Is Detroit’s vacant land helping bumblebees bounce back?
Detroit has lost more than half of its population since the 1950s, leaving thousands of lots abandoned in of the city’s urban core as once-plentiful jobs in the auto industry were lost to automation and the economy plummeted.
It’s a scenario seen a multitude of Rust Belt cities, though many of them are beginning to make slow progress toward respective comebacks.
But a study released by the University of Michigan in May appears to show those economic struggles may have also created positive ecological influences for a portion of Detroit, where researchers found higher bumblebee populations than less-urbanized areas of the state.
Researchers say the study, published May 17 in the journal Royal Society Open Science, gives strong evidence that thousands of vacated residential properties in the Motor City may have led to the increases in bumblebee populations, potentially due to the lack of humans, many of whom use pesticides and herbicides and mow their lawns.
Paul Glaum, a PhD candidate at the University of Michigan and one of the authors of the study, said he and his colleagues studied 30 urban farms and gardens in five Michigan cities to collect the data, with an increase in the number of bees appearing only in Detroit. It was an unexpected finding because “there’s such a strong decline outside of Detroit in even less-urbanized areas,” he said.
“But then once we sampled in Detroit, we found a particularly surprising uptick in the amount of bumblebee abundance and in bumblebee diversity,” Glaum said. “And because bumblebee nests all start either right on top of or under ground, we are hypothesizing that it has a strong connection to the high amount of vacancies in Detroit.”
What is considered “vacant land” can vary based on method, but Glaum said that the research team’s metrics determined that roughly 33 percent of Detroit is considered vacant. As land begins to return to nature in Detroit, wild bumblebees may have more opportunities to create nesting sites and find flowers for food.
The study also found that urbanization appears to influence female and male bees differently, possibly due to behavioral differences between the sexes, Glaum said. Declines in bumblebee abundance and diversity because of increasing urbanization were propelled entirely by female workers but male bumblebee numbers were not affected by urbanization, the study notes.
Bees are crucial pollinators that buoy U.S. agriculture and maintain healthy ecosystems, but their numbers have plunged in North America in recent decades. Research shows part of the problem is the use of pesticides and herbicides on large agricultural tracts of land. But Glaum said less is known about bee populations in urban areas.
Naim Edwards, a program manager for Voices for Earth Justice in Detroit who helped Glaum and his research team secure locations for the study, said depending on the parameters used anywhere between a third and a fifth of the city is made up of vacant land on property once utilized for residential or industrial purposes. Large swaths of parkland left unattended by city maintenance have also “gone back to nature,” he said.
“When you see it in on the ground there’s a very suburban and rural feel in different parts of the city,” Edwards said. “So in a lot of ways it kind of shows what happens when humans get out of the way.”
Edwards, who also has a graduate degree from the University of Michigan’s Department of Ecology and Evolution, said Voices for Earth Justice Detroit promotes gardening and sustainable use of land, soil and water in the city, with several thousand urban farms and gardens found on more than 15 percent of the vacant land.
“You have bees living in lawns and lots and dead trees,” he said. “These are things we might remove from our built-in living environments. And gardens are providing food and resources for the bees. The less we do, the better the bees are.”
Kevin Boehnke runs an 800-square foot urban garden with his wife in Ann Arbor, Michigan, and took part in the bumblebee study. He said while Ann Arbor has less suburban sprawl than Detroit, the core of the city has been growing fast along with the number of urban gardens.
While Glaum’s research team did not see the kind of bumblebee abundance and diversity in Ann Arbor as they did in Detroit, Boehnke said the increase in urban gardens is helping to contribute “with pollinators and biodiversity.”
“It’s really nice to see that not only do we have all these kinds of community benefits but there’s also these ecological benefits being provided with these varieties of plants where bees can make homes,” he said.
Glaum said he wants to continue his research on bees in urban settings, but in the meantime he wants the bumblebee study to contribute to reimagining how cities can be used.
“Even though individual action is really important, as we learn in the study, the physical layout of the landscape is a huge driver for the ability of these bees to survive and succeed in an environment,” he said. “I think those are fascinating places to create new ideas for urban centers and what it means to integrate human development with what we consider the natural world. And maybe kind of erase some of the walls we built between those two worlds.”