Research published Oct. 23 in the journal Nature Climate Change undermines the argument that substituting wood-based biofuel for fossil fuels would reduce carbon emissions.
“Most people assume that wood bioenergy will be carbon-neutral, because the forest re-grows and there’s also the chance of protecting forests from carbon emissions due to wildfire,” said Tara Hudiburg, the paper's lead author and an Oregon State University doctoral student in the College of Forestry. “However, our research showed that the emissions from these activities proved to be more than the savings.”
Using data from thousands of forest plots in Oregon, Washington and California, Hudiburg and her co-authors calculated carbon storage and emissions under current forest management practices and then projected changes under three different thinning/biofuel scenarios.
Two involved thinning of varying intensity in fire-prone forests in the three states. The third called for widespread harvesting of trees up to 2 feet in diameter on public and private lands. The study assumed the harvested wood be burned to produce heat and power, converted to cellulosic ethanol and, in the case of larger, more valuable trees, milled into wood products.
The scientists took into account carbon dioxide emissions in harvesting, transportation and biofuel production as well as carbon credits for reducing wildfire and fossil fuel emissions, and long-term storage in lumber for housing. In some areas with relatively low forest productivity and high fire frequency, greenhouse gas emissions did not rise under the treatment scenarios. But in most they did.
"We are not saying that any project will increase emissions compared to current levels, whether they are from decomposition, wildfire, or harvest," Hudiburg said in an email. "We are saying that on average, this is what happens in West Coast forests, and if implemented widely will increase regional emissions -- contrary to policy goals."
Total West Coast carbon emissions rose 2%, 6% or 14% under the three treatment schemes.
The study dealt solely with emissions and did not consider other potential benefits of forest thinning, such as reducing wildfire risk, which is projected to increase with global warming.
"In this study region," the authors wrote, carbon storage in forests "is more beneficial in contributing to reduction of anthropogenic carbon dioxide emissions than increasing harvest to substitute fossil fuels with bioenergy from forests."
-- Bettina Boxall
Photo: Loggers use a machine that cuts and piles whole trees to thin an area in the Black Hills National Forest in South Dakota. Credit: Associated Press / Doug Dreyer