Trees may help police urban neighborhoods

For centuries, city trees have been given a bad rap: Criminals and carjackers could use them to hide behind, according to conventional wisdom. Drug users would use them to sit under. King Edward I even required English towns 800 years ago to clear trees on either side of main streets to ensure robbers couldn’t hide behind them.

But new studies in three American cities suggest that trees can help prevent crime and make an otherwise unsafe neighborhood safer, according to an article by Richard Conniff in Environment: Yale that sums up the studies and their impact.

One Baltimore study, by two Yale graduates, compared neighborhoods with the same housing stock, density and income level and showed that that the one with more trees tended to have a significantly lower crime rate.

“It’s just an association,” said co-author Austin Troy, now at the University of Vermont. “But it’s a very strong association.”

Another study in 2012, using different methodologies found similar results in Portland, Ore. In 2011, a Philadelphia study found a significant reduction in crime – including a 7 to 8 percent decrease in gun assaults across most of the city – as the result of a program to clean up and plant trees on 4,300 vacant lots.

The question, of course is why? Conniff cites previous studies that showed having trees and grass in a neighborhood reduces stress and anxiety, encourages exercise and makes people act more civilly. He notes that the idea fits the “broken window” theory that crime will flourish in places where it appears no one cares about the neighborhood: In these cases, trees speak to a neighborhood that does care, therefore deterring crime.

Boston Globe columnist Gareth Cook wrote about this idea before here. The article in the Yale magazine can be found here.