The adaptive potential of Douglas-fir to Drought:twenty years of collaborative investigation

PHILIPPE ROZENBERG; DALLA-SALDA GUILLERMINA; VINCENT SEGURA; MANUELA RUIZ-DIAZ; ALEJANDRO MARTINEZ-MEIER; HERVÉ COCHARD; CHAUVIN THIBAUD; ANNE SOPHIE SERGENT; MARÍA ELENA FERNANDEZ

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Conferencia; adapting forest ecosystems and wood products to biotic and abiotic stress; 2019

During the last 50 years, Douglas-fir became a key conifer species in France for forest managers andthe wood industry. The French Douglas-fir forest comes from seed orchards composed of trees fromthe most temperate and humid coastal parts of the natural range. Global warming increases theirvulnerability to drought stress. During the last 30 years, these stands have suffered diebacksassociated to drought and heat waves. During the last 20 years, we developed genetic,dendroecological and ecophysiological studies of the Douglas-fir adaptation potential to drought.We found that wood density, wood anatomy and resistance to cavitation play a major role.Cavitation process seems to start in the latewood and to finish in the transition part betweenearlywood and latewood. We showed that intra-ring density variables were significantly related withsurvival to drought and with resistance to cavitation in different parts of the tree and at variousgenetic levels. We established with common garden experiments that variable climatic selectionpressures in the natural area have shaped local adaptation at different geographical scales, withprovenances from the warmer and dryer parts showing increased wood density and resistance tocavitation and more efficient xylem cell wall pits. However, these global trends does not obscurestrong within-provenance variation, contrasting genetic determinism of ring density variables andcomplex relationships between the variables involved at different spatial, geographical and timescales. Nevertheless, the observed adaptation strategies suggest that the French plantations maycross their adaptive limit shortly after the global warming exceeds 2°C. We were able to reveal thatbeside the consistent statistical and explanatory trends of Douglas-fir resistance to drought, therewas a multifaceted network of relationships revealing the force and the complexity of the Douglasfirevolutionary potential of adaptation to drought.