New research has added to the growing list of challenges facing the nation’s pollinators. A study, published this week in Proceedings of the National Academy of Sciences, suggests that agricultural changes in the Northern Great Plains — particularly the expansion of corn and soybean cropland — could be putting a strain on honeybee colonies by infringing on grasslands and other types of land cover more suitable for pollinators to forage on.
The study finds that from at least 2006 to 2014, corn and soybean cropland has been increasing in parts of the Dakotas where beekeepers already house their colonies. This could be a problem, the researchers suggest, because beekeepers typically try to avoid these types of crops when selecting sites for their apiaries.
“There’s a lot of other research provided that shows that there are profound changes taking place in the Northern Great Plains,” said Clint Otto, a research ecologist with the U.S. Geological Survey and lead author of the new study. “The paper…takes a bee-centric view of these land-use changes and how it affects habitat suitability for supporting commercial honeybees.”
A growing national interest in the production of biofuels — renewable fuels made from plant matter or other organic materials — has sparked a recent uptick in the planting of crops that can be used for that purpose. Corn and soybeans are both common ingredients.
The use of biofuels has been touted as one method of cutting down on greenhouse gas emissions in the transportation sector. The Environmental Protection Agency already requires refiners to mix a certain amount of renewable fuel, mainly corn-based ethanol, into the gasoline they produce. And some companies are beginning to produce biofuels for use in boats and planes, as well.
Increased subsidies and the growing market for biofuels have likely helped contribute to the rise in corn and soybean cultivation in the Northern Great Plains, the researchers note — an expansion that can come at the cost of grasslands and wetlands.
The new study grew out of an interest in investigating the effects his type of agricultural expansion might have on the ecosystem, compared to what is produced by the natural environment in the region. Plant pollination, carried out by bees and other insects, is estimated to have an economic value of $15 billion a year, and the Northern Great Plains serve as a hub for commercial beekeeping, supporting up to 40 percent of the nation’s honeybee colonies.
While the new study doesn’t actually draw any connections between biofuel cropland and pollinator health, experts believe that corn and soybean cropland is less than ideal for the bees when it comes to foraging. Corn, in particular, is thought to be a poor forage crop for honeybees, who tend to prefer other types of plants — and corn pollen is primarily spread by wind, rather than insects, anyway. Additionally, these crops are often treated with pesticides and herbicides that could be harmful to pollinators, the researchers noted in the study.
“Recent field studies conducted in the [Northern Great Plains] have shown that apiaries surrounded by larger scale agricultural land covers, including biofuels, have lower honeybee colony overwintering survival rates and increased physiological stress,” they wrote.
Bret Adee, a beekeeper and co-owner of the South Dakota-based Adee Honey Farms (who was not involved with the new study), noted that “the more diverse the plant resources the better” when it comes to managing healthy bees. The types of agricultural land typically thought to be best for pollinators are the type often cultivated in conjunction with cattle farming, such as clover and alfalfa fields, he said.
To conduct the study, researchers first identified approximately 18,000 sites in North and South Dakota where beekeepers had registered apiaries. They then used maps of the region from 2006 to 2014 to quantify changes over time in the type of land cover around these apiaries. They found significant gains in the biofuel crop area surrounding apiary locations during the study period — an increase of 1.2 million hectares, or more than 4,600 square miles, in all. At the same time, grassland cover around these sites decreased.
Next, the researchers gathered data on the types of land cover in which beekeepers in the region had chosen to place their apiaries in the past and fed that information into a model that showed them which types of land beekeepers most preferred and which they avoided.
The researchers found that apiary placement was most strongly associated with grasslands, as well as alfalfa fields and open water. On the other hand, apiary placement was negatively associated with biofuel crops — in other words, beekeepers were less likely to place their colonies near that type of environment.
What all of these results essentially mean is that the type of land cover most avoided by beekeepers is increasing around their apiaries at the expense of the types of habitats they most prefer. In other words, if this type of agricultural expansion continues, it may mean that beekeepers will be increasingly less able to place their apiaries in the kinds of habitats they consider most desirable. Whether this translates into actual health concerns for the bees remains to be seen, Otto noted — the new paper doesn’t actually suggest that honeybee populations are declining as a result.
However, a few other studies have suggested this could be the case. At least two studies have suggested that land use changes in the Northern Great Plains can affect honeybee survival and productivity. And another study, published just last year, indicated that wild bees could be affected as well. That paper suggested a link between wild bee declines and the conversion of natural habitats for the cultivation of row crops, particularly corn.
Adee, the South Dakota beekeeper, suggested there’s room for both to thrive.
Increased crop rotation, for instance, adds diversity to the landscape, which is good for bees, he noted. And rotating crops is also good for the soil and can help reduce the risk of insect infestations, cutting down on the need for pesticides — a win for both the plants and the pollinators. A practice called intercropping, in which multiple types of crops are sown together, could also produce similar results when possible.
“So we get the benefit of healthier fields, healthier soils and forages for the bees,” Adee said. “If this idea takes hold…I think we have some real possibilities for a rebounding of the bees.”
The U.S. Department of Agriculture already works with landowners in the region on the development of conservation programs, Otto noted. And he added that his research team is currently involved in helping the agency develop new conservation efforts by figuring out what types of plants are most favored by pollinators in the Northern Great Plains.
Ultimately, any land use policy should be evaluated in terms of its costs and benefits to society, Otto suggested. The development of biofuels has a clear environmental purpose — but it also contributes to landscape changes that are still not entirely understood.
“What I hope is that other people can take this information and say, okay how do we use it now to make wiser decisions about how we manage lands out here,” Otto said.