Site-scale soil conditions influencing the decline of Aleppo pine stands in Mediterranean Spanish woodland

Abstract

Abstract • Background and Aims. Vegetative decline in individuals of plant populations is a phenomenon that involves multiple factors, both biotic and abiotic, that lead to highly irregular and complex spatial patterns of mortality at stand or forest scale. Although it might be assumed that site soil conditions are a predisposing factor to this phenomenon, very little research has specifically focused on this aspect, hence the lack of knowledge in this regard is evident. • Methods. Soil characterization was carried out at 20 sites (10 with evidence of decline and another 10 with no signs of decline) and the results were related to their role as modulation factor of the drought effects, which is the main cause of the observed decline in Aleppo pine stands in the Comunidad Valenciana (Spain). • Results. The soil properties which were found to be the most explanatory are those associated with soil quality in terms of available space for root exploration, which is vital for nutrition and, above all, water uptake. Episodes of decline are associated with stands where soils present a shallow effective depth due to a low degree of profile development or through marked textural anisotropy because of particularly clayey horizons that cause abrupt changes in permeability and aeration. • Conclusion. The inherent soil diversity acts as a predisposing driver to this physiological process that generates a heterogeneous spatial mosaic of patches with different degrees of decline.