Healthy Development Measurement Toolkit

Indicator ES.2.d Number of trees

Data Source

Tree data provided by Science Application International Corporation and the Federal Bureau of Investigation, 2007.

Map prepared by City and County of San Francisco, Department of Public Health, Environmental Health Section using ArcGIS software.

Table data is presented by planning neighborhood. Detailed information regarding census data, geographic units of analysis, their definitions, and their boundaries can be found in the HDMT at the following links:

http://www.thehdmt.org/etc/Geographic_Units_of_Analysis.September_2009.pdf

http://www.thehdmt.org/data_map_methods.php

Explanation and Limitations

In 2004, the San Francisco Urban Forest Council invited a research team from the United States Department of Agriculture (USDA) Forest Service to study San Francisco's urban forest. The team's report, issued in early 2005, was the first comprehensive analysis of San Francisco's urban forest, that is, all of the trees growing within the city limits. The study calculated the surface area covered by tree canopies in San Francisco and found that forest canopy covers approximately 12% of San Francisco. This compares to 10% in Los Angeles, 27% in New York City, 28% in Chicago and 34% in Seattle.

San Francisco"s tree canopy is compromised of all trees found within city limits, located on a mixture of public and privately owned land. It is owned and managed by a diverse mix of city, county, state and federal agencies, as well as the private sector.

Tree canopy cover is not the only measure in appraising a city"s urban forest. It is equally important to collect quantitative information on tree size, age distribution, tree species, and tree condition. The city is currently collaborating with the United States Department of Agriculture (USDA) Forest Service to obtain this information.

As noted in the Urban Forest Plan "As the trees in the urban forest grow, they remove contaminants from the atmosphere. The UFORE [the Urban Forests Effects Model] report found that each year, over 287 tons of ozone, particulates, nitrous oxides, sulfur dioxide and carbon monoxide are taken out of the air by the urban forest. The value of this environmental benefit is $1.3 million per year. In addition, San Francisco"s trees remove 5,100 tons of carbon from the atmosphere and store approximately 194,000 tons as biomass." (page 10)

San Francisco Planning Code Section 143 requires that a project sponsor provide an in-lieu payment to the Department of Public Works/Bureau of Urban Forests for a tree to be planted and maintained within the neighborhood should it not be possible to plant a tree every 20 feet.

For more information about trees in San Francisco, visit: http://www.sfgov.org/site/uploadedfiles/bdsupvrs/leganalyst/021-00_Tree%20_Programs.pdf. See also, Seattle"s Urban Forest Assessment Sustainability Matrix (July 2000): http://www.ci.seattle.wa.us/environment/documents/sustainability%20matrix.pdf

Why is this a Community Health Indicator?

Trees provide natural cooling through the shading of streets and buildings thereby reducing exposure to UV radiation and the risk of skin cancer, as well as energy demand and consumption. Trees also capture air pollution, reduce carbon dioxide, increase oxygen, and help capture storm-water runoff, filtering water to reduce the amount of mercury, oil, and lead going into the Bay. Trees can also serve as buffers to traffic, reducing pedestrian injuries. Several studies show that the presence of forests, trees and other vegetation improves adult recovery from mental fatigue, leading to a reduction in socially unacceptable behavior and crime, as well as fewer behavior problems among children.^a,b