A lone Baltimore rowhouse surrounded by vacant lots. Depopulation has left the city with an excess of such spaces. Patrick Semansky/AP

Chris Swan is spending years studying a unique ecosystem—the vacant lots of Baltimore—looking for the best ways to bring the city’s dead spaces back to life.

On a frigid day in the West Baltimore neighborhood Harlem Park, ecologist Chris Swan parks his pickup on a block where vacant lots outnumber houses. On the tailgate, he organizes envelopes of native wildflower seeds: Liatris squarrosa, Pycnanthemum muticum, Monarda bradburiana. For the next several hours, Swan, who teaches ecology at the University of Maryland, Baltimore County, will sprinkle the seeds over an acre and a half of scrubby land, lots that once held the neat brick rowhomes that still define much of Baltimore’s working-class housing stock.

Perennial wildflowers are best sown in fall or winter. “The seeds have to sit over the winter and kind of crack open,” Swan says. Trowel in hand, bundled in camouflage hunting gear against the cold, he’s an odd sight on this desolate street. His project is an oddity as well: He’s searching for the combination of native species that can thrive in the poor soil left behind after homes are demolished.

Some 14,000 vacant lots pockmark the city of Baltimore, where decades of population decline have left some blocks nearly abandoned. And there may soon be many more. Over the next few years, the state of Maryland plans to spend $75 million on tearing down and stabilizing thousands of the estimated 16,000 vacant or abandoned buildings in the city, with a goal of attracting future development. The idea behind Swan’s wildflower experiment is to help the city restore some biodiversity and reduce polluted run-off by converting these swaths of fallow land into temporary prairies while they await—hopefully—the return of new construction.

Swan is one of only a handful of ecologists in the world who do experiments in urban vacant lots—for that matter, ecologists rarely experiment in cities at all. His work is part of the Baltimore Ecosystem Study, a massive long-term research project launched in 1997. The study is a collaboration between natural, physical, and social scientists, all working to illuminate how urban ecosystems function. “We have a long tradition in ecology of doing experimentation to try and understand different ecological processes,” says ecologist Emma Rosi of the Cary Institute of Ecosystem Studies, who leads the project. “But in urban ecosystems, there are very few experiments, because it’s really challenging. People have lots of different uses for the land.”

Several researchers in other cities are looking at what to do with such under-utilized urban land, but very few are actively experimenting on them; they might be assessing the species that are already there, but not those that could be. Nationally, as much as 15 percent of the land in some large American cities is vacant: Many older Rust Belt towns that have experienced major population loss are also exploring innovative ways to green these dead spaces. In Detroit, philanthropic dollars are helping community groups transform vacant lots into miniature parks, urban farms, and stormwater retention areas. In Philadelphia, the local horticulture society has been planting trees and grass in vacant lots for more than a decade. Cities often launch greening projects with environmental aims—like reducing polluted run-off—despite the lack of experimental research into what method works best. “Nobody's taking a scientific approach, doing the proper controls,” Swan says.

That’s in part because experimenting in the city is so challenging. With sparse data on what works best ecologically, cities often rely on landscape architects rather than ecologists to head these projects. “It's just that there’s demand to do something,” Swan says. “Science has always proceeded more slowly than need.”

Patience is key. Swan began this project in West Baltimore four years ago and plans to continue another five to ten. He hopes the city will use his data to improve the way it currently deals with vacant lots: Instead of having a team of workers “throw down a half-inch of topsoil and some contractor mix of grass” after knocking a building down, Swan envisions them sowing a native seed mix to his specifications. He’s trying to identify a mix that can tolerate poor soil while simultaneously improving it. Some plants—like bee balm, for example—are known to attract pollinators, which are in decline everywhere. (A side benefit: More pollinators may make nearby home gardens more productive.)

Certain plants are also more effective than others at absorbing water from the soil. That’s important because the compacted soil in vacant lots produces run-off, which eventually makes its way to the Chesapeake Bay. That run-off is laced with the toxins found in the soil of many vacant lots: things like lead, arsenic, and asbestos. The more toxin-laden water plants absorb, the less of it flows to the Bay (and into organisms we eat).

But Swan has learned firsthand why ecologists don’t often experiment in cities. Because the idea was so novel, it took several years of legal wrangling to hash out an initial agreement with the city, which owns the lots where he does his research. Then there was the day last spring, when he pulled up to his plots just in time to witness a wrecking crew demolishing a building next door, destroying several of his plots in the process. Or the time last summer when city workers mowed down all of his plants just before the mayor came to visit a new stormwater detention facility nearby. Swan suspects the workers didn’t want her to see what might look like overgrown weeds to an untrained eye.

In early summer, Swan’s experimental plots come alive with wildflowers. (Photo courtesy Chris Swan)

Swan’s experimental lots are surrounded by wooden fencing but otherwise resemble many other vacant lots in Baltimore, which are populated mainly by invasive plants like crabgrass. The soil, Swan says, is “horrible.” It tends to be very alkaline, because of fragments of concrete and brick. Swan conducted his first experiment here in 2014. He cleared plots and sprinkled seeds in most, leaving a few untreated for comparison. The plots were mowed twice a year for the following three years, but otherwise left alone. (The city typically mows vacant lots four times a year.) The neglect was purposeful. “The city doesn't have a lot of money,” Swan says. “If we take a cheap approach, can we get it to work?”

So far, the results are promising. After three years, nearly half the species on some of Swan’s plots were native. Among them were black-eyed Susans and purple coneflowers, clumps of orange butterfly weed and sprays of yellow coreopsis. A big question remains, however: Will those plants reproduce on their own, or will he need to reseed every year or two? The latter would make transforming a vacant lot into a meadow a more expensive proposition.

It’s a question that will take years to answer. And Swan has to figure out which plants best suit his purposes. That, too, will take more time. “The data collection,” he says, “is enormous.” Twice a year, he and his team take dozens of measurements on thousands of plants. They count flowers and weigh seeds and track chlorophyll levels. They measure soil moisture, and scan leaves to calculate how much water particular plants take up. This summer, Swan plans to fly a drone outfitted with a special camera that helps assess plant health over the plots.

But when it comes to dealing with the ecosystem’s dominant organism, high-tech equipment is no help. People are another reason ecology experiments in the city are so rare: The goals of neighbors don’t always align with those of the researcher. “Science is hard, but this is really, really hard,” Swan says. “I have a Ph.D in biology, not human relations.” His plots border busy streets and occupied homes, as well as a church. He works with a local foundation that has helped him connect with neighbors, and he’s in contact with neighborhood community associations. He says that, overall, the response has been favorable. “The positive has far outweighed the negative,” he says.

A patch of orange-flowered butterfly weed, a native species. (Photo courtesy Chris Swan)

Not everyone is pleased though. Some neighbors say the lots look unkempt, and dislike how high the plants grow. “It’s just a yard of weeds,” says Al Wylie, president of the Harlem Park Neighborhood Council, a local community organization. “We are constantly calling the city to get it cut but it just grows wild.” Swan’s first study included a species that wasn’t supposed to grow over 30 inches high, but some of his plants shot up around four feet; he’s since been vigilant about using shorter plants. That’s no comfort to Wiley. “No matter what you plant anywhere, there's always going to be weeds and grass that grow up in it,” he says. “You still have to maintain it.”

Swan also has passionate supporters in the neighborhood. Joy Ross is president of another neighborhood organization, the Harlem Park West Community Association. The back of her home looks out on the lots. She’s lived there for more than a decade, and she says the fencing has deterred illegal dumping and drug activity. She’s also noticed other changes she attributes directly to Swan’s plots. “I’m a country girl, so it’s so cool to see Echinacea,” she says. “Oh my gosh, there’s a swallowtail! There’s lightning bugs! You didn’t see that before.”

Nuisance or natural wonder, Swan’s plots are by their nature temporary. His agreement with the city stipulates that as soon as a developer expresses interest in one of his experimental lots, he must hand them over immediately. The city, after all, needs be a city again, not a wildflower meadow. Even if the city were to convert its vacant lots to prairie, he sees that as a stopgap, a way of sprucing up a neglected neighborhood and encouraging new growth—converting an abandoned lot to a field of wildflowers both makes a community slightly more livable and sends a positive signal to potential developers.

If nothing else, Swan believes his results will help the city manage its vacant spaces in ways that benefit the surrounding neighborhoods, rather than compounding their problems. “The idea is to take a problem which is huge,” he says, “and try and work towards a way of managing that space that’s better than it is now.”

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