Varying climate sensitivity at the dry distribution edge of Pinus sylvestris and P. nigra

Abstract Rear edge populations, those residing at the low-latitude margins of species ranges, represent a critical genetic diversity for species conservation, management, and evolutionary potential. The present study analyses climate-radial growth relations for Pinus sylvestris and Pinus nigra at their dry distribution limit in the Mediterranean basin. The study was conducted in native relict forests of the two species in SE Spain, analyzing radial growth variability and climate-growth relations over time and between different ecological conditions. The lack of strong precipitation signals found could be due to high tree density, appropriate microclimatic conditions and/or high local adaptation. However, previous September temperatures exerted a negative impact on radial growth at all sites, presumably as a result of a prolonged summer drought. By contrast, high temperatures during winter and spring boosted radial growth at most locations. Both the negative and positive effects of temperature have gained relevancy in the last decades and can determine future performance of these Mediterranean pinewoods. Besides common patterns, recorded site-specific signals in climate-growth relationships reveal the influence of different ecological conditions. In this respect, tree-growth variability increased at low elevation coupled with increasing aridity, indicating higher vulnerability to rapid climate changes at low elevations. In contrast, the lack of strong precipitation signals and positive effects of temperatures at high elevation, could buffer the impact of drought and favor the persistence of P. sylvestris and P. nigra rear edge populations.