United States 

Department of 

Agriculture

Forest Service

Pacific Southwest 

Research Station

General Technical 

Report

PSW-GTR-228

April 2010

Community

Benefits, Costs, and Strategic Planting

Northern California Coast

Tree Guide

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

Aaron M.N. Crowell, and Qingfu Xiao
Authors

E. Gregory McPherson is a research forester, James R. Simpson is a forest

meteorologist, Paula J. Peper is an ecologist, and Aaron M.N. Crowell is a

landscape architect, U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station, Center for Urban Forest Research, 1731 Research Park Dr.,

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

Air, and Water Resources, University of California, Davis, 1731 Research Park Dr.,

Davis, CA 95618.

Photo credit

Center for Urban Forest Research

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.
i

Northern California Coast

Community Tree Guide:

Benefits, Costs, and Strategic

Planting

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

Aaron M.N. Crowell, and Qingfu Xiao

USDA Forest Service

Pacific Southwest Research Station

Albany, CA

April 2010

Contributing Organizations

Center for Urban Forest Research

USDA Forest Service, Pacific Southwest Research Station

Davis, CA

Department of Land, Air, and Water Resources

University of California, Davis

Davis, CA

Sponsoring Organization

USDA Forest Service

State and Private Forestry

Urban and Community Forestry Program
ii

Abstract

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

Aaron M.N.; Xiao, Qingfu. 2010. Northern California coast community tree

guide: benefits, costs, and strategic planting. Gen. Tech. Rep. PSW-GTR-228.

Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest

Research Station. 118 p.

Trees make our cities more attractive and provide 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 and coniferous trees in the

Northern California Coast region derived from models based on research carried out

in Berkeley, California. Average annual net benefits (benefits minus costs) increase

with mature tree size and differ based on location: $29 (public) to $41 (yard) for a

small tree, $42 (public) to $60 (yard) for a medium tree, $101 (public) to $122

(yard) for a large tree, $142 (public) to $146 (yard) for a large conifer. 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, urban forestry, benefit-cost analysis.
iii

Green infrastructure is a significant component of communities in the Northern California Coast region.

Center for Urban Forest Research
iv

Summary

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

trees and a coniferous tree in the Northern California Coast region: the species

chosen as representative because of their size at about 20 years after planting are

camphor (Cinnamomum camphora), cherry plum (Prunus cerasifera), velvet ash

(Fraxinus velutina) and Monterey pine (Pinus radiata), respectively (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). We assume

a 55-percent survival rate over a 40-year timeframe. Tree care costs and mortality

rates are based on results from a survey of municipal and commercial arborists.

Benefits are calculated by using tree growth curves and numerical models that consider regional climate, building characteristics, air pollutant concentrations, and

prices.

The measurements used in modeling environmental and other benefits of trees

are based on indepth research carried out in Berkeley, California. Given the Northern California Coast region’s large and diverse geographical area, this approach

provides first-order approximations. 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 planting projects.

Large trees provide the greatest benefits. Average annual benefits over 40 years

increase with mature tree size:

• $41 to $51 for a small tree (18 ft tall 20 years after planting)

• $57 to $71 for a medium tree (22 ft tall 20 years after planting)

• $115 to $135 for a large tree (34 ft tall 20 years after planting)

• $161 to $176 for a conifer (38 ft tall 20 years after planting)

Benefits associated with increased property value and energy savings account

for the largest proportion of total benefits in this region. Reduced stormwater

runoff, lower levels of air pollutants, and less carbon dioxide 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 carbon dioxide

(CO2

) emissions and thereby reduces atmospheric CO2. Similarly, energy savings

that reduce pollutant emissions at powerplants account for important reductions in

gases that produce ozone, a major component of smog.

Benefits and costs

quantified

Average annual

benefits
v

Average annual costs over 40 years for tree care range from $10 to $33 per tree.

• $10 (yard) and $17 (public) for a small tree

• $11 (yard) and $24 (public) for a medium tree

• $13 (yard) and $28 (public) for a large tree

• $15 (yard) and $33 (public) for a conifer

Planting, pruning, and tree removal are the greatest costs for trees (annualized

to $2 to $22 per tree per year). Tree care expenditures tend to increase with mature

tree size because of increased labor and equipment costs.

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

are as follows:

• $29 to $41 for a small tree

• $42 to $60 for a medium tree

• $101 to $122 for a large tree

• $142 to $146 for a conifer

The environmental benefits alone, including energy savings, stormwater-runoff

reduction, improved air quality, and reduced atmospheric CO2

, are greater than tree

care costs.

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

when summed over the entire 40-year period:

• $1,640 (yard) and $1,179 (public) for a small tree

• $2,392 (yard) and $1,679 (public) for a medium tree

• $4,868 (yard) and $4,034 (public) for a large tree

• $5,855 (yard) and $5,685 (public) for a conifer

Private trees produce higher net benefits than public trees. Our survey results

indicate that this is primarily due to higher maintenance costs for street and park

trees. The standard of care is often higher for public trees because municipalities

need to manage risk, maintain required clearances for pedestrians and vehicles, and

repair damage to sidewalks and curbing caused by tree roots.

To demonstrate how communities can adapt the information in this report to

their needs, the benefits and costs of different planting projects are determined for

two fictional cities interested in increasing their urban forest. In the hypothetical

city of Martha Falls, net benefits and benefit-cost ratios (BCRs) are calculated for a

planting of 1,000 trees (15 gal or No. 15). Energy prices, planting, and monitoring

costs are adjusted to reflect local prices and anticipated project costs. Total project

Costs

Average annual net

benefits

Net benefits

summed over

40 years
vi

costs are $1,162,736, benefits total $4.2 million, and net benefits are $3.0 million

($76 per tree per year). The BCR is 3.61:1, indicating that $3.61 is returned for

every $1 invested. The net benefits and BCRs by mature tree size are:

• $37,956 (2.01:1) for 50 small trees

• $181,992 (2.19:1) for 150 medium trees

• $2.3 million (3.79:1) for 700 large trees

• $485,619 (4.53:1) for 100 pine trees

Increased property values (77 percent) and reduced energy costs (17 percent)

account for more than 90 percent of the estimated benefits. Reduced stormwater

runoff (4 percent), improved air quality (1 percent) and atmospheric CO2

 reduction

(1 percent) make up the remaining benefits.

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

benefits were compared to determine if a proposed policy that favors planting smallstature trees would be cost effective compared to the current policy of planting

large-stature trees where space permits. Over a 40-year period, the net benefits are:

• $707 per tree for a small tree

• $1,185 per tree for a medium tree

• $3,427 per tree for a large tree

Based on this analysis, the city of Melvinville decided to retain their policy.

They now require tree shade plans that show how developers will achieve 50 percent

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

Table of Contents

1 Chapter 1: Introduction

1 The Northern California Coast Region

5 Chapter 2: Identifying Benefits and Costs of Urban and Community

Forests

5 Benefits

5 Saving Energy

8 Reducing Atmospheric Carbon Dioxide

10 Improving Air Quality

14 Reducing Stormwater Runoff and Improving Hydrology

17 Aesthetics and Other Benefits

20 Costs

20 Planting and Maintaining Trees

22 Conflicts With Urban Infrastructure

24 Wood Salvage, Recycling, and Disposal

25 Chapter 3: Determining Benefits and Costs of Community Forests in

Northern California Coast Communities

25 Overview of Procedures

25 Approach

30 Reporting Results

31 Findings of This Study

31 Average Annual Net Benefits

32 Average Annual Costs

35 Average Annual Benefits

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

 Your Community

41 Applying Benefit-Cost Data

41 Martha Falls City Example

46 City of Melvinville Example

50 Increasing Program Cost-Effectiveness

50 Increasing Benefits

50 Reducing Program Costs

55 Chapter 5: General Guidelines for Selecting and Placing Trees

55 Guidelines for Energy Savings

55 Maximizing Energy Savings From Shading

57 Planting Windbreaks for Heating Savings
viii

58 Selecting Trees to Maximize Benefits

59 Guidelines for Reducing Carbon Dioxide

61 Guidelines for Reducing Stormwater Runoff

62 Guidelines for Improving Air Quality Benefits

64 Avoiding Tree Conflicts With Infrastructure

67 General Guidelines to Maximize Long-Term Benefits

70 Glossary

76 Common and Scientific Names

78 Acknowledgments

78 Metric Equivalents

79 References

91 Appendix 1: Additional Resources

93 Appendix 2: Benefit-Cost Information Tables

103 Appendix 3: Procedures for Estimating Benefits and Costs

103 Approach

103 Overview

104 Growth Modeling

106 Reporting Results

106 Benefit and Cost Valuation

107 Calculating Benefits

107 Calculating Energy Benefits

109 Atmospheric Carbon Dioxide Reduction

112 Stormwater Benefits

113 Aesthetic and Other Benefits

114 Calculating Costs

114 Planting

115 Pruning

115 Tree and Stump Removal

115 Pest and Disease Control

116 Irrigation Costs

116 Other Costs for Public and Yard Trees

117 Calculating Net Benefits

117 Benefits Accrue at Different Scales
ix

The Northern California Coast region is characterized by gently rolling hills, numerous views of oceans, rivers, and streams, and a

diverse tree cover.

Center for Urban Forest Research
This Page Left Blank Intentionally
1

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 1: Introduction

The Northern California Coast Region

From small towns surrounded by vineyards, forests, and the sea, to the city of

San Francisco, the Northern California Coast region (fig.1) contains a diverse

assemblage of communities. Home to approximately 8 million people, this region

extends south along a band bordering the Pacific Ocean from the Oregon border

to Santa Maria and Lompoc. It sweeps inland around the San Francisco Bay to

include the cities of Richmond, Oakland, and San Jose. Boundaries correspond with

Sunset Climate Zones 15 through 17 (Brenzel 2001) and USDA Hardiness Zones 9

Geographic scope

of the Northern

California Coast

region

Figure 1—The Northern California Coast

region (shaded area)

extends south along

a band bordering the

Pacific Ocean from

the Oregon border

to Santa Maria, and

sweeps inland around

the San Francisco Bay.
2

GENERAL TECHNICAL REPORT PSW-GTR-228

and 10. The Pacific Ocean influences the climate1 in this region, allowing a greater

number of tree species to thrive than in regions farther north and inland. The

annual temperature cycle is relatively mild, with chilly winters and mild summers.

Temperatures are influenced by marine air much of the time, and some areas are

almost frostless. A humidifying blanket of fog tends to moderate summer temperatures in the northern parts of this region. Summer afternoon winds are an integral

part of this climate and can be dispersed by plantings on the windward side of

buildings. Annual precipitation throughout the region ranges from 20 to 50 in

annually, with nearly all rainfall during winter (November–April).

In the Northern California Coast region, as elsewhere, urban forest canopies

protect us from the elements, clean the water we drink and the air we breathe, generally improve the quality of life, and form a living connection to earlier generations who planted and tended these trees.

As the region’s communities continue to expand during the coming decades,

sustaining healthy community forests is integral to the quality of life that residents

experience. The role of 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. The simple act of planting trees provides opportunities to connect residents with nature and with each other. Neighborhood tree

plantings and stewardship projects stimulate involvement and investment by local

citizens, businesses, and governments for the betterment of their communities

(fig. 2). Community forests bring opportunity for economic renewal, combating

development woes, improving human health, and increasing the quality of life for

community residents.

Northern California Coast 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 CO2

; providing wildlife habitat; increasing

property values; slowing vehicular traffic; enhancing community attractiveness and

investment; and promoting human health and well-being.

This guide builds upon previous studies by the U.S. Department of Agriculture

Forest Service in the San Francisco Bay Area (Simpson and McPherson 2007),

San Francisco (Maco et al. 2003, Nowak et al. 2007), Berkeley (Maco et al. 2005),

1

 Words in bold are defined in the glossary.

Northern California

Coast communities

can derive many

benefits from community forests

Quality of life improves with trees
3

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Chicago and Sacramento (McPherson 1998, McPherson et al. 1997), and Tree

Guides for the San Joaquin Valley, Southern California Coast and other regions

(McPherson et al. 1999, 2000) to extend existing knowledge of urban forest

services in the Northern California Coast. 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 benefits and costs for trees in residential yards and along streets and

in parks.

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

local tree planting projects.

These guidelines are specific to the Northern California Coast and are based on

measurements and calculations from open-growing urban trees in this region.

Street, park, and privately owned shade trees are integral to urban communities. They impact every resident. Their benefits are myriad. However, with municipal tree programs dependent on taxpayer-supported general funds, communities are

Scope defined

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

residents to work together to build better communities.

Audience and

objectives

Center for Urban Forest Research
4

GENERAL TECHNICAL REPORT PSW-GTR-228

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 cost-effectiveness

(McPherson 1995). If tree plantings are proven to benefit communities, then

monetary 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 Northern California Coast communities—providing a tool for municipal tree

managers, planners, arborists, and community and environmental groups to increase public awareness and support for trees (Dwyer and Miller 1999).

This tree guide addresses a number of questions about the environmental and

aesthetic benefits of community tree plantings in Northern California Coast communities:

• How can tree-planting programs improve environmental quality, conserve

energy, and add value to communities?

• Where should residential yard and public trees be placed to maximize their

benefits?

• How can conflicts between trees and power lines, sidewalks, and buildings

be minimized?

What will this tree

guide do?

Trees in Northern California Coast

communities enhance quality of

life. Center for Urban Forest Research
5

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 2: Identifying Benefits and Costs of Urban

and Community Forests

This chapter describes benefits and costs of public and privately managed trees.

Services and associated economic value of community forests are described.

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 to maintain quality of life and sustain economic growth. Conserving energy with shade trees can reduce the need for 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 was 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. The cost of peak load reduction was $63/kW, considerably less than the

$150/kW amount that is deemed cost-effective for energy conservation measures by

the California Energy Commission (see http://www.fs.fed.us/psw/programs/cufr/

products/3/cufr_148.pdf). Like electric utilities throughout the country, utilities in

the Northern California Coast region could invest in shade tree programs as a costeffective energy conservation measure.

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.

• Windspeed reduction reduces the infiltration of outside air into interior

spaces, especially where conductivity is relatively high (e.g., glass windows) (Simpson 1998).

Trees and other vegetation on individual building sites may lower air temperatures 5 °F compared with sites 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). These “hot spots” in cities

How trees work to

save energy

Trees lower

temperatures
6

GENERAL TECHNICAL REPORT PSW-GTR-228

are called urban heat islands. A recent study for New York City compared trees,

living roofs, and light surfaces and found that curbside tree planting was the most

effective heat island mitigation strategy (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. Trees that shade

west-facing walls help keep buildings cool (fig. 4). In the winter, allowing the sun

to strike the southern side of a building can warm interior spaces. However, the

trunks and bare branches of deciduous trees that shade south- and east-facing walls

may increase heating costs during winter by blocking 40 percent or more of winter

irradiance (McPherson 1984).

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 reduce windspeed and resulting air infiltration by up to 50 percent, translating into potential

annual heating savings of 10 to 12 percent (Heisler 1986). Reductions in windspeed

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 increase

home energy efficiency and save

money

Windbreaks reduce

heat loss
7

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

reduce heat transfer through conductive materials as well. Cool winter winds,

blowing against windows, can contribute significantly to the heat loss of buildings

by increasing the gradient between inside and outside temperatures. Windbreaks

reduce air infiltration and conductive heat loss from buildings.

Shading and climate effects of 36,485 municipal trees in Berkeley, California,

reduced annual electricity used for air conditioning by 3,469 MWh, for a retail

savings of $458,994 ($12.58/tree) (Maco et al. 2005). Total annual savings of

natural gas for heating was 7,209 MBtu, for a savings of $94,072 ($2.58/tree).

Net energy savings were split: 17 percent winter heating and 83 percent summer

air conditioning. Citywide savings totaled $553,066, and the average savings per

tree was $15.16, but exceeded $30 for large species like London planetree (see

“Common and Scientific Names” section).

In the San Francisco Bay Area, 6.6 million existing trees provide annual energy

savings valued at $327 million (Simpson and McPherson 2007). In the Northern

California Coast region there is ample opportunity to “retrofit” communities with

more sustainable landscapes through strategic tree planting and care of existing

trees.

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.

Retrofit for more

savings
8

GENERAL TECHNICAL REPORT PSW-GTR-228

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 melting polar ice caps, which could raise sea level by 6 to 37 in (Hamburg et al. 1997). With more than one-third of the world’s population living in

coastal areas (Cohen et al. 1997), the effects could be disastrous. Increasing frequency and duration of extreme weather events will continue to tax emergency

management resources. Some plants and animals may become extinct as habitat

becomes restricted.

Urban forests have been recognized as important storage sites for carbon

dioxide (CO2

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

time, private markets dedicated to reducing CO2

 emissions by trading carbon credits

are emerging (McHale et al. 2007). Damage costs of CO2

 emissions range from

about $5 to $15 per metric tonne (t) (Tol 2005). For every $18 spent on a tree

planting project in Arizona, 1t of atmospheric CO2

 was reduced (McPherson and

Simpson 1999). The Climate Action Reserve’s (2008) Urban Forest Project Reporting Protocol provides guidance for tree planting and stewardship projects aimed at

providing 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.

On the other hand, vehicles, chain saws, chippers, and other equipment release

CO2

 during the process of planting and maintaining trees. And eventually, all trees

die, and most of the CO2

 that has accumulated in their biomass is released into the

atmosphere through burning or 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.

Typically, CO2

 released owing to tree planting, maintenance, and other

program-related activities is about 2 to 8 percent of annual CO2

 reductions obtained

through sequestration and reduced powerplant emissions (McPherson and Simpson

Trees reduce CO2

Some tree-related

activities release

CO2

Avoided CO2

emissions
9

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

1999). 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 tree maintenance operations, as well as decomposition of wood from

pruned or dead trees.

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

and cool buildings influence potential CO2

 emission reductions. The regional

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).
10

GENERAL TECHNICAL REPORT PSW-GTR-228

weighted average emission rate is 651 lbs CO2/kWh (US EPA 2003), a relatively

small amount because of the clean mix of fuels that produce energy to heat and

cool buildings. The region’s relatively low CO2

 emission rate means smaller benefits from reduced energy demand relative to other regions with higher emission

rates. Nevertheless, tree planting programs targeted to maximize energy savings

will provide climate protection dividends in the Northern California Coast region.

A study of Berkeley’s municipal forest found that 36,485 trees sequestered

3025 t of atmospheric CO2

 annually, valued at $49,602 (Maco et al. 2005). Net

sequestration of CO2

 by the San Francisco Bay Area’s 6.6 million trees is 696,686 t

worth $2.3 million annually (Simpson and McPherson 2007).

A study in Chicago focused on the carbon sequestration benefit of residential

tree canopy cover. 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.

A comprehensive study of CO2

 reduction by Sacramento’s urban forest found

the region’s 6 million trees offset 1.8 percent of the total CO2

 emitted annually as

a byproduct of human activities (McPherson 1998). This savings could be substantially increased through strategic planting and long-term stewardship that maximizes future energy savings from new tree plantings.

Since 1990, the Sacramento Tree Foundation, a nonprofit organization, has

partnered with the Sacramento Municipal Utility District to plant trees for energy

savings and atmospheric CO2 reduction. Nearly 500,000 trees have been planted

with the help of local residents. These trees are estimated to have offset CO2

emissions by 807,394 t and provided 12,313 GWh of cooling energy savings and

3.54 MW of capacity savings (Sarkovich 2009).

Improving Air Quality

In the United States, 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 particle matter (PM10) exceeds levels for

healthy air. Air pollution is a serious health threat to many city dwellers, causing

asthma, coughing, headaches, respiratory and heart disease, and cancer (Smith

1990). Short-term increases in O3

 concentrations have been statistically associated

with increased mortality for 95 large U.S. cities (Bell et al. 2004). Impaired health

results in increased social costs for medical care, greater absenteeism, and reduced

longevity.

CO2 reduction

through community

forestry

Trees improve air

quality
11

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Six counties in the Northern California Coast region have been designated

nonattainment areas for the 8-hour O3

 standard: Alameda, Contra Costa, Marin,

San Francisco, San Mateo, and Santa Clara (US EPA 2009). Tree planting is one

practical strategy for communities in these areas to meet and sustain mandated air

quality standards.

The U.S. Environmental Protection Agency (EPA) has recognized tree planting as a measure for reducing O3

 in state implementation plans (Nowak et al.

2006). Air quality management districts in California have funded tree planting

projects to control PM10 and other air pollutants. These policy decisions are creating new opportunities to plant and care for trees as a method for controlling air

pollution (Bond 2006, Hughes 2008, Luley and Bond 2002; for more information

see www.treescleanair.org).

Urban forests provide several air quality benefits (fig. 6):

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

, nitrogen dioxide [NO2], and

sulfur dioxide [SO2

]) through leaf surfaces.

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

• 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).

Trees can 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

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

with temperature and atmospheric levels of NO2

. As well, the O3-forming potential differs considerably for different tree species (Benjamin and Winer 1998).

Genera having the greatest relative effect on increasing O3 are sweetgum, blackgum, sycamore, poplar, and oak (Nowak 2000). A computer simulation study for

Atlanta found that it would be very difficult to meet EPA ozone standards by

using trees because of the high BVOC emissions from pines and other vegetation

(Chameides et al. 1988). Although removing trees reduced BVOC emissions, this

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). In the Los Angeles basin, increased

Trees affect ozone

formation
12

GENERAL TECHNICAL REPORT PSW-GTR-228

planting of low BVOC-emitting tree species would 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 leaf stomata: tiny openings in the

leaves. Secondary methods of pollutant removal include adsorption of gases on

plant surfaces and uptake through bark pores (lenticels). 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

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).

Trees absorb

gaseous pollutants
13

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

altering their metabolism and growth. At high concentrations, pollutants cause

visible damage to leaves, such as stippling and bleaching (Costello et al. 2003).

Although they may pose health hazards to plants, pollutants such as nitrogenous

gases can be sources of essential nutrients for trees.

Trees intercept small airborne particles. Some particles that impact 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 washes 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 release oxygen as a product of photosynthesis. Net annual oxygen

production differs depending on tree species, size, health, and location. A healthy

tree, for example, a 32-ft-tall ash, produces about 260 lb of net oxygen annually

(McPherson 1997). A typical person consumes 386 lb of oxygen per year. Therefore, two medium-sized, healthy trees can supply the oxygen required for a single

person over the course of a year. In colder climates, oxygen release will be less

than in areas with longer growing seasons.

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. Emissions avoided because of trees 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 new coal-fired powerplant, the tree reduces emissions of SO2

by 0.38 lb, NO2 by 0.27 lb, 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 CO2

emissions by 200 lb.

Although air pollutants removed and avoided owing to energy savings from

Berkeley’s municipal forest had substantial value ($143,228 annually), the releases

of BVOCs meant the trees produced a negative net air-quality benefit ($20,621)

(Maco et al. 2005). The ability of trees to produce net air-quality benefits differed

dramatically among species; those without high BVOC emissions produced significant benefits. Large-canopied trees with large leaf surface areas and low BVOC

emissions produced the greatest benefits. Annually, on a per-tree basis, the most

valuable street tree species included many large, old trees, such as American and

Chinese elm.

Trees intercept

particulate matter

Trees release

oxygen
14

GENERAL TECHNICAL REPORT PSW-GTR-228

A tree canopy cover of 23 percent in the San Francisco Bay Area was estimated to remove 247 tons of air pollution at an estimated value of $8.8 million

(Simpson and McPherson 2007). Over one-half of this total benefit accrued in

Santa Clara County. Increasing the region’s tree canopy cover by 3 percent

(4.3 million additional trees) was estimated to remove additional air pollutants,

a service valued at $783,000 each year.

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 (fig. 7). These evaporative emissions are a principal component of smog, and parked vehicles are a primary source.

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

Tree shade

prevents evaporative hydrocarbon

emissions

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

air quality.

Center for Urban Forest Research
15

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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 pavement surfaces, buildings, and landscapes. Also, many older cities have

combined sewer outflow systems, and during large rain events excess runoff can

mix with raw sewage. Rainfall interception by trees can reduce the magnitude of

this problem during large storms. Trees are mini-reservoirs, controlling runoff at

the source, thereby reducing runoff volumes and erosion of watercourses, as well as

delaying the onset of peak flows. Trees can reduce runoff in several ways (fig. 8):

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

runoff volumes and delaying the onset of peak flow.

• Roots increase the rate at which rainfall infiltrates soil by creating root

channels. This increases 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 soil moisture, increasing the

soil’s capacity to store rainfall. This benefit is minimal during winter.

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. 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 into receiving water bodies. 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 tree architecture, rainfall

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

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.

Trees reduce runoff
16

GENERAL TECHNICAL REPORT PSW-GTR-228

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 lack of evergreen species (Xiao et al. 1998). However,

average tree canopy interception ranged from 6 to 13 percent (150 gal per tree),

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).
17

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

close 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 Berkeley, California, the municipal forest reduced runoff by 7.2 million ft3

,

valued at $215,645 per year (Maco et al. 2005). Tree species with the highest rate

of interception were coast redwood, Monterey cypress, American elm, and blue

gum. In the San Francisco Bay area, the existing canopy (23 percent) reduced

runoff by 2.5 million ft3, with an estimated value of $102 million (Simpson and

McPherson 2007).

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

plantations or nurseries 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). However, the use of reclaimed water

for irrigation has limitations. For example, many species are sensitive to high

salinity levels.

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

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

to the landscape. In this way, trees soften 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).

Consumer surveys have found that preference ratings increase with the presence

of trees in the commercial streetscape. In contrast to areas without trees, shoppers

shop more often and longer in well-landscaped business districts. They were

willing to pay more for parking and up to 11 percent more for goods and services

(Wolf 2005).

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).

Urban forests can

treat wastewater

Beautification

Attractiveness of

retail settings

Public safety

benefits
18

GENERAL TECHNICAL REPORT PSW-GTR-228

Well-maintained trees increase the “curb appeal” of properties (fig. 9).

Research comparing sales prices of residential properties with different numbers

of trees suggests 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 residential 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 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). In Portland, Oregon, street trees

added on average $7,020 to the sales price of a home (Donovan and Butry 2008).

Scientific studies confirm our intuition 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). Deskworkers 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

Property value

benefits

Social and psychological benefits

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

environment.

Center for Urban Forest Research
19

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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.

The presence of trees in cities provides public health benefits and improves

the well-being of those who live, work, and play in cities. Physical and emotional

stress has both short-term and long-term effects. Prolonged stress can compromise

the human immune system. A series of studies on human stress caused by general

urban conditions and city driving show that views of nature reduce the stress response of both body and mind (Parsons et al. 1998). Urban green also appears to

have an “immunization effect,” in that people show less stress response if they

have had a recent view of trees and vegetation. Hospitalized patients with views

of nature and time spent 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 sunnier parts of the Northern

California Coast region. Trees reduce exposure to ultraviolet light, thereby lowering the risk of harmful effects from skin cancer and cataracts (Tretheway and

Manthe 1999).

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, twice the level at which noise becomes a health risk. Thick strips of

vegetation in conjunction with landforms or solid barriers can reduce highway

noise by 6 to15 decibels. Plants absorb more high-frequency noise than low frequency, which is advantageous to humans, as higher frequencies are most distressing to people (Cook 1978).

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). Native plants are particularly valuable because they support

wildlife. Also, regionally appropriate and native plant selections reduce potential

resource inputs.

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

service programs and grassroots-led urban and community forestry programs

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

and community forestry provides educational opportunities for residents who want

Human health

benefits

Noise reduction

Wildlife habitat

Jobs and environmental education
20

GENERAL TECHNICAL REPORT PSW-GTR-228

to learn about nature through first-hand 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 pavement management costs by protecting

paving from weathering. The asphalt paving on streets contains stone aggregate in

an oil binder. Tree shade lowers the street surface temperature and reduces 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 asphalt is

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).

Costs

Planting and Maintaining Trees

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

come at a price. A national survey reported that communities in the California

Figure 10—Natural areas within cities are refuges for wildlife and help connect city dwellers with

their ecosystems.

Shade can reduce

street maintenance

Center for Urban Forest Research
21

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Coast region spent an average of $14.73 per tree, in 1994, for street- and park-tree

management (Tschantz and Sacamano 1994). This amount is relatively high compared with average expenditures in other regions. Nationwide, the single largest

expenditure was for tree pruning, followed by tree removal/disposal, and tree

planting.

Our survey of municipal foresters in Berkeley, Pleasanton, Redwood City, and

San Jose indicates that on average they are spending about $10 to $20 per tree

annually. Most of this amount is for pruning ($5 to $15 per tree) and removal and

disposal ($1 to $2 per tree), and administration ($1 per tree). Other municipal

departments incur costs for infrastructure repair and trip-and-fall claims resulting

from root-buckled pavement that range from $0 to $25 per tree depending on city

policy.

Frequently, trees in new residential subdivisions are planted by developers,

whereas cities and counties and volunteer groups plant trees on existing streets and

parklands. In some cities, tree planting has not kept pace with removals. Moreover,

limited growing space in cities or preferences for flowering trees results in increased planting of smaller, shorter lived species that provide fewer benefits than

larger trees do.

Municipal costs of

tree care

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.

Center for Urban Forest Research
22

GENERAL TECHNICAL REPORT PSW-GTR-228

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. An analysis of data for Sacramento suggested that households typically spent about $5 to $10 annually per tree

for pruning and pest and disease control (Summit and McPherson 1998). Our

survey of four commercial arborists in the Northern California Coast region

indicated that expenditures typically range from $10 to $20 per tree. Expenditures

are usually greatest for planting, pruning, and pest and disease control.

Conflicts With Urban Infrastructure

Like other cities across the United States, communities in the Northern California

Coast 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 (Randrup et al. 2001a). In a survey of 18 California cities, it was

reported that on average, cities spend $11.22 per tree on the repair of sidewalks

damaged by tree roots each year (McPherson 2000). As well, 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 parts of the Bay area, tree growth and deteriorating infrastructure in tight

municipal budget times are causing cities to shift repair costs to homeowners. 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

should not always bear full responsibility. 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):

• Cities are downsizing their municipal 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.

Residential costs

vary

Tree roots can

damage sidewalks

Costs of conflicts
23

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

• Sidewalk damage was the second most common reason that street and park

trees were removed. Thousands of healthy urban trees are lost each year

and their benefits forgone because of this problem.

• 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. Other strategies include meandering sidewalks around trees, suspending

sidewalks above tree roots, and replacing concrete sidewalks with recycled rubber

sidewalks.

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

susceptible to invasion (Randrup et al. 2001b). 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 due to the fact that 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 winter 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. Windstorms also

incur cleanup costs. Although serious natural catastrophes are infrequent, they can

result in large expenditures.

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

electric rates. Large trees under power lines require frequent pruning, which can

make them unattractive (fig. 12). Frequent crown reduction reduces the benefits

these trees could otherwise provide. Moreover, increased costs for pruning are

passed on to customers.

Cleaning up after

trees

Large trees under

power lines can be

costly
24

GENERAL TECHNICAL REPORT PSW-GTR-228

Wood Salvage, Recycling, and Disposal

According to our survey, most Northern California Coast region cities are recycling

green waste from urban trees as mulch, compost, and firewood. 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. Hauling

and recycling costs can be nearly offset by revenues from sales of mulch, milled

lumber, and firewood. The cost of wood disposal may be higher depending on

geographic location and the presence of exotic pests that require elaborate wastewood disposal (Bratkovich 2001). Growing markets for urban wood products and

biomass feedstock for biopower plants could turn this cost into a revenue source.

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.

Recycling green

waste may pay for

itself

Center for Urban Forest Research
25

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 3: Determining Benefits and Costs of

Community Forests in Northern California Coast

Communities

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

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

report results for representative small, medium, and large broadleaf trees and for a

representative conifer.

Estimates of benefits and costs 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 the 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 vary, depending

on differences in climate, air pollutant concentrations, tree-maintenance practices,

and other factors. Given the Northern California Coast region’s large geographical

area, with many different climates, soils, and types of community forestry programs, the approach used here provides first-order approximations. These findings

can be used for general planning purposes, but should not be applied to estimate

benefits produced by individual trees in the landscape. The tree benefit values

reported here can be easily adapted and adjusted to provide a general accounting

for local planting projects. They provide a basis for decisions that set priorities and

influence management direction, but are not suitable for determining whether a

specific tree should be removed or retained (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 (about 27 ft from

the east, south, and west walls of the residence) and a public streetside or park

location. 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, property value increase) 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 using “typical” tree species. More
26

GENERAL TECHNICAL REPORT PSW-GTR-228

information on data collection, modeling procedures, and assumptions can be found

in appendix 3.

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

species, we report results for a small broadleaf evergreen tree, the camphor

(Cinnamomum camphora), a medium deciduous tree, the cherry plum (Prunus

cerasifera), a large deciduous tree, the velvet ash (Fraxinus velutina), and a conifer,

the Monterey pine (Pinus radiata) (See “Common and Scientific Names” section)

(figs. 13 through 16). The conifer is included as a windbreak tree located more

than 50 ft from the residence so it does not shade the building. Tree dimensions

are derived from growth curves developed from street trees in Berkeley, California

(Maco et al. 2005) (fig. 17). Although camphor is often considered a medium or

large tree, it is slow growing. Our data from street trees in Berkeley found that 20

years after planting it was 4 ft shorter, 2 ft narrower, and had 44 percent of the

leaf surface area of the cherry plum. The latter difference is significant because leaf

area drives benefit production. Although camphor can ultimately become a largestature tree, it is representative of a small tree in this 40-year analysis because of its

relatively slow growth and small leaf area. Similarly, although cherry plum is often

considered a small tree, it is representative of a medium tree here because of its

relatively rapid growth (reaches a height of 30 ft in 40 years) and large leaf surface

area.

The selection of these species was based on data availability, and not intended

to endorse their use in large numbers. In fact, the cherry plum has a poor form for

a street tree, Monterey pine is subject to pitch canker, and velvet ash is susceptible

to mistletoe and the emerald ash borer, the latter a potentially serious pest that may

threaten all ash trees in California. 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 Berkeley, Pleasanton, Redwood City, and San Jose. In

addition, commercial arborists from Arborwell, Bartlett Tree Experts, Mayne Tree

Expert Co., and S.P. McClenahan Co. provided information on tree-management

costs on residential properties.

Benefits are calculated with numerical models and data from the region (e.g.,

powerplant pollutant emission factors for emission reductions owing to energy savings) and from local sources (e.g., San Francisco Bay area climate data for energy

effects). Changes in building energy use from tree shade were based on computer

simulations that incorporated building, climate, and shading effects. Sequestration,

the net rate of CO2

 storage in above- and belowground biomass over the course of

Tree care costs

based on survey

findings
27

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 14—The cherry plum

represents medium trees in this

guide.

Figure 13—The camphor tree represents small trees in this guide.

Center for Urban Forest Research

Center for Urban Forest Research
28

GENERAL TECHNICAL REPORT PSW-GTR-228

Figure 15—The velvet ash represents

large trees in this guide.

Figure 16—The Monterey pine

represents coniferous trees in

this guide.

Center for Urban Forest Research

Center for Urban Forest Research
29

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 17—Tree growth curves are based on data

collected from street trees in Berkeley, California. Data

for representative small, medium, and large broadleaf

trees and conifer trees are for the camphor, cherry

plum, velvet ash, and Monterey pine, 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.
30

GENERAL TECHNICAL REPORT PSW-GTR-228

one growing season, was calculated with tree growth data and biomass equations

for urban trees. Emission reductions were calculated as the product of energy

savings and CO2

 emission factors for electricity and heating. Annual consumption

of gasoline and diesel fuel by the community forestry divisions was converted into

CO2 equivalent emissions to estimate CO2 released by tree maintenance activities.

Hourly meteorological data for windspeed, solar radiation, and precipitation, as

well as hourly concentrations for NO2, O3, SO2, and PM10 were used with a numerical model to calculate pollutant dry deposition per tree. Energy savings resulting in

reduced emissions of criteria air pollutants (VOCs, NO2, PM10) from powerplants

and space heating equipment were calculated using utility-specific emission factors

for electricity and heating fuels. A numerical interception model accounted for the

volume of rainfall stored in tree crowns using information on crown projection

areas (area under tree dripline), leaf areas, and water depths on canopy surfaces

with hourly meteorological and rainfall data. The value of aesthetic and other

benefits was captured from research that has quantified differences in sales prices

of properties that are associated with trees. Anderson and Cordell (1988) found that

each large front-yard tree was associated with a 0.88-percent increase in sales price.

In this analysis, aesthetic benefits reflect the contribution of a large front-yard tree

to local residential sales prices, with adjustments that account for the location of the

tree (e.g., front or back yard, residential or commercial land use) and its growth

rate.

Regional electricity and natural gas prices are used in this study to quantify

the dollar value of energy savings. Costs of preventing or repairing damage from

pollution, flooding, or other environmental risks were used to estimate society’s

willingness to pay for clean air and water (Wang and Santini 1995). 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. Appendix 3

contains more detailed information on methods used to calculate benefits and costs

and assign monetary value to tree services.

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 45

Tree benefits based

on numerical models

Tree mortality

included
31

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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

are 3 percent per year for the first 5 years and 0.57 percent per year for the remainder of the 40-year period. This 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). In appendix 2, results

are reported at 5-year intervals for 40 years.

Findings of This Study

Average Annual Net Benefits

Average annual net benefits (benefits minus costs) per tree increase with mature

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

• $29 to $41 for a small tree

• $42 to $60 for a medium tree

• $101 to $122 for a large tree

• $142 to $146 for a conifer

Benefits associated with increased property value and energy savings account

for the largest proportion of total benefits in this region. Reduced stormwater

runoff, lower levels of air pollutants and less 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 pollutant emissions at powerplants account for important reductions in gases that produce

ozone, a major component of smog. Environmental benefits alone, including

energy savings, stormwater-runoff reduction, improved air quality, and reduced

atmospheric CO2, are greater than tree care costs.

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

the velvet ash and Monterey pine, can be substantially greater than those from

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

public tree are $29, $42, and $101, respectively. Conifers provide the highest level

of benefits, on average $142 for a public tree. The largest average annual net benefits from yard trees stemmed from a tree opposite the west-facing wall of a house:

$41, $60, and $122 for small, medium, and large broadleaf trees, respectively. The

pine tree windbreak provides an average annual net benefit of $146 per tree regardless of location because it is too far away to shade the residence.

Average annual net

benefits increase

with tree size

Large trees provide

the most benefits
32

GENERAL TECHNICAL REPORT PSW-GTR-228

The large yard tree opposite a west wall produces a net annual benefit of $170

at year 40. In the same location, 40 years after planting, the small, medium, and

pine produce annual net benefits of $80, $81, and $172, respectively.

Forty years after planting at a typical public site, the small, medium, and large

trees and the conifer provide annual net benefits of $60, $41, $133, and $157,

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:

• $1,640 (yard) and $1,179 (public) for a small tree

• $2,392 (yard) and $1,679 (public) for a medium tree

• $4,868 (yard) and $4,034 (public) for a large tree

• $5,855 (yard) and $5,685 (public) for a conifer

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

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

20 years after planting, the total value of environmental benefits alone ($55) is five

times the total annual cost ($11). Environmental benefits total $25, $34, and $48

for the small, medium, and pine tree, whereas tree care costs are lower, $5, $11,

and $15, respectively. Adding the value of aesthetics and other benefits to the

environmental benefits results in substantial net benefits.

Net benefits are slightly less for public trees (table 2) than yard trees. Based on

our survey findings, public trees are about twice as expensive to maintain as private

trees. The standard of care is often high for public trees because of their prominence and potential risk.

Average Annual Costs

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

as follows:

• $10 (yard) and $17 (public) for a small tree

• $11 (yard) and $24 (public) for a medium tree

• $13 (yard) and $28 (public) for a large tree

• $15 (yard) and $33 (public) for a conifer

Costs increase with mature tree size because of added expenses for pruning and

removing larger trees.

Net annual benefits

at year 40

Year 20: environmental benefits

exceed tree care

costs

Costs of tree care
33

Northern California Coast 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

Camphor tree Cherry plum Velvet ash Monterey pine

Small tree Medium tree Large tree Conifer tree

18 ft tall 22 ft tall 34 ft tall 38 ft tall

16-ft spread 18-ft spread 22-ft spread 24-ft spread

LSA = 313 ft2 LSA = 705 ft2 LSA = 1,372 ft2 LSA = 2,235 ft2

Resource Total Resource Total Resource Total Resource Total

Benefit category units value units value units value units value

Dollars Dollars Dollars Dollars

Electricity savings ($0.2131/kWh) 94 kWh 19.99 134 kWh 28.58 215 kWh 45.85 143 kWh 30.58Natural gas savings ($0.0173/kBtu) 122 kBtu 2.10 157 kBtu 2.71 234 kBtu 4.04 469 kBtu 8.11

Carbon dioxide ($0.003/lb) 84 lb 0.28 143 lb 0.48 189 lb 0.63 191 lb 0.64Ozone ($1.25/lb) 0.12 lb 0.16 0.14 lb 0.17 0.20 lb 0.25 0.29 lb 0.36Nitrous oxide ($1.25/lb) 0.10 lb 0.12 0.11 lb 0.14 0.17 lb 0.21 0.24 lb 0.30Sulfur dioxide ($1.77/lb) 0.02 lb 0.04 0.03 lb 0.04 0.04 lb 0.07 0.04 lb 0.08Small particulate matter

($2.92/lb) 0.26 lb 0.77 0.17 lb 0.50 0.28 lb 0.80 0.22 lb 0.63

Volatile organic compounds

($0.53/lb) 0.00 lb 0.00 0.01 lb 0.00 0.01 lb 0.00 0.01 lb 0.00

Biogenic volatile organic

compounds ($0.53/lb) 0.00 lb 0.00 0.00 lb 0.00 0.00 lb 0.00 -0.27 lb - 0.14

Rainfall interception

($0.006/gal) 315 gal 1.73 321 gal 1.76 535 gal 2.94 1,402 gal 7.71

Environmental subtotal 25.19 34.39 54.80 48.28

Other benefits 18.70 38.14 74.52 112.45

Total benefits 43.89 72.53 129.32 160.73Total costs 4.74 10.56 11.20 14.96

Net benefits 39.15 61.97 118.12 145.77

LSA = leaf surface area.
34

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 2—Estimated annual benefits and costs for a public tree (street/park) 20 years after planting Camphor tree Cherry plum Velvet ash Monterey pine Small tree Medium tree Large tree Conifer tree 18 ft tall 22 ft tall 34 ft tall 38 ft tall 16-ft spread 18-ft spread 22-ft spread 24-ft spread LSA = 313 ft2 LSA = 705 ft2 LSA = 1,372 ft2 LSA = 2,235 ft2 Resource Total Resource Total Resource Total Resource Total Benefit category units value units value units value units value Dollars Dollars Dollars Dollars Electricity savings ($0.2131/kWh) 65 kWh 13.78 89 kWh 18.96 127 kWh 27.04 143 kWh 30.58 Natural gas savings ($0.0173/kBtu) 142 kBtu 2.46 180 kBtu 3.10 261 kBtu 4.50 469 kBtu 8.11

Carbon dioxide ($0.003/lb) 67 lb 0.23 116 lb 0.39 135 lb 0.45 192 lb 0.64Ozone ($1.25/lb) 0.12 lb 0.16 0.14 lb 0.17 0.20 lb 0.25 0.29 lb 0.36Nitrous oxide ($1.25/lb) 0.10 lb 0.12 0.11 lb 0.14 0.17 lb 0.21 0.24 lb 0.30Sulfur dioxide ($1.77/lb) 0.02 lb 0.04 0.03 lb 0.04 0.04 lb 0.07 0.04 lb 0.08Small particulate matter

($2.92/lb) 0.26 lb 0.77 0.17 lb 0.50 0.28 lb 0.80 0.22 lb 0.63

Volatile organic compounds

($0.53/lb) 0.00 lb 0.00 0.01 lb 0.00 0.01 lb 0.00 0.01 lb 0.00

Biogenic volatile organic

compounds ($0.53/lb) 0.00 lb 0.00 0.00 lb 0.00 0.00 lb 0.00 0.00 lb - 0.14

Rainfall interception

($0.006/gal) 315 gal 1.73 321 gal 1.76 535 gal 2.94 1,402 gal 7.71

Environmental subtotal 19.28 25.07 36.27 48.28

Other benefits 21.22 43.28 84.56 127.59

Total benefits 40.50 68.35 120.83 175.87Total costs 9.23 22.54 23.07 26.24

Net benefits 31.27 45.81 97.76 149.63

LSA = leaf surface area.
35

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Over the 40-year period, tree planting is the single greatest cost for private

trees, averaging approximately $4 per tree per year (see app. 2). Based on our

survey, we assume in this study that a 15-gal yard tree is planted at a cost of $145.

Annualized expenditures for tree pruning are the most important cost for public

trees ($10 to $22 per tree per year).

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

$5 to $15, whereas public tree care costs average $9 to $26.

Average Annual Benefits

Average annual benefits over 40 years, including energy savings, stormwater runoff

reduction, aesthetic value, air quality improvement, and carbon dioxide (CO2

)

sequestration increase with mature tree size (figs. 18 and 19, for detailed results

see app. 2):

• $41 to $51 for a small tree

• $57 to $71 for a medium tree

• $115 to $135 for a large tree

• $161 to $176 for a conifer

Energy savings—

In the Northern California Coast region, trees provide significant energy benefits

that tend to increase with tree size. For example, average annual net energy benefits

over 40 years are $27 for the small camphor opposite a west-facing wall, and $51

for the larger velvet ash. Average annual net energy benefits for public trees are

slightly less than for yard trees because public trees are assumed to provide general

climate effects but do not shade buildings as effectively. Annual benefits range from

$19 for the small public tree to $36 for the large public velvet ash. For species of

all sizes, energy savings increase as trees mature and their leaf surface areas increase

(figs. 18 and 19).

As expected in a region with warm summers and mild winters, cooling savings

account for most of the total energy benefit. Average annual cooling savings for the

small and large trees range from $17 to $24 and $31 to $47, respectively. The

Monterey pine in a windbreak reduces heating costs by $8 on average.

Average annual net energy benefits for residential trees are greatest for a tree

located west of a building because the effect of shade on cooling costs is maximized. A yard tree located east of a building produces the least net energy benefit

because it has the least benefit during summer, and the greatest adverse effect on

Energy benefits are

crucial
36

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 3—Estimated annual costs 20 years after planting for a private tree opposite the west-facing wall and a public tree Camphor tree Cherry plum Velvet ash Monterey pine Small tree Medium tree Large tree Conifer tree 18 ft tall 22 ft tall 34 ft tall 38 ft tall

16-ft spread 18-ft spread 22-ft spread 24-ft spread

LSA = 313 ft2 LSA = 705 ft2 LSA = 1,372 ft2 LSA = 2,235 ft2

Costs Private: Public Private: Public Private: Public Private: Public

west tree west tree west tree west tree

$/yr/tree

Tree and planting 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Pruning 0.26 5.46 5.19 18.02 5.19 18.02 5.19 18.02Remove and dispose 1.26 1.02 1.51 1.22 1.69 1.36 2.75 2.22Pest and disease 2.93 0.01 3.52 0.01 3.93 0.01 6.39 0.01Infrastructure 0.24 1.72 0.29 2.07 0.33 2.31 0.53 3.76Irrigation 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Cleanup 0.04 0.30 0.05 0.36 0.06 0.40 0.09 0.65Liability and legal 0.00 0.03 0.00 0.03 0.01 0.04 0.01 0.06Administration and other 0.00 0.70 0.00 0.84 0.00 0.94 0.00 1.53

Total costs 4.74 9.23 10.56 22.54 11.20 23.07 14.96 26.24Total benefits 43.89 40.50 72.53 68.35 129.31 120.83 160.72 175.87

Total net benefits 39.15 31.27 61.96 45.81 118.11 97.76 145.76 149.63

Note: Prices for removal and disposal are included to account for expected mortality of citywide planting.LSA = leaf surface area.
37

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Figure 18—Estimated annual benefits and costs for a small

(camphor), medium (cherry plum), and large (velvet ash)

broadleaf tree, and a conifer (Monterey pine) located west of

a residence. Costs are greatest during the initial establishment

period, and benefits increase with tree size.

Figure 19—Estimated annual benefits and costs for public small

(camphor), medium (cherry plum), and large (velvet ash) broadleaf tree, and a conifer (Monterey pine).
38

GENERAL TECHNICAL REPORT PSW-GTR-228

heating costs from shade in winter (see also fig. 4). Trees located south of a building provide intermediate net benefits. Net energy benefits also reflect speciesrelated traits such as size, form, branch pattern and density, and time in leaf.

Stormwater runoff reduction—

Benefits associated with rainfall interception, reducing stormwater runoff, are substantial for all tree types. The camphor, a broadleaf evergreen tree, intercepts 420

gal/year on average over a 40-year period with an estimated annual value of $2. The

cherry plum, velvet ash, and Monterey pine intercept 369 gal/year, 673 gal/year,

and 1,673 gal/year on average, with annual values of $2, $4, and $9, respectively.

The camphor intercepts more rainfall than the larger cherry plum because of its

evergreen foliage.

As metropolitan areas in the region grow, the amount of impervious surface

increases. The role that trees can play in protecting water quality by reducing

stormwater runoff is substantial.

Aesthetic and other benefits—

Benefits associated with property value account for the largest portion of total

benefits. As trees grow and become more visible, they can increase a property’s

sales price. Average annual values associated with these aesthetic and other benefits

for yard trees are $21, $36, $77, and $105 for the small, medium, and large deciduous trees and for the conifer, respectively. The values for public trees are $23, $40,

$88, and $119, respectively. The values for yard trees are slightly less than for

public trees because off-street trees contribute less to a property’s curb appeal than

more prominent street trees. Because these estimates are based on median home sale

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

local economies and market fluctuations.

Carbon dioxide reduction—

Net atmospheric CO2

 reductions accrue for all tree types. Average annual net

reductions range from a low of 57 lbs ($0.19) for the small tree on the eastern side

of the house to a high of 226 lbs ($0.75) for a large conifer tree. The deciduous ash

tree opposite west-facing house walls produced 204 lbs of CO2

 reduction owing in

part to reduced powerplant emissions associated with energy savings. The values for

the camphor are lowest for CO2 reduction because of the relatively small impacts of

shade from the small-growing tree on energy consumption and emission reductions.

Aesthetic benefits

are substantial
39

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Forty years after planting, average annual avoided emissions and sequestered

and released CO2

 for a yard tree opposite a west wall are 202, 299, 363, and 413

lbs, respectively, for the small, medium, and large broadleaf trees and the conifer.

Air quality improvement—

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

powerplant emissions owing to energy savings minus biogenic volatile organic compounds (BVOCs) released by trees. Average annual air quality benefits range from

$1 to $2 per tree. The large-stature Monterey pine produces the greatest benefit

because of its size, although it does emit 0.34 lbs of BVOCs on average each year.

The ability of trees to reduce particulates, ozone, and nitrogen dioxides in the

air has the highest monetary value. For example, the average annual monetary

value for an ash tree is estimated to be $1.06 for particulates, $0.32 for ozone, and

$0.25 for nitrogen dioxides. The value of reducing sulfur dioxides and VOCs is

less.

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

improvement for a yard tree opposite a west wall are $3, $1, $4, and $4, respectively, for the small, medium, and large trees and the conifer.

Annual air quality

benefits average

$1 to $2 per tree
40

GENERAL TECHNICAL REPORT PSW-GTR-228
41

Northern California Coast 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

Martha Falls City Example

The hypothetical city of Martha Falls is located in the Northern California Coast

region and has a population of 24,000. Most of its street trees were planted in the

1930s, with sweetgum and London planetrees as the dominant species. Currently,

the tree canopy cover is sparse because most of the trees have died and 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. 20).

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 Martha Falls over a 5-year period. Trained volunteers

will plant 15-gal trees in the following proportions: 70 percent large-maturing, 15

percent medium-maturing, and 5 percent small-maturing deciduous trees and 10

percent conifers. One hundred trees will be planted in parks, and the remaining 900

trees will be planted along Main Street and other downtown streets.

The Martha 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

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
42

GENERAL TECHNICAL REPORT PSW-GTR-228

future benefits these groups will receive from trees in terms of air quality, hydrology, energy, carbon dioxide (CO2

) reduction, and property value. Such a district

would require voter approval of a special assessment that charges recipients for tree

planting and maintenance costs in proportion to the tangible 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 trees’ services will be distributed

over the 40-year life of the project.

As a first step, the Martha Falls city forester and Green Team decided to use the

values in appendix 2, tables 6 to 17, to quantify total cumulative benefits and costs

over 40 years for the proposed planting of 1,000 public trees—700 large, 150

medium, and 50 small trees and 100 conifers.

Figure 20—The Green Team is motivated to re-green their community

by planting 1,000 trees in 5 years.

The first step: determine tree planting

numbers

Center for Urban Forest Research
43

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Before setting up a spreadsheet to calculate benefits and costs, the team considered which aspects of Martha Fall’s urban and community forestry project differ

from the regional values used in this guide (the methods for calculating the values

in appendix 2 are described in appendix 3):

1. The prices of electricity and natural gas in Martha Falls are $0.11/kWh and

$0.0125/kBtu, respectively. They are not $0.213/kWh and $0.0173/kBtu as

assumed 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 about $1 per tree for

large public trees. Thus, an adjustment is necessary.

3. Planting will cost $140 per tree. The guide assumes planting costs of $145 per

public tree. The costs will be slightly lower for Martha Falls because some labor

will be provided by trained volunteers.

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, some adjusted for Martha Falls where necessary,

are entered into the second column. The third column contains the resource units

(RU) 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 dollar values, obtained by multiplying the RU values by tree numbers,

prices, and 40 years.

To adjust for different electricity prices, the forester multiplied electricity

saved for a large public tree in the RU column (145.5 kWh) by the Martha Falls

price for electricity ($0.11/kWh). This value ($16.01 per tree per year) was then

multiplied by the number of trees planted and 40 years ($16.01 × 700 trees × 40

years = $448,171) 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.

To adjust cost figures, the city forester changed the planting cost from $145

assumed in the guide to $140 (table 4). This planting cost was annualized by

dividing the cost per tree by 40 years ($140/40 = $3.50 per tree per year). Total

planting costs were calculated by multiplying this value by 700 large trees and 40

years ($98,000).

The second step:

adjust for local

prices of benefits

The third step:

adjust for local costs
44

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 4—Spreadsheet calculations of benefits and costs for the Martha Falls planting project (1,000 trees) over 40 years 700 large trees 150 medium trees 50 small trees 100 conifer trees 1,000 total trees Percentage Price Annual Total Annual Total Annual Total Annual Total Total Annual of positive Benefits (adjusted) per tree value per tree value per tree value per tree value value per tree services Resource Resource Resource Resource Dollars units Dollars units Dollars units Dollars units Dollars Dollars Dollars Percent Electricity (kWh) 0.1100 145.51 448,171 89.57 59,116 77.84 17,125 169.48 74,571 598,983 14.97 14.28 Natural gas (kBtu) 0.0125 274 95,900 184 13,800 162 4,050 491 24,550 138,300 3.46 3.30 Net carbon dioxide (lb) 0.0033 158 14,776 134 2,685 82 548 226 3,019 21,029 0.53 0.50 Ozone (lb) 1.25 0.26 9,106 0.16 1,201 0.16 400 0.37 1,851 12,558 0.31 1.50 Nitrous oxide (lb) 1.25 0.20 7,005 0.12 901 0.12 300 0.29 1,451 9,656 0.24 Sulfur dioxide (lb) 1.77 0.04 1,981 0.03 318 0.03 106 0.05 354 2,759 0.07 Small particulate matter (lb) 2.92 0.36 29,469 0.16 2,807 0.35 2,046 0.35 4,093 38,415 0.96 Volatile organic

compounds (lb) 0.53 0.01 148 0.01 32 0.00 0 0.01 21 201 0.01 

Biogenic volatile

organic compounds (lb) 0.53 0.00 0 0.00 0 0.00 0 -0.34 -719 -719 -0.02 

Hydrology (gal) 0.0055 673 103,642 369 12,177 420 4,620 1,673 36,806 157,245 3.93 3.75Aesthetics and other

benefits ($) 87.52 2,450,560 40.39 242,340 23.26 46,520 119.27 477,080 3,216,500 80.41 76.68

Total benefits 3,160,757 335,377 75,716 623,077 4,194,927 104.87 100.00

Price Annual Total Annual Total Annual Total Annual Total Total Value Percentage

Costs (adjusted) per tree value per tree value per tree value per tree value value per tree of costs

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – Dollars – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – Percent

Tree and planting 140 3.50 98,000 3.50 21,000 3.50 7,000 3.50 14,000 140,000 3.50 12.04Pruning 19.46 544,878 15.69 94,141 9.62 19,242 21.57 86,298 744,558 18.61 64.03Remove and dispose 1.59 44,404 1.43 8,567 1.20 2,408 2.45 9,781 65,160 1.63 5.60Pest and disease 0.01 192 0.01 37 0.01 10 0.01 44 283 0.01 0.02Infrastructure repair 2.30 64,499 2.05 12,318 1.72 3,449 3.65 14,585 94,851 2.37 8.16Irrigation 0.00 0 0.00 0 0.00 0 0.00 0 0 0.00 0.00Cleanup 0.40 11,083 0.35 2,117 0.30 593 0.63 2,506 16,299 0.41 1.40Liability and legal 0.04 1,078 0.03 206 0.03 58 0.06 244 1,585 0.04 0.14Admin. and other 2.50 2.50 70,000 2.50 15,000 2.50 5,000 2.50 10,000 100,000 2.50 8.60

Total costs 834,133 153,385 37,760 137,458 1,162,736 29.07 100.00

Net benefit 2,326,624 181,992 37,956 485,619 3,032,191 75.80Benefit/cost ratio 3.79 2.19 2.01 4.53 3.61Net benefit per tree 83.09 30.33 18.98 121.40Note: Adjusted values are for electricity, natural gas, tree and planting, and administrative and other costs.
45

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

The administration, inspection, and outreach costs are expected to average

$2.50 per tree per year, or a total of $100 per tree for the project’s life. Consequently, the total administration cost for large trees is $2.50 × 700 large trees × 40

years ($70,000). The same procedure was followed to calculate costs for the

medium and small deciduous trees and conifers.

Subtracting total costs from total benefits yields net benefits:

• $37,956 for 50 small trees

• $181,992 for 150 medium trees

• $2.3 million for 700 large trees

• $485,619 for 100 conifer trees

Annual benefits over 40 years total $4.2 million ($105 per tree per year), and

annual costs total $1.2 million ($29 per tree per year). The total net annual benefits

for all 1,000 trees over the 40-year period are $3.0 million, or $76 per tree. To

calculate this average annual net benefit per tree, the forester divided the total net

benefit by the number of trees planted (1,000) and 40 years ($3,032,191/1,000

trees/40 years = $75.80). Dividing total benefits by total costs yielded benefit-cost

ratios (BCRs) of 2.01, 2.19, 3.79, and 4.53 for small, medium, and large deciduous

trees and conifers. The BCR for the entire planting is 3.61, indicating that $3.61

will be returned for every $1 invested.

It is important to remember that this analysis assumes 45 percent of the planted

trees die and are not replaced. Also, it does not account for the time value of

money from a municipal 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

$1.2 million over 40 years, and the average annual cost will be about $29,000

($1,162,736 / 40 years); however, expenditures are front-loaded because relatively

more funds will be needed initially for planting and stewardship. The fifth and last

step is to identify the distribution of services that the trees will provide. The last

column in table 4 shows the distribution of services as a percentage of the total:

• Energy savings = 17 percent (cooling = 14 percent, heating = 3 percent)

• Carbon dioxide reduction = 1 percent

• Stormwater-runoff reduction = 4 percent

• Aesthetics/property value increase = 77 percent

• Air quality = 1 percent

The fourth step:

calculate net benefits and benefitcost ratios for public

trees

The final step:

determine how

services are distributed, and link

these to sources

of revenue
46

GENERAL TECHNICAL REPORT PSW-GTR-228

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 ($1.2 million), fees could be

distributed in the following manner:

• $204,000 from electric and natural gas utilities for energy savings (17

percent). (It is more cost-effective for utility companies to plant trees to

reduce peak energy demand than to meet peak needs through added infrastructure).

• $6,000 from local industry for atmospheric CO2

 reduction offsets (1

percent).

• $44,000 from the stormwater-management district for water quality

improvement associated with reduced runoff (4 percent).

• $891,000 from property owners for increased property values (77 percent).

• $17,000 from air quality management district for net reduction in air

pollutants (1 percent).

Whether project 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 i-Tree Street (formerly STRATUM), part of the i-Tree

software suite, that simplifies these calculations for analysis of existing street tree

populations (http://www.itreetools.org).

City of Melvinville Example

As a municipal cost-cutting measure, the hypothetical city of Melvinville plans to

stop planting street trees in areas of new development. Instead, developers will be

required to plant front-yard trees, thereby reducing costs to the city. The community forester and concerned citizens believe that, although this policy will result in

cost savings for the city, developers may plant trees with smaller mature size than

the city would have. Currently, Melvinville’s policy is to plant large-growing trees

based on each site’s available growing space (fig. 21). Planting smaller stature trees

could result in services “forgone” whose value will exceed cost savings. To evaluate

this possible outcome, the community forester and concerned citizens decided to

compare costs and benefits of planting small, medium, and large trees for a hypothetical street-tree planting project in Melvinville.

Distributing costs of

tree management to

multiple parties
47

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

As a first step, the city forester and concerned citizens decided to quantify the

total cumulative benefits and costs over 40 years for a typical street tree planting of

1,500 trees in Melvinville. For comparison purposes, the planting includes 500

small trees, 500 medium trees, and 500 large trees. Data in appendix 2 are used for

the calculations; however, three aspects of Melvinville’s urban and community

forestry program are different than assumed in this tree guide:

• The price of electricity is $0.17/kWh, not $0.213/kWh.

• The trees will be irrigated for the first 5 years at a cost of approximately

$0.50 per tree annually.

• Planting costs are $450 per tree for 24-in box trees instead of the $145 per

15-gal container tree.

To calculate the dollar value of total benefits and costs for the 40-year period,

the last column in appendix 2 (40-year average), tables 6 to 14, is multiplied by 40

years. As 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 for cooling we multiply electricity saved for each tree

Figure 21—The fictional city of Melvinville’s policy to plant as large a tree as the site will

handle has provided ample benefits in the past. Here, a large-stature tree has been planted.

The first step:

calculate benefits

and costs over

40 years

The second step:

adjust for local

prices of benefits

Center for Urban Forest Research
48

GENERAL TECHNICAL REPORT PSW-GTR-228

type in the RU column by the number of trees and 40 years (large public tree: 146

kWh × 500 trees × 40 years = 2,920,000 kWh). This value is multiplied by the

price of electricity in Melvinville ($0.17/kWh × 2,920,000 kWh = $496,400) 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 $851,400 in total benefits. The medium and large trees provide

$1.2 million and $2.4 million, respectively.

To adjust cost figures, we add a value for irrigation by multiplying the annual

cost by the number of trees by the number of years irrigation will be applied

($0.50 × 500 trees × 5 years = $1,250). We multiply 500 trees by the unit planting

cost ($450) to obtain the adjusted cost for planting in Melvinville (500 × $450 =

$225,000). The average annual 40-year costs for other items are taken from

appendix 2 and multiplied by 40 years and the appropriate number of trees to

compute total costs. These 40-year cost values are entered into table 5.

Subtracting total costs from total benefits yields net benefits for the small

($353,560), medium ($592,409), and large ($1.7 million) trees. The total net

benefit for the 40-year period is $2.7 million (total benefits -total costs), or $1,773

per tree ($2.7 million/1,500 trees) on average (table 5).

The net benefits per public tree planted are as follows:

• $707 for a small tree

• $1,185 for a medium tree

• $3,427 for a large tree

By not investing in street-tree planting, the city would save $675,000 in initial

planting costs. There is a risk, however, that developers will not plant the largest

trees possible. If the developer planted 1,500 small trees, benefits would total $1.1

million (3 × $353,560 for 500 small trees). If 1,500 large trees were planted,

benefits would total $5.1 million. Planting all small trees would cost the city $4

million in forgone services. This amount far exceeds the savings of $675,000

obtained by requiring developers to plant new street trees, and suggests that, when

turning over the responsibility for tree planting to others, the city should be very

careful to develop and enforce a street tree ordinance that requires planting large

trees where feasible.

Based on this analysis, the city of Melvinville decided to retain the policy of

promoting planting of large trees where space permits. They now require tree shade

plans that show how developers will achieve 50 percent shade over streets, sidewalks, and parking lots within 15 years of development.

The third step:

adjust for local costs

The fourth step:

calculate cost savings and benefits

forgone
49

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 5—Spreadsheet calculations of benefits and costs for the Melvinville planting project (1,500 trees) over 40 years

500 large 500 medium 500 small 1,500 tree total Percentage

Price Resource Total Resource Total Resource Total Resource Total Average/ of positive

Benefits (adjusted) units value units value units value units value tree services

Dollars Dollars Dollars Dollars Dollars Dollars Percent

Electricity (kWh) 0.17 2,920,000 496,400 1,800,000 306,000 1,560,000 265,200 6,280,000 1,067,600 711.73 23.66Natural gas (kBtu) 0.0173 5,480,000 68,600 3,680,000 46,000 3,240,000 40,600 12,400,000 155,200 103.47 3.44Net carbon dioxide (lb) 0.0033 3,160,000 10,600 2,680,000 9,000 1,640,000 5,400 7,480,000 25,000 16.67 0.55Ozone (lb) 1.25 5,190 6,400 3,140 4,000 3,200 4,000 11,530 14,400 9.60 0.32Nitrous oxide (lb) 1.25 3,960 5,000 2,390 3,000 2,390 3,000 8,740 11,000 7.33 0.24Sulfur dioxide (lb) 1.77 890 1,600 540 1,000 520 1,000 1,950 3,600 2.40 0.08Small particulate matter (lb) 2.92 7,220 21,200 3,140 9,200 7,100 20,800 17,460 51,200 34.13 1.13Volatile organic compounds (lb) 0.53 170 0 100 0 90 0 360 0 0.00 0.00Biogenic volatile organic

compounds (lb) 0.53 0 0 -60 0 0 0 -60 0 0.00 0.00

Hydrology (gal) 0.0055 13,460,000 74,000 7,380,000 40,600 8,400,000 46,200 29,240,000 160,800 107.20 3.56Aesthetics and other

benefits ($) 1,750,400 807,800 465,200 3,023,400 2,015.60 67.01

Total benefits 2,434,200 1,226,600 851,400 4,512,200 3,008.13 100.00

Total Total Total Total Average/ Percentage

Costs value value value value tree of costs

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – Dollars – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – Percent

Tree and planting 450 225,000 225,000 225,000 675,000 450.00 36.43Pruning 389,198 313,802 192,417 895,417 596.94 48.33Remove and dispose 31,717 28,557 24,082 84,356 56.24 4.55Pest and disease 137 122 103 363 0.24 0.02Infrastructure 46,071 41,060 34,491 121,622 81.08 6.56Irrigation 0.05 1,250 1,250 1,250 3,750 2.50 0.20Cleanup 7,917 7,056 5,927 20,899 13.93 1.13Liability and legal 770 686 576 2,032 1.35 0.11Admin and other 18,692 16,659 13,994 49,345 32.90 2.66

Total costs 720,752 634,191 497,840 1,852,783 1,235.19 100.00

Net benefits 1,713,448 592,409 353,560 2,659,417 1,772.94Benefit/cost ratio 3.38 1.93 1.71 2.44 

(Net benefit per tree) 3,426.90 1,184.82 707.12 1,772.94 Note: Adjusted values are for electricity, tree and planting, and irrigation.
50

GENERAL TECHNICAL REPORT PSW-GTR-228

This analysis assumed 45 percent of the planted trees died. It did not account

for the time value of money from a capital investment perspective, but this could be

done by using the municipal discount rate.

Increasing Program Cost-Effectiveness

What if the program you have designed is promising in terms of stormwater-runoff

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.

Improved tree selection can increase benefits. For example, conifers and

broadleaf evergreens intercept rainfall, which is during the winter in this region.

Also, they intercept particulate matter year round as well as reduce windspeeds and

provide shade, which lowers summer cooling and winter heating costs. Locating

trees with evergreen foliage in yards, parks, school grounds, and other open-space

areas can increase benefits.

You can further increase energy benefits 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 east and 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 net benefit / total program cost

Cutting costs is one strategy to increase cost effectiveness. A substantial percentage of total program costs occur during the first 5 years and are associated with

What if costs are

too high?

Work to increase

survival rates

Target tree plantings

with highest return

Customize planting

locations

Reduce upfront and

establishment costs
51

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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 young tree care, irrigation, and

structural pruning (fig. 22).

• Provide improved followup care to increase tree survival and reduce

replacement costs.

• Select and locate trees to avoid conflicts with infrastructure.

• Select quality nursery stock with well-formed roots and crowns, which

often results in reduced pavement damage, improved survival, and less

pruning.

Figure 22—Trained volunteers can plant and maintain young trees,

allowing the community to accomplish more at less cost and providing

satisfaction for participants.

Tree Trust
52

GENERAL TECHNICAL REPORT PSW-GTR-228

• Maintain a single dominant leader by pruning young trees to reduce future

pruning costs. Also, prune young trees to eliminate and minimize defects.

This will reduce the risk of failure, increase longevity, and reduce conflicts

with vehicles.

• Increase planting space; make cutouts larger, meander sidewalks, and use

structural soils to reduce future costs associated with infrastructure conflicts.

• Select species that are tolerant of harsh conditions and with a low potential

to damage nearby pavement.

• Mulch newly planted trees to conserve soil moisture.

• Minimize competition from turf and weeds to encourage rapid

establishment.

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.

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

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.

Although organizing and training volunteers requires labor and resources, it is

usually less costly than contracting the work. 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/saws. 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 structural and corrective pruning

(Costello 2000). Ideally, young trees should be inspected and pruned every other

year for the first 5 years after planting. Pruning thereafter, depending on species,

should occur about every 5 years to correct structural problems. For most trees, it’s

a good idea to maintain a single leader to height of no less than about 20 ft. This

will facilitate clearance pruning of street trees to prevent conflicts with vehicles.

Use less expensive

stock where

appropriate

Prune early
53

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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 has been pruned every 3 to 5

years; frequent pruning is also less stressful. Specifications should be developed

for tree pruning for each species and should emphasize structural development, not

thinning or shaping. Although pruning frequency varies by species and location, a

return frequency of about 5 to 8 years is usually sufficient for mature trees (Miller

1997).

 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, do not forget to consider services 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 and pride, reduced violence, and enhanced

human health and well-being can be substantial (fig. 23). 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.

Match tree to site

It all adds up—trees

pay us back

Figure 23—Trees pay us back in both tangible and intangible ways.

Center for Urban Forest Research
54

GENERAL TECHNICAL REPORT PSW-GTR-228
55

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Chapter 5: General Guidelines for Selecting and

Placing Trees

In this chapter, general guidelines for selecting and locating trees are presented.

Residential trees and trees in public places are considered.

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

(fig. 4). Electricity use for cooling is highest during the afternoon when temperatures are warmest and incoming sunshine is greatest. Most heat gain comes through

the west-facing window and wall. Therefore, the west side of a home is the most

important side to shade (Sand 1994).

Depending on building orientation and window placement, sun shining through

windows can heat a home quickly during the morning hours. The south and east

side are the next most important sides to shade when considering the net impact of

tree shade on energy savings (fig. 24). Deciduous trees provide summer shade and

allow more winter solar heat gain than evergreens.

Trees located too far from south walls do not provide summer shade and may

block winter sunshine depending on leaf retention. This can increase heating costs

because during winter the sun is lower in the sky and shines on the south side of

homes (fig. 25). The warmth the sun provides is an asset, so do not plant evergreen

Where should shade

trees be planted?

Figure 24—Locate trees to shade west and east windows

(from Sand 1993).

Figure 25—Select solar-friendly trees for

southern exposures and locate them close

enough to provide winter solar access and

summer shade (from Sand 1991).
56

GENERAL TECHNICAL REPORT PSW-GTR-228

trees closer than 50 feet from the south side of a home. Depending on size, they are

likely to block southern exposures and solar collectors. Use solar-friendly trees to

the south and east because their crowns are dense during summer, sparse during

winter, and they are early to drop leaves and late to leaf out. The bare branches

of these deciduous trees allow most sunlight to strike the building (some solarunfriendly deciduous trees can reduce sunlight striking the south side of buildings

by 50 percent even without leaves) (Ames 1987). Examples of solar-friendly trees

include most species and cultivars of maples, hackberry, honey locust, Kentucky

coffeetree, and Japanese pagoda tree (see “Common and Scientific Names” section). Some solar-unfriendly trees include most oaks, sycamore, most elms, basswood, river birch, and horse chestnut (McPherson et al. 1994).

To maximize summer shade and minimize winter shade, locate shade trees no

farther than 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. 26).

Figure 26—Trees south of a home before and after

pruning. Lower branches are pruned up to increase

heat gain from winter sun (from Sand 1993).
57

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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 that impinge on the

building can make it difficult to maintain exterior walls and windows. To avoid

these conflicts, keep trees at least 10 ft away from the home depending on mature

crown spread. Trees beyond 50 ft of the home do not effectively shade windows

and walls. In fire-prone areas, conifers should not be planted within about 30 ft of

a home. A few individual specimens, though, can be planted within 30 ft, assuming

they are well maintained and sufficiently pruned up.

Paved patios and driveways can become heat sinks that warm the home during

the summer. 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 location service 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. 27), usually the north and west side of homes in the

Northern California Coast 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. 28). 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

branches to self-prune. Most conifers can be spaced about 6 to 10 ft on center. If

there is room for two or more rows, then space rows 10 to 15 ft apart.

Conifers 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 are not prone to

breaking or branch shedding. Large windbreak trees for communities in the region

include afghan pine and drooping she-oak. Good windbreak species for smaller

sites include Arizona cypress and Canary Island pine.

Plant dense

evergreens
58

GENERAL TECHNICAL REPORT PSW-GTR-228

In settings where wildland fire is relatively unlikely, evergreens planted close to

the home create air spaces 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 cottonwood and silver maple because of their invasive

roots, weak or brittle wood, and large size, and ginkgos because of their sparse

shade and slow growth.

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. SelectTree, a

Web-based tree selection program is a valuable resource for comparing tree traits

(http://selectree.calpoly.edu/). 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.

Figure 27—Evergreens protect a building from dust and cold

by reducing windspeeds (from Sand 1993).

Figure 28—Midwinter shadows from a well-located

windbreak and shade trees do not block solar

radiation on the south-facing wall (from Sand 1993).

There are many

choices

Picking the right

tree
59

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Use the following practices to plant and manage trees strategically to maximize

energy conservation benefits:

• Increase community-wide tree canopy cover, and target shade to streets,

parking lots, and other paved surfaces, as well as air-conditioned buildings.

• Shade west-facing windows and walls.

• Select solar-friendly trees opposite east- and south-facing walls.

• Shade air conditioners, but don’t obstruct airflow.

• Avoid planting trees too close to utilities and buildings.

• Create multirow, evergreen windbreaks where space permits, 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 from

such trees are primarily due to sequestration. Fast-growing trees sequester more

CO2 initially than slow-growing trees, but this advantage can be lost if the fastgrowing trees die at younger ages. Large trees have the capacity to store more CO2

than smaller trees (fig. 29). Use the Center for Urban Forest Research Tree Carbon

Calculator (CTCC) to compare sequestration rates for different tree species in this

region (http://www.fs.fed.us/ccrc/topics/urban-forests/ctcc/). To maximize CO2

sequestration, select tree species that are well suited to the site where they will be

planted, relatively pest free, and long-lived. Consult resources such as Pests of

Landscape Trees and Shrubs (Dreistadt et al. 1994), and for information on abiotic

disorders, refer to Abiotic Disorders of Landscape Plants (Costello et al. 2003).

Consult online resources at www.ipm.ucdavis.edu, Sunset Western Garden Book

(Brenzel 2001), and your local University of California Cooperative Extension

Horticulture Advisors, landscape professionals, and arborists to select the 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 tree and stump removal.

Maximizing energy

savings from trees
60

GENERAL TECHNICAL REPORT PSW-GTR-228

• Use native trees, particularly oaks, whenever practical and appropriate.

• Create a diverse assemblage of habitats, with trees of different ages and

species, to promote a continuous canopy cover over time. Do not rely on a

few favored species such as sycamores. Diversity is a key to developing

sustainable landscapes. New, introduced insect and disease pests are a

constant threat to urban trees. It is also important to avoid species that are

invasive and can spread in natural habitats.

• Group species with similar environmental tolerances and irrigation needs.

• Reduce the areas devoted to unused turf. Turf requires irrigation and

maintenance often associated with relatively large amounts of greenhouse

gas emissions. Consider environmentally friendly landscapes such as lowwater-use vegetation, coarse wood chip mulch, and decomposed granite.

Figure 29—Compared with small trees, large trees can store more carbon, filter

more air pollutants, intercept more rainfall, and provide greater energy savings.

Center for Urban Forest Research
61

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

• Consider the project’s lifespan when selecting species. Although fastgrowing species, e.g., willows, poplars, tulip poplars, alders, Monterey

pines, etc., will sequester more CO2

 initially than slow-growing species,

many are short-lived and begin to decline in 30 years or less. Redwoods on

the other hand, are fast-growing, but generally long-lived. Unfortunately

they require ample irrigation to thrive unless situated along the coast.

• Avoid removing trees by considering other alternatives. Alternatives should

include, but are not limited to:

• Crown reduction to improve safety

• Changing project design

• Bridging over roots

• Ramping sidewalks

• Using flexible paving materials or thinner sections

• Using permeable paving materials and enlarging tree wells (cut-outs)

• Reducing sidewalk width

• Relocating pavement

• Use of geogrids or other ”no-dig” pavement systems

• Using a coarse gravel base material under sidewalks

• Using reinforced concrete sidewalk panels supported on piers

• Covering surface roots with soil

• Provide ample space (favorable rooting space) belowground for tree roots

to grow so that they grow reasonably well and can maximize CO2

 sequestration and tree longevity.

• When trees die or are removed, salvage as much wood as possible for use

in furniture, art pieces, and other long-lasting products to delay decomposition.

• Plant trees, shrubs, and vines (e.g., grape arbors) 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 mini-reservoirs, controlling stormwater 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.
62

GENERAL TECHNICAL REPORT PSW-GTR-228

When considering trees to maximize rainfall interception benefits, consider the

following:

• Select tree species with architectural features that maximize interception,

such as large leaf surface area and rough surfaces that store water (Metro

2002).

• Increase interception by planting large trees where possible.

• Plant evergreen tree species and those that retain their leaves throughout

much of the winter when precipitation is greatest (e.g., southern magnolia,

camphor, coast live oak).

• Select conifers because they have high interception rates, but avoid shading

south-facing windows to maximize solar heat gain in winter.

• 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

seasonal inundation, are long-lived, wide-spreading, and fast-growing

(Metro 2002).

• Along streets, sidewalks, and parking lots, plant trees in engineered soils

designed to capture runoff from adjacent paving and promote deep root

growth (fig. 30).

• Do not pave over streetside planting strips for easier weed control; this can

reduce tree health and increase runoff.

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.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Tree planting and management guidelines to improve air quality include the

following (Nowak 2000, Smith and Dochinger 1976):

• It is important to allow adequate space for root growth to ensure longterm survival. Planting projects should emphasize large cut-outs, wide

planting strips, increasing space every time pavement must be repaired

due to root-pavement conflicts, and avoiding soil compaction where trees

and landscapes are planned. Engineered soil mixes can also be used to

facilitate root development in mass-graded sites and planting areas surrounded by pavement.

• Select species that tolerate pollutants that are present in harmful concentrations. For example, in areas with high ozone 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.

Figure 30—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).
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GENERAL TECHNICAL REPORT PSW-GTR-228

• Species with long leaf stems (e.g., ash, maple) and hairy plant parts (e.g.,

oak, birch, and sumac) are especially efficient interceptors.

• Effective uptake depends on proximity to the pollutant source and the

amount of biomass. Where space permits, plant multilayered stands near

the source of pollutants.

• Consider the local meteorology and topography to promote airflow that can

“flush” pollutants out of the city along streets and greenspace corridors.

Use columnar-shaped trees instead of spreading forms to avoid trapping

pollutants under the canopy and obstructing airflow.

• In areas with unhealthy ozone concentrations, maximize use of plants that

emit low levels of biogenic volatile organic compounds to reduce ozone

formation (e.g., birches, elms, maples). Consider beneficial effects from

large trees, such as urban heat island reduction and pollutant uptake,

relative to their species-based biogenic volatile organic compound emissions.

• To reduce emissions of volatile organic compounds and other pollutants,

plant trees to shade parked cars and conserve energy.

• Sustain large, healthy trees; they produce the most benefits.

Avoiding Tree Conflicts With Infrastructure

Conflicts between trees and infrastructure create lose-lose situations. Examples

include trees growing into power lines, blocking traffic signs, and roots heaving

sidewalks. Trees lose because often they must be altered or removed to rectify the

problem. People lose directly because of the additional expense incurred to eliminate the conflict. They lose indirectly owing to benefits forgone when a large tree

is replaced with a smaller tree, or too frequently, no tree at all. Tree conflicts with

infrastructure are usually avoidable with good planning and judicious tree selection.

SelectTree, a Web-based tree selection program contains a wealth of information on

trees for the region (http://selectree.calpoly.edu/).

• Before planting, contact your local utility company, such as PG&E’s Call

Before You Dig, 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.
65

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

• Avoid planting shallow-rooting species near sidewalks, curbs, and paving.

Tree roots can heave pavement if planted too close to sidewalks and patios.

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. When space is limited, use smaller trees. Use strategies to

reduce infrastructure damage by tree roots, such as meandering sidewalks

around trees, ramping sidewalks over tree roots, root barriers, and deflectors (Costello and Jones 2003).

• Select only small trees (<25 ft tall) for location under overhead power

lines, and do not plant directly above underground water and sewer lines

(fig. 31). Avoid locating trees where they will block illumination from

streetlights or views of street signs in parking lots, commercial areas, and

along streets.

Figure 31—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).
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GENERAL TECHNICAL REPORT PSW-GTR-228

For trees to deliver benefits over the long term, they require enough soil

volume to grow and 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 size trees.

Maintenance requirements and public safety issues 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 landscape professional for horticultural

information on tree traits.

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 (41-cm) diameter at

breast height with 640 ft2 (59.5 m2) of crown projection area (under the dripline) requires 1,000 ft3

(28 m3) of soil (from Costello and Jones 2003). The ultimate tree size is defined by the projected size

of the crown and the diameter of the tree at breast height.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

General Guidelines to Maximize 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 industry standards. Avoid trees that have been improperly pruned during

nursery propagation to develop main scaffolds that are too low. Many nurseries

prune to develop main scaffold branches 5 to 7 ft above the top of the containers. It

is very difficult to prune such trees to achieve adequate clearances needed in street

plantings. Make sure that the species you select is adapted to the site’s growing

conditions and is architecturally suited to the purpose at hand.

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 2 in of the soil surface. If there are no

roots in the upper portion of the root ball, excess soil has been placed over the top

of the root ball, and the root ball that has developed is undersized or poorly

formed. Such trees should be avoided.

The roots of containerized trees should be shaved (outer 1/2 to 1 in of the root

ball trimmed away) carefully with a sharp blade or saw to ensure that roots will

grow horizontally and radially outward into the backfill and native soil. In addition, the soil on top of the root ball should also be removed down to where the first

main root originates. This will prevent deep planting and future rooting problems.

Another way to evaluate the quality of the tree before planting is to gently rock

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 tell-tale

sign of a poorly anchored tree. If the tree is balled and burlapped, be careful not to

move the trunk too vigorously, as this could loosen the roots. It is also a good idea

to remove the burlap or fold it down at least half way. Better yet, cut as much of it

away as possible without disturbing the root ball.

Dig the planting hole 1 in shallower than the depth of the root ball to prevent

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

A good tree is wellanchored

Plant the tree in the

right size hole
68

GENERAL TECHNICAL REPORT PSW-GTR-228

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. 33). Once the tree has

been backfilled, loosen the surrounding soil with a shovel or digging bar to reduce

compaction and encourage root growth.

Planting trees in urban plazas, commercial areas, and parking lots poses special

challenges owing to limited soil volume and poor soil structure. Engineered soils

and other soil volume expansion solutions can be placed under the hardscape to

increase rooting space while meeting engineering requirements. For more information on engineered soils see Reducing Infrastructure Damage by Tree Roots: A

Compendium of Strategies (Costello and Jones 2003) and Up With Roots (Urban

2008).

Use additional soil to build a berm outside the root ball that is 6 in high and 3

ft in diameter. Soak the root ball, and gently rock it to settle it in. Apply water

directly to the rootball, as water applied outside of the rootball typically will not

readily move into the rootball owing to textural differences between the soil in the

rootball and the backfill. Apply water to the backfill soil to encourage rooting

there. Handle only the ball so the trunk is not loosened. Cover the basin with a 2-

to 4-in-thick layer of mulch, but avoid placing mulch against the tree trunk. Water

Figure 33—Prepare a broad planting area, plant the tree with the root flare at ground level, and

provide a berm/water ring to retain water (drawing courtesy of ISA).
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

the new tree three times a week and increase the amount of water until the tree is

established. Water more frequently during very hot, dry, or windy weather. Generally, a tree requires about 1 in of water per week. Add 3 to 5 gal each watering for

a 15-gal tree, and more for a larger size. A rain gauge or soil moisture sensor

(tensiometer) can help determine tree watering needs.

Water trees as needed to facilitate rapid establishment and rapid growth. Once

established, water trees as needed to maintain reasonable growth and health.

• Inspect your tree several times a year, and contact a local landscape professional if problems develop.

• It is a good idea to stake a tree after planting to keep it from leaning

because of wind. However, the stake should be removed within a year after

the tree has rooted sufficiently to keep it upright. If your tree needs staking

to keep it upright, remove the stake and ties after one year or as soon as the

tree is rigid enough to stand alone. 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.

It may be necessary to stake a tree for several years until it has developed

sufficient caliper to resist vandalism. Trees that have been propagated with

lower laterals often don’t need to be staked.

• Avoid removing lower lateral branches because they support rapid growth

and help to develop taper.

• Reapply mulch and irrigate the tree as needed.

• Retain but shorten lower lateral branches during the first few years. Prune

the young tree to maintain a central main trunk and equally spaced

branches. For more information, see Costello (2000). As the tree matures,

have it pruned by a certified arborist or other experienced professional to

remove dead or damaged branches.

• Retain or develop a single, dominant leader by careful structural pruning.

Lateral branches should be kept to less than half the diameter of the trunk

by pruning. This will prevent lower laterals from becoming dominant

(competing with the leader) and ultimately interfering with traffic.

• By keeping your tree healthy, you maximize its ability to produce shade,

intercept rainfall, reduce atmospheric CO2

, and provide other benefits.

For additional information on nursery tree selection, planting, establishment,

and care, see the CalFire standards and specifications located on the Urban Forest

Ecosystem Institute Web site (http://www.ufei.org/Standards&Specs.html). Additional resources are listed in appendix 1.
70

GENERAL TECHNICAL REPORT PSW-GTR-228

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.

avoided 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.

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 be toxic. Emission rates (ug/g/hr) used for this

report follow Benjamin and Winer (1998):

camphor—0.0 (isoprene); 0.0 (monoterpene)

cherry plum—0.0 (isoprene); 0.1 (monoterpene)

velvet ash— 0.0 (isoprene); 0.0 (monoterpene)

Monterey pine—0.0 (isoprene); 0.8 (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.

Ccf—One hundred cubic feet.

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.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

climate effects—Impact on residential space heating and cooling (lb CO2/tree per

year) from trees located more than 50 ft (15 m) 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—Trees or shrubs that retain their leaves during the winter.

contract rate—The percentage of residential trees cared for by commercial

arborists; the proportion of trees contracted out for a specific service (e.g., pruning

or pest management).

control costs—The marginal cost of reducing air pollutants when using best

available control technologies.

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.

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 (1.37 m) 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 CO2

, nitrogen oxides (NO2), sulfur dioxide (SO2),

and particulate matter (PM10) output resulting from the consumption of electricity,

natural gas, or any other fuel source.

evapotranspiration (ET)—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.
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GENERAL TECHNICAL REPORT PSW-GTR-228

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.

interception—Rainfall held on tree leaves and stem surfaces.

kBtu—A unit of work or energy, measured as 1,000 British thermal units. One

kBtu is equivalent to 0.293 kWh.

kilowatt-hour (kWh)—A unit of work or energy, measured as 1 kW (1,000 watts)

of power expended for 1 hour. One kWh is equivalent to 3.412 kBtu.

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.

MBtu—A unit of work or energy, measured as 1,000,000 British thermal units.

One MBtu is equivalent to 0.293 MWh.

metric tonne (t)—A measure of weight equal to 1,000,000 grams (1000 kg) or

2,205 lbs.

municipal forester—A person who manages public street and/or park trees

(municipal forestry programs) for the benefit of the community.

MWh (megawatt-hour)—A unit of work or energy, measured as one Megawatt

(1,000,000 watts) of power expended for 1 hour. One MWh is equivalent to 3.412

MBtu.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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.

NO2

—See nitrogen oxides.

O3

—See ozone.

ozone (O3)—A strong-smelling, pale blue, reactive toxic chemical gas consisting 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

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.

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/year per tree, or rainfall intercepted in gallons/year per tree.

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.
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GENERAL TECHNICAL REPORT PSW-GTR-228

sequestration—Removal of CO2 from the atmosphere by trees through the processes of photosynthesis and respiration (lb CO2

/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 (lb CO2

/tree per

year) from trees located within 50 ft (15 m) of a building.

SO2

—See sulfur dioxide.

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—Rainfall that travels down the tree trunk and onto the ground.

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.

surface saturation storage capacity—The amount of rainfall that adheres to leaf

and stem surfaces during an event, usually measured in terms of depth (centimeters

or inches).

therm—A unit of heat equal to 100,000 Btus or 100 kBtu. Also, 1 kBtu is equal to

0.01 therm.

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 emissions—Carbon dioxide released when growing, planting, and

caring for trees.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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, rather than do without nonmarket, public goods and services provided by environmental amenities such as trees and forests.
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GENERAL TECHNICAL REPORT PSW-GTR-228

Common and Scientific Names

Common name Scientific name

Plants:

Afghan pine Pinus brutia Ten. var. eldarica (Medw.) Silba

Alder Alnus spp. Mill.

American elm Ulmus americana L.

Arizona cypress Cupressus arizonica Greene

Austrian pine Pinus nigra J.F. Arnold

Basswood Tilia L.

Birch Betula spp.

Black acacia Acacia melanoxylon R. Br.

Blackgum Nyssa spp.

Black locust Robinia pseudoacacia L.

Black oak Quercus velutina Lam.

Blue gum Eucalyptus globulus Labill.

Callery pear Pyrus calleryana Decne.

Camphor Cinnamomum camphora (L.) J. Presl

Canary Island pine Pinus canariensis C. Sm.

Cherry plum Prunus cerasifera Ehrh.

Chinese elm Ulmus parvifolia Jacq.

Chinese pistache Pistacia chinensis Bunge

Coast live oak Quercus agrifolia Née var. oxyadenia (Torr.) J.T. Howell

Coast redwood Sequoia sempervirens (Lamb. ex D. Don) Endl.

Cottonwood Populus spp.

Drooping she-oak Casuarina stricta Aiton

Elms Ulmus spp.

Evergreen pear Pyrus kawakamii Hayata

Ginkgo Ginkgo biloba L.

Green ash Fraxinus pennsylvanica Marsh.

Hackberry Celtis spp.

Honey locust Gleditsia triacanthos L.

Horse chestnut Aesculus hippocastanum L.

Japanese maple Acer palmatum Thunb.

Japanese pagoda tree Styphnolobium japonicum (L.) Schott

Kentucky coffeetree Gymnocladus dioicus (L.) K. Koch

London planetree Platanus hybrida Brot.

Maple Acer spp.

Monterey cypress Cupressus macrocarpa Hartw. ex Gord.

Monterey pine Pinus radiata D. Don

Oak Quercus spp.

Poplar Populus spp.

Red maple Acer rubrum L.

River birch Betula nigra L.

Silver maple Acer saccharinum L.

Southern magnolia Magnolia grandiflora L.

Sumac Rhus spp.

Sweetgum Liquidambar styraciflua L.

Sycamore Platanus spp.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Common name Scientific name

Tulip poplar Liriodendron tulipifera L.

Velvet ash Fraxinus velutina Torr.

Victorian box Pittosporum undulatum Vent.

White ash Fraxinus americana L.

Willows Salix spp.

Insects:

Aphid Aphidoidea

Emerald ash borer Agrilus planipennis Fairmaire

Pathogens:

Anthracnose Glomerella cingulata (Stoneman) Spauld. & H. Schrenk

Dutch elm disease Ophiostoma ulmi (Buisman) Nannf. and Ophiostoma

novo-ulmi (Brasier)

Leaf spot Sirosporium diffusum (Heald & F.A. Wolf)

Mistletoe Phoradendron flavescens (Pursh) Nutt

Pitch canker disease Fusarium moniliforme var. subglutinans

Wollenw. & Reinking

Sudden oak death Phytophthora ramorum (S. Werres, A.W.A.M.

deCock & W.A. Man in’t Veld)
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GENERAL TECHNICAL REPORT PSW-GTR-228

Acknowledgments

Dr. Larry Costello (University of California Cooperative Extension Service), Bruce

Hagan, Bailey Hudson (Urban Forestry Consulting), Doug Wildman (Friends of the

Urban Forest), and John Melvin (CalFire) provided helpful reviews of this work.

Jerry Koch, Betsy Reeves, and Tim Wesig from the city of Berkeley provided

valuable information and support for this report. Scott Maco, Jesse Hoekstra,

Tommy Mouton, and Kelaine Vargas (Forest Service, Center for Urban Forest

Research) assisted with data collection and provided technical assistance.

We are indebted to those who provided tree care expenditure information:

Gordon Mann (Redwood City), Lisa Hagopian (city of Pleasanton), Ralph Mize

(city of San Jose), Jerry Koch (city of Berkeley), Richard Huntington (Mayne Tree

Expert Co.), Peter Andreucci (Bartlett Tree Experts), Peter Sortwell (Arborwell),

and John McClenahan (S.P. McClenahan Co.).

Klaus Scott, California Air Resources Board, conducted preliminary analyses

that were critical to the development of this report.

Our thanks to Keith Cline (U.S. Department of Agriculture, Forest Service,

State and Private Forestry), who provided invaluable support for this project.

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 2.54 Centimeters (cm)

Feet (ft) .305 Meters (m)

Square feet (ft2

) .0929 Square meters (m2)

Cubic feet (ft3

) .0283 Cubic meters (m3)

Miles (mi) 1.61 Kilometers (km)

Square miles (mi2

) 2.59 Square kilometers (km2)

Gallons (gal) .00378 Cubic meters (m3)

Ounces (oz) 28.4 Grams (g)

Ounces 2.83 x 107 Micrograms (μg)

Pounds (lb) .454 Kilograms (kg)

Pounds per square foot (lb/ft2) 4.882 Kilograms per square meter

(kg/m2)

Tons (ton) .907 Metric tonnes (t)

Thousand British thermal units (kBtu) 1.05 Megajoules (MJ)

Thousand British thermal units .293 Kilowatt-hours (kWh)

Degrees Fahrenheit (° F) .556(F-32) Degrees Celsius
79

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

References

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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:

Bratkovich 2001. Utilizing municipal trees: ideas from across the country.

Head et al. 2001. Best management practices for community trees: a technical

guide to tree conservation in Athens-Clarke County, Georgia.

Miller 1997. Urban forestry: planning and managing urban greenspaces.

Morgan [N.d.] An introductory guide to community and urban forestry in

Washington, Oregon, and California.

Morgan 1993. A technical guide to urban and community forestry.

Pokorny 2003. Urban tree risk management: a community guide to program

design and implementation.

Swiecki and Bernhardt 2006. A field guide to insects and diseases of California

oaks.

For additional information on tree selection, planting, establishment, and care, see

the following references:

Alliance for Community Trees: http://actrees.org. (October 9, 2009).

Bedker et al. 1995. How to prune trees. NA-FR-01-95.

California Oak Mortality Task Force: http://www.suddenoakdeath.org.

(October 9, 2009).

Center for Urban Forest Research Tree Carbon Calculator: http://

www.fs.fed.us/ccrc/topics/urban-forests/ctcc/. (October 13, 2009).

Costello 2000. Training young trees for structure and form.

Fazio [N.d.]. Tree City USA Bulletin series. International Society of

Arboriculture (ISA) brochures. (www.isa-arbor.com and

www.treesaregood.com).

Gilman 1997. Trees for urban and suburban landscapes.

Gilman 2002. An illustrated guide to pruning.
92

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Hargrave et al. 2002. Planting trees and shrubs for long-term health.

MI-07681-S.

Harris et al. 1999. Arboriculture.

Haugen 1998. How to identify and manage Dutch elm disease.

Hightshoe 1988. Native trees, shrubs, and vines for urban and rural America.

International Society of Arboriculture: http://www.isa-arbor.com.

National Arbor Day Foundation: http://www.arborday.org. (October 9, 2009).

Sudden Oak Death Best Management Practices: http://

www.plantmanagementnetwork.org/php/shared/sod/.

TreeLink: http://www.treelink.org.

Trees for Urban and Suburban Landscapes (Gilman 1997).

Trowbridge and Bassuk 2004. Trees in the urban landscape.

Urban Forest Ecosystems Institute. http://www.ufei.org/Standards&Specs.html.

(October 9, 2009).

Watson and Himelick 1997. Principles and practice of planting trees and

shrubs.

These suggested references are only a starting point. Your local cooperative

extension agent, CalFire urban forester or landscape professional can provide

you with up-to-date and local information.
93

Northern California Coast 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

(camphor), medium (cherry plum), and large (velvet ash) broadleaf trees and a

representative conifer (Monterey pine) (see “Common and Scientific Names”

section). Data are presented as annual values for each 5-year interval after planting

(tables 6 to 17). Annual values incorporate effects of tree loss. Based on the results

of our survey, we assume that 45 percent of the trees planted die by the end of the

40-year period.

For the benefits tables (tables 6, 9, 12, and 15), 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 (kWh)

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 (CO2

) 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, and 16), 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, and south walls). Although tree and planting costs occur at

year one, 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 annual net benefits are calculated by subtracting total costs from total

benefits and are presented in tables 8, 11, 14, and 17. 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.
94

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 6—Annual benefits at 5-year intervals and 40-year average for a representative small tree (camphor tree) 40-year Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average Benefits/tree RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Cooling (kWh): Yard: west 17 3.65 34 7.27 57 12.14 94 19.99 131 27.93 165 35.19 195 41.46 221 47.10 114 24.34 Yard: south 13 2.72 26 5.50 44 9.32 74 15.73 104 22.20 132 28.13 159 33.83 183 38.96 92 19.55 Yard: east 13 2.79 26 5.59 43 9.27 71 15.04 98 20.87 123 26.20 144 30.72 163 34.79 85 18.16 Public 12 2.58 24 5.15 40 8.52 65 13.78 90 19.09 112 23.95 131 28.01 149 31.66 78 16.59 Heating (kBtu): Yard: west 28 0.48 55 0.95 86 1.48 122 2.10 158 2.73 191 3.30 219 3.78 245 4.22 138 2.38 Yard: south 27 0.47 53 0.92 80 1.38 101 1.75 123 2.12 142 2.45 146 2.51 149 2.57 103 1.77 Yard: east -7 -0.13 -14 -0.24 -29 -0.50 -70 -1.20 -111 -1.92 -149 -2.57 -174 -3.00 -196 -3.39 -94 (1.62) Public 33 0.57 64 1.11 100 1.73 142 2.46 185 3.19 224 3.87 257 4.44 287 4.96 162 2.79 Net energy (kBtu):

Yard: west 199 4.13 396 8.22 655 13.62 1,060 22.09 1,468 30.66 1,842 38.49 2,164 45.24 2,454 51.32 1,280 26.72

Yard: south 155 3.19 312 6.42 517 10.70 839 17.47 1,164 24.31 1,462 30.58 1,733 36.34 1,977 41.53 1,020 21.32Yard: east 124 2.66 248 5.35 406 8.77 636 13.83 868 18.95 1,080 23.63 1,268 27.72 1,436 31.40 758 16.54Public 154 3.15 306 6.25 500 10.25 789 16.24 1,081 22.29 1,348 27.81 1,572 32.45 1,773 36.62 940 19.38

Net carbon dioxide (lb)

Yard: west 16 0.05 32 0.11 52 0.17 84 0.28 116 0.39 146 0.49 175 0.58 202 0.67 103 0.34Yard: south 13 0.04 26 0.09 43 0.14 68 0.23 94 0.32 119 0.40 143 0.48 166 0.55 84 0.28Yard: east 9 0.03 19 0.06 30 0.10 46 0.15 63 0.21 79 0.26 96 0.32 113 0.38 57 0.19Public 13 0.04 26 0.09 43 0.14 67 0.23 92 0.31 116 0.39 139 0.46 160 0.53 82 0.27

Air pollution (lb)a:

Ozone uptake 0.02232 0.03 0.04884 0.06 0.08061 0.10 0.12420 0.16 0.17155 0.21 0.21904 0.27 0.27742 0.35 0.33580 0.42 0.16 0.20

Nitrous oxide uptake +

avoided 0.01801 0.02 0.03780 0.05 0.06200 0.08 0.09586 0.12 0.13154 0.16 0.16600 0.21 0.20345 0.25 0.23972 0.30 0.12 0.15

Sulfur dioxide uptake +

avoided 0.00377 0.01 0.00791 0.01 0.01311 0.02 0.02083 0.04 0.02892 0.05 0.03667 0.06 0.04491 0.08 0.05283 0.09 0.03 0.05

Small particulate matter

uptake + avoided 0.00648 0.02 0.04505 0.13 0.13152 0.38 0.26337 0.77 0.39912 1.17 0.53367 1.56 0.66537 1.95 0.79389 2.32 0.35 1.04

Volatile organic compounds avoided 0.00072 0.00 0.00144 0.00 0.00236 0.00 0.00375 0.00 0.00516 0.00 0.00645 0.00 0.00757 0.00 0.00858 0.00 0.00 0.00

Biogenic volatile organic

compounds released 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00 0.00

Avoided + net uptake 0.051 0.08 0.141 0.25 0.290 0.59 0.508 1.08 0.736 1.60 0.962 2.11 1.199 2.63 1.431 3.14 0.66 1.44

Hydrology (gal rainfall

interception) 61 0.34 124 0.68 202 1.11 315 1.73 437 2.40 560 3.08 741 4.07 921 5.07 420 2.31

Aesthetics and other benefits:

Yard 9.32 11.95 15.29 18.70 22.13 25.55 28.91 32.16 20.50Public 10.57 13.56 17.35 21.22 25.12 28.99 32.80 36.49 23.26

Total benefits:Yard: west 13.91 21.21 30.78 43.89 57.18 69.71 81.44 92.36 51.31Yard: south 12.97 19.40 27.83 39.22 50.77 61.72 72.43 82.44 45.85Yard: east 12.42 18.29 25.86 35.50 45.30 54.63 63.65 72.14 40.97Public 14.18 20.84 29.44 40.50 51.71 62.38 72.42 81.85 46.67

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent during the remaining 35 years, for a total mortalityof 45 percent. RU = resource unit.a Values are the same for yard and public trees.
95

Northern California Coast 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

(camphor tree)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and planting:a

Yard 29.00 3.63

Public 29.00 3.63

Pruning:

Yard 0.09 0.28 0.27 0.26 5.01 4.84 4.67 4.50 2.04

Public 2.98 5.87 5.66 5.46 17.34 16.67 15.99 15.32 9.62

Remove and dispose:

Yard 1.00 0.71 0.98 1.26 1.55 1.86 2.17 2.50 1.40

Public 1.50 0.57 0.79 1.02 1.25 1.50 1.75 2.02 1.20

Pest and disease:

Yard 1.16 1.77 2.36 2.93 3.49 4.03 4.55 5.04 2.94

Public 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01

Infrastructure repair:

Yard 0.10 0.15 0.20 0.24 0.29 0.34 0.38 0.42 0.24

Public 0.69 1.05 1.39 1.72 2.04 2.35 2.64 2.91 1.72

Irrigation: 

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cleanup: 

Yard 0.02 0.03 0.03 0.04 0.05 0.06 0.06 0.07 0.04

Public 0.12 0.18 0.24 0.30 0.35 0.40 0.45 0.50 0.30

Liability and legal:

Yard 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00

Public 0.01 0.02 0.02 0.03 0.03 0.04 0.04 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 0.28 0.42 0.56 0.70 0.83 0.95 1.07 1.18 0.70

Total costs:

Yard 31.37 2.93 3.84 4.74 10.40 11.13 11.84 12.54 10.31

Public 34.58 8.11 8.68 9.23 21.86 21.92 21.96 21.98 17.20

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent

during the remaining 35 years, for a total mortality of 45 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 (camphor tree)

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 - 17 18 27 39 47 59 70 80 41

Yard: south - 18 16 24 34 40 51 61 70 36

Yard: east - 19 15 22 31 35 44 52 60 31

Public - 20 13 21 31 30 40 50 60 29

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent

during the remaining 35 years, for a total mortality of 45 percent.

See table 6 for annual benefits and table 7 for annual costs.
96

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 9—Annual benefits (dollars per tree) at 5-year intervals and 40-year average for a representative medium tree (cherry plum) 40-year Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average Benefits/tree RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Cooling (kWh): Yard: west 26 5.52 60 12.74 97 20.75 134 28.58 168 35.86 188 39.96 206 43.95 222 47.35 138 29.34 Yard: south 21 4.57 47 9.99 75 15.88 101 21.52 126 26.85 142 30.37 159 33.79 172 36.74 105 22.47 Yard: east 22 4.70 47 9.92 72 15.39 96 20.47 118 25.21 131 27.91 143 30.54 154 32.90 98 20.88 Public 21 4.42 44 9.40 68 14.42 89 18.96 109 23.17 119 25.39 129 27.54 138 29.44 90 19.09 Heating (kBtu): Yard: west 43 0.74 85 1.46 124 2.14 157 2.71 188 3.24 206 3.55 223 3.85 237 4.10 158 2.72 Yard: south 43 0.75 86 1.48 123 2.13 153 2.65 181 3.13 198 3.43 215 3.71 229 3.95 154 2.65 Yard: east 4 0.06 -31 -0.54 -87 -1.50 -154 -2.66 -217 -3.74 -255 -4.41 -293 -5.06 -324 -5.59 -170 -2.93 Public 46 0.79 94 1.62 140 2.42 180 3.10 217 3.75 242 4.18 266 4.59 286 4.94 184 3.17 Net energy (kBtu): 

Yard: west 302 6.25 682 14.20 1,098 22.90 1,498 31.29 1,870 39.10 2,081 43.51 2,285 47.80 2,459 51.44 1,534 32.06

Yard: south 258 5.32 555 11.47 868 18.01 1,163 24.17 1,441 29.98 1,623 33.80 1,801 37.51 1,952 40.69 1,208 25.12Yard: east 224 4.76 435 9.39 635 13.89 807 17.82 966 21.47 1,054 23.51 1,140 25.49 1,220 27.31 810 17.95Public 253 5.21 535 11.02 816 16.84 1,069 22.07 1,304 26.92 1,433 29.57 1,558 32.13 1,668 34.38 1,080 22.27

Net carbon dioxide (lb): 

Yard: west 26 0.09 61 0.20 101 0.34 143 0.48 184 0.61 222 0.74 261 0.87 299 1.00 162 0.54

Yard: south 23 0.08 52 0.18 86 0.29 121 0.40 156 0.52 192 0.64 229 0.76 265 0.89 141 0.47Yard: east 19 0.06 39 0.13 60 0.20 81 0.27 104 0.35 131 0.44 159 0.53 188 0.63 98 0.33Public 23 0.08 52 0.17 84 0.28 116 0.39 149 0.50 182 0.61 216 0.72 250 0.83 134 0.45

Air pollution (lb):a

Ozone uptake 0.02760 0.03 0.06391 0.08 0.10156 0.13 0.13887 0.17 0.17784 0.22 0.21251 0.27 0.24925 0.31 0.28539 0.36 0.16 0.20

Nitrous oxide uptake +

avoided 0.02463 0.03 0.05373 0.07 0.08338 0.10 0.11143 0.14 0.13928 0.17 0.16039 0.20 0.18212 0.23 0.20271 0.25 0.12 0.15

Sulfur dioxide uptake +

avoided 0.00524 0.01 0.01175 0.02 0.01860 0.03 0.02522 0.04 0.03173 0.06 0.03648 0.06 0.04134 0.07 0.04590 0.08 0.03 0.05

Small particulate matter

uptake + avoided 0.01286 0.04 0.05169 0.15 0.10676 0.31 0.16976 0.50 0.22493 0.66 0.22746 0.66 0.22991 0.67 0.23205 0.68 0.16 0.46

Volatile organic

compounds avoided 0.00118 0.00 0.00250 0.00 0.00386 0.00 0.00511 0.00 0.00627 0.00 0.00695 0.00 0.00761 0.00 0.00819 0.00 0.01 0.00

Biogenic volatile organic

compounds released: -.00012 0.00 -.00072 0.00 -.00177 0.00 -.00312 0.00 -.00438 0.00 -.00438 0.00 -.00438 0.00 -.00438 0.00 0.00 0.00

Avoided + net uptake 0.071 0.11 0.183 0.32 0.312 0.58 0.447 0.86 0.576 1.11 0.639 1.20 0.706 1.29 0.770 1.37 0.46 0.85

Hydrology (gal rainfall

interception) 59 0.33 142 0.78 230 1.27 321 1.76 415 2.29 503 2.76 595 3.27 686 3.77 369 2.03

Aesthetics and other

benefits:

 Yard 29.84 35.61 37.86 38.14 37.55 36.54 35.30 33.94 35.60

Public 33.86 40.41 42.96 43.28 42.61 41.46 40.06 38.51 40.39

Total benefits:Yard: west 36.62 51.11 62.94 72.53 80.67 84.76 88.53 91.53 71.08Yard: south 35.67 48.36 58.00 65.33 71.45 74.94 78.13 80.66 64.07Yard: east 35.10 46.23 53.80 58.85 62.76 64.45 65.88 67.02 56.76Public 39.58 52.70 61.92 68.35 73.42 75.60 77.47 78.88 65.99

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent during the remaining 35 years, for a total mortalityof 45 percent. RU = resource unit.a Values are the same for yard and public trees.
97

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 11—Annual net benefits (dollars per tree) at 5-year intervals and 40-year average for a representative

medium tree (cherry plum)

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 5 48 59 62 69 72 80 81 60

Yard: south 4 45 54 55 60 62 69 70 53

Yard: east 4 43 49 48 51 52 57 57 45

Public 5 44 53 46 51 52 39 41 42

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent during the remaining 35 years, for a total mortality of 45 percent.

See table 9 for annual benefits and table 10 for annual costs.

Table 10—Annual costs (dollars per tree) at 5-year intervals and 40-year average for a representative medium

tree (cherry plum)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and planting:a

Yard 29.00 3.63

Public 29.00 3.63

Pruning: 

Yard 0.09 0.28 0.27 5.19 5.01 4.84 0.12 0.11 2.13

Public 2.98 5.87 5.66 18.02 17.34 16.67 30.54 29.25 15.69

Remove and dispose:

Yard 1.00 0.77 1.14 1.51 1.90 2.30 2.71 3.14 1.68

Public 1.50 0.62 0.92 1.22 1.53 1.85 2.19 2.53 1.43

Pest and disease

Yard 1.07 1.91 2.73 3.52 4.27 5.00 5.68 6.33 3.51

Public 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01

Infrastructure repair: 

Yard 0.09 0.16 0.23 0.29 0.36 0.42 0.38 0.53 0.29

Public 0.64 1.13 1.61 2.07 2.50 2.91 3.29 3.65 2.05

Irrigation: 

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cleanup: 

Yard 0.02 0.03 0.04 0.05 0.06 0.07 0.07 0.09 0.05

Public 0.11 0.19 0.28 0.36 0.43 0.50 0.57 0.63 0.35

Liability and legal: 

Yard 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00

Public 0.01 0.02 0.03 0.03 0.04 0.05 0.06 0.06 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 0.26 0.46 0.65 0.84 1.02 1.18 1.34 1.48 0.83

Total costs:

Yard 31.27 3.15 4.40 10.56 11.61 12.64 8.96 10.21 11.29

Public 34.49 8.30 9.15 22.54 22.87 23.17 37.98 37.60 24.02

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30

percent during the remaining 35 years, for a total mortality of 45 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.
98

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 12—Annual benefits (dollars per tree) at 5-year intervals and 40-year average for a representative large tree (velvet ash) 40-year Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average Benefits/tree RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Cooling (kWh): Yard: west 27 5.80 84 17.87 151 32.12 215 45.85 266 56.76 306 65.28 347 73.90 372 79.21 221 47.10 Yard: south 19 4.02 59 12.67 111 23.71 162 34.52 212 45.12 257 54.73 302 64.40 328 69.82 181 38.62 Yard: east 18 3.77 54 11.54 98 20.99 141 30.15 186 39.66 228 48.56 270 57.49 291 62.04 161 34.28 Public 16 3.41 48 10.31 88 18.80 127 27.04 167 35.70 206 43.84 244 52.05 267 56.96 146 31.01 Heating (kBtu): Yard: west 33 0.57 91 1.57 163 2.82 234 4.04 295 5.10 347 5.99 398 6.88 421 7.28 248 4.28 Yard: south 34 0.58 90 1.55 159 2.75 227 3.92 286 4.94 336 5.80 386 6.66 410 7.09 241 4.16 Yard: east -44 -0.76 -143 -2.47 -189 -3.27 -220 -3.79 -207 -3.58 -173 -2.99 -138 -2.39 -101 -1.75 -152 -2.62 Public 38 0.66 103 1.78 183 3.16 261 4.50 327 5.64 381 6.58 435 7.52 462 7.98 274 4.73 Net energy (kBtu):

Yard: west 306 6.38 929 19.44 1,670 34.94 2,385 49.89 2,958 61.86 3,409 71.27 3,865 80.77 4,138 86.48 2,458 51.38

Yard: south 222 4.60 684 14.22 1,272 26.47 1,846 38.43 2,403 50.06 2,904 60.53 3,407 71.07 3,686 76.90 2,053 42.78Yard: east 133 3.01 398 9.07 796 17.73 1,195 26.36 1,654 36.09 2,105 45.57 2,559 55.11 2,810 60.29 1,456 31.65Public 198 4.07 587 12.09 1,065 21.96 1,529 31.54 2,001 41.34 2,438 50.41 2,877 59.56 3,134 64.94 1,729 35.74

Net carbon dioxide (lb):

Yard: west 24 0.08 73 0.24 132 0.44 189 0.63 240 0.80 282 0.94 327 1.09 363 1.21 204 0.68Yard: south 19 0.06 57 0.19 106 0.35 154 0.51 203 0.68 249 0.83 296 0.99 333 1.11 177 0.59

Yard: east 9 0.03 26 0.09 56 0.19 88 0.29 128 0.43 170 0.57 214 0.71 249 0.83 118 0.39Public 18 0.06 51 0.17 93 0.31 135 0.45 179 0.60 221 0.74 264 0.88 299 1.00 158 0.53

Air pollution (lb):a

Ozone uptake 0.02160 0.03 0.06662 0.08 0.13163 0.16 0.20107 0.25 0.28160 0.35 0.36529 0.46 0.45770 0.57 0.55175 0.69 0.26 0.32

Nitrous oxide uptake +

avoided: 0.01906 0.02 0.05757 0.07 0.11063 0.14 0.16501 0.21 0.22301 0.28 0.27967 0.35 0.34001 0.43 0.39103 0.49 0.20 0.25

Sulfur dioxide uptake +

avoided: 0.00441 0.01 0.01358 0.02 0.02560 0.05 0.03778 0.07 0.05049 0.09 0.06275 0.11 0.07575 0.13 0.08647 0.15 0.04 0.08

Small particulate matter

uptake + avoided 0.00781 0.02 0.05185 0.15 0.14323 0.42 0.27524 0.80 0.40912 1.20 0.54043 1.58 0.66898 1.96 0.79121 2.31 0.36 1.06

Volatile organic

compounds avoided 0.00097 0.00 0.00291 0.00 0.00540 0.00 0.00782 0.00 0.01015 0.01 0.01224 0.01 0.01434 0.01 0.01553 0.01 0.01 0.00

Biogenic volatile organic

compounds released 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00000 0.00 0.00 0.00

Avoided + net uptake 0.054 0.08 0.193 0.33 0.416 0.77 0.687 1.33 0.974 1.92 1.260 2.50 1.557 3.10 1.836 3.65 0.87 1.71

Hydrology (gal rainfall

interception) 59 0.32 192 1.05 360 1.98 535 2.94 734 4.04 940 5.17 1,167 6.42 1,401 7.70 673 3.70

Aesthetics and other

benefits:

Yard 78.38 73.10 73.53 74.52 76.01 77.98 80.38 83.16 77.13Public 88.94 82.94 83.44 84.56 86.25 88.48 91.21 94.37 87.52

Total benefits:Yard: west 85.24 94.16 111.67 129.31 144.63 157.86 171.75 182.22 134.61Yard: south 83.45 88.89 103.10 117.74 132.71 147.01 161.94 172.54 125.92

Yard: east 81.82 83.64 94.20 105.45 118.49 131.79 145.71 155.65 114.59Public 93.47 96.59 108.47 120.83 134.15 147.31 161.16 171.66 129.20

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent during the remaining 35 years, for a total mortalityof 45 percent. RU = resource unit.a Values are the same for yard and public trees.
99

Northern California Coast 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

(velvet ash)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and planting:a

Yard 29.00 3.63

Public 29.00 3.63

Pruning: 

Yard 0.09 5.53 5.36 5.19 5.01 0.12 0.12 0.11 3.07

Public 2.98 19.36 18.69 18.02 17.34 31.82 30.54 29.25 19.46

Remove and dispose:

Yard 1.00 0.84 1.26 1.69 2.14 2.61 3.09 3.61 1.87

Public 1.50 0.68 1.02 1.36 1.72 2.10 2.49 2.91 1.59

Pest and disease:

Yard 1.11 2.09 3.03 3.93 4.81 5.65 6.48 7.28 3.94

Public 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01

Infrastructure repair: 

Yard 0.09 0.17 0.25 0.33 0.40 0.47 0.54 0.61 0.33

Public 0.66 1.24 1.79 2.31 2.81 3.29 3.75 4.20 2.30

Irrigation: 

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cleanup: 

Yard 0.02 0.03 0.04 0.06 0.07 0.08 0.09 0.10 0.06

Public 0.11 0.21 0.31 0.40 0.48 0.57 0.65 1.69 0.40

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 0.05 0.06 0.06 0.07 0.04

Admin/inspect/other: 

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 0.27 0.50 0.73 0.94 1.14 1.34 1.52 1.70 0.93

Total costs:

Yard 31.31 8.67 9.95 11.20 12.43 8.94 10.33 11.73 12.90

Public 34.53 22.02 22.56 23.07 23.56 39.18 39.03 38.86 28.35

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent

during the remaining 35 years, for a total mortality of 45 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 (velvet ash)

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 54 85 102 118 132 149 161 170 122

Yard: south 52 80 93 107 120 138 152 161 113

Yard: east 51 75 84 94 106 123 135 144 102

Public 59 75 86 98 111 108 122 133 101

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent

during the remaining 35 years, for a total mortality of 45 percent.

See table 12 for annual benefits and table 13 for annual costs.
100

GENERAL TECHNICAL REPORT PSW-GTR-228 Table 15—Annual benefits (dollars per tree) at 5-year intervals and 40-year average for a representative conifer tree (Monterey pine) 40-year Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average Benefits/tree RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value RU Value Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Dollars Cooling (kWh): Yard: west 37 7.82 72 15.42 110 23.42 143 30.58 185 39.46 234 49.86 272 57.93 303 64.49 169 36.12 Yard: south 37 7.82 72 15.42 110 23.42 143 30.58 185 39.46 234 49.86 272 57.93 303 64.49 169 36.12 Yard: east 37 7.82 72 15.42 110 23.42 143 30.58 185 39.46 234 49.86 272 57.93 303 64.49 169 36.12 Public 37 7.82 72 15.42 110 23.42 143 30.58 185 39.46 234 49.86 272 57.93 303 64.49 169 36.12 Heating (kBtu): Yard: west 187 3.23 273 4.71 371 6.41 470 8.11 557 9.61 634 10.94 694 11.99 743 12.84 491 8.48 Yard: south 187 3.23 273 4.71 371 6.41 470 8.11 557 9.61 634 10.94 694 11.99 743 12.84 491 8.48 Yard: east 187 3.23 273 4.71 371 6.41 470 8.11 557 9.61 634 10.94 694 11.99 743 12.84 491 8.48 Public 187 3.23 273 4.71 371 6.41 470 8.11 557 9.61 634 10.94 694 11.99 743 12.84 491 8.48 Net energy (kBtu):

Yard: west 554 11.06 996 20.13 1,470 29.84 1,905 38.69 2,408 49.07 2,973 60.80 3,412 69.92 3,769 77.33 2,186 44.60

Yard: south 554 11.06 996 20.13 1,470 29.84 1,905 38.69 2,408 49.07 2,973 60.80 3,412 69.92 3,769 77.33 2,186 44.60Yard: east 554 11.06 996 20.13 1,470 29.84 1,905 38.69 2,408 49.07 2,973 60.80 3,412 69.92 3,769 77.33 2,186 44.60Public 554 11.06 996 20.13 1,470 29.84 1,905 38.69 2,408 49.07 2,973 60.80 3,412 69.92 3,769 77.33 2,186 44.60

Net carbon dioxide (lb):

Yard: west 50 0.17 93 0.31 142 0.47 192 0.64 247 0.83 308 1.03 363 1.21 413 1.38 226 0.75

Yard: south 50 0.17 93 0.31 142 0.47 192 0.64 247 0.83 308 1.03 363 1.21 413 1.38 226 0.75Yard: east 50 0.17 93 0.31 142 0.47 192 0.64 247 0.83 308 1.03 363 1.21 413 1.38 226 0.75Public 50 0.17 93 0.31 142 0.47 192 0.64 247 0.83 308 1.03 363 1.21 413 1.38 226 0.75

Air pollution (lb):a

Ozone uptake 0.06445 0.08 0.12444 0.16 0.19803 0.25 0.28834 0.36 0.39041 0.49 0.50514 0.63 0.63384 0.79 0.77022 0.96 0.37 0.47

Nitrous oxide uptake +

avoided 0.06379 0.08 0.11478 0.14 0.17391 0.22 0.23863 0.30 0.31095 0.39 0.39101 0.49 0.47069 0.59 0.54943 0.69 0.29 0.36

Sulfur dioxide uptake +

avoided 0.01055 0.02 0.02052 0.04 0.03192 0.06 0.04423 0.08 0.05861 0.10 0.07504 0.13 0.09119 0.16 0.10705 0.19 0.05 0.10

Small particulate matter

uptake + avoided 0.02835 0.08 0.05860 0.17 0.11627 0.34 0.21618 0.63 0.34389 1.01 0.49586 1.45 0.66572 1.95 0.85100 2.49 0.35 1.01

Volatile organic

compounds avoided 0.00264 0.00 0.00468 0.00 0.00687 0.00 0.00889 0.00 0.01120 0.01 0.01378 0.01 0.01578 0.01 0.01741 0.01 0.01 0.01

Biogenic volatile organic

compounds released -.00733 0.00 -.05331 -0.03 -.14390 -0.08 -.27063 -0.14 -.39476 -0.21 -.51433 -0.27 -.62917 -0.33 -.73958 -0.39 -0.34 -0.18

Avoided + net uptake 0.162 0.26 0.270 0.48 0.383 0.79 0.526 1.23 0.720 1.78 0.967 2.44 1.248 3.16 1.556 3.95 0.73 1.76

Hydrology (gal rainfall

interception) 252 1.38 596 3.28 980 5.39 1,402 7.71 1,840 10.12 2,296 12.63 2,768 15.23 3,250 17.87 1,673 9.20

Aesthetics and other:

Yard 104.77 116.82 117.01 112.45 106.53 100.36 94.33 88.60 105.11Public 118.89 132.55 132.77 127.59 120.88 113.88 107.04 100.53 119.27

Total benefits:

Yard: west 117.64 141.02 153.50 160.72 168.33 177.25 183.86 189.13 161.43

Yard: south 117.64 141.02 153.50 160.72 168.33 177.25 183.86 189.13 161.43

Yard: east 117.64 141.02 153.50 160.72 168.33 177.25 183.86 189.13 161.43Public 131.75 156.76 169.26 175.87 182.68 190.77 196.56 201.06 175.59

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent during the remaining 35 years, for a total mortalityof 45 percent. RU = resource unit.a Values are the same for yard and public trees.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Table 16—Annual costs (dollars per tree) at 5-year intervals and 40-year average for a representative conifer

tree (Monterey pine)

40-year

Costs Year 5 Year 10 Year 15 Year 20 Year 25 Year 30 Year 35 Year 40 average

Dollars

Tree and planting:a

Yard 29.00 3.63

Public 29.00 3.63

Pruning: 

Yard 0.09 5.53 5.36 5.19 0.13 0.12 0.12 0.11 1.70

Public 2.98 19.36 18.69 18.02 33.11 31.82 30.54 29.25 21.57

Remove and dispose: 

Yard 1.00 1.40 2.08 2.75 3.42 4.09 4.75 5.42 2.89

Public 1.50 1.13 1.68 2.22 2.76 3.29 3.83 4.37 2.45

Pest and disease:

Yard 1.11 3.48 4.99 6.39 7.69 8.87 9.95 10.93 6.23

Public 0.00 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.01

Infrastructure repair:

Yard 0.09 0.29 0.42 0.53 0.64 0.74 0.83 0.91 0.52

Public 0.66 2.06 2.95 3.76 4.50 5.17 5.77 6.30 3.65

Irrigation: 

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Cleanup: 

Yard 0.02 0.05 0.07 0.09 0.11 0.13 0.14 0.16 0.09

Public 0.11 0.35 0.51 0.65 0.77 0.89 0.99 1.08 0.63

Liability and legal:

Yard 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.02 0.01

Public 0.01 0.03 0.05 0.06 0.08 0.09 0.10 0.11 0.06

Admin/inspect/other: 

Yard 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Public 0.27 0.44 1.20 1.53 1.83 2.10 2.34 2.55 1.48

Total costs:

Yard 31.31 10.75 12.92 14.96 11.99 13.95 15.80 17.54 15.06

Public 34.53 23.39 25.07 26.24 43.05 43.37 43.58 43.67 33.47

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent

during the remaining 35 years, for a total mortality of 45 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 17—Annual net benefits (dollars per tree) at 5-year intervals and 40-year average for a representative

conifer tree (Monterey pine)

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 86 130 141 146 156 163 168 172 146

Yard: south 86 130 141 146 156 163 168 172 146

Yard: east 86 130 141 146 156 163 168 172 146

Public 97 133 144 150 140 147 153 157 142

Note: Annual values incorporate effects of tree loss. We assume that 15 percent of trees planted die during the first 5 years, 30 percent

during the remaining 35 years, for a total mortality of 45 percent.

See table 15 for annual benefits and table 16 for annual costs.
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GENERAL TECHNICAL REPORT PSW-GTR-228
103

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Appendix 3: Procedures for Estimating Benefits

and Costs

Approach

Overview

Because benefits from trees differ owing to regional differences in tree growth,

climate, air pollutant concentrations, rainfall patterns, building characteristics, and

other factors, we divided the United States into 16 climate zones. A reference city

is designated for each climate zone, and intensive data are collected for modeling

tree benefits. Criteria for selection as a reference city include:

• Updated inventory of trees by address.

• Detailed information on tree management costs.

• Long-tenured city foresters who can help age trees because they know

when they were planted or when different neighborhoods were developed

and street trees planted.

• Good contacts within other city departments to obtain data on sidewalk

repair costs, trip/fall costs, and litter cleanup costs.

• Capability to provide the resources needed to conduct the study, including

an aerial lift truck for 5 days to sample foliar biomass. .

The city of Berkeley was selected as the reference city for the Northern

California Coast region because it best met these criteria. During 2004, data were

collected on tree growth and size for predominant street tree species in Berkeley,

and other geographic information was assembled to model tree benefits. A subset

of these data is used in this guide, and the entire data set is incorporated into the

i-Tree Streets (formerly STRATUM) database for the Northern California Coast

region (see www.itreetools.org).

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 street-side 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.
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GENERAL TECHNICAL REPORT PSW-GTR-228

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

species, we report results for small (camphor), medium (cherry plum), and large

(velvet ash) broadleaf trees and a representative conifer (Monterey pine) (see

“Common and Scientific Names” section). The selection of these species was based

on data availability, and not intended to endorse their use in large numbers. In fact,

the cherry plum has a poor form for a street tree and velvet ash is susceptible to the

emerald ash borer (Agrilus planipennis), a pest that may threaten all ash in California. Relying on too few species can increase the likelihood of catastrophic loss

owing to pests, diseases, or other threats. 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 Berkeley, California. An inventory

of Berkeley’s’ street trees was provided by the city of Berkeley. The inventory

included 36,485 trees representing 279 species.

Tree-growth models developed from Berkeley data were used as the basis for

modeling tree growth for this report. Using Berkeley’s tree inventory, a stratified

random sample of 21 tree species was measured to establish relations among tree

age, size, leaf area, and biomass. The species were as follows:

• Black acacia (Acacia melanoxylon R. Br.)

• Japanese maple (Acer palmatum Thunb.)

• Camphor tree (Cinnamomum camphora (L.) J. Presl.)

• Blue gum eucalyptus (Eucalyptus globulus Labill.)

• Velvet ash (Fraxinus velutina Torr.)

• Ginkgo (Ginkgo biloba L.)

• Sweetgum (Liquidambar styraciflua L.)

• Tulip poplar (Liriodendron tulipifera L.)

• Southern magnolia (Magnolia grandiflora L.)

• Chinese pistache (Pistacia chinensis Bunge)
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

• Monterey pine (Pinus radiata D. Don)

• Victorian box (Pittosporum undulatum Vent.)

• London planetree (Platanus hybrida Brot.)

• Cherry plum (Prunus cerasifera Ehrh.)

• Callery pear (Pyrus calleryana Decne.)

• Evergreen pear (Pyrus kawakamii Hayata)

• Coast live oak (Quercus agrifolia Née var. oxyadenia (Torr.) J.T. Howell)

• Black locust (Robinia pseudoacacia L.)

• Coast redwood (Sequoia sempervirens (Lamb. ex D. Don) Endl.)

• American elm (Ulmus americana L.)

• Chinese elm (Ulmus parvifolia Jacq.)

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 to 5.9 in

• 6 to 11.9 in

• 12 to 17.9 in

• 18 to 23.9 in

• 24 to 29.9 in

• 30 to 35.9 in

• 36 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 by sonar measuring device), tree crown and bole height (to

nearest 0.5 m by clinometer), crown diameter in two directions (parallel and

perpendicular to nearest street to nearest 0.5 m by sonar measuring device), tree

condition and location. Replacement trees were sampled when trees from the

original sample population could not be located. In total, 701 trees were measured.

Field work was conducted in summer 2004.

Crown volume and leaf area were estimated from computer processing of treecrown images obtained by using 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).
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GENERAL TECHNICAL REPORT PSW-GTR-228

Linear regression was used to fit predictive models with d.b.h. as a function of

age for each of the 21 sampled species. Predictions of LSA, crown diameter, and

height metrics were modeled as a function of d.b.h. using best-fit models. After

inspecting the growth curves for each species, we selected the typical small, medium, large, and conifer 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

45 percent of the hypothetical planted trees died over the 40-year period. Annual

mortality rates were 3 percent for the first 5 years, and 0.57 percent per year after

that. This 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.

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 Berkeley, Pleasanton, Redwood City, and San Jose. In

addition, commercial arborists from Arborwell, Bartlett Tree Experts, Mayne Tree

Expert Co., and S.P. McClenahan Co. provided information about tree-management

costs on residential properties.
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

Pricing benefits—

Electricity and natural-gas prices for utilities serving the Northern California Coast

region service area were used to quantify energy savings for the region. Costs of

preventing or repairing damage from pollution, flooding, or other environmental

risks were used to estimate what society is willing to pay for clean air and water

(Wang and Santini 1995). 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.

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 Northern California Coast region.

The house was a one-story, wood-frame, building with a basement and total

conditioned floor area of 2,180 ft2, window area (double-glazed) of 262 ft2,

and wall and ceiling insulation of R11 and R25, 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 San Francisco International Airport (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 $0.213/kWh and $1.73/therm, respectively.

Electricity and natural-gas prices were for 2006 for Pacific Gas and Electric (PG&E

2006a, 2006b, respectively). Homes were assumed to have central air conditioning

and natural-gas heating.
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GENERAL TECHNICAL REPORT PSW-GTR-228

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 deciduous trees and a conifer at three tree-to-building

distances, following methods outlined by McPherson and Simpson (1999). The

small tree (camphor) had a visual density of 82 percent during summer and winter.

The medium tree (cherry plum) had a density of 80 percent during summer and 40

percent during winter. The large tree (velvet ash) had a visual density of 79 percent

during summer and 29 percent during winter, and the conifer (Monterey pine) had a

density of 85 percent year round. Crown densities for calculating 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 the region’s climate

based on consultation with the senior forestry supervisor (Koch 2004). Large trees

were leafless November 1 through April 1, medium trees November 1 through

March 15, and small trees and conifers were evergreen. 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, 68 percent at 20 to 40 ft, and 4

percent at 40 to 60 ft (McPherson and Simpson 1999). Results are reported for

trees shading east-, south-, and west-facing surfaces. The conifer is included as a

windbreak tree located greater than 50 ft from the residence so it does not shade

the building. 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. 1999).

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 cover for Berkeley was 23 percent, and

building cover was estimated to be 25 percent based on Simpson and McPherson

(2007). Canopy cover was calculated to increase by 1.9, 2.5, 3.9, and 4.7 percent
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

for 20-year-old small, medium, and large broadleaf trees and the conifer, 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 air temperature and wind

reductions on energy use. Climate effects accrued for both public and yard trees.

Calculating windbreak effects—

Trees near buildings result in additional windspeed reductions beyond those from

the aggregate effects of trees throughout the neighborhood. This leads to a small

additional reduction in annual heating energy use of about 1 percent per tree for

conifers in the Northern California Coast region (McPherson and Simpson 1999).

Yard and public conifer trees were assumed to be windbreaks, and therefore located

where they did not increase heating loads by obstructing winter sun. Windbreak

effects were not attributed to deciduous trees because their crowns are leafless

during winter and do not block winds near ground level.

Atmospheric Carbon Dioxide Reduction

Calculating reduction in CO2 emissions from powerplants—

Conserving energy in buildings can reduce carbon dioxide (CO2

) emissions from

powerplants. These emission reductions were calculated as the product of energy

savings for heating and cooling based on CO2 emission factors (table 18) and were

based on data for the Northern California Coast region where the average fuel mix

is 43 percent natural gas, 26 percent hydro/renewable, 23 percent nuclear, 5 percent

biomass/other and 3 percent coal (US EPA 2003). The value of $0.003 per lb CO2

reduction (table 18) was based on the average value in 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 by using tree height and d.b.h.

data with biomass equations (Pillsbury et al. 1998). Volume estimates were converted to green and dry-weight estimates (Markwardt 1930) and divided by 78

percent to incorporate root biomass. Dry-weight 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 biomass each year.

Calculating CO2

 released by power equipment—

Tree-related emissions of CO2

, based on gasoline and diesel fuel consumption during tree care in our survey cities, were calculated by using the value
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GENERAL TECHNICAL REPORT PSW-GTR-228

0.78 lb CO2/in d.b.h. This amount may overestimate CO2 release for 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 of <10 micron diameter (PM10)

were considered. Changes in average annual emissions and their monetary values

were calculated in the same way as for CO2

, by using utility-specific emissions

factors for electricity and heating fuels (Ottinger et al. 1990, US EPA 1998). The

price of emissions savings were derived from models that calculate the marginal

damage cost of different pollutants to meet air quality standards (Wang and Santini

1995). Emissions concentrations were obtained from US EPA (2003), and population estimates from the U.S. Census Bureau (2003).

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

Table 18—Emissions factors and implied values for carbon dioxide and criteria air pollutants

Emission factor Electricitya Natural gasb Implied valuec

Pounds per Pounds per million

megawatt hour British thermal units Dollars per pound

Carbon dioxide 651.000 11.80000 0.00334

Nitrous oxide 0.445 0.01020 1.25

Sulfur dioxide 0.134 0.00006 1.77

Small particulate matter 0.169 0.00075 2.92

Volatile organic compounds 0.044 0.00054 0.53

a US EPA 2003, except Ottinger et al. 1990 for volatile organic compounds.

b US EPA 1998.

c Carbon dioxide from Pearce 2003. Value for others based on methods of Wang and Santini (1995) using emissions concentrations

from US EPA (2003) and population estimates from the U.S. Census Bureau (2003).
111

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

(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 2001 were selected as representative for modeling deposition based on a review of mean PM10 and O3

 concentrations for the years 1996–2004. The O3

, NO2, and SO2 data were from Oakland and

PM10 from San Pablo (California Air Resources Board 2004). Hourly air temperature and windspeed data were obtained for Berkeley (CIMIS 2004). To set a value

for pollutant uptake by trees, we used the procedure described above for emissions

reductions (table 18). The monetary value for NO2

 was used for O3.

Estimating BVOC emissions from trees—

Annual emissions for biogenic volatile organic compounds (BVOCs) were estimated

for the three 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

(micrograms of carbon per gram of dry foliar biomass per hour), 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 Berkeley

during the summer of 2004. 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 2001 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 owing to pollutant uptake and avoided powerplant

emissions. The O3

 reduction benefit from lowering summertime air temperatures,

thereby reducing hydrocarbon emissions from anthropogenic and biogenic sources,

were estimated as a function of canopy cover following McPherson and Simpson

(1999). They used peak summer air temperature reductions of 0.2 °F for each

percentage of increase in canopy cover. Hourly changes in air temperature were

calculated by reducing this peak air temperature at every hour based on hourly
112

GENERAL TECHNICAL REPORT PSW-GTR-228

maximum and minimum temperatures for that day, as well as maximum and

minimum values of total global solar radiation for the year. However, this analysis

does not incorporate the effects of lower summer air temperatures on O3

 formation

rates owing to atmospheric processes.

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 drips from leaf surfaces, flows down

the stem surface to the ground, or evaporates. 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 leaf

surface area 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 0.04 in for all trees. Hourly meteorological and rainfall data for

2005 from the CIMIS (California Irrigation Management Information System)

Oakland Foothills Station (Station: ID #149; latitude 37°46' N, longitude 122°10'

W) were used for this simulation. Annual precipitation during 2005 was 22.2 in.

Storm events less than 0.1 in were assumed to not 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—

Berkeley’s Stormwater/Drainage Construction Program was not funded at the time

this research was conducted. The benefit of runoff reduction was estimated by using

costs associated with collection, conveyance, and treatment—single-family residential sewer service fees ($3.02/Ccf/dwelling unit). In Berkeley, the sewer service fee

is a conservative proxy for a desired level of service. At $0.004/gal, this fee is

below the average price for stormwater runoff reduction ($0.01/gal) assessed in

similar studies (Maco et al. 2005).
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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 net benefit 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 in the East and South to the Midwest region, and the need to extrapolate results from front-yard trees on residential

properties to trees in other locations (e.g., backyards, streets, parks, and nonresidential land).

A large tree adds value to a home—

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 Northern California

Coast region would gain from selling a home with a large tree.

The sales price of residential properties differed widely by location within the

region. By averaging the values for several cities, we calculated the average home

price for Northern California Coast communities as $631,267 in 2004. Therefore,

the value of a large tree that added 0.88 percent to the sales price of such a home

was $5,567. To estimate annual benefits, the total added value was divided by the

LSA of a 40-year-old velvet ash ($5,567/3,348 ft2

) to yield the base value of LSA,

$1.66/ft2

. This value was multiplied by the amount of LSA added to the tree during

1 year of growth.

Calculating the aesthetic value of a residential yard tree—

To calculate the base value for a large tree on private residential property, we

assumed that a 40-year-old ash in the front yard increased the property sales price

by $5,567. Approximately 75 percent of all yard trees, however, are in backyards

(Richards et al. 1984). Lacking specific research findings, it was assumed that
114

GENERAL TECHNICAL REPORT PSW-GTR-228

backyard trees had 75 percent of the impact on “curb appeal” and sales price compared to front-yard trees. The average annual aesthetic benefit for a tree on private

property was estimated as $1.11/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 base value of a public tree—

The base value of a public tree was calculated in the same way as front-yard trees.

However, because street and park trees may be adjacent to land with little value or

resale potential, an adjusted value was calculated. A citywide street tree reduction

factor (82 percent) was applied to prorate trees’ value based on the assumption that

public trees adjacent to different land uses make different contributions to property

sales prices. For this analysis, the land use factor reflects the proportion of street

trees in Berkeley by land use and the reduction factor is the value of a tree in an

area of that use relative to single-home residential. Land use and reduction factors,

shown respectively, were single-home residential (59 percent, 100 percent), multihome residential (8 percent, 75 percent), small commercial (12 percent, 66 percent), industrial/institutional/large commercial (6 percent, 50 percent), and park/

vacant/other (2 percent, 50 percent) (Gonzales 2004, McPherson 2001).

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).

After reviewing the literature and recognizing an absence of data, we made the

conservative estimate that park trees have half (50 percent) as much impact on

property prices as street trees.

Given these assumptions, typical large street and park trees were estimated to

increase property values by $1.36 and $0.83/ft2

 LSA, respectively. Assuming that

80 percent of all municipal trees were on streets and 20 percent in parks, a

weighted average benefit of $1.26/ft2

 LSA was calculated for each tree.

Calculating Costs

Tree management costs were estimated based on surveys of municipal foresters and

commercial arborists in the region.

Planting

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

mulching the tree. Based on our survey of municipal and commercial arborists,

planting costs depend on tree size. Costs ranged from $36 for a volunteer-planted
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Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

tree to $960 for a 36-in box tree. In this analysis, we assumed that a 15 gal tree was

planted at a cost of $145.

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 during the first 5

years after planting, at a cost of $17.50 per tree. After this training period, pruning

occurred once every 7 years for public trees. Pruning costs were $50, $165, and

$315 for small (<20 ft tall), medium (20 to 40 ft tall), and large trees (>40 ft tall).

More expensive equipment and more time was required to prune large trees than

small trees. After factoring in pruning frequency, annualized costs were $3.50,

$7.14, $23.57, and $45.00 per tree for public young, small, medium, and large

trees, respectively.

Pruning costs for yard trees—

Based on findings from our survey of commercial arborists in the region, pruning

cycles for yard trees were more frequent than reported for public trees: 3, 4, 5, and

6 years for young, small, medium, and large trees, respectively. However, survey

findings indicate that only 20 percent of all private trees are professionally pruned,

and the number of professionally pruned trees grows as the trees grow (Summit and

McPherson 1998). Accordingly, 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. Using these contract rates, along with average pruning

prices ($25, $100, $250, and $450 for young, small, medium, and large trees,

respectively), the average annual costs for pruning a yard tree were $0.10, $0.30,

$6.00, and $15.30 for young, small, medium, and large trees, respectively.

Tree and Stump Removal

The costs for tree removal and disposal were $14/in d.b.h. for public trees, and

$30/in d.b.h. for yard trees. Stump removal costs were $15/in d.b.h. for public and

$6/in d.b.h. for yard trees. Therefore, total costs for removal and disposal of trees

and stumps were $29/in d.b.h. for public trees, and $36/in d.b.h. for yard trees.

Pest and Disease Control

Expenditures for pest and disease control in the Northern California Coast region

are negligible for public trees but substantial for yard trees. They averaged about
116

GENERAL TECHNICAL REPORT PSW-GTR-228

$5 per tree per year or approximately $0.55/in d.b.h. for private trees. Results of

our survey indicated that yard trees were most frequently treated for anthracnose,

aphids, sudden oak death, and leaf spot.

Irrigation Costs

Rain falls fairly regularly during winter throughout most of the region and additional irrigation is not usually needed after establishment when trees are planted

into landscapes with installed irrigation. Frequently, trees are watered for the first

summer after planting. We included initial irrigation costs with planting costs in

this report.

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, litigation/liability, and

inspection/administration. Cost data were obtained from the municipal arborist

survey and assume that 80 percent of public trees are street trees and 20 percent are

park trees. Costs for park trees tend to be lower than for street trees because there

are fewer conflicts with infrastructure such as power lines and sidewalks.

Infrastructure conflict costs—

Many Northern California Coast municipalities have a substantial number of large,

old trees and deteriorating sidewalks. 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 Northern California Coast communities were greater than most other regions, exceeding $20 per tree on an annual

basis in some cities. Roots from most trees in residential yards do not damage sidewalks and sewers. Therefore, we did not include this cost for yard trees.

Liability costs—

Urban trees can incur costly payments and legal fees owing to trip-and-fall claims.

A survey of Western U.S. cities showed that an average of 8.8 percent of total treerelated expenditures was spent on tree-related liability (McPherson 2000). Communities in our survey report spending on average $0.07 per tree for tree-related

liabilities annually.

Litter and storm cleanup costs—

The average annual per-tree cost for litter cleanup (i.e., street sweeping, stormdamage cleanup) was $0.72/tree ($0.06/in d.b.h.). This value was based on average
117

Northern California Coast Community Tree Guide: Benefits, Costs, and Strategic Planting

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.

Green-waste disposal costs—

Green-waste disposal and recycling costs were minimal for our survey of Northern

California Coast communities, where most green waste is recycled as mulch,

compost, firewood, or other products. Fees from the sale of these products largely

offset the costs of processing, hauling, and tipping. Disposal costs for yard trees

were also negligible.

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 $1.36 per tree ($0.15/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 UV

radiation) and greater psychological well-being through visual and direct contact

with plants. However, on the cost side, increased health care may be incurred

because of nearby trees owing to allergies and respiratory ailments related to

pollen. We assumed that these intangible benefits and costs were 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.
118

GENERAL TECHNICAL REPORT PSW-GTR-228

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 (B) 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, minus

release owing to 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)

equal the costs for residential yard trees (CY ) and public trees (CP ):

CY = P + T + R + D + I + S + Cl + L

CP

 = P + T + R + D + I + S + Cl + L + G

where

P = cost of tree and planting

T = average annual tree pruning cost

R = annualized tree and stump removal and disposal cost

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 of tree-related claims

G = annual program administration, inspection, and other costs

Net benefits are calculated as the difference between total benefits and costs:

Net benefits = B - C
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