Dendroecology in common gardens: Population differentiation and plasticity in resistance, recovery and resilience to extreme drought events in Pinus pinaster

Quantifying intraspecific genetic variation and phenotypic plasticity of traits involved in drought tolerance is essential to forecast forest tree vulnerability to climate change. Tree ring analysis was applied to retrospectively assess the resistance, recovery and resilience of a Mediterranean pine in the face of extreme climate episodes. We combined a dendrochronological approach with the analysis of common-garden tests to disentangle genetic, environment and genetic-by-environment effects in growth responses of 10 P. pinaster populations to two extreme climatic events. Trees were 43 years old and had experienced two intense droughts, in 1995 and 2005. Drought events caused drastic reductions in secondary growth, but trees showed high capacity to recover pre-drought growth rates. The differences in the characteristics of the two drought events and the environmental distance between sites strongly modulated maritime pine responses to extreme droughts. However, a common among-population signal across sites and events was detected in the drought response strategy. Among-population variation in response to extreme droughts was evident for the resistance and recovery components, two strategies that appeared to trade-off between each other. Populations from Atlantic climates showed higher resistance but lower recovery capacity, whereas Mediterranean origins prioritised recovery over resistance. Mediterranean populations showed a more conservative strategy that indicated an adaptive advantage under water stress, reflected in greater long-term survival. The abovementioned relationships were clear in the site where the impact of the drought events was strongest, but not in the more favourable site. Differences in relationships between sites reflect that strategies of populations to cope with drought are strongly context dependent. Based on these results, we infer that future extreme droughts will differentially affect P. pinaster populations across the natural range of the