Red cedar trees' growth improved following the Clean Air Act and during the Great Depression.
The Clean Air Act was passed in 1970, it was "drastically revised" and expanded in 1990, the Environmental Protection Agency reported.
"Under the Clean Air Act, EPA sets limits on certain air pollutants, including setting limits on how much can be in the air anywhere in the United States. This helps to ensure basic health and environmental protection from air pollution for all Americans. The Clean Air Act also gives EPA the authority to limit emissions of air pollutants coming from sources like chemical plants, utilities, and steel mills," the EPA reported.
Scientists studied 100-years'-worth of red cedar tree rings to find out the Act's impact on their health, a Kansas State University press release reported.
The research team chose red cedars for their study because they grow slowly and thrive on "surface soil moisture." These factors make the tree more susceptible to environmental factors, and great indicators of the environment's effect on local plant life.
"There is a clear shift in the growth, reflecting the impact of key environmental legislation," Jesse Nippert, associate professor of biology, said.
"There are two levels of significance in this research. 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," he said.
The trees were located "downwind" from the Ohio River Valley coal power plants, the area experiences high rates of acidic pollution.
The team analyzed the trees' isotopes to discover physiological changes and their relation to atmospheric conditions.
"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."
The team also noticed evidence of the tree's recovery during the Great Depression era, most likely because the coal plant was less productive in the dismal economy.
"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.
