Ozone is considered to be the most important air pollutant in Austria. During the last two decades, ambient ozone concentrations have increased by up to 0.5 ppb per year on average in forested areas. In order to assess the ozone impact on forests, a nationwide map was modeled based on a modified AOT40 concept, taken into account i. the altitude dependent adaptation to pre-industrial ozone levels, ii. the ozone uptake and iii. the hemeroby of Austrian forests. It became obvious, that 61 % of the Norway spruce (Picea abies) forests have been heavily loaded with ozone at a level of more than 10.000 ppb.h. This ozone risk map has been verified under an extensive tree-physiological research program at three field study sites exposed to different ambient ozone levels. Data from mature Norway spruce trees suggested, that several metabolic reactions were changed according to the ozone level. Thus, it was possible to establish five tree-physiological attributes with significant ozone induced changes: transpiration rate, light saturated electron transport rate, saturated fresh weight of needles, repair-capacity of damaged photosystems and dry matter of needles. In combination, these ozone sensitive parameters finally verified the modeled ozone risk at the study sites.
