US researchers have revealed that certain types of city trees may help lower property and violent crime rates.
The study, conducted by the researchers with the US Forest Service's Pacific Northwest (PNW) and Southern Research Stations, is the first to examine the effects of trees and other factors on crime occurrence in Portland, Ore.
Geoffrey Donovan and his colleague Jeffrey Prestemon analysed police reports from 2005 to 2007 for property and violent crimes, taking into consideration the quality of tree coverage in the area where the incident occurred.
The researchers conducted statistical analyses to explore the relationships among crime and more than two dozen variables they compiled, including the number and size of trees on a lot and the size of trees on surrounding areas.
They concluded that areas with large trees had lower levels of crime while numerous small trees were associated with an increase in crime.
“We wanted to find out whether trees, which provide a range of other benefits, could improve quality of life in Portland by reducing crime, and it was exciting to see that they did,” said Donovan.
“Although a burglar alarm may deter criminals, it won't provide shade on a hot summer day, and it certainly isn't as nice to look at as a tree,” he added.
"We believe that large street trees can reduce crime by signaling to a potential criminal that a neighborhood is better cared for and, therefore, a criminal is more likely to be caught. Large yard trees also were associated with lower crime rates, most likely because they are less view-obstructing than smaller trees," said Donovan.
Their analysis suggested that small yard trees might actually increase crime by blocking views and providing cover for criminals - an effect homeowners can reduce by keeping trees pruned and carefully choosing the location of new trees.
The study is posted online in advance of its appearance in a forthcoming printed issue of the journal ‘Environment and Behavior’.
