Changes in forests and their relationship to air quality

Recent changes in European and North American forests do not demonstrate the existence of forest health problems resulting from regional air quality. For each reported change, there are unconfirmed but plausible explanations that do not rely on air pollution as a mechanism. The possibility of forest health problems caused by regional air quality cannot be ruled out, however. Mechanisms of impact involving ozone may be operative in some commercial forest regions of the United States and West Germany. Whether ozone is affecting forest productivity remains to be determined. Impact mechanisms involving acidic deposition are plausible but may of no practical significance in many forests. Significant impacts of acid inputs are most plausible for high-elevation forests receiving high rates of acidic deposition. Substantial new research programs on air quality and forests are underway in Europe and North America. Dose-response studies and epidemiological surveys are receiving considerable support. These activities are providing data that will support qualitative near-term risk assessments.