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Ozone (O3) exposure at Italian background sites exceeds UN/ECE concentration-based critical levels (CLec), if expressed in terms of AOT40. Yet the occurrence of adverse effects of O3 on forests and crops is controversial. Possible reasons include (i) ability of response indicators to provide an unbiased estimate of O3 effects, (ii) setting of current CLec in terms of cut-off value and accumulation level, (iii) response functions adopted to infer a critical level, (iv) environmental limitation to O3 uptake and (v) inherent characteristics of Mediterranean vegetation. In particular, the two latter points suggest that critical levels based on accumulated stomatal flux (CLef) can be a better predictor of O3 risk than CLec. While this concept is largely acknowledged, a number of factors may limit its applicability for routine monitoring. This paper reviews levels, uptake and vegetation response to O3 in Italy over recent years to discuss value, uncertainty and feasibility of different approaches to risk assessment. [Copyright &y& Elsevier]

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Over the last decades much of the work on the impact of air pollution on forests in Europe has concentrated on central and northern countries. The southern part of Europe has received far less attention, although air pollutants--especially the photochemical ones--can reach concentrations likely to have adverse effects on forest vegetation. Although international forest condition surveys present serious problems where data consistency is concerned, they reveal considerable year-by-year species-specific fluctuations rather than a large-scale forest decline. Cases of obvious decline related to environmental factors are well circumscribed: (1) the deterioration of some coastal forestsdue to the action of polluted seaspray; (2) the deterioration of reforestation projects, especially conifers, mainly due to the poor ecological compatibility between species and site; and (3) the decline ofdeciduous oaks in southern Italy and of evergreen oaks in the Iberian peninsula apparently due to the interaction of climate stresses andpests and diseases. However, besides obvious deterioration, changes in environmental factors can provoke situations of more subtle stress. The most sensitive stands are Mediterranean conifer forests and mesophile forests of the Mediterranean-montane plane growing at the edges of the natural ecological distribution. Evergreen sclerophyllous forests appear less sensitive to variations in climatic parameters, since they can adapt quite well to both drought and the action of UV-B rays. Several experiments were carried out to test the sensitivity of Mediterranean forest species to air pollutants. Most of those experiments used seedlings of different species treated with pollutant concentrations too high to be realistic, so it is difficult to derive adequate information on the response of adult trees in field conditions. Ozone has been proved to cause foliar injury in a variety of native forest species in different Southern European countries, while the effect [ABSTRACT FROM AUTHOR]