Impact of ozone on Mediterranean forests: a review.

Ozone impact on Mediterranean forests remains largely under-investigated, despite strong photochemical activity and harmful effects on crops. As representative of O3 impacts on Mediterranean vegetation, this paper reviews the current knowledge about O3 and forests in Italy. The intermediate position between Africa and European mid-latitudes creates a complex patchwork of climate and vegetation. Available data from air quality monitoring stations and passive samplers suggest O3 levels regularly exceed the critical level (CL) for forests. In contrast, relationships between O3 exposure and effects (crown transparency, radial growth and foliar visible symptoms) often fail. Despite limitations in the study design or underestimation of the CL can also affect this discrepancy, the effects of site factors and plant ecology suggest Mediterranean forest vegetation is adapted to face oxidative stress, including O3. Implications for risk assessment (flux-based CL, level III, non-stomatal deposition) are discussed.