Interactive effects of tree species mixture and climate on foliar and woody trait variation in a widely distributed deciduous tree

Despite increasing reports of severe drought and heat impacts on forest ecosystems, community-level processes, which could potentially modulate tree responses to climatic stress, are rarely accounted for. While numerous studies indicate a positive effect of species diversity on a wide range of ecosystem functions and services, little is known about how species interactions influence tree responses to climatic variability. We quantified the intraspecific variation in 16 leaf and wood physiological, morphological, and anatomical traits in mature beech trees (Fagus sylvatica L.) at six sites located along a climatic gradient in the French Alps. At each site, we studied pure beech and mixed stands with silver fir (Abies alba Mill.) or downy oak (Quercus pubescens Willd.). We tested how functional traits differed between the two species mixtures (pure vs. mixed stands) within each site and along the climatic gradient. We found significant changes in many traits along the climatic gradient as...