NCPA - National Center for Policy Analysis

New Research On Forests And Greenhouse Gases

May 25, 2001

Scientists say forests absorb the principal greenhouse gas, carbon dioxide (CO2), which many blame for global warming. But two new studies from North Carolina's Duke University cast doubt on the ability of forests to consume the gas -- at least without additional cultivation.

One of the studies published in the journal Nature concentrated on the growth of pine trees exposed to higher levels of CO2 than are found in the atmosphere -- while the other focused on the amount of carbon accumulated in the soil.

  • In the tree study, the pines initially absorbed a large amount of the gas and grew 34 percent faster for three years -- but then reverted back to typical growth rates.
  • The soil study found that soil around exposed trees did accumulate carbon, but much of it was released back into the air when organic material in the soil decomposed.
  • Scientists connected with the study concluded that previous estimates of forests' carbon-absorbing abilities were "unduly optimistic."

But other scientists have called the research into question.

  • They say that forests can take a long time to adjust to changes in the environment -- and the conditions noted so far may be only a prelude to other shifts.
  • Also, small changes in the amounts of carbon in soil are difficult to detect.
  • Some scientists involved in related experiments looking at the absorption of the gas by croplands and grasslands said they thought some of the researchers' conclusions were gloomier than their data.

The Duke researchers did discover that the pines -- although flooded with a beneficial gas -- were prevented from growing faster by a lack of other nutrients, most notably nitrogen. The link became clear when nitrogen was added to the enriched pine plots and the growth rate soared once again.

Source: Andrew C. Revkin, "2 New Studies Challenge the Role of Trees in Reducing Levels of Greenhouse Gases," New York Times, May 24, 2001.


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