A Michigan study found that perennial biofuel crops, like prairie grass, increase native bee abundance and diversity. Image: Holly Drankhan
By Holly Drankhan
A hand-held vacuum seems an unlikely tool in a field ecologist’s repertoire.
But sucking up bees from sunflowers was a necessary step in assessing how human energy needs may affect Michigan pollinators.
Researchers from Michigan State University and the University of Wisconsin recently published a study in the journal PLOS ONE comparing the effects of two types of biofuel production on Michigan bee populations.
Biofuels are fuels derived from renewable plant or animal sources that can reduce dependence on fossil fuels.
The Michigan study compared two sources of biofuels: annual biofuel crops, such as corn or soybeans, and perennial biofuel crops, like prairie or switchgrass.
Both types of bioenergy production have pros and cons, said Minnesota DNR Biofuels Program Manager Mark Lindquist.
The cellulose in the cell walls of grasses and stems is harder to break down than the simple starches in corn and soybeans. This can make energy production from prairies less efficient, said Lindquist. However, prairie grasses provide pesticide-free natural habitat for wildlife and are better at reducing greenhouse gas emissions when they are used as a biofuel.
“There are opportunities for both of these kinds of production systems to address the needs of pollinators, but it takes some thought and it takes some planning,” said Lindquist.
Researchers identified areas of Michigan’s Lower Peninsula where marginal land was occupied by each type of biofuel crop. Marginal land has poor soil and little profit potential. That makes it most likely to be used for biofuel production, according to the study.
Using computer software and digitalized maps, researchers modeled what would happen if they converted nearly 1.5 million acres of annual cropland to grass, as well as the same amount of perennial grassland to corn or soybean.
The models were supplied with bee counts taken in the field. With hand-held vacuums, researchers collected and counted bees from potted sunflowers placed in existing annual cropland and prairies. From this data, they predicted the effect of each landscape change.
Bee abundance and diversity increased when perennial grasslands were produced on the land and decreased when it was converted to annual crops, said study author and former MSU researcher Ashley Bennett. Grasslands support more natural habitat for these beneficial insects.
Native bees are in decline from habitat loss, insecticide use and pathogens, said Bennett. This loss has a number of negative impacts.
“Without native bees providing pollination services to native plants, we could also begin seeing declines in native plant populations,” said Bennett. “Similarly without native bees proving pollination services to crops, farmers lose this free service and would have to further supplement crop pollination by using and paying for managed bees, like the honey bee.”
The predictive models were based upon prior work funded by the U.S. Department of Energy’s Great Lakes Bioenergy Research Center, said co-author Timothy Meehan, now a staff scientist for the National Ecological Observatory Network. Similar biofuel scenarios predicted a similar beneficial effect on insects that are natural enemies to pests that attack crops.
The researchers hope that their study will help biofuel policy makers consider both ecological and economic consequences of producing biofuels.
“Biofuels policy may be driven by a lot of different considerations, but the relative importance of each one may depend on changing national political needs,” said Rufus Isaacs, a professor and Extension specialist for the MSU Department of Entomology. “Right now, I think there is a significant national focus on pollinators and a recognition that we need clean forage for bees and other insects to visit.”
The models also identify areas of the state where converting annual crops to grassland would most help bees. These include portions of Tuscola, Sanilac, Gratiot and Monroe counties. This could help policy makers use limited budgets for environmental conservation most effectively, said Isaacs.
There is no data yet for the rest of the Great Lakes region. However, Bennett and Meehan expect that because states like Illinois and Indiana have similar insecticide use on cropland and also historic prairies, the two biofuel scenarios would have similar outcomes for pollinators and pest control.