John Butnor, Chris Maier, and Kurt Johnson from the SRS Biological Foundations of Southern Forest Productivity and Sustainability unit developed the Automatic Carbon Efflux System (ACES) to more effectively measure the carbon that moves out through the soil as part of the carbon cycle.

As a key element in the process of photosynthesis, carbon dioxide is absorbed through the leafy canopy of the forest, then released back into the atmosphere by living organisms: as much as half of this respiration comes from decomposition in the forest soil. Tree roots, living wood, and nocturnal respiration are also part of this efflux of carbon dioxide from forest ecosystems.

"There is a great deal of interest in determining how much carbon dioxide forests can remove from the atmosphere and retain, or sequester, as carbon pools or sinks," says inventor John Butnor. "Accurately measuring carbon dioxide respiration from the forest is essential to truly understanding the carbon cycle. The ACES system gives us a way to dynamically measure soil and woody tissue respiration rates as they fluctuate during the day and change with the seasons."

Several methods have been used to measure carbon flux before ACES. In one method, a closed, static chamber is placed on the ground, using an alkali trap to catch carbon dioxide emitted from the soil. Another method involves taking periodic samples of soil in the same location and running gas chromatography tests to determine changes in carbon concentration over time. Both of these methods are time-consuming, require a technician to take measurements manually, and are sometimes inaccurate. Recent studies have demonstrated that closed measurement techniques underestimate gas flux.
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Contact: John Butnor
jbutnor@fs.fed.us
802-951-6771 x1230
Southern Research Station - USDA Forest Service
26-Feb-2004