Red cedars show that Clean Air Act is reducing pollution, improving forests

Ecologists studying centuries-old eastern red cedar trees in the Central Appalachian Mountains of West Virginia say the trees are recovering from decades of sulfur pollution and acid rain.

The research team spent four years studying the trees which are in an area downwind of the Ohio River Valley coal power plants. The area experienced high amounts of acidic pollution -- caused by sulfur dioxide emissions -- in the 20th century.

By studying more than 100 years of eastern red cedar tree rings, the scientists found that the trees have improved in growth and physiology in the decades since the Clean Air Act was passed in 1970.

"There is a clear shift in the growth, reflecting the impact of key environmental legislation," says Jesse Nippert, associate professor of biology at Kansas State University.

Researchers analyzed tree rings back to the early 1900s, when sulfur dioxide deposition throughout the Ohio River Valley began to increase. They were able to compare the trees' growth patterns and changes in physiology to changes in atmospheric chemistry during the 20th century. Results showed that despite increased carbon dioxide -- which tends to increase plant growth -- tree growth and physiology declined for the majority of the 20th century when acidic pollution was high.

But scientists noticed a dramatic change around 1980, 10 years after the Clean Air Act was enacted.

"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."

Another interesting finding from the tree ring analysis: Results from the Great Depression era in the 1930s were very similar to the results from post-1980. Because of the suppressed economy during the Great Depression, coal power plants were less productive and the Ohio River Valley had reduced fossil fuel emissions. Similar to the post-1980 data, data from the 1930s showed improved tree growth and physiology.

"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 findings appear in the scientific journal Proceedings of the National Academy of Sciences of the United States of America, or PNAS, in the article "Evidence of recovery of Juniperus virginiana trees from sulfur pollution after the Clean Air Act." 

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