Assessing Urban Forest 

Effects and Values

Northern 

Research Station

Resource Bulletin NRS-37

United States

Department of 

Agriculture

Forest Service

Chicago’s Urban Forest
Published by: For additional copies:

USDA FOREST SERVICE USDA Forest Service 

11 CAMPUS BLVD SUITE 200 Publications Distribution

NEWTOWN SQUARE PA 19073-3294 359 Main Road

 Delaware, OH 43015-8640

February 2010 Fax: (740)368-0152

Visit our homepage at: http://www.nrs.fs.fed.us

Abstract

An analysis of trees in Chicago, IL, reveals that this city has about 3,585,000 trees with 

canopies that cover 17.2 percent of the area. The most common tree species are white 

ash, mulberry species, green ash, and tree-of-heaven. Chicago’s urban forest currently 

stores about 716,000 tons of carbon valued at $14.8 million. In addition, these trees 

remove about 25,200 tons of carbon per year ($521,000 per year) and about 888 tons 

of air pollution per year ($6.4 million per year). Trees in Chicago are estimated to reduce 

annual residential energy costs by $360,000 per year. The structural, or compensatory, 

value is estimated at $2.3 billion. Information on the structure and functions of the urban 

forest can be used to inform urban forest management programs and to integrate urban 

forests within plans to improve environmental quality in the Chicago area.

The Authors

DAVID J. NOWAK is a research forester and project leader, ROBERT E. HOEHN III, is a 

forester, DANIEL E. CRANE is an information technology specialist, JACK C. STEVENS 

is a forester, with the U.S. Forest Service’s Northern Research Station at Syracuse, NY. 

CHERIE LEBLANC FISHER is a social scientist with the U.S. Forest Service’s Northern 

Research Station at Evanston, IL.

Manuscript received for publication 30 September 2009

Acknowledgments

Chicago’s UFORE data collection was a collaborative effort involving fi eld technicians 

and advisors from the U.S. Forest Service, Chicago Park District, and the City of Chicago. 

Special thanks to Aaron Durnbaugh, Suzanne Malec-McKenna, Grace Rink, and Joyce 

Coffee of Chicago’s Department of Environment for their leadership on this project. 

Sincere thanks also to Adam Schwerner, Jerome Scott, and Ellen Sargent of the Chicago 

Park District, Joe McCarthy and Rob Sproule of the Chicago Streets and Sanitation’s 

Bureau of Forestry, Cesar Hernandez and Edde Jones of Chicago’s Department of 

Environment, and the staff of WRD Environmental for their help and support. The data 

collection was accomplished by six hard-working and dedicated fi eld interns: Amanda 

Braus, Ian Cumpston, Douglas Lynch, and Linda Pinto of WRD Environmental; and Benee 

Hardy and Kevin James of the Chicago Park District.
1

Executive Summary

Trees in cities can contribute signifi cantly to human health and environmental quality. 

Unfortunately, little is known about the urban forest resource and what it contributes 

to the local and regional society and economy. To better understand the urban forest 

resource and its numerous values, the U.S. Forest Service, Northern Research Station, 

developed the Urban Forest Effects (UFORE) model. Results from this model are 

used to advance the understanding of the urban forest resource, improve urban forest 

policies, planning and management, provide data to support the potential inclusion of 

trees within environmental regulations, and determine how trees affect the environment 

and consequently enhance human health and environmental quality in urban areas.

Forest structure is a measure of various physical attributes of the vegetation, including 

tree species composition, number of trees, tree density, tree health, leaf area, biomass, 

and species diversity. Forest functions, which are determined by forest structure, 

include a wide range of environmental and ecosystem services such as air pollution 

removal and cooler air temperatures. Forest values are an estimate of the economic 

worth of the various forest functions.

To help determine the vegetation structure, functions, and values of the urban forest in 

Chicago, a vegetation assessment was conducted during the summer of 2007. For this 

assessment, one-tenth acre fi eld plots were sampled and analyzed using the UFORE 

model. This report summarizes results and values of:

• Forest structure

• Potential risk to forest from insects or diseases

• Air pollution removal

• Carbon storage

• Annual carbon removal (sequestration)

• Changes in building energy use

Urban forests 

provide numerous 

benefi ts to society, 

yet relatively little 

is known about this 

important resource.

In 2007, the UFORE 

model was used to 

survey and analyze 

Chicago’s urban 

forest.

The calculated 

environmental 

benefi ts of the 

urban forest are 

signifi cant, yet 

many environmental 

and social benefi ts 

still remain to be 

quantifi ed.

Chicago Urban Forest Summary 

Feature Measure

Number of trees 3,585,000

Tree cover 17.2%

Most common species white ash, mulberry, green ash, 

tree-of-heaven

Percentage of trees < 6-inches diameter 61.2%

Pollution removal 888 tons/year ($6.4 million/year)

Carbon storage 716,000 tons ($14.8 million)

Carbon sequestration 25,200 tons/year ($521,000/year)

Building energy reduction $360,000/year

Increased carbon emissions -$25,000/year

Structural value $2.3 billion

Ton – short ton (U.S.) (2,000 lbs)

David Nowak, U.S. Forest Service
2

Urban Forest Effects Model 

and Field Measurements

Though urban forests have many functions and values, currently only a few of these 

attributes can be assessed due to a limited ability to quantify all of these values thorugh 

standard data analyses. To help assess the city’s urban forest, data from 745 fi eld plots 

located throughout the city were analyzed using the Forest Service’s Urban Forest 

Effects (UFORE) model.1

UFORE is designed to use standardized fi eld data from randomly located plots and 

local hourly air pollution and meteorological data to quantify urban forest structure and 

its numerous effects, including:

• Urban forest structure (e.g., species composition, tree density, tree health, leaf 

area, leaf and tree biomass, species diversity, etc.).

• Amount of pollution removed hourly by the urban forest, and its associated 

percent air quality improvement throughout a year. Pollution removal is 

calculated for ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide and 

particulate matter (<10 microns).

• Total carbon stored and net carbon annually sequestered by the urban forest.

• Effects of trees on building energy use and consequent effects on carbon 

dioxide emissions from power plants.

• Compensatory value of the forest, as well as the value of air pollution removal 

and carbon storage and sequestration.

• Potential impact of infestations by Asian longhorned beetles, emerald ash 

borers, gypsy moth, or Dutch elm disease.

For more information go to http://www.ufore.org

In the fi eld, one-tenth acre plots were selected based on a randomized grid-based pattern at a 

density of approximately 1 plot for every 198 acres. The study is broken into smaller areas by 

using zoning maps. 

The plots were 

divided among the 

following zoning 

districts: downtown 

(14 plots; 1.5 

percent of city 

area), industrial 

(145 plots; 18.8 

percent), open 

space (53 plots; 

7.4 percent), 

planned developed 

(65 plots; 11.7 

percent), residential 

multi-family unit (85 plots; 10.6 percent), residential single family (311 plots; 40.9 percent), 

and shopping (72 plots; 9.1 percent).

Benefi ts ascribed to 

urban trees include:

• Air pollution 

removal

• Air temperature 

reduction

• Reduced building 

energy use

• Absorption 

of ultraviolet 

radiation

• Improved water 

quality

• Reduced noise

• Improved 

human comfort

• Increased 

property value

• Improved 

physiological & 

psychological 

well-being

• Aesthetics

• Community 

cohesion

David Nowak, U.S. Forest Service
3

A cooperative effort among the U.S. Forest Service, and City of Chicago Department 

of Environment, Greencorps Chicago, Chicago Park District, Chicago Department 

of Street and Sanitation’s Bureau of Forestry, and WRD Environmental designed, 

supervised and collected the data for analysis; data collection took place during the 

leaf-on season to properly assess tree canopies. Within each plot, data included landuse, ground and tree cover, shrub characteristics, and individual tree attributes of 

species, stem diameter at breast height (d.b.h.; measured at 4.5 ft.), tree height, height 

to base of live crown, crown width, percentage crown canopy missing and dieback, 

and distance and direction to residential buildings.2

To calculate current carbon storage, biomass for each tree was calculated using 

equations from the literature and measured tree data. Open-grown, maintained trees 

tend to have less biomass than predicted by forest-derived biomass equations.3

 To 

adjust for this difference, biomass results for open-grown urban trees are multiplied by 

0.8.3

 No adjustment is made for trees found in natural stand conditions. Tree dryweight biomass was converted to stored carbon by multiplying by 0.5.

To estimate the gross amount of carbon sequestered annually, average diameter growth 

from the appropriate genera and diameter class and tree condition was added to the 

existing tree diameter (year x) to estimate tree diameter and carbon storage in year x+1.

Air pollution removal estimates are derived from calculated hourly tree-canopy 

resistances for ozone, and sulfur and nitrogen dioxides based on a hybrid of big-leaf 

and multi-layer canopy deposition models.4, 5 As the removal of carbon monoxide 

and particulate matter by vegetation is not directly related to transpiration, removal 

rates (deposition velocities) for these pollutants were based on average measured values 

from the literature6, 7 that were adjusted depending on leaf phenology and leaf area. 

Particulate removal incorporated a 50 percent resuspension rate of particles back to the 

atmosphere.8

Seasonal effects of trees on residential building energy use were calculated based 

on procedures described the literature9

 using distance and direction of trees from 

residential structures, tree height, and tree condition data.

Compensatory values were based on valuation procedures of the Council of Tree 

and Landscape Appraisers, which uses tree species, diameter, condition, and location 

information.10

To learn more about UFORE methods11 visit: 

http://www.nrs.fs.fed.us/tools/UFORE/ or www.ufore.org

Field Survey Data

Plot Information

• Land use type

• Percent tree 

cover

• Percent shrub 

cover

• Percent plantable

• Percent ground 

cover types

Tree parameters

• Species

• Stem diameter

• Total height

• Height to crown 

base

• Crown width

• Percent foliage 

missing

• Percent dieback

• Crown light 

exposure

• Distance and 

direction to 

buildings from 

trees

David Nowak, U.S. Forest Service
4

Tree Characteristics of the Urban Forest

The urban forest of Chicago has an estimated 3,585,000 trees with a standard error 

(SE) of 344,000. Tree cover in Chicago is estimated at 17.2 percent based on digital 

cover mapping of 2008 imagery.12 The four most common species in the urban forest 

are white ash (6.0 percent), mulberry (5.2 percent), green ash (4.9 percent), and treeof-heaven (4.7 percent). The 10 most common species, including unidentifi ed dead 

trees, account for 45.7 percent of all trees; their relative abundance is illustrated below. 

In total, 103 tree species were sampled in Chicago; these species and their relative 

There are an abundance are presented in Appendix IV.

estimated 3.6 million 

trees in Chicago 

with canopies that 

cover 17.2 percent 

of the city.

The 10 most 

common species 

account for 45.7 

percent of the total 

number of trees.

Tree density is 

highest in open 

space, and lowest in 

shopping areas.

The highest density of trees occurs in the open space (94.5 trees/acre), followed by the 

residential single family (23.8 trees/acre) and the residential multi-family unit (16.5 

trees/acre). The overall tree density in Chicago is 24.3 trees/acre, which is comparable to 

other city tree densities (Appendix I) that range between 14.4 to 119.2 trees/acre. Trees 

that have diameters less than 6 inches account for 61.2 percent of the population. Land 

uses that contain the most leaf area are single family residential (50.5 percent of total 

tree leaf area), open space (24.7 percent) and multi-family residential (10.1 percent).

David Nowak, U.S. Forest Service

white ash

6.0% mulberry

5.2%

green ash

4.9% tree of heaven

4.7%

silver maple

4.6%

American elm

4.5%

European 

buckthorn

4.5%

Norway maple

4.0%

dead trees

boxelder 3.8%

3.5%

other species

54.3%

0

10

20

30

40

50

60

70

80

90

100

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

Trees per acre

Number of Trees

Total Trees

Per acre
5

David Nowak, U.S. Forest Service

0

0.5

1

1.5

2

2.5

3

0

10,000

20,000

30,000

40,000

50,000

60,000

Tree Leaf Area Index

Tree Leaf Area (acres)

Leaf Area (ac)

LAI

0

5

10

15

20

25

30

35

40

Percent

d.b.h. class (in.)

0

10

20

30

40

50

60

Percent

* native to North America and one other continent, excluding South America

** native to North America and South America, and one other continent

Urban forests are a mix of native tree species that existed prior to the development 

of the city and exotic species that were introduced by residents or other means. 

Thus, urban forests often have a tree diversity that is higher than surrounding native 

landscapes. An increased tree diversity can minimize the overall impact or destruction 

by a species-specifi c insect or disease, but the increase in the number of exotic plants 

can also pose a risk to native plants if some of the exotic species are invasive plants 

that can potentially out-compete and displace native species. In Chicago, about 51.9 

percent of the trees are from species native to Illinois. Trees with a native origin 

outside of North America are mostly from Eurasia (10.3 percent of the species). Nearly 51.9 percent 

of the tree species 

in Chicago are 

native to Illinois.

Urban forests are 

a mix of native 

tree species that 

existed prior to the 

development of 

the city and exotic 

species that were 

introduced by 

residents or other 

means.
6

Urban Forest Cover and Leaf Area

Dominant ground cover types include impervious surfaces (excluding buildings) (31.7 

percent), herbaceous (28.0 percent), and buildings (25.7 percent).

Healthy leaf area 

equates directly 

to tree benefi ts 

provided to the 

community.

Silver maple is 

currently the most 

dominant species 

in Chicago’s urban 

forest based on 

relative leaf area and 

relative population.

Many tree benefi ts are linked directly to the amount of healthy leaf surface area of the 

plant. In Chicago trees that dominate in terms of leaf area are silver maple, Norway 

maple, and green ash.

Tree species with relatively large individuals contributing leaf area to the population 

(species with percent of leaf area much greater than percent of total population) are 

littleleaf linden, Norway maple, and silver maple. Smaller trees in the population 

are European buckthorn, northern white cedar, and viburnum species (species with 

percent of leaf area much less than percent of total population). A species must also 

constitute at least 1 percent of the total population to be considered as relatively large 

or small trees in the population.

The importance values (IV) are calculated using a formula that takes into account the 

relative leaf area and relative abundance. The most important species in the urban 

forest, according to calculated IVs, are silver maple, Norway maple, and green ash. 

High importance values do not mean that these trees should necessarily be used in the 

future, rather that these species currently dominate the urban forest structure.

Common 

Name

%

Popa

%

LAb IVc

silver maple 4.6 12.5 17.1

Norway 

maple

4.0 11.4 15.4

green ash 4.9 7.5 12.4

mulberry 5.2 5.6 10.8

white ash 6.0 3.9 9.9

American

 elm

4.5 3.9 8.4

tree-of-

 heaven

4.7 2.6 7.3

littleleaf

 linden

1.5 5.0 6.5

honeylocust 3.3 2.6 5.9

European

 buckthorn

4.5 0.7 5.2

a

 percent of population

b

 percent of leaf area

c

 Percent Pop + Percent LA 

David Nowak, U.S. Forest Service

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Downtown

Industrial

Open Space

Planned Develop

Res. Multi Unit

Res. Single Fam

Shopping

Chicago

water bare soil

herbaceous duff/mulch cover

impervious surfaces (excluding buildings buildings

0

2

4

6

8

10

12

Percent

% of total leaf area

% of all trees
7

Air Pollution Removal by Urban Trees

Poor air quality is a common problem in many urban areas. It can lead to human 

health problems, damage to landscape materials and ecosystem processes, and reduced 

visibility. The urban forest can help improve air quality by reducing air temperature, 

directly removing pollutants from the air, and reducing energy consumption in 

buildings, which consequently reduce air pollutant emissions from the power plants. 

Trees also emit volatile organic compounds that can contribute to ozone formation. 

However, integrative studies have revealed that an increase in tree cover leads to reduced 

ozone formation.13

Pollution removal by trees in Chicago was 

estimated using the UFORE model in conjunction 

with fi eld data and hourly pollution and weather 

data for the year 2000. Pollution removal was 

greatest for ozone (O3

), followed by particulate 

matter less than ten microns (PM10), nitrogen 

dioxide (NO2

), sulfur dioxide (SO2), and carbon 

monoxide (CO). It is estimated that trees remove 888 tons of air pollution (CO, NO2

, 

O3

, PM10, SO2) per year with an associated value of $6.4 million (based on estimated 

2007 national median externality costs associated with pollutants14).

The average percentage of air pollution removal during the daytime, in-leaf season was 

estimated to be:

• O3

 0.45% • PM10 0.40%

• SO2

 0.44% • NO2 0.27%

• CO 0.002%

Peak 1-hour air quality improvements during the in-leaf season for heavily-treed areas 

were estimated to be:

• O3

 13.4% • PM10 9.9%

• SO2

 14.1% • NO2 6.3%

• CO 0.05%

The urban forest of 

Chicago removes 

approximately 888 

tons of pollutants 

each year, with a 

societal value of 

$6.4 million/year.

General urban 

forest management 

recommendations 

to improve air 

quality are given in 

Appendix II.

David Nowak, U.S. Forest Service

Chicago water tower from Hancock.

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

0

50

100

150

200

250

300

350

CO NO2 O3 PM10 SO2

Value (dollars)

Pollution removed (tons)

Pollution Removed

Value (U.S. Dollars)

commons.wikimedia.orgPrimeromundo, CC-BY-SA license, 
8

Carbon Storage and Sequestration

Climate change is an issue of global concern. Urban trees can help mitigate climate 

change by sequestering atmospheric carbon (from carbon dioxide) in tissue and by 

reducing energy use in buildings, and consequently reducing carbon dioxide emissions 

from fossil-fuel based power plants.15

Trees reduce the amount of carbon in the atmosphere by sequestering carbon in new 

tissue growth every year. The amount of carbon annually sequestered is increased 

with healthier trees and larger diameter trees. Gross sequestration by trees in Chicago 

is about 25,200 tons of carbon per year with an associated value of $521,000. Net 

carbon sequestration in the Chicago urban forest is estimated at about 17,700 tons.

Carbon storage:

Carbon currently 

held in tree tissue 

(roots, stems, and 

branches).

Carbon 

sequestration:

Estimated amount 

of carbon removed 

annually by 

trees. Net carbon 

sequestration 

can be negative if 

emission of carbon 

from decomposition 

is greater than 

amount sequestered 

by healthy trees.

Carbon storage by trees is another way trees can infl uence global climate change. As trees 

grow, they store more carbon by holding it in their accumulated tissue. As trees die and 

decay, they release much of the stored carbon back to the atmosphere. Thus, carbon 

storage is an indication of the amount of carbon that can be released if trees are allowed 

to die and decompose. Maintaining healthy trees will keep the carbon stored in trees and 

when trees die, utilizing the wood in long-term wood products or to help heat buildings 

or produce energy will help reduce carbon emissions from wood decomposition or from 

power plants. Trees in Chicago are estimated to store 716,000 tons of carbon ($14.8 

million). Of all the species sampled, silver maple stores and sequesters the most carbon 

(approximately 14.8% of the total carbon stored and 10.7% of all sequestered carbon).

David Nowak, U.S. Forest Service

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

0

50,000

100,000

150,000

200,000

250,000

Sequestration (tons)

Storage (tons)

d.b.h. class

Carbon Storage 

Carbon Sequestration

0

10,000

20,000

30,000

40,000

50,000

60,000

0

500

1,000

1,500

2,000

2,500

3,000

Value ($)

Sequestration (tons)

Carbon Sequestration

U.S. Dollars

- -
9

Trees Affect Energy Use in Buildings

Trees affect energy consumption by shading buildings, providing evaporative cooling, 

and blocking winter winds. Trees tend to reduce building energy consumption in 

the summer months and can either increase or decrease building energy use in the 

winter months, depending on the location 

of trees around the building. Estimates of 

tree effects on energy use are based on fi eld 

measurements of tree distance and direction 

to space-conditioned residential buildings.9

Based on average state energy costs in 

February 2009, trees in Chicago are 

estimated to reduce energy costs from 

residential buildings by $360,000 annually. 

Trees are estimated to slightly increase the 

amount of carbon released by fossil-fuel 

based power plants. However, this estimated 

increase in emissions (1,200 tons) is more 

than offset by annual carbon sequestration by 

trees (25,200 tons).

Trees affect energy 

consumption by 

shading buildings, 

providing 

evaporative cooling, 

and blocking winter 

winds. 

Interactions 

between buildings 

and trees are 

estimated to reduce 

residential heating 

and cooling costs 

by $360,000 per 

year.

Annual energy savings due to trees near residential buildings.

Note: negative numbers indicate an increase in energy use or carbon emissions.

Heating Cooling Total

MBTUa -198,400 n/a -198,400

MWHb -1,700 20,600 18,900

Carbon avoided (t) -3,600 2,400 -1,200

a

Million British Thermal Units

b

Megawatt-hour

Annual savingsc (U.S. $) in residential energy expenditures during heating 

and cooling seasons. Note: negative numbers indicate a cost due to increased 

energy use or carbon emissions

Heating Cooling Total

MBTUa -1,808,000 n/a -1,808,000

MWHb -190,000 2,360,000 2,170,000

Carbon avoided -75,100 50,400 -24,700

a

Million British Thermal Units

b

Megawatt-hour

c

Based on state-wide energy costs

David Nowak, U.S. Forest Service

Dennis Haugen, U.S. Forest Service, bugwood.org
10

Structural and Functional Values

Urban forests have a structural value based on the tree itself (e.g., the cost of having 

to replace the tree with a similar tree). The structural value10 of the urban forest in 

Chicago is about $2.3 billion. The structural value of an urban forest tends to increase 

with a rise in the number and size of healthy trees.

Urban forests also have functional values (either positive or negative) based on the 

functions the tree performs. Annual functional values also tend to increase with 

increased number and size of healthy trees, and are usually on the order of several 

million dollars per year. There are many other functional values of the urban forest, 

though they are not quantifi ed here (e.g., reduction in air temperatures and ultra-violet 

radiation, improvements in water quality). Through proper management, urban forest 

values can be increased. However, the values and benefi ts also can decrease as the 

amount of healthy tree cover declines.

Structural values:

• Structural value: $2.3 billion

• Carbon storage: $14.8 million

Annual functional values:

• Carbon sequestration: $521,000

• Pollution removal: $6.4 million

• Reduced energy costs: $360,000

More detailed information on the urban forest in Chicago can be found at http://nrs.

fs.fed.us/data/urban. Additionally, information on other urban forest values can be 

found in Appendix I and information comparing tree benefi ts to estimates of average 

carbon emissions in the city, average automobile emissions, and average household 

emissions can be found in Appendix III.

Urban forests have 

a structural value 

based on the tree 

itself.

Urban forests also 

have functional 

values based on the 

functions the tree 

performs.

Large, healthy, 

long-lived trees 

provide the greatest 

structural and 

functional values.

A map of priority 

planting locations 

for Chicago is found 

in Appendix IV.

A list of tree species 

found in Chicago is 

in Appendix V.

Richard Webb, self-employed horticulturist, 

bugwood.org

0

50

100

150

200

250

300

350

Structural value (millions of dollars)
11

Potential Insect and Disease Impacts

Various insects and diseases can infest urban forests, potentially killing trees and 

reducing the health, value and sustainability of the urban forest. As various pests have 

differing tree hosts, the potential damage or risk of each pest will differ. Four exotic 

pests were analyzed for their potential impact: Asian longhorned beetle, gypsy moth, 

emerald ash borer, and Dutch elm disease.

The Asian longhorned beetle (ALB)16 is an insect that bores into and kills a wide range 

of hardwood species. This beetle, which has recently reappeared in the Chicago region 

after having been eradicated, represents a potential loss to the Chicago urban forest of 

$1.3 billion in structural value (53.6 percent of live tree population).

Asian longhorned 

beetle

Emerald ash borer

Gypsy moth

Kenneth R. Law 

USDA APHIS PPQ 

(www.invasive.org)

David Cappaert

Michigan State University

(www.invasive.org)

USDA Forest Service Archives 

(www.invasive.org)

Dutch elm disease

The gypsy moth (GM)17 is a defoliator that feeds on many species causing widespread 

defoliation and tree death if outbreak conditions last several years. This pest could 

potentially result in damage to or a loss of $595 million in structural value of 

Chicago’s trees (19.5 percent of live tree population).

Emerald ash borer (EAB)18 has killed thousands of ash trees in Michigan, Ohio, and 

Indiana. EAB has the potential to affect 11.9 percent of Chicago’s live tree population 

($295 million in structural value).

American elm, one of the most important street trees in the 20th century, has been 

devastated by Dutch elm disease (DED). Since fi rst reported in the 1930s, it has killed 

more than 50 percent of the native elm population in the United States.19 Although 

some elm species have shown varying degrees of resistance, Chicago possibly could lose 

USDA Forest Service 5.5 percent of its trees to this disease ($31 million in structural value).

0

200

400

600

800

1000

1200

1400

1600

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1,800,000

2,000,000

ALB GM EAB DED

Structural value ($ millions)

Number of trees

Population at risk

Compensatory Value
12

Chicago Parks

To help understand more about the trees in Chicago’s park land, which currently 

encompass approximately 7,700 acres, a separate analysis was conducted for parks in 

the city. For this analysis, only 6,300 acres of park land were sampled due to recent 

increases in park land and differences in GIS park boundary fi les at the time of the 

fi eld sample selection. Thus current park trees benefi ts are likely about 20 percent 

higher than reported here. During the sampling of the city of Chicago, 53 of the 745 

plots sampled fell within park land. Additional plots were sampled to bring the sample 

total in parks to 158 plots.

Orestek, CC-BY-SA license, 

commons.wikimedia.org

Chicago Parks 

contain:

• 274,000 trees

• Tree density of 

43.2 trees per 

acre

• At least 58 

different 

species of trees

Most common tree 

species in Chicago 

Parks

• Green ash

• European 

buckthorn

• Hawthorn

Legend

3DUNODQG

Chicago
13

Based on this sample, parks in Chicago are estimated to contain 274,000 trees (7.6 

percent of the city’s tree population) with an average tree density of 43.2 trees per acre. 

The most common live trees in parks are green ash (7.0 percent) followed by European 

buckthorn (6.7 percent) and hawthorn species (6.0 percent), however standing dead 

trees comprise 7.3 percent of the population. There were a total of 58 different species 

of trees sampled.

green ash

7.0%

European 

buckthorn

6.7%

hawthorn

6.0%

sugar maple

5.4%

buckthorn

5.4%

linden

5.3%

honeylocust

4.5%

mulberry

4.4% northern red 

oak

4.2%

white ash

4.1%

2ther Vpecies

47.0%

Park tree cover is estimated at 31.6 percent with an overall leaf area index (LAI) of 

1.3. The majority of the trees were less than or equal to 6 inches in diameter (59.0 

percent). The leaf surface area of parks trees is equal to 12.5 square miles.

0

5

10

15

20

25

30

35

Percent

dbh class (in.)

The ten most 

common species 

account for 53.0 

percent of the 

total park tree 

population.

Park tree cover is 

estimated at 31.6 

percent.

Park trees less than 

6 inches in diameter 

account for 59.0 

percent of the 

population.

David Cappaert, Michigan State University, 

bugwood.org, 5110042
14

Leaf area has a strong correlation with benefi ts that the trees produce for the ecosystem, 

such as pollution removal. Green ash contributes 12.1 percent of the leaf area in parks, 

followed by littleleaf linden (8.9 percent) and Norway maple (7.0 percent).

0

2

4

6

8

10

12

14

Percent

Park trees have an estimated structural value of $192 million. Additional functional 

benefi ts provided by park trees are:

Carbon storage: 52,700 tons ($1.1 million)

Carbon sequestration: 1,600 tons/year ($32,800/year)

Air pollution removal: 64 tons/year ($344,000/year)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

Structural Value (millions of dollars)

Tree species that 

contribute the most 

leaf surface area in 

parks are:

• green ash

• littleleaf linden

• Norway maple

Park trees remove 

about 1,600 tons of 

carbon per year and 

about 64 tons of air 

pollution per year.

David Nowak, U.S. Forest Service
15

The risk to park trees from various pests and diseases are:

• Asian longhorned beetle – potential threat to 134,300 trees (49.0 percent of 

park trees)

• Gypsy moth – potential threat to 83,400 trees (30.5 percent of park trees)

• Emerald ash borer – potential threat to 31,700 trees (11.6 percent of park trees)

• Dutch elm disease – potential threat to 9,200 trees (3.4 percent of park trees)

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

60,000,000

70,000,000

80,000,000

90,000,000

100,000,000

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

ALB GM EAB DED

U.S. Dollars

Number of Trees

Number of TreeV

Value

Data from this report provide the basis for a better understanding of the urban forest 

resource and the ecosystem services and values provided by this resource. Managers and 

citizens can use these data to help develop improved long-term management plans and 

policies to sustain a healthy urban tree population and ecosystem services for future 

generations. Improved planning and management to sustain healthy tree populations 

can lead to improved environmental quality and quality of life for Chicago’s residents.

Millennium Park in Chicago.

J. Crocker, CC-BY-SA license, commons.wikimedia.org

Asian longhorned 

beetle is a potential 

threat to 49.0 percent 

of the park trees.

Tree species 

with the greatest 

structural value are:

• green ash

• honeylocust

• bur oak

Pennsylvania Department of Conservation 

and Natural Resources, Forestry Archive, 

bugwood.org, 5017015
16

David Nowak, U.S. Forest Service

Chicago’s Urban Forestry Efforts

Mayor Richard M. Daley has made it a priority to improve and expand Chicago’s 

urban forest. Since 1989, Chicago has taken many steps toward this goal, including: 

commissioning the Chicago Urban Forest Climate Project to better understand the 

effects of vegetation infl uences local climate, energy use, and air quality; establishing 

the Bureau of Forestry within the Department of Streets and Sanitation to plant and 

maintain the over 540,000 parkway trees; taking aggressive action to limit the impact 

of harmful invasive species such as the Asian longhorned beetle, preventing the loss of 

more than half of our city trees; and developing a plan, Chicago’s Urban Forest Agenda 

2009, to address future challenges and set sustainable landscape goals for the city. 

These efforts refl ect the city’s strong commitment to protect and improve the quality 

of the urban forest and make Chicago a more livable city.

This report contributes to the signifi cant research efforts made to understand the role 

of the urban forest in mitigating and adapting to climate change. In 2008, Chicago 

released its Climate Action Plan outlining 26 strategies to reduce greenhouse gas 

emissions by 80 percent below 1990 levels by 2050, with the midterm reduction target 

of 15.1 million metric tons of CO2

 equivalents, or 25 percent below 1990 levels by 

2020 (CO2

 equivalent is the concentration of CO2 that would cause the same level 

of radiative forcing as a given type and concentration of greenhouse gas). Tree related 

strategies include expanding the tree canopy to mitigate emissions and adaptation 

actions to prepare the urban forest for a changing climate. For more information about 

the Chicago Climate Action Plan, visit www.chicagoclimateaction.org

A view toward the Sears Tower down Wentworth Avenue in Chicago.

A mcmurray, CC-BY-SA license, commons.wikimedia.org

Efforts made since 

1989 to improve and 

expand Chicago’s 

urban forest:

• Commissioned 

the Chicago 

Urban Forest 

Climate Project

• Established 

the Bureau of 

Forestry to plant 

and maintain 

parkway trees

• Acted to limit 

the impact of 

invasive species

• Developed 

Chicago’s 

Urban Forest 

Agenda 2009
17

Appendix I. Comparison of Urban Forests

A commonly asked question is, “How does this city compare to other cities?” Although comparison among cities 

should be made with caution as there are many attributes of a city that affect urban forest structure and functions, 

summary data are provided from other cities analyzed using the UFORE model.

I. City totals, trees only

City

% Tree 

cover

Number of 

trees

Carbon 

storage (tons)

Carbon 

sequestration 

(tons/yr)

Pollution 

removal 

(tons/yr)

Pollution value 

U.S. $

Calgary, Canadaa 7.2 11,889,000 445,000 21,400 326 2,357,000

Atlanta, GAb 36.7 9,415,000 1,344,000 46,400 1,663 12,213,000

Toronto, Canadac 20.5 7,542,000 992,000 40,300 1,212 8,952,000

New York, NYb 20.9 5,212,000 1,350,000 42,300 1,677 11,834,000

Chicago, ILd 17.2 3,585,000 716,000 25,200 888 6,398,000

Baltimore, MDe 21.0 2,627,000 597,000 16,200 430 3,123,000

Philadelphia, PAb 15.7 2,113,000 530,000 16,100 576 4,150,000

Washington, DCf 28.6 1,928,000 526,000 16,200 418 2,858,000

Boston, MAb 22.3 1,183,000 319,000 10,500 284 2,092,000

Woodbridge, NJg 29.5 986,000 160,000 5,560 210 1,525,000

Minneapolis, MNh 26.4 979,000 250,000 8,900 306 2,242,000

Syracuse, NYe 23.1 876,000 173,000 5,420 109 836,000

San Francisco, CAa 11.9 668,000 194,000 5,100 141 1,018,000

Morgantown, WVi 35.5 658,000 93,000 2,890 72 489,000

Moorestown, NJg 28.0 583,000 117,000 3,760 118 841,000

Jersey City, NJg 11.5 136,000 21,000 890 41 292,000

Freehold, NJg 34.4 48,000 20,000 545 22 162,000

II. Per acre values of tree effects

City

No. of 

trees

Carbon Storage 

(tons)

Carbon sequestration 

(tons/yr)

Pollution removal 

(lbs/yr)

Pollution value 

U.S. $

Calgary, Canadaa 66.7 2.5 0.12 3.7 13.2

Atlanta, GAb 111.6 15.9 0.55 39.4 144.8

Toronto, Canadac 48.3 6.4 0.26 15.5 57.3

New York, NYb 26.4 6.8 0.21 17.0 59.9

Chicago, ILd 24.3 4.8 0.17 12.0 43.3

Baltimore, MDe 50.8 11.6 0.31 16.6 60.4

Philadelphia, PAb 25.1 6.3 0.19 13.6 49.2

Washington, DCf 49.0 13.4 0.41 21.3 72.7

Boston, AMb 33.5 9.1 0.30 16.1 59.3

Woodbridge, NJg 66.5 10.8 0.38 28.4 102.9

Minneapolis, MNh 26.2 6.7 0.24 16.4 60.1

Syracuse, NYe 54.5 10.8 0.34 13.5 52.0

San Francisco, CAa 22.5 6.6 0.17 9.5 34.4

Morgantown, WVi 119.2 16.8 0.52 26.0 87.8

Moorestown, NJg 62.1 12.4 0.40 25.1 89.5

Jersey City, NJg 14.4 2.2 0.09 8.6 30.8

Freehold, NJg 38.3 16.0 0.44 34.9 130.1

Data collection group

a

 City personnel f Casey Trees Endowment Fund b

 ACRT, Inc. g New Jersey Department of Environmental Protection c

 University of Toronto h Davey Resource Group

d Various Departments of the City of Chicago i West Virginia University e

 U.S. Forest Service 
18

Appendix II. General Recommendations for Air Quality Improvement

Urban vegetation can directly and indirectly affect local and regional air quality by altering the urban atmospheric 

environment. Four main ways that urban trees affect air quality are:

Temperature reduction and other microclimatic effects

Removal of air pollutants

Emission of volatile organic compounds (VOC) and tree maintenance emissions

Energy conservation in buildings and consequent power plant emissions

The cumulative and interactive effects of trees on climate, pollution removal, and VOC and power plant 

emissions determine the overall impact of trees on air pollution. Cumulative studies involving urban tree impacts 

on ozone have revealed that increased urban canopy cover, particularly with low VOC emitting species, leads 

to reduced ozone concentrations in cities. Local urban forest management decisions also can help improve air 

quality.

Urban forest management strategies to help improve air quality include:

Strategy Reason

Increase the number of healthy trees Increase pollution removal

Sustain existing tree cover Maintain pollution removal levels

Maximize use of low VOC-emitting trees Reduces ozone and carbon monoxide formation

Sustain large, healthy trees Large trees have greatest per-tree effects

Use long-lived trees Reduce long-term pollutant emissions from planting and removal

Use low maintenance trees Reduce pollutants emissions from maintenance activities

Reduce fossil fuel use in maintaining vegetation Reduce pollutant emissions

Plant trees in energy conserving locations Reduce pollutant emissions from power plants

Plant trees to shade parked cars Reduce vehicular VOC emissions

Supply ample water to vegetation Enhance pollution removal and temperature reduction

Plant trees in polluted or heavily populated areas Maximizes tree air quality benefi ts

Avoid pollutant-sensitive species Improve tree health

Utilize evergreen trees for particulate matter Year-round removal of particles
19

Appendix III. Relative Tree Effects

The urban forest in Chicago provides benefi ts that include carbon storage and sequestration, and air pollutant 

removal. To estimate a relative value of these benefi ts, tree benefi ts were compared to estimates of average carbon 

emissions in the city20, average passenger automobile emissions21, and average household emissions.22

General tree information:

Average tree diameter (d.b.h.) = 7.7 in.

Median tree diameter (d.b.h.) = 4.3 in.

Average number of trees per person = 1.3

Number of trees sampled = 1,697

Number of species sampled = 103

Average tree effects by tree diameter:

The Chicago urban forest provides:

Carbon storage equivalent to:

Amount of carbon (C) emitted in city in 15 days or

Annual carbon emissions from 430,000 automobiles or 

Annual C emissions from 215,700 single family houses

Carbon monoxide removal equivalent to:

Annual carbon monoxide emissions from 86 automobiles or

Annual carbon monoxide emissions from 400 single family 

houses

Nitrogen dioxide removal equivalent to:

Annual nitrogen dioxide emissions from 10,200 automobiles 

or

Annual nitrogen dioxide emissions from 6,800 single family 

houses

Sulfur dioxide removal equivalent to:

Annual sulfur dioxide emissions from 110,400 automobiles 

or

Annual sulfur dioxide emissions from 1,900 single family 

houses

Particulate matter less than 10 micron (PM10) removal 

equivalent to:

Annual PM10 emissions from 809,000 automobiles or

Annual PM10 emissions from 78,100 single family houses

Annual C sequestration equivalent to:

Amount of C emitted in city in 0.5 days or

Annual C emissions from 15,100 automobiles or

Annual C emissions from 7,600 single family homes

a

 miles = number of automobile miles driven that produces emissions equivalent to tree effect

Carbon sequestration

Pollution

Carbon storage removal

D.b.h.

Class (inch) (lbs) ($) (miles) a (lbs/yr) ($/yr) (miles)a (lbs) ($)

1-3 6 0.06 20 1.8 0.02 6 0.05 0.17

3-6 37 0.38 130 5.5 0.06 20 0.2 0.60

6-9 127 1.32 470 10.9 0.11 40 0.4 1.56

9-12 304 3.15 1,110 17.6 0.18 65 0.7 2.65

12-15 538 5.56 1,970 23.8 0.25 87 1.1 3.99

15-18 859 8.89 3,150 32.4 0.34 119 1.2 4.48

18-21 1,286 13.31 4,710 42.8 0.44 157 1.7 5.95

21-24 1,709 17.68 6,260 48.3 0.50 177 1.5 5.50

24-27 2,258 23.36 8,270 60.0 0.62 220 1.8 6.48

27-30 3,116 32.24 11,410 72.0 0.75 264 2.7 9.81

30+ 5,160 53.38 18,900 95.7 0.99 350 2.7 9.86
20

Appendix IV. Tree Planting Index Map

To determine the best locations to plant trees, high resolution tree canopy and impervious cover maps from 

Chicago12 were used in conjunction with 2000 U.S. Census data to produce an index of priority planting areas. 

Index values were produced for each census block group with the higher the index value, the higher the priority 

of the area for tree planting. This index is a type of “environmental equity” index with areas with higher human 

population density and lower tree cover tending to get the higher index value. The criteria used to make the index 

were:

• Population density: the greater the population density, the greater the priority for tree planting

• Tree stocking levels: the lower the tree stocking level (the percent of available greenspace (tree, grass, and 

soil cover areas) that is occupied by tree canopies), the greater the priority for tree planting

• Tree cover per capita: the lower the amount of tree canopy cover per capita (m2

/capita), the greater the 

priority for tree planting

Each criteria was standardized23 on a scale of 0 to 1 with 1 representing the census block group with the highest 

value in relation to priority of tree planting (i.e., the census block group with highest population density, lowest 

stocking density or lowest tree cover per capita were standardized to a rating of 1). Individual scores were 

combined and standardized based on the following formula to produce an overall priority planting index (PPI) 

value between 0 and 100:

PPI = (PD * 40) + (TS * 30) + (TPC * 30)

Where PPI = index value, PD is standardized population density, TS is standardized tree stocking, and TPC is 

standardized tree cover per capita.

0 3 6 9 12 1.5

Kilometers

Chicago

Legend

PPI

0.0 - 10.0

10.1 - 20.0

20.1 - 30.0

30.1 - 40.0

40.1 - 50.0

50.1 - 60.0

60.1 - 70.0

70.1 - 80.0

80.1 - 90.0

90.1 - 100.0

NA
21

Appendix V. List of Species Sampled in Chicago

Continued

% % Potential pest b

Genus Species Common Name Population Leaf Area IVa ALB GM EAB DED

Acer negundo Boxelder 3.5 1.3 4.8 

Acer palmatum Japanese maple 0.3 0.1 0.4 

Acer platanoides Norway maple 4.0 11.4 15.4 

Acer rubrum Red maple 0.7 1.0 1.7 

Acer saccharinum Silver maple 4.6 12.5 17.1 

Acer saccharum Sugar maple 2.2 2.4 4.6 

Acer species Maple 0.1 0.2 0.3 

Aesculus species Buckeye species 0.1 0.1 0.2 

Ailanthus altissima Tree of heaven 4.7 2.6 7.3

Amelanchier arborea Downy serviceberry 0.1 <0.1 0.1

Amelanchier species Serviceberry 0.3 <0.1 0.3

Betula nigra River birch 0.5 0.1 0.6  

Betula papyrifera Paper birch 0.1 0.2 0.3  

Betula populifolia Gray birch 0.1 <0.1 0.1  

Carpinus caroliniana American hornbeam 0.1 <0.1 0.1

Carya ovata Shagbark hickory 0.1 <0.1 0.1

Carya species Hickory 0.2 0.1 0.3

Catalpa species Catalpa 0.2 0.3 0.5

Catalpa speciosa Northern catalpa 0.4 0.3 0.7

Celtis occidentalis Northern hackberry 1.7 2.2 3.9

Celtis occidentalis Common hackberry 0.2 <0.1 0.2

Celtis species Hackberry 0.2 <0.1 0.2

Cercis canadensis Eastern redbud 0.3 0.1 0.4

Cornus fl orida Flowering dogwood 0.1 <0.1 0.1

Cornus species Dogwood 0.1 <0.1 0.1

Cotinus coggygria Smoke tree 0.1 <0.1 0.1 

Crataegus crus-galli Cockspur hawthorn 0.3 <0.1 0.3 

Crataegus phaenopyrum Washington hawthorn 0.3 0.3 0.6 

Crataegus species Hawthorn 3.3 1.7 5.0 

Elaeagnus angustifolia Russian olive 0.1 0.1 0.2 

Euonymus atropurpureus Eastern wahoo 0.1 <0.1 0.1

Fraxinus americana White ash 6.0 3.9 9.9  

Fraxinus nigra Black ash 0.1 0.1 0.2  

Fraxinus pennsylvanica Green ash 4.9 7.5 12.4  

Fraxinus species Ash 0.3 <0.1 0.3  

Ginkgo biloba Ginkgo 0.1 0.1 0.2

Gleditsia triacanthos Honeylocust 3.3 2.6 5.9
22

Appendix V continued.

Continued

% % Potential pest b

Genus Species Common Name Population Leaf Area IVa ALB GM EAB DED

Gymnocladus dioicus Kentucky coffeetree 0.2 <0.1 0.2

Hamamelis virginiana Witch hazel 0.1 <0.1 0.1 

Hibiscus syriacus Rose-of-sharon 0.5 <0.1 0.5 

Juglans nigra Black walnut 0.4 1.4 1.8

Juniperus species Juniper 0.9 0.1 1.0

Juniperus virginiana Eastern red cedar 0.8 0.3 1.1

Ligustrum species Privet 0.4 <0.1 0.4

Ligustrum vulgare Common privet 0.2 <0.1 0.2

Liquidambar styracifl ua Sweetgum 0.2 0.1 0.3 

Lonicera species Honeysuckle 0.1 <0.1 0.1

Magnolia denudata Chinese magnolia 0.2 0.1 0.3

Magnolia species Magnolia 0.1 0.1 0.2

Malus pumila Apple 0.1 0.1 0.2  

Malus species Crabapple 1.3 1.3 2.6  

Morus alba White mulberry 0.1 0.5 0.6

Morus rubra Red mulberry 0.3 0.2 0.5

Morus species Mulberry 5.2 5.6 10.8

Other species Other species 0.6 0.6 1.2

Picea abies Norway spruce 0.3 0.8 1.1

Picea pungens Blue spruce 1.0 0.8 1.8

Picea species Spruce 0.5 0.7 1.2

Pinus resinosa Red pine 0.1 <0.1 0.1

Pinus species Pine 0.4 0.1 0.5

Pinus strobus Eastern white pine 0.4 0.1 0.5

Platanus occidentalis American sycamore 0.2 1.3 1.5 

Populus alba White poplar 0.2 0.1 0.3 

Populus deltoides Eastern cottonwood 3.2 6.0 9.2 

Populus species Aspen 0.4 0.3 0.7  

Populus tremuloides Quaking aspen 0.1 0.1 0.2  

Prunus cerasifera Cherry plum 0.1 0.1 0.2 

Prunus persica Nectarine 0.2 <0.1 0.2 

Prunus serotina Black cherry 1.3 1.2 2.5 

Prunus serrulata Kwanzan cherry 0.4 0.4 0.8 

Prunus species Cherry 1.6 0.6 2.2 

Prunus virginiana Common chokecherry 0.2 <0.1 0.2 

Pyrus calleryana Callery pear 0.2 <0.1 0.2 

Pyrus species Pear 0.3 0.1 0.4 
23

Appendix V continued.

% % Potential pest b

Genus Species Common Name Population Leaf Area IVa ALB GM EAB DED

Quercus alba White oak 0.8 1.0 1.8 

Quercus macrocarpa Bur oak 0.4 1.8 2.2 

Quercus muehlenbergii Chinkapin oak 0.1 <0.1 0.1 

Quercus palustris Pin oak 0.2 0.5 0.7 

Quercus rubra Northern red oak 1.7 2.5 4.2 

Quercus x macnabiana McNab’s oak 0.2 0.2 0.4 

Rhamnus cathartica European buckthorn 4.5 0.7 5.2

Rhamnus species Buckthorn 2.3 0.6 2.9

Rhododendron species Rhododendron 0.2 <0.1 0.2

Rhus typhina Staghorn sumac 0.1 <0.1 0.1 

Robinia pseudoacacia Black locust 0.5 0.8 1.3 

Salix exigua Sandbar willow 0.1 <0.1 0.1  

Salix species Willow 0.1 <0.1 0.1  

Syringa reticulata Japanese tree lilac 0.2 <0.1 0.2

Syringa species Lilac 0.9 0.1 1.0

Taxus species Yew 1.7 0.4 2.1

Thuja occidentalis Northern white cedar 3.0 0.5 3.5

Tilia americana American basswood 1.6 3.0 4.6  

Tilia cordata Littleleaf linden 1.5 5.0 6.5  

Tilia species Linden 2.0 1.8 3.8  

Tilia tomentosa Silver linden 0.1 0.2 0.3  

Ulmus americana American elm 4.5 3.9 8.4  

Ulmus parvifolia Chinese elm 0.4 0.8 1.2  

Ulmus pumila Siberian elm 1.6 1.4 3.0 

Ulmus rubra Slippery elm 0.1 <0.1 0.1  

Ulmus species Elm 0.7 0.2 0.9  

Viburnum prunifolium Black haw 0.4 0.1 0.5

Viburnum species Viburnum 1.0 0.2 1.2

Viburnum trilobum High-bush cranberry 0.1 <0.1 0.1

a

 IV = importance value (% population + % leaf area)

b

 ALB = Asian longhorned beetle; GM = gypsy moth; EAB = emerald ash borer; DED = Dutch elm disease

Note: 3.8 percent of the population was classifi ed as dead and is not included in this table
24

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home. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Area 

State and Private Forestry. http://www.na.fs.fed.us/

fhp/eab

19 Stack, R.W.; McBride, D.K.; Lamey, H.A. 1996. 

Dutch elm disease. PP-324 (revised). Fargo, 

ND: North Dakota State University, Cooperative 

Extension Service. http://www.ext.nodak.edu/

extpubs/plantsci/trees/pp324w.htm
26

Explanation of Calculations of Appendix III and IV

20 Total city carbon emissions were based on 2003 

U.S. per capita carbon emissions, calculated as 

total U.S. carbon emissions (Energy Information 

Administration, 2003, Emissions of Greenhouse 

Gases in the United States 2003. http://www.eia.

doe.gov/oiaf/1605/1605aold.html) divided by 

2003 total U.S. population (www.census.gov). Per 

capita emissions were multiplied by Minneapolis 

population to estimate total city carbon emissions.

21 Average passenger automobile emissions per 

mile were based on dividing total 2002 pollutant 

emissions from light-duty gas vehicles (National 

Emission Trends http://www.epa.gov/ttn/chief/

trends/index.html) by total miles driven in 2002 by 

passenger cars (National Transportation Statistics 

http://www.bts.gov/publications/national_

transportation_statistics/2004/).

Average annual passenger automobile emissions 

per vehicle were based on dividing total 2002 

pollutant emissions from light-duty gas vehicles 

by total number of passenger cars in 2002 

(National Transportation Statistics http://www.

bts.gov/publications/national_transportation_

statistics/2004/).

Carbon dioxide emissions from automobiles 

assumed 6 pounds of carbon per gallon of gasoline 

with energy costs of refi nement and transportation 

included (Graham, R.L.; Wright, L.L.; Turhollow, 

A.F. 1992. The potential for short-rotation woody 

crops to reduce U.S. CO2

 emissions. Climatic 

Change. 22: 223-238.)

22 Average household emissions based on average 

electricity kWh usage, natural gas Btu usage, fuel oil 

Btu usage, kerosene Btu usage, LPG Btu usage, and 

wood Btu usage per household from:

Energy Information Administration. Total Energy 

Consumption in U.S. Households by Type of 

Housing Unit, 2001 www.eia.doe.gov/emeu/recs/

recs2001/detailcetbls.html. 

CO2

, SO2, and NOx power plant emission per 

KWh from:

U.S. Environmental Protection Agency. U.S. 

power plant emissions total by year www.epa.gov/

cleanenergy/egrid/samples.htm.

CO emission per kWh assumes one-third of 1 

percent of C emissions is CO based on:

Energy Information Administration. 1994. 

Energy use and carbon emissions: non-OECD 

countries. DOE/EIA-0579(94). Washington, 

DC: Department of Energy, Energy Information 

Administration. http://tonto.eia.doe.gov/bookshelf

PM10 emission per kWh from: 

Layton, M. 2004. 2005 Electricity environmental 

performance report: electricity generation and air 

emissions. Sacramento, CA: California Energy 

Commission. 

http://www.energy.ca.gov/2005_energypolicy/

documents/2004-11-15_workshop/2004-11-

15_03-A_LAYTON.PDF

CO2

, NOx, SO2, PM10, and CO emission per Btu 

for natural gas, propane and butane (average used 

to represent LPG), Fuel #4 and #6 (average used to 

represent fuel oil and kerosene) from:

Abraxas energy consulting. http://www.

abraxasenergy.com/emissions/ 

CO2

 and fi ne particle emissions per Btu of wood 

from:

 Houck, J.E.; Tiegs, P.E.; McCrillis, R.C.; Keithley, 

C.; Crouch, J. 1998. Air emissions from residential 

heating: the wood heating option put into 
27

environmental perspective. In: Proceedings of U.S. 

EPA and Air and Waste Management Association 

conference: living in a global environment, V.1: 

373-384.

CO, NOx and SOx emission per Btu of wood based 

on total emissions from wood burning (tonnes) 

from: 

Residential Wood Burning Emissions in British 

Columbia. 2005. http://www.env.gov.bc.ca/air/

airquality/pdfs/wood_emissions.pdf.

Emissions per dry tonne of wood converted to 

emissions per Btu based on average dry weight per 

cord of wood and average Btu per cord from:

Kuhns, M.; Schmidt, T. 1988. Heating with wood: 

species characteristics and volumes I. NebGuide 

G-88-881-A. Lincoln, NE: University of Nebraska, 

Institute of Agriculture and Natural Resources, 

Cooperative Extension.

23 Standardized value for population density was 

calculated as PD = (n – m)/r, where PD is the 

value (0-1), n is the value for the census block 

(population / km2

), m is the minimum value for all 

census blocks, and r is the range of values among all 

census blocks (maximum value – minimum value). 

Standardized value for tree stocking was calculated 

as TS = 1 – [t/(t+g)], where TS is the value (0-1), 

t is percent tree cover, and g is percent grass cover. 

Standardized value for tree cover per capita was 

calculated as TPC = 1 – [(n – m)/r], where TPC is 

the value (0-1), n is the value for the census block 

(m2

/capita), m is the minimum value for all census 

blocks, and r is the range of values among all census 

blocks (maximum value – minimum value).
Printed on Recycled Paper

Nowak, David J.; Hoehn, Robert E. III; Crane, Daniel E.; Stevens, Jack C.; Leblanc 

Fisher, Cherie. 2010. Assessing urban forest effects and values, Chicago’s 

urban forest. Resour. Bull. NRS-37. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northern Research Station. 27 p.

An analysis of trees in Chicago, IL, reveals that this city has about 3,585,000 trees 

with canopies that cover 17.2 percent of the area. The most common tree species 

are white ash, mulberry species, green ash, and tree-of-heaven. Chicago’s urban 

forest currently stores about 716,000 tons of carbon valued at $14.8 million. In 

addition, these trees remove about 25,200 tons of carbon per year ($521,000 per 

year) and about 888 tons of air pollution per year ($6.4 million per year). Trees in 

Chicago are estimated to reduce annual residential energy costs by $360,000 per 

year. The structural, or compensatory, value is estimated at $2.3 billion. Information 

on the structure and functions of the urban forest can be used to inform urban 

forest management programs and to integrate urban forests within plans to improve 

environmental quality in the Chicago area.

KEY WORDS: urban forestry, ecosystem services, air pollution removal, carbon 

sequestration, tree value
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