Sidewalk trees discourage city crime, study says

Researchers from the U.S. Forest Service say big, leafy trees help deter city crime. Why? Because appearance really matters.
Written by Andrew Nusca, Contributor on

One of the things that bothers me most about my new home in Philadelphia is the lack of trees.

That's not to say there aren't any -- there are plenty of big, leafy, deciduous trees all over my neighborhood. Their shades of red, orange and yellow at this time of year are a stunning sight, and there's nothing quite like autumn in the northeastern United States.

But my block? Well, it's lacking.

Many years ago, my West Philadelphia neighborhood was not as nice as it is today. (And some would argue, rightly, that it's still not quite "nice.") Decades ago, for specific reasons unknown, the strip of grass out front of the homes on my side of the block was paved over. Many trees were removed.

Now, an otherwise leafy neighborhood filled with century-old homes has a decidedly barren bald spot. The concrete radiates heat in the summer and funnels wind in the winter. And there's little to be done when the sidewalk, now twice as wide, is used illegally as a driveway.

It's no surprise, then, that the average price of a home on this block is half that of the block before it, despite the exact same housing stock. Moreover, more crime incidents have been recorded here than on greener blocks. The spread of concrete, benign as it is, is more suited for a gas station than for the front lawn of a residence.

According to a new study, there may be some truth to that gut feeling. Researchers with the U.S. Forest Service's Pacific Northwest and Southern Research Stations found that certain types of city trees may help lower property and violent crime rates.

The study -- the first of its kind -- looked at the effects of trees and other factors on crime in Portland, Ore.

Most city officials know that the presence of trees helps resist the heat island effect of a dense city, reduces greenhouse gases in the atmosphere and provide shade for pedestrians and residents. But can they reduce crime?

Yes, according to research forester Geoffrey Donovan. Working with colleague Jeffrey Prestemon, Donovan found that big, leafy, large trees -- the kind I'm missing on my block -- were associated with a reduction in crime.

Skinny, small trees? An increase in crime.

Using crime data from the Portland Police Bureau from 2005 to 2007, the researchers paired it with aerial photographs, onsite visits and information from the Multnomah County Tax Assessor's Office on 2,813 single-family homes.

What they found is that the canopy size of both street and yard trees and the number of trees growing on a lot had the most effect on crime occurrence.

"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 in a statement. "Large yard trees also were associated with lower crime rates, most likely because they are less view-obstructing than smaller trees."

Meanwhile, small yard trees may actually increase crime because they provide cover for criminals, the researchers suggest.

Without a doubt, the study is limited, and the researchers say they plan to replicate it in other cities before drawing any grand conclusions. (Using different types of homes, I humbly suggest.)

But it's a little bit of science to bolster the idea that a good-looking block helps keep crime at bay.

Their research will be published in a forthcoming issue of the journal Environment and Behavior.

This post was originally published on Smartplanet.com

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