Air pollution controls help trees rebound
STOWE, Vt. — The gray trunks of red spruce trees killed by acid rain once heavily scarred the mountain forests of the Northeast. Now those forests are mostly green, with the crowns of red spruce peeking out of the canopy and saplings thriving below.
A main reason, scientists say, is a government-enforced reduction in the kind of air pollution that triggers acid rain.
“We’ve seen it go full arc from declining for some unknown reason, to figuring out the reason, to them doing something about the cause and then the tree responding and rebounding again,” said Paul Schaberg, a plant physiologist. It’s just an amazing science arc.”
In the 1960s through the 1980s, pollution — mostly from coal-powered plants in the Midwest and car emissions carried by the wind and deposited as acidic rain, snow and fog — devastated Northeast forests and lakes, leaching nutrients from soil and killing aquatic life.
Red spruce are particularly sensitive to acid rain and, at the height of the die-off, some forests lost 50 percent of them.
In the 1980s, University of Vermont scientist Hubert Vogelmann brought national attention to the acid rain issue by linking air pollution to forest damage on the slopes of Vermont’s Green Mountains. Airborne chemicals reacted with water and oxygen and then, carried by the wind, were deposited as acidic rain, snow and fog.
The images of dead trees littering mountains in the 1980s helped inspire changes to the Clean Air Act in 1990. The amendments proposed by President George H.W. Bush in 1989 mandated reductions in certain gas emissions and boosted regulation of toxic pollutants.
The researchers examined 658 red spruce trees in 52 plots in Vermont, New Hampshire, New York, Massachusetts and Maine. They found that 75 percent of the trees and 90 percent of the plots showed increasing growth since 2001. They credit cleaner air and a warming climate that extended the growing season.