New concern about acid rain: trees' immune systems may be damaged by pollution. (Environment).

Acid rain may be even more damaging to forests than previously thought: Not only does acid rain wilt and destroy trees' leaves and needles, but new research shows it also leaches their life-sustaining metal nutrients from topsoil.

The news comes from University of California-Riverside

scientists who experimented on trees in Chile's pristine forests--far removed from industrial pollutants--to learn how forest ecosystems are supposed to work if left alone. The scientists were surprised to discover that trees obtain their essential metal elements (such as potassium, magnesium, and calcium) almost exclusively from atmospheric deposits in the soil, not from weathered rocks buried deep in the soil. And they were alarmed to learn just how small a pool of these nutrients is available to nourish the trees.

"The small size of this upper soil nutrient pool has important implications for industrially influenced forests in the northeastern United States and in Europe," says UC-Riverside earth scientist Martin Kennedy. "These forests may be more vulnerable to the effects of acid rain than we had previously thought."

The scientists' findings reveal acid rain's potential to leach more of these vital metal elements from the topsoil than are being deposited, and the result can be injurious or even deadly to trees. In Germany, trees are already dying from magnesium deficiency caused by acid rain's nutrient leaching.

Acid rain occurs when sulfur dioxide and nitrogen oxides, byproducts from the burning of fossil fuels such as coal, react in the atmosphere to form acidic compounds. The resulting mild solution of sulfuric acid and nitric acid becomes acid rain when it falls to the ground with precipitation--rain, fog, and snow. While scientists have long known that acid rain weakens trees by damaging their leaves, limiting the nutrients available to them, and exposing them to toxic substances slowly released from the soil, new research from the University of Vermont (UVM) shows that acid rain weakens many trees' immunity to environmental stress.

Acid-rain-induced calcium deficiency, which makes trees more vulnerable to winter freezing injury, is a known factor in the decline of red spruce, sugar maple, and flowering dogwood species. Now UVM researchers find that balsam fir, white pine, and eastern hemlock are also falling prey to environmental stress as a result of calcium depletion.

"If extensive, the decline of individual species would radiate through plant communities. It would alter the competition and survival of populations, perhaps even species, including animals at higher levels of the forest food chains," says Donald DeHayes, dean of the University of Vermont's School of Natural Resources. He explains that deficiencies in plants are passed on to herbivores, so, potentially, birds eating calcium-deficient plant material could have less calcium for egg production, insects could have weaker exoskeletons, and mammals could have weaker bones. The quantity or quality of milk production could be at risk as well, which would carry over acid rain's damaging effects from the ecosystem to the economic system, DeHayes warns.

As scientists sound their alarms, some U.S. politicians are responding. The Clean Power Act, a bill currently under consideration by the U.S. Senate, proposes a comprehensive power plant cleanup package that would reduce acid-rain-causing emissions and other environmental hazards nationwide.

"This important new research shows the insidious harm that acid rain is causing to our trees and wildlife," says Senator James Jeffords (Independent-Vermont), co-author of the Clean Power Act. "We know how to stop acid rain, but have not had the will to do so."

Sources: University of California-Riverside, 900 University Avenue, Riverside, California 92521. Telephone 1-909-787-1012; Web site www.ucr.edu.

University of Vermont, Burlington, Vermont 05405. Telephone 1-802-656-31 31; Web site www.uvm.edu.