New research argues evolution matters for urban climate resilience
As cities around the world search for ways to adapt to climate change, many are turning to nature for help.
Trees cool neighborhoods during extreme heat. Wetlands absorb floodwaters and filter pollution. Oyster reefs soften storm surge along coastlines. These nature-based solutions are increasingly seen as a more sustainable way to protect communities while improving quality of life.
But according to new research co-authored by Nancy Grimm, Regents Professor and Virginia M. Ullman Professor of Ecology, there is a critical factor cities often overlook: Nature itself is changing.
The paper, published in Science, argues that plants, animals and microbes used in nature-based solutions are constantly adapting to urban environments through evolution, and those changes could either strengthen or weaken how well these systems work over time.
“Nature-based solutions are not static assets,” said Marina Alberti, professor of urban design and planning at the University of Washington and lead author of the paper. “Their performance depends on ecological and evolutionary processes that continue after design and deployment.”
Grimm has spent years studying how cities function as ecosystems. The new paper grew out of two major collaborations: NATURA, an international research network focused on nature-based solutions for urban resilience, and a National Science Foundation-funded research coordination network led by Alberti that explored eco-evolutionary processes in cities.
As researchers from different disciplines came together through workshops and meetings, they began asking a new question: How might evolution affect the long-term success of nature-based solutions?
That question became the foundation of the paper, which argues that cities create unusually intense environmental pressures. Urban heat islands, pollution, drought and fragmented habitats all force organisms to adapt rapidly. While evolution was once thought to occur only over extremely long time scales, scientists now know some species can evolve much faster than previously believed.
“Cities are places where that is quite possible because the selective pressures are really high,” Grimm said.
Those changes could have direct consequences for how cities respond to climate threats. Wetlands, for example, are often used to absorb floodwaters and improve water quality, and much of that cleaning power comes from microbes that break down pollutants and excess nutrients. But those microbes can evolve quickly in response to new contaminants entering urban waterways, including plastics and chemicals from personal care products.
“The best defense against some of these novel pollutants may actually depend on organisms adapting to deal with them,” Grimm said.
Other examples involve coastal ecosystems. Marsh grasses and oyster reefs can reduce erosion and soften storm surges during extreme weather events, while urban trees and vegetation in places like Phoenix help cool neighborhoods during dangerous heat waves. Yet evolution does not always work in ways that benefit people.
“The objective of organisms is to survive and reproduce,” Grimm explained. “They aren’t necessarily trying to benefit people.”
That distinction is one of the paper’s central ideas. A species may evolve traits that help it survive pollution, heat or drought while simultaneously reducing the ecosystem services humans depend on. A drought-tolerant tree, for instance, might survive extreme heat but grow more slowly and provide less shade. Microbes that evolve resistance to contaminants may become less effective at filtering water.
“Survival and function can diverge,” Alberti said. “Organisms may adapt to urban stressors in ways that help them persist but reduce the function cities rely on them to provide.”
The researchers describe this possibility as a “functional trap” — when nature adapts in ways that maintain survival but reduce the benefits people expect from green infrastructure. They also emphasize the importance of maintaining genetic diversity within urban ecosystems so species have the capacity to adapt to future conditions.
“That’s an important consideration,” Grimm said. “Maintaining that genetic variability for populations to be able to evolve to deal with future conditions.”
In Phoenix, Grimm points to the Indian Bend Wash greenbelt as one example of a successful nature-based solution. Originally designed in the 1970s to reduce flood damage, the project created a corridor that safely absorbs floodwaters while also providing parks, recreation and public green space.
“The primary objective was preventing floodwater from destroying property, and it has done that very successfully,” she said.
Still, she said, future climate conditions may require cities to rethink which species they plant and why. As Phoenix becomes hotter and drier, planners may need to focus less on water-intensive trees and more on native desert species capable of adapting to future conditions.
“We shouldn’t just be thinking about what the traits of those species are now,” Grimm said, “but how they potentially might evolve into what the future is going to look like.”
The researchers hope the paper encourages planners, scientists and policymakers to think beyond short-term climate solutions and consider how ecosystems may change over decades. Nature-based solutions can still play a major role in helping cities become more resilient, Grimm said, but only if cities recognize that nature is dynamic, not fixed.
“If we’re thinking into the future,” Grimm added, “evolutionary processes have to be considered as well.”