Conflicting studies over the years have reached differing conclusions about the relationship between urban vegetation and crime. One school of thought believes urban greenery provides a natural hiding place for criminals, another argues that "trees actually decrease crime either by attracting more people to public places (Jane Jacobs' 'eyes on the street' theory) or by signifying to criminals that people care about their neighborhood (James Q. Wilson's 'broken windows' theory).
A recent study conducted by a team of environmental researchers, led by Austin Troy of the University of Vermont, on the relationship between crime and vegetation in Baltimore seeks to end the debate. According to Jaffe, researchers "report an inverse relationship between tree canopy and a variety of crimes in the Baltimore city and county regions."
And their nuanced findings help to explain the prior confusion. "While low dense brush seems to increase it [crime], tall broad canopies seem to decrease it. That nuanced conclusion harmonizes with another study published earlier this year, in which U.S.D.A. Forest Service researcher Geoffrey Donovan (who has also linked urban tree coverage to home prices) reports the same mixed tree-crime associations in Portland, Oregon."