Out Of Gas

Turns out that turning wood from West Coast forests into biofuels may not do anything for the climate after all. Contrary to earlier estimates, a new study finds that even highly efficient wood-to-biofuel operations would increase carbon dioxide emissions from forests in Washington, Oregon and California.

“Most people assume that wood bioenergy will be carbon-neutral, because the forest re-grows,” and there’s also the chance of reducing carbon emissions caused by wildfires, says Tara Hudiburg, a doctoral candidate at Oregon State University (OSU) in Corvallis and the lead author of the Nature Climate Change study. Indeed, earlier studies had suggested that using Western trees for biofuel would be carbon-neutral or even reduce greenhouse gas emissions.

To test those results, the researchers gathered data from thousands of plots in 80 forest types in 19 eco-regions, ranging from temperate rainforests to semi-arid woodlands. The plots included both public and private lands and different forest management approaches. About 98 percent of the forests in the study region are now believed to be “carbon sinks,” meaning that under current management they trap more carbon than they release to the atmosphere.

To see if that would stay true in the future, the researchers used 27 factors — including things like the role of forest fires and insect infestations, and the energy used by different biofuel processes – to develop emissions estimates under four basic scenarios. One was “business as usual,” or current forest management practices, while a second assumed forests were managed primarily to prevent forest fires. A third included additional levels of tree cutting to prevent fires, in order provide better economic returns. The fourth assumed significant bioenergy production in concert with fire reduction.

When compared to “business as usual,” all of the alternatives increased carbon emissions, the study found. Emissions increased by 2 percent when forests were managed just for fire prevention, by 6 percent under fire control with better economic return, and by 14 percent under higher bioenergy production. In general, “projected forest biomass removal and use for bioenergy in any form will release more carbon dioxide to the atmosphere than current forest management practices,” Hudiburg says.

The one exception, the authors note, was if forests in high fire-risk zones become weakened due to insect outbreaks or drought, which impairs their growth and ability to store carbon. It’s possible that thinning these fire-prone forests and using the wood for bioenergy production would result in lower emissions.

It’s also possible, however, that emissions would be even higher than calculated if biofuel production processes aren’t perfectly efficient. Under more realistic efficiency levels, Hudiburg says, “we project that the use of these forests for high bioenergy production would increase carbon emissions 17 percent from their current level.”

“If our ultimate goal is to reduce greenhouse gas emissions, producing bioenergy from forests will be counterproductive,” concludes OSU’s Beverly Law, a co-author of the study. “Some of these forest management practices may also have negative impacts on soils, biodiversity and habitat. These issues have not been thought out very fully.” The bottom line, the authors say, is that it appears that any increase in harvest volume on the West Coast, for any reason, will result in average increases in emissions. And they write that the study suggests that “energy policy implemented without full carbon accounting, and an understanding of the underlying processes, risks increasing rather than decreasing emissions.” David Malakoff | October 23, 2011

Source: Tara W. Hudiburg, Beverly E. Law, Christian Wirth & Sebastiaan Luyssaert (2011). Regional carbon dioxide implications of forest bioenergy production. Nature Climate Change doi:10.1038/nclimate1264

Image © Vlue | Dreamstime.com