What Should Grow in a Vacant Lot?
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.”
“Oh my gosh, there’s a swallowtail! There’s lightning bugs! You didn’t see that before.”
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.