Climatic signals of tree-ring width and intra-annual density fluctuations in Pinus pinaster and Pinus pinea along a latitudinal gradient in Portugal

Tree-ring width integrates the prevailing environmental conditions during the whole growing season (annual resolution). Other wood anatomical traits, like intra-annual density fluctuations (IADFs), imprint environmental conditions within the growing season (sub-annual resolution). IADFs are anatomically characterized by latewood-like cells within earlywood or earlywood-like cells within latewood. Under climate change scenarios, it is increasingly important to understand which traits are more relevant in the adjustment of long-lived species. We established a latitudinal transect along Portugal and compared tree-ring width and the frequency of IADFs in Pinus pinaster growing under temperate and Mediterranean climate, and of P. pinaster and P. pinea growing under Mediterranean climate. Pinus pinaster growing under temperate and Mediterranean climate showed similar correlations between climate and tree-ring width, whereas P. pinaster and P. pinea under Mediterranean climate presented a different pattern of climate–growth correlations. We therefore suggest that the climate–growth response is species dependent. However, the climate–IADFs correlation was driven by site conditions and less related to the species. We propose that the correlations between climate and growth are conserved within the distribution range of a species, whereas IADFs function as a finer morphological adjustment to the environmental conditions during the growing season.