Ozone (O₃) is considered the most dangerous regional air pollutant for forest vegetation in Europe. Both exceedance of critical levels and occurrence of visible symptoms on native plants have often been reported at many sites throughout Europe. On the other hand, effects on growth and crown condition, although reported, are much less clear and documented. Overall, the knowledge relating to actual exposure and effects of ozone on forests in Europe is fragmented, and comparable large-scale information is limited. Within the framework of the EU and UN/EGE Level II forest monitoring programFrance, Italy, Spain and Switzerland have been particularly active in initiating O₃ measurements by passive sampling and investigating symptoms and effects at a number of forest sites as well as at experimental sites under controlled conditions. This activity provided the basis for a new, co-operative project aimed at investigating O₃ levels, risks and actual and potential effects at intensive monitoring plots in South-Western Europe. The project considers 83 sites spread over 1600 km in latitude (from Northern France to Southern Italy and Spain), 2000 km in longitude (from Western Spain to Eastern Italy) and between 5 and 1900 m a.s.l.
The main tree species in this project include Fagus sylvatica L., Picea abies (L.) Karst., Abies alba Mill., Pinus cembra, P. halepensis, P. mugo, P. pinea, P. pinaster, P, sylvestris, Pseudotsuga menziesii, Quercus cerris, Q. ilex, Q. petraea L., Q. robur, Q. suber. This paper provides an overview of the project background, aims, structure and expected results.