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The Bee Frequency: How Does Lawn Mowing Affect Bee Populations?
Lawns are a common sight in the United States. The scientists in this study found previous research showing that lawns mowed frequently or treated with chemicals had limited flowering plants for pollinators. The scientists hypothesized that mowing less and providing fewer chemical treatments to lawns could increase the diversity of flowering plants. In turn, more flowering plants would improve the abundance of bees on lawns. They tested their hypothesis with this study.
The Bee Frequency: How Does Lawn Mowing Affect Bee Populations?
Meet the Scientists
Susannah Lerman
Ecologist | Wildlife Biologist
Alexandra Contosta
Soil Biogeochemist
Joan Milam
Melittologist
What Kinds of Scientists Did This Research?
Research Ecologist: This scientist studies the relationship between living things and their living and nonliving environment.
Soil Biogeochemist: This scientist studies the interactions between the biotic (living) and abiotic (nonliving) components of soils.
Melittologist: This scientist studies bees.
Thinking About Science
Scientists use many different tools and technologies to complete research. They are increasingly using high-tech, computer-based instruments that require special knowledge or skills. However, not all scientific endeavors require high-tech equipment. Many sciences still use the same technologies that scientists used many years ago. For instance, scientists studying chemistry may still use beakers. Scientists have used beakers in chemistry since the 1800s, and modern beakers are similar to the ones used then.
Scientists may also use their creativity to find simple items at the grocery store that they can use for experiments. In this study, the scientists evaluated how mowing lawns affects bees. The easiest way to capture and learn about bees is to use inexpensive, disposable plastic bowls painted with bright, fluorescent colors that make the bowls resemble flowers. Soapy water inside the bowls prevented the bees from flying away before the scientists could identify and count them.
The scientific process requires a great deal of creativity. As you read this study, think about a question you want to investigate using the scientific process. What tools or technologies could you use to test your question?
Thinking About the Environment
Green, grassy lawns cover a large portion of the United States (figure 1). The scientists in this study found that grass lawns cover more than 400 million acres in the United States. That’s an area approximately equivalent to the State of Alaska, the largest State in the United States. You may see lawns at homes, at schools, near businesses, in parks, and at golf courses.
Figure 1. Lawns are areas covered mostly in grass. Many lawns are small but, together, they cover a large part of the United States.
Courtesy photo by Michelle Andrews.
Lawns can be easy to maintain, attractive, and provide a good place to play or picnic. Chemical-free lawns can also be good for the environment. For instance, lawns can slow stormwater runoff, store carbon, and lower temperatures caused by the urban heat island effect. These benefits are especially important in urban and suburban areas with limited green space.
While lawns do have benefits, the scientists knew that most lawns are not an ideal habitat for many plants and animals. Keeping lawns looking good often requires chemical treatments that can pollute waterways and can also kill some pollinators. Lawns also require frequent mowing to maintain a tidy look. In fact, there are even some places in the United States where the law requires mowing! While mowing makes a lawn look neat, scientists know that frequent mowing can make it difficult for native plants and animals to survive (figure 2).
Figure 2A. Frequent mowing can lead to a lawn with fewer plant species. While it provides a tidy look that many people enjoy, a mowed lawn is not the ideal habitat for wildlife.
Courtesy photo by Jessica Nickelsen.
Figure 2B. What differences do you notice between the freshly mowed lawn (left) and the unmown portions (right) of the lawn?
Courtesy photo by Jessica Nickelsen.
Figure 2C. In this figure, again look closely to see the freshly mowed lawn (left) and the unmown lawn (right). What differences do you notice in this photo between the mowed lawn and the unmown portion? How does this photo compare to the photo in figure 2B?
Courtesy photo by Babs McDonald.
Introduction
Lawns are a common sight in the United States. As discussed in “Thinking About the Environment,” lawns can have both good and bad effects on the environment and on pollinators. Because humans find lawns so desirable, removing lawns altogether is not likely to happen.
The scientists found previous research showing that lawns mowed frequently or treated with chemicals had limited flowering plants for pollinators. Without frequent mowing and treatment with chemicals, however, lawns are home to numerous native, flowering plants (figure 3).
Figure 3. Lawns do not always provide a good habitat for pollinators, but lawns that are allowed to grow do have many flowering plants that wildlife can use.
USDA Forest Service photo by Susannah Lerman.
Pollinators are in decline across much of the United States. Therefore, the scientists determined that lawns with flowering plants could play an important role in providing habitat and food to pollinators (figure 4). This determination is especially important in suburban and urban areas where there isn’t a lot of natural pollinator habitat.
Figure 4. Notice the pollinator enjoying the flowering plants in this lawn.
Courtesy photo by Babs McDonald.
The scientists hypothesized that mowing less and providing fewer chemical treatments to lawns could increase the diversity of flowering plants. In turn, more flowering plants would improve the abundance of bees on lawns.
Reflection Section
Methods
The scientists conducted their research in the city of Springfield, Massachusetts (figure 5). They chose 16 homes in the city that had similar lawns of approximately the same size. The lawns had no or limited flower gardens and were separated by at least 500 meters.
Number Crunch
The scientific team used a Toro 19-inch push mower (figure 6) to mow lawns from May through September during 2013 and 2014. They used the same mowing techniques and equipment for each lawn and left all grass clippings on the lawn after mowing.
Figure 6. The scientists mowed each lawn with a basic lawn mower.
USDA Forest Service photo by Susannah Lerman.
To determine the impact mowing had on the 16 lawns, the scientists chose 1 of 3 mowing regimes:
• Mowed every 7 days (every week)
• Mowed every 12 to 14 days (every 2 weeks)
• Mowed every 18 to 21 days (every 3 weeks)
The scientists also sampled flowering plants and bees at each lawn 5 times per year, for a total of 10 times per lawn. All sampling took place before mowing. They identified and counted flowering plants, then added them up to calculate each lawn’s total floral abundance.
To sample bees, the scientists strategically placed 30 plastic pan traps filled with soapy water across each lawn to catch the greatest number of bees (figure 7). They left the pan traps on each lawn for 24 hours.
Because pan traps often collected mostly small bees, the scientists also swept each yard with hand nets for 15 minutes to catch larger bees. They followed a standard process (figure 8) while sweeping with the hand net.
Figure 8. A hand net (also called an aerial net) is lightweight; has a long, thin handle; sometimes has a flexible hoop; and includes a soft bag. These nets are ideal for collecting delicate specimens, including many pollinators like bees, moths, or butterflies. Scientists typically use this type of net to “scoop” insects from the air or off a plant, but they can also “pancake” the nets flat against the ground to catch insects on or near the ground.
Courtesy photo by Michelle Andrews.
The scientists brought the collected bees to a lab to wash, pin, identify, and label them, and then entered the information into a database (figure 9).
Figure 9. The scientists identified and pinned all the bees they collected. Identifying and pinning the bees enabled the scientists to visualize the different bee species that might be impacted by changing how people mow lawns.
Courtesy photo by Michelle Andrews.
Reflection Section
Findings
After 2 years of lawn mowing and 10 sampling events per lawn, the scientists collected a total of 4,587 bees. They identified a total of 93 bee species on the lawns and an additional 8 species as part of another study, for a total of 101 species. This represents about 25 percent of bee species recorded in Massachusetts.
Of those 93 species identified in the lawn mowing study, 10 species accounted for 78 percent of all 4,587 bees identified. The sweat bee (figure 10) was the most common type of bee found, accounting for 42 percent of all bees collected. During the same 2-year period, the scientists identified 54 different flowering plants and found another 11 unidentifiable plants.
Figure 10. Sweat bees are a diverse group of bees. Some species are blue or green in color, like this green metallic sweat bee. As the name suggests, these bees are attracted to human sweat, which they eat for salt. Luckily, they are not aggressive toward humans unless they feel threatened.
U.S. Geological Survey Bee Monitoring and Inventory Lab photo by Wayne Boo.
Number Crunch
The lawns with the greatest diversity of bee species were those that scientists mowed weekly (table 1). However, these lawns also had many single captures. Single captures are bee species from which scientists only captured one bee over the course of the entire study, rather than bees that scientists caught frequently and in high numbers.
The lawns that had the greatest number of bees were those that scientists mowed once every 12 to 14 days (every 2 weeks). The scientists found that lawns mowed every 18 to 21 days (every 3 weeks) had significantly higher grass and 2½ times more flowers. Lastly, the scientists found that yard characteristics, such as lawn size or tree canopy cover, did not impact the abundance of bees or flowering plants.
Table 1. Those lawns mowed once every 7 days had a high diversity of bee species, but fewer total bees. Lawns mowed in the other regimes had a lower diversity of bee species, but more total bees.
Reflection Section
Discussion
The scientists believe the results of the study partially supported their hypothesis. Although lawns do not have the same habitat quality as a native habitat, people can manage lawns to provide more resources for bees. The scientists suggest a “lazy lawnmower” approach of mowing less frequently, with every 2 weeks as the sweet spot. Less frequent lawn mowing results in the growth of more flowering plants and increases the abundance of bees. Although the study results indicated a lower diversity of bee species when mowing less, the scientists believe a lower diversity of species would not impact the role of bees in the ecosystem.
These findings are important, as lawns are common across the United States. Those who have lawns in urban, suburban, and even rural areas can actively add flowers to gardens to attract bees. Even those without specially designed gardens can support bees by managing lawns to encourage spontaneous flower growth.
The scientists recognized that these results are limited because they include only one city from one region of the United States. Additionally, there may be barriers to acceptance of the “lazy lawnmower” approach. For one, many people simply prefer a tidy lawn that is easy to care for. The scientists also recognize that certain laws in some parts of the country prevent lawns with taller plants. However, the scientists believe the “lazy lawnmower” approach to lawn management is an easy and inexpensive method for improving urban and suburban areas for bees.
Reflection Section
Adapted from Lerman, S., et al. 2018. To Mow or to Mow Less: Lawn mowing frequency affects bee abundance and diversity suburban yards. Biological Conservation. 221:160-174.
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In this FACTivity, we’ll demonstrate the pollination process and will see how effectively pollinators can move pollen between flowers. Materials: Roll of paper towels Markers Plastic Bowls Construction Paper (optional)...FACTivity – The Bee Frequency
In this FACTivity, we’ll demonstrate the pollination process and will see how effectively pollinators can move pollen between flowers. Materials: Roll of paper towels Markers Plastic Bowls Construction Paper (optional)...
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Print this lawn sign to let your neighbors know that you’re mowing less and supporting pollinator habitat. The QR code directs to the Northern Research Station’s website where you can...Spotlight – Bee Proud Lawn Sign
Print this lawn sign to let your neighbors know that you’re mowing less and supporting pollinator habitat. The QR code directs to the Northern Research Station’s website where you can... -
Use this sign to let your neighbors know – “We’re mowing less to improve pollinator habitat!” The QR code directs viewers to the Northern Research Station’s webpage where you can...Spotlight – Lazy Lawn Mower Alert Sign
Use this sign to let your neighbors know – “We’re mowing less to improve pollinator habitat!” The QR code directs viewers to the Northern Research Station’s webpage where you can...
Glossary
View All Glossaryabundance
(ə bən dənt(s)): A large quantity; plenty.
anther
(an(t) thǝr): The part of the stamen of a flower that produces and contains pollen and is usually borne on a stalk.
canopy
(ka nə pē): A protective covering: such as, the uppermost spreading branchy layer of a forest.
cross-pollinate
(krȯs pä lǝ nāt): To pollinate (a flower or plant) with pollen from another flower or plant.
fertilization
(fǝr tǝ lǝ zā shǝn): The joining of an egg cell and a sperm cell (pollen in a plant) to form the first stage of an embryo (a seed in a plant).
floral
(flȯr ǝl): Of, relating to, or depicting flowers.
hypothesize
(hī pä thǝ sīz): To make an assumption or idea that is proposed for the sake of argument so that it can be tested to see if it might be true.
nectar
(nek tǝr): In botany, a liquid made by the flowers of plants.
oligolege
(ǝ lē gǝ lāj): Pollinator species which requires the pollen of a particular plant for development and survival.
parasitic
(per ə si tik): Of or relating to parasites or their way of life; being a parasite, which is an organism living in, on, or with another organism in order to obtain nutrients, grow, or multiply often in a state that directly or indirectly harms the host.
pollen
(pä lǝn): The tiny particles in the anthers of a flower that fertilize the seeds and usually appear as fine yellow dust
pollinator
(pä lǝ nā tǝr): An agent (such as an insect) that pollinates flowers.
regime
(rā zhēm or ri zhēm): A regular course of treatment.
stigma
(stig mǝ): On the female flower, the sticky knob which collects pollen from pollinators.
urban heat island effect
(ǝr bǝn hēt ī lǝnd ē fekt): An urban area that is significantly warmer than its surrounding rural areas due to human activities.
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Susannah Lerman
Ecologist | Wildlife Biologist
My favorite experience is discovering exciting birds and insects in our backyards and neighborhood parks. I spend a lot of time exploring local habitats and talking with neighbors about the...View Profile -
Alexandra Contosta
Soil Biogeochemist
One of my favorite science experiences happened during my first field ecology job. I was working for the USDA Forest Service in the White Mountains of New Hampshire and Maine....View Profile -
Joan Milam
Melittologist
My favorite experiences are catching uncommon bees throughout North America with fellow bee scientists (called “melittologists”) and identifying them in my lab. I especially enjoy catching bees that collect pollen...View Profile
Standards addressed in this Article:
Next Generation Science Standards
- ESS3.C-M1Human activities have significantly altered the biosphere, sometimes damaging or destroying natural habitats and causing the extinction of other species. But changes to Earth’s environments can have different impacts (negative and positive) for different living things.
- ETS1.B-M2There are systematic processes for evaluating solutions with respect to how well they meet criteria and constraints of a problem.
- LS2.A-M1Organisms, and populations of organisms, are dependent on their environmental interactions both with other living things and with nonliving factors.
- LS2.A-M3Growth of organisms and population increases are limited by access to resources.
- LS2.C-M1Ecosystems are dynamic in nature; their characteristics can vary over time. Disruptions to any physical or biological component of an ecosystem can lead to shifts in all its populations.
- LS2.C-M2Biodiversity describes the variety of species found in Earth’s terrestrial and oceanic ecosystems. The completeness or integrity of an ecosystem’s biodiversity is often used as a measure of its health.
- LS4.D-M1Changes in biodiversity can influence humans’ resources, such as food, energy, and medicines, as well as ecosystem services that humans rely on—for example, water purification and recycling.
Social Studies Standards
- People, Places, and Environments
- Science, Technology, and Society
Note To Educators
The Forest Service's Mission
The Forest Service’s mission is to sustain the health, diversity, and productivity of the Nation’s forests and grasslands to meet the needs of present and future generations. For more than 100 years, our motto has been “caring for the land and serving people.” The Forest Service, an agency of the U.S. Department of Agriculture (USDA), recognizes its responsibility to be engaged in efforts to connect youth to nature and to promote the development of science-based conservation education programs and materials nationwide.
What Is the Natural Inquirer?
Natural Inquirer is a science education resource journal to be used by students in grade 6 and up. Natural Inquirer contains articles describing environmental and natural resource research conducted by Forest Service scientists and their cooperators. These scientific journal articles have been reformatted to meet the needs of middle school students. The articles are easy to understand, are aesthetically pleasing to the eye, contain glossaries, and include hands-on activities. The goal of Natural Inquirer is to stimulate critical reading and thinking about scientific inquiry and investigation while teaching about ecology, the natural environment, and natural resources.
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Meet the Scientists
Introduces students to the scientists who did the research. This section may be used in a discussion about careers in science.
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What Kinds of Scientist Did This Research?
Introduces students to the scientific disciplines of the scientists who conducted the research.
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Thinking About Science
Introduces something new about the scientific process, such as a scientific habit of mind or procedures used in scientific studies.
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Thinking About the Environment
Introduces the environmental topic being addressed in the research.
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Introduction
Introduces the problem or question that the research addresses.
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Method
Describes the method the scientists used to collect and analyze their data.
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Findings & Discussion
Describes the results of the analysis. Addresses the findings and places them into the context of the original problem or question.
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Reflection Section
Presents questions aimed at stimulating critical thinking about what has been read or predicting what might be presented in the next section. These questions are placed at the end of each of the main article sections.
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Number Crunches
Presents an easy math problem related to the research.
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Glossary
Defines potentially new scientific or other terms to students. The first occurrence of a glossary word is bold in the text.
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Citation
Gives the original article citation with an internet link to the original article.
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FACTivity
Presents a hands-on activity that emphasizes something presented in the article.
Science Education Standards
You will find a listing of education standards which are addressed by each article at the back of each publication and on our website.
We Welcome Feedback
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Contact
Jessica Nickelsen
Director, Natural Inquirer program -
Email
Education Files
Project Learning Tree
If you are a trained Project Learning Tree educator, you may use “Charting Diversity” as an additional resource.
Related Resources from the Natural Inquirer
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Additional Resources
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USDA Forest Service: Pollinators
Visit WebsiteLearn more about pollinators and pollinators research.
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USDA Forest Service: Want to help bees? Take a break from lawn mowing
Visit WebsiteRead a Forest Service blog post about this research.
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Pollinators Live
Visit WebsiteWhile pollinators may come in small sizes, they play a large and often undervalued role in the production of the food we eat, the health of flowering plants, and the future of wildlife. A decline in the numbers and health of pollinators over the last several years poses a significant threat to the integrity of biodiversity, to global food webs, and to human health, according to scientists. Pollinators LIVE brings the excitement of pollinators to you through webcasts, webinars and online education resources.
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USDA Forest Service: "Gardening for Pollinators"
Visit WebsiteLearn more about gardening for pollinators.
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USDA Forest Service: "Inside Agroforestry—Learn How You Can Use Agroforestry to Help Pollinators"
Visit WebsiteRead more about how you can use agroforestry to help pollinators.
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USDA Forest Service: "Forest Service Is Aflutter with Native Plant and Pollinator Gardens"
Visit WebsiteLearn more about native plant and pollinator gardens.
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The Xerces Society for Invertebrate Conservation
Visit WebsiteThe Xerces Society for Invertebrate Conservation is an international nonprofit organization that protects the natural world through the conservation of invertebrates and their habitats
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Project Learning Tree: "Pollinators: Why They’re Important and How Schools Can Help"
Visit WebsiteLearn more about how schools can help pollinators.
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National Environmental Education Foundation: "Create a Place for Pollinators"
Visit WebsiteRead about ways you can create spaces for pollinators.