Contrary to convention, vegetation, when well-maintained, can lower the rates of certain types of crime, such as aggravated assault, robbery and burglary, in cities, according to a Temple University study, "Does vegetation encourage or suppress urban crime? Evidence from Philadelphia, PA," published in the journal, Landscape and Urban Planning.

"There is a longstanding principle, particularly in urban planning, that you don't want a high level of vegetation, because it abets crime by either shielding the criminal activity or allowing the criminal to escape," said Jeremy Mennis, associate professor of geography and urban studies at Temple. "Well-maintained greenery, however, can have a suppressive effect on crime."

After establishing controls for other key socioeconomic factors related to crime, such as poverty, educational attainment and population density, Mennis, along with environmental studies major Mary Wolfe, examined socioeconomic, crime and vegetation data, the latter from satellite imagery.

They found that the presence of grass, trees and shrubs is associated with lower crime rates in Philadelphia, particularly for robberies and assaults.

The authors surmise this deterrent effect is rooted in the fact that maintained greenery encourages social interaction and community supervision of public spaces, as well the calming effect that vegetated landscapes may impart, thus reducing psychological precursors to violent acts. They offer their findings and related work as evidence for urban planners to use when designing crime prevention strategies, especially important in an age when sustainability is valued.

Mennis said rather than decreasing vegetation as a crime deterrent, their study provides evidence that cities should be exploring increasing maintained green spaces.

"Increasing vegetation, supporting sustainability -- they are a nice complement to so many city initiatives beyond increasing aesthetics and improving the environment," he said.

"Reducing stormwater runoff, improving quality of life, reducing crime -- all of these objectives are furthered by increasing well-managed vegetation within the city."

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