The Bioenergy Balancing Act

Forest Service Research Shows Increased Use of Wood Energy Can Cut Carbon Emissions Over Time

Looking down into a wood to energy gasifier used to produce electricity for a Forest Service district office. Photo by Tom Elder, U.S. Forest Service.
Looking down into a wood to energy gasifier used to produce electricity for a Forest Service district office. Photo by Tom Elder, U.S. Forest Service.

Wood-based energy has been proposed as an alternative to fossil energy sources such as coal and natural gas, a way to reduce the carbon emissions that lead to atmospheric warming and changing climatic conditions. But debate continues about whether substituting wood for natural gas or coal actually reduces emissions, and how long it takes for the use of wood for bioenergy to become “carbon neutral.”

The carbon absorbed and stored in growing forests plays a big part in these calculations. If demand for wood for energy increases, prices and markets for all wood products will change—and so will investment in forest management and land use, which in turn will affect the amount of carbon stored in growing forests. What would happen if wood bioenergy really took off in the U.S. like it has in Europe, which has doubled its exports of wood pellets from the U.S. over the last two years?

U.S. Forest Service scientists with the Center for Integrated Forest Science (CIFS) and the Forest Products Laboratory (FPL) recently published results of a study that projects the effects on carbon emissions by a large shift to wood-based energy in the United States.

Using models developed for the Forest Service 2010 Resources Planning Act (RPA) Assessment, David Wear from the Southern Research Station CIFS and Prakash Nepal and Ken Skog from FPL explored two different scenarios to evaluate the potential effects of the expanded use of wood for energy on net carbon emissions over time.  

In the first scenario, bioenergy use increases in line with the last few years (in 2012, wood fuel provided about two percent of feedstock energy used in the U.S.), while in the second scenario wood energy use expands substantially over the next 50 years.

Unlike other studies, the Forest Service research accounts for how a shift to wood-based energy would affect land use, harvesting, wood products markets, and forest regrowth.

“Under the expanded scenario, we found that up to 80 percent of carbon emitted as a result of land and management changes would be offset in 50 years due to regrowth of forests and price-induced changes in land use and management,” said Wear. “Forest land is predicted to decline under most RPA scenarios, but we found that high wood energy use would result in the retention of an estimated 8.6 million acres in forest land nationwide.”

The researchers found that replacing natural gas with wood in the expanded scenario would result in a 49 percent decrease in carbon emissions per unit energy in 50 years. For coal, the result would be about a 73 percent offset.

“Projected carbon emission offsets over the 50-year period vary substantially by region, with only 16 percent in the North, as opposed to 50 percent in the West and 95 percent in the South,” said Wear. “This is not only due to forest regrowth, which is faster in the South and the West, but also because of shifts in competitive advantage among regions producing wood products under the expanded use of bioenergy. For example, it’s already common in the South for forest area and tree planting to increase in response to higher prices for wood products.”

The researchers also found that the complex market interactions among foreign countries and U.S. regions in response to increasing wood energy demand might also have significant impact on carbon emission offsets in particular regions.

“Caution should be taken when applying our results to broad policy questions,” said Wear. “Responses of the real world markets to such a strong expansion of bioenergy use in the U.S. may differ from our modeling, as may the responses of landowners. We provide this information to help answer questions about the carbon neutrality of wood bioenergy and to guide further research and discussion.”

Read the full text of the article.

For more information, email David Wear at dwear@fs.fed.us.

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