Air pollution and forest health: establishing cause and effect in the forest.

I participated in a NATO Advanced Research Workshop titled “Effects of Air Pollution on Forest Health and Biodiversity in Forests of the Carpathian Mountains,” in Stara Lesna, Slovakia from May 22–26, 2001. Researchers from Canada, Czech Republic, Poland, Romania, Slovakia, Ukraine, and the U.S. met to present their results from a three-year cooperative study of tree health and air quality monitoring in forests of the Carpathian Mountains in Central Europe. Much of the work reported related to assessing the crown condition of trees in permanent plots in natural or managed (planted) forests in the mountains. The endpoint was tree condition, with results extrapolated to the forests in the Carpathian range. From this I learned that, of the 50,000 trees evaluated, European beech (Fagus sylvatica) was the most healthy, while Norway spruce (Picea abies) (the principal forest tree) and white fir (Abies alba) sustained crown defoliation of up to 12.8%. The cause of this crown defoliation and tree decline was usually attributed to “air pollution” as a generic term and an automatic assumption. It is well known that deposition of heavy metals and acidic sulfur and nitrogen compounds can cause tree decline and predispose affected trees to bark beetles and climatic damage. Chemical analyses can also be done to detect metals and sulfur compounds in trees and soils. Sometimes these analyses were done, but most often the assumption was that crown defoliation was caused by air pollution. The assumption was that given sufficient exposure to high enough concentrations of toxic elements, sooner or later there will be a visible adverse response.