Community gardens in higher-income Boulder neighborhoods have fewer varieties of bees than their medium-income counterparts, new CU Boulder research suggests. Scientists suggest that people in these neighborhoods tend to apply more landscaping practices, such as using fertilizers, which could impact bees鈥� habitats.
Asia Kaiser checked on the听jalape帽o pepper plants the team grew in the community gardens in Boulder County.听(Credit: John Russell/CU Boulder)
Top: A听halictid, colloquially known as a sweat bee,听the team collected from the urban gardens. The bee was covered in pollen.听Bottom: A听grasshopper on a jalapeno pepper plant.听(Credit: Asia Kaiser)
appeared May 22 in the journal Urban Ecosystems.听
鈥淏ees are so important for local ecosystems through their pollination services. The landscape would not look the same without our pollinators,鈥� said Asia Kaiser, a doctoral student in the Department of Ecology and Evolutionary Biology at CU Boulder.听
The result came as a surprise to Kaiser and Julian Resasco, assistant professor in the Department of Ecology and Evolutionary Biology and the paper鈥檚 senior author, because it contradicted previous studies.听
Prior research showed that wealthier urban neighborhoods tend to have more trees and green space. As a result, a greater diversity of animal species tends to live in these areas, a pattern called the luxury effect.听
Ecologists Kaiser and Resasco wanted to explore how insects in urban gardens respond to the neighborhoods that surround them. Specifically, they are interested in how the urban environment could affect insects like bees that pollinate garden crops.听
The jalape帽o test
Last spring, the team planted about 70 jalape帽o pepper plants in seven large community gardens across Boulder and Louisville. Using traps, the team collected more than 3,000 insects and other arthropods such as spiders from the gardens.听
The researchers found that neighborhoods with more artificial structures鈥攑avement, roads and rooftops that prevent water from soaking into the ground鈥攈ad lower numbers of pollinators. At the same time, wealthier neighborhoods had fewer species of bees.
Landscaping practices and the type of plants that are more common in wealthier neighborhoods may contribute to lower bee biodiversity, Kaiser said. These communities tend to have more mature trees, which are different from plants found in native bees鈥� habitats. People living in these neighborhoods may also use more pesticides, fertilizers, water and mulch to support these plants, creating worse soil conditions for bees to nest in.听
鈥淢ost of the bees found in these gardens, such as long-horn bees and squash bees, nest in the ground, so they are sensitive to changes in the soil,鈥� Kaiser said.听
In addition, the jalape帽o pepper fruits grew larger in gardens with higher bee diversity, suggesting the important role that pollinators play in ecosystems.
Other arthropods鈥攊ncluding pests like beetles and pest-eating predators like spiders鈥攖hrived in wealthier neighborhoods, the team found. It remains unclear why these critters were doing well, but Kaiser suspected they might be benefiting from the abundant food sources in the urban gardens.听
鈥淚t鈥檚 interesting that different animal groups are being impacted by different features of the urban environment,鈥� Kaiser said.听
She added that Colorado residents can plant more native plants and provide natural cover such as bare soil and downed wood for insects to nest in to promote bee diversity.听
Urban oases
Next, the team plans to expand the experiments to community gardens in Denver. This will allow them to evaluate pollinator diversity in neighborhoods with a wider range of urbanization and socioeconomic status, including lower-income areas.听
鈥淯rban community gardens can be really important sources of nutrition in cities where nutritious food is often hard to come by,鈥� Resasco said. 鈥淯nderstanding how different aspects of urbanization affect arthropod biodiversity and how that in turn affects the yield of these crops is very important.鈥�
