Reforestation of arable land saves up to nine times more carbon than using it for producing biofuel, according to a study by researchers from the World Land Trust, a conservation group dedicated to preserving rainforests.
The study, published in Science in August, is based on a literature review of the carbon savings achieved by different types of biofuels, including second-generation biofuels derived from wood or cellulose.1 It compares average savings with the carbon that would be sequestered by reforesting farmland in the tropics and temperate regions.
The study concludes: “In all cases, forestation of an equivalent area of land would sequester two to nine times more carbon over a 30-year period than the emissions avoided by the use of biofuel.”
For example, using sugarcane to make ethanol saves emissions of about 60 tonnes of carbon per hectare over 30 years. This compares to 170mtC/ha for reforesting tropical cropland (see figure).
This gap would be more pronounced if growing the sugarcane resulted in deforestation either directly or by replacing land needed for food crops. Converting tropical forest to cropland leads to a loss of around 200mtC/ha, almost all in the first two years.
Only conversion of woody biomass to biofuels achieves a similar carbon saving to reforestation, the study says – but this only applies in temperate regions where forests sequester less carbon. The technologies needed to make such second-generation biofuels are still at the development stage (ENDS Report 382, pp 26-29 ).
Bioethanol from crops would achieve similar emissions savings to reforestation after about 90 years. However, according to Dominick Spracklen, one of the researchers, “we chose 30 years as transport will still be using the internal combustion engine. Longer than that, we are likely to have moved on to carbon-free forms of transport.”
The study recommended that policy-makers divert their attention away from biofuels and focus on increasing the efficiency of fossil fuel use, conserving the existing forests and savannahs, and restoring natural forest and grassland habitats on cropland that is not needed for food”.
Unfortunately, the study does not address the viability of its proposals. For example, it does not examine how much land used for biofuels could actually be reforested.
Mr Spracklen admitted the shortcoming but said that its main point – to show that biofuels are not a good way to tackle climate change – remained valid. “It doesn’t make sense to promote biofuels if your main aim is to reduce carbon,” he said. “There are other reasons to promote them – improving fuel security, for example – but policy-makers should not hide those behind a climate change agenda.”
Michael Palmer of Oklahoma State University writes that “cellulosic conversion demands uniform feedstocks, which translates into high-input and environmentally destructive biofuel monocultures. Such monocultures are unlikely to be sustainable.”2A second letter, from the Soil Science Society of America among others, takes issue with the use of the leaves and stems of maize plants to make biofuels – one of the feedstocks highlighted by President George Bush for use as biofuel.3 “Removing corn stover [from cropland] will intensify soil erosion ten-fold or more,” it argues.