Mixed stands reduce Abies alba tree-ring sensitivity to summer drought in the Vosges mountains, western Europe

•We study tree-ring responses to climate of Abies alba in western European mountains.•We compare responses of pure stands to those of three different mixtures.•Climatic drivers are temperature at high elevation and drought at low altitude.•Mixture reduces A. alba sensitivity to summer drought.•Mixture effects depend on local climatic conditions. In most dendroecological studies, climate–tree growth relationships are established for trees growing on pure stands. However, response to climate may be affected by inter-species interactions and local constraints, which beg the question of the effect of mixture on tree growth response under various ecological conditions. To assess these effects, climate–tree growth relationships of pure Abies alba stands were compared to those of three different mixtures: A. alba with Fagus sylvatica, with Picea abies and with both species. 151 stands (456 A. alba trees) were sampled in the Vosges mountains in north-eastern France under three contrasted climates, from low altitude and dry conditions (mean precipitation in July 900m). We sampled adult trees and homogeneous stand conditions to clearly assess differences in sensitivity to climate. Climate–tree growth relationships were evaluated from 12 A. alba chronologies (four mixtures×three climatic conditions) through pointer years and response function analyses. Late previous summer conditions and current summer soil water deficit and temperature played a major role on A. alba growth. Results showed greater sensitivity to temperature at high elevation, and to summer drought at low altitude and under dry conditions. Mixture allowed maintaining a higher level of A. alba growth during extreme climatic events and reduced A. alba response to summer drought especially under the driest contexts. Different facilitation processes may explain mixture effects such as changes in rooting depth, water input by stemflow and rainfall interception. This differentiated functioning of mixed forests highlights their importance for adapting forest management to climate change.