This article, based on a series of studies by the Univeristy of Illinois College of Agricultural, Consumer and Environmental Sciences, describes the psychological effect of trees on urban communities: how they bring people together and build a sense of community. Available online at the resource link below.

Prow, Tina. Illinois Steward, Volume 7, Number 4, Winter 1999

http://www.lhhl.uiuc.edu/media/thepoweroftrees.htm

http://www.aces.uiuc.edu/~herl/power_of_trees/power_of_trees1.html