Sourcing the Future of Wood Bioenergy
Some of the biggest bioenergy debates stem from a “food or fuel” problem, where agricultural lands have been devoted to growing grain as inputs for biofuels, at the cost of food production. According to a study by Searchinger et. al. of corn-based ethanol production, the large scale substitution of corn ethanol over traditional fossil fuels in the United States would not reduce carbon emissions as anticipated but would increase them because of carbon releases associated with land-use conversions abroad—conversions made to keep up with the demand for corn. If the Searchinger et al. hypothesis were to hold true, carbon emissions from such land use changes would rise along with future biofuel demand.
Advancements in commercial technology have made it more practical to take advantage of wood and cellulose-based biomass for energy. But is the ability of wood biomass to recycle and store carbon emissions while substituting for fossil fuels—usually at a net benefit—undermined by land changes made to meet demand for biomass energy? Together with coauthors Brent Sohngen and Anne Riddle, we challenge the Searchinger et al. hypothesis in a recent paper. We argue that marginal lands, those not productive enough to produce traditional crops, together with wood from the pulpwood sector hold sufficient potential for wood biomass production to meet future bioenergy demand. Such an outcome need not drive up food prices and thus nor promote land use changes abroad. Our study included an evaluation of existing marginal lands to determine if they could produce enough cellulose-based materials for biomass fuel; these lands include idle or unused agricultural plots, former tobacco and cotton lands, and other lands not well suited for food crop production. Using a dynamic optimization forest management model, we show that industrial forests supplemented by fuelwood plantations on the marginal lands are able to efficiently produce large quantities of biomass without disturbing current croplands uses. Therefore, crop prices do not rise and the land use changes abroad, posited by Searchinger et al., do not occur.
Another important element of wood bioenergy lies in the overall breakdown of inputs. We categorized the sources as either fuelwood, including wood residues, and pulpwood (trees grown for the production of paper products). We then generated two scenarios under modest and high future demand for biomaterial. We find that a large portion of the wood directed to the bioenergy sector would eventually be drawn from pulpwood, and supplemented by 1.25 to 2.5 million acres of fuelwood from marginal lands. In the high-demand sequence, pulpwood made up a large portion of the biomass for energy but, nevertheless, pulpwood prices did not increase excessively.
Ultimately, wood bioenergy is a form of renewable energy that will likely contribute substantially to US energy security in the 21st century, and perhaps beyond. It is because of this role that its potential effects on land use and carbon emissions must be understood in the context of present and future demand. If components of wood bioenergy are sourced from marginal lands, infringement on food production will be avoided, thereby preventing indirect additions to carbon emissions via land conversions abroad.