United States

Department of 

Agriculture

Forest Service

Northern 

Research Station

State and Private

Forestry

General Technical 

Report NRS-62

June 2010

David J. Nowak, Susan M. Stein, Paula B. Randler, Eric J. Greenfi eld, 

Sara J. Comas, Mary A. Carr, and Ralph J. Alig

Sustaining America’s Sustaining America’s 

Urban Trees and Forests

A Forests on the Edge Report
ABSTRACT

Nowak, David J.; Stein, Susan M.; Randler, Paula B.; 

Greenfi eld, Eric J.; Comas, Sara J.; Carr, Mary A.;

Alig, Ralph J. 2010. Sustaining America’s urban 

trees and forests: a Forests on the Edge report. 

Gen. Tech. Rep. NRS-62. Newtown Square, PA: 

U.S. Department of Agriculture, Forest Service, 

Northern Research Station. 27 p.

Close to 80 percent of the U.S. population lives in 

urban areas and depends on the essential ecological, 

economic, and social benefi ts provided by urban trees 

and forests. However, the distribution of urban tree 

cover and the benefi ts of urban forests vary across the 

United States, as do the challenges of sustaining this 

important resource. As urban areas expand across the 

country, the importance of the benefi ts that urban forests 

provide, as well as the challenges to their conservation 

and maintenance, will increase. The purpose of this 

report is to provide an overview of the current status and 

benefi ts of America’s urban forests, compare differences 

in urban forest canopy cover among regions, and discuss 

challenges facing urban forests and their implications for 

urban forest management. 

Key Words: Urban forest, urbanization, land 

management, ecosystem services

AUTHORS

David J. Nowak is a project leader and 

Eric J. Greenfi eld is a forester, U.S. Department 

of Agriculture, Forest Service, Northern Research 

Station, 5 Moon Library, SUNY-ESF, Syracuse, NY 

13210; Susan M. Stein is a private forest-land studies 

coordinator and Paula B. Randler and Sara J. Comas

are natural resource specialists, U.S. Department of 

Agriculture, Forest Service, Cooperative Forestry 

Staff, Mailstop 1123, 1400 Independence Avenue, 

SW, Washington, DC 20250-1123; Mary A. Carr is 

a technical publications editor, U. S. Forest Service, 

Ecosystem Management Coordination Publishing Arts, 

1835 Black Lake Boulevard SW, Olympia, WA 98512; 

Ralph J. Alig is a research forester and team leader, 

U.S. Department of Agriculture, Forest Service, Pacifi c 

Northwest Research Station, Forest Sciences Laboratory, 

3200 SW Jefferson Way, Corvallis, OR 97331.

INTRODUCTION

While the aesthetic values of urban forests might 

be eye-catching, the many critical services they 

provide tend to be overlooked. In addition to 

being attractive, urban forests provide a myriad of 

essential services to the more than 220 million people 

who live in urban areas in the United States (U.S. Census 

Bureau 2001)—including reduced energy use, improved 

water quality, diverse wildlife habitat, and increased 

human health and well-being. Urban forests are an 

essential component of America’s “green infrastructure” 

(see box) and their benefi ts extend well beyond the cities 

and towns where they are located. 

The care and management of many urban forests 

can be complicated by natural and social factors 

including: insects and diseases; wildfi re; natural 

catastrophic events (such as ice storms and wind 

storms, including hurricanes); invasive plants; climate 

change; development; air pollution; lack of adequate 

management; and other social factors. As urban 

expansion continues, such challenges are likely to 

increase and new ones might emerge.

Urban forests offer aesthetic values and critical services.

Larry Korhnak

AP Photo: The Plain Dealer, Lisa DeJong
3

About Forests on the Edge 

Sponsored by the State and Private Forestry, 

Cooperative Forestry staff of the U.S. Forest 

Service, in cooperation with Forest Service 

Research and Development and other partners, the 

Forests on the Edge project uses data prepared 

and analyzed by scientists across the country to 

increase public understanding of the contributions 

of and pressures on America’s forests, and to 

create new tools for strategic planning. This 

publication was also sponsored by the Resources 

Planning Act (RPA) Assessment staff of the U.S. 

Forest Service. For details on Forests on the Edge 

and previous reports, visit the Forest Service Open 

Space website at http://www.fs.fed.us/openspace/

fote. 

or lost in the future. Although the results are summarized 

at the county scale, it is at both the local and regional 

levels where landowners, communities, and agencies 

can come together to plan for sustainable growth while 

conserving the ability of urban and rural forests to 

provide valuable ecosystem services and economic 

opportunity far into the future. 

AMERICA’S URBAN FORESTS

T

he term urban forest refers to all publicly and 

privately owned trees within an urban area—

including individual trees along streets and in 

backyards, as well as stands of remnant forest (Nowak 

et al. 2001). Urban forests are an integral part of 

community ecosystems, whose numerous elements (such 

as people, animals, buildings, infrastructure, water, and 

air) interact to signifi cantly affect the quality of urban 

life. 

The key to defi ning urban forests is to defi ne urban 

land. The term “urban” connotes areas with relatively 

high amounts of people and artifi cial surfaces. The 

U.S. Census Bureau has a specifi c defi nition of urban 

based on population density (urbanized areas and urban 

clusters); this defi nition was used in this report to delimit 

urban areas (Appendix 1). Urban land and population 

data were derived from U.S. Census data (U.S. Census 

Bureau 2007). 

This report is one of 

several produced by 

the U.S. Department 

of Agriculture, 

Forest Service, as 

part of the Resources 

Planning Act (RPA) 

Assessment and 

Forests on the Edge 

projects. The report 

is intended for use by 

urban forest managers 

and by organizations 

that support urban 

forest management 

to help increase 

awareness among 

the general public 

of the importance of 

urban forests, their 

many benefi ts, and the various factors that challenge the 

management of these critical resources. It also presents 

data used to compare tree cover among counties across 

the conterminous United States (the lower 48 states). 

Alaska and Hawaii were not included in the analyses 

because of incomplete cover data. The report concludes 

with a list of tools for cost-effective management.

Similar to other national assessments, fi ndings may not 

completely capture specifi c details at all levels or in 

specifi c localities. However, results can help foster an 

understanding of where, nationwide, vital urban forest 

contributions are most signifi cant and could be enhanced 

America’s Green Infrastructure

America’s forests are sometimes referred 

to as “green infrastructure” to emphasize 

the critical public benef ts they provide. The 

term has been def ned as “an interconnected 

network of green space that conserves 

natural ecosystem values and functions 

and provides associated benef ts to human 

populations” (Benedict and McMahon 2002). 

Urban forests are an integral part of this 

structure, providing a lattice of green in an 

otherwise artif cial landscape. “The value of 

an urban forest is equal to the net benef ts 

that members of society obtain from it” 

(McPherson et al. 1997).

Urban forests provide green space in 

the urban landscape.

© iStockphoto.com/Christopher Arndt
4

Geopolitical boundaries are often used to delimit the 

boundaries of “places” (such as towns and cities). 

However, places can encompass signifi cant amounts 

of rural land (for example, some so-called cities are 

actually large counties), and places do not always truly 

delimit urban areas so much as they defi ne community 

boundaries. State reports document tree and other 

vegetative cover within both urban and community 

boundaries at the state, county, sub-county, and place 

levels (Nowak and Greenfi eld 2008, USDA Forest 

Service 2009).

In 2000, 3.1 percent of the conterminous United 

States was classifi ed as urban (Nowak et al. 2005), 

yet this small percentage of land supports 79 percent 

of the population, or more than 220 million people 

(U.S. Census Bureau 2001). Urban land is expanding 

at a considerable rate and is projected to increase 

substantially over the next half-century (Alig et al. 

2004, Nowak and Walton 2005) (Appendix 1). The 

Northeast and Southeast are the most urbanized regions 

of the country (Alig and Healy 1987, Alig et al. 2004, 

Nowak et al. 2005) (Fig. 1), and four states in the 

Northeast are projected to be more than half urban land 

by 2050: Rhode Island, New Jersey, Massachusetts, and 

Connecticut (Appendix 1). 

Based on photo-interpretation, tree cover in urban 

areas of the conterminous United States is estimated at 

35.1 percent (20.9 million ac) (Appendix 2). As urban 

areas expand, the amount of urban forest will increase 

and urban forests will become increasingly critical to 

sustaining environmental quality and human well-being 

in urban areas. Careful planning and management will be 

crucial to maintain and enhance urban forest benefi ts.

New York City’s Central Park, the f rst landscaped park in 

America, constitutes a huge urban forest containing some 

26,000 trees. 

What’s Urban Forestry?

Management of urban trees and associated 

resources to sustain urban forest cover, 

health, and numerous socioeconomic and 

ecosystem services is known as urban 

forestry. Because of land jurisdiction issues, 

urban foresters typically focus on trees 

located along streets as well as in public 

parks and natural areas. However, since 

one of the main goals of urban forestry 

is to optimize forest benef ts for society, 

urban foresters can also help guide the 

management of trees on private lands, 

which typically dominate the overall urban 

forest composition. An arborist specializes in the care of trees.

A coastal Oregon village.

© iStockphoto.com/Terraxplorer

Casey Trees © iStockphoto.com/Lori Howard
5

Figure 1—Percentage of the county classif ed as urban (2000).

URBAN FOREST BENEFITS

G

iven that close to 80 percent of the population of the 

conterminous United States lives in an urban area, 

the benefi ts provided by urban forests touch most 

U.S. citizens. Nationally, urban forests in the United 

States are estimated to contain about 3.8 billion trees, 

with an estimated structural asset value of $2.4 trillion 

(Nowak et al. 2002).1

 This dollar value refl ects only a 

portion of the total worth of an urban forest. Urban trees 

also provide innumerable annual ecosystem services 

that affect both the local physical environment (such 

as air and water quality) and the social environment 

(such as individual and community well-being) that 

infl uence urban quality of life (Nowak and Dwyer 2007). 

Urban forest services and benefi ts include, but are not 

limited to:

1

 Structural asset value is based, in part, on extrapolations 

of estimated replacement costs of trees of the same size, 

condition, species, and location. Trees are a valuable asset to the urban community.

www.treespayusback.com

Percent Urban Land

0% - 1%

1.1% - 5%

5.1% - 10%

10.1% - 25%

25.1% - 100%
6

• Local climate and energy use—Trees infl uence 

thermal comfort, energy use, and air quality by 

providing shade, transpiring moisture, and reducing 

wind speeds. The establishment of 100 million 

mature trees around residences in the United States 

is said to save about $2 billion annually in reduced 

energy costs (Akbari et al. 1988, 1992; Donovan 

and Butry 2009).

• Air quality—Trees improve air quality by lowering 

air temperatures, altering emissions from building 

energy use and other sources, and removing air 

pollutants through their leaves. Urban trees in the 

conterminous United States remove some 784,000 

tons of air pollution annually, with a value of 

$3.8 billion (Nowak et al. 2006).

• Climate change—Urban trees can affect climate 

change by directly storing carbon within their tissues 

and by reducing carbon emissions from power plants 

through lowered building energy use. Urban trees 

in the conterminous United States currently store 

770 million tons of carbon, valued at $14.3 billion 

(Nowak and Crane 2002).

• Water fl ow and quality—Trees and soils improve 

water quality and reduce the need for costly storm 

water treatment (the removal of harmful substances 

washed off roads, parking lots, and roofs during 

rain/snow events), by intercepting and retaining 

or slowing the fl ow of precipitation reaching the 

ground. During an intense storm in Dayton, OH, 

for example, the tree canopy was estimated to reduce 

potential runoff by 7 percent (Sanders 1986). 

• Noise abatement—Properly designed plantings 

of trees and shrubs can signifi cantly reduce noise 

(Anderson et al. 1984). Wide plantings (around 

100 ft) of tall dense trees combined with soft ground 

surfaces can reduce apparent loudness by 50 percent 

or more (6 to 10 decibels) (Cook 1978). 

• Wildlife and biodiversity—Urban forests help 

create and enhance animal and plant habitats and 

can act as “reservoirs” for endangered species 

(Howenstine 1993). Urban forest wildlife offer 

enjoyment to city dwellers (Shaw et al. 1985) and 

can serve as indicators of local environmental health 

(VanDruff et al. 1995).

• Soil quality—Trees and other plants help remediate 

soils at landfi lls and other contaminated sites by 

absorbing, transforming, and containing a number 

of contaminants (Westphal and Isebrands 2001).

Trees provide homes for urban wildlife.

The shade of trees keeps people cool.

© iStockphoto.com/Alina Pavlova

AP Photo: Dayton Beach News-Journal, Jessica Webb
7

• Real estate and business—Landscaping with 

trees—in yards, in parks and greenways, along 

streets, and in shopping centers—can increase 

property values and commercial benefi ts (Anderson 

and Cordell 1988; Corrill et al. 1978; Donovan and 

Butry 2008; Dwyer et al. 1992; Wolf 2003, 2004). 

One study found that on average, prices for goods 

purchased in Seattle were 11 percent higher in 

landscaped areas than in areas with no trees 

(Wolf 1998).

• Individual well-being and public health—The 

presence of urban trees and forests can make the 

urban environment a more aesthetic, pleasant, and 

emotionally satisfying place in which to live, work, 

and spend leisure time (Dwyer et al. 1991; Taylor 

et al. 2001a, 2001b; Ulrich 1984). Urban trees also 

provide numerous health benefi ts; for example, 

tree shade reduces ultraviolet radiation and its 

associated health problems (Heisler et al. 1995), 

and hospital patients with window views of trees 

have been shown to recover faster and with fewer 

complications than patients without such views 

(Ulrich 1984).

• Community well-being—Urban forests make 

important contributions to the economic vitality and 

character of a city, neighborhood, or subdivision. 

Furthermore, a stronger sense of community and 

empowerment to improve neighborhood conditions 

in inner cities has been attributed to involvement 

in urban forestry efforts (Kuo and Sullivan, 2001a, 

2001b; Sommer et al. 1994a, 1994b; Westphal 1999, 

2003).

Numerous health and recreational benef ts are associated with 

urban trees.

AP Photo: Williamsport Sun-Gazette, Mark Nance

COMPARING OUR URBAN FORESTS

Where in the United States are urban forests 

providing the greatest relative canopy cover and 

thereby potentially providing the greatest benefi ts? 

Where is there potentially available space to increase 

tree canopy cover in urban areas? This report takes a 

coarse look at these questions, using the best available 

national data and presenting results at the county level. 

Appendix 2 contains a detailed description of the 

methods used and limitations of the data and analyses.

Comparing Urban Tree Cover

Tree canopy cover can serve as an indicator of the 

extent to which trees and forests are providing critical 

services to local residents. A national assessment of 

urban tree cover, or the amount of urban land covered 

by tree canopies, can illustrate how urban tree cover 

and associated benefi ts vary across the United States. In 

addition, these data can be used to compare urban cover 

estimates among counties.

Variations in Urban Tree Cover

The amount of urban forest canopy cover varies 

widely in cities across the United States, depending 

in part on the location and size of the city, population 

density, development intensity, and surrounding natural 

vegetative cover. In urban areas, tree cover and density 

are typically greatest in parks, forests, and residential 

lands (Nowak et al. 1996). Cities in naturally forested 

regions average nearly twice the percentage tree cover of 

cities in grassland regions, and more than three times the 

The Boston Commons, the nation’s oldest public park.

© Dave Newman/Dreamstime.com
8

percentage tree cover of cities in desert regions (Nowak 

et al. 2001). This difference is in part due to the capacity 

for natural regeneration of trees in forested regions and 

along streams in grassland regions. However, urban tree 

cover in forested regions is often limited by land use 

activities (such as buildings or constant mowing and 

burning) that limit tree regeneration. In addition, tree 

cover in grassland and desert areas is often limited by 

insuffi cient precipitation and local natural seed sources.

The density of trees in a city also varies based on such 

factors as intensity of development, natural vegetation 

type, tree management, and tree size distribution. 

Average tree density in some U.S. cities has been found 

to range from 14.4 trees per ac in Jersey City, NJ, to 

111.6 trees per ac in Atlanta, GA (Nowak et al. 2008).

Tree cover estimates used in the analysis were based 

on National Land Cover Database (NLCD) estimates 

derived from Landsat satellite imagery taken around 

2001 (Homer et al. 2004, USGS 2008, Yang et al. 2003). 

Percentage tree cover in urban areas is typically greater 

in the Eastern United States (Fig. 2). It is estimated 

that up to 80 percent of urban areas in some counties 

(such as Fayette County, Tennessee) are covered by tree 

canopies. However, the canopy cover estimates given 

in Figure 2 are conservative because the canopy cover 

map underestimates canopy cover by an average of 9.7 

percent (Greenfi eld et al. 2009) (Appendix 2). 

Considering tree cover in relation to population density, 

tree canopy cover per person (square feet of tree cover 

per capita) is typically greatest in the Southeast and New 

England states (Fig. 3), with values exceeding 10,000 ft2

per person in several counties. Again these estimates are 

probably conservative considering the typical underestimation of canopy cover discussed previously.

Figure 2—Percentage tree cover in urban areas (2000).

Percent Urban Tree Canopy

0% - 10%

10.1% - 20%

20.1% - 30%

30.1% - 50%

50.1% - 80%

No Urban Land
9

Figure 3—Urban canopy (ft2) per person (urban canopy / urban population).

Comparing Tree Cover Among Counties

Because various regions of the United States have 

differing degrees of underestimation of tree cover 

(Greenfi eld et al. 2009) and because population densities 

in urban areas vary among counties, county tree cover 

was compared only with other counties in the same 

ecological mapping unit (to avoid differences due to 

cover mapping methods) and having a similar population 

density (to avoid comparing heavily populated areas 

with sparsely populated areas) (Appendix 2). To 

compare tree cover among like counties, tree cover was 

standardized on a score between 0 (lowest cover in class) 

and 1 (highest cover in class) (Fig. 4). In the cases where 

there were not at least two other counties in the same 

grouping or where there was no urban land, counties did 

not receive a score. 

Counties given the highest index value (highlighted 

in darkest green in Figure 4) are those that have the 

greatest relative cover (and benefi ts) compared to similar 

counties with similar population density in the region. 

However, unlike the map illustrating actual tree cover 

(Fig. 2), indexed counties with high relative tree cover 

are found in most every state.

Denver has an extensive network of parks.

© iStockphoto.com/David Parsons

0.0 - 250.0

250.1 - 1,000.0

1,000.1 - 5,000.0

5,000.1 - 10,000.0

10,000.1 - 103,300.0

No Urban Land

Urban Canopy (ft ) Per Person 2
10

A low index score for urban tree canopy cover does 

not necessarily mean that a county is doing a poor job 

of sustaining urban tree cover, but rather could be an 

indication of land-use restrictions or other factors. For 

example, some counties may have a high proportion of 

agricultural land or other land uses that limit tree cover 

within urban boundaries. Detailed information on county 

land cover can be found in state assessments reports 

(such as Nowak and Greenfi eld 2008, 2009; USDA 

Forest Service 2009). Local investigation of the reasons 

why particular counties scored relatively low compared 

to their neighbors could potentially help communities 

develop ways to increase canopy cover if desired.

Potential Opportunities 

for Expanding Urban Forest Cover 

As introduced above, the current urban tree cover 

pattern exhibited across the United States is the result 

of numerous physical and social forces that both limit 

and enhance canopy cover. These forces vary by region, 

specifi c location, development, population, and other 

social and physical factors. Throughout urban areas, 

particularly areas with low tree cover, there are several 

Figure 4—Urban tree canopy index for counties (2000); 0.00 is the lowest rating, 1.00 is the highest.

opportunities to enhance canopy. However, the questions 

should be asked: should one increase canopy in specifi c 

areas, and if so, by how much? Enhancing urban canopy 

cover will generally increase the benefi ts derived from 

urban forests; however, it can also potentially increase 

costs and risk (such as fi re risk, energy costs, water 

usage) and it can change wildlife habitat and recreation 

opportunities. Thus, maximum tree cover may not be 

optimal tree cover. Optimal canopy cover is based 

on a mix of costs (ecological, social, and economic); 

community desires; and services (ecological, social, and 

economic) provided by tree cover.

Therefore, the context of existing community goals and 

ecosystem processes is critical when deciding whether 

to develop plans to enhance canopy and determining the 

amount of space and locations of these spaces. In some 

cases, particularly in the arid West, expansion of canopy 

cover could be limited by local natural resources (such 

as water). In other areas, particularly forested regions, 

canopy expansion can be limited by human processes 

(for example, impervious surfaces or mowing). 

Careful determination of the desirability of increasing 

canopy cover with optimal results related to trees 

Urban Tree Canopy Index

0.00 - 0.20

0.21 - 0.40

0.41 - 0.60

0.61 - 0.80

0.81 - 1.00

Not Applicable
11

species, locations, and canopy health will hinge on full 

consideration of all the long-term costs associated with 

canopy cover change along with all the potential benefi ts 

and community desires. 

Once the decision to increase canopy cover is made, 

effective long-term management plans for increasing 

canopy cover also will address optimal locations to 

plant trees relative to infrastructure, use constraints, 

and human populations; desired ecosystems from the 

increased canopy; and tree species best suited to local 

conditions and desired ecosystem services—such as 

planting drought-tolerant species in low-rainfall areas. 

With a focus on sustaining long-term canopy cover 

and tree health at minimal cost, increasing canopy 

cover can be accomplished through tree planting and/or 

management actions that facilitate natural regeneration.

Increasing urban tree canopy, but at what cost?

© Elena Elisseeva/Dreamstime.com

Seeking the Best Fit: 

Drought-Tolerant Species 

in Low-Rainfall Areas

Drought-tolerant trees, or drought “avoiders,” 

are built for survival in drier, less hospitable 

climates. Their success is due to the presence of 

various mechanisms that help them to use water 

eff ciently, such as extensive root systems, thick 

waxes on leaves and bark, and leaf cells that 

function well with little water (Coder 1999).

With a yearly average rainfall of less than 10 

inches, the city of Scottsdale, AZ, has taken 

several measures to prepare for stringent water 

conservation, including the planting of droughttolerant shrubs and trees in the downtown areas 

(City of Scottsdale 2007). 

To aid Scottsdale and other Arizona communities 

with such efforts, the Arizona Department of 

Water Resources has produced a list of native, 

drought-tolerant, and low-water-use plants, 

trees, and shrubs (Arizona Municipal Water 

Users Association 2004). These include the 

California fan palm (Washingtonia fi lifera), honey 

mesquite (Prosopis glandulosa), sweet acacia 

(Acacia smalli), and evergreen elm (Ulmus 

parvifolia). 

Drought-tolerant acacia trees can help conserve water.

© iStockphoto.com/Scott Leigh
12

Urban forests face a number of challenges including wind, wildlf res, invasive plants, and insect pests. AP Photo: Evan Vucci

AP Photo: Reed Saxon

Richard Old, XID Services, Inc., Bugwood.org

AP Photo: Mel Evans

URBAN FOREST CHALLENGES

T

hroughout the country, urban forests face a myriad 

of management challenges. Like forests in rural 

and ex-urban settings, urban forests are exposed to 

a broad range of human-caused and natural challenges, 

all of which can be compounded by climate change. 

However, the proximity of urban forests to relatively 

high numbers of people and associated development 

can considerably increase the level and complexity of 

management challenges. These challenges include:

• Insects and diseases—Urban forests across the 

country are severely affected by numerous insects 

and diseases, many of them introduced from other 

places, that have caused or have the potential to 

cause signifi cant damage. Some invasive species—

such as the gypsy moth, emerald ash borer, and the 

fungi that cause Dutch elm disease and chestnut 

blight—have caused catastrophic tree mortality that 

has virtually eliminated dominant tree species in 

some places (Dozier 2000, Liebhold et al. 1995). 

Endemic pests such as mountain pine beetle have 

also caused severe damage to urban forests (Ellig 

2008).

• Wildfi re—Uncontrolled fi res, or wildfi res, can 

cause substantial damage to urban forests and 

dramatically alter the urban landscape, especially 

in urban areas adjacent to wildlands (often referred 

to as the wildland-urban interface) (Spyratos et al. 

2007). High population growth and urban expansion 

in California, for example, have led to a substantial 

increase in fi re ignitions in wildland-urban interface 

areas (Syphard et al. 2007).

• Natural catastrophic events—Urban forests can 

be greatly affected by natural catastrophic events 

such as ice storms, snow, and severe wind, which 

can result in broken branches or uprooted trees 

among other impacts (Greenberg and McNab 1998, 
13

Irland 2000, Proulx and Greene 2001, Valinger and 

Fridman 1997). Such events can cause damage to 

people and property.

• Invasive plants—Kudzu (Pueraria lobata), English 

ivy (Hederal helix), European buckthorn (Rhamnus 

cathartica), and, in some areas, Norway maple (Acer 

plantanoides), are among the invasive plants that can 

degrade or modify urban forests in part by removing 

and replacing native plants and altering ecosystem 

structure. English ivy and kudzu have been known 

to cover acres of canopy trees (Dozier 2000, Webb 

et al. 2001).

• Additional development—Development within and 

around urban areas in forested regions can lead to 

decreases in forest area and fragmentation of forest 

stands, which can signifi cantly affect plant and 

wildlife populations, forest biodiversity and health 

(Nowak et al. 2005), and parcelization of forested 

areas (where stands remains intact but have multiple 

landowners), which can affect the available timber 

supply and forest management (Zhang et al. 2005). 

• Air pollution—Forest ecosystems can be 

substantially affected by air pollution, especially 

from regional deposition of ozone, nitrogen, sulfur, 

and hydrogen (Stolte 1996). Ozone has been 

documented to reduce tree growth (Pye 1988), 

reduce resistance to bark beetle, and increase 

susceptibility to drought (Stolte 1996). Beckett et 

al. (1998) reviewed several reports and surmised 

that pollutant particles can have a wide variety of 

effects on trees and that heavy metals and other toxic 

particles can accumulate in urban soils, causing 

damage and death in some species. 

• Climate change—In the United States, climate 

change is expected to produce warmer air 

temperatures, altered precipitation patterns, and 

more extreme temperature and precipitation events 

(EPA 2009, IPCC 2007), all of which can cause 

changes in urban forests (Iverson and Prasad 

2001, Johnston 2004). Climate change also has the 

potential to exacerbate all of the other urban forest 

threats discussed above. 

• Other changes over time—Urban forests also are 

constantly changing through time as a result of 

land development, ownership changes, tree growth 

and mortality, natural regeneration, tree planting, 

and tree maintenance and management activities. 

These changes present additional challenges for 

maintaining urban forest cover, health, and benefi ts.

URBAN FOREST MANAGEMENT ISSUES

T

he management of urban forests typically involves 

a variety of activities such as inventorying tree 

populations; enacting tree and land use planning 

ordinances and policies; developing and implementing 

long-term management and maintenance plans, 

annual work plans, and budgets; and promoting 

community education and participation (Dwyer et al. 

1992, Elmendorf et al. 2003). Effective urban forest 

management nationwide has often been hampered by 

challenges such as inconsistent management approaches, 

lack of funding, weak linkages with other resource 

management programs, and inadequate planning 

that fails to consider the surrounding ecosystem, the 

community, and the regional context. 

As understanding of the ecological and economic 

values of trees increases, so does recognition of the 

importance of urban forest management. Close to 

1,000 communities in the United States have signed a 

climate protection agreement that includes tree planting 

and urban forest maintenance as forms of reducing 

global warming. In recognition of the importance 

of urban forestry, the U.S. Conference of Mayors 

recently conducted an urban forestry survey of 135 

U.S. cities with populations of 30,000 or more. Their 

fi nal report (City Policy Associates 2008) recognizes 

“the invaluable role of urban forests in the protection of 

public health and the reduction of harmful greenhouse 

gases.” According to the results, 95 percent of the cities 

surveyed have adopted tree management ordinances; 

47 percent have enlarging tree canopy as a goal; and 70 

percent maintain tree inventories (55 percent of which 

are up to date). 

Planning is an important part of urban forest management.

Larry Korhnak
14

Challenges to Comprehensive Management

Despite such widespread recognition for the importance 

of comprehensive management, the level of resources 

allocated to the management of urban forests varies 

greatly from one urban area to another. The diversity 

of forest cover types, land uses, population densities, 

and land ownerships across many urban areas calls for 

complex, long-term urban forest management plans 

(Dwyer et al. 2000). However, because of a lack of 

funding, volunteer time, and information on appropriate 

management, many urban areas are unable to initiate, 

complete, or implement even the most basic of urban 

forest management plans (Dwyer et al. 1992, Elmendorf 

et al. 2003). Some communities have no urban forestry 

department; many that do tend to focus on planting 

and managing trees in public places, particularly along 

streets and in parks, which account for only a small 

portion of the overall urban forest canopy. 

Comprehensive urban forest management considers 

all trees and associated elements across the entire 

jurisdiction to adequately address a heterogeneous 

landscape held by numerous land owners. A fi rst step in 

developing a proper management plan is to assess the 

current composition and distribution of a community’s 

trees and their associated ecosystem services. This basic 

urban forest information, combined with community 

desires related to forests and ecosystem services, can 

provide a strong foundation for developing long-term 

management plans.

However, such long-term management and planning can 

be complicated at the regional scale where urban forests 

cross multiple community, county, or other government 

jurisdictions. In these cases, a coordinated multijurisdictional effort can help to sustain optimal urban 

forest benefi ts across a region. 

Urbanization of Rural and Exurban Forests

Rural and exurban forests in the vicinity of urban lands 

will be considerably affected by population growth and 

associated urban expansion. As these surrounding forests 

become urbanized, management and policy decisions 

become more complex—with more stakeholders and 

more at stake than ever before (Bradley 1984; Stein 

et al. 2005, 2007). Issues such as timber harvesting, 

fi re protection, ecological functions, recreational uses, 

scenic views, wildlife, invasive species, and forest 

fragmentation become more contentious and diffi cult 

to handle as urbanization increases (Bradley 1984; 

Hammer et al. 2004; Mehmood and Zhang 2001; 

Riitters et al. 2002; Stein et al. 2007, 2009). 

Effective attention to such challenges becomes crucial 

as urbanization results in the conversion of large rural 

and exurban forests to smaller urban forests. Projections 

indicate that, between 2000 and 2050, urbanization will 

subsume a total of 29.2 million ac of forest land—an 

area about the size of Pennsylvania (Nowak and Walton 

2005) (Fig. 5). These emerging urban forests, which will 

consist of remnant forest stands along with scattered 

Community Accomplishments Reported

More than 7,000 communities nationwide, serving 177 

million residents, have already made a serious commitment 

to urban forest management, according to the Community 

Accomplishment Reporting System (CARS). Managed by 

the U.S. Forest Service, CARS is a database that tracks the 

capacity of communities to manage their forest resources. 

The digital dataset contains information on the number of 

communities in each state that have adopted practices to 

protect and manage their forests, whether by staff ng, laws, 

plans, advocacy groups, or inventories. The dataset also 

serves as a measure of sustainability, because if communities 

are doing such activities, their forests are more likely to be 

sustained. 

Casey Trees

Community involvement, like this planting party, will help 

sustain urban forests and parks for years to come.
15

trees affected by numerous land uses and ownerships, 

will need to be managed effectively to ensure healthy 

trees and forests that can sustain environmental quality 

and human well-being. With increasing urbanization, 

urban forest management will likely take on a relatively 

higher regional and national importance because as rural 

and exurban forest areas decline, the services of the 

remaining urban and non-urban forests will become even 

more critical to the regional and national population.

Figure 5—Percentage (A) and acreage (B) of non-urban forest subsumed by projected urban growth (2000-2050), by state. From 

Nowak and Walton (2005).

Larry Korhnak

Urban expansion complicates forest management.

A

B

Percent Forest Loss

0.1% - 1%

1.1% - 5%

5.1% - 10%

10.1% - 20%

20.1% - 30%

30.1% - 40%

40.1% - 48.2%

Forest Loss (Acres)

5,297 - 10,000

10,001 - 50,000

50,001 - 100,000

100,001 - 250,000

250,001 - 500,000

500,001 - 1,000,000

1,000,001 - 2,159,686
16

Tools for Cost-Effective Management

The costs to maintain and manage urban forests are 

substantial. A statewide survey of 18 California cities 

revealed an annual expenditure of close to $80 million. 

Most of these funds were spent on addressing problems 

related to the growth of street tree roots, which are 

severely impeded by sidewalks, curbs, gutters, and street 

pavement (McPherson 2000). However, most urban 

forests do not require such intensive management, and 

the overall benefi ts of urban forests likely outweigh their 

planning and management costs. With proper planning 

and management, costs can be reduced and benefi ts 

enhanced. 

Innovative tools2

 are currently available or under 

development that may help to minimize the costs 

and boost the effectiveness of future urban forest 

management. These include:

• i-Tree—A state-of-the-art, peer-reviewed, and 

easy-to-use suite of urban forestry analysis tools 

for collecting and analyzing information on urban 

forests. i-Tree uses local data to statistically assess 

urban forest composition and its effects and values 

related to air pollution removal; carbon storage and 

sequestration; building energy use; and urban runoff, 

stream fl ow, and water quality. Software, training, 

and technical support are free. Visit: http://www.

itreetools.org/. 

• Report pests: i-Ped (Inventory Pest Evaluation, 

Detection, and Reporting)—A specialized i-Tree 

tool for establishing a long-term, large-scale urban 

pest detection and reporting system. Visit the i-Tree 

Web site above for this and other tools, or simply 

report observations and concerns to state foresters 

(fi nd yours at: http://www.stateforesters.org) or state 

cooperative extension service (visit: http:/www.

csrees.usda.gov/Extension/). 

• Urban Forest Project Reporting Protocol—Helps 

communities measure, monitor, verify, and reduce 

greenhouse gas emissions through planned tree 

planting and maintenance activities that increase 

the storage of carbon in trees. Visit: http://www.

fs.fed.us/psw/programs/cufr/ and http://www.

climateregistry.org/about.html.

• TreeLink—A networking Website for citizens, 

cities, and sponsors that provides up-to-date 

technological information and grassroots organizing 

tools such as email listserves, publications, and links 

to local urban forestry resources. Visit: http://www.

treelink.org/. 

• CITYgreen—A software program used to calculate 

the monetary values of the economic and ecological 

benefi ts (including stormwater run-off, air pollution 

removal, and carbon storage) provided by the 

trees and other green spaces in specifi c locations 

areas. Visit: http://www.americanforests.org/

productsandpubs/citygreen/. 

• Urban Forestry South—Contains state and 

nonprofi t contacts in the southern states as well 

as an extensive online library and Web links 

on a wide range of topics. Visit: http://www.

urbanforestrysouth.org/.

• SelecTree and Tree Browser—California-based 

resource that can help fi nd the name of a tree or 

choose a tree with desired attributes; also provides 

research, community, and technical resources for 

learning about the importance of protecting healthy 

urban forests and incorporating urban wood into the 

marketplace. Visit: http://www.ufei.org/. The state of 

Utah also has a similar site, Tree Browser, at: http://

treebrowser.org.

• Forest Service Web sites—Numerous Forest 

Service Web sites provide information on urban 

forest management, including the Northern Research 

Station (http://www.nrs.fs.fed.us/units/urban); the 

Urban Natural Resources Institute (http://www.

UNRI.org); the Center for Urban Forest Research 

(http://www.fs.fed.us/psw/programs/cufr/); and 

Interface South (http://www.interfacesouth.org/). For 

other helpful links, visit: http://www.fs.fed.us/ucf. 

Casey Trees

i-Tree data collection tool.

2

 The use of trade, fi rm, or corporation names in this 

publication is for the information and convenience of the 

reader. Such does not constitute an offi cial endorsement or 

approval by the United States Department of Agriculture or 

Forest Service of any product or service to the exclusion of 

others that may be suitable.
17

• State forestry agencies—State forestry agencies 

can also be an important source of urban forestry 

information. To fi nd a contact for your state, visit: 

http://www.stateforesters.org/about_nasf#.

• Additional resources—In addition to the tools 

listed above, there are many other sources of urban 

forest management expertise including: consulting 

foresters and private tree care fi rms, the Cooperative 

Extension Service (http://www.csrees.usda.gov/

Extension/), land grant universities, urban forestry 

centers, and numerous nonprofi t groups such as 

Climate Action Registry (http://www.climateregistry.

org/), the National Urban and Community Forestry 

Council (http://www.treelink.org/nucfac/), the 

International Society of Arboriculture (http://www.

isa.org), the Society of Municipal Arborists (http://

www.urban-forestry.com), American Forests (http://

www.americanforests.org), and the National Arbor 

Day Foundation (http://www.arborday.org/), which 

sponsors numerous programs such as National Arbor 

Day and Tree City USA awards. 

AP Photo: Bebeto Matthews

Inventorying urban forests.

CONCLUSIONS

M

anagement decisions of today will infl uence the 

amount and types of benefi ts derived from the 

urban forest for future generations. Knowledge of 

urban forest ecology and how to conserve these essential 

resources will be critical to developing appropriate 

management strategies to enhance optimal urban forest 

cover and to sustain urban forest health and benefi ts 

into the future. Management plans to sustain or enhance 

healthy urban tree cover will be most successful when 

they incorporate local tree data and consider relevant 

local social and ecological factors and costs, including 

community desires relative to canopy cover and 

associated ecosystem services.

Lack of urban forest management could lead to the loss 

of urban tree canopy cover and health, and to shifts or 

loss of species that would diminish the quality of the 

urban environment and numerous ecosystem services 

derived from trees and forests. These potential changes 

could increase environmental management and human 

health costs, as well as decrease the quality of life of 

urban residents.

By understanding threats to urban forests (including 

invasive species, fi re, air pollution, lack of management 

capability, and development pressures), as well as the 

continued urbanization of rural and exurban forests, 

management efforts can be directed to help reduce 

various threats and sustain important urban forest 

resources. Regional urban forest plans can help improve 

long-term resource and environmental sustainability 

by integrating vegetation management issues across a 

region. Long-term planning and management can reduce 

the risks associated with various urban forest threats and 

ensure ecosystem services that will continue to improve 

urban environmental quality and enhance human quality 

of life and well-being. 

Together, local and regional landowners, communities, 

and agencies can plan for sustainable growth while 

conserving the beauty and benefi ts of America’s 

treasured urban forests.
18

AP Photo: Nature Consortium, Ron Wurzer

Promoting urban forests for future generations to enjoy.

ACKNOWLEDGMENTS

T

his report was funded in part by the U.S. Forest 

Service, State and Private Forestry, Cooperative 

Forestry staff; and the RPA Assessment staff. The 

authors wish to thank the following peer-reviewers for 

their valuable feedback on the report and analyses: John 

Ball, University of South Dakota; John Dwyer, Morton 

Arboretum; and Linda Langner, U.S. Forest Service, 

Research and Development. We also thank the following 

Forest Service employees for their reviews: Keith Cline 

and Susan Mockenhaupt, Washington Offi ce; Laurie 

Tippin, Pacifi c Southwest Region; Janet Valle, Northern 

and Intermountain Region; Phil Rodbell, Northeastern 

Area; and Susan Ford, Intermountain Region. We greatly 

appreciated the input of the staff of several state forestry 

agencies, including: Susan Reisch, Georgia Forestry 

Commission; Drew Todd, Ohio Department of Natural 

Resources; Paul Ries, Oregon Department of Forestry; 

David Stephenson, Idaho Department of Lands; Sarah 

Gracie, Kentucky Division of Forestry; and Charlie 

Marcus, Florida Division of Forestry.

We also thank Larry Payne, former director, State 

and Private Forestry, Cooperative Forestry staff, and 

Assistant Director Steve Marshall, for their inspiration 

and support.

Metrics Table 

When you know: Multiply by: To fi nd:

Feet (ft) 0.305 Meters (m)

Acres (ac) 0.405 Hectares (ha)

Miles (mi) 1.609 Kilometers (km)

Square feet (ft2

) .0929 Square meters (m2) 

Square miles (mi2

) 2.59 Square kilometers (km2)

U.S. tons (ton) 0.91 Metric tons (tonne)

LITERATURE CITED 

Akbari, H.; Davis, S.; Dorsano, S.; Huang, J.; Winnett, 

S. 1992. Cooling our communities: a guidebook 

on tree planting and light-colored surfacing.

Washington, DC: U.S. Environmental Protection 

Agency. 217 p.

Akbari, H.; Huang, J.; Martien, P.; Rainier, L.; 

Rosenfeld, A.; Taha, H. 1988. The impact 

of summer heat islands on cooling energy 

consumption and global CO2

 concentrations.

In: Proceedings of ACEEE 1988 summer study in 

energy effi ciency in buildings Vol 5. August 1988. 

Washington DC: American Council for an EnergyEffi cient Economy: 11-23.

Alig, R.J.; Healy, R.G. 1987. Urban and built-up land 

area changes in the United States: an empirical 

investigation. Land Economics. 63(3): 215-226.

Alig, R.; Kline, J.; Lichtenstein, M. 2004. Urbanization 

on the U.S. landscape: looking ahead in the 21st 

century. Landscape and Urban Planning. 69(2-3): 

219-234.

Anderson, L.M.; Cordell, H.K. 1988. Infl uence of trees 

on residential property values in Athens, Georgia 

(USA): a survey based on actual sales prices.

Landscape and Urban Planning. 15: 153-164.

Anderson, L.M.; Mulligan, B.E.; Goodman, L.S. 1984. 

Effects of vegetation on human response to 

sound. Journal of Arboriculture. 10(2): 45-49.

Arizona Municipal Water Users Association. 2004. 

Landscape plants for the Arizona desert: guide 

to growing more than 200 low-water-use plants.

48 p. http://amwua.org/plants_index.html. (21 

September 2009).

Beckett, K.P.; Freer-Smith, P.H.; Taylor, G. 1998. Urban 

woodlands: their role in reducing the effects of 

particulate pollution. Environmental Pollution. 

99(3): 347-360.

Benedict, M.A.; McMahon, E.T. 2002. Green 

infrastructure: smart conservation for the 21st 

century. Renewable Resources Journal. 20(3): 

12-17.

Bradley, G.A., ed. 1984. Land use and forest resources 

in a changing environment: the urban/forest 

interface. Seattle, WA: University of Washington 

Press. 222 p.
19

City Policy Associates. 2008. Protecting and 

developing the urban tree canopy: a 135-city 

survey. Washington, DC: United States Conference 

of Mayors. 34 p. http://www.usmayors.org/trees/

treefi nalreport2008.pdf. (9 December 2009).

City of Scottsdale, Arizona. 2007. Recommended 

plants for downtown. In: Design standards and 

policies manual, Appendix 8-1A. 11 p. http://www.

scottsdaleaz.gov/Assets/documents/projects/

downtown/DowntownPlants.pdf. (10 December 

2009).

Coder, K.D. 1999. Tree selection for drought 

resistance. Athens, GA: University of Georgia, 

Daniel B. Warnell School of Forest Resources. 3 p.

Cook, D.I. 1978. Trees, solid barriers, and 

combinations: alternatives for noise control.

In: Hopkins, G., ed. Proceedings: national urban 

forest conference. Syracuse, NY: SUNY College of 

Environmental Science and Forestry: 330-339. 

Corrill, M.; Lillydahl, J.; Single, L. 1978. The effects of 

greenbelts on residential property values: some 

fi ndings on the political economy of open space.

Land Economics. 54: 207-217.

Donovan, G.H.; Butry, D. 2008. Market-based 

approaches to tree valuation. Arborist News. 

August: 52-55. www.isa-arbor.com. (9 December 

2009).

Donovan, G.H.; D. Butry. 2009. The value of 

shade: estimating the effect of urban trees on 

summertime electricity use. Energy and Buildings. 

41(6): 662-668.

Dozier, H. 2000. Invasive plants and the restoration 

of the urban forest ecosystem. Chapter 9 In: 

Duryea, M.L.; Binelli, E.K.; Korhnak, L.V., eds. 

Restoring the urban forest ecosystem. Circular 1266, 

Fact Sheet FOR98. [CD-ROM]. Gainesville, FL: 

University of Florida, School of Forest Resources 

and Conservation, Florida Cooperative Extension 

Service, Institute of Food and Agricultural Sciences. 

24 p. http://edis.ifas.ufl .edu/topic_book_restoring_

the_urban_forest_ecosystem. (01 April 2009). 

Dwyer, J.F.; McPherson, E.G.; Schroeder, H.W.; 

Rowntree, R.A. 1992. Assessing the benefi ts and 

costs of the urban forest. Journal of Arboriculture. 

18(5): 227-234.

Dwyer, J.F.; Nowak, D.J.; Noble, M.H.; Sisinni, S. 

2000. Connecting people with ecosystems in 

the 21st century: an assessment of our nation’s 

urban forests. PNW-GTR-490. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacifi c 

Northwest Research Station. 483 p.

Dwyer, J.F.; Schroeder, H.W.; Gobster, P.H. 1991. The 

signifi cance of urban trees and forests: toward 

a deeper understanding of values. Journal of 

Arboriculture. 17: 276-284.

Ellig, T. 2008. MSU deals with mountain pine 

beetle infestation. Bozeman, MT: Montana State 

University News Service. December 1. http://www.

montana.edu/cpa/news/nwview.php?article=6595. 

(August 5, 2009).

Elmendorf, W.F.; Cotrone, V.J.; Mullen, J.T. 2003. 

Trends in urban forestry practices, programs, 

and sustainability: contrasting a Pennsylvania, 

U.S. study. Journal of Arboriculture. 29(4): 237-248.

Greenberg, C.H.; McNab, W.H. 1998. Forest 

disturbance in hurricane-related downbursts in 

the Appalachian mountains in North Carolina.

Forest Ecology and Management. 104: 179-191.

Greenfi eld, E.G.; Nowak, D.J.; Walton, J.W. 2009. 

Assessment of 2001 NLCD percent tree and 

impervious cover estimates. Photogrammetric 

Engineering and Remote Sensing. 75(11): 1279-

1287.

Hammer, R.B.; Stewart, S.I.; Winkler, R.L.; Radeloff, 

V.C.; Voss, P.R. 2004. Characterizing dynamic 

spatial and temporal residential density patterns 

from 1940 to 1990 across the north central United 

States. Landscape and Urban Planning. 69: 183-199.

Heisler, G.M.; Grant, R.H.; Grimmond, S.; Souch, C. 

1995. Urban forests—cooling our communities?

In: Kollin, C.; Barratt, M., eds. Proceedings: 7th 

national urban forest conference. Washington, DC: 

American Forests: 31-34.

Homer, C.G.; Gallant, A. 2001. Partitioning the 

conterminous United States into mapping zones 

for Landsat TM land cover mapping. Unpublished 

U.S. Geologic Survey report. http://landcover.usgs.

gov/pdf/homer.pdf. (1 August 2008).

Homer, C.; Huang, C.; Yang, L.; Wylie, B.; Coan, M. 

2004. Development of a 2001 national land cover 

database for the United States. Photogrammetric 

Engineering and Remote Sensing. 70(7): 829-840.
20

Howenstine, W.L. 1993. Urban forests as part of the 

whole ecosystem. In: Kollin, C.; Mahon, J.; Frame, 

L., eds. Proceedings: 6th national urban forest 

conference. Washington, DC: American Forests: 

118-120.

Intergovernmental Panel on Climate Change [IPCC]. 

2007. Climate change 2007: the physical science 

basis—summary for policymakers. Geneva: IPCC 

Secretariat. 18 p. http://www.ipcc.ch/pdf/assessmentreport/ar4/wg1/ar4-wg1-spm.pdf. (15 July 2008).

Irland, L. 2000. Ice storms and forest impacts. Science 

of the Total Environment. 262: 231-242.

Iverson, L.R.; Prasad, A.M. 2001. Potential changes in 

tree species richness and forest community types 

following climate change. Ecosystems. 4: 186-199.

Johnston, M. 2004. Impacts and adaptation for 

climate change in urban forests. [Presentation]. 

6th Canadian urban forest conference, 

19-23 October, Kelowna, B.C. 15 p. http://www.

treecanada.ca/cufc6/proceedings/papers/Johnston.

pdf. (01 April 2009).

Kuo, F.E; Sullivan, W.C. 2001a. Environment and 

crime in the inner city: does vegetation reduce 

crime? Environment and Behavior. 33(3): 343-365.

Kuo, F.E.; Sullivan, W.C. 2001b. Aggression and 

violence in the inner city: impacts of environment 

via mental fatigue. Environment and Behavior. 

33(4): 543-571.

Liebhold, A.M.; MacDonald, W.L.; Bergdahl, D.; 

Mastro, V.C. 1995. Invasion by exotic forest pests: 

a threat to forest ecosystems. Monograph 30, 

supplement to Forest Science 41(2). Bethesda, MD: 

Society of American Foresters. 50 p.

McPherson, E.G. 2000. Expenditures associated with 

confl icts between street tree root growth and 

hardscape in California, United States. Journal 

of Arboriculture. 26(6): 289–297.

McPherson, E.G.; Nowak, D.; Heisler, G.; Grimmond, 

S.; Souch, C.; Grant, R.; Rowntree, R. 1997. 

Quantifying urban forest structure, function, and 

value: the Chicago Urban Forest Climate Project.

Urban Ecosystems. 1: 49-61.

Mehmood, S.R.; Zhang, D. 2001. Forest parcelization 

in the United States: a study of contributing 

factors. Journal of Forestry. 99(4): 30-34.

Nelson, A.C. 2006. Leadership in a new era. Journal of 

the American Planning Association. 72 (4): 393-407.

Nowak, D.J.; Crane, D.E. 2002. Carbon storage 

and sequestration by urban trees in the USA.

Environmental Pollution. 116(3): 381-389.

Nowak, D.J.; Crane, D.E.; Dwyer, J.F. 2002. 

Compensatory value of urban trees in the United 

States. Journal of Arboriculture. 28(4): 194-199.

Nowak, D.J.; Crane, D.E.; Stevens, J.C. 2006. Air 

pollution removal by urban trees and shrubs 

in the United States. Urban Forestry and Urban 

Greening. 4: 115-123.

Nowak, D.J.; Dwyer, J.F. 2007. Understanding the 

benefi ts and costs of urban forest ecosystems. In: 

Kuser, J., ed. Urban and community forestry in the 

Northeast. New York: Springer: 25-46.

Nowak, D.J.; Greenfi eld, E.J. 2009. Urban and 

community forests of New England. Gen. Tech. 

Rep. NRS-GTR-38. Newtown Square, PA: U.S. 

Department of Agriculture, Forest Service, Northern 

Research Station. 62 p.

Nowak, D.J.; Hoehn, R.E.; Crane, D.E.; Stevens, J.C.; 

Walton, J.T.; Bond. J. 2008. A ground-based 

method of assessing urban forest structure and 

ecosystem services. Arboriculture and Urban 

Forestry. 34(6): 347-358.

Nowak, D.J.; Noble, M.H.; Sisinni, S.M.; Dwyer, J.F. 

2001. Assessing the U.S. urban forest resource.

Journal of Forestry. 99(3): 37-42.

Nowak, D.J.; Rowntree, R.A.; McPherson, E.G.; Sisinni, 

S.M.; Kerkmann, E.; Stevens, J.C. 1996. Measuring 

and analyzing urban tree cover. Landscape and 

Urban Planning. 36: 49-57.

Nowak, D.J.; Walton, J.T. 2005. Projected urban 

growth and its estimated impact on the U.S. forest 

resource (2000–2050). Journal of Forestry. 103(8): 

383-389.

Nowak, D.J.; Walton, J.T.; Dwyer, J.F.; Myeong, S.; 

Kaya, L.G. 2005. The increasing infl uence of 

urban environments on U.S. forest management.

Journal of Forestry. 103(8): 377-382. 

Proulx, O.J.; Greene, D.F. 2001. The relationship 

between ice thickness and northern hardwood 

tree damage during ice storms. Canadian Journal 

of Forest Research. 31: 1758-1767.

Pye, J.M. 1988. Impact of ozone on the growth and 

yield of trees: a review. Journal of Environmental 

Quality. 17: 347-360.
21

Riitters, K.H.; Wickham, J.D.; O’Neill, R.V.; Jones, 

K.B.; Smith, E.R.; Wade, T.G.; Smith, J.H. 2002. 

Fragmentation of continental United States 

forests. Ecosystems. 5: 815-822.

Sanders, R.A. 1986. Urban vegetation impacts on the 

urban hydrology of Dayton, Ohio. Urban Ecology. 

9: 361-376.

Shaw, W.W.; Magnum, W.R.; Lyons, J.R. 1985. 

Residential enjoyment of wildlife resources by 

Americans. Leisure Science. 7: 361-375.

Sommer, R.; Learey, F.; Summit, J.; Tirell, M. 1994a. 

Social benefi ts of resident involvement in tree 

planting: compressions with developer planted 

trees. Journal of Arboriculture. 20(6): 323-328.

Sommer, R.; Learey, F.; Summitt, J.; Tirrell, M. 1994b. 

Social benefi ts of residential involvement in tree 

planting. Journal of Arboriculture. 20(3): 170-175.

Spyratos, V; Bourgeron, P.S.; Ghil, M. 2007. 

Development at the wildland–urban interface 

and the mitigation of forest-fi re risk. Proceedings 

of the National Academy of Sciences. 104(36): 

14272-14276.

Stein, S.; Alig, R.J.; White, E.M.; Comas, S.J.; Carr, M.; 

Eley, M.; Elverum, K.; O’Donnell, M.; Theobald, 

D.M.; Cordell, K.; Haber, J.; Beauvais, T.W. 2007. 

National forests on the edge: development 

pressures on America’s national forests and 

grasslands. Gen. Tech. Rep. PNW-GTR-728. 

Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacifi c Northwest Research Station. 

26 p.

Stein, S.; McRoberts, R.E.; Alig, R.J.; Nelson, M.D.; 

Theobald, D.; Eley, M.; Dechter, M.; Carr, M. 

2005. Forests on the edge: housing development 

on America’s private forests. Gen. Tech. Rep. 

PNW-GTR-636. Portland, OR: U.S. Department 

of Agriculture, Forest Service, Pacifi c Northwest 

Research Station. 16 p.

Stein, S.; McRoberts, R.E.; Mahal, L.G.; Carr, M.A.; 

Alig, R.J.; Comas, S.J.; Theobald, D.M.; Cundiff, A. 

2009. Private forests, public benefi ts: increased 

housing density and other pressures on private 

forest contributions. Gen. Tech. Rep. PNW-GTR795. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacifi c Northwest Research Station. 

74 p.

Stolte, K. 1996. The symptomology of ozone injury to 

pine foliage. In: Miller, P.R.; Stolte, K.W.; Duriscoe, 

D.M.; Pronos, J., tech coords. Evaluating ozone 

air pollution effects on pines in the western United 

States. Gen. Tech. Rep. PSW-GTR-155. Albany, 

CA: U.S. Department of Agriculture, Forest Service, 

Pacifi c Southwest Research Station: 11-18.

Syphard, A.D.; Radeloff, V.C.; Keeley, J.E.; Hawbaker, 

T.J.; Clayton, M.K.; Stewart, S.I.; Hammer, R.B. 

2007. Human infl uence on California fi re regimes.

Ecological Applications. 17(5): 1388-1402.

Taylor, A.F.; Kuo, F.E.; Sullivan, W.C. 2001a. Coping 

with ADD: The surprising connection to green 

play settings. Environment and Behavior. 33(1): 

54-77.

Taylor, A.F.; Kuo, F.E.; Sullivan, W.C. 2001b. Views of 

nature and self discipline: evidence from innercity children. Journal of Environmental Psychology. 

21: 49-63.

Ulrich, R.S. 1984. View through a window may 

infl uence recovery from surgery. Science. 224: 

420-421.

U.S. Department of Agriculture [USDA], Forest Service. 

2009. Northern Research Station publications 

and data. http://www.nrs.fed.us/data/urban. 

(01 December 09).

U.S. Department of Commerce, Census Bureau [U.S. 

Census Bureau]. 2001. Statistical abstract of the 

United States, 2001. Table 1046. http://www.

census.gov/prod/www/statistical-abstract-us.html; 

http://www.census.gov/prod/2002pubs/01statab/statab01.html.

U.S. Department of Commerce, Census Bureau [U.S. 

Census Bureau]. 2007. U.S census data. www.

census.gov. (15 January 2007). 

U.S. Environmental Protection Agency [EPA]. 

2009.Climate change. http://www.epa.gov/

climatechange/basic info. (01 April 2009).

U.S. Geological Survey [USGS]. 2008. Multiresolution land characteristics consortium.

www.mrlc.gov. (1 August 2008).

Valinger, E.; Fridman, J. 1997. Modeling probability 

of snow and wind damage in Scots pine stands 

using tree characteristics. Forest Ecology and 

Management. 97: 215-222.
22

VanDruff, L.W.; Leedy, D.L.; Stearns, F.W. 1995. Urban 

wildlife and human well-being. In: Sukopp, H.; 

Numata, M.; Huber, A., eds. Urban ecology as the 

basis of urban planning. Amsterdam: SPB Academic 

Publishing: 203-211.

Webb, S.L.; Pendergast, T.H.; Dwyer, M.E. 2001. 

Response of native and exotic maple seedling 

banks to removal of exotic, invasive, norway 

maple. Journal of the Torrey Botanical Society. 

128: 141-149.

Westphal, L.M. 1999. Empowering people through 

urban greening projects: does it happen? In: 

Kollin, C., ed. Proceedings: 1999 national urban 

forest conference. Washington, DC: American 

Forests: 60-63.

Westphal, L.M. 2003. Urban greening and social 

benefi ts: a study of empowerment outcomes.

Journal of Arboriculture. 29(3): 137-147.

Westphal, L.M.; Isebrands, J.G. 2001. 

Phytoremediation of Chicago’s brownfi elds: 

consideration of ecological approaches to social 

issues. In: Brownfi elds 2001 Proceedings, Chicago 

IL. http://nrs.fs.fed.us/pubs/jrnl/2001/nc_2001_

Westphal_001.pdf. (29 April 2008).

Wolf, K.L. 2003. Public response to the urban 

forest in inner-city business districts. Journal of 

Arboriculture. 29(3): 117-126.

Wolf, K.L. 2004. Trees and business district 

preferences: a case study of Athens, Georgia US.

Journal of Arboriculture. 30(6): 336-346.

Wolf, K.L. 1998. Trees in business districts: positive 

effects on consumer behavior! Fact Sheet #5. 

Seattle: University of Washington, College of Forest 

Resources, Center for Urban Horticulture. 2 p. http://

www.cfr.washington.edu/research.envmind/CityBiz/

Biz3Ps-FS5.pdf. (09 December 2009).

Yang, L.; Huang, C.; Homer, C.G.; Wylie, B.K.; Coan, 

M.J. 2003. An approach for mapping large-area 

impervious surfaces: synergistic use of 

Landsat-7 ETM+ and high spatial resolution 

imagery. Canadian Journal of Remote Sensing. 

29(2): 230-240.

Zhang, Y.; Zhang, D.; Schelhas, J. 2005. Small-scale 

non-industrial private forest ownership in the 

United States: rationale and implications for 

forest management. Silva Fennica. 39(3): 443-454. Larry Korhnak
23

APPENDIX 1–AMERICA’S URBAN LANDS

Defining Urban Land

Urban land has various defi nitions and 

levels of signifi cance (Alig and Healy 1987). 

Urban lands typically have relatively high 

numbers of people and extensive artifi cial 

surfaces. This report uses the U.S. Census 

Bureau’s (2007) defi nition of urban land, 

based on population density—with urban 

land generally being areas with a population 

density of at least 500 people per square mile. 

To be classifi ed as urban, an area of land must 

meet one of the following defi nitions: 

• One or more block groups or census 

blocks with a population density of 

1,000 people/mi2

.

• Surrounding block groups and census 

blocks with a population density of 

500 people/mi2

.

• Less densely settled blocks that form 

enclaves or indentations, or are used 

to connect discontinuous areas.

More specifi cally, urbanized areas are 

places with 50,000 or more people. Urban 

clusters, a concept new to the 2000 census, 

are territories with 2,500 to 50,000 people, 

encompassing many places typically 

considered suburban (U.S. Census Bureau 

2007).

Highest Percentages and Amounts 

of Urban Lands

In 2000, 3.1 percent of the conterminous 

United States was classifi ed as urban, with 

percentage urban land varying from 0.2 

percent in Wyoming, Montana, North Dakota, 

and South Dakota, to 36.2 percent in New 

Jersey (Table 1). In terms of area, states 

with the highest amounts of urban land 

were California (5.1 million ac), Texas 

(4.6 million ac), and Florida (4.0 million ac). 

The regions with highest percentage urban 

land were the Northeast (9.7 percent) and 

Southeast (7.5 percent); regions with highest 

amounts of urban land were the Northeast 

(12.7 million ac) and North Central 

(12.2 million ac).

Table 1—Urban land growth in the United States (1990-2000)

Urban Land Urban Land Growth

 1990 2000 1990-2000

State (ac) (%) (ac) (%) (ac) (%)

KS 463,600 0.9 554,000 1.1 90,400 0.2

ND 80,300 0.2 93,200 0.2 13,100 0.0

NE 251,300 0.5 292,600 0.6 41,300 0.1

SD 94,900 0.2 107,700 0.2 12,800 0.0

Great Plains 890,100 0.5 1,047,500 0.5 157,400 0.1

IA 467,800 1.3 523,100 1.5 55,400 0.0

IL 1,938,800 5.4 2,304,300 6.4 365,500 1.0

IN 1,136,400 4.9 1,423,600 6.1 287,100 1.2

MI 1,797,000 4.8 2,178,700 5.8 382,000 1.0

MN 859,200 1.6 1,009,900 1.9 150,700 0.3

MO 1,005,500 2.3 1,168,300 2.6 162,800 0.4

OH 2,204,900 8.3 2,568,400 9.7 363,500 1.4

WI 874,500 2.4 1,060,800 3.0 186,300 0.5

North Central 10,283,800 3.5 12,237,400 4.2 1,953,400 0.7

CT 975,300 30.6 1,134,500 35.5 158,900 5.0

DE 141,300 10.9 194,500 15.0 53,100 4.1

MA 1,536,500 29.2 1,797,200 34.2 260,700 5.0

MD 957,000 14.3 1,156,500 17.3 199,400 3.0

ME 202,100 1.0 227,800 1.1 25,700 0.1

NH 259,000 4.4 362,000 6.1 103,000 1.7

NJ 1,551,800 31.2 1,804,900 36.2 253,000 5.1

NY 2,265,700 7.2 2,539,500 8.1 273,800 0.9

PA 2,175,300 7.5 2,730,000 9.4 554,800 1.9

RI 213,000 30.2 253,500 35.9 40,500 5.7

VT 80,800 1.3 94,900 1.5 13,800 0.2

WV 291,600 1.9 361,300 2.3 69,900 0.5

Northeast 10,649,300 8.1 12,655,700 9.7 2,006,500 1.5

CA 4,349,100 4.3 5,086,400 5.0 737,400 0.7

OR 539,200 0.9 658,300 1.1 119,100 0.2

WA 1,091,700 2.5 1,367,500 3.1 275,800 0.6

Pacif c Coast 5,980,200 2.9 7,112,200 3.4 1,132,200 0.5

AZ 765,800 1.0 1,074,200 1.5 308,100 0.4

CO 649,900 1.0 815,000 1.2 165,100 0.2

ID 201,900 0.4 260,700 0.5 58,800 0.1

MT 141,800 0.2 166,800 0.2 24,700 0.0

NM 352,100 0.5 481,600 0.6 129,500 0.2

NV 215,700 0.3 348,200 0.5 132,200 0.2

UT 351,900 0.6 442,100 0.8 90,200 0.2

WY 96,100 0.2 108,200 0.2 11,900 0.0

Rocky Mountains 2,775,500 0.5 3,696,400 0.7 921,000 0.2

AL 910,100 2.8 1,140,900 3.4 230,800 0.7

AR 468,800 1.4 582,400 1.7 113,700 0.3

KY 643,500 2.5 778,600 3.0 135,200 0.5

LA 901,900 3.0 1,066,300 3.5 164,300 0.5

MS 490,800 1.6 599,500 2.0 108,700 0.4

OK 647,700 1.4 743,300 1.7 95,600 0.2

TN 1,198,000 4.4 1,557,800 5.8 359,800 1.3

TX 3,704,400 2.2 4,575,200 2.7 870,800 0.5

South Central 8,965,200 2.3 11,044,100 2.8 2,078,700 0.5

FL 3,093,300 8.3 4,017,900 10.8 924,700 2.5

GA 1,702,100 4.5 2,396,900 6.4 694,900 1.8

NC 1,624,200 5.0 2,278,100 7.1 653,600 2.0

SC 907,400 4.6 1,194,000 6.0 286,600 1.4

VA 1,252,600 4.8 1,522,200 5.9 269,600 1.0

Southeast 8,579,700 5.6 11,408,900 7.5 2,829,400 1.8

Totala

 48,162,800 2.5 59,241,500 3.1 11,078,500 0.6

a Summary for lower 48 states including Washington, DC.

Source: Nowak et al. 2005.

23
24

Table 1 also shows that urban land in the conterminous 

United States increased from 2.5 percent of land being 

urban in 1990 to 3.1 percent in 2000, an increase in 

area about the size of Vermont and New Hampshire 

combined. States with the greatest increase in percentage 

of urban land between 1990 and 2000 were Rhode Island 

(5.7 percent), New Jersey (5.1 percent), Connecticut 

(5.0 percent), and Massachusetts (5.0 percent). States 

with the greatest increase in area of urban land were 

Florida (925,000 ac), Texas (871,000 ac), and California 

(737,000 ac). Seven of the 10 states with the greatest 

increase in percentage urban land between 1990 and 

2000 were in the Northeast; the remainder were in the 

Southeast.

In aggregate, the Southeast had the greatest increase 

in percentage urban land between 1990 and 2000 

(1.8 percent of the land area), followed by the Northeast 

(1.5 percent). Regions with greatest area of urban growth 

were the Southeast (2.8 million ac) and the South Central 

(2.1 million ac).

Between 1990 and 2000, most of the urban expansion 

across the United States occurred in forested (averaging 

33.4 percent of the expansion nationwide) or agricultural 

(32.7 percent) land. Within each state, urban areas 

expanded into various cover types in differing 

proportions. States with the highest proportion of 

development occurring in forests were Rhode Island 

(64.8 percent), Connecticut (64.1 percent), and Georgia 

(64.0 percent) (Table 2). States with most area of forest 

land converted to urban were Georgia (444,000 ac), 

North Carolina (366,000 ac), and Pennsylvania 

(237,000 ac) (Table 3).

Projections: Urbanization and Forests, 2000-2050

Given the urban growth patterns of the 1990s, urban 

land is projected to rise substantially in the future—from 

3.1 percent of conterminous United States in 2000 to 

8.1 percent in 2050, an increase in area greater than the 

size of Montana. It is estimated that the amount of built 

environment in the United States by 2025 will be double 

the amount that existed in 2000 (Alig et al. 2004, Nelson 

2006). The changing landscape due to urbanization will 

have signifi cant impacts on land management and efforts 

to sustain environmental quality in urban and urbanizing 

areas.

Projected future growth patterns may be affected by 

demographic shifts (such as population growth) and 

economic conditions (for example, growth in personal 

Table 2—States with the highest percentage of urban land 

expansion within various land cover types, 1990-2000

State % of expansion

 Forest areas

Rhode Island 64.8

Connecticut 64.1

Georgia 64.0

Massachusetts 62.9

West Virginia 62.2

 Agricultural lands

Nebraska 68.9

Indiana 66.8

Illinois 64.8

Wisconsin 62.0

Idaho 54.6

 Woody wetland areas

Florida 14.4

New Jersey 8.6

Rhode Island 7.9

Massachusetts 6.1

Michigan 6.1

 Herbaceous wetland areas

Minnesota 7.4

Maine 6.3

Florida 6.1

Massachusetts 4.2

Delaware 4.0

Table 3—States with the highest amount of urban land 

expansion within various land cover types, 1990-2000

Urban land expansion

State acres

 Forest areas

Georgia 444,410

North Carolina 365,510

Pennsylvania 236,570

Texas 184,390

Florida 174,250

 Agricultural lands

Texas 365,520

Pennsylvania 252,360

Illinois 236,720

Indiana 191,820

Ohio 184,580

 Woody wetland areas

Florida 133,190

North Carolina 32,670

Georgia 27,600

Michigan 23,330

New Jersey 21,870

 Herbaceous wetland areas

Florida 56,660

Minnesota 1 1,190

Massachusetts 1 1,000

Georgia 9,240

Texas 7,960
25

income) (Alig et al. 2004), but most urban growth is 

projected to occur around the more heavily urbanized 

areas, with signifi cant expansion in the East and along 

the west coast. By 2050, four states are projected to be 

more than half urban land: 

• Rhode Island (70.5 percent urban), 

• New Jersey (63.6 percent), 

• Massachusetts (61.0 percent), and 

• Connecticut (60.9 percent) (Nowak and Walton 

2005).

Nationwide, by 2050, about 5.3 percent of forest 

land remaining outside of urban areas is projected to 

be subsumed by urban growth. This amount can be 

substantially higher at the individual state level, with 

Rhode Island (48.2 percent), New Jersey (40.4 percent), 

Massachusetts (37.0 percent), Connecticut 

(35.8 percent), and Delaware (32.5 percent) projected 

to have the greatest percentage of their current non-urban 

forest land transformed by urban growth. 

While northeastern states tended to have the highest 

percentage of forest land that is projected to be taken 

over by urbanization by 2050, southern states tend to be 

highest in total amount of forest land to be transformed 

(Fig. 5). Between 2000 and 2050, North Carolina is 

projected to have 2.16 million ac of forest land changed 

by urbanization, followed by Georgia with 1.92 million 

ac, New York with 1.68 million ac, Pennsylvania with 

1.57 million ac, and Texas with 1.54 million ac. The 

total projected amount of U.S. forest land projected to 

be subsumed by urbanization between 2000 and 2050 is 

about 29.2 million ac, an area approximately the size of 

Pennsylvania.

© Gabriel Eckert, Dreamstime.com
26

APPENDIX 2–METHODS AND DATA CONSTRAINTS

Methods

Most of the data presented in this report were derived 

from two sources: (1) the multi-resolution land 

characteristics consortium’s National Land Cover 

Database (NLCD) (Homer et al. 2004, USGS 2008, 

Yang et al. 2003); and (2) the U.S. Census Bureau 

(U.S. Census Bureau 2007). The NLCD, released in 

early 2007, was used to develop estimates related to 

tree cover. NLCD is processed from 2001 Landsat 

satellite imagery and provides estimates of percentage 

tree canopy and impervious surface cover within 

30-m (approximately 98-ft) pixels or cells across the 

state. The tree canopy percentages in this report are 

calculated using the land area (not including water) 

of the geopolitical units derived from the U.S. Census 

cartographic boundary data and NLCD. In addition 

to percentage tree cover, tree canopy cover per capita 

was calculated as tree canopy cover (m2

) divided by 

the number of people (derived from U.S. Census data) 

within the area of analysis. Data analyses were based 

on urban lands only (Appendix 1) and summarized on 

the county basis. In addition to illustrating variations 

in urban tree cover and tree cover per capita, an urban 

canopy index was developed.

The urban canopy index, displayed in Figure 3, is a 

standardized score that allows for comparison of canopy 

cover among counties within the same mapping zone 

and same population density class. 

For this comparison, the following three urban 

population density classes were established:

• Density class 1—0 to 1,499.9 people/mi2

• Density class 2—1,500 to 1,999.9 people/mi2

• Density class 3—2,000 or more people/mi2

Mapping zones were delimited within the NLCD to 

increase classifi cation accuracy and effi ciency (Fig. 6). 

The mapping units represent relatively homogeneous 

ecological conditions (Homer and Gallant 2001). 

To assign counties within a mapping zone, centroid 

(geometric center) points of the county were used. For 

three or more counties in the same mapping zone and 

population density class, a standardized tree canopy 

score based on the range of values within that zone and 

class was assigned to each county. The standardized 

score is calculated as:

Standardized score = (tree canopy percentage 

within urban lands in county – minimum tree 

canopy percentage in group) / range of tree canopy 

percentage in group. 

Counties were assigned a standardized score between 

0.00 (lowest rating) and 1.00 (highest rating) for each 

mapping zone and population grouping. Counties did 

not receive a score if there were not at least two other 

counties in the same grouping.

Data Accuracy and Application

Scale Issues

The data presented in this report yield the most 

comprehensive and up-to-date assessment of urban 

forests in the conterminous United States. The data 

allow for relative comparisons among counties. The 

U.S. Census generalized cartographic boundary data are 

simplifi ed and smoothed extracts of the Topologically 

Integrated Geographic Encoding and Referencing 

(TIGER) database, with a target scale range of 

1:5,000,000 (U.S. Census Bureau 2007). Because of this 

scale and generalization, border simplifi cation has an 

impact on the attribute measurements that are derived 

from the boundary data, especially for small areas and 

at the local scale. The 2001 NLCD also has local-scale 

data and application limitations, and users of the data 

are cautioned that the NLCD was not designed for local 

application (Homer et al. 2004). 

Tree Canopy Cover Estimates

A recent analysis of 127 census places and 20 counties 

sampled throughout the conterminous United States 

compared NLCD tree canopy and impervious surface 

cover estimates with high-resolution (1 m [3 ft] or 

less resolution) aerial photo-interpreted estimates 

(Greenfi eld et al. 2009). This analysis revealed that 

NLCD underestimates tree canopy, on average, by about 

9.7 percent compared to photo-interpreted values. Thus, 

the absolute estimates of urban tree cover (Fig. 2) and 

tree cover per capita (Fig. 3) based on the NLCD maps 

are likely conservative. For more refi ned and locally 

appropriate data, local fi eld- or high-resolution (3 ft or 

less) image analyses are recommended (such as i-Tree 

[http://www.itreetools.org] and Urban Tree Canopy 

Assessments (UTC) [www.nrs.fs.fed.us/

urban/utc]).
27

Figure 6—Mapping zones of the conterminous United States relative to states and land cover (NLCD 2001).

Despite the potential underestimates in tree canopy 

cover values, relative comparisons of tree cover among 

counties (Fig. 4) in this report are reasonable because the 

under-prediction of tree cover is likely fairly consistent 

within each mapping zone. Higher resolution cover data 

will probably provide more accurate results at the local 

scale, but the NLCD cover maps provide a cost-effective 

way to consistently assess and compare the relative 

differences of urban cover types regionally. 

National Urban Tree Cover Estimate

Because NLCD tends to underestimate tree cover, 

we photo-interpreted tree cover in urban areas using 

imagery from Google Earth. Images were taken on 

various dates but were typically from the mid to late 

2000s. Within urban and community areas of the 

lower 48 states, 15,000 randomly located points were 

photo-interpreted in relation to tree cover. Community 

areas were defi ned as areas within U.S. Census place 

boundaries. From this sample, 8,594 points fell within 

urban areas. If a state did not have at least 100 urban 

points, the sample was increased in these states to reach 

a minimum of 100 randomly sampled points. The total 

number of urban points interpreted was 9,436. Tree 

cover was calculated as the percent of total points in 

the urban areas that fell upon tree canopies. Urban tree 

cover within each state was weighted by total urban land 

in the state to calculate national urban tree cover in the 

conterminous United States.

Land Cover

Open Water

Perennial Ice/Snow

Developed, Open Space

Developed, Low Intensity

Developed, Medium Intensity

Developed, High Intensity

Barren Land (Rock, Sand, Clay)

Deciduous Forest

Evergreen Forest

Mixed Forest

Shrub/Scrub

Grassland/Herbaceous

Pasture/Hay

Cultivated Crops

Woody Wetlands

Emergent Herbaceous Wetlands
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, 

national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, 

genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance 

program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication 

of program information (Braille, large print, audiotape, etc.) should contract USDA’s TARGET Center at 202-720-2600 (voice and TDD). 

To f le a complaint of discrimination, write to USDA, Director, Off ce of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 

20250-9410, or call 800-795-3272 (voice) or 202-720-6382 (TDD). USDA is an equal opportunity provider and employer.

FORESTS ON THE EDGE 

Forests on the Edge is a project of the U.S. Department 

of Agriculture, Forest Service, State and Private Forestry, 

Cooperative Forestry staff, in conjunction with Forest 

Service Research and Development and other partners. 

The project aims to increase public understanding of the 

contributions of and pressures on America’s forests, and 

to create new tools for strategic planning. The f rst report 

(Stein et al. 2005) identif ed private forested watersheds 

in the conterminous United States most likely to 

experience housing development. Subsequent reports 

have provided more in-depth discussion and data on 

the location and impacts of future house development 

in rural areas. This report presents an overview of the 

current status of and benef ts from America’s urban 

forests across the Nation, the pressures that challenge 

them, and the implications for urban forest management.

Future Forests on the Edge work will include 

assessments of additional contributions and risks, and 

construction of an Internet-based system that permits 

users to view, combine, and depict results for selected 

contribution and threat layers.

For further information on Forests on the Edge, contact: 

Susan Stein, 

U.S. Forest Service, Cooperative Forestry staff

1400 Independence Avenue, SW, Mailstop 1123

Washington, DC 20250-1123 

(202) 205-0837 

sstein@fs.fed.us 

http://www.fs.fed.us/openspace/fote/ 

© Socrates/Dreamstime.com

Photos on front cover, from top then left to right: Oleksandr Burtovyy/Dreamstime.com; AP Photo: Damian Dovarganes; AP Photo: 

The Daily Times, Lucas Ian Coshenet; Photo by Larry Korhnak; AP Photo: Julie Jacobson.