Assessing climate–growth relationships under contrasting stands of co-occurring Iberian pines along an altitudinal gradient

Current decreasing precipitation and increasing temperatures, together with the growing likelihood of extreme drought events, may heighten the vulnerability of several tree populations in Mediterranean areas. In this study, we analysed tree-ring-width chronologies of three coexisting pine species (Pinus nigra Arn., Pinus pinaster L., and Pinus sylvestris L.) across an altitudinal gradient in the Cuenca Mountain Range (central-eastern Spain), along with soil conditions and stand structure. We quantified climate–growth relationships between basal area increment indexes and regional mean temperature and precipitation minus potential evapotranspiration (P-PET); drought sensitivity was defined as the percentage of growth reduction during an extreme drought event. Local climatic data spanning the 20th century yielded a warming trend and increasing extreme drought events since the onset of the 1980s. The P. nigra populations located at the lower altitudinal border showed the most significant correlation (negative) between mean temperature and declining growth trends. Contrasting to P. nigra, the studied P. pinaster population, also located at lower elevations, showed the higher correlations (positive) between P-PET and the higher mean growth. Aside from growth–climate relationships our results suggest a major effect of soil conditions and stand structure on tree growth and climate–growth responses. Old P. nigra stands showed the lower mean growth, while thinned stands, about 130 years old, located at the core of the elevation range showed positive growth trends resembling a positive relationship with winter-to-spring temperatures and the higher soil organic matter content. P. nigra and P. sylvestris trees growing on soils with low total nitrogen seem to be more negatively affected by drought than would be expected under a linear elevation-related response.

► Local climatic data yielded a warming trend and increasing extreme drought events.
► Growth of Pinus nigra progressively declined as aridity increased at the lower stand.
► Favourable conditions showed lower drought sensitivity and higher growth trends.
► Sensitivity to extreme drought events was increasingly limiting within age.
► Diminishing precipitation exerted greater impact on radial growth in lower stands.