The Virtues of Switchgrass as an Alternative Fuel
With rising gas prices and global temperatures, corn-based ethanol seemed to promise a bright energy future. Now, as corn's dark side becomes ever clearer, switchgrass offers a better alternative as well as a first step to restoring the prairie that once blanketed this country's heartland.
If cultivated properly, switchgrass may also improve habitat. In a 1997 study, for example, a team of researchers in Wisconsin observed 17 bird species inhabiting both harvested and unharvested fields of switchgrass in the southwestern part of the state. Ten of the 17 were grassland birds considered to be "species of management concern" for reasons ranging from declining numbers to vanishing grassland habitat. Among them were shortgrass species, including the western meadowlark and the grasshopper sparrow; mid-grass birds, such as the eastern meadowlark and the dickcissel; and tallgrass species, including the Henslow's sparrow and the sedge wren.
"There was actually a greater diversity and a higher number of birds in the harvested switchgrass than in the unharvested plots," says Laura Paine, now with the Wisconsin Department of Agriculture. She concludes that farmers could grow switchgrass for profit while also providing habitat benefits for imperiled grassland bird species. "That's a win-win situation," she says.
But others are not so sure of the benefits of switchgrass monocultures. Michael Palmer, an ecologist at Oklahoma State University, concedes that switchgrass is better for the environment than corn. "But here's a plant that typically occurs with anywhere from 60 to 100 other species. If we start having these massive monocultures of switchgrass, it's an invitation to all sorts of diseases, and that's a prediction for massive crop failures."
Additionally, some ornithologists, including Greg Butcher, Audubon's director of bird conservation, contend that a mixed prairie landscape would be vastly better for biodiversity. "Switchgrass by itself is not good habitat for birds," he says. "Birds need grasslands for a variety of reasons. Different plants produce food for birds at different times and attract insects, some of which are eaten by birds, at different times. All this means diverse grasslands will attract more species of birds than a monoculture will."
Help could come from research conducted by the University of Minnesota's David Tilman and colleagues. They've found that if degraded agricultural lands were planted with a diverse mixture of prairie species, including western wheatgrass, big bluestem, and little bluestem; vascular plants such as sundial lupine and rounded-headed bush clover; and forbs such as rigid goldenrod and tall blazing star, the energy yield could exceed that from switchgrass alone by more than 200 percent. "Our research shows that biofuels made from a diverse mix of prairie plants can eliminate about 15 to 25 percent of the global warming problem the world faces," Tilman says. At the same time, these cultivated prairies would feature greater biodiversity, providing even better habitat for many animals.
Tilman's research may herald a new direction in biofuels research. Collins, for example, has already planted a diverse array of prairie grasses in experimental plots to study how they will do--a "polyculture," as opposed to a monoculture. But even Tilman admits that it's too soon to say whether farmers can make a go of it economically. "I see two competing ideas, and I don't know which one will win," he says. It's even possible that switchgrass monocultures will work in some environments and polycultures in others.
Currently, however, federal research into finding suitable tallgrass crops for making cellulosic ethanol is concentrated primarily on switchgrass.
Regardless, Mark Downing, an agricultural economist and senior scientist at the Oak Ridge National Laboratory, believes we've already crossed a key threshold. "I've never seen such a focus on the environment and sustainability," he says--including within the Bush administration. "The Secretary of Energy is breathing down my neck to make some progress before Bush leaves office. The issue now is, how are we going to do this? Because of concern about global warming and environmental sustainability, we've decided that biofuels are important. Now we can really get down to the brass tacks of figuring out how to do it."
If the effort can be sustained over the next five to ten years, the prairie grasses that created America's breadbasket may well lead the country toward a more sustainable future. "This is one of my dreams," says Tilman, "to see this happen."
As scientists and engineers look to replace fossil fuels and fight global warming with renewable energy sources made from vegetation, Audubon and other environmental groups are sounding a note of caution. Creating energy from cellulosic biomass such as switchgrass, trees, and other plant materials holds great promise, but carries its own costs. Here are some guidelines.
* No farm or energy subsidies should be given for biofuel crops grown on land that was converted from native habitat or forest.
* There should be support for research into a broad range of technologies and vegetation for biofuels.
* Larger incentives should be paid for growing native species and polyculture crops.
* A minimum 10-inch stubble should remain after grass crops are harvested to ensure some cover for wildlife.
* Soil conservation plans should be required, including buffer zones to protect water resources.
* The extraction of biomass from forests should be done sustainably to maintain fish and wildlife habitat and soil and water quality.