Sunday September 11, 2016

The tricky relationship between trees and crime

One of the successful plantings of a new tree in the Brentwood park.

One of the successful plantings of a new tree in the Brentwood park. (Natasha Frakes/CBC)

Listen 8:36

Some residents of a Calgary neighbourhood object to having more trees in their local park, because they fear the trees will attract criminals.

Ellen Burgess, one opponent of the newly planted trees told CBC "if you give people more places to hide, more naughty things will be done."

But recent research suggests the opposite:  trees don't give burglars and highwaymen a place to hide, rather they may reduce crime in a neighbourhood.

One piece of research from 2001 focused on a public housing project in Chicago, where some buildings had trees out front, others did not. The research found that buildings with fewer trees or barren yards had more crime reports, while buildings with trees had fewer crimes. Because residents of the project were randomly assigned to various apartments, the differences in crime couldn't be attributed to factors like income.

A more recently published article in the journal Landscape and Urban Planning focused on Cincinnati. The city's trees were being killed by the Emerald Ash Borer beetle. Researchers took advantage of the spread of the beetle to study the relationship between trees and crime. They found that when a tree is killed and removed, crime in the area tends to go up.

A 2012 study called The Effect of Trees on Crime in Portland, Oregon, also found a connection between trees and crime.

It found that whether a tree on private property deters or welcomes crime may be related to the height of a tree. If a tree is 42 feet tall or higher, it's associated with lower crime. If the tree is shorter, it's associated with higher crime.

The reason?

The bushy part of a 42 foot tall tree starts above the first story windows of a house, allowing a clear view out. Shorter trees block the view, and can therefore be used as hiding places for burglars or other miscreants.