By Paige Boyle and Lindsey Kemmerling, Minneapolis-St. Paul Long Term Ecological Research Program, University of Minnesota
For six years now, our team has been working to assess the ecological and social benefit of urban lawns through our work with the Minneapolis - St. Paul Metropolitan Area (MSP) Long Term Ecological Research program. An overarching goal of this research is to determine if bee lawns actually support bees.
As part of this effort, we have been routinely sampling 80 or so home lawns each summer to determine vegetation composition of lawns across MSP (Figure 1). Over the five year period, we have observed over 150 plant species in lawns, and have found that these lawns contain a great amount of diversity, between 8 and 48 species per lawn. Although grasses make up a majority of lawn cover, broadleaf plants account for a vast majority of observed species. Many of these broadleaf species have potential to provide forage for pollinators within a lawn setting.
So, the plants are there – but are they flowering?
Over the four years where we recorded flowering data, we observed 91 flowering species, with an average of 6.6 flowering species per lawn. The most common flowering species were plants commonly considered to be weeds: dandelion, black medic, and wood sorrel. White clover was also quite common; this plant may be considered weedy or an intentional component of a low-input or bee lawn mix, depending on the lawn.
So, the flowers are there – but are the bees visiting them?
On these same lawns, we surveyed bumble bees for two years. The most common bee species we found were the common eastern bumble bee and the red-belted bumble bee. Bumble bees were most commonly found visiting white clover and thyme.
So, the bees sometimes visit lawn flowers – but what about the rest of the yard?
In addition to surveying bees on lawns, we also surveyed bees on ornamental plantings in the same yards. We saw more bumble bees on ornamental flowers, and, importantly, we identified 14 individuals of the endangered rusty patched bumble bee across 8 different properties. Rusty patched bumble bees were found visiting bee balm, creeping bell flower, hosta, Joe pye weed, purple coneflower, and blazing star.
So, what’s next?
We’re now testing what characteristics of lawns and ornamental plantings (area planted and species composition) and broader spatial factors (amount of greenspace, buildings, and roads in the surrounding landscape) determine the bee community that could be found in a residential yard.