Shutterstock

Believe it or not, a new study of canopy coverage in Baltimore suggests maybe they can.

Silly as it may seem to the public, there's an intense disagreement among scholars about the impact urban trees have on a city's crime rate. Some are convinced urban greenery increases crime — arguing that low trees and shrubs, in particular, create a natural hiding place for criminals. A 2001 case study of auto thieves in Washington, D.C., found that offenders often target areas near dense vegetation because it can "reduce effort and risk by offering concealment."

Others are convinced that urban trees have exactly the opposite effect. This crowd argues that trees actually decrease crime either by attracting more people to public places (Jane Jacobs' "eyes on the street" theory) or by signifying to criminals that people care about their neighborhood (James Q. Wilson's "broken windows" theory). Another 2001 study, this one of public housing in Chicago, found that "the greener a building’s surroundings were, the fewer crimes reported."

Where better to settle the score once and for all than Baltimore? If trees can have a positive impact on crime in the land of The Wire, then it seems safe to assume they can have an impact anywhere.

Well somebody tell Omar the game just changed. In the June issue of Landscape and Urban Planning, a team of environmental researchers led by Austin Troy of the University of Vermont report an inverse relationship between tree canopy and a variety of crimes in the Baltimore city and county regions. All told, Troy and colleagues conclude that "a 10% increase in tree canopy was associated with a roughly 12% decrease in crime."

For the study, the researchers examined crime and canopy rates over a long stretch of area from inner city Baltimore to the exurbs of Baltimore County. The crime rates varied greatly across the region: those in the city were 3.5 times the national average per block, while those in the outskirts were "nearly non-existent." (They limited their study to robberies, burglaries, thefts, and shootings, since assaults typically take place indoors.) So too did the canopy rates: some parts of the city have no greenery; some parts of the county achieve 87 percent coverage.

Troy and his colleagues ran all types of models to analyze the relationship between crime and canopy. Even after controlling for factors known to influence crime statistics — income, race, population density, and the like — they found the aforementioned link between more trees and less crime. While they doubt the connection is "purely causal," the strength of their figures suggest "some genuine relationship between trees and crime."

The results were not entirely straightforward. In some pockets of Baltimore city, for instance, the presence of trees indeed seemed to increase crime rates, just as some of the previous literature suggests. That was especially true in the outer harbor areas of Brooklyn Park, Wagners Point, and Dundalk — places with poorly groomed vegetation where "the concealment value of the vegetation outweighs its deterrent effect":

This last result clarifies much of the confused relationship between urban greenery and urban crime: While low dense brush seems to increase it, tall broad canopies seem to decrease it. That nuanced conclusion harmonizes with another study published earlier this year, in which U.S.D.A. Forest Service researcher Geoffrey Donovan (who has also linked urban tree coverage to home prices) reports the same mixed tree-crime associations in Portland, Oregon. If the evidence tells us anything certain, it's to keep your shrubbery close, but your canopies closer.

Top image: MR /Shutterstock.com

About the Author

Most Popular

  1. Life

    Say Goodbye to Spain's Glorious Three-Hour Lunch Break

    Catalonia plans to shorten work hours—but don’t call it the end of the siesta.

  2. Environment

    Let's All Swim in the Once-Filthy Canals of Paris

    Unlike many cities, the French capital has made good on its promise to re-open urban waterways to bathers. How did they do it?  

  3. Uber drivers sit in their cars waiting for passengers.
    Equity

    What Uber Drivers Say About Uber

    Researchers conducted in-depth interviews and discovered a lot about the pitfalls of working in the rideshare business.

  4. Design

    What's Inside a Neighborhood in a Box?

    On the outskirts of New York City, a new housing model aimed at Millennials asks: What is city living?

  5. Maps

    U.S. Transportation Funding Is Not Created Equal

    Some states shoulder the lion’s share of state and local road costs; others lean on Uncle Sam.