by EG McPherson, JR Simpson, M Livingston
Urban Forestry and Urban Greening 2:73-862003
Trees planted strategically to shade buildings can reduce energy use for cooling and heating. To determine the energy savings from existing trees and from sites where trees could be planted to shade buildings, aerial imagery from 21 California cities was analyzed. For each city, at least 3,495 sample points were randomly chosen and identified as to land use type, presence of tree, presence of suitable planting space for a tree (i.e., presence of a pervious surface), and distance and direction from tree site to nearest building. This information was extrapolated from the individual city to represent all urban areas of that city’s climate region. The results indicate there are approximately 177 million energy-saving trees in California, reducing energy use by 2.5% overall and by 10% at peak energy times. There are estimated to be another 242 million sites for energy-saving trees. If 50 million of these were planted, the result would be an additional 1.1% energy saved overall and 4.5% reduction in peak load demand. If total planting and maintenance costs average $50/tree, the energy savings involved would be well within the range considered cost-effective.