Biofuel not so efficient?

The Wood Technology Society
30 Dec 2011

Harvesting biofuel may increase rather than offset carbon dioxide emissions, a study has revealed.

Researchers at Oregon State University (OSU) in the USA claim that biofuel production in west coast forests actually causes more carbon dioxide to be released than it saves.

The popular view of biofuel from forests as an energy efficient means of reducing greenhouse gas emissions is a flawed one, thinks Tara Hudiburg, a doctoral candidate at OSU and lead author of the study ‘Regional carbon dioxide implications of forest bioenergy production’.

‘[Biomass removal] releases more carbon emissions per unit of biomass harvested than if the biomass had just been left intact in the forest,’ she says. ‘Wood energy is not as efficient as fossil fuel energy and even after you account for the displaced emissions associated with fossil fuel extraction and refining, wood still does not do better than the current system.’

Hudiburg’s team conducted lifecycle assessments on a wide variety of forests in the west coast states, including private, public, old, young, arid, wet, hardwood and softwood.

‘We tried to incorporate everything we could imagine would produce or save emissions in this lifecycle assessment. In doing so we realised that an interdisciplinary team of scientists would have made the study even more comprehensive.’

Removing wood from forests for biomass has an impact on forest management techniques, says Hudiburg. Her team found current forest management approaches complement natural forest growth, and help ensure the forest acts as a carbon sink. Increasing the harvest of biomass weakens this sink, she says, as it reduces the net carbon uptake, which equates to an increase in emissions.

‘Currently, most of the time, non-merchantable wood is left to decompose in the forest,’ she says. ‘This still releases carbon emissions, but slowly. Burning it for energy is an immediate release of CO2.’ Often forest management consists of thinning forests to make it easier to deal with fires and insect problems, a process that produces biomass that is burned for energy, as part of what is believed to be an emission reduction strategy. ‘It is suggested that the thinning [should] be increased and cover more areas. We tested whether this will actually reduce emissions and found that for most forests in our region it does not. This does not mean that thinning for habitat restoration or fire management should stop. It just means that it should not be a carbon emission reduction strategy.’

Wood is considered a renewable energy source, but Hudiburg warns of confusing renewable with green or carbon-neutral energy. ‘Energy needs to be decarbonised. Wood is a carbon-based energy source just like fossil fuel. It is renewable because it grows back under sustainable management practices. But this does not mean it is carbon neutral. Some of the biomass removed takes hundreds of years to grow back, while some only takes a couple of decades. The timescale for climate change and policy to reduce emissions is shorter than this.’

She adds that we should be wary of rushing through seemingly green policies without fully considering their implications.

‘We cannot assume substituting fossil fuels with any kind of energy will be a viable emissions reduction strategy without doing a full carbon account. Also, the accounting has to include the baseline forest carbon uptake or it does not truly measure the impact of a new management strategy.’

With sustainability being such a pressing issue, Hudiburg highlighted the danger of basing policy on theories that we want to be true without subjecting them to the proper scientific rigour first. ‘We want an answer and everyone wants good news. We also don’t really want to reduce consumption so we are searching for energy that will allow us to maintain our current usage. Unfortunately, wood is not the ideal solution.’