Proof the Clean Air Act Reduces Pollution, Improves Forest Systems Revealed in New Study

The Clean Air Act of 1970 effectively restored the vitality of forest systems that had undergone decades of abuse from sulfur pollution and acid rain, according to a new study examining centuries-old eastern red cedar trees in the Central Appalachian Mountains of West Virginia.

Downwind from the Ohio River Valley coal power plants, the region experienced high amounts of acidic pollution caused by sulfur dioxide emissions during the 20th century. However, in analyzing data from the trees going back as far as 500 years, researchers detected a period of marked improvement in the trees' health starting 10 years after the Clean Air Act was passed.

"There are two levels of significance in this research," Jesse Nippert, an associate professor of biology from Kansas State University and a co-author of the study, said in a statement. "One is in terms of how we interpret data from tree rings and how we interpret the physiology of trees. The other level of significance is that environmental legislation can have a tremendous impact on an entire ecosystem."

In fact, the researchers found that the post-1980 data aligned with another period well known for its reduction in fossil fuel emissions: the Great Depression. With the economy in a suppressed state, coal power plants were less productive and the Ohio River Valley underwent a period of reduced output during the 1930s.

"It's kind of interesting that those two very important periods in our history match up perfectly in terms of the responses seen throughout this whole forest ecosystem," Nippert said.

The team focused on red cedar trees for a number of reasons, including their sensitivity to environmental change due to their reliance on surface soil moisture.

"Our data clearly shows a break point in 1982, where the entire growth patterns of the trees in this forest started on a different trajectory," Nippert said. "It took 10 years for that landmark environmental legislation to reduce sulfur dioxide emissions, but it eventually did. When it did, we saw an entire ecosystem recover from years of acidic pollution."