Dec 19 2018
Excessively high ozone levels still prevail in European forests. Even remote locations are known to have high ozone concentrations because precursors responsible for the formation of this pollutant are transported over long distances.
Visible ozone symptoms on a field maple leaf (Acer campestre L.). The dark dots represent collapsed cells, whose cell walls have been oxidized by ozone. (Image credit: Marcus Schaub, WSL)
However, there is good news: ozone concentrations are reducing gradually but steadily throughout Europe. These latest trends have been reported by Forest researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL).
ICP Forests is a network of forest sites spread across Europe and earmarked to analyze the impacts of air pollutants on forests. Since 2000, researchers have been measuring the concentrations of ozone on 233 research locations in 18 countries, and so far, they have noticed a slight but statistically substantial reduction in mean summer concentrations. However, Southern Switzerland continues to be one among the many regions to have the highest ozone levels in Europe; in Northern Europe, areas are less impacted.
On several sites of the ICP Forests monitoring network, the aggressive pollutant leads to visible symptoms on needles and leaves. The development of symptoms relies on the type of species and how well the trees are supplied with nutrients, water, and light. Moreover, ozone would not only impact tree growth and water metabolism, but it would also contribute to forest degradation and their essential services: these include protection against natural hazards and of biodiversity, provision of clean groundwater and air, and timber for energy and construction.
WSL scientists have summed up these results in ICP Forests Brief No. 3. Their main messages are as follows:
- Ozone is a gaseous air pollutant that occurs in remote regions—owing to the transport of airborne pollutants over long distances—at levels that cause visible symptoms in plants.
- In spite of a substantial reduction, ozone levels at ICP Forests’ sites continue to surpass the threshold value beyond which adverse effects can take place.
- Foliar symptoms caused by ozone have been noticed on woody plant species throughout Europe.
- More observational and long-term monitoring analyses are required to better measure dose-response associations and a possible effect on forest growth.