ORNL-led study shows forests thrive with increased ...( nse to elevated carbon dioxide levels w...)

nse to elevated carbon dioxide levels was explained by increased absorption of light. With greater leaf area, however, the response was an increased efficiency of conversion of light energy to organic matter. In separating the overall response into leaf area and light-use efficiency, the analysis meshes well with broader scale analyses based on satellite imagery, Norby said.

Norby notes that this analysis will be especially valuable as a benchmark to evaluate predictions of ecosystem and global models.

"Climate change predictions are dependent on assumptions about the interaction between the biosphere and atmosphere," Norby said. "However, the contribution of carbon dioxide fertilization to the future carbon global carbon cycle has been uncertain and the models are poorly constrained by experimental data. The close agreement of the productivity predictions of models with the new experimental data should add confidence to overall model results."

Norby cautioned against viewing these results as a reason to ignore the steadily increasing amount of carbon dioxide in the atmosphere.

"Although carbon dioxide fertilization of forests might slow the rate of increase of atmospheric carbon dioxide, a 23 percent increase in productivity is insufficient to stabilize the concentration in the atmosphere," he said. "The increase in productivity demonstrated in these experiments will most likely be tempered by the stresses of climate warming, ozone pollution or insufficient nitrogen supply. In addition, some of the increased organic matter entering the forest is not sequestered in wood but is rapidly returned to the atmosphere. Understanding the controls on carbon processing by ecosystems remains a priority research challenge."

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Contact: Ron Walli
wallira@ornl.gov
865-576-0226
DOE/Oak Ridge National Laboratory
8-Dec-2005

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