Friday, June 1, 2012

Trees and crime?


Tree canopy in the island city of Montreal

What to do about trees? You know, the CO2-sucking kind. Do they influence crime opportunity? I doubt they cause or solve it. Do they matter at all? I've written about the crime and tree theory before. 

New research calls for a revisit.

Yesterday my Safe Cascadia colleague Tod Schneider found the latest evidence. It was a study called "The relationship between tree canopy and crime rates across and urban-rural gradient in the greater Baltimore region".
First, what does CPTED have to say? 

CPTED guidelines generally mention trees only in passing. A typical example is the Tempe, Arizona CPTED guidelines on the Florida DOCA website. Those guidelines, as others like them, practically ignore canopy. They do suggest pruning for better sight lines and street lighting. But mostly trees are invisible in guidelines, unlike in the real world where they are not. 

When urban planner Elisabeth Miller and I wrote Saskatoon's CPTED guidelines we spent a bit more time on trees. We drew on research showing the positive effects of trees, particularly a recent Portland, Oregon study.

Our conclusion: "Tall trees, especially those older trees with large trunks, are often associated with beauty and should be retained." 

And what does this latest research say? In the June issue of the journal Landscape and Urban Planning, US Forest Service researchers concluded "a 10% increase in tree canopy was associated with a roughly 12% decrease in crime." 

Canopy along Moscow street
It's not the definitive word, of course. Yet their tree/crime relationship held statistically for public and private areas. It also held for different socioeconomic neighborhoods. It didn't matter if low crime rich areas had more tree canopies and poorer areas didn't. They controlled for other factors like public versus private land. Same result.

One exception - a patch of industrial, abandoned areas where canopies made things worse. Yet they were the exception not the rule. Mostly the study results suggest tree canopies contribute to safety. 

What to do about trees? Plant, prune and leave them alone.  

3 comments:

  1. I suspect that the trees in the lower crime areas were indicators of the neighborhoods themselves, the kind of neighborhoods taken care of by it's residents, thus sending the signal to offenders that it has guardians. Broken windows, anyone?

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  2. Just goes to show you how good Mother Nature can do for the souls of many. Plant, prune, and leave them alone. Thats right.

    -Tony Salmeron

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  3. Thanks Tim. Yes the relationship in their study was correlational meaning patterns are happening, but we can't exactly say why. Stands to reason one of those causes is guardianship.

    Thanks also Tony about Mother Nature. You remind me how she can be indifferent to us when she's storming or earthquaking, but nuturing when we help her along and pay attention to our surroundings. That's why I tell my CPTED students to stop obsessing on site plans and get outside to see for yourself.

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