Predicting Ozone Fluxes, Impacts, and Critical Levels on European Forests

Tropospheric ozone (O₃) is considered to be more damaging to vegetation than any other air pollutant. Public concerns, evidence from research, and increasing scientific knowledge are all driving widespread discussions on ozone risk assessment and dose-response relationships for European forests. In particular, there is high uncertainty concerning the effect of ozone on individual tree diameter increment and forest growth. However, the contrasting results may arise from the different data used as input in terms of sample size and characteristics, and/or from differing methodological choices.

This study therefore aims to make use of over 200 long-term monitoring plots across Europe where ozone concentrations have been measured since 2000, in parallel to forest and vegetation variables. Ozone related effects and critical levels on selected endpoints such as tree growth will be derived by quantifying ozone fluxes, and by (i) applying multiple and various statistical techniques that also consider for other abiotic and biotic environmental factors. The outputs will be validated and up-scaled in space and time by (ii) developing an “Ozone-version” of the physiological process-based model CASTANEA, and (iii) coupling the DO₃SE model with the forest succession (“gap”) model ForClim. Data sources from various networks will be explored and applied for model calibrations, validations, and applications.

The outlined ensemble of statistical and mechanistic model simulations will allow us to detect environmental tipping points leading to strong decrease in stand productivity. This allows for the determination of species-specific, site-specific, and climate change-specific critical ozone levels, which will be an important contribution to the objectives of the UNECE WG on Effects.