Backers of a program to clean up vacant lots say the effort helps reduce gun violence.  Many cities have  paid or volunteer crews that clean up vacant lots. The Land Care program in Philadelphia may be the nation's largest, with trash removed and grass and trees planted on about 4500 publicly or privately owned parcels. Robert Grossman directs the Landcare Program for the Philadelphia Horticultural Society.  He told a Medical College of Wisconsin forum in Milwaukee that cleaning and greening is not designed to be the last use for the urban land.

"The intention is to improve the appearance of it," he says.

An epidemiology professor at the University of Pennsylvania says there appear to be other benefits to cleaning and marinating the urban land. Charles Branas says less gun crime, for example.

"Gun crime was significantly reduced, partly because use took an interest in the case.,"

Philadelphia still has another  30-thousand vacant lots, and re-use of some of the LandCare properties  has been slow because of lack of willing investors.  But  Milwaukee Mayor Tom Barrett  says the Philadelphia program is similar to what he's trying to ramp up in his city, as part of  Milwaukee's attempt to win a grant from a national mayor's challenge run by Bloomberg Philanthropies.