American Forests advocates that every city set a tree canopy goal for their community as an important step in ensuring that their valuable green infrastructure is maintained at minimum thresholds, even as the community continues to develop. American Forests offers some general goal guidelines based on geographic and climate conditions and land use categories. However, each community must first identify what their tree canopy cover is, and then set their own goals to help meet environmental and quality of life goals, including federal and local clean air and water regulations. Once a specific goal is determined, the local government can pursue that goal using policies, procedures, and budget.

Setting Tree Canopy Goals
American Forests recommends an average 40% tree canopy, east of the Mississippi and in the Pacific Northwest. Refer to the chart below for tree cover percentages based on land use and geographic area. These goals are based on an evolution of thinking about how and why we quantify the urban forest.  Three early surveys (1986, 1989 and 1991) focused on the health and condition of public street trees. Our understanding of the environmental benefits of urban forests grew at the same time as the technology improved to more accurately measure its extent.   These two developments in tandem made it possible to measure actual landcover, quantify their environmental benefits, and for the first time link tree canopy cover goals to community-wide goals for clean air and water.

The Evolution of Quantifying the Urban Forest
In 1986, the National Urban Forest Council (NUFC) conducted a survey to understand the condition of the nation’s street trees, based on a 20-city survey. The first, “State of Our City Forests” (American Forests Magazine June, 1986) reported that urban forests in those cities were in decline, with the average city losing 4 trees for every one planted.

Recognizing the need for more widespread and statistically reliable information, the Council organized a more comprehensive survey. The results were published in the, “1989 Street Tree Survey of U.S. Cities and Towns”,  (The American Forestry Association: Washington DC, July 1990). It was the first national inventory conducted on the species, size and condition, and budgets of US street trees based on 413 cities in 30 states. This survey was conducted in cooperation with the National Urban Forest Council, USDA Forest Service, The National Association of State Foresters, Michigan State University, and urban and community foresters. A summary of this study, “The State of the Urban Forest”, J. James Kielbaso and Vincent Cotrone is in the Proceedings of the Fourth Urban Forestry Conference, Phillip Rodbell, editor. American Forests October 1989, pp.11-18.

In 1991, American Forests (formerly known as the American Forestry Association) conducted a follow up survey of 20 cities. The findings revealed the continued decline of city street trees, including the alarming statistic that the average life of a downtown street tree is just 13 years.

While each of these three surveys brought to the public’s attention the alarming decline of our nation’s public trees, none of them was able to quantify the extent of a city’s street tree population at that time. Even more enlightening of these early surveys, was the inability to quantify a community’s entire urban forest population. Since only about 10% of an urban forest is composed of street trees, we were missing most of the story.

Today, thanks to researchers and Geographic Information Systems computer technology, we know so much more about the extent, composition, ecological and economic benefits of the urban forest. In fact, many people now broaden the term, urban forests to urban ecosystems recognizing the complex ecological interactions between trees and other landcover, soils, air, water, and people.

American Forests has conducted more than 40 Urban Ecosystem Analyses in regions around the country.  Reports can be viewed at: http://www.americanforests.org/resources/urbanforests/analysis.php Satellite and aerial imagery not only allow us to accurately quantify the extent of the forest and other landcovers, but by comparing recent with historic imagery, we can also see how urban landcover has changed over time.  Based on current landcover percentages in urban areas across the country and in our judgment, reasonable increases, American Forests has developed suggested tree canopy guidelines as a starting point for communities to set their own goals. While the goals listed below provide general guidelines, each community must measure their current canopy cover and then develop tree cover targets based on their unique mix of climate, geography, land cover, and land use patterns.

Why Set Tree Canopy Goals?
Tree cover in urban areas east of the Mississippi has declined by about 30% over the last 20 years while the foot print of the urban areas has increased by 20%. With this decline in tree cover, significant air and water management costs have increased.

Tree cover is directly related to environmental quality. Maintaining a robust enough tree cover to function as green infrastructure reduces the need and expense of building infrastructure to manage air and water resources. Local agencies can use CITYgreen software to calculate the environmental and economic values of the ecosystem services that trees provide. American Forests' intent is to help communities calculate the value of their trees so that city leaders can make better decisions about integrating "green" into their urban infrastructure.

For metropolitan areas east of the Mississippi and in the Pacific Northwest:

For metropolitan areas in the Southwest and dry West:

National Urban Tree Deficit

An estimated 634,407,719 trees are currently missing from metropolitan areas across the United States as the result of urban and suburban development. These calculations are based on American Forests' Urban Ecosystem Analyses conducted over the past six years in ten select cities. Using satellite imagery, American Forests has been able to document the decline of city trees in areas across the United States.

The National Urban Tree Deficit is the number of "average urban trees" we need in metropolitan areas to bring the tree canopy level up to American Forests' conservative recommendations. The average urban tree is defined as one having 133 square feet of canopy cover.

Within urban areas of the 48 contiguous U.S. using Council of Government boundaries, American Forests estimated the area of forest cover using classified satellite imagery. The urban areas were then segmented by region to adjust for variation in natural forest cover. The regional recommended tree covers were subtracted from the actual tree cover to produce the total deficit area. Finally, the total deficit area was divided by the area of an average urban tree (133 square feet) which yielded a 634,407,719 tree deficit in the U.S. Support for this study was provided by the USDA Forest Service, private corporations, and foundations.

What You Can Do

• Plant a tree in your yard
• Encourage your community to plant trees on public space. Measure the benefits provided by trees with CITYgreen and Regional Ecosystem Analysis
• Contribute to American Forests tree planting fund