Understanding the relative contributions of competition and climate on individual tree growth is critical to project realistic forest dynamics under projected climate scenarios. Furthermore, present competition levels may reflect legacies of past use. Here, we analyze the effects of climate, site conditions and competition on radial growth in three Scots pine stands located along an altitudinal gradient in central Spain. Current stand structure and retrospective analyses of radial growth (basal area increment, BAI) were used to model changes in tree growth as a function of a spatially-explicit competition index (CI) and climate. Linear mixed-effects models were employed to model BAI and to quantify the growth responses to climate of trees under low and high competition levels. Competition effects on growth were steady over time regardless of tree age. High competition levels negatively affected growth since negative exponential functions characterized the CI-BAI relationships. Tree growth sensitivity to climate increased with decreasing competition intensity. Growth at high elevations was mainly limited by low winter temperatures, whereas warm spring enhanced growth at middle elevations and warm late summer temperatures constrained growth at low elevation. Growth responsiveness to climate is enhanced under low competition levels. Overall, current competition is a more relevant driver of recent growth than climate. Proactive forest management should be adopted to reduce the vulnerability of Scots pine forests currently subjected to higher competition levels and warmer and drier conditions. © 2015 Elsevier B.V.

We would like to thank Javier Donés (Director of Montes de Valsaín), CENEAM, Montes de Valsaín, National Parks Autonomous Agency (OAPN), JCyL and all the participants involved in the International Tree-Ring Summer School in 2012 in Valsaín (Segovia-Spain) (Touchan et al., 2013), and especially Kenza Garah, Maria Tabakova, Virginia Garófano-Gómez and Clara Rodriguez-Morata for their help with the fieldwork, and Ramzi Touchan and Dave Meko for their support during the study. We thank Victor Lechuga for his help in calculating the competition index. R. Sánchez-Salguero is grateful for the postdoctoral fellowship of Fondo Europeo de Desarrollo Regional (FEDER)-Programa de Fortalecimiento de las capacidades en I+D+i de las Universidades 2014-2015 de la Junta de Andalucía. This study was funded by the projects CoMo-ReAdapt (CGL2013-48843-C2-1-R) and FORRISK (Interreg IV B SUDOE 2007-2013) and was carried out within the framework of the COST FP1106 network STReESS. J. Madrigal-González was supported by the project VULPINECLIM (CGL2013-44553-R). We are grateful to Silvia Dingwall for the language review. We thank the editor and two anonymous reviewers for improving the manuscript.

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