When I moved from small-town Oregon to Paris’s 11th arrondissement last summer, the city seemed like a poem in gray: cobblestones, seven-story buildings, the steely waters of the Seine. But soon I started noticing the green woven in with the gray. Some of it was almost hidden, tucked inside the city’s large blocks, behind the apartment buildings lining the streets. I even discovered a sizable public park right across the street from my building, with big trees, Ping-Pong tables, citizen-tended gardens, and “wild” areas of vegetation dedicated to urban biodiversity. To enter it, you have to go through the gate of a private apartment building. Very Parisian.
Dense cities like Paris are busy and buzzy, a mille-feuille of human experience. They’re also good for the climate. Shorter travel distances and public transit reduce car usage, while dense multifamily residential architecture takes less energy to heat and cool. But when it comes to adapting to climate change, suddenly everyone wants green space and shade trees, which can cool and clean the air—the classic urban trade-off between density and green space.
Or, you know, maybe there’s no big trade-off at all. A new analysis of cities around the world published today in the journal People and Nature found only a weak relationship between population density and urban greenery. The team of scientists, led by Rob McDonald, an urban ecologist at the Nature Conservancy, compared satellite images with population-density data in 629 cities across the world. Globally, denser cities had less open space overall than if everyone had private yards, but the amount of public open space was basically unrelated to density and had more to do with history, policy, and culture. One calculation, using data from the Organization for Economic Cooperation and Development for cities outside the U.S., found that a 10 percent increase in density was associated with a 2.9 percent decline in tree cover. Overall, there was a lot of variability, and there were a lot of outliers: Some cities and neighborhoods have both high density and lots of trees or open space. “Density is not destiny,” McDonald told me.
Broadly speaking, the researchers found two ways to avoid the trade-off between density and green space. Take Singapore, one of the densest countries in the world. There, plants are installed on roofs and facades, turning the familiar gray landscape of skyscrapers and overpasses into a living matrix. By law, developers must replace any natural area that they develop with green space somewhere on the building. Meanwhile, in Curitiba, the largest city in southern Brazil, which has tripled in population since 1970, dense housing is built around dedicated bus lanes and interwoven with large public parks and conservation areas. Curitiba also uses planted areas to help direct and soak up stormwater, buffering residential areas from floods. In Singapore, nature shares space with the built environment, while Curitiba packs people in tightly and then spares land for other species inside the boundaries of the city.
— Emma Marris, The Atlantic