Assessing Urban Forest 

Effects and Values

Northeastern 

Research Station

Resource Bulletin NE-166

United States

Department of 

Agriculture

Forest Service

Minneapolis’ 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

May 2006 Fax: (740)368-0152

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

Abstract

An analysis of trees in Minneapolis, MN, reveals that the city has about 979,000 trees with 

canopies that cover 26.4 percent of the area. The most common tree species are green ash, 

American elm, and boxelder. The urban forest currently stores about 250,000 tons of carbon 

valued at $4.6 million. In addition, these trees remove about 8,900 tons of carbon per year 

($164,000 per year) and trees and shrubs combined remove about 384 tons of air pollution 

per year ($1.9 million per year). The structural, or compensatory, value is estimated at $756 

million. Information on the structure and functions of the urban forest can be used to improve 

and augment support for urban forest management programs and to integrate urban forests 

within plans to improve environmental quality in the Minneapolis area.

The Authors

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

biological sciences technician, DANIEL E. CRANE is an information technology specialist, 

JACK C. STEVENS is a forester, and JEFFREY T. WALTON is a research forester with 

the Forest Service’s Northeastern Research Station at Syracuse, NY. JERRY BOND is a 

consulting urban forester and GREG INA is a manager of geographic information systems/

information technology with the Davey Resource Group at Kent, OH.
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 USDA Forest Service, Northeastern 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 for 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, such as 

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 Minneapolis, a vegetation assessment was conducted during the summer of 2004. 

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 • Carbon storage

• Risk of insect pests and diseases • Annual carbon removal (sequestration)

• Air pollution removal • Changes in building energy use

More detailed information can be found at: www.fs.fed.us/ne/syracuse/Data/data.htm.

Urban forests 

provide numerous 

benefi ts to society, 

yet relatively little 

is known about this 

important resource.

In 2004, the UFORE 

model was used to 

survey and analyze 

Minneapolis’ urban 

forest.

The calculated 

environmental 

benefi ts of the 

Minneapolis 

urban forest 

are signifi cant, 

yet many 

environmental and 

social benefi ts 

still remain to be 

quantifi ed.

Minneapolis Urban Forest Summary

Feature Measure

Number of trees 979,000

Tree cover 26.4%

Most common species green ash, American elm, 

boxelder

Percentage of trees 

 < 6-inches diameter

47.3%

Pollution removal 384 tons/year ($1.9 million/year)

Carbon storage 250,000 tons ($4.6 million)

Carbon sequestration 8,900 tons/year ($164,000/year)

Building energy reduction $216,000/year

Avoided carbon emissions $16,000/year

Structural values $756 million

Ton – short ton (U.S.) (2,000 lbs)
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. To help assess the city’s urban forest, data from 110 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 energy use in buildings and consequent effects on carbon 

dioxide emissions from power plants.

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

and carbon storage and sequestration.

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

borers, gypsy moth, and Dutch elm disease.

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

In the fi eld, one-tenth acre plots were randomly located within a grid pattern at a 

density of approximately one plot every 340 acres. In Minneapolis, service districts 

were used to divide the analysis into smaller 

zones. The plots were divided among the 

following service districts: River District 

(49 plots), Lakes District (31 plots), and 

Minnehaha District (30 plots).

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
3

Field data were collected by Davey Resource Group during the leaf-on season to 

properly assess tree canopies. Within each plot, data included land use, 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 energy use in residential 

building was 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.fs.fed.us/ne/syracuse/Data/data.htm or www.ufore.org

Field Survey Data

Plot Information

• Land use type

• Percent tree cover

• Percent shrub 

cover

• Percent plantable

• Percent ground 

cover types

• Shrub species / 

dimensions

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
4

Tree Characteristics of the Urban Forest

The urban forest of Minneapolis has an estimated 979,000 trees and a tree cover of 

26.4 percent. Trees with diameters less than 6 inches account for 47.3 percent of the 

population. The three most common species are green ash (21.6 percent), American 

elm (17.1 percent), and boxelder (9.1 percent). The 10 most common species account 

for 75 percent of all trees; their relative abundance is illustrated below.

There are an 

estimated 979,000 

trees in Minneapolis 

with canopies that 

cover 26.4 percent 

of the city.

The 10 most 

common species 

account for 75 

percent of the total 

number of trees.

Tree density is 

highest in the Lakes 

District, lowest in 

the River District.

American elm

white mulberry

northern

hackberry

Norway maple

blue spruce

silver maple

northern white 

cedar

boxelder

Austrian pine

green ash

other species

The highest density of trees occurs in the Lakes District (31.6 trees/acre), followed by 

the Minnehaha District (29.0 trees/acre) and the River District (19.8 trees/acre). The 

overall tree density in Minneapolis is 26.2 trees/acre, which is within the range of other 

city tree densities (Appendix I), of 14.4 to 119.2 trees/acre.

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

River District Lakes District Minnehaha District

Number of Trees

0

5

10

15

20

25

30

35

Trees per acre

Total Trees

Per acre
5

Urban forests are a mix of native trees 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 exotics species are invasive plants 

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

80 percent of the trees are species native to North America, while 74 percent are native 

to the state. Species exotic to Minnesota make up 26 percent of the population. Most 

exotic tree species have an origin from Eurasia (9.2 percent of the species).

Nearly threequarters of the 

tree species in 

Minneapolis are 

native to Minnesota.

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.

*North America + refers to tree species that are native to North America and one other continent.

0

5

10

15

20

25

30

1-34-67-9

10-1213-1516-1819-2122-2425-2728-30

30+

d.b.h. class

Percent

0

10

20

30

40

50

60

70

80

90

100

North America

Minnesota

Eurasia

Asia

North America +

Europe

Unknown

Percent

*
6

Urban Forest Cover and Leaf Area

Trees cover about 26.4 percent of Minneapolis and shrubs cover 6 percent of the city. 

Dominant ground cover types include herbaceous (e.g., grass, gardens) (34.0 percent), 

impervious surfaces (excluding buildings) (e.g., driveways, sidewalks, parking lots) 

(33.6 percent), and buildings (18.0 percent).

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

the plant. In Minneapolis, trees that dominate in terms of leaf area are green ash, 

American elm, and silver maple.

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

(species with percentage of canopy much greater than percentage of population) are 

silver maple, bur oak, and sugar maple. Smaller trees in the population are American 

basswood, northern white cedar, and boxelder (species with percentage of canopy 

much less than percentage of 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.

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

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

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

Healthy leaf area 

equates directly 

to tree benefi ts 

provided to the 

community.

Green ash has the 

greatest importance 

to the Minneapolis 

urban forest based 

on relative leaf 

area and relative 

population.

Common 

 Name

%

Popa

%

LAb IVc

green ash 21.6 24.8 46.4

American 

 elm

17.1 16.1 33.2

silver maple 3.3 10.5 13.8

Norway 

 maple

4.2 7.6 11.8

boxelder 9.1 1.4 10.5

northern 

 hackberry

4.3 4.0 8.3

bur oak 1.9 5.4 7.3

white 

 mulberry

4.3 1.2 5.5

northern 

 white cedar

4.8 0.9 5.7

0

5

10

15

20

25

green ash

American elm

silver maple

Norway

maple

Bur oak

northern hackberry

Siberian elm

Sugar maple

Austrian pine

boxelder

Percent

% of total leaf area

% of all trees

a

Percent population

bPercent leaf area

c

Importance value (%Pop + %LA)

water

bare soil

herbaceous

0 10 20 30 40 50 60 70 80 90 100

River District

Lakes District

Minnehaha District

Minneapolis

Percent

duff/mulch cover

impervious surfaces (excluding buildings)

buildings
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 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.12

Pollution removal by trees and shrubs in Minneapolis was estimated using fi eld data 

and hourly pollution and weather data for 2000. Pollution removal was greatest for 

particulate matter less than ten microns (PM10), followed by ozone (O3

), nitrogen 

dioxide (NO2

), sulfur dioxide (SO2), and carbon monoxide (CO). It is estimated that 

trees and shrubs remove 384 tons of air pollution (CO, NO2

, O3, PM10, SO2) per 

year with an associated value of $1.9 million (based on estimated national median 

externality costs associated with pollutants13). Trees remove about four times more air 

pollution than shrubs in Minneapolis.

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

estimated to be:

• O3

 0.58% • NO2 0.36%

• PM10 0.57% • CO 0.002%

• SO2

 0.57%

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

(100% tree cover) was estimated to be:

• O3

 14.9% • NO2 7.2%

• PM10 11.1% • CO 0.05%

• SO2

 15.5%

The urban forest 

of Minneapolis 

removes about 384 

tons of pollutants 

each year, with a 

value to society of 

$1.9 million/year.

General urban 

forest management 

recommendations 

to improve air 

quality are given in 

Appendix II.

0

20

40

60

80

100

120

140

160

CO NO2 O3 PM10 SO2

Pollution removed (tons) 

0

100

200

300

400

500

600

700

800

900

1000

Dollars (thousands) 

Pollution Removed

Value (U.S. Dollars)

2 3 10 2
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, consequently reducing carbon dioxide emissions 

from fossil-fuel based power plants.14

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. Minneapolis’ trees gross sequestration is 

about 8,900 tons of carbon per year with an associated value of $164,000. Net carbon 

sequestration in the Minneapolis urban forest is about 4,200 tons.

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

American

elm

green

ash

honeylocust

Norway

maple

silver maple

bur oak

boxelder

blue

spruce

white

mulberry

northern

catalpa

Sequestration (tons)

-3,000

2,000

7,000

12,000

17,000

22,000

27,000

32,000

Value (U.S. dollars)

0

20,000

40,000

60,000

80,000

100,000

120,000

0 - 33 - 66 - 9

9 - 12

12 - 1515 - 1818 - 21

21 - 2424 - 27

27 - 30

30+

d.b.h. class

Storage (tons)

0

500

1,000

1,500

2,000

2,500

Sequestration (tons)

Carbon Storage 

Carbon Sequestration

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 into the atmosphere. Thus, 

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

allowed to die and decompose. Trees in Minneapolis are estimated to store 250,000 

tons of carbon ($4.6 million). Of all the species sampled, American elm stores and 

sequesters the most carbon (about 18.6 percent of the total carbon stored and 19.2 

percent of all sequestered carbon).
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 2002 energy costs, trees in Minneapolis are estimated to reduce energy costs 

from residential buildings by $221,000 annually. Trees also provide an additional 

$15,900 in value by reducing the amount of carbon released by fossil-fuel based power 

plants (a reduction of 900 tons of carbon emissions).

Trees affect energy 

consumption by 

shading buildings, 

providing 

evaporative cooling, 

and blocking winter 

winds. 

Interactions 

between buildings 

and trees save an 

estimated $221,000 

in heating and 

cooling costs.

Lower energy use in 

residential buildings 

reduced carbon 

emissions from 

power plants by 900 

tons ($15,900).

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 -174,000 n/a -174,000

MWHb -1,100 17,900 16,800

Carbon avoided (t) -3,100 4,000 900 

a

Million British Thermal Units

b

Megawatt-hour

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

heating and cooling seasons. Note: negative numbers indicate a cost 

due to increased energy use or carbon emissions.

Heating Cooling Total 

MBTUa -1,182,000 n/a -1,182,000

MWHb -96,000 1,499,000 1,403,000

Carbon avoided -57,500 73,400 15,900

a

Million British Thermal Units

b

Megawatt-hour

c

Based on state-wide energy cost
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 urban forest in 

Minneapolis is about $756 million. 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 ultraviolet 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: $756 million

• Carbon storage: $4.6 million

Annual functional values:

• Carbon sequestration: $164,000

• Pollution removal: $1.9 million

• Lower energy costs and carbon emission reductions: $237,000

More detailed information on the urban forest in Minneapolis can be found at www.

fs.fed.us/ne/syracuse/Data/data.htm. Additionally, information on other urban 

forest values can be found in Appendix I and information comparing tree benefi ts to 

estimates of average carbons 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.

0

20

40

60

80

100

120

140

160

green

ash

American

elm

honeylocust

silver maple

bur oak

Norway maple

boxelder

northern

hackberry

blue spruce

northern white cedar

Structural value (millions of dollars)
11

Asian longhorned 

beetle

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)15 is an insect that bores into and kills a wide range 

of hardwood species. ALB represents a potential loss to the Minneapolis urban forest 

of $487 million in structural value (68.1 percent of the tree population).

The gypsy moth (GM)16 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 a loss of $80 million in structural value (10.1 percent of the tree 

population).

Emerald ash borer (EAB)17 has killed thousands of ash trees in Michigan, Ohio, and 

Indiana. EAB has the potential to affect 22.0 percent of the population ($148 million 

in structural value).

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

devastated by the 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.18

Although some elm species have shown varying degrees of resistance, Minneapolis 

possibly could lose 17.1 percent of its trees to this disease ($141 million in structural 

value).

0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

ALB GM EAB DED

Number of trees

0

100

200

300

400

500

600

Compensatory value ($ millions)

Population at risk

Compensatory Value

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)
12

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 1,611,000

Atlanta, GAb 36.7 9,415,000 1,344,000 46,400 1,663 8,321,000

Toronto, Canadac 20.5 7,542,000 992,000 40,300 1,212 6,105,000

New York, NYb 20.9 5,212,000 1,350,000 42,300 1,677 8,071,000

Baltimore, MDd 21.0 2,627,000 597,000 16,200 430 2,129,000

Philadelphia, PAb 15.7 2,113,000 530,000 16,100 576 2,826,000

Washington, DCe 28.6 1,928,000 523,000 16,100 418 1,956,000

Boston, MAb 22.3 1,183,000 319,000 10,500 284 1,426,000

Woodbridge, NJf 29.5 986,000 160,000 5,560 210 1,037,000

Minneapolis, MNg 26.4 979,000 250,000 8,900 306 1,527,000

Syracuse, NYd 23.1 876,000 173,000 5,420 109 568,000

San Francisco, CAa 11.9 668,000 194,000 5,100 141 693,000

Morgantown, WVh 35.5 658,000 93,000 2,890 72 333,000

Moorestown, NJf 28.0 583,000 117,000 3,760 118 576,000

Jersey City, NJf 11.5 136,000 21,000 890 41 196,000

Freehold, NJf 34.4 48,000 20,000 545 22 110,000

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 9.0

Atlanta, GAb 111.6 15.9 0.55 39.4 98.6

Toronto, Canadac 48.3 6.4 0.26 15.5 39.1

New York, NYb 26.4 6.8 0.21 17.0 40.9

Baltimore, MDd 50.8 11.6 0.31 16.6 41.2

Philadelphia, PAb 25.1 6.3 0.19 13.6 33.5

Washington, DCe 49.0 13.3 0.41 21.3 49.7

Boston, MAb 33.5 9.1 0.30 16.1 40.4

Woodbridge, NJf 66.5 10.8 0.38 28.4 70.0

Minneapolis, MNg 26.2 6.7 0.24 16.4 40.9

Syracuse, NYd 54.5 10.8 0.34 13.5 35.4

San Francisco, CAa 22.5 6.6 0.17 9.5 23.4

Morgantown, WVh 119.2 16.8 0.52 26.0 60.3

Moorestown, NJf 62.1 12.4 0.40 25.1 61.3

Jersey City, NJf 14.4 2.2 0.09 8.6 20.7

Freehold, NJf 38.3 16.0 0.44 34.9 88.2

Data collection group

a

 City personnel e Casey Trees Endowment Fund b

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

 University of Toronto g Davey Resource Group d

 U.S. Forest Service h West Virginia University
13

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
14

Appendix III. Relative Tree Effects

The urban forest in Minneapolis 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 city19, average passenger automobile emissions20, and average household emissions.21

General tree information:

Average tree diameter (d.b.h.) = 10.3 in.

Median tree diameter (d.b.h.) = 6.7 in.

Average number of trees per person = 2.6

Number of trees sampled = 278

Number of species sampled = 41

Average tree effects by tree diameter:

Carbon storage Carbon sequestration

Pollution

removal

D.b.h. 

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

1-3 8 0.08 30 2.4 0.02 9 0.4 0.86

3-6 44 0.40 160 6.2 0.06 23 0.4 0.95

6-9 124 1.15 460 12.0 0.11 44 0.6 1.34

9-12 268 2.47 980 18.7 0.17 69 0.8 1.86

12-15 483 4.45 1,770 24.5 0.23 90 0.8 1.81

15-18 721 6.64 2,640 30.3 0.28 111 0.9 2.01

18-21 1,068 9.84 3,910 37.7 0.35 138 0.8 1.84

21-24 1,303 12.00 4,770 40.7 0.37 149 0.9 1.99

24-27 1,516 13.97 5,550 31.4 0.29 115 1.7 3.75

27-30 2,883 26.55 10,560 75.3 0.69 276 0.7 1.69

30+ 4,338 39.96 15,890 91.2 0.84 334 1.1 2.51

a

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

The Minneapolis urban forest provides:

Carbon storage equivalent to:

Amount of carbon (C) emitted in city in 40 days or

Annual C emissions from 150,000 automobiles or 

Annual C emissions from 75,500 single family houses 

Carbon monoxide removal equivalent to:

Annual carbon monoxide emissions from 31 automobiles or

Annual carbon monoxide emissions from 100 single family 

houses 

Nitrogen dioxide removal equivalent to:

Annual nitrogen dioxide emissions from 2,900 automobiles or

Annual nitrogen dioxide emissions from 1,900 single family 

houses 

Sulfur dioxide removal equivalent to:

Annual sulfur dioxide emissions from 19,900 automobiles or

Annual sulfur dioxide emissions from 300 single family houses 

Particulate matter less than 10 micron (PM10) removal 

equivalent to:

Annual PM10 emissions from 315,600 automobiles or

Annual PM10 emissions from 30,500 single family houses 

Annual C sequestration equivalent to:

Amount of C emitted in city in 1.4 days or

Annual C emissions from 5,300 automobiles or

Annual C emissions from 2,700 single family homes
15

Appendix IV. List of Species Sampled in Minneapolis

Continued

Potential pest b

Genus Species Common Name % Population % Leaf Area IV a ALB GM EAB DED

Abies concolor white fi r 0.3 0.9 1.2

Acer negundo boxelder 9.1 1.4 10.5 o

Acer platanoides Norway maple 4.2 7.6 11.8 o

Acer saccharinum silver maple 3.3 10.5 13.8 o

Acer saccharum sugar maple 1.0 3.5 4.5 o

Acer rubrum red maple 1.0 1.0 2.0 o

Aesculus pavia red buckeye 0.4 1.2 1.6 o

Aesculus hippocastanum horsechestnut 0.3 0.4 0.7 o

Betula papyrifera paper birch 1.1 1.4 2.5 o o

Betula pendula European white birch 0.6 0.2 0.8 o o

Catalpa speciosa northern catalpa 0.7 1.2 1.9

Celtis occidentalis northern hackberry 4.3 4.0 8.3

Fraxinus pennsylvanica green ash 21.6 24.8 46.4 o o

Gleditsia triacanthos honeylocust 2.2 1.3 3.5

Juglans nigra black walnut 0.9 0.2 1.1

Juniperus species juniper 0.3 0.5 0.8

Malus species crabapple 2.6 0.8 3.4

Morus alba white mulberry 4.3 1.2 5.5 o

Other species other species 0.9 0.3 1.2

Picea pungens blue spruce 3.3 1.9 5.2

Picea glauca white spruce 1.4 1.4 2.8

Pinus nigra Austrian pine 2.6 3.1 5.7

Pinus strobus eastern white pine 0.7 0.8 1.5

Pinus resinosa red pine 0.4 0.7 1.1

Pinus sylvestris Scotch pine 0.4 0.1 0.5

Populus nigra black poplar 0.6 0.1 0.7 o o

Populus balsamifera balsam poplar 0.4 0.0 0.4 o o

Populus deltoides eastern cottonwood 0.3 0.2 0.5 o o

Prunus serrulata Kwanzan cherry 0.8 0.1 0.9 o

Prunus serotina black cherry 0.4 0.0 0.4 o
16

Appendix IV continued.

a

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

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

Prunus x cistena purpleleaf sand cherry 0.4 0.0 0.4 o

Pseudotsuga menziesii douglas fi r 0.4 0.3 0.7

Quercus macrocarpa bur oak 1.9 5.4 7.3 o o

Quercus alba white oak 0.4 1.1 1.5 o o

Quercus rubra northern red oak 0.4 0.1 0.5 o o

Sorbus aucuparia European mountain 

ash

0.4 0.1 0.5

Thuja occidentalis northern white cedar 4.8 0.9 5.7

Tilia americana American basswood 1.3 0.2 1.5 o o

Tilia cordata littleleaf linden 1.0 1.6 2.6 o o

Ulmus americana American elm 17.1 16.1 33.2 o o

Ulmus pumila Siberian elm 1.7 3.3 5.0 o

Potential pestb

Genus Species Common Name % Population % Leaf Area IVa ALB GM EAB DED
17

References

1 Nowak, D.J.; Crane, D.E. 2000. The Urban Forest 

Effects (UFORE) Model: quantifying urban 

forest structure and functions. In: Hansen, M.; 

Burk, T., eds. Integrated tools for natural resources 

inventories in the 21st century. Proceedings of 

IUFRO conference. Gen. Tech. Rep. NC-212. St. 

Paul, MN: U.S. Department of Agriculture, Forest 

Service, North Central Research Station: 714-720.

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

2005. The urban forest effects (UFORE) model: 

fi eld data collection manual. V1b. [Newtown 

Square, PA]: U.S. Department of Agriculture, 

Forest Service, Northeastern Research Station. 34 p. 

http://www.fs.fed.us/ne/syracuse/Tools/downloads/

UFORE_Manual.pdf

3 Nowak, D.J. 1994. Atmospheric carbon dioxide 

reduction by Chicago’s urban forest. In: 

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

eds. Chicago’s urban forest ecosystem: results of 

the Chicago Urban Forest Climate Project. Gen. 

Tech. Rep. NE-186. Radnor, PA: U.S. Department 

of Agriculture, Forest Service, Northeastern Forest 

Experiment Station: 83-94.

4 Baldocchi, D. 1988. A multi-layer model for 

estimating sulfur dioxide deposition to a 

deciduous oak forest canopy. Atmospheric 

Environment. 22: 869-884.

5 Baldocchi, D.D.; Hicks, B.B.; Camara, P. 1987. A 

canopy stomatal resistance model for gaseous 

deposition to vegetated surfaces. Atmospheric 

Environment. 21: 91-101.

6 Bidwell, R.G.S.; Fraser, D.E. 1972. Carbon 

monoxide uptake and metabolism by leaves.

Canadian Journal of Botany. 50: 1435-1439. 

7 Lovett, G.M. 1994. Atmospheric deposition of 

nutrients and pollutants in North America: an 

ecological perspective. Ecological Applications. 4: 

629-650.

8 Zinke, P.J. 1967. Forest interception studies in the 

United States. In: Sopper, W.E.; Lull, H.W., eds. 

Forest hydrology. Oxford, UK: Pergamon Press: 

137-161.

9 McPherson, E.G.; Simpson, J.R. 1999. Carbon 

dioxide reduction through urban forestry: 

guidelines for professional and volunteer tree 

planters. Gen. Tech. Rep. PSW-171. Albany, CA: 

U.S. Department of Agriculture, Forest Service, 

Pacifi c Southwest Research Station. 237 p. Can 

be accessed through http://www.fs.fed.us/psw/

publications/gtrs.shtml

10 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.

11 Nowak, D.J.; Crane, D.E.; Stevens, J.C.; Ibarra, M. 

2002. Brooklyn’s urban forest. Gen. Tech. Rep. 

NE-290. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Research 

Station. 107 p.

12 Nowak D.J.; Dwyer, J.F. 2000. Understanding 

the benefi ts and costs of urban forest ecosystems.

In: Kuser, John E., ed. Handbook of urban and 

community forestry in the northeast. New York: 

Kluwer Academics/Plenum: 11-22.

13 Murray, F.J.; Marsh L.; Bradford, P.A. 1994. New 

York state energy plan, vol. II: issue reports.

Albany, NY: New York State Energy Offi ce.

14 Abdollahi, K.K.; Ning, Z.H.; Appeaning, A., eds. 

2000. Global climate change and the urban 

forest. Baton Rouge, LA: GCRCC and Franklin 

Press. 77 p.

15 Northeastern Area State and Private Forestry. 2005. 

Asian Longhorned Beetle. Newtown Square, PA: 
18

U.S. Department of Agriculture, Northeastern Area 

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

us/fhp/alb/

16 Northeastern Area State and Private Forestry. 

2005. Gypsy moth digest. Newtown Square, PA: 

U.S. Department of Agriculture, Forest Service, 

Northeastern Area State and Private Forestry. 

http://www.na.fs.fed.us/fhp/gm/

17 Northeastern Area State and Private Forestry. 2005. 

Forest health protection emerald ash borer 

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

18 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
19

Explanation of Calculations of Appendix III

19 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.

20 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.)

21 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 
20

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.
Printed on Recycled Paper

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

Jeffrey T. 2006. Assessing urban forest effects and values, Minneapolis’ 

urban forest. Resour. Bull. NE-166. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Research Station. 20 p.

An analysis of trees in Minneapolis, MN, reveals that the city has about 979,000 

trees with canopies that cover 26.4 percent of the area. The most common tree 

species are green ash, American elm, and boxelder. The urban forest currently 

stores about 250,000 tons of carbon valued at $4.6 million. In addition, these 

trees remove about 8,900 tons of carbon per year ($164,000 per year) and trees 

and shrubs combined remove about 384 tons of air pollution per year ($1.9 

million per year). The structural, or compensatory, value is estimated at $756 

million. Information on the structure and functions of the urban forest can be used 

to improve and augment support for urban forest management programs and 

to integrate urban forests within plans to improve environmental quality in the 

Minneapolis area.

Keywords: urban forestry; ecosystem services; air pollution removal; carbon 

sequestration; tree value
Headquarters of the Northeastern Research Station is in Newtown Square, 

Pennsylvania. Field laboratories are maintained at:

Amherst, Massachusetts, in cooperation with the University of Massachusetts

Burlington, Vermont, in cooperation with the University of Vermont

Delaware, Ohio

Durham, New Hampshire, in cooperation with the University of New Hampshire

Hamden, Connecticut, in cooperation with Yale University

Morgantown, West Virginia, in cooperation with West Virginia University

Parsons, West Virginia

Princeton, West Virginia

Syracuse, New York, in cooperation with the State University of New York, 

College of Environmental Sciences and Forestry at Syracuse University

Warren, Pennsylvania

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