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

Background and aims Decline in tree species is a complex phenomenon involving multiple factors, among edaphic conditions are assumed to play an important role as factor of predisposition of forests to this process. In this regard, scarce information exists on the effects of the internal variability of the soil with depth on the predisposition to decline, an aspect that requires further evaluation. Methods Characterization of the internal variability of soil was carried out at 20 sites (10 with evidence of decline and 10 with no signs of decline) and the results analyzed to determine their role in modulating the effect of drought, which is the main cause of the observed decline in Aleppo pine stands in the Comunidad Valenciana (Spain). Results The soil properties found to be the most explanatory were 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 have 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 internal variability of the soil, closely linked to the degree of pedogenetic development, is identified as a factor that plays an important role in predisposing the vegetation to the effects of drought.