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The intersection of North 3rd St. and Diamond St. in Philadelphia, Pa, in 2006, one year after a city-supported greening program planted trees on the once vacant lot.

Could Trees Help Stop Crime?

Researchers think turning more vacant lots green might work.

Crime-fighting is expensive. Cops aren’t cheap and neither are prosecutors, judges, and all the other layers that make up the justice system. But trees and some grass? They’re a comparative bargain, and now the federal government wants to know whether they’re also an effective crime-fighting tool.

Under a $6 million federal grant, public health and criminology experts from three major universities are conducting a series of experiments that will turn vacant lots into oases of green in three troubled cities. Although the concept of clearing away blight to hinder crime has long been popular, the current research is intended to generate statistical evidence to more clearly link the correlation.

Marc Zimmerman, a professor of psychology and public health at the University of Michigan School of Public Health, who is leading the study, thinks it’s worth exploring the power of the plant. “If you live in a bad neighborhood and you plant some trees and do some community revitalization, do you think it will make a difference?” Zimmerman asked. “A lot of skeptics will say ‘well, duh! Of course it does.’ And others might say, ‘huh? How can that make a difference?’ But we don’t really know. It hasn’t been adequately tested it.”

Zimmerman, who is also director of the public-health school’s youth violence center, is overseeing the five-year grant, which comes from the Centers for Disease Control and Prevention. He is working with researchers from the University of Pennsylvania and Rutgers University who will focus on greening projects in Flint, Mich., Youngstown, Ohio, and Camden, N.J.

The experiments involve comparing community gardens, and similar heavily trafficked public spaces, to vacant lots that are randomly assigned to become either plots of tended grass or “control” spaces that receive no care at all.

The project comes on top of a separate study by the University of Pennsylvania to determine the relationship between urban blight and the prevalence of open-air drug markets and violence. The study, underwritten with $2.7 million from the National Institutes of Health, began two years ago and will start reporting its results in 2016.

The corner of Norris St. and 5th St. in 2003, left, and in 2013, right, in Philadelphia, Pa.

The corner of Norris St. and 5th St. in 2003, left, and in 2013, right, in Philadelphia, Pa.

Academic curiosity into how criminals and residents respond to a decayed environment grew as the Broken Windows theory of crime gained traction in policing circles in the 1990s. (The concept centers on the idea that dilapidated buildings and abandoned lots breed fear and disorder.)

In 2000, Philadelphia became home to one of the first mass greening efforts that specifically focused on poor neighborhoods, with a program led by the Pennsylvania Horticultural Society. In 2003, the city financed an expansion of the program.

Since the early 2000s, more than $20 million in taxpayer money has been spent on these spaces, said Robert Grossmann, a senior director of the horticultural society. Grossmann said he expected that one-third of Philadelphia’s estimated 40,000 vacant lots would be cleaned and greened by the end of 2016.

The society-city collaboration caught the interest of experts on crime and public health at the University of Pennsylvania who started to wonder about its impact on violence.

A study led by Charles Branas, an epidemiologist at Penn and his colleague John MacDonald, a criminologist, reported that greening vacant lots “was associated with consistent reduction in gun assaults” across the city. They crunched crime data from 1999 to 2008 in areas where lots were newly planted and compared the figures to lots that were left untouched. Figuring in the effects of the city’s greening efforts, the researchers calculated that, citywide, gun assaults dropped 8 percent while reports of disorderly conduct rose 28 percent. The increase in crime reports, Branas said, grew out of concerns by residents who who lived near the freshly planted vegetation. They were more likely to call the police and complain about disorder, he said, adding, “If you clean a space, people will want to protect it.’’

Lt. John Walker, a 25-year veteran of the Philadelphia police force, who runs the detective bureau in the western half of the city, applauded the researchers’ findings but still described them as “common sense.”

“If you clean things up and make things look good, people are more likely to take care of their neighborhood,” Walker said. “People are less likely to hang in those areas where the streets are maintained. You will see less kids hanging on the corners.”

Michelle Kondo, a scientist with the U.S. Forest Service, is co-author of a recent study in Youngstown, a former steel town of about 60,000 where burglaries and felony assaults decreased around empty land that was rehabilitated. And residents noticed.

Barbara Cole, a longtime Youngstown homeowner, described how rowdy young people in her neighborhood withdrew from street corners when nearby abandoned homes were replaced with spaces of manicured grass and healthy trees.

“It is nice to look at beautiful fields than raggedy houses,” Cole said. “To me, it makes sense for the government to how greening can improve things. It’s worth the money,” she added. “It will get people motivated. People will want to keep it up.”