United States 

Department of 

Agriculture

Forest Service

Pacific Southwest 

Research Station

General Technical 

Report

PSW-GTR-219

March 2009

Community

Benefits, Costs, and Strategic Planting

Lower Midwest

Tree Guide

Paula J. Peper, E. Gregory McPherson, James R. Simpson, Kelaine E. Vargas, 

and Qingfu Xiao
The Forest Service of the U.S. Department of Agriculture is dedicated to the

principle of multiple use management of the Nation’s forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry

research, cooperation with the States and private forest owners, and management of the national forests and national grasslands, it strives—as directed by

Congress—to provide increasingly greater service to a growing Nation.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its

programs and activities on the basis of race, color, national origin, age, disability,

and where applicable, sex, marital status, familial status, parental status, religion,

sexual orientation, genetic information, political beliefs, reprisal, or because all or

part of an individual’s income is derived from any public assistance program. (Not

all prohibited bases apply to all programs.) Persons with disabilities who require

alternative means for communication of program information (Braille, large print,

audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice

and TDD).

To file a complaint of discrimination write USDA, Director, Office of Civil Rights,

1400 Independence Avenue, S.W. Washington, DC 20250-9410, or call (800) 795-

3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and

employer.

Authors

Paula J. Peper is an ecologist, E. Gregory McPherson is a research forester,

James R. Simpson is a forest meteorologist, and Kelaine E. Vargas is a landscape

architect, U.S. Department of Agriculture, Forest Service, Pacific Southwest

Research Station, Center for Urban Forest Research, 1731 Research Park Drive,

Davis, CA 95618; Qingfu Xiao is a research hydrologist, Department of Land, Air,

and Water Resources, University of California, Davis. Xiao is located at the Pacific

Southwest Research Station, Center for Urban Forest Research.
i

Lower Midwest Community Tree

Guide: Benefits, Costs, and

Strategic Planting

Paula J. Peper, E. Gregory McPherson, James R. Simpson,

Kelaine E. Vargas, and Qingfu Xiao

U.S. Department of Agriculture, Forest Service

Pacific Southwest Research Station

Albany, California

General Technical Report PSW-GTR-219

March 2009

This work was sponsored by the U.S. Department of Agriculture, Forest Service,

State and Private Forestry, Urban and Community Forestry Program; the State of

Indiana Department of Natural Resources, Division of Forestry, Urban Forestry

Program; and the City of Indianapolis, Department of Parks and Recreation.
ii

Abstract

Peper, Paula J.; McPherson, E. Gregory; Simpson, James R.; Vargas, Kelaine

E.; Xiao, Qingfu. 2009. Lower Midwest community tree guide: benefits, costs,

and strategic planting. Gen. Tech. Rep. PSW-GTR-219. Albany, CA: U.S.

Department of Agriculture, Forest Service, Pacific Southwest Research Station.

115 p.

Even as they increase the beauty of our surroundings, trees provide us with a great

many ecosystem services, including air quality improvement, energy conservation,

stormwater interception, and atmospheric carbon dioxide reduction. These benefits

must be weighed against the costs of maintaining trees, including planting, pruning,

irrigation, administration, pest control, liability, cleanup, and removal. We present

benefits and costs for representative small, medium, and large deciduous trees in the

Lower Midwest region derived from models based on indepth research carried out

in Indianapolis, Indiana. Average annual net benefits increase with tree size and

differ based on location: $4 (public) to $12 (yard) for a small tree, $12 (public) to

$24 (yard) for a medium tree, and $47 (public) to $60 (yard) for a large tree. Two

hypothetical examples of planting projects are described to illustrate how the data in

this guide can be adapted to local uses, and guidelines for maximizing benefits and

reducing costs are given.

Keywords: Ecosystem services, Lower Midwest, urban forestry, benefit-cost

analysis.
iii

In the Lower Midwest region, trees play an environmental, cultural, and historical role in communities.
iv

Summary

This report quantifies benefits and costs for representative small, medium, and large

deciduous trees in the Lower Midwest region. The species chosen as representative

are eastern redbud, littleleaf linden, and northern hackberry (see “Common and

Scientific Names” section). The analysis describes “yard trees” (those planted in

residential sites) and “public trees” (those planted on streets or in parks). Benefits

are calculated based on tree growth curves and numerical models that consider

regional climate, building characteristics, air pollutant concentrations, and prices.

Tree care costs and mortality rates are based on results from a survey of municipal

and commercial arborists. We assume a 50-percent survival rate over a 40-year

timeframe.

The measurements used in modeling environmental and other benefits of trees

are based on indepth research carried out in Indianapolis, Indiana. Given the Lower

Midwest region’s diverse geographical area, this approach provides general approximations based on some necessary assumptions that serve as a starting point for more

specific local calculations. It is a general accounting that can be easily adapted and

adjusted for local planting projects. Two examples are provided that illustrate how

to adjust benefits and costs to reflect different aspects of local urban forest improvement projects.

Large trees provide the most benefits. Average annual benefits increase with

mature tree size and differ based on tree location. The lowest values are for yard

trees on the southern side of houses, and the highest values are for yard trees on the

western side of houses. Values for public trees are intermediate. Average annual

benefits range as follows:

• $15 to $21 for a small tree

• $27 to $35 for a medium tree

• $58 to $73 for a large tree

Benefits associated with reduced level of stormwater runoff and increased

aesthetic and other benefits reflected in higher property values account for the

largest proportion of total benefits in this region. Reduced levels of energy use, air

pollutants, and carbon dioxide (CO2

) in the air are the next most important benefits.

Energy conservation benefits differ with tree location as well as size. Trees

located opposite west-facing walls provide the greatest net heating and cooling

energy savings. Reducing heating and cooling energy needs reduces CO2

 emissions

and thereby reduces atmospheric CO2

. Similarly, energy savings that reduce demand

from powerplants account for important reductions in gases that produce ozone, a

major component of smog, and other air pollutants.

Benefits and costs

quantified

Average annual

benefits
v

The benefits of trees are offset by the costs of caring for them. Based on our

surveys of municipal and residential arborists, the average annual cost for tree care

ranges from $9 to $24 per tree. (Values below are for yard and public trees, respectively.)

• $9 and $16 for a small tree

• $10 and $18 for a medium tree

• $13 and $24 for a large tree

Pruning costs, annualized over 40 years, are a significant expense ($2 to $8 per

tree per year). Public trees also incur a significant administrative expense ($4 to $6

per tree per year). Planting ($4 per tree per year) and removal and disposal annualized over 40 years ($2 to $3 per tree per year) are the next greatest costs. During the

establishment period, costs for labor-intensive hand watering were low, estimated to

be $0.23 per year for 5 years.

Average annual net benefits (benefits minus costs) per tree for a 40-year period

differ with tree location and tree size and range from a low of $4 to a high of

$60 per tree.

• $4 for a small public tree to $12 for a small yard tree on the west side of a

house

• $12 for a medium public tree to $24 for a medium yard tree on the west

side of a house

• $47 for a large public tree to $60 for a large yard tree on the west side of a

house

Environmental benefits alone, including energy savings, stormwater runoff

reduction, improved air quality, and reduced atmospheric CO2

, can be nearly twice

the cost of tree care.

Net benefits for a yard tree opposite a west wall and a public tree are substantial

when summed over the 40-year period (values below are for public trees and yard

trees opposite a west wall, respectively):

• $149 and $475 for a small tree

• $454 and $923 for a medium tree

• $1,809 and $2,356 for a large tree

Yard trees produce higher net benefits than public trees, primarily because of

lower maintenance costs.

To demonstrate ways that communities can adapt the information in this report

to their needs, examples of two fictional cities interested in improving their urban

Costs

Average annual net

benefits

Net benefits

summed over

40 years
vi

forest have been created. The benefits and costs of different planting projects are

determined. In the hypothetical city of Flint Falls, net benefits and benefit-cost

ratios (BCRs; total benefits divided by costs) are calculated for a planting of 1,000

trees (3-in caliper) assuming a cost of $200 per tree, 43 percent mortality rate, and

40-year analysis. Total benefits are $2.46 million, total costs are about $822,000,

and net benefits are $1.63 million ($40.89 per tree per year). The BCR is 2.99:1,

indicating that $2.99 is returned for every $1 invested. The net benefits and BCRs

(in parentheses) by mature tree size are:

• $9,306 (1.30:1) for 50 eastern redbud trees

• $119,526 (1.80:1) for 200 littleleaf linden

• $1,506,670 (3.35:1) for 750 northern hackberry

Reduced stormwater runoff benefits account for 41 percent of the estimated

benefits. Increased property values reflecting aesthetic and other benefits of trees

account for 35 percent of the estimated benefits, and reduced energy costs for

another 16 percent. Air quality improvement (6 percent) and atmospheric CO2

reduction (2 percent) make up the remaining benefits.

In the fictional city of Sandy Creek, long-term planting and tree care costs and

benefits were compared to determine if current fashion for planting small flowering

trees instead of the large stately trees that were once standard is substantially

affecting the level of benefits residents are receiving. Over a 40-year period, the net

benefits are:

• $58 for a small tree

• $367 for a medium tree

• $1,668 for a large tree

Based on this analysis, the city of Sandy Creek decided to strengthen its tree

ordinance, requiring developers to plant large trees wherever feasible and to create

tree shade plans that show how they will achieve 50-percent shade over streets,

sidewalks, and parking lots within 15 years of development.
vii

Contents

1 Chapter 1. Introduction

1 The Lower Midwest Region

5 Chapter 2. Benefits and Costs of Urban and Community Forests

5 Benefits

5 Saving Energy

8 Reducing Atmospheric Carbon Dioxide

11 Improving Air Quality

14 Reducing Stormwater Runoff and Improving Hydrology

17 Aesthetics and Other Benefits

22 Costs

22 Planting and Maintaining Trees

23 Conflicts With Urban Infrastructure

25 Wood Salvage, Recycling, and Disposal

27 Chapter 3. Benefits and Costs of Community Forests in Lower Midwest

Communities

27 Overview of Procedures

27 Approach

28 Reporting Results

32 Findings of This Study

32 Average Annual Net Benefits

35 Average Annual Costs

35 Average Annual Benefits

39 Air Quality Improvement

40 Carbon Dioxide Reduction

41 Chapter 4. Estimating Benefits and Costs for Tree Planting Projects in

Your Community

41 Applying Benefit-Cost Data

41 Flint Falls Example

46 City of Sandy Creek Example

49 Increasing Program Cost-Effectiveness

49 Increasing Benefits

50 Reducing Program Costs
viii

53 Chapter 5. General Guidelines for Selecting and Placing Trees

53 Guidelines for Energy Savings

53 Maximizing Energy Savings From Shading

55 Planting Windbreaks for Heating Savings

56 Selecting Trees to Maximize Benefits

57 Guidelines for Reducing Carbon Dioxide

58 Guidelines for Reducing Stormwater Runoff

60 Guidelines for Improving Air Quality Benefits

61 Guidelines for Avoiding Conflicts With Infrastructure

62 Guidelines for Maximizing Long-Term Benefits

66 Glossary

71 Common and Scientific Names

72 Metric Equivalents

72 Acknowledgments

73 References

89 Appendix 1: Additional Resources

91 Appendix 2: Benefit–Cost Information Tables

99 Appendix 3: Procedures for Estimating Benefits and Costs
ix

The green infrastructure is a significant component of communities in the Lower Midwest region.
1

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 1. Introduction

The Lower Midwest Region

From the Ouachita Mountains of Kansas and Arkansas to the bluegrass country of

Kentucky, the Lower Midwest region sweeps across eight states containing a diverse

assemblage of municipalities (fig. 1). The climate1 of this region corresponds to

Sunset climate zone 35 (Brenzel 2001) and is characterized by hot, humid summers, and winters that are cold but milder than the areas to the north. Average

summer high temperatures can range from the low 100s to as high as 114 degrees

Fahrenheit (F). Every few years, arctic air masses come through during winter,

dropping temperatures to as low as the -20s F in northern and central portions of

the region. Precipitation comes in all seasons and averages range from 36 to 42 in

annually. This varies extensively with as little as 11 in falling in southeast Kansas

Figure 1—The Lower Midwest contains a diverse assemblage of municipalities extending from the

Ouachita Mountains of Arkansas and Oklahoma to the bluegrass country of Kentucky.

1 Words in bold are defined in the glossary.

Scope of the Lower

Midwest region
2

GENERAL TECHNICAL REPORT PSW-GTR-219

compared to over 50 in falling in Arkansas lowlands. In some areas like southern

Indiana and Illinois, more rain tends to fall during warmer months when leaves are

on trees than during dormant months. The growing season ranges from 150 to 240

days.

As the communities of the Lower Midwest continue to grow and change during the coming decades, growing and sustaining healthy community forests is

integral to the quality of life that residents experience. In the Lower Midwest, the

urban forest is a distinctive feature of the landscape that protects us from the elements, cleans the water we drink and the air we breathe, and forms a living connection to earlier generations who planted and tended the trees.

The role of our urban forests in enhancing the environment, increasing community attractiveness and livability, and fostering civic pride takes on greater

significance as communities strive to balance economic growth with environmental

quality and social well-being. Planting trees provides opportunities to connect

residents with nature and with each other (fig. 2). Neighborhood tree plantings and

stewardship projects stimulate investment by local citizens, businesses, and governments for the betterment of their communities. Community forests bring opportunity for economic renewal, combating development woes, improving human health,

and increasing the quality of life for community residents.

Figure 2—Tree planting and stewardship programs provide opportunities for local residents

to work together to build better communities. Pam Louks

Lower Midwest

communities can

derive many benefits from community

forests
3

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Lower Midwest communities can promote energy efficiency through tree

planting and stewardship programs that strategically locate trees to save energy and

minimize conflicts with urban infrastructure. The same trees can provide additional

benefits by reducing stormwater runoff; improving local air, soil, and water quality; reducing atmospheric carbon dioxide (CO2

); providing wildlife habitat; increasing property values; slowing traffic; enhancing community attractiveness and

investment; and promoting human well-being.

Although trees can provide many benefits to residents of the Lower Midwest,

there may be concern over the introduction of nonnative trees that they may prove

to be invasive, particularly in riparian areas, provide habitat for nonnative fauna,

and encroach on nearby native habitats. These concerns are valid, considering for

example, the invasion of the tree of heaven (see “Common and Scientific Names”

section) throughout the region (Midwest Invasive Plants Network 2006) and of

Russian olive throughout the Western United States (Brock 1998). Careful species

selection in collaboration with your local extension agent or city forester can allay

these concerns while allowing local communities to reap the many benefits of trees

in urban areas. It is important to maintain species and age diversity to insure the

health and sustainability of the urban forest.

This guide builds upon studies by the USDA Forest Service in Chicago and

Sacramento (McPherson et al. 1994, 1997), and other regional tree guides from

the Center for Urban Forest Research (McPherson et al. 1999b, 2000, 2003, 2004,

2006a, 2006b, 2007; Vargas et al. 2007a, 2007b) to extend knowledge of urban

forest benefits in the Lower Midwest. The guide:

• Quantifies benefits of trees on a per-tree basis rather than on a canopycover basis (it should not be used to estimate benefits for trees growing in

forest stands).

• Describes management costs and benefits.

• Details how tree planting programs can improve environmental quality,

conserve energy, and add value to communities.

• Explains where to place residential yard and public trees to maximize their

benefits and cost-effectiveness.

• Describes ways to minimize conflicts between trees and power lines,

sidewalks, and buildings.

• Illustrates how to use this information to estimate benefits and costs for

local tree planting projects.

Quality of life improves with trees

Scope defined
4

GENERAL TECHNICAL REPORT PSW-GTR-219

These guidelines are specific to the Lower Midwest, and are based on data and

calculations from open-growing urban street trees in Indianapolis, Indiana.

Street, park, and shade trees are components of all Lower Midwest communities, and they affect every resident. Their benefits are myriad. However, with

municipal tree programs dependent on taxpayer-supported general funds, communities are forced to ask whether trees are worth the price to plant and care for over

the long term, thus requiring urban forestry programs to demonstrate their costeffectiveness (McPherson 1995). If tree plantings are proven to benefit communities, then financial commitment to tree programs will be justified. Therefore, the

objective of this tree guide is to identify and describe the benefits and costs of

planting trees in Lower Midwest communities—providing a tool for municipal tree

managers, arborists, and tree enthusiasts to increase public awareness and support

for trees (Dwyer and Miller 1999).

Audience and

objectives
5

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 2. Benefits and Costs of Urban and

Community Forests

This chapter describes benefits and costs of publicly and privately managed

trees and presents the functional benefits and associated economic value of community forests. Expenditures related to tree care and management are assessed—

a necessary process for creating cost-effective programs (Dwyer et al. 1992,

Hudson 1983).

Benefits

Saving Energy

Energy is essential for quality of life and for economic growth. Conserving energy

by greening our cities is often more cost-effective than building new powerplants.

For example, while California was experiencing energy shortages in 2001, its 177

million city trees were providing shade and conserving energy. Annual savings to

utilities were an estimated $500 million in wholesale electricity and generation

purchases (McPherson and Simpson 2003). Planting 50 million more shade trees in

strategic locations would provide savings equivalent to seven 100-megawatt powerplants. In 2001, it cost $150 to 250 to produce, purchase, or conserve a kW at the

summertime peak. Hence, peak load reduction measures that cost less than $150 per

kW saved are considered cost-effective. The cost of peak load reduction for the

Lower Midwest was $63 per kW, considerably less than the $150 per kW benchmark for cost-effectiveness. Utility companies in the Lower Midwest and throughout the country can invest in shade tree programs as a cost-effective energy

conservation measure to lower peak energy demands.

Trees modify climate and conserve building energy use in three principal ways

(fig. 3):

• Shading reduces the amount of heat absorbed and stored by built surfaces.

• Evapotranspiration converts liquid water to water vapor and thus cools

the air by using solar energy that would otherwise result in heating of the

air.

• Reducing windspeed reduces the infiltration of outside air into interior

spaces and conductive heat loss, especially where conductivity is relatively

high (e.g., glass windows) (Simpson 1998).

How trees work to

save energy
6

GENERAL TECHNICAL REPORT PSW-GTR-219

Summer temperatures in cities can be 3 to 8 °F warmer than temperatures in

the surrounding countryside. This is known as the urban heat island effect. Trees

and other vegetation can combat this warming effect at small and large scales. On

individual building sites, trees may lower air temperatures up to 5 °F compared

with outside the greenspace. At larger scales (6 mi2), temperature differences

of more than 9 °F have been observed between city centers and more vegetated

suburban areas (Akbari et al. 1992). A recent study for New York City compared

trees, living roofs, and light surfaces and found that street trees provide the “greatest cooling potential per unit area” (Rosenzweig et al. 2006).

For individual buildings, strategically placed trees can increase energy efficiency in the summer and winter. Because the summer sun is low in the east and

west for several hours each day, solar angles should be considered (fig. 4). Trees

that shade east and, especially, west walls help keep buildings cool. In the winter,

allowing sunlight to strike the southern side of a building can warm interior spaces.

Figure 3—Trees save energy for heating and cooling by shading buildings, lowering summertime

temperatures, and reducing windspeeds. Secondary benefits from energy conservation are reduced water

consumption and reduced pollutant emissions by powerplants (drawing by Mike Thomas).

Trees lower

temperatures

Trees increase

energy efficiency

and save money
7

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

However, the trunks and bare branches of deciduous trees that shade south- and

east-facing walls during winter may increase heating costs by blocking 40 percent

or more of winter sun (McPherson 1984).

Windbreaks reduce air infiltration and conductive heat loss from buildings.

Rates at which outside air infiltrates a building can increase substantially with

windspeed. In cold, windy weather, the entire volume of air, even in newer or

tightly sealed homes, may change every 2 to 3 hours. Windbreaks can reduce windspeed and resulting air infiltration by up to 50 percent, translating into potential

annual heating savings of 10 to 12 percent (Heisler 1986). Windspeed reductions

also decrease heat transfer through windows, walls, and roofs by reducing the

overall heat transfer coefficient for these surfaces. If located correctly, trees planted

as windbreaks can also serve as living snowfences, storing and directing the movement of snow (for more information see Brandle and Nickerson 1996).

Trees provide greater energy savings in the Lower Midwest than in milder

climate regions because they can have greater effects during the hot summers and

cold winters. An average energy-efficient home in Rock Valley, Iowa, spends about

$385 each year for heating and $115 for cooling. A computer simulation demonstrated that three 25-ft tall trees—two on the west side and one on the east side of

Figure 4—Paths of the sun on winter and summer solstices (from Sand 1991).

Summer heat gain is primarily through east- and west-facing windows and walls.

The roof receives most irradiance, but insulated attics reduce heat gain to living

spaces. The winter sun, at a lower angle, strikes the south-facing surfaces.
8

GENERAL TECHNICAL REPORT PSW-GTR-219

the house—were estimated to save $9 each year for heating (2.5 MBtu) and $43 for

cooling (940 kWh), a 10-percent reduction in annual heating and cooling costs

(McPherson et al. 1993).

Conserving energy by greening our cities is important because it can be more

cost-effective than building new powerplants (for more information, see the Center

for Urban Forest Research’s research summaries “Green Plants or Powerplants?”

and “Save Dollars with Shade” [Geiger 2001, 2002a]). In the Lower Midwest

region, there is ample opportunity to “retrofit” communities with more sustainable

landscapes through strategic tree planting and care of existing trees.

Reducing Atmospheric Carbon Dioxide

Global temperatures have increased since the late 19th century, with major warming

periods from 1910 to 1945 and from 1976 to the present (IPCC 2007). Human

activities, primarily fossil fuel consumption, are adding greenhouse gases to the

atmosphere, and current research suggests that the recent increases in temperature

can be attributed in large part to increases in greenhouse gases (IPCC 2007).

Higher global temperatures are expected to have a number of adverse effects,

including increasing the number and extent of wildfires, an aspect of particular

concern in parts of the Lower Midwest (McKenzie et al. 2004). Increasing frequency of extreme weather events will continue to tax emergency management

resources.

Urban forests have been recognized as important storage sites for carbon

dioxide (CO2

), the primary greenhouse gas (Nowak and Crane 2002). Private

markets dedicated to reducing CO2

 emissions by trading carbon credits are emerging (Chicago Climate Exchange 2007, CO2e.com 2007, McHale 2003). Carbon

credits have sold for as much as EUR 33 per ton (about $52 at April 2008 exchange

rates; European Climate Exchange 2006), and the social costs of CO2

 emissions (an

estimate of the monetary value of worldwide damage done by CO2

 emissions from

human activities) are estimated to range from £4 to £27 per ton ($14 to $54 per

ton) (Pearce 2003). For comparison, for every $20 spent on a tree planting project

in Arizona, 1 ton of atmospheric CO2

 was reduced (McPherson and Simpson 1999).

As carbon trading markets become accredited and prices rise, these markets could

provide monetary resources for community forestry programs.

Urban forests can reduce atmospheric CO2

 in two ways (fig. 5):

• Trees directly sequester CO2

 in their stems and leaves while they grow.

• Trees near buildings can reduce the demand for heating and air conditioning, thereby reducing emissions associated with power production.

Retrofit for more

savings

Trees reduce CO2
9

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 5—Trees sequester carbon dioxide (CO2) as they grow and indirectly reduce CO2 emissions

from powerplants through energy conservation. At the same time, CO2 is released through decomposition and tree care activities that involve fossil-fuel consumption (drawing by Mike Thomas).

At the same time, the positive impact of trees on CO2 is offset by some emissions. To provide a complete picture of atmospheric CO2

 reductions from tree

plantings, it is important to consider CO2

 released into the atmosphere through tree

planting and care activities, as well as decomposition of wood from pruned or dead

trees. During the process of planting and maintaining trees, vehicles, chain saws,

chippers, and other equipment release CO2 (fig. 5). Typically, CO2

 released from

Some tree-related

activities release

CO2
10

GENERAL TECHNICAL REPORT PSW-GTR-219

tree planting, maintenance, and other tree-related activities is about 2 to 8 percent

of annual CO2

 reductions obtained through sequestration and reduced powerplant emissions (McPherson and Simpson 1999). And eventually, all trees die,

and most of the carbon that has accumulated in their structure is released into the

atmosphere as CO2

 through decomposition. The rate of release into the atmosphere

depends on if and how the wood is reused. For instance, recycling of urban wood

waste into products such as furniture can delay the rate of decomposition compared

to its reuse as mulch. Tree waste can also be used as a fuel source to generate

electricity. If this biomass fuel replaces a more carbon-intensive form of electricity

production, there will be an overall reduction in atmospheric CO2

.

Regional variations in climate and the mix of fuels that produce energy to

heat and cool buildings influence potential CO2

 emission reductions. The average

emission rate in Indianapolis, Indiana, is 2,183 lb of CO2

 per MWh (US EPA

2006), a large amount, because 100 percent of Indianapolis’s power is generated

from fossil fuels like coal and natural gas. On the other hand, communities in other

states like Illinois, have lower emission rates (average 1,155 lb of CO2

 per MWh)

because nearly half of Illinois’ power is nuclear-generated (US EPA 2006). Cities

in the Lower Midwest with relatively high CO2 emission rates will see greater

benefits from reduced energy demand relative to other areas with lower emissions

rates.

A study of the municipal trees of Indianapolis found that sequestrations and

reduced emissions attributable to the 117,500 publicly owned trees equaled 16,344

tons of CO2

 (Peper et al. 2008) annually. Approximately 2,198 tons of CO2 is

released from decaying trees and during maintenance, with a positive net reduction

in atmospheric CO2 owing to trees of 14,146 tons.

Another study in Chicago focused on the carbon sequestration benefit of

residential tree canopy. Tree canopy cover in two residential neighborhoods was

estimated to sequester on average 0.112 lb/ft2

, and pruning activities released 0.016

lb/ft2

 (Jo and McPherson 1995). Net annual carbon uptake was 0.096 lb/ft2.

Grass-roots tree-planting efforts to reduce atmospheric CO2

 can be very successful. Since 1990, Trees Forever, an Iowa-based nonprofit organization, has

planted trees for energy savings and atmospheric CO2 reduction with utility sponsorships. Over 1 million trees have been planted in 400 communities with the help

of 120,000 volunteers. These trees are estimated to offset CO2 emissions by 50,000

tons annually. Based on an Iowa State University study, survival rates are an

amazing 91 percent indicating a highly trained and committed volunteer force

(Ramsay 2002).

Reduced CO2

emissions

CO2 reduction

through community

forestry
11

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Improving Air Quality

Approximately 159 million people live in areas where ozone (O3) concentrations

violate federal air quality standards. About 100 million people live in areas where

dust and other small particulate matter (PM10) exceed levels for healthy air. Communities in Illinois, Indiana, and Ohio are among the cities previously listed in the

U.S. EPAs (Environmental Protection Agency) Green Book (US EPA 2006) as

being in violation of federal air quality standards for PM10 but are currently listed

as maintenance areas (previously nonattainment areas), no longer in violation of

federal air quality standards for PM10 or 8-hour ozone levels. Air pollution is a

serious health threat to many city dwellers, causing asthma, coughing, headaches,

respiratory and heart disease, and cancer (Smith 1990). Impaired health results in

increased social costs for medical care, greater absenteeism, and reduced longevity.

Recently, the EPA recognized tree planting as a measure in state implementation plans for reducing O3

. Air quality management districts have funded tree

planting projects to control PM10. These policy decisions are creating new opportunities to plant and care for trees as a method for controlling air pollution (Luley

and Bond 2002; for more information see www.treescleanair.org [USDA FS

2006b] and the Center for Urban Forest Research’s research summary Trees—The

Air Pollution Solution [Geiger 2006]).

Urban forests provide a number of air quality benefits:

• They absorb gaseous pollutants (e.g., O3

, nitrogen dioxide [NO2], and

sulfur dioxide [SO2

]) through leaf surfaces (fig. 6).

• They intercept PM10 (e.g., dust, ash, pollen, smoke) (fig. 6).

• They release oxygen through photosynthesis.

• They transpire water and shade surfaces, which lowers air temperatures,

thereby reducing O3

 levels.

• They reduce energy use, which reduces emissions of pollutants from

powerplants, including NO2, SO2, PM10, and volatile organic compounds

(VOCs) (fig. 6).

• They shade paved surfaces and parked cars, reducing hydrocarbon emissions (fig. 6).

Trees may also adversely affect air quality. Most trees emit biogenic volatile

organic compounds (BVOCs) such as isoprenes and monoterpenes that can

contribute to O3

 formation. The contribution of BVOC emissions from city trees to

O3

 formation depends on complex geographic and atmospheric interactions that

Trees improve air

quality

Trees affect ozone

formation
12

GENERAL TECHNICAL REPORT PSW-GTR-219

have not been studied in most cities. Some complicating factors include variations

with temperature and atmospheric levels of NO2

.

A computer simulation study for Atlanta suggested that it would be very difficult to meet EPA ozone standards in the region by using trees because of the high

BVOC emissions from native pines and other vegetation (Chameides et al. 1988).

The results, however, were not straightforward. A later study showed that although

removing trees reduced BVOC emissions, any positive effect was overwhelmed by

increased hydrocarbon emissions from natural and anthropogenic sources owing

to the increased air temperatures associated with tree removal (Cardelino and

Chameides 1990). A similar finding was reported for the Houston-Galveston area,

where deforestation associated with urbanization from 1992 to 2000 increased

Figure 6—Trees absorb gaseous pollutants, retain particles on their surfaces, and release oxygen

and volatile organic compounds. By cooling urban heat islands and shading parked cars, trees can

reduce ozone formation (drawing by Mike Thomas).
13

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

surface temperatures. Despite the decrease in BVOC emissions, O3 concentrations

increased because of the enhanced urban heat island effect during simulated episodes (Kim et al. 2005).

As well, the O3

-forming potential of tree species differs considerably (Benjamin and Winer 1998). Trees emitting the greatest relative amount of BVOCs are

sweetgum, blackgum, sycamore, poplar, and oak (Nowak 2000). In a study in the

Los Angeles basin, increased planting of low-BVOC-emitting tree species was

shown to reduce O3 concentrations, whereas planting of medium and high emitters

would increase overall O3

 concentrations (Taha 1996). A study in the Northeastern

United States, however, found that species mix had no detectable effects on O3

concentrations (Nowak et al. 2000). Although new trees increased BVOC emissions, ambient VOC emissions were so high that additional BVOCs had little effect

on air quality. These potentially negative effects of trees on one kind of air pollution must be considered in light of their great benefit in other areas.

Trees absorb gaseous pollutants through stomates, tiny openings in the leaves.

Other methods of pollutant removal include adsorption of gases to plant surfaces

and uptake through bark pores. Once gases enter the leaf, they diffuse into intercellular spaces, where some react with inner leaf surfaces and others are absorbed by

water films to form acids. Pollutants can damage plants by altering their metabolism and growth. At high concentrations, pollutants cause visible damage to leaves,

such as spotting and bleaching (Costello and Jones 2003). Although some pollutants

may pose health hazards to plants, pollutants such as nitrogenous gases can also be

sources of essential nutrients for them.

Trees intercept small airborne particles. Some particles that are intercepted by

a tree are absorbed, but most adhere to plant surfaces. Species with hairy or rough

leaf, twig, and bark surfaces are efficient interceptors (Smith and Dochinger 1976).

Intercepted particles are often resuspended to the atmosphere when wind blows the

branches, and rain will wash some particulates off plant surfaces. The ultimate fate

of these pollutants depends on whether they fall onto paved surfaces and enter the

stormwater system, or fall on pervious surfaces, where they are filtered in the soil.

Urban forests clean the air we breathe by releasing oxygen as a byproduct of

photosynthesis. Net annual oxygen production varies depending on tree species,

size, health, and location. A typical person consumes 675 lb of oxygen per year

(Perry and LeVan 2003). Urban forests in the United States are estimated currently

to produce 67 million tons of oxygen annually, enough oxygen to offset human

oxygen consumption for about two-thirds of the U.S. population (Nowak et al.

2007).

Trees absorb

gaseous pollutants

Trees intercept

particulate matter
14

GENERAL TECHNICAL REPORT PSW-GTR-219

Trees near buildings can reduce the demand for heating and air conditioning,

thereby reducing emissions of PM10, SO2

, NO2, and VOCs associated with electric

power production, an effect that can be sizable. For example, a strategically located

tree can save 100 kWh in electricity for cooling annually (McPherson and Simpson

1999, 2002, 2003). Assuming that this conserved electricity comes from a typical

new coal-fired powerplant in the Lower Midwest, the tree reduces emissions of SO2

by 1.25 lb, NO2 by 0.39 lb (US EPA 2003), and PM10 by 0.84 lb (US EPA 1998).

The same tree is responsible for conserving 60 gal of water in cooling towers and

reducing annual CO2 emissions by 200 lb.

In Fayetteville, Arkansas, the tree canopy over nearly 29,000 acres was estimated to remove 731,000 lb of air pollutants annually with a value of $1.6 million

(American Forests 2002). The area experienced a substantial 18 percent decline in

heavy canopy cover between 1985 and 2000 owing to increased development. If the

loss in canopy continues at its current 18 percent rate, estimates are that air quality

benefits will be reduced to $1.3 million and carbon storage will decline from

330,000 to 273,000 thousand tons. Chicago’s 50.8 million trees were estimated to

remove 234 tons of PM10, 210 tons of O3

, 93 tons of SO2, and 17 tons of carbon

monoxide in 1991. This environmental service was valued at $9.2 million (Nowak

1994).

Trees in a Davis, California, parking lot were found to improve air quality by

reducing air temperatures 1 to 3 °F (Scott et al. 1999). By shading asphalt surfaces

and parked vehicles, trees reduce hydrocarbon emissions (VOCs) from gasoline that

evaporates out of leaky fuel tanks and worn hoses (for more information, see our

research summary Where Are All the Cool Parking Lots? [Geiger 2002b]). These

evaporative emissions are a principal component of smog, and parked vehicles are a

primary source (fig. 7). In California, parking-lot tree plantings can be funded as

an air quality improvement measure because of the associated reductions in evaporative emissions.

Reducing Stormwater Runoff and Improving Hydrology

Urban stormwater runoff is a major source of pollution entering wetlands, streams,

lakes, and oceans. Healthy trees can reduce the amount of runoff and pollutants in

receiving waters (Cappiella et al. 2005). This is important because federal law

requires states and localities to control nonpoint-source pollution, such as runoff

from pavements, buildings, and landscapes. Trees are mini-reservoirs, controlling

runoff at the source, thereby reducing runoff volumes and erosion of watercourses,

Tree shade

prevents evaporative hydrocarbon

emissions
15

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

as well as delaying the onset of peak flows. Trees can reduce runoff in several

ways (fig. 8; for more information, see our research summary Is All Your Rain

Going Down the Drain? [Geiger 2003]):

• Leaves and branch surfaces intercept and store rainfall, thereby reducing

runoff volumes and delaying the onset of peak flows.

• Roots reduce soil compaction, increasing the rate at which rainfall infiltrates soil and the capacity of soil to store water, reducing overland flow.

• Tree canopies reduce soil erosion by diminishing the impact of raindrops

on barren surfaces.

• Transpiration through tree leaves reduces moisture levels in the soil,

increasing the soil’s capacity to store rainfall.

Rainfall that is stored temporarily on canopy leaf and bark surfaces is called

intercepted rainfall. Intercepted water evaporates, drips from leaf surfaces, and

flows down stem surfaces to the ground. Tree surface saturation generally occurs

after 1 to 2 in of rain has fallen (Xiao et al. 2000). During large storm events, rainfall exceeds the amount that the tree crown can store, about 50 to 100 gal per tree.

Figure 7—Trees planted to shade parking areas can reduce hydrocarbon emissions and improve air

quality.
16

GENERAL TECHNICAL REPORT PSW-GTR-219

The interception benefit is the amount of rainfall that does not reach the ground

because it evaporates from the crown. As a result, the volume of runoff is reduced

and the time of peak flow is delayed. Trees protect water quality by substantially

reducing runoff during small rainfall events that are responsible for most pollutant

washoff. Therefore, urban forests generally produce more benefits through water

quality protection than through flood control (Xiao et al. 1998, 2000).

The amount of rainfall trees intercept depends on their architecture, rainfall

patterns, and climate. Tree-crown characteristics that influence interception are the

Figure 8—Trees intercept a portion of rainfall that evaporates and never reaches the ground. Some

rainfall runs to the ground along branches and stems (stemflow), and some falls through gaps or

drips off leaves and branches (throughfall). Transpiration increases soil moisture storage potential

(drawing by Mike Thomas).

Trees reduce runoff
17

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

trunk, stem, and surface areas, textures, area of gaps, period when leaves are present, and dimensions (e.g., tree height and diameter). Trees with coarse surfaces

retain more rainfall than those with smooth surfaces. Large trees generally intercept

more rainfall than small trees do because greater surface areas allow for greater

evaporation rates. Tree crowns with few gaps reduce throughfall to the ground.

Species that are in leaf when rainfall is plentiful are more effective than deciduous

species that have dropped their leaves during the rainy season.

Studies that have simulated urban forest effects on stormwater runoff have reported reductions of 2 to 7 percent. Annual interception of rainfall by Sacramento’s

urban forest for the total urbanized area was only about 2 percent because of the

winter rainfall pattern and sparsity of evergreen species (Xiao et al. 1998). However, average interception in canopied areas ranged from 6 to 13 percent (150 gal

per tree), similar to values reported for rural forests. Broadleaf evergreens and

conifers intercept more rainfall than deciduous species in areas where rainfall is

highest in fall, winter, or spring (Xiao and McPherson 2002).

In Albuquerque, a city with approximately one-quarter the rainfall of the

Lower Midwest region, the canopy of the 21,000 municipal park trees reduced

runoff by more than 11 million gal, with an estimated value of $56,000 (Vargas et

al. 2006). In contrast, in Montgomery, Alabama, a city with about half as many

people but many more trees and approximately 50 in more rain than Albuquerque,

the tree canopy was estimated to reduce runoff by 1.7 billion gal, valued at $454

million per 20-year construction cycle (American Forests 2004). According to a

recent study, the 117,500 municipal trees of Indianapolis, Indiana, were estimated

to intercept approximately 319 million gal of stormwater annually, with an estimated value of $1.9 million (Peper et al. 2008).

Urban forests can provide other hydrologic benefits, too. For example, tree

plantations, nurseries, or landscapes can be irrigated with partially treated wastewater. Infiltration of water through the soil can be a safe and productive means of

water treatment. Reused wastewater applied to urban forest lands can recharge

aquifers, reduce stormwater-treatment loads, and create income through sales of

nursery or wood products. Recycling urban wastewater into greenspace areas can be

an economical means of treatment and disposal while at the same time providing

other environmental benefits (USDA NRCS 2005).

Aesthetics and Other Benefits

Trees provide a host of aesthetic, social, economic, and health benefits that should

be included in any benefit-cost analysis. One of the most frequently cited reasons

Urban forests can

treat wastewater
18

GENERAL TECHNICAL REPORT PSW-GTR-219

that people plant trees is for beautification. Trees add color, texture, line, and form

to the landscape, softening the hard geometry that dominates built environments.

Research on the aesthetic quality of residential streets has shown that street trees are

the single strongest positive influence on scenic quality (Schroeder and Cannon

1983).

In surveys, consumers have shown greater preference for commercial streetscapes with trees. In contrast to areas without trees, shoppers shop more often and

longer in well-landscaped business districts. They are willing to pay more for

parking and up to 11 percent more for goods and services (Wolf 1999).

Research in public housing complexes found that outdoor spaces with trees

were used significantly more often than spaces without trees. By facilitating interactions among residents, trees can contribute to reduced levels of domestic violence, as well as foster safer and more sociable neighborhood environments

(Sullivan and Kuo 1996).

Well-maintained trees increase the “curb appeal” of properties (fig. 9). Research documenting the increase in dollar value that can be attributed to trees is

difficult to conduct and is still in early stages, but some studies comparing sales

Figure 9—Trees beautify a neighborhood, increasing property values and

creating a more sociable environment.

For beautification

Attractiveness of

retail settings

Public safety

benefits

Property value

benefits
19

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

prices of residential properties having different numbers of trees have suggested

that people are willing to pay 3 to 7 percent more for properties with ample trees

versus few or no trees. One of the most comprehensive studies of the influence of

trees on home property values was based on actual sales prices and found that each

large front-yard tree was associated with about a 1-percent increase in sales price

(Anderson and Cordell 1988). A much greater value of 9 percent ($15,000) was

determined in a U.S. Tax Court case for the loss of a large black oak on a property

valued at $164,500 (Neely 1988). Depending on average home sales prices, the

value of this benefit can contribute significantly to cities’ property tax revenues.

Scientific studies confirm that trees in cities provide social and psychological

benefits. Humans derive substantial pleasure from trees, whether it is inspiration

from their beauty, a spiritual connection, or a sense of meaning (Dwyer et al. 1992,

Lewis 1996). After natural disasters, people often report a sense of loss if their

community forest has been damaged (Hull 1992). Views of trees and nature from

homes and offices provide restorative experiences that ease mental fatigue and help

people to concentrate (Kaplan and Kaplan 1989). Desk workers with a view of

nature report lower rates of sickness and greater satisfaction with their jobs compared to those having no visual connection to nature (Kaplan 1992). Trees provide

important settings for recreation and relaxation in and near cities. The act of

planting trees can have social value, as bonds between people and local groups

often result.

A series of studies on human stress caused by general urban conditions shows

that views of nature reduce the stress response of both body and mind (Parsons et

al. 1998), improving general well-being. Urban green also appears to have a positive effect on the human immune system. Hospitalized patients who have views of

nature and spend time outdoors need less medication, sleep better, have a better

outlook, and recover more quickly than patients without connections to nature

(Ulrich 1985). Skin cancer is a particular concern in the sunny Lower Midwest

region. Shade from trees reduces exposure to ultraviolet (UV) light, thereby

lowering the risk of harmful effects from skin cancer and cataracts (Tretheway

and Manthe 1999). At the latitudes of the Lower Midwest, the ultraviolet protection

factor provided by trees increases from approximately 2 under a 30-percent canopy

cover to approximately 15 under a 90-percent canopy cover (Grant et al. 2002).

Because early exposure to UV radiation is a risk factor for later development of

skin cancer, planting trees around playgrounds, schools, day care centers, and ball

fields can be especially valuable in helping reduce the risk of later-life cancers.

Social and psychological benefits

Human health

benefits
20

GENERAL TECHNICAL REPORT PSW-GTR-219

Certain environmental benefits from trees are more difficult to quantify than

those previously described, but can be just as important. Noise can reach unhealthy

levels in cities. Trucks, trains, and planes can produce noise that exceeds 100

decibels (dB), twice the level at which noise becomes a health risk. Thick strips

of vegetation in conjunction with landforms or solid barriers can reduce some

highway noise and have a psychological effect (Cook 1978), but if vegetation is

used as the only sound barrier, the amount necessary to achieve measurable reductions in noise (about 200 ft for a 10-dB reduction) may be impractical (U.S. Department of Transportation 1995). Other studies have shown that the performance

of noise barriers is increased when used in combination with vegetative screens

(van Rentergehm et al. 2002).

Numerous types of wildlife inhabit cities and are generally highly valued by

residents. For example, older parks, cemeteries, and botanical gardens often contain

a rich assemblage of wildlife. Remnant woodlands and riparian habitats within

cities can connect a city to its surrounding bioregion (fig. 10). Wetlands, greenways

(linear parks), and other greenspace can provide habitats that conserve biodiversity

(Platt et al. 1994).

Urban forestry can provide jobs for both skilled and unskilled labor. Public

service programs and grassroots-led urban and community forestry programs

Figure 10—Natural areas within

cities are refuges for wildlife and

help connect city dwellers with

their ecosystems.

Noise reduction

Wildlife habitats
21

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 11—Although shade trees can be expensive to maintain, their shade can reduce the

costs of resurfacing streets (McPherson and Muchnick 2005), promote pedestrian travel,

and improve air quality directly through pollutant uptake and indirectly through reduced

emissions of volatile organic compounds from cars.

provide horticultural training to volunteers across the United States. Also, urban

and community forestry provides educational opportunities for residents who want

to learn about nature through firsthand experience (McPherson and Mathis 1999).

Local nonprofit tree groups and municipal volunteer programs often provide educational material and hands-on training in the care of trees and work with area

schools.

Tree shade on streets can help offset the cost of managing pavement by protecting it from weathering. The asphalt paving on streets contains stone aggregate

in an oil binder. Tree shade lowers the street surface temperature, thereby reducing

heating and volatilization of the binder (McPherson and Muchnick 2005). As a

result, the aggregate remains protected for a longer period by the oil binder. When

unprotected, vehicles loosen the aggregate, and much like sandpaper, the loose

aggregate grinds down the pavement. Because most weathering of asphalt-concrete

pavement occurs during the first 5 to 10 years when new street tree plantings

provide little shade, this benefit mainly applies when older streets are resurfaced

(fig. 11). In snowier communities, the benefit from summer shade can be offset by

winter shade that prolongs snow and ice accumulation, and may result in greater

Jobs and environmental education

Shade can reduce

street maintenance
22

GENERAL TECHNICAL REPORT PSW-GTR-219

use of salt and sand. Further study is needed to evaluate the seasonal effects of tree

shade on paving condition and safety.

Costs

The environmental, social, and economic benefits of urban and community forests

come, of course, at a price. A national survey reported that communities in the

Lower Midwest region spent an average of about $1.94 per tree, in 1994, for streetand park-tree management (Tschantz and Sacamano 1994). This amount is relatively low, with only two national regions spending less than this and eight regions

spending more. Nationwide, the single largest expenditure was for tree pruning,

followed by tree removal/disposal, and tree planting. The survey did not include

non-tree-care costs, such as money spent on infrastructure repair, litigation, and

cleanup.

Our survey of municipal foresters in Carmel, Terre Haute, and Indianapolis,

Indiana, and Cincinnati and Marietta, Ohio, indicates that they are spending about

$20 per tree annually. The greatest costs are for pruning ($5 to $8 per tree) and

administration and inspection ($4 to $6 per tree). Planting ($4 per tree) and removal and disposal ($2 to $3 per tree) are the next most costly.

Annual expenditures for tree management on private property have not been

well documented. Costs differ considerably, ranging from some commercial or

residential properties that receive regular professional landscape service to others

that are virtually “wild” and without maintenance. Our survey of commercial

arborists in the Lower Midwest indicated that expenditures typically range from

$9 to $13 per tree. Expenditures are usually greatest for pruning, planting, and

removal.

Planting and Maintaining Trees

Planting costs include the cost of the tree and the cost for planting, staking, and

mulching. Based on our survey of Lower Midwest municipal and commercial

arborists, planting costs differ with tree size and range from $106 for a 2-in

diameter at breast height (4.5 ft; d.b.h.) tree to $550 for a 5-in d.b.h. tree.

Pruning cycles differ by city and by tree size and range from once every 2 to

5 years for new trees to once in 7 to 10 years for large, mature trees. However,

there are cities where pruning is conducted on an as-needed or reactive basis. The

cost for pruning young trees ranged from $10 to $20 for a public tree and from

$50 to $70 for a yard tree; the cost to prune a large, mature tree was about $180

for public trees and ranged from $230 to $900 for yard trees.

Municipal costs of

tree care

Residential costs

differ
23

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Because of the region’s rainy, humid summer climate, most trees do not require

irrigation throughout their lives, and because most are planted in areas that are

already irrigated, such as parkways or other landscaped areas, the cost for additional water for the trees is negligible and is ignored for the purposes of this guide.

Newly planted trees, however, require additional watering at least for the first year

to successfully establish. The costs of irrigation for public trees are estimated at

about $1.75 for the first 5 years, mainly for the labor costs involved in visiting the

trees with a water truck or other time-intensive methods. No additional costs are

included for establishment watering of yard trees, as the few minutes of labor

necessary are considered negligible.

At the end of a tree’s life, removal costs can be substantial, especially for large

trees. Removal and disposal of small trees (under 3 in d.b.h.) cost between $10 and

$50, but a large tree may cost several thousand dollars to remove. According to our

survey, total costs for removal of trees and stumps are approximately $26 to $62

per in d.b.h. for yard trees and $19 to $33 per in d.b.h. for public trees.

Conflicts With Urban Infrastructure

Like other cities across the United States, communities in the Lower Midwest

region are spending millions of dollars each year to manage conflicts between trees

and power lines, sidewalks, sewers, and other elements of the urban infrastructure.

According to our survey, cities in the region are spending about $1 to $2 per tree

annually on sidewalk, curb, and gutter repair costs. This amount is far less than the

$11.22 per tree reported for 18 California cities (McPherson 2000). In addition, the

figures for California apply only to street trees and do not include repair costs for

damaged sewer lines, building foundations, parking lots, and various other

hardscape elements.

In some cities, decreasing budgets are increasing the sidewalk-repair backlog

and forcing cities to shift the costs of sidewalk repair to residents. This shift has

significant impacts on residents in older areas, where large trees have outgrown

small sites and infrastructure has deteriorated. It should be noted that trees are not

always fully responsible for these problems. In older areas, in particular, sidewalks

and curbs may have reached the end of their 20- to 25-year service life, or may

have been poorly constructed in the first place (Sydnor et al. 2000).

Efforts to control the costs of these conflicts are having alarming effects on

urban forests (Bernhardt and Swiecki 1993, Thompson and Ahern 2000):

Tree roots can

damage sidewalks

Costs of conflicts
24

GENERAL TECHNICAL REPORT PSW-GTR-219

• Cities are downsizing their urban forests by planting smaller trees. Although small trees are appropriate under power lines and in small planting

sites, they are less effective than large trees at providing shade, absorbing

air pollutants, and intercepting rainfall.

• Thousands of healthy urban trees are lost each year and their benefits

forgone because of sidewalk damage, the second most common reason that

street and park trees were removed.

• Most cities surveyed were removing more trees than they were planting.

Residents forced to pay for sidewalk repairs may not want replacement

trees.

Cost-effective strategies to retain benefits from large street trees while reducing

costs associated with infrastructure conflicts are described in Reducing Infrastructure Damage by Tree Roots (Costello and Jones 2003). Matching the growth characteristics of trees to the conditions at the planting site is one important strategy.

Tree roots can also damage old sewer lines that are cracked or otherwise

susceptible to invasion. Sewer repair companies estimate that sewer damage is

minor until trees and sewers are over 30 years old, and roots from trees in yards are

usually more of a problem than roots from trees in planter strips along streets. The

latter assertion may be because the sewers are closer to the root zone as they enter

houses than at the street. Repair costs typically range from $100 for sewer rodding

(inserting a cleaning implement to temporarily remove roots) to $1,000 or more

for sewer excavation and replacement.

Most communities sweep their streets regularly to reduce surface-runoff pollution entering local waterways. Street trees drop leaves, flowers, fruit, and branches

year round that constitute a significant portion of debris collected from city streets.

When leaves fall and rains begin, tree litter can clog sewers, dry wells, and other

elements of flood-control systems. Costs include additional labor needed to remove

leaves, and property damage caused by localized flooding. Wind and ice storms

also incur cleanup costs.

The cost of addressing conflicts between trees and power lines is reflected in

electric rates. Large trees under power lines require more frequent pruning than

better suited trees, which can make large trees appear less attractive (fig. 12).

Frequent crown reduction reduces the benefits these trees could otherwise provide.

Moreover, increased costs for pruning are passed on to customers.

Cleaningup after

trees
25

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 12—Large trees planted under power lines can require extensive pruning, which increases

tree care costs and reduces the benefits of those trees, including their appearance. The use of small

trees, like those shown here, will reduce pruning costs and maintain benefits.

Wood Salvage, Recycling, and Disposal

According to our survey, many Lower Midwest cities are recycling green waste

from urban trees as firewood, mulch, and compost. Some powerplants will use this

wood to generate electricity, thereby helping defray costs for hauling and grinding.

Generally, the net costs of waste-wood disposal are less than 1 percent of total tree

care costs, and cities and contractors may break even. The cost of wood disposal

may be higher depending on geographic location and the presence of exotic pests

that require special waste-wood disposal processes. In some cities within the region,

income from sales of firewood, mulch, and compost exceeds the cost of hauling

and disposal. For example, Indianapolis chips 84 percent of its tree removals for

use by the city and partners as mulch. Savings to the city exceed the cost of mulching by $30 per ton.

Recycling green

waste may pay for

itself
26

GENERAL TECHNICAL REPORT PSW-GTR-219
27

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 3. Benefits and Costs of Community

Forests in Lower Midwest Communities

This chapter presents estimated benefits and costs for trees planted in typical

residential yards and public sites. Because benefits and costs differ with tree size,

we report results for representative small, medium, and large deciduous trees

and for a representative conifer.

Estimates are initial approximations, as some benefits and costs are intangible or difficult to quantify (e.g., impacts on psychological health, crime, and

violence). Limited knowledge about physical processes at work and their interactions makes estimates imprecise (e.g., fate of air pollutants trapped by trees

and then washed to the ground by rainfall). Tree growth and mortality rates are

highly variable throughout the region. Benefits and costs also differ, depending

on differences in climate, pollutant concentrations, maintenance practices, and

other factors. Given the Lower Midwest region’s diverse landscape, with different climates, soils, and types of community forestry programs, the approach

used here provides first-order approximations. It is a general accounting that can

be easily adapted and adjusted for local planting projects. It provides a basis for

decisions that set priorities and influence management direction (Maco and

McPherson 2003).

Overview of Procedures

Approach

In this study, annual benefits and costs are estimated over a 40-year planning

horizon for newly planted trees in three residential yard locations (east, south,

and west of the residence) and a public streetside or park location (app. 2).

Henceforth, we refer to trees in these hypothetical locations as “yard” trees

and “public” trees, respectively. Prices are assigned to each cost (e.g., planting,

pruning, removal, irrigation, infrastructure repair, liability) and benefit (e.g.,

heating/cooling energy savings, air pollutant mitigation, stormwater runoff

reduction, and aesthetic and other benefits measured as increases in property

value) through direct estimation and implied valuation of benefits as environmental externalities. This approach makes it possible to estimate the net benefits

of plantings in “typical” locations by using “typical” tree species. More information on data collection, modeling procedures, and assumptions can be found in

appendix 3.
28

GENERAL TECHNICAL REPORT PSW-GTR-219

To account for differences in the mature size and growth of different tree

species, we report results for a small (eastern redbud), medium (littleleaf linden),

and large (northern hackberry) deciduous tree (figs. 13 to 16) (see “Common and

Scientific Names” section). Tree dimensions are derived from growth curves

developed from street trees in Indianapolis, Indiana (Peper et al. 2008) (fig. 16).

The selection of these species is based on data availability and representative

growth and is not intended to endorse their use in large numbers. Relying on too

few species can increase the likelihood of catastrophic loss owing to pests, disease,

or other threat.

Frequency and costs of tree management are estimated based on surveys with

municipal foresters from Carmel, Indianapolis, and Terre Haute, Indiana, and

Cincinnati and Marietta, Ohio. In addition, several commercial arborists from

Brownsburg, Carmel, and Indianapolis, Indiana, and Gallipolis and Columbus,

Ohio, provided information on tree management costs on residential properties.

Benefits are calculated with numerical models and data both from the region

(e.g., pollutant emission factors for avoided emissions from energy savings) and

from local sources (e.g., Indianapolis climate data for energy effects). Regional

electricity and natural gas prices are used in this study to quantify energy savings.

Damage costs and control costs are used to estimate willingness to pay. For example, the value of stormwater runoff reduction owing to rainfall interception by

trees is estimated by using marginal control costs. If a community or developer is

willing to pay an average of $0.01 per gal of treated and controlled runoff to meet

minimum standards, then the stormwater runoff mitigation value of a tree that

intercepts 1,000 gal of rainfall, eliminating the need for control, should be $10.

Reporting Results

Results are reported in terms of annual value per tree planted. To make these calculations realistic, however, mortality rates are included. Based on our survey of

regional municipal foresters and commercial arborists, this analysis assumes that

50 percent of the planted trees will die over the 40-year period. Annual mortality

rates are 2 percent per year for the first 5 years and 1.4 percent per year for the

remainder of the 40-year period. This accounting approach “grows” trees in different locations and uses computer simulation to calculate the annual flow of

benefits and costs as trees mature and die (McPherson 1992). In appendix 2, results

are reported at 5-year intervals for 40 years.

Tree care costs

based on survey

findings

Tree benefits based

on numerial models

Tree mortality

included
29

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 13—The eastern redbud represents small trees in this guide.

Figure 14—The littleleaf linden represents medium trees in this guide.
30

GENERAL TECHNICAL REPORT PSW-GTR-219

Figure 15—The northern hackberry represents large trees in this guide.
31

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 16—Tree growth curves are based on data

collected from street trees in Indianapolis, Indiana.

Data for representa-tive small, medium, and large

trees are for the eastern redbud, littleleaf linden, and

northern hackberry, respectively. Differences in leaf

surface area among species are most important for

this analysis because functional benefits such as

summer shade, rainfall interception, and pollutant

uptake are related to leaf area.
32

GENERAL TECHNICAL REPORT PSW-GTR-219

Findings of This Study

Average Annual Net Benefits

Average annual net benefits (benefits minus costs) per tree over a 40-year period

increase with mature tree size (for detailed results see app. 2):

• $4 to $12 for a small tree

• $12 to $24 for a medium tree

• $47 to $60 for a large tree

Our findings demonstrate that average annual net benefits from large trees like

the hackberry are substantially greater than those from small trees like the eastern

redbud. Average annual net benefits for the small, medium, and large deciduous

public trees are $3, $11, and $43, respectively. The largest average annual net

benefits, however, stem from yard trees opposite the west-facing wall of a house:

$12, $24, and $60, for small, medium, and large deciduous trees, respectively.

At year 40, the large yard tree opposite a west wall produces a net annual

benefit of $80. In the same location, 40 years after planting, the eastern redbud

and littleleaf linden produce annual net benefits of $14 and $32. Forty years after

planting at a typical public site, the small, medium, and large deciduous trees

provide annual net benefits of $4, $17, and $64, respectively.

Net benefits for a yard tree opposite a west house wall and a public tree also

increase with size when summed over the entire 40-year period:

• $475 (yard) and $149 (public) for a small tree

• $923 (yard) and $454 (public) for a medium tree

• $2,356 (yard) and $1,809 (public) for a large tree

Twenty years after planting, average annual benefits for all trees exceed costs

of tree planting and management (tables 1 and 2). For a large hackberry in a yard

20 years after planting, the total value of environmental benefits alone ($51) is over

six times the total annual cost ($8). Environmental benefits total $14 and $22,

respectively, for the eastern redbud and littleleaf linden, and tree care costs are $3

and $7, respectively. Adding the value of aesthetics and other benefits to the

environmental benefits results in even greater net benefits.

Net benefits for public trees at 20 years ($10, $18, and $57 for small, medium,

and large deciduous trees, respectively; table 2) are less than yard trees ($19, $29,

and $70) for two main reasons: public tree care costs are greater because public

trees generally receive more intensive care than private trees; and energy benefits

are lower for public trees than for yard trees because public trees are assumed to

provide general climate effects, but not to shade buildings directly.

Large trees provide

greater benefits

Net annual benefits

at year 40

Net benefits

summed over

40 years

Year 20: environmental benefits

exceed tree care

costs
33

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 1—Estimated annual benefits and costs for a private tree (residential yard) opposite the west-facing wall

20 years after planting

Eastern redbud Littleleaf linden Northern hackberry

small tree medium tree large tree

20 ft tall 29 ft tall 51 ft tall

20-ft spread 24-ft spread 36-ft spread

LSA = 1,056 ft2 LSA = 1,414 ft2 LSA = 4,718 ft2

Resource Total Resource Total Resource Total

Benefit category units value units value units value

Dollars Dollars Dollars

Electricity savings ($0.0680/kWh) 72 kWh 4.93 122 kWh 8.30 247 kWh 16.79

Natural gas savings ($0.97/therm) -0.15 therms -0.14 0.26 therms 0.25 0.20 therms 0.20

Carbon dioxide ($0.00334/lb) 171 lb 0.57 296 lb 0.99 653 lb 2.18

Ozone ($0.82/lb) 0.19 lb 0.16 0.29 lb 0.24 0.62 lb 0.51

Nitrogen dioxide ($0.82/lb) 0.17 lb 0.14 0.28 lb 0.23 0.59 lb 0.49

Sulfur dioxide ($1.50 /lb) 0.57 lb 0.86 0.93 lb 1.40 2.01 lb 3.02

Small particulate matter ($0.99/lb) 0.19 lb 0.19 0.25 lb 0.25 0.39 lb 0.39

Volatile organic compounds ($0.30/lb) 0.00 lb 0.01 0.07 lb 0.02 0.16 lb 0.05

Biogenic volatile organic compounds

($0.30/lb) 0 lb 0 -0.17 lb -0.05 0 lb 0

Rainfall interception ($0.006/gal) 1,101 gal 6.83 1,644 gal 10.19 4,390 gal 27.22

Environmental subtotal 13.53 21.82 50.84

Other benefits 7.95 14.80 26.59

Total benefits 21.48 36.61 77.43

Total costs 2.86 7.40 7.65

Net benefits 18.63 29.22 69.78

LSA = leaf surface area.
34

GENERAL TECHNICAL REPORT PSW-GTR-219

Table 2—Estimated annual benefits and costs for a public tree (street/park) 20 years after planting

Eastern redbud Littleleaf linden Northern hackberry

small tree medium tree large tree

20 ft tall 29 ft tall 51 ft tall

20-ft spread 24-ft spread 36-ft spread

LSA = 1,056 ft2 LSA = 1,414 ft2 LSA = 4,718 ft2

Resource Total Resource Total Resource Total

Benefit category units value units value units value

Dollars Dollars Dollars

Electricity savings ($0.0680/kWh) 31 kWh 2.12 47 kWh 3.23 103 kWh 7.03

Natural gas savings ($0.97/therm) 2 therms 1.62 2 therms 2.33 5 therms 4.56

Carbon dioxide ($0.00334/lb) 102.39 lb 0.34 158.52 lb 0.53 392.84 lb 1.31

Ozone ($0.82/lb) 0.19 lb 0.16 0.29 lb 0.24 0.62 lb 0.51

Nitrogen dioxide ($0.82/lb) 0.17 lb 0.14 0.28 lb 0.23 0.59 lb 0.49

Sulfur dioxide ($1.50 /lb) 0.57 lb 0.86 0.93 lb 1.40 2.01 lb 3.02

Small particulate matter ($0.99/lb) 0.19 lb 0.19 0.25 lb 0.25 0.39 lb 0.39

Volatile organic compounds ($0.30/lb) 0.04 lb 0.01 0.07 lb 0.02 0.16 lb 0.05

Biogenic volatile organic compounds

($0.30/lb) 0 lb 0.00 0 lb -0.05 0 lb 0.00

Rainfall interception ($0.006/gal) 1,101 gal 6.83 1,644 gal 10.19 4,390 gal 27.22

Environmental subtotal 12.26 18.37 44.57

Other benefits 8.97 16.69 29.98

Total benefits 21.23 35.06 74.55

Total costs 11.17 16.82 17.71

Net benefits 10.06 18.23 56.85

LSA = leaf surface area.
35

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Average Annual Costs

Averaged over 40 years, the costs for yard and public trees, respectively, are

as follows:

• $9 and $16 for a small tree

• $10 and $18 for a medium tree

• $13 and $24 for a large tree

Annualized over the 40-year period, tree planting is the single greatest cost for

yard trees, averaging $4 per tree per year (see app. 2 tables 7, 10, 13). Based on

our survey, we assume in this study that a 2-in diameter at breast height (d.b.h.)

yard tree is planted at a cost of $160. The cost for planting a 2-in d.b.h. public tree

is $155. For public trees, where safety is particularly important and conflicts with

infrastructure are greater, pruning is the greatest cost, with average annual costs of

$5 to $8. Comparatively, annual pruning costs for yard trees are $2 to $6. At $4 to

$6 per tree per year, administrative costs are significant for public trees. Removal

and disposal expenditures, annualized over 40 years, average $2 to $3 per tree.

Table 3 shows annual management costs 20 years after planting for yard trees

to the west of a house and for public trees. Annual costs for yard trees range from

$3 to $8, and public tree care costs are $11 to $18. In general, public trees are

more expensive to maintain than yard trees because of their prominence and

because of the greater need for public safety.

Average Annual Benefits

Average annual benefits, including stormwater reduction, aesthetic value, air

quality improvement, and carbon dioxide (CO2

) sequestration increase with mature

tree size (figs. 17 and 18; for detailed results see app. 2):

• $15 to $21 for a small tree

• $27 to $35 for a medium tree

• $58 to $73 for a large tree

Stormwater runoff reduction—

By intercepting rain and snow before it reaches the stormwater treatment system,

trees can reduce runoff. Of the environmental benefits provided by trees in the

Lower Midwest, stormwater runoff reduction benefits are the greatest. The hackberry intercepts 4,808 gal per year on average over a 40-year period with an implied value of $30. The eastern redbud and littleleaf linden intercept 1,116, and

1,870 gal per year on average, with values of $7 and $12, respectively. Forty years

Costs of tree care

Stormwater runoff

reduction benefits

are crucial
36

GENERAL TECHNICAL REPORT PSW-GTR-219

after planting, stormwater runoff reductions equal 1,814, 3,526, and 8,382 gal for

the small, medium, and large deciduous trees, respectively.

As the cities of the Lower Midwest continue to grow, the amount of impervious

surface will continue to increase dramatically. The role that trees, in combination

with other strategies such as rain gardens and structural soils, can play in reducing

stormwater runoff is substantial.

Energy savings—

Energy benefits are the next largest environmental benefit and tend to increase

with mature tree size. For example, average annual net energy benefits over the

40-year period are $4 for the small eastern redbud tree opposite a west-facing wall,

$8 for the littleleaf linden, and $15 for the larger hackberry. For species of all sizes,

energy savings increase as trees mature and their leaf surface area increases (figs. 17

and 18).

Table 3—Estimated annual costs 20 years after planting for a private tree opposite the west-facing wall and a

public tree

Eastern redbud Littleleaf linden Northern hackberry

small tree medium tree large tree

20 ft tall 29 ft tall 51 ft tall

20-ft spread 24-ft spread 36-ft spread

LSA = 1,056 ft2 LSA = 1,414 ft2 LSA = 4,718 ft2

Private Public Private Public Private Public

Costs west tree west tree west tree

Dollars per tree per year

Pruning 0.52 2.99 4.20 5.60 4.20 5.60

Remove and dispose 1.95 1.77 2.67 2.43 2.88 2.62

Pest and disease 0.09 0.11 0.12 0.15 0.13 0.16

Infrastructure 0.17 1.19 0.24 1.63 0.26 1.75

Cleanup 0.12 0.82 0.16 1.12 0.18 1.21

Liability and legal 0.01 0.04 0.01 0.05 0.01 0.06

Admin. and other 0.00 4.26 0.00 5.85 0.00 6.30

Total costs 2.86 11.17 7.40 16.82 7.65 17.71

Total benefits 21.48 21.23 36.61 35.06 77.43 74.55

Total net benefits 18.63 10.06 29.22 18.23 69.78 56.85

Note: Prices for removal and disposal are included to account for expected mortality of citywide planting.

LSA = leaf surface area.

Energy savings are

substantial
37

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 17— Estimated annual benefits and costs for a small (eastern

redbud), medium (littleleaf linden), and large (northern hackberry)

deciduous tree located west of a residence. Costs are greatest during

the initial establishment period, whereas benefits increase with tree

size.

Figure 18—Estimated annual benefits and costs per tree for

public small (eastern redbud), medium (littleleaf linden), and

large (northern hackberry) deciduous tree.
38

GENERAL TECHNICAL REPORT PSW-GTR-219

As might be expected in a region with hot, humid summers, cooling savings are

substantial. Trees planted on the west side of buildings have the greatest total

energy benefits because the effect of shade on cooling costs is maximized without

blocking the warming rays of the winter sun. A yard tree located south of a home

produced the least total energy benefit because it had the least benefit during the

summer and the greatest adverse effect from shade on heating costs in winter. Trees

located east of a building provided intermediate benefits. Total energy benefits also

reflect species-related traits such as size, form, branch pattern, and density, as well

as time in leaf.

Average annual total energy benefits for public trees were less than for yard

trees and ranged from $3, $5, and $11 for the redbud, linden, and hackberry,

respectively.

Air Quality Improvement—

Air quality benefits are defined as the sum of pollutant uptake by trees and avoided

powerplant emissions from energy savings minus biogenic volatile organic compounds (BVOCs) released by trees. Average annual air quality benefits for the 40-

year period are $1 for the redbud, $2 for the linden, and $4 for the hackberry.

These relatively low air quality benefits reflect the clean air in the Lower Midwest

region, where cities previously listed by the U.S. EPA for being in violation of

federal air quality standards are now considered maintenance areas and no longer

in violation. Contrast these results with the air quality benefits of a large tree in the

Northeast region ($13; McPherson et al. 2007), Midwest region ($7.65; McPherson

et al. 2006c), and southern California ($28.38; McPherson 2000) where air quality

is poorer.

Reduced sulfur dioxide emissions due to trees reducing energy use produce the

greatest air quality benefit. Over 40 years, the hackberry, for example, is estimated

to reduce an average of 1.86 lb of sulfur dioxide from the air annually, valued at

$2.79. Average annual reductions in ozone, nitrogen oxides, and particulate matter

(PM10) for the large tree are valued at $0.56, $0.47, and $0.44, respectively. Of

the three species, only the linden is an emitter of BVOCs (0.21 lb per year), but

the 40-year average cost of these emissions are nearly negligible at $-0.06 per tree.

Forty years after planting, the average annual monetary values of air quality

improvement for the redbud, linden, and hackberry are $2, $3, and $5, respectively.
39

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Carbon dioxide reduction—

Net atmospheric CO2

 reductions accrue for all tree types. Average annual net reductions range from a high of 591 lbs ($1.97) for a large public tree to a low of 37 lbs

($0.12) for a small tree on the southern side of the house. Deciduous trees opposite

west-facing house walls generally produce the greatest CO2

 reduction because of

reduced powerplant emissions associated with energy savings. The values for the

redbud tree are lowest for CO2 reduction reflecting this small tree’s minor effect on

energy savings and sequestration.

Forty years after planting, net CO2 benefits for a yard tree opposite a west wall

are 203, 389, and 715 lb for the small, medium, and large deciduous tree, respectively. Releases of CO2

 associated with tree care activities account for less than

1 percent of net CO2

 sequestration.

Aesthetic and other benefits—

Aesthetic and other benefits reflected in property values account for a significant

portion of total benefits. As trees grow and become more visible, they can increase a

property’s sales price. Annual values averaged over 40 years associated with these

aesthetic and other benefits for yard trees are $8, $12, and $22 for the small,

medium, and large deciduous trees, respectively. The values for public trees are $8,

$14, and $24, respectively. The values for yard trees are slightly less than for public

trees because offstreet trees contribute less to a property’s curb appeal than more

prominent street trees. Because our estimates are based on median home sales

prices, the effects of trees on property values and aesthetics will differ depending on

local economies.
40

GENERAL TECHNICAL REPORT PSW-GTR-219
41

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 4. Estimating Benefits and Costs for Tree

Planting Projects in Your Community

This chapter shows two ways that benefit-cost information presented in this guide

can be used. The first hypothetical example demonstrates how to adjust values

from the guide for local conditions when the goal is to estimate benefits and

costs for a proposed tree planting project. The second example explains how to

compare net benefits derived from planting different types of trees. The last section

discusses actions communities can take to increase the cost-effectiveness of their

tree programs.

Applying Benefit-Cost Data

Flint Falls Example

The hypothetical city of Flint Falls is located in the Lower Midwest region and

has a population of 24,000. Most of its street trees were planted decades ago, with

English elms and silver maples (see “Common and Scientific Names” section) as

the dominant species. Currently, the tree canopy cover is sparse because a number

of trees died after drought conditions made them more susceptible to pests, and

they have not been replaced. Many of the remaining street trees are in declining

health. The city hired an urban forester 2 years ago and an active citizens group,

the Green Team, has formed (fig. 19).

Initial discussions among the Green Team, local utilities, the urban forester,

and other partners led to a proposed urban forestry program. The program intends

to plant 1,000 trees in Flint Falls over a 5-year period. Trained volunteers will

plant 3-in diameter trees in the following proportions: 75 percent large-maturing

trees, 20 percent medium-maturing trees, and 5 percent small-maturing trees. One

hundred trees will be planted in parks, and the remaining 900 trees will be planted

along Main Street and other downtown streets. Mortality rates for earlier planting

projects have been high, so the Green Team and the urban forester will concentrate

their planting efforts in areas that are likely to be most successful, including planting spaces with sufficient soil capacity for trees to grow and as little conflict with

infrastructure as possible, and that maximize environmental benefits. They expect

to find a number of good suggestions for planting in chapter 5 of this guide.

The Flint Falls City Council has agreed to maintain the current funding level

for management of existing trees. Also, they will advocate formation of a municipal tree district to raise funds for the proposed tree-planting project. A municipal

tree district is similar in concept to a landscape assessment district, which receives
42

GENERAL TECHNICAL REPORT PSW-GTR-219

revenues based on formulas that account for the services different customers

receive. For example, the proximity of customers to greenspace in a landscape

assessment district may determine how much they pay for upkeep. A municipal

tree district might receive funding from air quality districts, stormwater management agencies, electric utilities, businesses, and residents in proportion to the value

of future benefits these groups will receive from trees in terms of air quality,

hydrology, energy, carbon dioxide (CO2), and property value. The formation of

such a district would require voter approval of a special assessment that charges

recipients for tree planting and maintenance costs in proportion to the benefits they

receive from the new trees. The council needs to know the amount of funding

required for tree planting and maintenance, as well as how the benefits will be

distributed over the 40-year life of the project.

Figure 19—The (hypothetical) Green Team is motivated to re-green their

community by planting 1,000 trees in 5 years.
43

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

As a first step, the Flint Falls city forester and Green Team decided to use the

tables in appendix 2 to quantify total cumulative benefits and costs over 40 years

for the proposed planting of 1,000 public trees—750 large, 200 medium, and 50

small deciduous.

Before setting up a spreadsheet to calculate benefits and costs, the team considered which aspects of Flint Falls’ urban and community forestry project differ

from the regional values used in this guide (the methods for calculating the values

in app. 2 are described in app. 3):

1. The prices of electricity and natural gas in Flint Falls are $0.075 per kWh and

$1.15 per therm, not $0.068 per kWh and $0.973 per therm as used in this

guide. It is assumed that the buildings that will be shaded by the new street trees

have air conditioning and natural-gas heating.

2. The Green Team projected future annual costs for monitoring tree health and

implementing their stewardship program. Administration costs are estimated to

average $2,500 annually for the life of the trees or $2.50 per tree each year. This

guide assumed an average annual administration cost of $3.88 per tree. Thus, an

adjustment is necessary.

3. Planting will cost $200 per tree. The guide assumes planting costs of $155 per

tree. The costs will be higher for Flint Falls because they have decided to plant

larger trees.

To calculate the dollar value of total benefits and costs for the 40-year period,

the forester created a spreadsheet table (table 4). Each benefit and cost category

is listed in the first column. Prices, adjusted where necessary for Flint Falls, are

entered into the second column. The third column contains the resource units

(RUs) per tree per year associated with the benefit or the cost per tree per year,

which can be found in appendix 2. For aesthetic and other benefits, the dollar

values for public trees are placed in the RU columns. The fourth column lists the

40-year total values, obtained by multiplying the RU values by tree numbers,

prices, and 40 years.

To adjust for higher electricity prices, the forester multiplied electricity

saved for a large public tree in the RU column (98 kWh) by the Flint Falls price

for electricity ($0.075/kWh). This value ($7.35 per tree per year) was multiplied

by the number of trees planted and 40 years ($7.35 × 750 trees × 40 years =

$220,500) to obtain cumulative air-conditioning energy savings for the large public

trees (table 4). The process was carried out for all benefits and all tree types.

First step: determine tree planting

numbers

Second step: adjust

for local prices of

benefits

Third step: adjust for

local costs

Fourth step: calculate net benefits and

benefits-cost ratios

for public trees
44

GENERAL TECHNICAL REPORT PSW-GTR-219 Table 4—Spreadsheet calculations of benefits and costs for the Flint Falls planting project (1,000 trees) over 40 years 50 small trees 200 medium trees 750 large trees 1,000 total trees Adjusted Resource Total Resource Total Resource Total Total Percentage Benefits price units value units value units value value of benefits Dollars RU/tree/yr Dollars RU/tree/yr Dollars RU/tree/yr Dollars Dollars $/tree/yr Electricity (kWh) 0.0750 29 4,350 45 27,000 98 220,500 251,850 6.30 10.2 Natural gas (therms) 1.15 1 2,300 2 18,400 4 138,000 158,700 3.97 6.5 Net carbon dioxide (lb) 0.00334 91 608 150 4,008 374 37,475 42,091 1.05 1.7 Ozone (lb) 0.825 0.20 330 0.32 2,112 0.68 16,829 19,271 0.48 | Nitrogen dioxide (lb) 0.825 0.16 264 0.27 1,782 0.57 14,106 16,152 0.40 | Sulfur dioxide (lb) 1.50 0.53 1,590 0.89 10,677 1.86 83,676 95,943 2.40 | Small particulate | matter (lb) 0.99 0.15 297 0.27 2,141 0.45 13,384 15,823 0.40 6.0

Volatile organic compounds |

(lb) 0.30 0.04 24 0.07 170 0.15 1,367 1,561 0.04 |

Biogenic volatile organic |

compounds (lb) 0.30 0.00 0 -0.21 -510 0.00 0 -510 -0.01 |

Hydrology (gal) 0.0062 1,116 13,838 1,870 92,752 4,808 894,288 1,000,878 25.02 40.7

Aesthetics and other 8.48 16,960 13.81 110,480 29.32 728,400 855,840 21.40 34.8

Total benefits 40,562 269,012 2,148,026 2,457,599 61.44 100.0

Costs $/tree/yr Total $ $/tree/yr Total $ $/tree/yr Total $ Total $ $/tree/yr Percentage

of costs

Tree and planting 5.00 10,000 5.00 40,000 5.00 150,000 200,000 5.00 24.3Pruning 4.54 9,077 6.26 50,057 8.47 254,064 313,198 7.83 38.1Remove and dispose 1.74 3,471 2.39 19,121 2.64 79,177 101,769 2.54 12.4Infrastructure repair 1.08 2,153 1.47 11,793 1.61 48,267 62,213 1.56 7.6Cleanup 0.74 1,487 1.02 8,144 1.11 33,332 42,964 1.07 5.2Liability and legal 0.03 68 0.05 370 0.05 1,515 1,953 0.05 0.2Admin. and other 2.50 5,000 2.50 20,000 2.50 75,000 100,000 2.50 12.2 Total costs 31,256 149,485 641,356 822,097 20.55 100.0Net benefit 9,306 119,526 1,506,670 1,635,502 40.89Benefit/cost ratio 1.30 1.80 3.35 2.99RU = resource unit.
45

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

To adjust cost figures, the city forester changed the planting cost from $155

assumed in the guide to $200 (table 4). This planting cost was annualized by dividing the cost per tree by 40 years ($200/40 = $5.00 per tree per year). Total planting

costs were calculated by multiplying this value by 750 large trees and 40 years

($150,000).

The administration, inspection, and outreach costs are expected to average

$2.50 per tree per year. Consequently, the total administration cost for large trees is

$2.50 × 750 large trees × 40 years ($75,000). The same procedure was followed to

calculate costs for the medium and small trees.

All costs and all benefits were summed. Annual benefits over 40 years for the

whole planting total $2.46 million ($61.44 per tree per year), and annual costs total

about $822,000 ($20.55 per tree per year). Subtracting total costs from total

benefits yields net benefits over the 40-year period:

• $9,306 or $4.65 per tree per year for small deciduous trees

• $119,526 or $14.94 per tree per year for medium deciduous trees

• $1,506,670 or $50.22 per tree per year for large deciduous trees

Dividing total benefits by total costs yielded benefit-cost ratios (BCRs) of 1.30,

1.80, and 3.35 for small, medium, and large deciduous trees, respectively. The

BCR for the entire planting is 2.99, indicating that $2.99 will be returned for every

$1 invested.

This analysis assumes 43 percent of the planted trees die and does not account

for the time value of money from a capital investment perspective. Use the municipal discount rate to compare this investment in tree planting and management with

alternative municipal investments.

The city forester and Green Team now know that the project will cost about

$822,000, and the average annual cost will be $20,550 ($822,000/40 years);

however, a higher proportion of funds will be needed initially for planting and

irrigation. The fifth and last step is to identify the distribution of functional benefits

that the trees will provide. The last column in table 4 shows the distribution of

benefits as a percentage of the total:

• Energy savings = 16 percent (cooling = 10 percent, heating = 6 percent)

• CO2

 reduction = 2 percent

• Air quality improvement = 6 percent

• Stormwater runoff reduction = 41 percent

• Aesthetics/property value increase = 35 percent

Final step:

determine how

benefits are distributed, and link

these to sources

of revenues
46

GENERAL TECHNICAL REPORT PSW-GTR-219

With this information the planning team can determine how to distribute the

costs for tree planting and maintenance based on who benefits from the services the

trees will provide. For example, assuming the goal is to generate enough annual

revenue to cover the total costs of managing the trees ($822,000), fees could be

distributed in the following manner:

• $131,520 from electric and natural gas utilities for peak energy savings (16

percent). (Utility companies invest in planting trees because it is more cost

effective to reduce peak energy demand than to meet peak needs through

added infrastructure.)

• $16,440 from local industry for atmospheric CO2

 reductions (2 percent).

• $49,320 from air quality management district for net reduction in air

pollutants (6 percent).

• $337,020 from the stormwater management district for water quality

improvement associated with reduced runoff (41 percent).

• $287,700 from property owners for increased property values (35 percent).

Whether funds are sought from partners, the general fund, or other sources,

this information can assist managers in developing policy, setting priorities, and

making decisions. The Center for Urban Forest Research has developed a computer

program called STRATUM that simplifies these calculations for analysis of existing

street tree populations (Maco and McPherson 2003; for more information, see

www.itreetools.org; USDA FS 2006a).

City of Sandy Creek Example

Ten years ago, as a cost-cutting measure, the hypothetical city of Sandy Creek

stopped planting street trees in areas of new development. Instead, developers were

required to plant front yard trees, thereby reducing costs to the city. The community forester and concerned citizens came to notice that instead of the large, stately

trees the city had once planted, developers were planting small flowering trees,

which were more aesthetically pleasing in early years, but would never achieve the

stature—or the benefits—of larger shade trees. To evaluate the consequences of

these changes, the community forester and citizens decided to compare the benefits

of planting small, medium, and large trees for a hypothetical street-tree planting

project in a new neighborhood in Sandy Creek.

As a first step, the city forester and concerned citizens decided to quantify

the total cumulative benefits and costs over 40 years for three potential street tree

planting scenarios in Sandy Creek. The scenarios compare plantings of 500 small

trees, 500 medium trees, and 500 large trees. Data in appendix 2 are used for the

Distributing costs of

tree management to

multiple parties

First step: calculate

benefits and costs

over 40 years
47

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

calculations; however, three aspects of Sandy Creek’s urban and community

forestry program are different from those assumed in this tree guide:

1. The price of electricity is $0.075/kWh, not $0.068/kWh.

2. The city will provide irrigation for the first 5 years at a cost of approximately

$0.50 per tree annually.

3. Planting costs are $225 per tree for trees instead of $155 per tree.

To calculate the dollar value of total benefits and costs for the 40-year period,

the last column in the appendix 2 tables (40-year average) is multiplied by 40

years. Because this value is for one tree, it must be multiplied by the total number

of trees planted in the respective small, medium, or large tree size classes. To adjust

for higher electricity prices, we multiply electricity saved per tree in the resource

unit (RU) column (tables 6, 9, 12, and 15) for each tree type by the number of

trees and 40 years (large tree: 98 kWh × 500 trees × 40 years = 1,960,000 kWh).

This value is multiplied by the price of electricity in Sandy Creek ($0.075/kWh ×

1,960,000 kWh = $147,000) to obtain cumulative air-conditioning energy savings

for the project (table 5).

All the benefits are summed for each size tree for a 40-year period. The 500

small trees provide $382,611 in total benefits. The medium and large trees provide

approximately $627,000 and $1.3 million, respectively.

To adjust cost figures, we add a value for irrigation by multiplying the annual

cost by the number of trees and by the number of years that irrigation will be

applied ($0.50 × 500 trees × 5 years = $1,250). We multiply 500 large trees by the

unit planting cost ($225) to obtain the adjusted cost for planting (500 × $225 =

$112,500). The average annual 40-year costs taken from appendix 2 for other items

are multiplied by 40 years and the number of trees to compute total costs. These

40-year cost values are entered into table 5. The total costs for the small, medium

and large trees are $353,850, $443,650, and $507,050.

Subtracting total costs from total benefits yields net benefits for the small

($28,761), medium ($183,405), and large ($833,846) trees (table 5). The net

benefits per street tree over the 40-year period are as follows:

• $58 for a small tree

• $367 for a medium tree

• $1,668 for a large tree

When small trees are planted instead of large trees, the residents of Sandy

Creek stand to lose more than $1,600 per tree. In a new neighborhood with 500

trees, the total loss of benefits would exceed $800,000 over the project lifetime.

Second step: adjust

for local prices of

benefits

Third step: adjust for

local costs

Fourth step: calculate cost savings

and benefits forgone
48

GENERAL TECHNICAL REPORT PSW-GTR-219

Based on this analysis, the city of Sandy Creek decided to develop and enforce

a street tree ordinance that requires planting large trees where possible and requires

tree shade plans that show how developers will achieve 50 percent shade over

streets, sidewalks, and parking lots within 15 years of development (fig. 20).

This analysis assumes that 43 percent of the planted trees died. It does not

account for the time value of money from a capital investment perspective, but this

could be done by using the municipal discount rate.

Table 5—Spreadsheet calculations of benefits and costs for the Sandy Creek planting project comparison

over 40 years

500 small 500 medium 500 large

Resource Resource Resource

unit Total value unit Total value unit Total value

Dollars Dollars Dollars

Benefits:

Electricity (kWh) 580,000 43,500 900,000 67,500 1,960,000 147,000

Natural gas (therms) 20,000 230 40,000 460 80,000 920

Net carbon dioxide (lb) 1,820,000 6,067 3,000,000 9,991 7,480,000 24,959

Ozone (lb) 3,930 3,244 6,340 5,231 13,580 11,206

Nitrogen dioxide (lb) 3,150 2,600 5,450 4,498 11,380 9,388

Sulfur dioxide (lb) 10,530 15,791 17,830 26,734 37,230 55,824

Small particulate

matter (lb) 2,960 2,934 5,480 5,436 8,980 8,899

Volatile organic

compounds (lb) 820 249 1,400 426 2,920 888

Biogenic volatile organic

compounds (lb) 0 0 -4,230 -1,286 0 0

Hydrology (gal) 22,320,000 138,334 37,400,000 231,800 96,160,000 596,199

Aesthetics and other benefits 169,661 276,264 485,613

Total benefits 382,611 627,055 1,340,896

Costs:

Tree and planting 112,500 112,500 112,500

Pruning 90,800 125,200 169,400

Remove and dispose 34,800 47,800 52,800

Infrastructure 21,600 29,400 32,200

Irrigation 1,250 1,250 1,250

Cleanup 14,800 20,400 22,200

Liability and legal 600 1,000 1,000

Admin. and other 77,400 106,000 115,600

Total costs 353,850 443,650 507,050

Net benefits 28,761 183,405 833,846

Benefit-cost ratio 1.08 1.41 2.64
49

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Increasing Program Cost-Effectiveness

What if the program you have designed looks promising in terms of stormwaterrunoff reduction, energy savings, volunteer participation, and additional benefits,

but the costs are too high? This section describes some steps to consider that may

increase benefits and reduce costs, thereby increasing cost-effectiveness.

Increasing Benefits

Improved stewardship to increase the health and survival of recently planted trees

is one strategy for increasing cost-effectiveness. An evaluation of the Sacramento

Shade program found that tree survival rates had a substantial impact on projected

benefits (Hildebrandt et al. 1996). Higher survival rates increase energy savings and

reduce tree removal and planting costs.

Figure 20—A policy such as Sandy Creek’s, to plant as large a tree

as the site will handle, has provided ample benefits in the past.

Here, large-growing trees have been planted.

Pam Louks

What if costs are too

high?

Work to increase

survival rates
50

GENERAL TECHNICAL REPORT PSW-GTR-219

Conifers and broadleaf evergreens intercept rainfall and particulate matter

year round as well as reduce windspeeds and provide shade, which lowers summer

cooling and winter heating costs. Locating these types of trees in yards, parks,

school grounds, and other open-space areas can increase benefits.

Energy benefits can be further increased by planting a higher percentage of

trees in locations that produce the greatest energy savings, such as opposite westfacing walls and close to buildings with air conditioning. Keep in mind that evergreen trees should not be planted on the southern side of buildings because their

branches and leaves block the warm rays of the winter sun. By customizing tree

locations to increase numbers in high-yield sites, energy savings can be boosted.

Reducing Program Costs

Cost effectiveness is influenced by program costs as well as benefits:

Cost effectiveness = total benefit / total program cost

Cutting costs is one strategy to increase cost effectiveness. A substantial percentage of total program cost occurs during the first 5 years and is associated with

tree planting and establishment (McPherson 1993). Some strategies to reduce these

costs include:

• Plant bare-root or smaller tree stock.

• Use trained volunteers for planting and pruning of young trees (fig. 21).

• Provide followup care to increase tree survival and reduce replacement

costs.

• Select and locate trees to avoid conflicts with infrastructure.

Where growing conditions are likely to be favorable, such as yard or garden

settings, it may be cost effective to use smaller, less expensive stock or bare-root

trees. In highly urbanized settings and sites subject to vandalism, however, large

stock may survive the initial establishment period better than small stock.

Although organizing and training volunteers requires labor and resources, it is

usually less costly than contracting the work, and it can help build more support for

your program. A cadre of trained volunteers can easily maintain trees until they

reach a height of about 20 ft and limbs are too high to prune from the ground with

pole pruners. By the time trees reach this size they are well established. Pruning

during this establishment period should result in trees that will require less care in

the long term. Training young trees can provide a strong branching structure that

requires less frequent thinning and shaping (Costello 2000). Ideally, young trees

should be inspected and pruned every other year for the first 5 years after planting.

Target tree planting

with highest return

Reduce up-front and

establishment costs

Customize planting

locations

Prune early
51

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 21—Trained volunteers can plant and maintain young trees,

allowing the community to accomplish more at less cost and providing

satisfaction for participants.

Pam Louks

As trees grow larger, pruning costs may increase on a per-tree basis. The

frequency of pruning will influence these costs, as it takes longer to prune a tree

that has not been pruned in 10 years than one that was pruned a few years ago.

Although pruning frequency differs by species and location, a return frequency

of about 5 to 8 years is usually sufficient for older trees (Miller 1997).

Investing in the resources needed to promote tree establishment during the first

5 years after planting is usually worthwhile, because once trees are established they

have a high probability of continued survival. If your program has targeted trees on

private property, then encourage residents to attend tree-care workshops. Develop

standards of “establishment success” for different types of tree species. Perform

Use less expensive

stock where appropriate
52

GENERAL TECHNICAL REPORT PSW-GTR-219

periodic inspections to alert residents to tree health problems, and reward those

whose trees meet your program’s establishment standards. Replace dead trees as

soon as possible, and identify ways to improve survivability.

Carefully select and locate trees to avoid conflicts with overhead power lines,

sidewalks, and underground utilities. Time spent planning the planting will result in

long-term savings. Also consider soil type and irrigation, microclimate, and the

type of activities occurring around the tree that will influence its growth and

management.

When evaluating the bottom line—trees pay us back—do not forget to consider

benefits other than the stormwater-runoff reductions, energy savings, atmospheric

CO2

 reductions, and other tangible benefits. The magnitude of benefits related to

employment opportunities, job training, community building, reduced violence,

and enhanced human health and well-being can be substantial (fig. 22). Moreover,

these benefits extend beyond the site where trees are planted, furthering collaborative efforts to build better communities.

For more information on urban and community forestry program design and

implementation, see the list of additional resources in appendix 1.

Figure 22—Trees pay us back in tangible and intangible ways.

Brian Jorgenson

Match tree to site

It all adds up—trees

pay us back
53

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 5. General Guidelines for Selecting and

Placing Trees

Guidelines for Energy Savings

Maximizing Energy Savings From Shading

The right tree in the right place can save energy and reduce tree care costs. In

midsummer, the sun shines on the east side of a building in the morning, passes

over the roof near midday, and then shines on the west side in the afternoon (see

fig. 4). Electricity use is highest during the afternoon when temperatures are

warmest and incoming sunshine is greatest. Therefore, the west side of a home is

the most important side to shade (Sand 1993) (fig. 23).

Depending on building orientation and window placement, sun shining through

windows can heat a home quickly during the morning hours. The east side is the

second most important side to shade when considering the net impact of tree shade

on energy savings (fig. 23). Deciduous trees on the east side provide summer shade

and more winter solar heat gain than evergreens.

Trees located to shade south walls can block winter sunshine and increase

heating costs because during winter the sun is lower in the sky and shines on the

south side of homes (fig. 24). The warmth the sun provides is an asset, and planting

evergreen trees on the southern side of a home would block southern exposures and

solar collectors. Use solar-friendly trees to the south because the bare branches of

these deciduous trees allow most sunlight to strike the building (some solar-unfriendly deciduous trees can reduce sunlight striking the south side of buildings by

Figure 23—Locate trees to shade west and east

windows (from Sand 1993).

Where should shade

trees be planted?

Figure 24—Select solar-friendly trees for

southern exposures and locate them close

enough to provide winter solar access and

summer shade (from Sand 1991).
54

GENERAL TECHNICAL REPORT PSW-GTR-219

50 percent even without leaves) (Ames 1987). Examples of solar-friendly trees

include most species and cultivars of maples, crapemyrtle, honeylocust, sweetgum,

and zelkova (see “Common and Scientific Names” section). Some solar-unfriendly

trees include most oaks, sycamore, most elms, and river birch (McPherson et al.

1994).

To maximize summer shade and minimize winter shade, locate shade trees

about 10 to 20 ft south of the home. As trees grow taller, prune lower branches

to allow more sun to reach the building if this will not weaken the tree’s structure

(fig. 25).

Although the closer a tree is to a home the more shade it provides, roots of

trees that are too close can damage the foundation. Branches too close to the building can make it difficult to maintain exterior walls and windows. Trees should be a

minimum of 10 ft or farther from the home depending on mature crown spread, to

avoid these conflicts. It should be noted, however, that trees within 30 to 50 ft of

Figure 25—Trees south of a home before and

after pruning. Lower branches are pruned up to

increase heat gain from winter sun (from Sand

1993).
55

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

the home most effectively shade windows and walls. Hence, larger growing trees

may need pruning to avoid conflict with the structure and to systematically raise

the crown until it has cleared the roofline.

Paved patios and driveways can become heat sinks that warm the home during

the day. Shade trees can make them cooler and more comfortable spaces. If a home

is equipped with an air conditioner, shading can reduce its energy use, but do not

plant vegetation so close that it will obstruct the flow of air around the unit.

Plant only small-growing trees under overhead power lines, and avoid planting

directly above underground water and sewer lines if possible. Contact your local

utility company before planting to determine where underground lines are located

and which tree species should not be planted below power lines.

Planting Windbreaks for Heating Savings

A tree’s size and crown density can make it ideal for blocking wind, thereby

reducing the impacts of cold winter weather. Locate rows of trees perpendicular

to the prevailing wind (fig. 26), usually the north and west side of homes in the

Lower Midwest region.

Design the windbreak row to be longer than the building being sheltered

because windspeed increases at the edge of the windbreak. Ideally, the windbreak

should be planted upwind about 25 to 50 ft from the building and should consist

of dense evergreens that will grow to twice the height of the building they shelter

(Heisler 1986, Sand 1991). Avoid planting windbreaks that will block sunlight to

south and east walls (fig. 27). Trees should be spaced close enough to form a dense

screen, but not so close that they will block sunlight to each other, causing lower

Figure 26—Evergreens protect a building from dust and cold

by reducing windspeeds (from Sand 1993). Figure 27—Midwinter shadows from a welllocated windbreak and shade trees do not

block solar radiation on the south-facing wall

(from Sand 1993).

Plant dense evergreens
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GENERAL TECHNICAL REPORT PSW-GTR-219

branches to self-prune. Most conifers can be spaced about 6 ft on center. If there is

room for two or more rows, then space rows 10 to 12 ft apart.

Evergreens are preferred over deciduous trees for windbreaks because they

provide better wind protection. The ideal windbreak tree is fast growing, visually

dense, has strong branch attachments, and has stiff branches that do not self-prune.

Your local cooperative extension agent or urban forester can help you select appropriate trees for your area.

In settings where vegetation is not a fire hazard, evergreens planted close to the

home create airspaces that reduce air infiltration and heat loss. Allow shrubs to

form thick hedges, especially along north, west, and east walls.

Selecting Trees to Maximize Benefits

The ideal shade tree has a fairly dense, round crown with limbs broad enough

to partially shade the roof. Given the same placement, a large tree will provide

more shade than a small tree. Deciduous trees allow sun to shine through leafless

branches in winter. Plant small trees where nearby buildings or power lines limit

aboveground space. Columnar trees are appropriate in narrow side yards. Because

the best location for shade trees is relatively close to the west and east sides of

buildings, the most suitable trees will be strong and capable of resisting storm

damage, disease, and pests (Sand 1994). Examples of trees not to select for placement near buildings include cottonwoods and silver maples because of their invasive roots, weak wood, and large size, and ginkgos because of their sparse shade

and slow growth during youth.

When selecting trees, match the tree’s water requirements with those of surrounding plants. For instance, select low-water-use species for planting in areas that

receive little irrigation. Also, match the tree’s maintenance requirements with the

amount of care and the type of use different areas in the landscape receive. For

instance, tree species that drop fruit that can be a slip-and-fall problem should not

be planted near paved areas that are frequently used by pedestrians. Check with

your local landscape professional before selecting trees to make sure that they are

well suited to the site’s soil and climatic conditions.

Use the following practices to plant and manage trees strategically to maximize

energy conservation benefits:

• Increase community-wide tree canopy, and target shade to streets, parking

lots, and other paved surfaces, as well as air-conditioned buildings.

• Shade west- and east-facing windows and walls.

• Select solar-friendly trees opposite east- and south-facing walls.

There are many

choices

Picking the right

tree

Maximizing energy

savings from trees
57

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

• Shade air conditioners, but don’t obstruct airflow.

• Avoid planting trees too close to utilities and buildings.

• Where space permits, create multirow, evergreen windbreaks that are

longer than the building.

Guidelines for Reducing Carbon Dioxide

Because trees in common areas and other public places may not shelter buildings

from sun and wind and reduce energy use, carbon dioxide (CO2

) reductions are

primarily due to sequestration. Fast-growing trees sequester more CO2

 initially than

slow-growing trees, but this advantage can be lost if the fast-growing trees die at

younger ages. Large trees have the capacity to store more CO2 than smaller trees

(fig. 28). To maximize CO2

 sequestration, select tree species that are well suited to

the site where they will be planted. Consult with your local arborist to select the

Figure 28—Compared with small trees, large trees can store more carbon,

filter more air pollutants, intercept more rainfall, and provide greater energy

savings. Here maple trees line an Indianapolis street in Center Township.
58

GENERAL TECHNICAL REPORT PSW-GTR-219

right tree for your site. Trees that are not well adapted will grow slowly, show

symptoms of stress, or die at an early age. Unhealthy trees do little to reduce

atmospheric CO2

 and can be unsightly liabilities in the landscape.

Design and management guidelines that can increase CO2

 reductions include the

following:

• Maximize use of woody plants, especially trees, as they store more CO2

than do herbaceous plants and grasses.

• Plant more trees where feasible, and immediately replace dead trees to

compensate for CO2 lost through removal.

• Create diverse habitats, with trees of different ages and species, to promote

a continuous canopy cover over time.

• Group species with similar landscape maintenance requirements together

and consider how irrigation, pruning, fertilization, weed, pest, and disease

control can be minimized.

• Reduce CO2 associated with landscape management by using push mowers

(not gas or electric), hand saws (not chain saws), pruners (not gas/electric

shears), rakes (not leaf blowers), and employ landscape professionals who

don’t have to travel far to your site.

• Reduce maintenance by reducing turfgrass and planting drought-tolerant or

environmentally friendly landscapes.

• Consider the project’s lifespan when selecting species. Fast-growing species

will sequester more CO2

 initially than slow-growing species, but may not

live as long.

• Provide ample space belowground for tree roots to grow so that they can

maximize CO2

 sequestration and tree longevity.

• When trees die or are removed, salvage as much wood as possible for use

as furniture and other long-lasting products to delay decomposition.

• Plant trees, shrubs, and vines in strategic locations to maximize summer

shade and reduce winter shade, thereby reducing atmospheric CO2 emissions associated with power production.

Guidelines for Reducing Stormwater Runoff

Trees are minireservoirs, controlling runoff at the source because their leaves and

branch surfaces intercept and store rainfall, thereby reducing runoff volumes and

erosion of watercourses, as well as delaying the onset of peak flows. Rainfall

interception by large trees is a relatively inexpensive first line of defense in the

battle to control nonpoint-source pollution.
59

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

When selecting trees to maximize rainfall interception benefits, consider the

following:

• Select tree species with physiological features that maximize interception,

such as evergreen foliage, large leaf surface area, and rough surfaces that

store water (Metro 2002).

• Increase interception by planting large trees where possible (fig. 29).

• Plant trees that are in leaf when precipitation levels are highest.

• Plant low-water-use tree species where appropriate and native species that,

once established, require little supplemental irrigation.

• In bioretention areas, such as roadside swales, select species that tolerate

inundation, are long-lived, wide-spreading, and fast-growing (Metro 2002).

• Do not pave over streetside planting strips for easier weed control; this can

reduce tree health and increase runoff.

• Bioswales in parking lots and other paved areas store and filter stormwater

while providing good conditions for trees.

Figure 29—Trees can create a continuous canopy for maximum rainfall interception, even in commercial areas. In this example, a swale in the median

filters runoff and provides ample space for large trees. Parking-space-sized

planters contain the soil volume required to grow healthy, large trees (from

Metro 2002).
60

GENERAL TECHNICAL REPORT PSW-GTR-219

Guidelines for Improving Air Quality Benefits

Trees, sometimes called the “lungs of our cities,” are important because of their

ability to remove contaminants from the air. The amount of gaseous pollutants and

particulates removed by trees depends on their size and architecture, as well as local

meteorology and pollutant concentrations.

Along streets, in parking lots, and in commercial areas, locate trees to maximize shade on paving and parked vehicles. Shade trees reduce heat that is stored or

reflected by paved surfaces. By cooling streets and parking areas, trees reduce

emissions of evaporative hydrocarbons from parked cars and thereby reduce smog

formation (Scott et al. 1999). Large trees can shade a greater area than smaller

trees, but should be used only where space permits. Remember that a tree needs

space for both branches and roots. Keep in mind also that the soil along streets and

parking lots will likely be compacted, and measures to reduce this problem, such as

the use of engineered or structural soils, must be taken.

Tree planting and management guidelines to improve air quality include the

following (Nowak 2000, Smith and Dochinger 1976):

• Select species that tolerate pollutants that are present in harmful concentrations. For example, in areas with high ozone (O3

) concentration, avoid

sensitive species such as white and green ash, tulip, poplar, and Austrian

pine (Noble et al. 1988).

• Conifers have high surface-to-volume ratios and retain their foliage year

round, which may make them more effective than deciduous species. In

parking areas, however, species should be carefully chosen to avoid those

that give off sticky residues.

• Species with long leaf stems (e.g., ash, maple) and hairy plant parts (e.g.,

oak, birch, sumac) are especially efficient interceptors.

• Effective uptake depends on proximity to the pollutant source and the

amount of biomass. Where space and fire conditions permit, plant multilayered stands near the source of pollutants.

• In areas with unhealthy O3

 concentrations, maximize use of plants that emit

low levels of biogenic volatile organic compounds to reduce O3

 formation.

• Sustain large, healthy trees; they produce the most benefits.

• To reduce emissions of volatile organic compounds and other pollutants,

plant trees to shade parked cars and conserve energy.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Guidelines for Avoiding Conflicts With

Infrastructure

Trees can become liabilities when they conflict with power lines, underground

utilities, and other infrastructure elements. Guidelines to reduce conflicts with

infrastructure include the following:

• Before planting, contact your local before-digging company using the

national 811 number to locate underground water, sewer, gas, and telecommunications lines.

• Avoid locating trees where they will block streetlights or views of traffic

and commercial signs.

• Check with local transportation officials for sight visibility requirements.

Keep trees at least 30 ft away from street intersections to ensure visibility.

• Avoid planting shallow-rooting species near sidewalks, curbs, and paving

where tree roots can heave pavement if planted too close. Generally, avoid

planting within 3 ft of pavement, and remember that trunk flare at the base

of large trees can displace soil and paving for a considerable distance.

Consider strategies to reduce damage by tree roots such as meandering

sidewalks around trees (Costello and Jones 2003).

• Plant only small trees (<25 ft tall) under overhead power lines, and do not

plant directly above underground water and sewer lines (fig. 30). Avoid

locating trees where they will block illumination from streetlights or views

of street signs in parking lots, commercial areas, and along streets.

Maintenance requirements and public safety concerns influence the type of

trees selected for public places. The ideal public tree is not susceptible to wind

damage and branch drop, does not require frequent pruning, produces negligible

litter, is deep-rooted, has few serious pest and disease problems, and tolerates a

wide range of soil conditions, irrigation regimes, and air pollutants. Because relatively few trees have all these traits, it is important to match the tree species to the

planting site by determining what issues are most important on a case-by-case basis.

For example, parking-lot trees should be tolerant of hot, dry conditions, have

strong branch attachments, and be resistant to attacks by pests that leave vehicles

covered with sticky exudates. Check with your local horticultural extension agency,

state urban forestry program, or city forestry department for horticultural information on tree traits.
62

GENERAL TECHNICAL REPORT PSW-GTR-219

Guidelines for Maximizing Long-Term Benefits

Selecting a tree from the nursery that has a high probability of becoming a healthy,

trouble-free mature tree is critical to a successful outcome. Therefore, select

the very best stock at your nursery and, when necessary, reject nursery stock that

does not meet American National Standards Institute (ANSI) Z60-Nursery Stock

standards.

The health of the tree’s root ball is critical to its ultimate survival. If the tree

is in a container, check for matted roots by sliding off the container. Roots should

penetrate to the edge of the root ball, but not densely circle the inside of the container or grow through drain holes. As well, at least two large structural roots

should emerge from the trunk within 1 to 3 in of the soil surface. If there are no

roots in the upper portion of the root ball, it is undersized and the tree should not

be planted.

Figure 30—Know where power lines and other utility lines are before planting. Under power lines,

use only small-growing trees (“low zone”) and avoid planting directly above underground utilities.

Larger trees may be planted where space permits (“medium” and “tall zones”) (from ISA 1992).
63

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Another way to evaluate the quality of the tree before planting is to gently

move the trunk back and forth. A good tree trunk bends and does not move in the

soil, whereas a poor trunk bends a little and pivots at or below the soil line—a telltale sign of a poorly anchored tree.

Dig the planting hole 1 in shallower than the depth of the root ball to allow for

some settling after watering. Make the hole two to three times as wide as the root

ball and loosen the sides of the hole to make it easier for roots to penetrate. Place

the tree so that the root flare is at the top of the soil. If the structural roots have

grown properly as described above, the top of the root ball will be slightly higher

(1 to 2 in) than the surrounding soil to allow for settling. Backfill with the native

soil unless it is very rocky or sandy, in which case you may want to add composted

organic matter such as peat moss or shredded bark (fig. 31).

Planting trees in urban plazas, commercial areas, and parking lots poses special

challenges because of limited soil volume and poor soil structure. For trees to

deliver benefits over the long term they require enough soil volume to grow and

A good tree is wellanchored

Plant the tree in the

right size hole

Figure 31— Prepare a broad planting area, plant the tree with the root flare at or just above ground

level, and provide a berm/water ring to retain water (drawing courtesy of International Society of

Arboriculture). (Note that trunk flare shown here represents a tree grown under optimum conditions.

In trees grown under poorer conditions, the trunk flare may be hidden beneath the soil. These trees

should be rejected in favor of those grown more carefully, or at the very least, the soil should be

removed to expose the flare. See American National Standards Institute (ANSI) A 300—Tree

Planting Standards).
64

GENERAL TECHNICAL REPORT PSW-GTR-219

remain healthy. Matching tree species to the site’s soil volume can reduce sidewalk

and curb damage as well. Figure 32 shows recommended soil volumes for different-sized trees. Engineered or structural soils can be placed under the hardscape to

increase rooting space while meeting engineering requirements. For more information on structural soils see Reducing Infrastructure Damage by Tree Roots: A

Compendium of Strategies (Costello and Jones 2003).

Use the extra soil left after planting to build a berm outside the root ball that is

6 in high and 3 ft in diameter. Soak the tree, and gently rock it to settle it in. Cover

the basin with a 2- to 4-in layer of mulch, but avoid placing mulch against the tree

trunk. Water the new tree two to three times a week and increase the amount of

water as the tree grows larger. Generally, a tree requires about 1 in of water per

week. A rain gauge or soil moisture sensor (tensiometer) can help determine tree

watering needs, or contact your local cooperative extension agent or water conservancy district for recommendations.

After you’ve planted your tree, remember the following:

• Inspect your tree several times a year, and contact a local landscape professional if problems develop.

Figure 32—Developed from several sources by Urban (1992), this graph shows the relationship

between tree size and required soil volume. For example, a tree with a 16-in diameter at breast height

with 640 ft2

 of crown projection area requires 1,000 ft3 of soil (from Costello and Jones 2003).
65

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

• If your tree needed staking to keep it upright, remove the stake and ties

after 1 year or as soon as the tree can hold itself up. The staking should

allow some tree movement, as this movement sends hormones to the roots

causing them to grow and create greater tree stability. It also promotes

trunk taper and growth.

• Reapply mulch and irrigate the tree as needed.

• Leave lower side branches on young trees for the first year to increase

taper. Remove dead, dying, and broken branches in the first year. Once

established, prune young trees to maintain a central main trunk and equally

spaced branches. For more information, see Costello (2000), Gilman

(2002), and ANSI A 300 Maintenance Standard Practices—Young Trees

2008). As the trees mature, they should be pruned on a regular basis by a

certified arborist or other experienced professional.

• By keeping your tree healthy, you maximize its ability to produce shade,

intercept rainfall, reduce atmospheric CO2

, and provide other benefits.

For more information on tree selection, planting, establishment, and care, see

the resources listed in appendix 1.
66

GENERAL TECHNICAL REPORT PSW-GTR-219

Glossary

annual fuel utilization efficiency (AFUE)—A measure of space heating equipment efficiency defined as the fraction of energy output per energy input.

anthropogenic—Produced by humans.

biodiversity—The variety of life forms in a given area. Diversity can be categorized in terms of the number of species, the variety in the area’s plant and animal

communities, the genetic variability of the animals or plants, or a combination of

these elements.

biogenic—Produced by living organisms.

biogenic volatile organic compounds (BVOCs)—Hydrocarbon compounds from

vegetation (e.g., isoprene, monoterpene) that exist in the ambient air and contribute

to the formation of smog or may themselves be toxic. Emission rates (μg·g•-1·hr•-1)

used for this report follow Benjamin and Winer (1998):

• Celtis occidentalis—0.0 (isoprene); 0.0 (monoterpene)

• Tilia cordata—1.6 (isoprene); 2.9 (monoterpene)

• Cercis canadensis—0.0 (isoprene); 0.0 (monoterpene)

canopy—A layer or multiple layers of branches and foliage at the top or crown of

a forest’s trees.

canopy cover—The area of land surface that is covered by tree canopy, as seen

from above.

climate—The average weather for a particular region and period (usually 30

years). Weather describes the short-term state of the atmosphere; climate is the

average pattern of weather for a particular region. Climatic elements include

precipitation; temperature; humidity, sunshine; wind velocity; phenomena such as

fog, frost, and hailstorms; and other measures of weather.

climate effects—Impact on residential space heating and cooling (kilograms of

carbon dioxide per tree per year) from trees located more than 50 ft from a building owing to associated reductions in windspeeds and summer air temperatures.

community forests—The sum of all woody and associated vegetation in and

around human settlements, ranging from small rural villages to metropolitan

regions.

conifers—Cone-bearing evergreen trees with needle-like leaves.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

contract rate—The percentage of residential trees cared for by commercial

arborists; the proportion of trees for which a specific service (e.g., pruning or pest

management) is contracted.

control costs—The marginal cost of preventing, controlling, or mitigating an

impact.

crown—The branches and foliage at the top of a tree.

cultivar (derived from “cultivated variety”)—Denotes certain cultivated plants

that are clearly distinguishable from others by any characteristic, and that when

reproduced (sexually or asexually), retain their distinguishing characteristics. In

the United States, “variety” is often considered synonymous with “cultivar.”

damage costs—The total estimated economic loss produced by an impact.

deciduous—Trees or shrubs that lose their leaves every fall.

diameter at breast height (d.b.h.)—The diameter of a tree outside the bark

measured 4.5 ft above the ground on the uphill side (where applicable) of the tree.

dripline—The area beneath a tree marked by the outer edges of the branches.

emission factor—The rate of carbon dioxide, nitrogen dioxide, sulfur dioxide, and

small particulate matter output resulting from the consumption of electricity,

natural gas, or any other fuel source.

evapotranspiration—The total loss of water by evaporation from the soil surface

and by transpiration from plants, from a given area, and during a specified period.

evergreens—Trees or shrubs that are never entirely leafless. Evergreens may be

broadleaved or coniferous (cone-bearing with needlelike leaves).

greenspace—Urban trees, forests, and associated vegetation in and around human

settlements, ranging from small communities in rural settings to metropolitan

regions.

hardscape—Paving and other impervious ground surfaces that reduce infiltration

of water into the soil.

heat sinks—Paving, buildings, and other surfaces that store heat energy from the

sun.

hourly pollutant dry deposition—Removal of gases from the atmosphere by

direct transfer to natural surfaces and absorption of gases and particles by natural

surfaces such as vegetation, soil, water, or snow.
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GENERAL TECHNICAL REPORT PSW-GTR-219

interception—Amount of rainfall held on tree leaves and stem surfaces.

kWh (kilowatt-hour)—A unit of work or energy, measured as 1 kW (1,000 watts)

of power expended for 1 hour.

leaf area index (LAI)—Total leaf area per unit area of crown if crown were

projected in two dimensions.

leaf surface area (LSA)—Measurement of area of one side of a leaf or leaves.

mature tree—A tree that has reached a desired size or age for its intended use.

Size, age, and economic maturity differ depending on the species, location, growing conditions, and intended use.

mature tree size—The approximate size of a tree 40 years after planting.

metric tonne—A measure of weight (abbreviated “t”) equal to 1,000,000 grams

(1000 kg) or 2,205 pounds.

municipal forester—A person who manages public street or park trees (municipal

forestry programs) for the benefit of the community.

MWh (megawatt-hour)—A unit of work or energy, measured as 1 megawatt

(1,000,000 watts) of power expended for 1 hour. One MWh is equivalent to 3.412

MBtu.

nitrogen oxides (oxides of nitrogen, NOx

)—A general term for compounds of

nitric acid (NO), nitrogen dioxide (NO2

), and other oxides of nitrogen. Nitrogen

oxides are typically created during combustion processes and are major contributors

to smog formation and acid deposition. NO2 may cause numerous adverse human

health effects.

ozone (O3

)—A strong-smelling, pale blue, reactive toxic chemical gas with molecules of three oxygen atoms. It is a product of the photochemical process involving the Sun’s energy. Ozone exists in the upper layer of the atmosphere as well as

at the Earth’s surface. Ozone at the Earth’s surface can cause numerous adverse

human health effects. It is a major component of smog.

peak flow (or peak runoff)—The maximum rate of runoff at a given point or

from a given area, during a specific period.

photosynthesis—The process in green plants of converting water and CO2

 into

sugar by using light energy; accompanied by the production of oxygen.

PM10 (particulate matter)—Major class of air pollutants consisting of tiny solid
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

or liquid particles of soot, dust, smoke, fumes, and mists. The size of the particles

(10 microns or smaller, about 0.0004 in or less) allows them to enter the air sacs

(gas-exchange region) deep in the lungs where they may be deposited and cause

adverse health effects. PM10 also reduces visibility.

reduced powerplant emissions—Reduced emissions of carbon dioxide (CO2

) or

other pollutants that result from reductions in building energy use owing to the

moderating effect of trees on climate. Reduced energy use for heating and cooling

results in reduced demand for electrical energy, which translates into fewer emissions by powerplants.

resource unit (RU)—The value used to determine and calculate benefits and costs

of individual trees. For example, the amount of air conditioning energy saved in

kWh/year per tree, air-pollutant uptake in pounds per year per tree, or rainfall

intercepted in gallons per tree per year.

riparian habitats—Narrow strips of land bordering creeks, rivers, lakes, or other

bodies of water.

seasonal energy efficiency ratio (SEER)—Ratio of cooling output to power

consumption; kBtu-output/kWh-input as a fraction. It is the Btu of cooling output

during normal annual usage divided by the total electric energy input in kilowatthours during the same period.

sequestration—Annual net rate that a tree removes CO2

 from the atmosphere

through the processes of photosynthesis and respiration (kg of CO2

 per tree per

year).

shade coefficient—The percentage of light striking a tree crown that is transmitted

through gaps in the crown. This is the percentage of light that hits the ground.

shade effects—Impact on residential space heating and cooling (kg of CO2

 per tree

per year) from trees located within 50 ft of a building.

solar-friendly trees—Trees that have characteristics that reduce blocking of winter

sunlight. According to one numerical ranking system, these traits include open

crowns during the winter heating season, leaves that fall early and appear late,

relatively small size, and a slow growth rate (Ames 1987).

stem flow—Amount of rainfall that travels down the tree trunk and onto the

ground.
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GENERAL TECHNICAL REPORT PSW-GTR-219

sulfur dioxide (SO2)—A strong-smelling, colorless gas that is formed by the

combustion of fossil fuels. Powerplants, which may use coal or oil high in sulfur

content, can be major sources of SO2

. Sulfur oxides contribute to the problem of

acid deposition.

therm—A unit of heat equal to 100,000 British thermal units (BTUs) or 100 kBtu.

throughfall—Amount of rainfall that falls directly to the ground below the tree

crown or drips onto the ground from branches and leaves.

transpiration—The loss of water vapor through the stomata of leaves.

tree or canopy cover—Within a specific area, the percentage covered by the crown

of an individual tree or delimited by the vertical projection of its outermost perimeter; small openings in the crown are ignored. Used to express the relative importance of individual species within a vegetation community or to express the

coverage of woody species.

tree litter—Fruit, leaves, twigs, and other debris shed by trees.

tree-related CO2

 emissions—CO2 released when growing, planting, and caring for

trees.

tree surface saturation storage capacity—The maximum volume of water that

can be stored on a tree’s leaves, stems, and bark. This part of rainfall stored on the

canopy surface does not contribute to surface runoff during and after a rainfall

event.

urban heat island—An area in a city where summertime air temperatures are 3

to 8 °F warmer than temperatures in the surrounding countryside. Urban areas are

warmer for two reasons: (1) dark construction materials for roofs and asphalt

absorb solar energy; and (2) few trees, shrubs, or other vegetation provide shade

and cool the air.

volatile organic compounds (VOCs)—Hydrocarbon compounds that exist in the

ambient air. VOCs contribute to the formation of smog or are themselves toxic.

VOCs often have an odor. Some examples of VOCs are gasoline, alcohol, and the

solvents used in paints.

willingness to pay—The maximum amount of money an individual would be

willing to pay for nonmarket, public goods and services provided by environmental

amenities such as trees and forests rather than do without.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Common and Scientific Names

Common name Scientific name

Plants:

American holly Ilex opaca Aiton

Ash Fraxinus spp.

Austrian pine Pinus nigra J.F. Arnold

Birch Betula spp.

Black oak Quercus velutina Lam.

Blackgum Nyssa spp.

Black walnut Juglans nigra L.

Blue spruce Picea pungens Engelm.

Callery pear Pyrus calleryana Dcne.

Cottonwood Populus spp.

Crabapple Malus spp.

Crapemyrtle Lagerstroemia indica L.

Eastern cottonwood Populus deltoides Bartram ex Marsh.

Eastern redbud Cercis canadensis L.

Eastern white pine Pinus strobus L.

Elm Ulmus spp.

English elm Ulmus procera Salisb.

Ginkgo Ginkgo biloba L.

Green ash Fraxinus pennsylvanica Marsh.

Honeylocust Gleditsia triacanthos L.

Littleleaf linden Tilia cordata Mill.

Maple Acer spp.

Mulberry Morus spp.

Norway maple Acer platanoides L.

Northern catalpa Catalpa speciosa (Warder) Warder ex Engelm.

Northern hackberry Celtis occidentalis L.

Northern red oak Quercus rubra L.

Oak Quercus spp.

Pear Pyrus spp.

Poplar Populus spp.

River birch Betula nigra L.

Russian olive Elaeagnus angustifolia L.

Siberian elm Ulmus pumila L.

Silver maple Acer saccharinum L.

Sugar maple Acer saccharum Michx.

Sumac Rhus spp.

Sweetgum Liquidambar styraciflua L.

Sycamore Platanus spp.

Tree-of-heaven Ailanthus altissima (P. Mill.) Swingle

Tulip tree Liriodendron tulipifera L.

White ash Fraxinus americana L.

Zelkova Zelkova serrata (Thunb.) Makino

Insects:

Emerald ash borer Agrilus planipennis Fairmaire
72

GENERAL TECHNICAL REPORT PSW-GTR-219

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 25,400 Microns

Inches (in) 25.4 Millimeters (mm)

Inches (in) 2.54 Centimeters (cm)

Feet (ft) 0.305 Meters (m)

Square feet (ft2) 0.0929 Square meters (m2)

Miles (mi) 1.61 Kilometers (km)

Square miles (mi2) 2.59 Square kilometers (km2)

Acre-feet 1233.6 Cubic meters (m3)

Gallons (gal) 0.00378 Cubic meters (m3

)

Ounces 28.35 Grams (g)

Ounces 28,349,523 Micrograms (μg)

Pounds (lb) 0.454 Kilograms (kg)

Pounds per square foot (lb/ft2

) 4.882 Kilograms per square meter

(kg/m2)

Tons (ton) 0.907 Metric tonne (t)

Million BTUs 0.2931 Megawatt hours (MWh)

Therms 29.31 Kilowatt hours (kWh)

Fahrenheit (°F) 0.56 (F•32) Celsius (°C)

Acknowledgments

A number of people assisted with data collection and provided technical assistance:

Scott Maco, Jim Jenkins, and Aren Dottenwhy (Davey Resource Group); Lindsey

Purcell, Paul Pinco, Perry Seitzinger, and Ashley Mulis (Forestry Section, Parks

and Recreation Department, Indianapolis, Indiana); Jim Stout (Mapping and

Geographic Infrastructure, Indianapolis, Indiana); Brian Brown (AMEC Earth &

Environmental, Inc); Stephanie Huang, Christine Yang, Aywon-Anh Nguyen, and

Linda George (Center for Urban Forest Research). A special thanks to Indiana

Community Tree Stewards and members of the Indiana Urban Forest Council, Inc.

for age-dating trees through ring counts.

Tree care expenditure information was provided by Lindsey Purcell and Paul

Pinco (City of Indianapolis, Indiana), Scott Brewer (City of Carmel, Indiana), Paul

Lindeman (City of Terre Haute, Indiana), Dave Gamstetter (City of Cincinnati,

Ohio), Steven Spilatro (City of Marietta, Ohio), Scott Swain (Tree Care Specialists

of Southern Ohio), David Kennedy (Kennedy’s Arboriculture LLC), Eric Loveland

and Aaron More (Brownsburg Tree Care), Felicia Clemons (Indiana Tree Service),

and Jud Scott (Vine & Branch).
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Harvey Holt (Purdue University), T. Davis Sydnor (Ohio State University),

Pam Louks (Indiana Community & Urban Forestry Program Coordinator), and

Drew Todd (Ohio Department of Natural Resources, Division of Forestry) provided

helpful reviews of this work.

Keith Cline and Philip Rodbell (U.S. Department of Agriculture, Forest

Service, State and Private Forestry) provided invaluable support for this project.

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Appendix 1: Additional Resources

Additional information regarding urban and community forestry program design

and implementation can be obtained from the following sources:

Utilizing Municipal Trees: Ideas From Across the Country by S.M. Bratkovich

Urban Forestry: Planning and Managing Urban Greenspaces by R.W. Miller

An Introductory Guide to Community and Urban Forestry in Washington, Oregon,

and California by N.R. Morgan

A Technical Guide to Urban and Community Forestry by N.R. Morgan

Urban Tree Risk Management: A Community Guide to Program Design and

Implementation edited by J.D. Pokorny

For additional information on tree selection, planting, establishment, and care

see the following resources:

Alliance for Community Trees: http://actrees.org

How to Prune Trees by P.J. Bedker, J.G. O’Brien, and M.E. Mielke

Training Young Trees for Structure and Form, a video by L.R. Costello

An Illustrated Guide to Pruning by E.F. Gilman

Planting Trees and Shrubs for Long-Term Health by R. Hargrave, G.R. Johnson,

and M.E. Zins

Arboriculture. 4th ed. by R.W. Harris, J.R. Clark, and N.P. Matheny

Trees and Ice Storms: The Development of Ice Storm-Resistant Urban Tree

Populations by R.J. Hauer, M.C. Hruska, and J.O. Dawson

How to Identify and Manage Dutch Elm Disease by L.M. Haugen

Native Trees, Shrubs, and Vines for Urban and Rural America by G.L. Hightshoe

International Society of Arboriculture: http://www.isa-arbor.com, including their

Tree City USA Bulletin series by J.R. Fazio

National Arbor Day Foundation: http://www.arborday.org

TreeLink: http://www.treelink.org

Trees for Urban and Suburban Landscapes by E.F. Gilman

The Urban Horticulture Institute: http://www.hort.cornell.edu/UHI/outreach/

recurbtree/index.html

Principles and Practice of Planting Trees and Shrubs by G.W. Watson and E.B.

Himelick

State urban forestry agencies and Web sites for the lower Midwest region:

Arkansas Forestry Commission, Community Forestry, 2780 North Garland Avenue,

Fayetteville, AR 72704; Phone: 479-442-8627 http://www.forestry.state.ar.us/

community/community.html
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Illinois Department of Natural Resources, Urban Conservation Program, One

Natural Resources Way, Springfield, IL 62702; Phone: 217-785-8771

http://dnr.state.il.us/conservation/forestry/Urban/

Indiana DNR, Division of Forestry, Urban Forestry Program, 6515 E 82nd Street,

Ste 204, Indianapolis, IN 46250; Phone: 317-915-9390, Fax: 317-915-9392

http://www.in.gov/dnr/forestry/6991.htm

Kansas Forest Service, Community Forestry, 1901 East 95 Street South, Haysville,

KS 67060; Phone: 316-788-0492 http://www.kansasforests.org/community/

index.shtml

Kentucky Division of Forestry, Urban Forestry, 627 Comanche Trail, Frankfort, KY

40601; Phone: 502-564-4496 http://www.forestry.ky.gov/programs/urban/

Missouri Department of Conservation, Urban and Community Forestry, P.O. Box

180, Jefferson City, MO 65102; Phone: 573-751-4115 x 3116 http://

mdc4.mdc.mo.gov/applications/MDCLibrary/MDCLibrary2.aspx?NodeID=147

Division of Forestry, Urban Forestry, 2045 Morse Road, Bldg. H-1, Columbus, OH

43229; Phone: 614-265-6707 http://www.dnr.state.oh.us/forestry/Home/urban/

defaultbu/tabid/5438/Default.aspx

Oklahoma Department of Agriculture, Forestry Division, Urban Forestry,

2800 N Lincoln Blvd., Oklahoma City, OK 73105; Phone: 405-522-6150;

http://www.forestry.ok.gov/ucf

These suggested references are only a starting point. Your local cooperative

extension agent or urban forester can provide you with up-to-date and local

information.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Appendix 2: Benefit–Cost Information Tables

Information in this appendix can be used to estimate benefits and costs associated

with proposed tree plantings. The tables contain data for representative small

(eastern redbud), medium (littleleaf linden), and large (northern hackberry) deciduous trees (see “Common and Scientific Names” section). Data are presented as

annual values for each 5-year interval after planting (tables 6 to 14). Annual values

incorporate effects of tree loss. Based on the results of our survey, we assume that

50 percent of the trees planted die by the end of the 40-year period.

For the benefits tables (tables 6, 9, 12), there are two columns for each

5-year interval. In the first column, values describe resource units (RUs): for

example, the amount of air conditioning energy saved in kilowatt hours per year

per tree, air pollutant uptake in pounds per year per tree, and rainfall intercepted in

gallons per year per tree. Energy and carbon dioxide benefits for residential yard

trees are broken out by tree location to show how shading effects differ among

trees opposite west-, south-, and east-facing building walls. The second column for

each 5-year interval contains dollar values obtained by multiplying RUs by local

prices (e.g., kWh saved [RU] x $/kWh).

In the costs tables (tables 7, 10, 13), costs are broken down into categories for

yard and public trees. Costs for yard trees do not differ by planting location (i.e.,

east, west, south walls). Although tree purchase and planting costs occur at year 1,

we divided this value by 5 years to derive an average annual cost for the first 5-year

period. All other costs are the estimated values for each year and not values averaged over 5 years.

Total net benefits are calculated by subtracting total costs from total benefits

and are presented in tables 8, 11, and 14. Data are presented for a yard tree opposite west-, south-, and east-facing walls, as well as for the public tree.

The last column in each table presents 40-year-average annual values. These

numbers were calculated by dividing the total costs and benefits by 40 years.
92

GENERAL TECHNICAL REPORT PSW-GTR-219 Table 6—Annual benefits at 5-year intervals and 40-year average for a representative small tree (eastern redbud) Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 40-year average RU $ RU $ RU $ RU $ RU $ RU $ RU $ RU $ RU $ Cooling (kWh): Yard: west 14 0.94 35 2.36 55 3.73 72 4.93 83 5.65 90 6.11 91 6.19 91 6.16 66 4.51 Yard: south 8 0.57 17 1.15 26 1.76 34 2.30 38 2.62 41 2.81 42 2.84 41 2.81 31 2.11 Yard: east 9 0.64 20 1.39 33 2.22 43 2.96 50 3.39 54 3.65 54 3.69 54 3.66 40 2.70 Public 8 0.56 17 1.13 24 1.66 31 2.12 35 2.39 38 2.57 38 2.59 38 2.57 29 1.95 Heating (therms): Yard: west 0.14 0.14 0.12 0.12 -0.01 -0.01 -0.15 -0.14 -0.26 -0.25 -0.36 -0.35 -0.41 -0.40 -0.44 -0.43 -0.17 (0.16) Yard: south -0.10 -0.09 -0.91 -0.89 -2.30 -2.24 -3.65 -3.55 -4.57 -4.45 -5.28 -5.14 -5.56 -5.41 -5.68 -5.53 -3.51 (3.41) Yard: east 0.19 0.19 0.22 0.22 0.11 0.10 -0.03 -0.03 -0.13 -0.13 -0.23 -0.22 -0.28 -0.28 -0.32 -0.31 -0.06 (0.06) Public 0.44 0.43 0.97 0.94 1.36 1.32 1.67 1.62 1.83 1.78 1.92 1.87 1.91 1.85 1.86 1.81 1.49 1.45 Net energy (kWh): Yard: west 152 1.07 359 2.48 548 3.72 710 4.78 805 5.40 863 5.76 870 5.80 862 5.73 646 4.34 Yard: south 74 0.47 77 0.26 28 -0.49 -27 -1.25 -72 -1.83 -115 -2.33 -138 -2.57 -154 -2.72 -41 (1.31) Yard: east 113 0.83 227 1.61 337 2.32 432 2.93 485 3.26 513 3.42 514 3.41 506 3.35 391 2.64

 Public 127 0.99 263 2.07 380 2.98 478 3.74 535 4.18 569 4.43 572 4.45 564 4.38 436 3.40Net carbon dioxide (lb):  Yard: west 33 0.11 83 0.28 130 0.43 171 0.57 194 0.65 206 0.69 206 0.69 203 0.68 153 0.51 Yard: south 19 0.06 32 0.11 39 0.13 46 0.15 46 0.15 42 0.14 38 0.13 34 0.11 37 0.12 Yard: east 25 0.08 53 0.18 83 0.28 109 0.37 123 0.41 128 0.43 127 0.43 125 0.42 97 0.32 Public 25 0.08 53 0.18 79 0.27 102 0.34 114 0.38 119 0.40 118 0.39 115 0.38 91 0.30Air pollution (lb)a

 Ozone uptake 0.039 0.03 0.094 0.08 0.143 0.12 0.191 0.16 0.230 0.19 0.266 0.22 0.292 0.24 0.319 0.26 0.20 0.16 Nitrogen dioxide

uptake+avoided 0.039 0.03 0.086 0.07 0.129 0.11 0.168 0.14 0.193 0.16 0.210 0.17 0.216 0.18 0.220 0.18 0.16 0.13

 Sulfur dioxide

uptake+avoided 0.125 0.19 0.280 0.42 0.435 0.65 0.571 0.86 0.654 0.98 0.708 1.06 0.720 1.08 0.719 1.08 0.53 0.79

 Small particulate matter

uptake+avoided 0.020 0.02 0.066 0.07 0.125 0.12 0.187 0.19 0.193 0.19 0.197 0.20 0.198 0.20 0.197 0.20 0.15 0.15

 Volatile organic

compounds avoided 0.010 0.00 0.022 0.01 0.034 0.01 0.045 0.01 0.051 0.02 0.055 0.02 0.056 0.02 0.055 0.02 0.04 0.01

 Biogenic volatile organic

compounds released 0.000 0.00 0.000 0.00 0.000 0.00 0.000 0.00 0.000 0.00 0.000 0.00 0.000 0.00 0.000 0.00 0.00 0.00

 Total air pollution

avoided + net uptake 0.233 0.28 0.548 0.64 0.866 1.01 1.162 1.35 1.321 1.54 1.435 1.67 1.482 1.71 1.510 1.73 1.07 1.24

Hydrology (gal)Rainfall interception 167 1.03 516 3.20 814 5.04 1,101 6.83 1,325 8.22 1,521 9.43 1,667 10.34 1,814 11.25 1,116 6.92

Aesthetics and other: Yard 14.59 12.17 10.03 7.95 6.06 4.41 3.04 1.94 7.52 Public 16.45 13.73 11.31 8.97 6.83 4.97 3.42 2.19 8.48Total benefits: Yard: west 17.08 18.77 20.24 21.48 21.85 21.95 21.57 21.33 20.53 Yard: south 16.43 16.38 15.73 15.03 14.13 13.31 12.65 12.32 14.50 Yard: east 16.80 17.80 18.68 19.43 19.48 19.35 18.92 18.68 18.64 Public 18.83 19.82 20.61 21.23 21.14 20.89 20.31 19.93 20.35

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and 40 percent during the remaining 35 years for a totalmortality of 50 percent. RU = resource unit.a Values are the same for yard and public trees.
93

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 7—Annual costs (dollars per tree) at 5-year intervals and 40-year average for a representative small tree

(eastern redbud)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and plantinga

:

 Yard 32 4

 Public 31 3.88

Pruning:

 Yard 0.29 0.56 0.54 0.52 4.06 3.92 3.79 3.65 2.20

 Public 6.56 3.33 3.16 2.99 5.28 4.96 4.63 4.31 4.54

Remove and dispose:

 Yard 0.64 0.99 1.48 1.95 2.39 2.79 3.14 3.42 1.95

 Public 0.40 0.90 1.35 1.77 2.18 2.54 2.86 3.12 1.74

Pest and disease:

 Yard 0.02 0.05 0.07 0.09 0.10 0.11 0.12 0.13 0.08

 Public 0.03 0.06 0.09 0.11 0.12 0.13 0.14 0.14 0.10

Infrastructure repair:

 Yard 0.05 0.09 0.14 0.17 0.21 0.23 0.25 0.27 0.16

 Public 0.35 0.67 0.95 1.19 1.37 1.50 1.58 1.60 1.08

Irrigation:

 Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

 Public 1.75 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.23

Cleanup:

 Yard 0.03 0.06 0.09 0.12 0.14 0.16 0.17 0.18 0.11

 Public 0.24 0.46 0.66 0.82 0.95 1.04 1.09 1.11 0.74

Liability and legal:

Yard 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01

Public 0.01 0.02 0.03 0.04 0.04 0.05 0.05 0.05 0.03

Admin./inspect/other:

 Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

 Public 1.26 2.41 3.42 4.26 4.93 5.40 5.68 5.77 3.87

Total costs:

 Yard 33.03 1.75 2.32 2.86 6.91 7.23 7.48 7.66 8.50

 Public 41.61 7.85 9.64 11.17 14.87 15.62 16.04 16.10 16.20

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and

40 percent during the remaining 35 years for a total mortality of 50 percent.

a Although tree and planting costs occur in year 1, this value was divided by 5 years to derive an average annual cost for the first

5-year period.

Table 8—Annual net benefits (dollars per tree) at 5-year intervals and 40-year average for a representative

small tree (eastern redbud)

Total net benefits Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 40-year

average

Dollars

Yard: west -16 17 18 19 15 15 14 14 12

Yard: south -17 15 13 12 7 6 5 5 6

Yard: east -16 16 16 17 13 12 11 11 10

Public -23 12 11 10 6 5 4 4 4

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and 40

percent during the remaining 35 years for a total mortality of 50 percent. See table 6 for annual benefits and table 7 for annual costs.
94

GENERAL TECHNICAL REPORT PSW-GTR-219 Table 9—Annual benefits (dollars per tree) at 5-year intervals and 40-year average for a representative medium tree (littleleaf linden) Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 40-year average RU $ RU $ RU $ RU $ RU $ RU $ RU $ RU $ RU $ Cooling (kWh): Yard: west 15 1.02 49 3.36 88 5.98 122 8.30 145 9.89 161 10.93 163 11.10 162 11.05 113 7.70 Yard: south 7 0.47 22 1.50 38 2.58 54 3.69 66 4.48 75 5.09 79 5.38 81 5.52 53 3.59 Yard: east 9 0.60 29 1.97 51 3.46 73 4.96 89 6.02 100 6.78 104 7.04 105 7.14 70 4.75 Public 7 0.47 21 1.41 34 2.34 47 3.23 57 3.85 63 4.31 66 4.49 67 4.55 45 3.08 Heating (therms): Yard: west 0.16 0.16 0.31 0.30 0.31 0.31 0.26 0.25 0.20 0.19 0.19 0.18 0.24 0.23 0.28 0.27 0.24 0.24 Yard: south 0.01 0.01 -0.63 -0.61 -1.80 -1.75 -3.14 -3.05 -4.15 -4.04 -4.76 -4.63 -4.76 -4.63 -4.68 -4.55 -2.99 (2.91) Yard: east 0.15 0.14 0.22 0.21 0.12 0.12 0.03 0.03 -0.04 -0.04 -0.04 -0.04 0.05 0.04 0.12 0.11 0.08 0.07 Public 0.42 0.41 1.15 1.12 1.83 1.78 2.40 2.33 2.77 2.69 3.03 2.95 3.10 3.02 3.11 3.02 2.23 2.17 Net energy (kWh): Yard: west 166 1.18 524 3.66 911 6.29 1,246 8.55 1,473 10.08 1,626 11.11 1,656 11.33 1,653 11.32 1,157 7.94 Yard: south 71 0.49 158 0.89 199 0.83 228 0.63 244 0.44 273 0.46 315 0.75 344 0.97 229 0.68 Yard: east 102 0.74 311 2.18 522 3.58 732 4.99 882 5.98 993 6.74 1,040 7.09 1,061 7.25 705 4.82

 Public 111 0.87 322 2.53 527 4.12 715 5.56 843 6.54 936 7.25 970 7.50 980 7.58 676 5.25Net carbon dioxide (lb): Yard: west 41 0.14 126 0.42 217 0.73 296 0.99 350 1.17 385 1.29 391 1.30 389 1.30 274 0.92 Yard: south 22 0.07 56 0.19 83 0.28 108 0.36 125 0.42 140 0.47 148 0.50 153 0.51 105 0.35 Yard: east 28 0.09 81 0.27 134 0.45 186 0.62 223 0.75 250 0.83 258 0.86 261 0.87 178 0.59 Public 27 0.09 74 0.25 118 0.40 159 0.53 187 0.62 207 0.69 212 0.71 214 0.71 150 0.50Air pollution (lb)a:

 Ozone uptake 0.037 0.03 0.112 0.09 0.196 0.16 0.286 0.24 0.366 0.30 0.446 0.37 0.514 0.42 0.581 0.48 0.32 0.26 Nitrogen dioxide

uptake+avoided 0.037 0.03 0.116 0.10 0.198 0.16 0.278 0.23 0.336 0.28 0.383 0.32 0.408 0.34 0.425 0.35 0.27 0.22

 Sulfur dioxide

uptake+avoided 0.118 0.18 0.380 0.57 0.663 0.99 0.933 1.40 1.124 1.69 1.263 1.89 1.314 1.97 1.335 2.00 0.89 1.34

 Small particulate matter

uptake+avoided 0.013 0.01 0.061 0.06 0.143 0.14 0.253 0.25 0.356 0.35 0.453 0.45 0.457 0.45 0.457 0.45 0.27 0.27

 Volatile organic compounds

avoided 0.009 0.00 0.030 0.01 0.053 0.02 0.074 0.02 0.089 0.03 0.099 0.03 0.103 0.03 0.104 0.03 0.07 0.02

 Biogenic volatile organic

compounds released -0.002 0.00 -0.027 -0.01 -0.079 -0.02 -0.173 -0.05 -0.279 -0.08 -0.378 -0.11 -0.378 -0.11 -0.378 -0.11 -0.21 -0.06

Total air pollution avoided

+ net uptake 0.212 0.25 0.673 0.82 1.174 1.45 1.650 2.08 1.993 2.56 2.267 2.94 2.416 3.10 2.525 3.20 1.61 2.05

Hydrology (gal)  Rainfall interception 203 1.26 630 3.90 1,096 6.80 1,644 10.19 2,136 13.24 2,639 16.36 3,083 19.11 3,526 21.86 1,870 11.59Aesthetics and other:  Yard 9.72 13.19 14.74 14.80 13.88 12.37 10.58 8.71 12.25 Public 10.97 14.87 16.62 16.69 15.65 13.95 11.93 9.82 13.81Total benefits:  Yard: west 12.56 21.99 30.00 36.61 40.93 44.07 45.43 46.39 34.75 Yard: south 11.80 18.99 24.10 28.07 30.54 32.61 34.03 35.26 26.92 Yard: east 12.07 20.36 27.02 32.68 36.41 39.26 40.74 41.90 31.31 Public 13.44 22.37 29.39 35.06 38.62 41.20 42.35 43.18 33.20

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and 40 percent during the remaining 35 years for a totalmortality of 50 percent. RU = resource unit.a Values are the same for yard and public trees.
95

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 10—Annual costs (dollars per tree) at 5-year intervals and 40-year average for a representative medium

tree (littleleaf linden)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and plantinga

:

 Yard 32.00 4.00

 Public 31.00 3.88

Pruning:

 Yard 0.29 0.56 4.33 4.20 4.06 3.92 8.83 8.51 3.91

 Public 6.56 3.33 5.92 5.60 5.28 4.96 11.12 10.35 6.26

Remove and dispose:

 Yard 0.34 1.39 2.05 2.67 3.25 3.79 4.28 4.73 2.64

 Public 0.40 1.26 1.87 2.43 2.96 3.45 3.90 4.31 2.39

Pest and disease 

 Yard 0.03 0.06 0.09 0.12 0.14 0.16 0.17 0.18 0.11

 Public 0.04 0.08 0.12 0.15 0.17 0.18 0.19 0.20 0.13

Infrastructure repair:

 Yard 0.07 0.13 0.19 0.24 0.28 0.32 0.30 0.37 0.22

 Public 0.49 0.94 1.32 1.63 1.87 2.04 2.16 2.22 1.47

Irrigation:

 Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

 Public 1.75 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.23

Cleanup: 

 Yard 0.05 0.09 0.13 0.16 0.19 0.22 0.20 0.25 0.15

 Public 0.33 0.65 0.91 1.12 1.29 1.41 1.49 1.53 1.02

Liability and legal: 

Yard 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Public 0.02 0.03 0.04 0.05 0.06 0.06 0.07 0.07 0.05

Admin./inspect/other:

 Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

 Public 1.74 3.38 4.74 5.85 6.70 7.33 7.75 7.97 5.30

Total costs:

 Yard 32.77 2.24 6.80 7.40 7.93 8.41 13.79 14.05 10.48

 Public 42.33 9.68 14.92 16.82 18.32 19.43 26.67 26.64 18.21

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and

40 percent during the remaining 35 years for a total mortality of 50 percent. RU = resource unit.

a Although tree and planting costs occur in year 1, this value was divided by 5 years to derive an average annual cost for the first

5-year period.

Table 11—Annual net benefits (dollars per tree) at 5-year intervals and 40-year average for a representative

medium tree (littleleaf linden)

40-year

Total net benefits Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Yard: west -20 20 23 29 33 36 32 32 24

Yard: south -21 17 17 21 23 24 20 21 16

Yard: east -21 18 20 25 28 31 27 28 20

Public -29 13 14 18 20 22 16 17 12

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and 40

percent during the remaining 35 years for a total mortality of 50 percent. RU = resource unit. See table 9 for annual benefits and

table 10 for annual costs.
96

GENERAL TECHNICAL REPORT PSW-GTR-219 Table 12—Annual benefits (dollars per tree) at 5-year intervals and 40-year average for a representative large tree (northern hackberry) Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 40-year average RU $ RU $ RU $ RU $ RU $ RU $ RU $ RU $ RU $ Cooling (kWh): Yard: west 74 5.01 165 11.22 213 14.47 247 16.79 264 17.93 269 18.30 266 18.11 256 17.42 219 14.91 Yard: south 27 1.86 67 4.58 101 6.84 128 8.71 148 10.05 161 10.97 168 11.45 170 11.55 121 8.25 Yard: east 40 2.70 96 6.55 134 9.08 162 11.03 180 12.22 189 12.85 191 13.00 189 12.83 148 10.03 Public 25 1.71 58 3.92 82 5.61 103 7.03 119 8.06 129 8.74 133 9.07 136 9.22 98 6.67 Heating (therms): Yard: west -0.06 -0.05 -0.27 -0.26 -0.01 -0.01 0.20 0.20 0.37 0.36 0.52 0.51 0.64 0.62 0.70 0.68 0.26 0.26 Yard: south -2.27 -2.21 -6.49 -6.31 -7.76 -7.55 -8.40 -8.18 -8.31 -8.08 -7.91 -7.69 -7.37 -7.17 -6.73 -6.55 -6.90 -6.72 Yard: east -0.19 -0.19 -0.55 -0.54 -0.24 -0.23 0.08 0.08 0.39 0.38 0.64 0.62 0.82 0.80 0.93 0.90 0.24 0.23 Public 1.39 1.35 2.82 2.74 3.88 3.78 4.68 4.56 5.15 5.01 5.37 5.22 5.40 5.26 5.25 5.11 4.24 4.13 Net energy (kWh): Yard: west 732 4.96 1,623 10.96 2,127 14.46 2,489 16.99 2,674 18.29 2,744 18.81 2,727 18.73 2,633 18.11 2,219 15.16 Yard: south 46 -0.35 24 -1.73 229 -0.72 440 0.53 646 1.96 823 3.28 947 4.28 1,025 5.00 523 1.53 Yard: east 378 2.51 909 6.02 1,312 8.85 1,631 11.11 1,836 12.60 1,953 13.47 1,994 13.80 1,979 13.73 1,499 10.26

Public 391 3.07 858 6.66 1,213 9.39 1,502 11.58 1,700 13.07 1,823 13.97 1,874 14.33 1,881 14.33 1,405 10.80

Net carbon dioxide (lb):

Yard: west 204 0.68 427 1.43 556 1.86 653 2.18 707 2.36 731 2.44 734 2.45 715 2.39 591 1.97Yard: south 77 0.26 141 0.47 220 0.74 293 0.98 352 1.18 397 1.33 426 1.42 439 1.47 293 0.98Yard: east 128 0.43 274 0.91 381 1.27 467 1.56 524 1.75 558 1.86 572 1.91 570 1.90 434 1.45Public 115 0.38 229 0.76 318 1.06 393 1.31 447 1.49 482 1.61 500 1.67 506 1.69 374 1.25

Air pollution (lb)a:

Ozone uptake 0.125 0.10 0.289 0.24 0.455 0.38 0.620 0.51 0.773 0.64 0.922 0.76 1.059 0.87 1.191 0.98 0.68 0.56Nitrogen dioxide uptake

+avoided 0.146 0.12 0.335 0.28 0.476 0.39 0.594 0.49 0.679 0.56 0.741 0.61 0.780 0.64 0.802 0.66 0.57 0.47

Sulfur dioxide uptake

+avoided 0.516 0.77 1.201 1.80 1.656 2.48 2.014 3.02 2.246 3.37 2.384 3.57 2.440 3.66 2.433 3.65 1.86 2.79

Small particulate matter

uptake+avoided 0.047 0.05 0.139 0.14 0.254 0.25 0.395 0.39 0.523 0.52 0.641 0.64 0.747 0.74 0.844 0.84 0.45 0.44

Volatile organic compounds

avoided 0.041 0.01 0.096 0.03 0.132 0.04 0.160 0.05 0.177 0.05 0.187 0.06 0.190 0.06 0.187 0.06 0.15 0.04

Biogenic volatile organic

compounds released 0 0 0 0 0 0 0 0 0 0 0 00 00 00 0

Total air pollution avoided

+ net uptake 0.876 1.06 2.060 2.48 2.973 3.54 3.783 4.46 4.398 5.14 4.874 5.64 5.215 5.97 5.458 6.19 3.70 4.31

Hydrology (gal)

Rainfall interception 959 5.95 2,115 13.11 3,254 20.18 4,390 27.22 5,443 33.75 6,481 40.18 7,439 46.12 8,382 51.97 4,808 29.81

Aesthetics and other:

Yard 14.68 22.20 25.89 26.59 25.24 22.61 19.30 15.74 21.53Public 16.56 25.03 29.19 29.98 28.46 25.50 21.76 17.75 24.28Total benefits:

Yard: west 27.33 50.18 65.92 77.43 84.78 89.69 92.58 94.40 72.79Yard: south 21.59 36.53 49.63 59.77 67.27 73.04 77.09 80.37 58.16Yard: east 24.63 44.73 59.73 70.94 78.48 83.77 87.11 89.53 67.36Public 27.01 48.05 63.36 74.55 81.91 86.90 89.86 91.93 70.45

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and 40 percent during the remaining 35 years for a totalmortality of 50 percent. RU = resource unit.a Values are the same for yard and public trees.
97

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 13—Annual costs (dollars per tree) at 5-year intervals and 40-year average for a representative large tree

(northern hackberry)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and plantinga:

Yard 32.00 4.00

Public 31.00 3.88

Pruning: 

Yard 0.29 4.47 4.33 4.20 9.47 9.15 8.83 8.51 5.83

Public 6.56 6.24 5.92 5.60 12.66 11.89 11.12 10.35 8.47

Remove and dispose:

Yard 1.08 1.51 2.21 2.88 3.52 4.12 4.68 5.22 2.89

Public 2.05 1.37 2.02 2.62 3.20 3.75 4.27 4.75 2.64

Pest and disease

Yard 0.04 0.07 0.10 0.13 0.15 0.17 0.19 0.20 0.12

Public 0.05 0.09 0.13 0.16 0.18 0.20 0.21 0.22 0.14

Infrastructure repair:

Yard 0.08 0.14 0.20 0.26 0.30 0.34 0.38 0.40 0.24

Public 0.55 1.02 1.42 1.75 2.02 2.22 2.36 2.45 1.61

Irrigation:

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 1.75 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.23

Cleanup:

Yard 0.05 0.10 0.14 0.18 0.21 0.24 0.26 0.28 0.17

Public 0.38 0.71 0.98 1.21 1.39 1.53 1.63 1.69 1.11

Liability and legal: 

Yard 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Public 0.02 0.03 0.04 0.06 0.06 0.07 0.07 0.08 0.05

Admin. and other:

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 1.98 3.68 5.12 6.30 7.25 7.97 8.48 8.79 5.78

Total costs:

 Yard 33.54 6.30 7.00 7.65 13.66 14.03 14.35 14.62 13.26

 Public 44.34 13.15 15.63 17.71 26.78 27.64 28.15 28.32 23.91

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and 40

percent during the remaining 35 years for a total mortality of 50 percent.

a

Although tree and planting costs occur in year 1, this value was divided by 5 years to derive an average annual cost for the first 5-year

period.

Table 14—Annual net benefits (dollars per tree) at 5-year intervals and 40-year average for a representative

large tree (northern hackberry)

40-year

Total net benefits Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Yard: west -6 44 59 70 71 76 78 80 60

Yard: south -12 30 43 52 54 59 63 66 45

Yard: east -9 38 53 63 65 70 73 75 54

Public -17 35 48 57 55 59 62 64 47

Note: Annual values incorporate effects of tree loss. We assume that 10 percent of trees planted die during the first 5 years and

40 percent during the remaining 35 years for a total mortality of 50 percent.

See table 12 for annual benefits and table 13 for annual costs.
98

GENERAL TECHNICAL REPORT PSW-GTR-219
99

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Appendix 3: Procedures for Estimating Benefits

and Costs

Approach

Pricing Benefits and Costs

In this study, annual benefits and costs over a 40-year planning horizon were estimated for newly planted trees in three residential yard locations (east, south, and

west of the dwelling unit) and a public streetside or park location. Trees in these

hypothetical locations are called “yard” and “public” trees, respectively. Prices were

assigned to each cost (e.g., planting, pruning, removal, irrigation, infrastructure

repair, liability) and benefit (e.g., heating/cooling, energy savings, air-pollution

reduction, stormwater-runoff reduction) through direct estimation and implied

valuation of benefits as environmental externalities. This approach made it possible

to estimate the net benefits of plantings in “typical” locations with “typical” tree

species.

To account for differences in the mature size and growth rates of different tree

species, we report results for a small (eastern redbud), medium (littleleaf linden),

and large (northern hackberry) deciduous tree (see “Common and Scientific

Names” section). Results are reported for 5-year intervals for 40 years.

Mature tree height is frequently used to characterize small, medium, and large

species because matching tree height to available overhead space is an important

design consideration. However, in this analysis, leaf surface area (LSA) and crown

diameter were also used to characterize mature tree size. These additional measurements are useful indicators for many functional benefits of trees that relate to

leaf-atmosphere processes (e.g., interception, transpiration, photosynthesis). Tree

growth rates, dimensions, and LSA estimates are based on tree growth modeling.

Growth Modeling

Growth models are based on data collected in Indianapolis, Indiana. The city’s

Parks and Recreation Department Forestry Section provided an inventory of

Indianapolis’s municipal trees that included 117,525 trees.

Tree-growth models developed from Indianapolis data were used as the basis

for modeling tree growth for this report. Using Indianapolis’s tree inventory, we

measured a stratified random sample of 19 of the most common tree species to

establish relations between tree age, size, leaf area, and biomass. The species were

as follows:
100

GENERAL TECHNICAL REPORT PSW-GTR-219

• Norway maple (Acer platanoides L.)

• Red maple (Acer rubrum L.)

• Silver maple (Acer saccharinum L.)

• Sugar maple (Acer saccharum Michx.)

• Northern catalpa (Catalpa speciosa (Warder) Warder ex Engelm.)

• Eastern redbud (Cercis canadensis L.)

• Northern hackberry (Celtis occidentalis L.)

• White ash (Fraxinus americana L.)

• Green ash (Fraxinus pennsylvanica Marsh.)

• Honeylocust (Gleditsia triacanthos L.)

• Black walnut (Juglans nigra L.)

• Crabapple (Malus spp.)

• Mulberry (Morus spp.)

• Blue spruce (Picea pungens Engelm.)

• Eastern white pine (Pinus strobus L.)

• Eastern cottonwood (Populus deltoids Bartram ex Marsh.)

• Callery pear (Pyrus calleryana Dcne.)

• Northern red oak (Quercus rubra L.)

• Littleleaf linden (Tilia cordata Mill.)

• Siberian elm (Ulmus pumila L.)

For the growth models, information spanning the life cycle of predominant

tree species was collected. The inventory was stratified into the following nine

diameter-at-breast-height (d.b.h.) classes:

• 0 to 2.9 in

• 3.0 to 5.9 in

• 6.0 to 11.9 in

• 12.0 to 17.9 in

• 18.0 to 23.9 in

• 24.0 to 29.9 in

• 30.0 to 35.9 in

• 36.0 to 41.9 in

• >42.0 in

Thirty to sixty trees of each species were randomly selected for surveying,

along with an equal number of alternative trees. Tree measurements included

d.b.h. (to nearest 0.1 cm [0.04 in] by sonar measuring device), tree crown height,
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

and bole height (to nearest 0.5 m [1.6 ft] by clinometer), crown diameter in two

directions (parallel and perpendicular to nearest street to nearest 0.5 m [1.6 ft] by

sonar measuring device), tree condition, and location. Replacement trees were

sampled when trees from the original sample population could not be located. Tree

age was determined by street-tree managers. Field work was conducted in August

2006.

Crown volume and leaf area were estimated from computer processing of

tree-crown images obtained with a digital camera. The method has shown greater

accuracy than other techniques (±20 percent of actual leaf area) in estimating

crown volume and leaf area of open-grown trees (Peper and McPherson 2003).

Linear and logarithmic regression was used to fit predictive models with d.b.h.

as a function of age for each of the 20 sampled species. Predictions of LSA, crown

diameter, and height metrics were modeled as a function of d.b.h. by using best-fit

models. After inspecting the growth curves for each species, we selected the typical

small, medium, and large tree species for this report.

Reporting Results

Results are reported in terms of annual values per tree planted. However, to make

these calculations realistic, mortality rates are included. Based on our survey of

regional municipal foresters and commercial arborists, this analysis assumed that

50 percent of the hypothetical planted trees died over the 40-year period. Annual

mortality rates were 2.0 percent for the first 5 years, and 1.14 percent per year

after that. The accounting approach “grows” trees in different locations and uses

computer simulation to directly calculate the annual flow of benefits and costs as

trees mature and die (McPherson 1992).

Benefits and costs are directly connected with tree-size variables such as trunk

d.b.h., tree canopy cover, and LSA. For instance, pruning and removal costs

usually increase with tree size, expressed as d.b.h. For some parameters, such as

sidewalk repair, costs are negligible for young trees but increase relatively rapidly

as tree roots grow large enough to heave pavement. For other parameters, such as

air-pollutant uptake and rainfall interception, benefits are related to tree canopy

cover and leaf area.

Most benefits occur on an annual basis, but some costs are periodic. For

instance, street trees may be pruned on regular cycles but are removed in a less

regular fashion (e.g., when they pose a hazard or soon after they die). In this

analysis, most costs and benefits are reported for the year in which they occur.
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However, periodic costs such as pruning, pest and disease control, and infrastructure repair are presented on an average annual basis. Although spreading one-time

costs over each year of a maintenance cycle does not alter the 40-year nominal

expenditure, it can lead to inaccuracies if future costs are discounted to the present.

Benefit and Cost Valuation

Source of cost estimates

Frequency and costs of tree management were estimated based on surveys with

municipal foresters from Indianapolis, Carmel, and Terre Haute, Indiana, and

Marietta and Cincinnati, Ohio. Several arborists from Brownsburg, Carmel, and

Indianapolis, Indiana, and Columbus and Gallipolos, Ohio, provided information

on tree management costs on residential properties.

Monetizing benefits

To monetize effects of trees on energy use, we take the perspective of a residential

customer by using retail electricity and natural-gas prices for utilities serving the

Lower Midwest, including Indianapolis and Louisville, Kentucky. The retail price

of energy reflects a full accounting of costs as paid by the end user, such as the

utility costs of power generation, transmission, distribution, administration, marketing, and profit. This perspective aligns with our modeling method, which calculates

energy effects of trees based on differences among consumers in heating and air

conditioning equipment types, saturations, building construction types, and base

loads.

The preferred way to value air quality benefits from trees is to first determine

the costs of damages to human health from polluted air, then calculate the value

of avoided costs because trees are cleaning the air. Economic valuation of damages

to human health usually uses information on willingness to pay to avoid damages

obtained via interviews or direct estimates of the monetary costs of damages (e.g.,

alleviating headaches, extending life). Empirical correlations developed by Wang

and Santini (1995) reviewed 5 studies and 15 sets of regional cost data to relate

per-ton costs of various pollutant emissions to regional ambient air quality measurements and population size. We use their damage-based estimates unless the

values are negative, in which case we use their control-cost-based estimates.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Calculating Benefits

Calculating Energy Benefits

The prototypical building used as a basis for the simulations was typical of post1980 construction practices and represents approximately one-third of the total

single-family residential housing stock in the Lower Midwest region. The house

was a one-story, wood-frame, slab-on-grade building with a conditioned floor area

of 2,070 ft2, window area (double-glazed) of 263 ft2, and wall and ceiling insulation of R13 and R31, respectively. The central cooling system had a seasonal

energy efficiency ratio (SEER) of 10, and the natural-gas furnace had an annual

fuel utilization efficiency (AFUE) of 78 percent. Building footprints were square,

reflecting average impacts for a large number of buildings (McPherson and

Simpson 1999). Buildings were simulated with 1.5-ft overhangs. Blinds had a

visual density of 37 percent and were assumed to be closed when the air conditioner was operating. Summer thermostat settings were 78 °F; winter settings were

68 °F during the day and 60 °F at night. Because the prototype building was larger,

but more energy efficient, than most other construction types, our projected energy

savings can be considered similar to those for older, less thermally efficient, but

smaller buildings. The energy simulations relied on typical meteorological data

from Indianapolis (Marion and Urban 1995).

Calculating energy savings

The dollar value of energy savings was based on regional average residential

electricity and natural-gas prices of $0.068/kWh and $0.973/therm (Indianapolis

Power and Light Company 2007, Citizens Gas and Coke Utility 2007). Homes

were assumed to have central air conditioning and natural-gas heating.

Calculating shade effects

Residential yard trees were within 60 ft of homes so as to directly shade walls

and windows. Shade effects of these trees on building energy use were simulated

for small, medium, and large trees at three tree-to-building distances, following

methods outlined by McPherson and Simpson (1999). Results of shade effects for

each tree were averaged over distance and weighted by occurrence within each of

three distance classes: 28 percent at 10 to 20 ft (3 to 6 m), 68 percent at 20 to 40 ft

(6 to 12 m), and 4 percent at 40 to 60 ft (12 to 18 m) (McPherson and Simpson

1999).
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GENERAL TECHNICAL REPORT PSW-GTR-219

The small tree (eastern redbud) had visual densities of 70 percent during

summer and 25 percent during winter, the medium tree (littleleaf linden) had visual

densities of 59 percent during summer and 12 percent during winter, and the large

tree (northern hackberry) had visual densities of 53 percent during summer and 12

percent during winter.

Leaf-off values for use in calculating winter shade were based on published

values where available (Hammond et al. 1980, McPherson 1984). Foliation periods

for deciduous trees were obtained from the literature (Hammond et al. 1980,

McPherson 1984) and adjusted for Indianapolis based on consultation with the city

arborist (Pinco 2007). The foliation periods of the small, medium, and larger trees

were 24 April–31 October.

Results are reported for trees shading east-, south-, and west-facing surfaces.

Our results for public trees are conservative in that we assumed that they do not

provide shading benefits. For example, in Modesto, California, 15 percent of total

annual dollar energy savings from street trees was due to shade and 85 percent due

to climate effects (McPherson et al. 1999a).

Calculating climate effects

In addition to localized shade effects, which were assumed to accrue only to

residential yard trees, lowered air temperatures and windspeeds from increased

neighborhood tree cover (referred to as climate effects) produced a net decrease

in demand for winter heating and summer cooling (reduced windspeeds by themselves may increase or decrease cooling demand, depending on the circumstances).

Climate effects on energy use, air temperature, and windspeed, as a function of

neighborhood canopy cover, were estimated from published values (McPherson and

Simpson 1999). Existing tree canopy plus building cover was 26 percent based on

estimates of urban tree cover for Indiana (Nowak and Crane 2002). Canopy cover

was calculated to increase by 3.1 percent, 4.6 percent, and 10.1 percent for 20-

year-old small, medium, and large deciduous and coniferous trees, respectively,

based on an effective lot size (actual lot size plus a portion of adjacent street and

other rights-of-way) of 10,000 ft2, and one tree on average was assumed per lot.

Climate effects were estimated by simulating effects of wind reductions and airtemperature reductions on energy use. Climate effects accrued for both public and

yard trees.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Atmospheric Carbon Dioxide Reduction

Calculating reduction in CO2 emissions from powerplants

Conserving energy in buildings can reduce carbon dioxide (CO2) emissions from

powerplants. Emission reductions were calculated as the product of energy savings

for heating and cooling with CO2 emission factors (table 15) based on data for

Indianapolis Power and Light Company, the local utility company in Indianapolis,

where the average fuel mix consists almost entirely of fossil fuels (99.9 percent)

power (U.S. EPA 2006). The value of $6.68 per ton CO2

 reduction (table 15) was

based on the average value given by Pearce (2003).

Calculating carbon storage

Sequestration, the net rate of CO2 storage in above- and belowground biomass

over the course of one growing season, was calculated from tree height and

d.b.h. data with volume equations (McHale et al., in press; Pillsbury et al. 1998).

Volume estimates were converted to green- and dry-weight estimates (Alden 1995,

Markwardt 1930) and divided by 78 percent to incorporate root biomass. Dryweight biomass was converted to carbon (50 percent) and these values were converted to CO2

. The amount of CO2 sequestered each year is the annual increment

of CO2

 stored as trees increase their biomass. There were four species for which

no urban tree volume equations were available. Harris’ general hardwoods biomass equation was used to estimate biomass for pear, crabapple, and American

holly (Tritton and Hornbeck 1982). Red maple biomass was estimated using a

forest-derived biomass equation (Ter-Mikaelian and Korzukhin 1997) with resulting estimates reduced by 20 percent to reflect the lower woody biomass levels of

open-grown trees.

Table 15—Emissions factors and implied values for carbon dioxide and criteria air pollutants

Emission factor Electricitya Natural gasb Implied valuec

Pounds per megawatt hour Pounds per therm Dollars per pound

Carbon dioxide 2,180 11.8 0.00334

Nitrogen dioxide 2.968 0.01020 0.82

Sulfur dioxide 11.966 0.00006 1.50

Small particulate matter 1.000 0.00075 0.99

Volatile organic compounds 0.999 0.00054 0.30

a U.S. EPA 2003, except Ottinger et al. 1990 for volatile organic compounds.

b U.S. EPA 1998.

c Carbon dioxide from Pearce 2003. Value for others based on methods of Wang and Santini (1995) using emissions concentrations

from U.S. EPA (2003) and population estimates from the U.S. Census Bureau (2006).
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GENERAL TECHNICAL REPORT PSW-GTR-219

Calculating CO2 released by power equipment

Tree-related CO2 emissions, based on gasoline and diesel fuel consumption during

tree care in our survey cities, were calculated by using the value 0.502 lbs of CO2

per in d.b.h. (Pinco 2007). This amount may overestimate CO2 release associated

with less intensively maintained residential yard trees.

Calculating CO2 released during decomposition

To calculate CO2 released through decomposition of dead woody biomass, we conservatively estimated that dead trees were removed and mulched in the year that

death occurred, and that 80 percent of their stored carbon was released to the

atmosphere as CO2

 in the same year (McPherson and Simpson 1999).

Calculating Reduction in Air Pollutant Emissions

Reductions in building energy use also result in reduced emission of air pollutants

from powerplants and space-heating equipment. Volatile organic hydrocarbons

(VOCs) and nitrogen dioxide (NO2)—both precursors of ozone (O3) formation—as

well as sulfur dioxide (SO2

) and particulate matter <10 microns in diameter (PM10)

were considered. Changes in average annual emissions and their monetary values

were calculated in the same way as for CO2, with utility-specific emissions factors

for electricity and heating fuels (Ottinger et al. 1990, U.S. EPA 1998). The price

of emissions savings was derived from models that calculate the marginal cost of

controlling different pollutants to meet air quality standards (Wang and Santini

1995). Emissions concentrations were obtained from U.S. EPA (2003) (table 15),

and population estimates from the U.S. Census Bureau (2006).

Calculating pollutant uptake by trees

Trees also remove pollutants from the atmosphere. The modeling method we

applied was developed by Scott et al. (1998). It calculates hourly pollutant dry

deposition per tree expressed as the product of deposition velocity (Vd = 1/[Ra + Rb

+ Rc]), pollutant concentration (C), canopy-projection area (CP), and a time step,

where Ra

, Rb, and Rc are aerodynamic, boundary layer, and stomatal resistances.

Hourly deposition velocities for each pollutant were calculated during the growing

season by using estimates for the resistances (Ra + Rb + Rc ) for each hour throughout the year. Hourly concentrations for O3

, PM10 , SO2, and NO2 for Indianapolis,
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Indiana, were obtained from the Environmental Protection Agency (U.S. EPA

2007), as well as hourly meteorological data (i.e., air temperature, windspeed, solar

radiation. The year 2003 was chosen because it most closely approximated longterm, regional climate records. To set a value for pollutant uptake by trees, we used

the procedure described above for emissions reductions (table 15). The monetary

value for NO2

 was used for ozone.

Estimating BVOC emissions from trees

Annual emissions for biogenic volatile organic compounds (BVOCs) were estimated for the four tree species by using the algorithms of Guenther et al. (1991,

1993). Annual emissions were simulated during the growing season over 40 years.

The emission of carbon as isoprene was expressed as a product of the base emission

rate (μg C per g dry foliar biomass per h), adjusted for sunlight and temperature

and the amount of dry, foliar biomass present in the tree. Monoterpene emissions

were estimated by using a base emission rate adjusted for temperature. The base

emission rates for the four species were based on values reported in the literature

(Benjamin and Winer 1998). Hourly emissions were summed to get monthly and

annual emissions.

Annual dry foliar biomass was derived from field data collected in Indianapolis, Indiana, during August 2006. The amount of foliar biomass present for each

year of the simulated tree’s life was unique for each species. Hourly air temperature and solar radiation data for 2003 described in the pollutant uptake section were

used as model inputs.

Calculating net air quality benefits

Net air quality benefits were calculated by subtracting the costs associated with

BVOC emissions from benefits associated with pollutant uptake and avoided powerplant emissions. The O3

-reduction benefit from lowering summertime air temperatures, thereby reducing hydrocarbon emissions from anthropogenic and biogenic

sources, was estimated as a function of canopy cover following McPherson and

Simpson (1999). Hourly changes in air temperature were calculated by reducing

this peak air temperature at every hour based on hourly maximum and minimum

temperature for that day, scaled by magnitude of maximum total global solar

radiation for each day relative to the maximum value for the year.
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Stormwater Benefits

Estimating rainfall interception by tree canopies

A numerical simulation model was used to estimate annual rainfall interception

(Xiao et al. 2000). The interception model accounted for water intercepted by the

tree, as well as throughfall and stem flow. Intercepted water is stored temporarily

on canopy leaf and bark surfaces. Rainwater evaporates or drips from leaf surfaces

and flows down the stem surface to the ground. Tree-canopy parameters that affect

interception include species, leaf and stem surface areas, shade coefficients (visual

density of the crown), foliation periods, and tree dimensions (e.g., tree height,

crown height, crown diameter, and d.b.h.). Tree-height data were used to estimate

windspeed at different heights above the ground and resulting rates of evaporation.

The volume of water stored in the tree crown was calculated from crownprojection area (area under tree dripline), leaf area indices (LAI, the ratio of LSA

to crown projection area), and the depth of water captured by the canopy surface.

Gap fractions, foliation periods, and tree surface saturation storage capacity

influence the amount of projected throughfall. Tree surface saturation was 1.0 mm

(0.04 in) for all trees.

Hourly meteorological and rainfall data for 2005 at the Indianapolis International Airport (IND) (Latitude: 39.717°, Longitude: -86.267°, Elevation: 790 ft,

NOAA COOPID: 124259) in Indianapolis, Indiana, were used in this simulation.

The year 2005 was chosen because, although the overall amount of rainfall was

higher, it most closely approximated the monthly distribution of the long-term

average rainfall. Annual precipitation at IND during 2005 was 43.7 in, which is

slightly higher than long-time annual average precipitation (42.5 in). Storm events

less than 0.1 in were assumed not to produce runoff and were dropped from the

analysis. More complete descriptions of the interception model can be found in

Xiao et al. (1998, 2000).

Calculating water quality protection and flood control benefit

The benefits that result from reduced peak runoff include reduced property damage

from flooding and reduced loss of soil and habitat from erosion and sediment flow.

Reduced runoff also results in improved water quality in streams, lakes, and rivers.

This can translate into improved aquatic habitats, less human illness owing to reduced contact with contaminated water and reduced stormwater treatment costs.

According to Brian Brown, the city of Indianapolis spends approximately $21

million annually on operations and maintenance of its stormwater management
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

system (Brown 2007). In addition, the Clean Streams-Healthy Neighborhoods

program is an investment of more than $3 billion over 20 years (Ray 2007). Thus,

total annual expenditures including capital improvements are $171 million. To

calculate annual runoff, we assigned curve numbers for each land use (USDA SCS

1986). Land use percentages were obtained from the city land use GIS layers

(Purcell 2007). We calculated runoff depth for each land use (5.7 in citywide) and

found the citywide total to be 84,956 acre-feet. The annual stormwater control cost

was estimated to be $0.006 per gallon of runoff.

Aesthetic and Other Benefits

Many benefits attributed to urban trees are difficult to translate into economic

terms. Beautification, privacy, wildlife habitat, shade that increases human comfort,

sense of place and well-being are services that are difficult to price. However, the

value of some of these benefits may be captured in the property values of the land

on which trees stand.

To estimate the value of these “other” benefits, we applied results of research

that compared differences in sales prices of houses to statistically quantify the

difference associated with trees. All else being equal, the difference in sales price

reflects the willingness of buyers to pay for the benefits and costs associated with

trees. This approach has the virtue of capturing in the sales price both the benefits

and costs of trees as perceived by the buyers. Limitations to this approach include

difficulty determining the value of individual trees on a property, the need to

extrapolate results from studies done years ago, and the need to extrapolate results

from front-yard trees on residential properties to trees in other locations (e.g., back

yards, streets, parks, and nonresidential land).

Anderson and Cordell (1988) surveyed 844 single-family residences in Athens,

Georgia, and found that each large front-yard tree was associated with a 0.88-percent increase in the average home sales price. This percentage of sales price was

used as an indicator of the additional value a resident in the Lower Midwest region

would gain from selling a home with a large tree.

We used the average median home price for Indianapolis, Indiana, St. Louis,

Missouri, Lexington and Louisville, Kentucky, Cincinnati and Dayton, Ohio

($135,400), as our starting point. Therefore, the value of a large tree that added

0.88 percent to the sales price of such a home was $1,192. To estimate annual

benefits, the total added value was divided by the LSA of a 30-year-old green ash

($1,192 per 4,076 ft2

) to yield the base value of LSA, $0.292 per ft2. This value

was multiplied by the amount of LSA added to the tree during 1 year of growth.
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GENERAL TECHNICAL REPORT PSW-GTR-219

Additionally, not all street trees are as effective as front-yard trees in increasing property values. For example, trees adjacent to multifamily housing units will

not increase the property value at the same rate as trees in front of single-family

homes. Therefore, a citywide street tree reduction factor (0.83) was applied to

prorate trees’ value based on the assumption that trees adjacent to different land

uses make different contributions to property sales prices. For this analysis, the

street reduction factor reflects the distribution of street trees in Indianapolis by

land use. Reduction factors were single-home residential (100 percent), multihome

residential (75 percent), small commercial (66 percent), industrial/institutional/

large commercial (66 percent), park/vacant/other (50 percent) (Gonzales 2004,

McPherson 2001).

Calculating the aesthetic and other benefits of residential yard

trees

To calculate the base value for a large tree on private residential property we

assumed that a 30-year-old white ash in the front yard increased the property sales

price by $1,192. Approximately 75 percent of all yard trees, however, are in back

yards (Richards et al. 1984). Lacking specific research findings, it was assumed that

back-yard trees had 75 percent of the impact on “curb appeal” and sales price

compared to front-yard trees. The average annual aesthetic and other benefits for a

tree on private property were, therefore, estimated as $0.21 per ft2

 LSA. To estimate annual benefits, this value was multiplied by the amount of LSA added to the

tree during 1 year of growth.

Calculating the aesthetic value of a public tree

The base value of street trees was calculated in the same way as yard trees. However, because street trees may be adjacent to land with little resale potential, an

adjusted value was calculated. An analysis of street trees in Modesto, California,

sampled from aerial photographs (sample size 8 percent of street trees), found that

15 percent were located adjacent to nonresidential or commercial property

(McPherson et al. 1999a). We assumed that 33 percent of these trees—or 5 percent

of the entire street-tree population—produced no benefits associated with property

value increases.

Although the impact of parks on real estate values has been reported (Hammer

et al. 1974, Schroeder 1982, Tyrvainen 1999), to our knowledge, the onsite and

external benefits of park trees alone have not been isolated (More et al. 1988).
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

After reviewing the literature and recognizing an absence of data, we made the

conservative estimate that park trees had half the impact on property prices of street

trees.

Given these assumptions, typical large street and park trees were estimated to

increase property values by $0.27 and $0.15 per ft2 LSA, respectively. Assuming

that 80 percent of all municipal trees were on streets and 20 percent in parks, a

weighted average benefit of $0.251/ft2 LSA was calculated for each tree.

Calculating Costs

Tree management costs were estimated based on surveys with municipal foresters

from Carmel, Indianapolis, and Terre Haute, Indiana, and Cincinnati and Marietta,

Ohio. In addition, several commercial arborists from Brownsburg, Carmel, and

Indianapolis, Indiana, and Gallipolos and Columbus, Ohio, provided information

on tree management costs on residential properties.

Planting

Planting costs include the cost of the tree and the cost for planting, staking, and

mulching the tree. Based on our survey of Lower Midwest municipal and commercial arborists, planting costs ranged widely from $106 for a 2-in d.b.h. tree to $550

for a 5-in tree. In this analysis we assumed that a 2-in yard tree was planted at a

cost of $160. The cost for planting a 2-in public tree was $155.

Pruning

Pruning costs for public trees

After studying data from municipal forestry programs and their contractors, we

assumed that young public trees were inspected and pruned once every 2 years

during the first 5 years after planting at a cost of $15 per tree. After this training

period, inspection and pruning occurred once every 5 years for small trees (< 20 ft

tall) at $20 per tree. More expensive equipment and more time was required to

prune medium trees once every 8 years ($60 per tree) and large trees once every 10

years ($180 per tree). After factoring in pruning frequency, annualized costs were

$7.50, $4, $7.50, and $18 per tree for public young, small, medium, and large

trees, respectively.
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GENERAL TECHNICAL REPORT PSW-GTR-219

Pruning costs for yard trees

Based on findings from our survey of commercial arborists in the Lower Midwest

region, pruning cycles for yard trees were 2, 3, 5, and 7 years for young, small,

medium, and large trees, respectively. Only about 20 percent of all private trees

were professionally pruned (contract rate), although the number of professionally

pruned trees grows as the trees grow. We assumed that professionals are paid to

prune all large trees, 60 percent of the medium trees, and only 6 percent of the

small and young trees and conifers (Summit and McPherson 1998). Using these

contract rates, along with average pruning prices ($50, $100, $200, and $400 for

young, small, medium, and large trees, respectively), the average annual costs for

pruning a yard tree were $0.30, $0.60, $4.80, and $11.20 for young, small, medium, and large trees, respectively.

Tree and Stump Removal

The costs for tree removal and disposal were $20 per in d.b.h. for public trees,

and $35 per in d.b.h. for yard trees. Stump removal costs were $6 per in d.b.h. for

public trees and $7 per in d.b.h. for yard trees. Therefore, total costs for removal

and disposal of trees and stumps were $26 per in d.b.h. for public trees, and $42

per in d.b.h. for yard trees. Removal costs of trees less than 3 inches in diameter

were $16 for public trees and $80 for yard trees.

Irrigation Costs

Costs for watering during the critical 5-year establishment period were estimated

at $2.00 for public trees per tree per year, mainly for the labor costs involved in

visiting the trees with a water truck or other time-intensive method. Beyond the

establishment period, it is assumed that trees have been planted into irrigated

landscapes and therefore the cost of additional water for the trees is negligible.

No costs for irrigating yard trees were included because these were also assumed

to be planted in irrigated landscapes where the cost of additional water is negligible

and the additional labor involved for extra watering during the first 5 years by the

resident was also considered negligible.

Pest and Disease Control

Pest and disease control measures in the Lower Midwest are minimal, with cities

spending only about $0.16 per tree per year and residential arborists $0.11 per tree

per year.
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Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

Other Costs for Public and Yard Trees

Other costs associated with the management of trees include expenditures for

infrastructure repair/root pruning, leaf-litter cleanup, and inspection/administration.

Infrastructure conflict costs

As trees and sidewalks age, roots can cause damage to sidewalks, curbs, paving, and

sewer lines. Sidewalk repair is typically one of the largest expenses for public trees

(McPherson and Peper 1995). Infrastructure-related expenditures for public trees in

Lower Midwest communities were approximately $2.23 per tree on an annual

basis. Roots from most trees in yards do not damage sidewalks and sewers. Therefore, the cost for yard trees was estimated to be only 10 percent of the cost for

public trees.

Litter and storm cleanup costs

The average annual cost per tree for litter cleanup (i.e., street sweeping, stormdamage cleanup) was $1.54 per tree ($0.135 per in d.b.h.). This value was based on

average annual litter cleanup costs and storm cleanup, assuming a large storm

results in extraordinary costs about once a decade. Because most residential yard

trees are not littering the streets with leaves, it was assumed that cleanup costs for

yard trees were 10 percent of those for public trees.

Inspection and administration costs

Municipal tree programs have administrative costs for salaries of supervisors and

clerical staff, operating costs, and overhead. Our survey found that the average

annual cost for inspection and administration associated with street- and park-tree

management was $6.41 per tree ($0.703 per in d.b.h.). Trees on private property do

not accrue this expense.

Calculating Net Benefits

Benefits Accrue at Different Scales

When calculating net benefits, it is important to recognize that trees produce

benefits that accrue both on- and offsite. Benefits are realized at four scales: parcel,

neighborhood, community, and global. For example, property owners with onsite

trees not only benefit from increased property values, but they may also directly

benefit from improved human health (e.g., reduced exposure to cancer-causing

ultraviolet radiation) and greater psychological well-being through visual and direct
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GENERAL TECHNICAL REPORT PSW-GTR-219

contact with plants. However, on the cost side, increased health care costs owing to

allergies and respiratory ailments related to pollen may be incurred because of

nearby trees. We assume that these intangible benefits and costs are reflected in

what we term “aesthetics and other benefits.”

The property owner can obtain additional economic benefits from onsite trees

depending on their location and condition. For example, carefully located onsite

trees can provide air-conditioning savings by shading windows and walls and

cooling building microclimates. This benefit can extend to adjacent neighbors who

benefit from shade and air-temperature reductions that lower their cooling costs.

Neighborhood attractiveness and property values can be influenced by the

extent of tree canopy cover on individual properties. At the community scale,

benefits are realized through cleaner air and water, as well as social, educational,

and employment and job training benefits that can reduce costs for health care,

welfare, crime prevention, and other social service programs.

Reductions in atmospheric CO2

 concentrations owing to trees are an example of

benefits that are realized at the global scale.

Annual benefits are calculated as:

B = E + AQ + CO2

 + H + A

where

E = value of net annual energy savings (cooling and heating)

AQ = value of annual air-quality improvement (pollutant uptake, avoided

powerplant emissions, and BVOC emissions)

CO2

 = value of annual CO2 reductions (sequestration, avoided emissions,

release from tree care and decomposition)

H = value of annual stormwater-runoff reductions

A = value of annual aesthetics and other benefits

On the other side of the benefit-cost equation are costs for tree planting and

management. Expenditures are borne by property owners (irrigation, pruning, and

removal) and the community (pollen and other health care costs). Annual costs (C)

are the sum of costs for residential yard trees (CY ) and public trees (CP

 )

where:

CY = P + T + R + D + I + S + Cl + L

CP

 = P + T + R + D + I + S + Cl + L + A where

P = cost of tree and planting

T = average annual tree pruning cost

R = annualized tree and stump removal and disposal cost
115

Lower Midwest Community Tree Guide: Benefits, Costs, and Strategic Planting

D = average annual pest- and disease-control cost

I = annual irrigation cost

S = average annual cost to repair/mitigate infrastructure damage

Cl = annual litter and storm cleanup cost

L = average annual cost for litigation and settlements from tree-related claims

A = annual program administration, inspection, and other costs

Net benefits are calculated as the difference between total benefits and costs:

Net benefits = B – C

Benefit-cost ratios (BCR) are calculated as the ratio of benefits to costs:

BCR = B / C

Limitations of This Study

This analysis does not account for the wide variety of trees planted in Lower

Midwest communities or their diverse placement. It does not incorporate the full

range of climatic differences within the region that influence potential energy, airquality, and hydrology benefits. Estimating aesthetics and other benefits is difficult

because the research in this area is not well developed. We considered only residential and municipal tree cost scenarios, but realize that the costs associated with

planting and managing trees can differ widely depending on program characteristics. For example, our analysis does not incorporate costs incurred by utility

companies and passed on to customers for maintenance of trees under power lines.

However, as described by examples in chapter 3, local cost data can be substituted

for the data in this report to evaluate the benefits and costs of alternative programs.

In this analysis, results are presented in terms of future values of benefits and

costs, not present values. Thus, findings do not incorporate the time value of money

or inflation. We assume that the user intends to invest in community forests and our

objective is to identify the relative magnitudes of future costs and benefits. If the

user is interested in comparing an investment in urban forestry with other investment opportunities, it is important to discount all future benefits and costs to the

beginning of the investment period. For example, trees with a future value of

$100,000 in 10 years have a present value of $55,840, assuming a 6-percent annual

interest rate.
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