Acid Rain Far More Hazardous Than Earlier Believed

by Cheryl Dorschner

The acid rain that results may actually create conditions in trees similar to compromised immune systems in humans, establishing a vulnerability with grave potential implications.

"As with immune-compromised humans, plants may appear and function as if they were healthy, until exposed to even a routine stress or disease, then experience declines far more exaggerated than expected," says Professor Donald DeHayes, Dean of the School of Natural Resources at The University of Vermont. DeHayes co-authored a study in a recent issue of the journal "Ecosystem Health."

Up to now, acid rain has been associated with the decline of forests in certain specific locations. DeHayes and colleagues previously documented the mechanism through which acid rain depletes calcium and weakens high elevation red spruce trees, making them more vulnerable to winter freezing injury.

Their new work shows that this mechanism is also applicable to other tree species, including balsam fir, white pine, and eastern hemlock. Because calcium is a critical ingredient in the plant's stress response system, acid rain's depletion of cellular calcium may suppress the capacity of trees to survive environmental stresses.

This connection between calcium deficiency and environmental stress exposure are common components in the declines of several tree species, including red spruce, sugar maple, and flowering dogwood. Their "immune response" hypothesis provides an overarching explanation of how acid rain ultimately threatens forests. The findings are especially relevant now because a growing assortment of human influences -- climate change, pollutants, and new pests and diseases, are burdening our forests.

"If extensive, the decline of individual species would radiate through plant communities," says DeHayes. "It would alter the competition and survival of populations, perhaps even species, including animals at higher levels of the forest food chains." DeHayes points out those calcium deficiencies in plants are passed on to herbivores, altering their nutrition. For instance, birds eating calcium- deficient plant material might have less calcium for egg production. Insects could experience weaker exoskeletons. Mammals could have weaker bones or change in the quantity or quality of milk production. The problems continue through the ecosystem and into economic system.

The research was funded through the EPA with long-term support of Vermont Sen. James Jeffords. "This important new research shows the insidious harm that acid rain is causing to our trees and wildlife," says Jeffords. We know how to stop acid rain, but have not had the will to do so." Jeffords, chairman of the Environment and Public Works Committee, is legislating for the Clean Power Act, which he co-authored and introduced in March 2001.