Knoxville News Sentinel
By Frank Munger
Published: November 17, 2008
One of Oak Ridge National Laboratory's most intriguing science experiments is coming to a close. Since 1998, researchers have used an elaborate outdoor system to pipe thousands of tons of carbon dioxide into stands of sweetgum trees a couple of miles from the main laboratory complex.
The project was designed to test hypotheses associated with global climate change. Valuable field data obtained from the Oak Ridge project and similar experiments at other sites were used to validate computer models that predict conditions as a result of increasing concentrations of CO2 in the atmosphere.
Automated pumps maintained the gaseous concentration at about 550 parts per million in the forest, roughly the atmospheric level of CO2 expected in 2050 and beyond.
Rich Norby, a physiological ecologist who headed the Oak Ridge project known as FACE, or Free-Air CO2 Enrichment, confirmed that the U.S. Department of Energy had pulled the funding on future operations and instructed researchers to wrap up activities over the next year. The current year's budget is $1.4 million, he said.
The carbon dioxide will be turned off after the 2009 growing season, Norby said, and about this time next year researchers will start harvesting trees at the experimental site. Trees will be chopped down, cut open, and subjected to a number of tests to precisely assess the influence of elevated CO2, he said.
Some of the research project's most valuable information may come after the trees are cut down, Norby said. Data collected over the past decade was obtained through "nondestructive" means in order to not interfere with natural processes at work, and those methods had limitations, he said.
While some scientists were reportedly upset that the forest experiments were being canceled, Norby was philosophical. All research projects - even the long-term ones - ultimately come to an end, and it's always difficult to say when is the right time to stop an experiment and move toward another, he said.
"We have argued keeping it going one extra year, but I think the folks at DOE gave it a fair hearing and reached a sort of useful compromise to get an extra year of data," Norby said. "We've been having a dialogue on this. It wasn't out of the blue," he said.
The 10-year experiment in Oak Ridge showed that higher levels of carbon dioxide enhanced productivity of sweetgum trees - at least for a while. Absorption of carbon dioxide and conversion to wood, leaves, roots and sugars took place at an increased rate.
"This is important because if forests across the Earth absorb carbon from the atmosphere a bit faster, the carbon dioxide from fossil fuel combustions won't build up quite as fast, and the greenhouse effect causing climate change will be slowed," Norby said, emphasizing that the change won't be stopped.
The increased productivity occurred mostly below ground, the scientist said. Instead of making more wood in the trunk, the trees enriched with carbon dioxide made more roots, he said. These fine roots only live for about a year and then deposit their carbon into the soil, he said.
"Although these results all sound like good news," Norby said, "recent results suggest that the responses might not be sustained indefinitely because there is not enough nitrogen in the forest soil."
The Oak Ridge scientist said he's looking ahead to a number of potential follow-on projects, perhaps one that looks at other climate factors, such as temperature or rainfall, or studies that address carbon dioxide impacts at other latitudes or altitudes.
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