City Policy Associates. Protecting and Developing the Urban Tree Canopy: A 135-City Survey. The United States Conference of Mayors, Washington, D.C. Canopy, Maintenance, Management, Municipal concerns, Trees, Urban, Urban trees This document outlines the results of a nationwide survey conducted by the Community Trees Task Force (within the U.S. Conference of Mayors). The aim of the survey was to more fully understand how individual cities across the country have approached the expansion and maintenance of their urban tree canopy.