Ozone and forests in South-Western Europe – What have we learned?

Monitoring of forest condition and ozone (O 3) at 83 sites in France, Italy, Luxenbourg, Spain and Switzerland resulted in a number of findings in relation to the knowledge of O 3 exposure (concentration and cumulative AOT40), feasibility of the assessment of stomatal O 3 flux and relationships between O 3 and crown defoliation of beech and visible symptoms on native vegetation. However, the project provides evidence of issues to be addressed within the current monitoring system (data quality, validation sites and response indicators) and indications as to how the monitoring of O 3 risk in the context of an effect-oriented monitoring program can be improved. Documented evidence for a potential risk to forest due to ozone requires an improvement in monitoring methods.