If you're hoping to grow grass for cellulosic biofuel production, you're looking for something hardy and tolerant of low nutrients -- something that requires minimal human help to get established fast and grow with lots of biomass. Unfortunately, that list of attributes is also a reasonable characterization of an invasive plant, which is now one of the leading environmental problems in the American West. Sensitive prairie grassland is increasingly overrun with tough customers like bufflegrass, cheatgrass, knapweed, and thistle.

Representatives of the Global Invasive Species Program, the Nature Conservancy and the International Union for Conservation of Nature released a report to the UN in Bonn, Germany, summarizing the above concern. "Some of the most commonly recommended species for biofuels production are also major invasive alien species," according to the report -- a concern shared by many invasive species researchers and policy experts.

As an example, switchgrass -- the poster child of the cellulosic ethanol industry and closely related to a number of invasive species such as torpedo grass -- is occasionally invasive and weedy itself, and its ecology and physiology closely resembles that of other invasive grasses. It's not inconceivable that the large-scale industrial production of plants with weedy characteristics could lead to the establishment of those species in areas where they are not desirable. The biofuels industry is more optimistic than the ecologists, but acknowledges the possibility.

Tim Seastedt, an ecologist at the University of Colorado, agrees with the conclusions of the report. "The invasive species we're dealing with here on the Front Range (of Colorado) tend to be winter-growing annuals that use C4 photosynthesis. That describes biofuel grasses, too. I'd consider it a concern for policymakers and managers." Ongoing research by members of his research group deal with invasive species in grasslands and their management.

Other ecologists, such as David Tilman at the University of Minnesota, suggest that biofuel production is best done not with single-species crops of exotic plants, but rather by "farming prairie" -- by encouraging the growth and development of tall-grass prairie composed of a mix of native species. His research suggests that such an approach would yield more energy to turn into biofuel than monoculture crops, and would further encourage the storage of carbon in soil and support populations of native birds and wildlife.