Grassland biofuels better for bees, researchers find

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Capital News Service
LANSING – A hand-held vacuum seems an unlikely tool in a field ecologist’s kit. 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 comparing the effects of two types of biofuel production on Michigan’s bee populations.


A Michigan study found that perennial biofuel crops, like prairie grasses, increase native bee abundance and diversity. Credit: Holly Drankhan

Biofuels are fuels derived from renewable plant or animal sources that can reduce dependence on fossil fuels.

The study compared two sources of biofuels: annual biofuel crops, such as corn and soybeans, and perennial biofuel crops, like prairie grass and 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. That can make energy production from prairies less efficient, Lindquist said. However, prairie grasses provide pesticide-free natural habitat for wildlife, are friendlier to bees and are better at reducing greenhouse gas emissions when they’re 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,” Lindquist said.
Researchers identified areas of the 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 digitized maps, researchers modeled what would happen if they converted nearly 1.5 million acres of annual cropland to grass, as well as converting 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 at existing annual cropland and prairies. From this data, they predicted the effect of each landscape change.
Bee abundance and diversity increased when perennial grasslands grew on the land and decreased when it was converted to annual crops, said study author and former MSU researcher Ashley Bennett.
In other words, grasslands support more natural habitat for these beneficial insects.
Native bees are in decline from habitat loss, insecticide use and pathogens, Bennett said.
That 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,” Bennett said. “Similarly, without native bees providing 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 models used to predict bee friendliness were based on 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 of pests that attack crops.
The researchers say they hope that their findings will help biofuel policymakers 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 help bees most. These include portions of Tuscola, Sanilac, Gratiot and Monroe counties. That could help policymakers use their limited budgets for environmental conservation most effectively, Isaacs said.
There’s no similar data yet for the rest of the Great Lakes region. However, Bennett and Meehan predicted that because states like Illinois and Indiana have similar insecticide use on cropland and historic prairies, the two biofuel scenarios would show similar outcomes for pollinators and pest control.
Holly Drankhan writes for Great Lakes Echo.
Additional resources for CNS editors:
Journal article “Modeling Pollinator Community Response to Contrasting Bioenergy Scenarios.”

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