Bee Abundance and Diversity in Suburban Yards

Research Issue

[photo:] Bee on lawn flower.

Widespread population declines of bees and other pollinators from habitat loss are a growing concern in the United States. However, cities and suburbs support a surprising level of bee richness and abundance, and nectar and pollen from spontaneous flowers such as dandelions, white clover and other ‘weedy’ species have the potential to support bee conservation in urban and suburban areas. Residential and commercial lawns, athletic fields, and golf courses cover an estimated 40 million acres in the United States, making these green spaces a potentially significant management tool for improving bee habitat.

Our Research

Lawn maintenance often results in a simplistic vegetation configuration that is dismissed as “sterile environments for biodiversity.” But could less rigorous lawn mowing make a difference to biodiversity in a suburban or urban setting? Given the cumulative area of lawns in urban and suburban areas in the U.S. and the millions of people that manage these systems, Susannah Lerman, a NRS researcher and adjunct professor at University of Massachusetts-Amherst, explored the effects of mowing less frequently on floral resources, and in turn, what are the implications of relaxed management practices on bee and other pollinator populations.

[photo:] Suburban house with weedy flowers in front yard attracts beesThe 2-year study included 16 single-family suburban yards in Springfield, Massachusetts, with average parcel size about a quarter acre. Lawns were not treated with herbicides or irrigated during the study, and did not have designated pollinator or vegetable gardens. The sites were predominantly comprised of lawns with limited cultivated floral resources or hedges. Lawns were mowed from May through September in 2013 and 2014. Each yard was assigned to a mowing frequency regime: mowed every week, every two weeks or every three weeks. To ensure households adhered to the experimental restrictions (e.g., frequency and height of mowing), researchers provided a free lawn mowing service and mowed all participating lawns for the duration of the study. Lawns were sampled for spontaneous flowers and bees prior to each mowing event.

The research team found that while mowing every 3 weeks resulted in as much as 2.5 times more lawn flowers (aka dandelions and clover) and greater diversity of bee species, the abundance of bees was greatest when lawns were mowed every 2 weeks. Further, the researchers documented 93 species of bees with supplemental observations reaching 111 bee species. This represents roughly a quarter of bee species recorded in Massachusetts.

Expected Outcomes

Decline in bee populations has been a significant ecological issue and has also drawn interest and concern from citizens. More research will be needed to determine whether the results in Springfield hold true in other cities throughout the nation, however the spontaneous flowers that were key to making lawns viable habitat in Springfield are common. This research gives homeowners who are motivated to manage their lawn to benefit wildlife an option that does not necessitate expensive plantings or more work. Mowing less frequently can improve pollinator habitat and can be a practical, economical, and timesaving alternative to lawn replacement or even planting pollinator gardens. Indeed, the greatest barrier to the “lazy lawnmower” approach explored in this study may be reconciling social pressure and homeowners’ own expectations of their lawns with gains realized in bee habitat.

Grants

This research was funded by the National Science Foundation.

Research Results

Lerman, Susannah B.; Contosta, Alexandra R.; Milam, Joan; Bang, Christofer 2018. To mow or to mow less: Lawn mowing frequency affects bee abundance and diversity in suburban yards. Biological Conservation. 221: 160-174. https://doi.org/10.1016/j.biocon.2018.01.025

Research Participants

Principal Investigator

  • Susannah Lerman, US Forest Service Northern Research Station, Research Ecologist

Research Partners

  • Last modified: June 21, 2018