Ore. November 1, 2010. Along with energy conservation and storm-water
reduction, scientists may soon be adding crime-fighting to the
list of benefits that urban trees provide. Researchers with the
U.S. Forest Service's Pacific Northwest (PNW) and Southern Research
Stations have published a new study that suggests that certain
types of city trees may help lower property and violent crime rates.
Their study—which is posted online in advance of its appearance
in a forthcoming printed issue of the journal Environment and Behavior—is
the first to examine the effects of trees and other factors on
crime occurrence in Portland, Ore.
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
Geoffrey Donovan, research forester with the PNW Research Station
who led the study. “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.”
Donovan and his colleague Jeffrey Prestemon,
with the Southern Research Station, obtained crime data from the
2005 to 2007 and grouped the incidents into seven categories. They
examined only crimes for which a physical address was given and
paired this information with additional data obtained from aerial
onsite visits, and the Multnomah County Tax Assessor’s Office.
Their sample of 2,813 single-family homes experienced 394 property
and 37 violent crimes.
The researchers then conducted statistical
analyses to explore the relationships among crime and more than
two dozen variables
compiled, including the number and size of trees on a lot and the
size of trees on surrounding areas. Of the tree variables analyzed,
canopy size of both street and yard trees and the number of trees
growing on a lot had the most effect on crime occurrence—large
trees were associated with a reduction in crime, while numerous
small trees were associated with an increase.
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,” Donovan
said. “Large yard trees also were associated with lower crime
rates, most likely because they are less view-obstructing than
In contrast, their analysis suggested that
small yard trees might actually increase crime by blocking views
and providing cover for
criminals—an effect that homeowners can mitigate by keeping
trees pruned and carefully choosing the location of new trees.
Donovan and Prestemon plan to continue this line of research and
may conduct similar studies in other cities.
To view the study’s
abstract online, visit http://eab.sagepub.com/content/early/2010/09/16/0013916510383238.abstract.
The PNW Research Station is headquartered in Portland, Oregon.
It has 11 laboratories and centers located in Alaska, Oregon, and
Washington and about 425 employees.