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Rare plants attract rare bees and birds in urban gardens

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Urban gardens can be biodiversity hotspots, but little is known about what drives biodiversity in low-frequency species in cities.

Plant species that are typically rare in urban areas but planted in urban gardens attract rare bees and bird species, according to a Dartmouth College-led study that examined urban gardens in northern California.results published in Ecological application, Women, older gardeners, and people who live closer to the garden tend to curate rarer plants.

Theresa Ong (right), assistant professor of environmental studies and lead author of the study, and co-author Azucena Lucatero, at Mi Jardin Verde in Watsonville, California, is one of the community gardens studied. (Photo courtesy of Teresa Ong)

“People’s planting of rare species seems to have a cascading effect on the accumulation of other rare bee and bird species,” says Teresa Ong, lead author and assistant professor of environmental studies.

Over 50% of the plants observed in urban gardens were classified as rare.

“This means people are planting a wide variety of rare plants. What we found was that what was rare in urban gardens could be fairly common elsewhere, “In less managed systems, that’s not always how we define rarity,” says Ong. It often happens.”

She suggests that in urban gardens, rare organisms may indeed be at high risk of extinction, but they may simply be less adaptable to urban environments and, in the case of plants, less common to grow. “The rarity status may indicate that urban gardens serve as important protected habitats for rare urban species, but what lies ahead for the species?” We can even predict what will happen,” says Ong.

purple finch (Haemorhous purpureus) at the University of Miami Bird Blind in Oxford, Ohio. (Photo by Andrew Cannizzaro / CC x 2.0)

purple finch (haemolus purpleus), for example, was one of the rare birds seen in the urban gardens that were part of the study, but is considered a fairly common species elsewhere. It is listed as a species of least concern on the International Union for Conservation of Nature’s Red List of Threatened Species.

“Their rare status in urban gardens may be cause for concern if their populations indicate they are declining. It may also provide more habitat than cities do, such as tree cover for birds in the wild,” says Ong.

This research is based on fieldwork at 18 community gardens in Santa Clara, Santa Cruz, and Monterey counties, California. Urban gardens change with the times. local habitat; landscape context such as ground cover and forest canopy cover; Socio-economic demographics of gardeners. All gardens use organic gardening practices where pesticides and pesticides are prohibited.

The team collected data from urban garden sites during two summers, 2015 and 2017, from May to September. Data for plants, bees, and birds were collected for him in 2015, and data for urban gardeners two years later. Each organism was sampled differently depending on the organism.

For plant data, researchers visited urban gardens and randomly sampled garden plots and surrounding walkways, focusing on vegetation such as cultivated plants and weeds. Plants were measured and classified into crops or ornamental species and cultivars.

For bird data, researchers stood in the center of each yard for 10 minutes and recorded every bird they saw or heard. For bee data, bees were captured using pan traps and aerial nets raised from the ground and later identified at the species level. The researchers also asked gardeners directly what plants they were growing in their gardens.

Using field data on plants, bees, and birds, the team modeled correlations between gardener demographics, rare plants grown by gardeners, and rarities of bird and bee species.

Plant, bee, or bird species were considered ‘rare’ only if they appeared in 1 of 18 urban gardens or 2 of 185 gardener survey responses. Of the 295 plants observed, more than half were classified as rare species in this study, with 159 plants representing 156 different species.

Taro (Colocasia esculenta) At Madeira Botanical Garden, Funchal, Portugal. (Photo credit: Nasser Halaweh / CC BY-SA 4.0)

“Taro(Colocasia esculenta), it was one of the rarer plants found in urban gardens, but because it is mainly cultivated, it is not a conservation concern,” says Ong. “This is a traditional crop planted by many cultures in Hawaii and Asia. It requires a lot of space to grow and is cooked for underground corms like sweet potato tubers, but It is not a common food in California.

Ong notes that gardeners growing less common crops like taro need to find less common habitats for other species, such as soils with more water needed for taro to grow well. I suspect that the land is also cultivated.

Previous research has shown that some rare plants are known to have specific relationships with rare honeybees and act as hosts for other plants.One such unusual plant-bee duo observed in this study includes ‘Bachelor’s Button’ (in the genus Centaurea foliage plant with showy stingray flowers belonging to the Asteraceae family) and a leafcutter (Megachile apicalis)whose female bees cut leaves cleanly to nest mainly in rotten wood.


Left: Bachelor button (Centaurea cyanus). (Photo by Azucena Lucatello).leaf cutting bee (Megachile apicalis) and thistle (Cirrus genus). (Photo by Malcolm Bowie)

One of the birds the team encountered and classified as rare in urban gardens was the American kestrel. (Falcos Pulverius). “It’s a small and very cute falcon, in fact it’s the most common and widely distributed falcon on the continent. Recently the population has been declining and it’s a concern. It’s an important predator of pests, so when it’s found in an urban garden, it’s a good sign because it shows that the garden can be managed in a way that provides habitat for species that are rare in cities,” Ong says. Researchers have found that gardens with more canopy cover—more trees—provide better habitats for rare birds.

Male American kestrel (Falcos Parverius) Raptor, Inc. (Photo by Greg Hume / CC BY-SA 3.0)

Explaining results about why rare plants are often planted by women, the elderly, and community members who live near urban gardens, Ong said: , And with age, you acquire wisdom and knowledge of cultivation techniques. However, many people not only want to take care of their neighborhood, but it may have something to do with taking pride in its landscape and community.

The team’s findings also showed that many rare plants found in urban gardens are weeds, so leaving weeds in the garden may actually be a good thing.