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January 2003, Vol. 12, No.1 | Return to Table of Contents
Study Shows Soil Warming May Stimulate Carbon Storage in Some Forests
Effect Would Slow Rate of Climate Change
Results of a decade-long Ecosystems Center study that appeared in the December 13, 2002, issue of Science magazine show that mid-latitude forest soils lose small amounts of carbon in response to soil warming. The study further documents soil conditions created by warming that may actually enhance carbon storage by plants. Stimulated carbon storage at the ecosystem level could slow the rate of climate change. The report challenges the assumptions made in some climate models that project large, long-term releases of the greenhouse gas carbon dioxide (CO2) in response to the warming of forest ecosystems.
The novel soil warming experiment, based at the Harvard Forest Long-Term Ecological Research site, was led by Jerry Melillo, co-director of The Ecosystems Center. Melillo and his colleagues found that, while warming accelerated the decay of organic material and, consequently, the release of CO2 from the soil, the response was limited and short-lived. Over the 10-year study period, only 11% of available soil carbon was lost to the atmosphere. The rest of the carbon was in a chemical form difficult for soil bacteria to break down and release. This phenomenon creates a built-in biochemical break on soil carbon release, says Melillo.
In addition, the study documents that soil warming increases nitrogen availability to plants. Nitrogen is the limiting nutrient to tree growth in many mid-latitude forests. An increase in nitrogen availability, the researchers contend, creates the conditions needed for plant growth, stimulating carbon storage in trees. They conclude that the amount of carbon stored in trees at their research site over the 10-year study period is at least equal to the carbon lost to the atmosphere from the soil.
Data from this study will be important to global climate modelers, according to Melillo. Some climate models show a "runaway warming feedback" with global warming leading to increased decomposition in forest soils and increased CO2 to the atmosphere, which contributes further to global warming. "Our study shows that this may not be the way things would occur," Melillo says. "When creating models, it's important to build in positive and negative feedbacks and where they are occurring on earth in order to generate more realistic climate prediction. Modelers need to consider the mosaic nature of the land surface."
Ecosystems Center staff who co-authored the paper with Melillo include Senior Research Specialist Paul Steudler; Research Assistants Heidi Lux and Sarah Morrisseu; and former Research Assistant Christine Catricala. Ecosystems Center consultant Frank Bowles, Principal of Research Designs in Woods Hole, was also an author, along with scientists from the University of New Hampshire. Melillo and his colleagues will continue the Harvard Forest soil warming study, with plans to conduct similar experiments in a boreal forest in China and a tropical forest in Brazil.
This project was funded by the U.S. Department of Energy, the National Science Foundation.
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