Differential tree-growth responses to local and large-scale climatic variation in two Pinus and two Quercus species in northwest Spain

We assessed the seasonal climatic response of 2 Pinus and 2 Quercus tree species in a littoral island in northwest Spain, analyzing earlywood, latewood, and total ring widths. We used bootstrapped response functions to identify the variables controlling growth, and we estimated the pure and shared effects of local climate components (temperature and water balance) and a large-scale atmospheric pattern (North Atlantic Oscillation, NAO) on tree growth using a variance partitioning approach. For all species, the response functions showed stronger climatic signals in latewood and total ring than in earlywood. The pure effects of temperature, water balance, and NAO on tree growth were significant. However, a null shared effect between local climate and NAO was evidenced due to the absence of a direct link between NAO in the previous autumn and the other significant climatic variables. Pinus pinaster was the species most sensitive to local climate, mainly to water availability during its active period as a consequence of higher water use efficiency. Quercus growth was negatively influenced by winter temperature, and growth of P. pinea and both Quercus species was inversely related to NAO in the previous autumn. The obtained results suggest that Q. robur and Q. pyrenaica have similar growth behaviour and climatic sensitivity. However, both P. pinea and P. pinaster showed contrasting growth dynamics and sensitivity in this Atlantic littoral island, despite their common Mediterranean origin.