A dramatic recovery of red spruce trees in the central Appalachian Mountains led West Virginia University researchers to pursue the driving factors behind improved forest health.
After a 50-year period of declining growth of the tree species prior to the Clean Air Act, a new study by Justin Mathias, a biology Ph.D. candidate, and Richard Thomas, chair and professor in the Department of Biology, found that declining air pollution alongside increases in atmospheric carbon dioxide and warmer spring temperatures have resulted in dramatic forest growth recovery.
“This is one of the few studies that documents the effect of elevated carbon dioxide on tree growth in a natural ecosystem,” said Mathias, a Wardensville, West Virginia, native.
Globally, forest ecosystems are responsible for removing nearly one third of carbon dioxide produced through fossil fuel emissions.
“This study confirms a large body of experimental work on the effects of elevated carbon dioxide on plant growth, but it also highlights the need to incorporate the effect of acidic pollution into earth system models,” Mathias said.
Despite progress toward reducing air pollution in the eastern U.S. following the Clean Air Act, there has been limited evidence of improved forest health due to cleaner air until now.
“This research provides direct evidence of the efficacy of the Clean Air Act on forest ecosystems and reinforces that basic science can and should objectively inform environmental policy,” Mathias said.
Mathias used carbon and nitrogen isotopic signatures in tree rings of red spruce across a 75-year time period to demonstrate simultaneous changes in the recovery of forest ecosystems since 1989, about 15 years after pollutant emissions began to decline in the U.S.
“We extracted an increment core from the trees. From this we not only measured the tree rings to understand changes in growth over time, but we also analyzed isotopes in the wood,” Mathias said. “Once a ring is formed during a given year, it doesn’t change in isotopic composition, and this can tell us about how the tree is growing.”
The study was conducted at three locations in the Monongahela National Forest. The central Appalachian Mountains sit downwind of the Ohio River Basin, where there is an extremely high concentration of coal fired power plants. Prior to 1970, acidic pollution levels in this region were some of the highest in the U.S., serving as an ideal location to examine forest health. Red spruce is also thought of as an indicator tree species of forest health.
“By looking at historical tree growth using tree rings, and the isotopes in the wood each year, it became clear to us that the period around 1989 was very important for red spruce forests in West Virginia,” Thomas said. “Justin did a great job of teasing apart all of the environmental factors affecting the growth of these trees to figure out that decreasing acid pollution, increasing atmospheric carbon dioxide and warmer spring temperatures all played an important role in the increased productivity of these forest ecosystems since 1989.”
The study was published in Global Change Biology, a leading ecology journal, on Sunday, May 20. The study was funded by the National Science Foundation.
Title: “Disentangling the effects of acidic air pollution, atmospheric CO2, and climate change on recent growth of red spruce trees in the Central Appalachian Mountains"
Published: May 20, 2018