By Michelle Werts

Eastern redcedar
Eastern redcedar. Credit: Jason Sharman, Vitalitree,

Two new studies reveal good news for two species of “red” trees: the eastern redcedar and the red spruce. And the good news is actually tied to old news: the 40-plus-year-old Clean Air Act. In 1970, Congress established the Clean Air Act to address the unsightly, unhealthy pollution and smog plaguing America’s cities and industrial centers. Now, scientists are starting to observe the long-reaching effects of the act.

A new study published in Proceedings of the National Academy of Sciences of the United States of America (PNAS) looked at 100- to 500-year-old eastern redcedar, Juniperus virginiana. Spending four years studying eastern redcedar tree rings in the Appalachian Mountains of West Virginia, the research team found that eastern redcedar growth improved after the passage of the Clean Air Act. For a majority of the 1900s, the studied trees did not grow as fast as in the previous decades and even centuries, which was unexpected considering carbon dioxide levels were higher — more carbon dioxide usually leads to increased plant growth in the short term. The scientists attribute this to the high acidic pollution, but less than 15 years after the passage of the Clean Air Act, the research reveals a shift in tree growth.

Red spruce
Red Spruce. Credit: USDA Forest Service Southern Research Station Archive,

Says research team member Dr. Jesse Nippert, Kansas State University associate professor of biology, in a release about the study, “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. 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.”

The eastern redcedar wasn’t the only tree suffering from the effects of acidic pollution, or acid rain, though. The red spruce suffered greatly in the mid to latter part of the 20th century from acid rain, leading to the tree’s decline. However, some U.S. Forest Service and University of Vermont scientists have recently noticed that after years of decline, in the last decade, the red spruce of New England are growing at a rate greater than the average growth rate of the last 100 years. While the researchers don’t know exactly what caused the red spruce’s recovery, as reported by, one of the theories is that the Clean Air Act — and thus a reduction in acid rain and pollution — may have played a big role.

This year, American Forests is planting more than 7,000 trees in Vermont’s Green Mountain National Forest, including red spruce, so this news of the recovery of two eastern favorites is welcome news indeed.