A University of Vermont botanist studying the decline of spruce firs high in the Green Mountains says in an article that a growing amount of circumstantial evidence indicates that acid rain is a significant factor in the trees' decline.
"Proving the impact of acid rain on forests is extremely difficult because forests grow slowly and are subject to a wide variety of influences," writes Hubert W. Vogelmann in the November issue of Natural History magazine. "Nevertheless, mounting evidence indicates that acidic rainfall may be impairing forest productivity and killing trees in several regions."
Acid rain, the result of chemical interactions in the atmosphere that turn the pollutants from coal-burning and automobile exhausts into sulfuric acid and nitric acid, has long been implicated in the destruction of aquatic life in Canadian and northern European lakes. Few scientists, however, have gone as far as Vogelmann in linking acid rain to the destruction of vegetation.
As recently as Aug. 30, Carl Bagge, president of the National Coal Association, told the Canadian Bar Association, "Scientists haven't found any sound evidence of acid rain damage to vegetation in the natural environment."
John Corliss, an Agriculture Department research scientist studying acid rain's effect on vegetation as part of a government-wide task force, said yesterday, "We haven't identified yet any clear direct or indirect relationship between vegetation decline and acid rain . But we're just beginning."
In his magazine article, Vogelmann reports that nearly 50 percent of the spruces on the high slopes of Camel's Hump Mountain in northern Vermont have died since 1965, and "tree density, basal area a measure of the amount of standing wood and seedling reproduction also have declined about 50 percent."
Vogelmann discounts the possibility that the trees' decline could have been caused by insects or disease, long-term growth cycles (during which a large number of trees will grow, mature and die within a few years of each other) or changes in climate. His researchers could find no insect culprits, he said, and the affected trees ranged in age from seedlings to 300-year-old spruces.
He points out, however, that the spruces under study grow in "a severe subarctic climate" on thin, naturally acidic soils. "These trees, already growing in a harsh environment, may be highly susceptible to the added insults of acid rain and heavy metals."