An experiment that pumps carbon dioxide into groups of trees growing outdoors, designed to test how forests will respond to global warming may be ended by the US Department of Energy.

This is not a nefarious plot to squash the results of global warming research, but a genuine disagreement among two groups of scientists over how to proceed in climate change research.

The US Department of Energy has funded nearly 10 years of research at Duke Forest in Durham NC, Oak Ridge National Laboratory in Tennessee, and Harshaw Experimental Forest in Wisconsin. At each forest, rings of plastic pipes release carefully measured amounts of CO₂ into the air around groups of trees.  The experiment is known as FACE, for Free Air Carbon dioxide Enrichment.

Results so far indicate that forests respond to the extra carbon dioxide, an essential plant nutrient, by increasing growth. However, unless the forests are on fertile ground, growth is concentrated in short-lived plant parts like leaves or needles and fine roots. These parts die and decompose, releasing their carbon back into the atmosphere. When fertility is higher, trees may retain more of the carbon in wood. However, fertility experiments are not yet complete.

Project scientists believe that a few more years of data are needed to determine the effects of soil fertility on the ability of trees to sequester carbon.  However, DOE scientists believe that the experiment has run its course and that it is time to sample the trees and soils as a final measure of the long-term impacts of the experiment.

Richard Norby, who oversees the experiment at Oak Ridge, said “"This comes up in all sorts of long-term experiments — when is the right time to say, `Enough,’ There’s no good answer to that."

Picture: Duke FACE Experiment, courtesy of Duke University

Sources:

• Duke FACE
• Oak Ridge FACE
• Aspen FACE
• The Associated Press: Gov’t wants to change course of forest experiments

Global warming will gradually increase the temperature of soils. Most models predict that increased soil temperature will allow fungi and bacteria to break down soil organic matter faster, releasing large amounts of carbon dioxide into the atmosphere. 

New research from the University of California – Irvine shows that, at least for dry soils of boreal spruce forests, rising temperatures cause fungi to dry out, reducing their rate of respiration. Instead of a feed-forward effect that increases greenhouse gas emissions,  Steven Allison and Kathleen Treseder found that warming boreal soils decreased fungal respiration.  Their work was published in Global Change Biology.

This does not remove all concerns about warming of forest soils. In areas of permafrost, where there is little microbial respiration, warming causes melting of the ice and accelerates microbial respiration.

Citation:

Allison, S. D., and K. K. Treseder. in press. Warming and drying suppress microbial activity and carbon cycling in boreal forest soils. Global Change Biology.

Sources:

• Fungi emit less carbon dioxide as climate warms – UC Irvine
• The Allison Lab, UC Irvine
• Global Change Biology

Research by Peter Curtis (Ohio State University) and colleagues shows that northern Michigan forests can store an average of 0.65 tons C per acre per year. This rate of storage is higher than earlier estimates such as those used to develop the Kyoto Protocol, and is consistent with other recent studies that show that temperate forests are more efficient carbon sinks than previously thought.

The use of forests as purchasable carbon offsets will become more attractive as we learn more about how much carbon forests can store. However, there is so much variation in the factors that influence carbon storage in forests that prolonged, broad research like that discussed in this article will be needed at many more locations.

Links:

Press release: Scientists Point To Forests For Carbon Storage Solutions

Research Paper:

Christopher M. Gough, Christoph S. Vogel, Hans Peter Schmid, and Peter S. Curtis. Controls on Annual Forest Carbon Storage: Lessons from the Past and Predictions for the Future. 2008. Bioscience 58(7): 609-622.

Cross posted at Sustainable Kentucky/Green Kentucky