohydrological and ecophysiological mechanisms operating in an emblematic refugial population of beech (Fagus sylvatica L.) in the Ciron river gorge in SW France. We will combine high-resolution microclimate and stable isotope data in water pools and treering cellulose with state-of-the-art, isotope-enabled ecophysiological and micrometeorological models in order to 1) unravel the effect of fine-scale variation in microclimate and edaphic conditions on tree water sources, 2) construct plot-level tree-ring isotope chronologies, 3) test for a genetic basis of the observed tree behaviour and 4) predict the long-term physiological responses of trees in this refugial population to climate change and forest and river management. The knowledge gained within HydroBeech will be highly relevant for predicting the performance of refugial forest tree populations under a warmer climate and for developing adequate climate mitigation strategies. It will also advance our mechanistic understanding of the tree-ring isotopic signal of deciduous species, which is crucial for both the field of dendro-ecology and climate research using tree-ring-based reconstructions.