Potential Ozone Risk for Selected Tree Species in Austria. Poster, Presented at the 26th Int. Symp. for Environmental Analytical Chemistry, Vienna April 9-12, 1996
Forest ecosystems are subject to numerous stressors, one of them being airborne pollutants. While the mean concentrations of SO2 and NOx significantly decrease with altitude a.s.l., or with the altitude above valley bottom, the ozone concentrations increase up to the timberline. The danger which is imminent on Forest ecosystems through higher ozone concentrations can be assessed with the help of effect-related limit concentrations of ozone (30 ppb for the 18h- and vegetation period mean) and in accordance with the provisional Critical Levels of the UN-ECE ("AOT40"). For both of the above-mentioned criteria, the evaluation shows frequent excesses in Austrian forests, which implies a danger for sensitive plants. However, according to the current standard of knowledge the major Austrian tree species, spruce (Picea abies), appears to be less sensitive; there have not been any concrete indications to the high ozone sensitivity of larch specified under VDI Guideline 2310 either. It is well possible that there is a danger to pine (Pinus sylvestris) and/or to deciduous trees (beech, Fagus sylvatica). Nevertheless one can assume that forest ecosystems, especially those at altitudes above 1,000m a.s.l., are subject to a latent or dormant stress caused by the permanent ozone input, even if that additive stressor were effective only in case of high total stress. By now, there have been no concrete indications of acute danger for Alpine forest systems. Ozone exposure maps allow a visualisation of the spatial distribution of ozone risk as a first step to verify ozone-caused tree injury. Because of great ozone concentration differences even within small regions due to dependence on elevation and day time, the calculation of spatial ozone distribution on the basis of point measurements has to be performed using measurement data and a statistical model considering this elevation and daytime dependence together with a digital elevation model that reflects the spatial pattern of influences to ozone increase and depletion. Series of hourly maps show the diurnal variation of the spatial ozone exposure pattern. Accumulated ozone exposure maps are calculated forAustria by running the model in hourly steps for the summer months and accumulating the hourly ozone concentration excesses of any threshold. The accumulated ozone exposure of 1993 and 1994 is calculated for different thresholds (AOT30, AOT40, AOT60) and related to areas of selected ozone sensitive tree species. The different patterns of potential ozone risk are discussed taking into account the distribution of selected tree species.
