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Bioenergy Choices Could Change US Bird Diversity

Posted on 18. January, 2011.

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Ambitious plans to expand acreage of bioenergy crops could have a major impact on birds in the US Upper Midwest, according to a study published in the online edition of the Proceedings of the National Academy of Sciences (PNAS).

Combining data from bird surveys and land usage, two University of Wisconsin–Madison researchers calculated changes in the number of bird species after widespread planting of bioenergy crops.

The study compared two approaches to bioenergy feedstocks: monocultures of annuals, such as corn, or perennial cultures of prairie plants and grasses.

Because diverse plantings are more conducive to a diversity of animals, the researchers were not surprised to find that a large-scale increase in row crops would decrease bird biodiversity, says co-author Claudio Gratton, an associate professor of entomology. The study showed that planting almost 23 million acres of corn or similar crops on marginal lands in the Upper Midwest could reduce the number of bird species by 7% to 65% in much of the region.

The decrease was especially acute in the diverse, hilly landscapes of southwest Wisconsin, where row crops are relatively rare.

Gratton and Tim Meehan, a postdoctoral fellow at the Great Lakes Bioenergy Research Center, wanted to know how changes in biofuel production would affect wildlife, particularly birds. To examine how many birds live on various landscapes today, they relied on the annual breeding bird survey, in which birdwatchers record every species they see or hear along preset routes.

The computer model that Meehan and Gratton developed showed that planting almost 21 million acres of perennial crops for bioenergy could increase bird biodiversity by 25 percent to 100 percent in some locales. The increase would be especially high in places like central Illinois and Iowa, where row crops are now dominant.

Today, almost all biofuel comes in the form of ethanol, used as a gasoline additive, but further increases in ethanol production could have widespread environmental effects. "You can look at ethanol and make a calculation about how much energy you can get out of the landscape, but what other effects will follow if you plant so much acreage in biofuel crops?" asks Gratton. He notes that crops can store carbon in the soil, tempering global warming, or affect the runoff of water, fertilizer or pesticide. "As biofuels continue to gain traction, these are going to be real environmental questions to consider," he says.

The researchers focused on plantings on marginal lands rather than top-grade cropland because of concerns that expanded biofuel production will take a further bite from food production. Although scientists have debated how corn ethanol will affect the supply and price of food, and whether it delivers a net global warming benefit, the study was the first to look at the biological impact of different strategies for growing bioenergy crops.

Today, most biofuel ethanol is made from corn, but the Great Lakes Bioenergy Research Center, housed at UW-Madison and Michigan State University, is focusing on techniques for extracting biofuels from cellulose, which would expand the possible sources of biofuels to include crops such as switchgrass and many types of inedible biomass. At that point, says Gratton, farmers and society as a whole will face a decision about what crops best serve social needs.

Land-use decisions are typically made based on a single factor such as crop productivity or profitability, Gratton says, in fact, changing how land is used usually has multiple impacts. As a result, he says, "People are starting to think about bundles of effects, on water quality, greenhouse gas emissions, or on beneficial insects that need certain habitats to survive."

Gratton says that the results of the survey were striking. “The more corn you have, the fewer bird species you are going to get. And the rarest species, which often tend to be grassland species, will take a particular hit. But when you increase the proportion of grasslands, you see a big increase in species richness, because the threatened species that require grasslands, like the bobolink, tend to increase the most."

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