Bees at solar farms in Minnesota rose more than 20 fold after ground cover changed
Bees at solar farms in Minnesota rose more than 20 fold after 2 developments swapped gravel and turf grass for native prairie plants and wildflowers, a federal study has found. The change is a habitat mechanism, not a mystery. Removing turf grass and gravel and planting native perennial flowers under and around solar panels turns idle ground into forage and nesting habitat that pollinators can actually use.
The study comes from Lee Walston, an Argonne National Laboratory landscape ecologist, working with colleagues at Argonne and the National Renewable Energy Laboratory, published in the journal Environmental Research Letters. Researchers tracked 2 solar developments built on retired farmland in southern Minnesota, Atwater Solar, 14 hectares generating 4.0 megawatts, and Eastwood Solar, 17 hectares generating 5.5 megawatts, both operated by Enel Green Power North America. Crews planted native prairie grasses and wildflowers on both sites in the summer and fall of 2017. From 2018 through 2022, researchers returned to each site 4 times every summer, 358 visits in total, to count bees, other insects and flowering plants.
Atwater Solar and Eastwood Solar, southern Minnesota, measured from 2018 to 2022 after native plantings went in during 2017.
Show the numbers
| Total insects | 3 |
| Flowering plant species | 7 |
| Native bees | 20 |
Over the 5 years, native bee abundance rose more than 20 fold, total insect abundance tripled, and the number of flowering plant species on site rose 7 fold. Researchers counted 729 native bees across the whole study, with more than 80% of them found after year 2, once the plantings had time to establish. The 2 most common bee families were the sweat bees, called Halictidae, at 70% of the count, and the family that includes bumblebees, called Apidae, at 20%.
It demonstrates that, if properly sited, habitat friendly solar energy can be a feasible way to safeguard insect populations and can improve the pollination services in adjacent agricultural fields.
Lee Walston, landscape ecologist and environmental scientist at Argonne National Laboratory, the study lead researcher. Source 2.
Bees crossed the fence to pollinate soybeans next door
The pollinators did not stay behind the fence. Bee visits to soybean flowers next to the restored habitat were about as frequent as visits next to land enrolled in the federal Conservation Reserve Program, a program that pays farmers to keep land in permanent grass instead of crops. Visits near the solar habitat ran about 2 times more often than at a soybean field roadside edge, and about 2.5 times more often than inside the interior of a soybean field. Every native bee the study recorded visiting a soybean flower was a bumblebee.
Ratios the study itself states, not raw bee counts. Bee visits to soybean flowers next to the solar habitat were about as frequent as visits next to land in the federal Conservation Reserve Program.
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| Soybean field roadside edges | 2 |
| Soybean field interior | 2.5 |
The effort to obtain these data was considerable, returning to each site 4 times every summer to record pollinator counts.
Heidi Hartmann, manager of the Land Resources and Energy Policy Program in the Argonne National Laboratory Environmental Sciences division. Source 2.
Minnesota has let solar developers choose this ground cover since 2016
Minnesota Statutes section 216B.1642 has let the owner of a ground mounted solar site larger than 40 kilowatts manage the ground under and around the panels for native perennial vegetation and pollinator foraging habitat since 2016. A site that wants to call itself pollinator friendly has to follow a pollinator plan set by the state Board of Water and Soil Resources and file a public vegetation management report. The law gives a developer the choice. This study is the field evidence for what 5 years of that choice produced at 2 real sites.