Ozone stresses European forests

The symptoms caused by the ozone on the leaves of the field maple ( Acer campestre ) appeared as pinhead-sized spots. (Photo: Marcus Schaub) Ozone causes visible damage to the foliage of European deciduous trees, as shown by a large-scale study led by the Swiss Federal Institute for Forest, Snow and Landscape Research WSL. The researchers found that some plants under certain environmental condition react particularly sensitively to ozone, which is toxic at ground level. Such plants are therefore well-suited as an early warning system. In a transnational field study, researchers have found significant visible damage caused by toxic ozone on the leaves of broadleaved trees - and this, despite the fact that the total ozone concentration remained stable or decreased slightly between 2005 and 2018. These visible foliar symptoms (abbreviated as VFS) were mainly observed on the upper side of the leaves as thin, light green, reddish, or dark brown pinhead-sized spots between the leaf veins. Older leaves were more severely affected.