Effect of atmospheric pollution on forested areas of Pinus radiata in the Basque Country (Spain): influence of highways

This study forms part of the E.P.O.C.A. project (Estudios en el Pirineo Occidental de la Contaminación Acida) and more specifically of the section ‘Determination of the possible impact on forested areas of the Basque Country’. The main aim of this section is to study the forested areas of Pinus radiata. Different methods have been used to establish the level of deterioration of the forested areas of Pinus radiata as well as the reasons behind this deterioration. The methods include inventories of forest damage; nutritional, biochemical and symptomatogical analyses of pine needles; and soil analysis and analysis of the content of the main ions of both dry and wet deposition under the forest canopy. We have observed symptoms of deterioration in areas of Pinus radiata near highways with heavy traffic. The damage observed, however, is not different from that found in other areas not influenced by highways. On the contrary, the evolution of forest damage between 1989 and 1990 indicates that those areas nearest to the highways are those that show a lower temporal increase in forest damage. The possible fertilizing action of carbon monoxide (CO), nitrogen dioxide (NO 2) and nitrate (NO 3) originating partly from automobile exhausts and the possible protective action of automobile smoke against pathogens are some of the hypotheses that may explain the positive influence of the highways.