A recently published study examines how insect communities respond to newly established habitat on solar energy sites in agricultural landscapes.
“The establishment and management of solar-pollinator habitat is a relatively novel concept and most of what is reported about the ecological and ecosystem services benefits of this practice is theorized from models and results from other habitat restoration studies,” the report’s authors wrote.
The report’s authors are Argonne National Laboratory’s Leroy Walston, Heidi Hartmann and Laura Fox, the National Renewable Energy Laboratory’s Jordan Macknick and James McCall, Lauren Jenkins, Ecology PhD Student at Duke University, and Jake Janski, Minnesota Native Landscapes.
“There is little empirical evidence on the establishment of vegetation at solar facilities and resulting biodiversity responses. Fundamental research is therefore needed to systematically describe the biodiversity outcomes of this novel land use across different regions and vegetation management practices,” the report said.
To address these basic research needs, the report’s authors conducted a longitudinal field study across five years (2018–2022) to understand how insect communities respond to newly established habitat on solar energy sites in agricultural landscapes.
They were also interested in understanding whether the establishment of solar-pollinator habitat resulted in any “spillover” effects in pollinator and beneficial insect visitation to nearby crop fields such as soybeans. Soybean is one of the most extensively grown crops worldwide and while it is capable of self-pollinating, studies have shown yield increases as a result of bee visitation.
The report’s authors said their objectives were to address the following three research questions:
- Does flowering plant abundance and diversity on solar sites increase over time?
- Does insect abundance and diversity within the solar sites increase over time?
- Does proximity to solar-pollinator habitat influence bee visitation to croplands near the solar facilities?
The study took place between 2018 and 2022 at two utility-scale solar energy facilities in southern Minnesota: the Atwater Solar Site and the Eastwood Solar Site.
Both solar energy sites are operated by Enel Green Power North America and are located in rural landscapes between 100 and 200 km from Minneapolis.
Construction for both sites was completed in 2017. The Atwater Solar Site has nameplate electrical capacity of 4 megawatts. The Eastwood Solar Site has a nameplate electrical capacity of 5.5 MW AC.
Prior to solar energy development, both sites were previously used for decades for row crop agricultural production. The solar facilities were constructed with plans to minimize impacts to soils. Both sites remained adjacent to row crop agriculture on at least two sides throughout the study.
After construction, both sites were prepared for restoration with native plantings of grasses and forbs.
Results of Study
Study results provide the first empirical field evidence on the interannual, temporal changes in insect communities following the planting of pollinator habitat at solar energy facilities, the report’s authors said.
Consistent with other studies, the team’s observations highlight the relatively rapid insect community responses to grassland restoration activities.
“As predicted, all habitat and biodiversity metrics increased each year following conversion from cropland to solar-pollinator habitat. By the end of the 5 year study period, we observed a 7-fold increase in flowering plant species richness, on average, within the onsite habitat transects.”
In that same time, abundance of insect pollinators and beneficial insects tripled, and insect group diversity increased by an average of 13% per year, the report said.
“Remarkably, we observed an exponential increase in the abundance of native bees, which increased over 20-fold during this study, with most observations occurring after Year 2.”
The findings on the solar sites were restricted to the experimental test plots which were planted with additional plant species and managed differently than the rest of the solar sites.
A total of 66 species of native grasses and forbs were planted throughout the two solar sites. An additional 61 species were planted in the experimental test plots.
Areas outside the experimental test plots were mowed more frequently and were also strategically grazed with sheep during the last two years of the project.
“Despite these differences, the dominant flowering native species observed in the experimental test plots were consistent with the observations of groundcover establishment within the larger PV array area,” the report said.
“Future research should be designed to examine site-level variation in vegetation management, with sampling designs that are more dispersed throughout the solar facilities, to better understand the biodiversity responses across the entire solar site.”
Along with observed annual increases in insect group abundance and diversity within the solar-pollinator habitat transects, “we also found positive effects of proximity to solar-pollinator habitat on bee visitation to nearby soybean fields.”
The insect community responses to solar-pollinator habitat the report’s authors observed both within the onsite habitat test plots and visitation to adjacent soybean fields underscores two important potential implications of solar-pollinator habitat, the report said.
First, solar-pollinator habitat can play an important role in conserving biodiversity in agricultural landscapes.
Given the increasing amount of ground-mounted solar energy that is expected to be developed by 2035, solar-pollinator habitat can offset losses of natural areas and restored grasslands in agricultural landscapes to support pollinators and their agricultural services, the report said.
Second, like other forms of agrivoltaics, solar-pollinator habitat could help mitigate land use conflicts associated with the conversion of farmland for solar energy production, the report said.
Conclusions
The establishment of solar-pollinator habitat can be a low impact approach to improve the ecological compatibility of utility-scale solar energy, the report said.
“However, the ecological effectiveness of this practice depends on a variety of factors including solar facility design, geographic region, and the role of solar-pollinator habitat in the ecological mitigation hierarchy.”
Solar-pollinator habitat “is unlikely to completely offset the residual ecological impacts of solar developments poorly sited in areas with high ecological value. In this context, solar-pollinator habitat may have the greatest potential for ecological benefit for solar energy facilities sited in areas that have been previously ecologically compromised, such as marginal farmland, former industrial or mine lands, and other disturbed sites,” the report said.
“In these situations, solar-pollinator habitat may be able to provide net biodiversity benefits. Given the design and operations of utility-scale PV facilities, solar-pollinator habitat could become a novel ecosystem made up of unique plant and animal assemblages based on the compatibility of seed mixes to be planted and unique site-level vegetation management practices.”
The report said that additional research is needed to understand the feasibility of solar-pollinator habitat across different regions and to meet different ecological goals (e.g. to conserve target insect or wildlife species) that will optimize the ecological compatibility of these novel renewable energy land uses.
