Some measures taken by green communities can be simple in concept, relatively inexpensive as municipal projects go, and extremely cost effective. In Philadelphia, where the horticultural society had a strong planting program before green was so stylish, Professor Susan Wachter's research on planting trees on vacant lots led to significant appreciation (more than 30 percent) in the value of adjacent lots. Philadelphia Greening has taken the art of planting trees and installing a uniform fence around vacant lots to a new level in neighborhood stabilization.