The team focused on red cedar trees because they are abundant, long-lived and a good recorder of environmental variability. Red cedar trees grow slowly and rely on surface soil moisture, which makes them sensitive to environmental change. Their abilities to live for centuries meant that researchers could analyze hundreds of years of tree rings, Nippert said.
The researchers analyzed the stable carbon isotopes within each tree ring as a recorder of physiological changes through time. Nippert's Stable Isotope Mass Spectrometry Laboratory at Kansas State University analyzed the samples. Researchers analyzed tree rings back to the early 1900s, when sulfur dioxide deposition throughout the Ohio River Valley began to increase.
By studying the stable isotopic signature in each tree ring, the researchers 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 Va
|Contact: Jesse Nippert|
Kansas State University