When I think of Miami, I think of palm trees. Phoenix brings to mind spiky, hardy desert plants like cactus and agave. And my memories of Midwestern summers heavily feature grassy lawns and the deep shade of elms.
These landscapes all seem so different—and yet, the view of identical checkerboards of lawns from an airplane window sometimes makes me forget which city I'm circling.
Researchers are starting to wonder whether we're headed the way of ticky-tacky yards—and why this might be happening. Since 2011, scientists have been exploring people's yards in six U.S. metropolitan areas–Los Angeles, Phoenix, Boston, Miami, Minneapolis-St. Paul, and Baltimore—to find out.
While each city is at a different stage in the process—and a clear view of country-wide patterns is still to come—early results suggest big cities' plants are more similar to those in other urban areas than to their own natural surroundings.
Will Pearse, a post-doc in ecology at the University of Minnesota, has done preliminary work on plant species collected in yards in four of the cities. At first glance, Miami, Baltimore, Boston, and the Twin Cities seemed to have a wide, unique range of different plant species. But when he looked at the plants in each city by how they were related genetically, he says, "It's the only moment in the last year that my jaw really did drop." A live oak in Miami and a bur oak in Minneapolis, for example, are different species, but are closely related when it comes to their evolutionary history. Take this into account, and "there's massive homogenization across the U.S."
Pearse and colleagues around the country are looking at ecological reasons behind this, while other researchers are delving into the social and societal factors that may drive blandification. When Peter Groffman, a microbial ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, and the project's principal investigator, gives talks about this project, people often say their yards look the way they do because that's how they like it. After all, if our homes are our castles, our yards are the feudal estates. That's what I thought, too, when I started my reign over our tenth of an acre in Santa Barbara, California. My husband and I put in raised beds for gardening, tore out the front lawn, and planted drought-tolerant Central Coast natives.
But both subtle pressures and more overt ones shape what's growing, particularly in our front yards. "The front yard is like the living room people have in their house that no one uses," says Laura Ogden, an anthropologist at Florida International University. It's a place where you keep up appearances, whether it's having your grass as green as the lawn on the other side, or putting in a native plant or two to send a message about your environmental politics. (Ouch! We stalled out on our eco-groovy yard after seeing neighbors' hot-pink Hong Kong orchid, orange Australian-native kangaroo paw—plus citrus trees ripe with hyper-local cocktail potential.)
More official forces shape yards, too: in some areas, homeowners' associations have stringent rules about what yards are supposed to look like. Tara Trammell, an urban ecologist who is a post-doc at the University of Utah, visited yards across the Los Angeles basin. In Orange County, most houses that Trammel visited had landscaping restrictions. Some homeowners' associations encourage drought-tolerant and native plants; others prohibited certain tree species. Ocean views often played a role, too: some HOAs forbid tall, difficult-to-trim trees—like kentia palm and star pine—to protect views, while others don't allow residents to trim trees. In California and elsewhere, there are semi-regular tales of woe from HOA residents who flout the rules. A Florida couple ran afoul of their homeowner's association earlier this year after hardscaping their yard to make it less water-thirsty.
Kelli Larson at Arizona State University and colleagues did an earlier survey of homeowners' associations in Phoenix; 20 percent of homeowners' associations surveyed had specific requirements when it came to lawns (either requiring or prohibiting them). Common species forbidden here included eucalyptus, mulberry, and Mexican palo verde.
Larson's work in Phoenix has revealed other surprising aspects of what's in people's yards. You might think that those moving to Phoenix from cooler climes would be the ones who want to bring their green, water-hungry lawns with them. But i n fact, the recently arrived tend to be more accepting of more desert-like xeriscaping than longtime Phoenicians.
As part of the nationwide survey, 1,600 residents in Phoenix and in each of the other five cities participated in phone surveys about their yards. From here, researchers found as many as 30 homes in each city, across a swath of neighborhoods and socioeconomic classes, to examine more closely. They then combed through each of these yards, identifying every plant species and taking plant clippings and soil samples; in some yards, they set up small weather stations to measure temperature, soil moisture, and humidity. Residents also toured researchers through their yards as part of an extensive interview about how the landscape had evolved.
The first house Ogden visited in Miami was that of an older Cuban couple who had been in the country for close to 30 years. Their backyard was filled with the guavas and mameys of their homeland; they brought out homemade mango shakes for the field crew.
Backyards are where the pretenses drop and where a resident's interests, pastimes, and even cultural history are on display. (Our absolute monarchy ended the moment our first son was born. Please ignore the overgrown tomatoes, the deflated baby pool, the shin-high weeds.)
Along with the residents' history, a house's history affects today's garden, too. People might replant flowerbeds and tinker with lawns, but large features—from box hedges to shade trees—usually stay rooted for decades, a builder's legacy. Working with developers and builders—as well as policymakers—may be critical for ecologists who want to think about how to shape the urban environment in the future.
And another place Ogden and others want to target their attention: big-box garden centers. While some people surveyed chose rare plants, like the homeowner in the Los Angeles study who tracked down a particular place on the East Coast for a bright, sunny spot, chain garden centers are "where most of us go for our plants, the products we use on our plants and lawns, and where we get some of our information about yard management," Ogden says. If big-box gardens turn out to be a force behind our increasingly similar yards—and the environmental impacts that go with them—they might also be a place to work on restoring uniqueness to our green thumbprints.