Can a tree help prevent crime? It just might. Two new studies, led by U.S. Forest Service researchers, took a closer look at urban green space in Philadelphia, Baltimore and Youngstown, Ohio. In each of these cities, adding green space to crime-ridden areas helped reduce crime rates, the researchers found.

In 2000, Philadelphia launched a program to plant vegetation along roadways to help soak up rainwater. Researchers looked at 52 of these vegetation plots and compared them with control plots that didn't receive the greenery upgrade. After tracking 14 types of crime in nearby areas, researchers found that narcotics possession in those areas decreased by 18 to 27 percent, even as the rate for the rest of the city rose by 65 percent.

Michelle Kondo, a social scientist and lead researcher with the forest service, speculated the increased presence of city trucks and vans in the landscaped areas — for planting and maintenance — was enough to deter illicit activity.

A similar effect was noted in Youngstown, Ohio — a depressed Midwestern town known for its high rates of crime and unemployment. From 2010 to 2014, city officials embarked on a project to reclaim some of the city's empty lots and derelict buildings by converting them into green space. In 2011, they added another initiative that gave local communities funding to plant green space in vacant lots in whatever method they chose — lawns, community gardens, playgrounds and more.

When Kondo and her team compared crime around these vegetation plots with undeveloped plots in nearby areas, they found the areas around new green spaces had lower crime rates than elsewhere in the city. Interestingly, the crime reduction was different depending upon the type of green space that was developed. For example, lots that were planted with grass and maintained by contractors saw a reduction in property crimes such as theft and burglary, whereas community-maintained plots saw a sharp reduction in violent crime. This suggests that different types of green space could be developed to deter certain types of crime.

A tidy yard is another line of defense

Kondo's study collaborates another forest service study conducted by researcher Morgan Grove on the link between lawn care and crime in downtown Baltimore. Grove's study looked at the level of lawn maintenance in 1,000 residential yards throughout Baltimore County. His team looked at everything from tree cover to litter to the presence of garden hoses. Not surprisingly, Grove found that well-maintained lawns were linked to lower crime rates than lawns that were given less care.

It's tempting to use income as the connection. After all, if you have the time and money to water your lawn, you probably live in a neighborhood that sees less crime. But Grove argued that the greenery itself helped to deter crime, by announcing to would-be criminals that there are "eyes on the street" that care for their neighborhood and would be more likely to report a crime.

The takeaway from these two studies is that urban green space may help to deter crime and could be a useful tool in city-wide crime prevention policies. We already know greenery is beautiful to look at and can help improve mood and health while reducing pollution. Now we can add crime-fighting to the list of vegetation's many benefits.

Need a better reason to plant a tree?