Trees killed by acid rain in Špindlerův Mlýn, Czech Republic © Flickr/kh1234567890
Air pollution has long been recognized as a detriment to the world’s flora. Pollutants such as nitrogen, sulphur dioxide, heavy metals and ozone can be conveyed in the atmosphere over great distances as gases or microscopic particles. Tree canopies are very efficient at capturing deposition of, or filtering, atmospheric pollutants of all kinds resulting in high inputs to forests. Deposition of pollutants can impact ecosystems directly or through soil acidification and eutrophication.
Ground-level ozone (O3), the most important air pollutant affecting forests worldwide, is known to reduce photosynthesis, growth, and other plant functions. It also enhances susceptibility to pathogens and results in leaf chlorosis or senescence and forest decline.
The deposition of atmospheric nitrogenous pollutants emitted from industrial, urban and agricultural sources is also of great importance as they affect growth, biodiversity and biogeochemical cycles in forest ecosystems in many areas. Nitrogen oxides (NOx) result in altered plant growth, enhanced sensitivity to secondary stresses, and eutrophication. At low levels and in nitrogen-limited ecosystems, such as boreal forests, nitrogen may enhance growth.
The importance of some industrial air pollutants, such as sulphur dioxide (SO2) and heavy metals, has risen in recent years as a result of the rapid industrialization of some countries which often lack adequate environmental considerations and controls. The major source of SO2 is from the combustion of fossil fuels containing sulphur. Impacts on vegetation include leaf chlorosis, reduced plant growth and vitality, and forest decline.
Abiotic disturbances and their influence on forest health
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