According to a recent study from Temple University that examined how crime rates correlate with patches of urban vegetation, more plants means less crime. "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."