Over recent decades, climate change has been particularly severe in the Mediterranean basin, where the intensity and frequency of drought events have had a significant effect on tree growth and mortality. In this context, differences in structural and physiological strategies between tree species could help to mitigate the damage inflicted by climate variability and drought events. Here, we used dendroecological approaches to observe common associations (synchrony) between indexed ring width in Pinus pinea and P. pinaster, as a measure of degree of dependence on climate variation or growth sensitivity to climate, as well as to analyze species growth responses to drought events through the Lloret’s indices of resistance, recovery and resilience. Based on data from 75 mixed and pure plots installed in the Northern Plateau of Spain, we used modeling tools to detect the effect of the mixture, along with climate and stand-related variables, on the short-term responses and long-term growth sensitivity to climate. Our results showed a trade-off between resistance and recovery after the drought episodes. In addition, different attributes of tree species, such as age and size as well as stand density seemed to act synergistically and compensate drought stress in different ways. The presence of age and quadratic mean diameter as covariates in the final synchrony model for P. pinaster reflected the influence of other variables as modulators of growth response to climate. Furthermore, differences in growth synchrony in mixed and monospecific composition suggested the existence of interactions between the two species and some degree of temporal niche complementarity. In mixed stands, P. pinaster exhibited a lower sensitivity to climate than in monospecific composition, whereas P. pinea enhanced its resistance to extreme droughts. These results allowed us to identify the species-specific behavior of P. pinea and P. pinaster to mitigate vulnerability to climate-related extremes.

We are grateful to the Forest Service of the Junta de Valladolid for their support during the field work. We also thank Adam Collins for revising the English. M. V. acknowledges the FPI scholarship program from the Spanish Ministry of Education. J.G.A. was supported by a Ramon y Cajal fellowship (RYC-2016-20528). This contribution has been supported within the framework of the projects PCIN2017-026, AGL2014- 51964-C2-2-R, AGL2017-83828-C2.1R and RTA2013-00011-C2.1, of the Spanish Ministry of Economy and Competitiveness, and 778322-CARE4C H2020. Finally, the authors are grateful to the anonymous reviewers whose comments and suggestions significantly improved both clarity and precision of the paper.

16 Pág. Instituto de Ciencias Forestales (ICIFOR)

Peer reviewed