Pinus halepensis and P. brutia provenances present similar resilience to drought despite contrasting survival, growth, cold tolerance and stem quality: Insights from a 45 year-old common garden experiment

To improve forest management strategies in the context of ongoing climate change, a better understanding of the inter- and intra-specific variability of tree performance is needed. Pinus halepensis and Pinus brutia, two major Mediterranean species providing crucial ecosystem services to human populations, have attracted increasing attention as potential candidates for assisted migration in the last decades for their growth performance and adaptation to drought. In this study, we compared 12 provenances of P. halepensis and 13 provenances of P. brutia originating from all around the Mediterranean basin in a common garden experiment established in 1976 in southeast France to identify the best species and provenances. Tree survival, circumference and height, as well as stem straightness and the presence of defects were measured and estimated based on forest inventories conducted in 1983, 1988, 1996 and 2021-22. In 2021, 427 trees were also cored and the resulting tree-ring width series were used to assess radial growth resistance, recovery and resilience to drought. Inter-individual variations in competition intensity were taken into account using a distance-dependent competition index, and did not show any significant relationship with tree resilience to drought, while it was negatively related with tree growth and positively with stem quality. We found only marginal differences among species and provenances in terms of growth response to drought. In contrast, there were strong inter- and intra-specific differences in terms of survival, cold tolerance, growth, and stem quality with P. brutia performing better than P. halepensis on average. Interestingly, provenances performances were not related to the climatic conditions at their origins suggesting that the observed inter- and intra-specific variability was not shaped by climatic gradients. This study is the first to compare P. halepensis and P. brutia resilience to drought and provides insights for the assisted migration of those species.