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As acidification of forests slows new climate-related threats to forest, ecosystems emerge

In the 1970s and 1980s, acid rain and concerns about related forest dieback in many parts of Europe led to heated debates, driving the negotiations on the UNECE Convention on Long-range Transboundary Air Pollution. An International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) was subsequently established under the Convention to keep close track of the health of the region’s forests.

According to the 2016 Convention assessment report, acidification of forest and other ecosystems is in decline or slowing. As a result of emission reductions under the Convention, deposition of acidifying pollutants such as sulphur are now much lower, and some forest ecosystems are showing signs of recovery.

However, while acidification trends have slowed, interactions between air pollution and climate change present additional stress factors for forest ecosystems. A group of scientists discussed these interactions at the sixth ICP Forests Scientific Conference “Air pollution, climate change and forest ecosystems: Evidence for effects, adaptation, and mitigation strategies”, held in Bucharest on 16 and 17 May 2017.

Experts discussed the impacts of ground-level ozone and nitrogen on forest ecosystems in a changing climate. Elevated ground-level ozone levels will decrease photosynthesis significantly, directly affecting plant growth and other plant functions. In addition, indirect effects of air pollution, such as nitrogen deposition, can cause nutrient imbalances and increase sensitivity to other damaging agents, which may also increase in a changing climate. The negative impact of more frequent and severe drought episodes and other weather extremes like storms, expected to result from climate change, will be magnified. At the same time, insect and fungal species might expand their distribution range, severely damaging forest ecosystems.

The reduced performance and impaired health of forests affects us all. By absorbing carbon dioxide and filtering the air we breathe, trees and other plants help mitigate climate change and improve air quality. Reduced tree and plant performance thus means less effective filtering capacities to clean our air. The quantification of the response of forest ecosystems to a changing environment is thus fundamental for determining the long-term sustainability of forest ecosystems, which ICP Forests experts will continue to research.