Unravelling the associations between climate, soil properties and forest management in Pinus pinaster decline in the Iberian Peninsula

• P. pinaster decline has been observed in the centre of the Iberian Peninsula.
• The role of abiotic and anthropogenic factors in P. pinaster decline was studied.
• Competition and water deficit appeared to operate as predisposing factors.
• Xeric sites may be close to the P. pinaster physiological tolerance threshold.

Forest decline may be a complex disease caused by the interaction of a number of interchangeable factors (both abiotic and biotic), leading to gradual deterioration of the forest. These factors have been classified as predisposing, inciting or contributing factors. Pinus pinaster Ait. is one of the most important forest species in Spain because of its protective value and the high timber yields obtained. Maritime pine decline has been observed in several forests in the centre of the Iberian Peninsula, manifested as transparency at the crown, small needles, foliage discolouration and premature tree death. The aim of this study was to unravel the role of predisposing, inciting and contributing factors in Mediterranean maritime pine decline in Spain. Various parameters were measured in 27 circular plots of radius 15 m in natural stands of P. pinaster ssp. mesogeensis. The data obtained indicated better forest health status in pure stands, in which thinning has been carried out, than in unthinned mixed stands. High values of total height and spring precipitation showed better forest health, whereas high tree density was associated with the poorest forest health status. The results suggest that predisposing factors such as competition and water deficit have triggered the decline of P. pinaster.