Anyone who has ever sat under a tree on a hot summer day has appreciated the cooling ability of trees, but trees can do more than just provide shade for a picnic. Trees cool our neighborhoods in the summer and save us money on energy costs and related water usage and air pollution. American Forests has developed a method for estimating the energy conservation benefits of trees from direct shading of one and two-story residential buildings. This method is the result of research conducted by Dr. Greg McPherson of the USDA Forest Service.

Trees are most effective when located to shade air conditioners, windows, or walls and when located on the side of the home receiving the most solar exposure. In many parts of the country the west side is most valuable, followed by the east and south, although this ranking can change based on geographical considerations.

American Forests has incorporated this research in CITYgreen software — a desktop GIS program that calculates the value of trees to urban environments. CITYgreen incorporates research from 11 cities distributed across the United States. The program considers all trees within 35 feet of residential structures less than 3 stories tall, disregarding trees further away with the assumption that they are too far away to provide significant shading.

In a study released in August 2001, American Forests found that tree cover in the metro Atlanta area saved residents approximately $2.8 million annually in reduced energy costs. In 1999, a 3.2 million acre area around Houston was found to benefit by $26 million annually as a result of the cooling effects of its tree cover. Similar trends have been found throughout the country.

Indirect effects of tree shading

Research by the USDA Forest Service and others has shown that trees strategically planted to shade homes can reduce air conditioning bills significantly. As a result, local power plants are not required to produce as much electricity, and thus emit less pollution, including carbon. In urban and suburban areas, the amount of this avoided carbon output outweighs even the amount of carbon sequestered by the natural forest as it grows.

Other initiatives

In 1991 American Forests established the Cool Communities program with the cooperation of the EPA and other partners in an effort to mobilize private citizens, businesses, and local governments to promote the use of trees as energy conservation tools. Based on research in the EPA’s guidebook, Cooling our Communities, the program successfully initiated pilot projects in seven communities around the country. In 1996 the project was completed with staggering results. In areas that had participated in the Cool Communities program public knowledge about the ecological and economic value of trees increased dramatically. In 1993, 79% of people surveyed in Miami knew that trees could help residents save money on their energy bills. By late 1996, this number was increased to 97%. Similar results were found around the country.

Additional Information can be found at:
CITYgreen Manual Trees and Energy Section