Here, we synthesize recent empirical research that targets these concerns to identify potential solutions for managing the land use–related trade-offs of cellulosic biofuels. We identify existing knowledge gaps but also conclude that current knowledge is sufficient to inform policies that will ensure environmental benefits. Policy is needed because many of these benefits are conditional, and the stakes are high because of the amount of land involved: In the United States alone, projected biomass needs require 33 to 40 Mha of productive land or >50 Mha of marginal land, whereas total US crop production currently uses 124 Mha. But with the proper safeguards, the likelihood of environmental payoff appears high. We organize our conclusions to articulate seven emerging principles that are relevant globally to the sustainability of cellulosic biofuel crop production.

—Robertson et al.

Phil Robertson, University Distinguished Professor of Ecosystem Science at Michigan State University and lead author on the study and GLBRC colleagues from MSU, the University of Wisconsin and the University of Maryland drew on ten years of empirical research to identify the emerging principles for managing the complex environmental tradeoffs of cellulosic biofuel.

1. Perennial vegetation, whether herbaceous grasses and dicots or short-rotation trees, offers environmental outcomes superior to those of annual crops—high net energy return on investment, greater soil C and N retention, and improved insect and wildlife habitat—with no observable impact on landscape water balances in humid temperate climates.

2. Polycultures appear thus far to offer little productivity advantage over monocultures, but neither do they harm productivity so long as they are dominated by high-productivity species.

3. Biodiverse plantings provide ecosystem services such as pollination, pest protection, and wildlife conservation that often benefit other cropping systems in the landscape, and relatively little plant diversity can provide disproportionately large benefits.

4. Carbon debt generated by stand establishment can be minimized by avoiding tillage and by avoiding lands with large C stores either above ground (such as forests) or below ground (such as wetlands).

5. Nitrogen fertilization can substantially discount the climate and water quality benefits of bioenergy crops if applied in excess of plant need; some high-productivity perennial crops require little if any supplemental N.

6. Food-fuel economic conflicts and C debt generated by ILUC can be avoided by establishing bioenergy crops on marginal lands not used for food production, and also by producing biomass from cover crops in annual cropping systems.

7. Economic appeal, relative to alternative land uses, is a sine qua non for landowners to be willing to convert their lands to bioenergy crop production.

A further, overarching principle is that there is no best crop for all locations. Rather, one must consider trade-offs with respect to desired outcomes.

—Robertson et al.

According to the researchers, these principles are enough to begin guiding sound policy decisions for producing sustainable biofuels. Looking forward, however, the team calls for more research on designing landscapes to provide the optimal suite of energy, climate and environmental benefits. They say that understanding how best to integrate benefits and tradeoffs will be key to the future success of cellulosic biofuels.

With biofuels, the stakes are high. But the returns are also high, and if we take key principles into account we can begin shaping the policies and practices that could help make cellulosic biofuels a triple win for the economy, the climate and for environmental sustainability in general.

—Phil Robertson

Additional GLBRC scientists contributing to this paper include Bradford Barham, Bruce Dale, Stephen Hamilton, Cesar Izaurralde, Randall Jackson, Douglas Landis, Scott Swinton, Kurt Thelen and James Tiedje.

Resources

• G. Philip Robertson, Stephen K. Hamilton, Bradford L. Barham, Bruce E. Dale, R. Cesar Izaurralde, Randall D. Jackson, Douglas A. Landis, Scott M. Swinton, Kurt D. Thelen, James M. Tiedje (2017) “Cellulosic biofuel contributions to a sustainable energy future: Choices and outcomes” Science Vol. 356, Issue 6345 doi: 10.1126/science.aal2324