You can have your biodiversity and eat it—and burn it—too. That’s the message from a recent study of natural biofuel production by a team of ecologists and economists from the University of Minnesota (see summary from NPR).
Wild living organisms provide critical natural infrastructure that supports human civilization. Clean air and water, protection from hurricanes, healthy fisheries, that sort of thing. Most of us appreciate that at some level. But in the rapidly changing modern world, with growing conflicts between feeding people, putting gas in our tanks, maintaining economic competitiveness, and (last and usually least, in practice) preserving some scraps of nature, the hard-nosed question arises: What can biodiversity do for me?
The Minnesota study provides an intriguing new answer to this question. The authors, led by Dave Tilman, show that cellulose biofuels from natural, diverse prairie vegetation could provide more usable energy, greater greenhouse gas reductions, and less agricultural chemical pollution than either corn grain ethanol or soybean biodiesel. And, importantly, the natural vegetation grows on degraded, nitrogen-poor soil so it doesn’t compete for fertile cropland critical to food production, as agro-intensive biofuel crops like corn and soybeans do.
How can this be? The main reason is that the system has been designed by nature, so to speak. That is, the prarie plants are naturally adapted to their soil and environment. So they require no watering or fertilizer after initial planting, no pesticide application (thus, also no pollution), and a small fraction of the energy inputs required to grow biofuel crops. The authors call this “low-input high-diversity” biofuel. Because of the high production efficiency of diverse natural vegetation, and the low energy inputs:
“[Low-input high-diversity] biomass . . . yields 51% more usable energy per hectare from degraded infertile land than does corn ethanol from fertile soils.”
But wait, there’s more. Biofuel production from naturally diverse vegetation not only produces lower carbon emissions than fossil fuels (as is also true of agricultural biofuels) it actually reduces carbon emissions:
“Both corn ethanol and soybean biodiesel are net carbon sources but do have 12% and 14% lower net greenhouse gas emissions, respectively, than combustion of the gasoline and diesel they replace. In contrast, [low-input high-diversity] biofuels are carbon negative, leading to net sequestration of atmospheric CO2 across the full life cycle of biofuel production and combustion.”
OK, so I said in the opening line that you can have your biodiversity and eat it (and burn it) too. That’s not strictly true, of course. But by periodically harvesting these perennial plants for biofuel you can, in an important sense, have them and burn them too. And by sparing land for food crop production you then have more to eat.
Sound too good to be true? For now it may be. Under present market conditions, with fossil fuels and agricultural biofuels heavily subsidized, the low-input high-diversity biofuels are not yet economically viable. But that is likely to change as fossil fuels are depleted, competition for land intensifies, and technologies for cellulose biofuels advance.
Tilman, D., J. Hill, and C. Lehman. 2006. Carbon-negative biofuels from low-input high-diversity grassland biomass. Science 314:1598-1600.
(Photo of prairie flowers by Roger Hill)