Greening of vacant/derelict sites may improve health and safety of nearby residents

Unfortunately this research, although potentially of great interest, has been reported in a way that it is difficult to draw conclusions..

http://www.uphs.upenn.edu/news/News_Releases/2011/11/more-green-crime/

So one needs to look at the original paper published in the American Journal of Epidemiology

http://www.uphs.upenn.edu/news/News_Releases/2011/11/more-green-crime/

vacant lot greening is associated with

- consistent reductions in gun assaults

in some areas

- reductions in vandalism

- reports by residents of reduced stress and greater exercise 

- increases in public nuisance crimes - possibly caused by the greened lots providing new gathering spaces