ORNL-led study shows forests thrive with increased CO2 levels

December 08, 2005

Forest productivity may be significantly greater in an atmosphere enriched with carbon dioxide, according to findings released today that challenge recent reports that question the importance of carbon dioxide fertilization.

The study, performed by researchers at the Department of Energy's Oak Ridge National Laboratory and 10 other institutions in the United States and Europe, revealed a strong relationship between productivity of forest plots in the current atmosphere and productivity in plots experimentally enriched with carbon dioxide.

"The median response indicated a 23 percent increase in productivity in the future atmosphere," said ORNL's Rich Norby, lead author of the paper to be published Dec. 13 in the Proceedings of the National Academy of Sciences. "What was especially surprising to the research team was the consistency of the response across a wide range of productivity."

Researchers analyzed data from four experiments in which young forest stands were exposed for multiple years to an atmosphere with a carbon dioxide concentration predicted to occur in the middle of this century. The experiments were conducted in a deciduous forest in Tennessee, a pine forest in North Carolina, a young hardwood stand in Wisconsin and a high-productivity poplar plantation in Italy.

The team calculated net primary productivity - the annual fixation of carbon by green plants into organic matter - for each of the sites from data on wood, leaf and fine-root production. The results proved surprising.

"When we got together to analyze these data, we expected to spend our time explaining the differences between sites," said Norby, a member of ORNL's Environmental Sciences Division. "We were really surprised and excited when all of the data fell neatly onto a single line."

More detailed analysis of the data revealed the mechanisms of the forest productivity response. In forest stands with a relatively low amount of leaf area, the response 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."
This study, funded primarily the DOE's Office of Science, Biological and Environmental Research and the National Science Foundation, reinforces earlier findings and challenges reports that question the importance of carbon dioxide fertilization based on observations of a few trees.

UT-Battelle manages Oak Ridge National Laboratory for the Department of Energy.

NOTE TO EDITORS: You may read other press releases from Oak Ridge National Laboratory or learn more about the lab at http://www.ornl.gov/news">http://www.ornl.gov/news>http://www.ornl.gov/news.

DOE/Oak Ridge National Laboratory

Related Atmosphere Articles from Brightsurf:

ALMA shows volcanic impact on Io's atmosphere
New radio images from ALMA show for the first time the direct effect of volcanic activity on the atmosphere of Jupiter's moon Io.

New study detects ringing of the global atmosphere
A ringing bell vibrates simultaneously at a low-pitched fundamental tone and at many higher-pitched overtones, producing a pleasant musical sound. A recent study, just published in the Journal of the Atmospheric Sciences by scientists at Kyoto University and the University of Hawai'i at Mānoa, shows that the Earth's entire atmosphere vibrates in an analogous manner, in a striking confirmation of theories developed by physicists over the last two centuries.

Estuaries are warming at twice the rate of oceans and atmosphere
A 12-year study of 166 estuaries in south-east Australia shows that the waters of lakes, creeks, rivers and lagoons increased 2.16 degrees in temperature and increased acidity.

What makes Saturn's atmosphere so hot
New analysis of data from NASA's Cassini spacecraft found that electric currents, triggered by interactions between solar winds and charged particles from Saturn's moons, spark the auroras and heat the planet's upper atmosphere.

Galactic cosmic rays affect Titan's atmosphere
Planetary scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) revealed the secrets of the atmosphere of Titan, the largest moon of Saturn.

Physics: An ultrafast glimpse of the photochemistry of the atmosphere
Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have explored the initial consequences of the interaction of light with molecules on the surface of nanoscopic aerosols.

Using lasers to visualize molecular mysteries in our atmosphere
Molecular interactions between gases and liquids underpin much of our lives, but difficulties in measuring gas-liquid collisions have so far prevented the fundamental exploration of these processes.

The atmosphere of a new ultra hot Jupiter is analyzed
The combination of observations made with the CARMENES spectrograph on the 3.5m telescope at Calar Alto Observatory (Almería), and the HARPS-N spectrograph on the National Galileo Telescope (TNG) at the Roque de los Muchachos Observatory (Garafía, La Palma) has enabled a team from the Instituto de Astrofísica de Canarias (IAC) and from the University of La Laguna (ULL) to reveal new details about this extrasolar planet, which has a surface temperature of around 2000 K.

An exoplanet loses its atmosphere in the form of a tail
A new study, led by scientists from the Instituto de Astrofísica de Canarias (IAC), reveals that the giant exoplanet WASP-69b carries a comet-like tail made up of helium particles escaping from its gravitational field propelled by the ultraviolet radiation of its star.

Iron and titanium in the atmosphere of an exoplanet
Exoplanets can orbit close to their host star. When the host star is much hotter than our sun, then the exoplanet becomes as hot as a star.

Read More: Atmosphere News and Atmosphere Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.