Air pollution

Abstract

The most important regional impacts of air pollution in Mediterranean forests arise from ozone and nitrogen deposition. Primary pollutants from urban centers, and hot summers lead to high photochemical activity for ozone formation in many Mediterranean regions. Ozone concentrations are typically high in rural and wildland areas removed from urban centers, and thus have the potential to impact Mediterranean forests. Ozone regularly exceeds concentrations where plant damage is expected in southern Europe and California. Chile has moderate ozone, while concentrations are typically lower in the Mediterranean regions of southern Africa and Australia. Anthropogenic nitrogen deposition primarily arises from atmospheric nitrogen oxides and ammonia. Nitrogen deposition is also high in southern Europe and California. Plant and insect community impacts of air pollution have been most studied in California. Although pollution exposure is also high in the Mediterranean basin, forest impacts there have not been widely studied. In California, both ozone and nitrogen deposition have been associated with increased bark beetle attacks and tree mortality. Other changes in insect herbivore communities have also been observed. We found that nitrogen deposition may affect the relationship between fruittree leafrollers and leaf expansion of California black oak. During a leafroller outbreak, trees with nitrogen addition treatments had lower densities of leafrollers, less leaf damage, and leaves had expanded further during early spring sampling.