Ozone exposure affects tree defoliation in a continental climate

- Crown defoliation is an aspecific indicator of tree damage.
- Defoliation of main tree species in Romania decreased since 2000 to 2010.
- Ozone concentration and AOT40 were the most important predictors of defoliation.
- Ozone uptake was not related to defoliation and was always under the critical level.
- Air pollution modelling helped to investigate ozone impacts on large-scale defoliation data.

Ground-level ozone (O3) affects trees through visible leaf injury, accelerating leaf senescence, declining foliar chlorophyll content, photosynthetic activity, growth, carbon sequestration, predisposing to pests attack and a variety of other physiological effects. Tree crown defoliation is one of the most important parameters that is representative of forest health and vitality. Effects of air pollution on forests have been investigated through manipulative experiments that are not representative of the real environmental conditions observed in the field. In this work we investigated the role of O3 concentration and other metrics (AOT40 and POD0) in affecting crown defoliation in temperate Romanian forests. The impacts of O3 were estimated in combination with nitrogen pollutants, climatic factors and orographic conditions, by applying a non-linear modelling approach (Random Forest and Generalised Regression Models). Ozone concentration and AOT40 under Romanian conditions were more important than meteorological parameters in affecting crown defoliation. In these particular conditions, POD0 never exceeded the critical level suggested by previous literature for forest protection, and thus was not important in affecting crown defoliation.

98