Air Pollution Effects on Forest Ecosystems in North America

Air Pollution Effects on Forest Ecosystems in North America
		by *David L. Peterson* National Biological Service
Air pollution poses a threat to forest ecosystems in several regions of North America. Although there are isolated impacts downwind from point sources such as industrial operations, the major impacts are from regional-scale exposure to ambient ozone and acid precipitation. Acidic deposition (including sulfur and nitrogen deposition) is fairly high in the northeastern United States and southeastern Canada, although symptomatic injury and changes in forest growth have not been clearly linked to a particular pollutant. Recent evidence, however, indicates that long-term inputs of acid precipitation may be altering the chemical equilibrium of some soils, which could result in a nutritional imbalance in trees.
Elevated levels of ozone have resulted in stress in several forest ecosystems of North America: (1) those adjacent to Mexico City (extensive mortality and reduced growth); (2) those in mountains of the Los Angeles Basin in California (mortality and growth reductions); (3) those in the central and southern Sierra Nevada (some reduced growth and widespread symptomatic injury); (4) those in the Rincon Mountains of Arizona (some symptomatic injury); and (5) those in the Great Smoky Mountains (some symptomatic injury).
Recent growth reductions and changes in forest health have been reported for several locations in North America although the role of air pollution in these "declines" must be evaluated in the context of a stress complex that includes climate, stand dynamics, and site factors. Although some lichens are known to be sensitive to air pollution, there is relatively little information on the effects of air pollutants on forest species other than trees. Only if monitoring programs are implemented soon will it be possible to detect how long-term pollutant deposition affects forest health and productivity.
		For further information: David L. Peterson National Biological Service Cooperative Park Studies Unit University of Washington AR-10 Seattle, WA 98195