Fungi associated with the decline of Pinus halepensis in Spain

Fungal species richness and composition within needles and twigs in 55 stands of Pinus halepensis, spread out over the whole Iberian Peninsula, were determined. The aim was to evaluate the relationships of fungal communities with local environmental variables, in order to analyze the potential causes of the current decline of this pine species in Spain. A total of 35 fungal taxa were isolated from 1980 moist chambers analysed (990 per vegetal tissue). A taxon within the Alternaria alternata complex was most frequent, followed by Leptostroma pinastri, Aspergillus niger, Diplodia pinea and Phomopsis sp. At the tree level, tissue was a significant response variable and a higher species richness was found in needles as compared to twigs. On the other hand, the multivariate analysis showed the environmental variables 'age', 'shadow', 'elevation', 'mean temperature', 'illumination' and 'availability of water' significantly influenced fungal species composition. In particular, 'mean temperature', was an important variable implicated in the general weakening of this thermophilic pine species, and appeared to be inversely correlated with the occurrence of several conifer pathogens such as Brunchorstia pinea, Cytospora sp., Diplodia pinea, Naemacyclus niveus, Pestalotiopsis stevensonii and Sclerophoma pythiophila. This study shows a possible combined effect of abiotic and biotic stresses in causing the general decline of Allepo pine in Spain.