Site and age condition the growth responses to climate and drought of relict Pinus nigra subsp. salzmannii populations in southern Spain

To assess if tree age may modulate the main climatic drivers of radial growth, two relict Pinus nigra subsp. salzmannii populations (María, most xeric site; Mágina, least xeric site) were sampled in southern Spain near the limits of the species range. Tree-ring width residual chronologies for two age groups (mature trees, age ≤ 100 years (minimum 40 years); old trees, age > 100 years) were built to evaluate their responses to climate by relating them to monthly precipitation and temperature and a drought index (DRI) using correlation and response functions. We found that drought is the main driver of growth of relict P. nigra populations, but differences between sites and age classes were also observed. First, growth in the most xeric site depends on the drought severity during the previous autumn and the spring of the year of tree-ring formation, whereas in the relatively more mesic site growth is mainly enhanced by warm and wet conditions in spring. Second, growth of mature trees responded more to drought severity than that of old trees. Our findings indicate that drought severity will mainly affect growth of relict P. nigra populations dominated by mature trees in xeric sites. This conclusion may also apply to similar mountain Mediterranean conifer relicts.
This project was funded through DIVERBOS (CGL2011-30285-C02-02) and INIA-RTA (RTA2010-00065-00-00). R. Sánchez-Salguero acknowledges a FPU (Formación de Profesorado Universitario) grant (AP2007-04747) (Ministerio de Educación, Spain). We also acknowledge the financial support from University of Córdoba-Campus de Excelencia CEIA3 and AEMET (Agencia Estatal de Meteorologia) for providing meteorological data. We thank Francisca de la Hoz and Angela Merino for their support during field works, and R. Arias for his assistance in the laboratory. J. J. Camarero thanks the support of ARAID and Globimed.