The monetary benefits of urban trees outweigh their maintenance and other associated costs. In a study of five U.S. cities, each dollar invested in urban trees returned between $1.37 and $3.09 in benefits. Benefits measured include energy savings, atmospheric CO2 absorption, air quality benefits, stormwater runoff reduction, and aesthetic and other benefits gauged by measuring increases in real estate values.
McPherson, Greg, James R. Simpson, Paula J. Peper, Scott E. Maco, and Qingfu Xiao. (2005). Municipal forest benefits and costs in five U.S. cities. Journal of Forestry 103(8), 411-416.