United States

Department of 

Agriculture

Forest Service

Northern 

Research Station

Resource Bulletin 

NRS-79

Assessing Urban Forest 

Effects and Values: 

Toronto’s Urban Forest

David J. Nowak

Robert E. Hoehn III

Allison R. Bodine

Eric J. Greenfield

Alexis Ellis

Theodore A. Endreny

Yang Yang

Tian Zhou

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

Published by: For additional copies:

U.S. FOREST SERVICE U.S. Forest Service

11 CAMPUS BLVD SUITE 200 Publications Distribution

NEWTOWN SQUARE PA 19073 359 Main Road

Delaware, OH 43015-8640

Fax: (740)368-0152

May 2013 Email: nrspubs@fs.fed.us

Abstract

An analysis of trees in Toronto, Ontario, Canada, reveals that this city has about 

10.2 million trees with a tree and shrub canopy that covers approximately 26.6 

percent of the city. The most common tree species are eastern white-cedar, sugar 

maple, and Norway maple. The urban forest currently stores an estimated 1.1 million 

metric tons of carbon valued at CAD$25.0 million. In addition, these trees remove 

about 46,700 metric tons of carbon per year (CAD$1.1 million per year) and about 

1,905 metric tons of air pollution per year (CAD$16.9 million per year). Trees in 

Toronto are estimated to reduce annual residential energy costs by CAD$9.7 million 

per year. The compensatory value is estimated at CAD$7.1 billion. Information on 

the structure and functions of the urban forest can be used to improve and augment 

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

plans to improve environmental quality in the Toronto area.

Cover Photo

Aerial shot of High Park and southwest end of Toronto. Photo by Urban Forestry, 

City of Toronto, used with permission.

Manuscript received for publication 8 February 2012

Acknowledgments

This report on Toronto’s tree canopy is based on collaboration between many 

individuals who contributed their time, data and expertise. Particular thanks go to: 

Rike Burkhardt, planner with the city of Toronto, whose assistance has been 

invaluable in this project.

Toronto and Region Conservation Authority for their regional i-Tree Eco/UFORE 

project coordination and collaboration.

Environment Canada for their data contributions.

City of Toronto Technical Services and Geospatial Competency Centre staff

for their technical support.

The Toronto forestry field crews who brought quality data in, on time.

Mike Boarman and Chris Sorrentino for assistance with spatial data analysis.

And last but not least, thanks to Toronto City Council for providing the support to 

make this research possible.
Assessing Urban Forest Effects and Values:

Toronto’s Urban Forest

David J. Nowak

Robert E. Hoehn III

Allison Bodine

Eric J. Greenfield

Alexis Ellis

Theodore A. Endreny

Yang Yang

Tian Zhou

Ruthanne Henry

The Authors

DAVID J. NOWAK is a research forester and project leader with the U.S. Forest 

Service’s Northern Research Station at Syracuse, New York.

ROBERT E. HOEHN III is a forester with the U.S. Forest Service’s Northern 

Research Station at Syracuse, New York.

ALLISON R. BODINE is a research urban forester with the Davey Institute at 

Syracuse, New York.

ERIC J. GREENFIELD is a forester with the U.S. Forest Service’s Northern 

Research Station at Syracuse, New York.

ALEXIS ELLIS is a research urban forester with the Davey Institute at 

Syracuse, NY.

THEODORE A. ENDRENY is a professor with the SUNY College of 

Environmental Science and Forestry at Syracuse, NY.

YANG YANG is a research assistant with the SUNY College of Environmental 

Science and Forestry at Syracuse, NY.

TIAN ZHOU is a research assistant with the SUNY College of Environmental 

Science and Forestry at Syracuse, NY.

RUTHANNE HENRY is a planner with the city of Toronto.
Aerial shot of High Park and the southwest end of Toronto. 

Photo by Urban Forestry, City of Toronto, used with permission.
CONTENTS

 Executive Summary 1

i-Tree Eco Model and Field Measurements 2

Tree Characteristics of the Urban Forest 4

Urban Forest Cover and Leaf Area 7

Air Pollution Removal by Urban Trees 22

Carbon Storage and Sequestration 24

Trees Affect Energy Use in Buildings 25

Structural and Functional Values 26

 Species Recommendations 27

Potential Insect and Disease Impacts 31

 Don Watershed Analysis 34

 Conclusion 38

 Appendices 40

 References 55

1

Urban forests provide 

numerous benefits to society, 

yet relatively little is known 

about this important resource 

in Toronto.

In 2008, the i-Tree 

Eco model was 

used to survey and 

analyze Tononto's 

urban forest.

The calculated environmental 

benefits of the urban forest 

are significant, yet many 

environmental and social 

benefits still remain to be 

quantified.

EXECUTIVE SUMMARY

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

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

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

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

developed the Urban Forest Eff ects (UFORE) model, which is now known and 

distributed as i-Tree Eco (www.itreetools.org). Results from this model are used to 

advance the understanding of the urban forest resource, improve urban forest policies, 

planning and management, provide data for the potential inclusion of trees within 

environmental regulations, and determine how trees aff ect the environment and 

consequently enhance human health and environmental quality in urban areas.

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

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

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

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

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

economic worth of the various forest functions.

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

in Toronto, a vegetation assessment was conducted during the summer of 2008. For 

this assessment, 0.04 hectare (one-tenth acre) fi eld plots were sampled and analyzed using 

the i-Tree Eco model. Th is report summarizes results and values of (Table 1):

• Forest structure

• Potential risk to forest from insects or diseases

• Air pollution removal

• Carbon storage

• Annual carbon removal (sequestration)

• Changes in building energy use

Th is study provides an update with more detailed information to the previous report 

“Every Tree Counts: A Portrait of Toronto’s Urban Forest”.1

Table 1.—Summary of urban forest features, Toronto, 2008

Feature Measure

Number of trees 10,220,000

Tree and shrub cover 26.6 %

Most common species eastern white-cedar, sugar maple, Norway maple

Trees <15.24 cm diameter 68.6%

Pollution removal 1,905 t/yr (CAD$16.9 million/yr)

Carbon storage 1.1 million t (CAD$25.0 million)

Carbon sequestration 46,700 t/yr (CAD$1.1 million/yr)

Building energy reduction CAD$9.7 million/yr

Avoided carbon emissions CAD$382,200/yr

Compensatory value CAD$7.1 billion

t = metric ton
2

I-TREE ECO MODEL AND FIELD MEASUREMENTS

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

attributes can be assessed. To help assess the city’s urban forest, data from 407 random 

fi eld plots located throughout the city were analyzed using the i-Tree Eco (formerly 

known as UFORE) model.2

i-Tree Eco uses standardized fi eld data from randomly located plots and local hourly 

air pollution and meteorological data to quantify urban forest structure and its 

numerous eff ects, including:

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

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

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

percent air quality improvement throughout a year. Pollution removal is 

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

particulate matter (<10 microns).

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

• Eff ects of trees on building energy use and consequent eff ects on carbon 

dioxide emissions from power plants.

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

and carbon storage and sequestration.

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

borer, gypsy moth, or Dutch elm disease.

In the fi eld, 0.04 hectare (one-tenth acre) plots were distributed on a randomized gridbased pattern at a density of approximately 1 plot for every 157 hectares (387 acres). 

In Toronto, land uses were used to divide the analysis into smaller zones based on city 

land-use map classifi cations.

Th e plots were divided among the following land uses:

• Parks (37 plots)—areas with parks and Toronto and Region Conservation 

Authority (TRCA) lands.

• Open space (19 plots)—areas with open space, including commercial, 

recreation, and agricultural.

• Commercial (30 plots)—areas with commercial land uses, including retail 

stores, shopping centers, etc.

• Industrial (44 plots)—areas with industrial land uses, including 

manufacturing and industrial parks.

• Institutional (25 plots)—areas with institutional land uses, including schools, 

hospitals, colleges, government buildings, etc.

• Utility and transportation (Utility & Trans; 14 plots)—areas with utility and 

transportation land uses, including power-generating facilities, sewage treatment 

facilities, limited access highways, railroad stations, shipyards, airports, etc.

Benefits ascribed to 

urban trees include:

• Air pollution removal

• Air temperature 

reduction

• Reduced building 

energy use

• Absorption of 

ultraviolet radiation

• Improved water 

quality

• Reduced noise

• Improved human 

comfort

• Increased property 

value

• Improved 

physiological & 

psychological wellbeing

• Aesthetics

• Community 

cohesion
3

• Multi-family residential (MF residential; 23 plots)—areas with multi-family 

dwellings.

• Single family residential (SF residential; 181 plots)—areas with single family 

dwellings.

• Other (31 plots)—areas that are vacant or do not fall into one of the other 

land-use categories.

• Unknown (3 plots)—areas of no data on the land-use map.

Field data were collected for the Forest Service by city personnel; data collection 

occurred during the leaf-on season to properly assess tree canopies. Within each plot, 

data included land use, ground and tree cover, shrub characteristics, and individual tree 

attributes of species, stem diameter at breast height (d.b.h.; measured at 1.37 m [4.5 

ft]), tree height, height to base of live crown, crown width, percentage crown canopy 

missing and dieback, and distance and direction to residential buildings.3

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

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

tend to have less biomass than predicted by forest-derived biomass equations.4

 To 

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

0.8.4

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

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

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

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

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

for ozone, and sulfur and nitrogen dioxides based on a hybrid of big-leaf and multilayer canopy deposition models.5,6 As the removal of carbon monoxide and particulate 

matter by vegetation is not directly related to transpiration, removal rates (deposition 

velocities) for these pollutants were based on average measured values from the 

literature7, 8 that were adjusted depending on leaf phenology and leaf area. Particulate 

removal incorporated a 50 percent resuspension rate of particles back to the atmosphere.9

Seasonal eff ects of trees on residential building energy use was calculated based on 

procedures described in the literature10 using distance and direction of trees from 

residential structures, tree height and tree condition data. As no Canadian city data 

are available on building energy eff ects from trees, data representing the buildings and 

climate zone of New York State were used.

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

Landscape Appraisers,11 which uses tree species, diameter, condition, and location 

information.2

To learn more about i-Tree Eco methods2 visit: http://nrs.fs.fed.us/tools/ufore/ or 

www.itreetools.org

Field Survey Data

Plot Information

• Land use

• Percent tree cover

• Percent shrub 

cover

• Percent plantable

• Percent ground 

cover types

• Shrub species/

dimensions

Tree parameters

• Species

• Stem diameter

• Total height

• Height to crown base

• Crown width

• Percent foliage 

missing

• Percent dieback

• Crown light 

exposure

• Distance and 

direction to 

buildings from trees
4

TREE CHARACTERISTICS OF THE URBAN FOREST

Th e urban forest of Toronto has an estimated 10.2 million treesa (standard error [SE] 

= 952,000) with a tree and shrub cover of approximately 26.6 percent (SE = 0.4). Th is 

cover estimate is based on random point sampling of 10,000 points from leaf-on aerial 

imagery from 2009. Th e three most common species (by number of trees) in the urban 

forest are eastern white-cedarb

 (15.6 percent), sugar maple (10.2 percent), and Norway 

maple (6.5 percent) (Fig. 1). Th e 10 most common species account for 57.7 percent 

of all trees (Fig. 1). One hundred and fi fteen tree species were sampled in Toronto 

(Appendix I). Trees that have diameters less than 15.24 centimeters account for 68.6 

percent of the population (Figs. 2-3).

a Includes cedar hedges >2.5 cm d.b.h. measured as trees as per the i-Tree Eco fi eld data 

collection protocol.

b Canadian common name of Th uja occidentalis.

Eastern whitecedar 

15.6% 

Sugar maple 

10.2% 

Norway maple 

6.5% 

White ash 

5.3% 

Manitoba maple 

5.0% Green ash 

3.6% 

White spruce 

3.3% 

Eastern 

hophornbeam 

Siberian elm 3.2% 

2.7% 

European crab 

apple 

2.3% 

other species 

42.3% 

Figure 1.—Urban tree species composition, Toronto, 2008.

0

5

10

15

20

25

30

35

40

45

50

Tree Population (percent) 

Diameter Class (d.b.h. in cm) 

Figure 2.—Percent of tree population by diameter class, Toronto, 2008.

There are an 

estimated 10.2 million 

trees in Toronto 

with tree and shrub 

canopy that covers 

26.6% of the region.
5

Th e highest density of trees occurs in the parks land-use category (501.5 trees/ha), 

followed by single family residential (180.9 trees/ha), and other land uses (152.2 trees/

ha) (Fig. 4). Th e overall tree density in Toronto is 160.4 trees/ha, which is comparable 

to other city tree densities measured using this methodology (Appendix II) that range 

from 22.5 to 275.8 trees/hectare.

Figure 3.—Percent of species population by diameter class for 10 

most common tree species, Toronto, 2008.

0

100

200

300

400

500

600

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Desntiy (trees per ha) 

Number of Trees (millions) 

Land Use 

Total number of trees

Number of trees per hectare

Figure 4.—Number of urban trees and tree density by land-use category, 

Toronto, 2008.

0

10

20

30

40

50

60

70

80

Species 

Species Population (percent) 

Diameter Class 

(d.b.h. in cm) -
6

Figure 5.—Percent of total population by area of native origin, Toronto, 2008.

0

10

20

30

40

50

60

70

80

Tree Population (percent) 

Native Origin 

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

Figure 6.—Impact of invasive species in natural areas, Toronto. A) Norway maple dominated slope: 

little ground vegetation, slope vulnerable to erosion, and little structural or biological diversity. 

B) Same slope 5 years after removal of Norway maples and replanting with native species. 

Photos by Ruthanne Henry, Toronto Parks, Forestry and Recreation.

A B

Urban forests are 

a mix of native tree 

species that existed 

prior to development 

and exotic species 

that were introduced 

by residents or other 

means.

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

exotic species that were introduced by residents or other means. Th us, urban forests 

often have a tree diversity that is higher than surrounding native landscapes. Increased 

tree diversity can minimize the overall impact or destruction by a species-specifi c insect 

or disease, but the increase in the number of exotic plants can also pose a risk to native 

plants if some of the exotics are invasive plants that can potentially out-compete and 

displace native species. In Toronto, about 64 percent of the trees are species native to 

Ontario. Trees with an origin outside of North America are mostly from Eurasia (15.7 

percent of the species) (Fig. 5).

Invasive species such as the Norway maple have had a strong impact on the native 

species biodiversity of Toronto’s natural areas (Fig. 6). To maintain the natural 

functions of habitat diversity and slope stability, certain areas within Toronto are 

being managed by invasive species removal and the replanting of native species. 
7

URBAN FOREST COVER AND LEAF AREA

Trees and shrubs cover about 26.6 percent of Toronto, an estimate based on photointerpretation of 10,000 random points for 2009 leaf-on aerial imagery.

Toronto was subdivided into neighborhoods (Fig. 7; Appendix III). In some 

neighborhoods, less than 30 points were sampled, so additional points were added 

and photo-interpreted in those neighborhoods to ensure a minimum of 30 points. 

Th ese same points also were interpreted in 2005 (leaf-off imagery) and 1999 (leaf-off 

imagery) to determine temporal changes in tree cover.

Results from 2009 Imagery

Tree cover was highest in the Rosedale-Moore Park (#98 in Fig. 8; 61.8 percent), 

Bridle Path-Sunnybrooke-York Mills (#41; 55.6 percent) and Mount Pleasant East 

(#99; 54.8 percent) neighborhoods (Figs. 7-8; Appendix III). It is notable that the fi ve 

neighborhoods with more than 50 percent canopy all overlap with a ravine or park 

(Fig. 9). Th e ravine areas have an estimated 60 percent tree cover, an estimate derived 

from geographic information system (GIS) analyses by city employees.

Figure 7.—Tree cover (percent) in Toronto neighborhoods, 2009.

Tree
8 

Figure 8.-Toronto neighborhoods, 2008. See Appendix Ill for numbering key. 

0 5,000 10,000 20,000 Meters 

Ravine and natural feature protection by-law 

D Toronto limits 

Figure 9.-Tree cover in ravines, Toronto. Ravines make up 11,097 hectares of land, or 17.5 percent 

of city land. Ravines under canopy make up 6,503 hectares, or 59 percent of the ravine area. 
9

Toronto’s dominant ground-cover includes herbaceous (e.g., grass, gardens; 37.9 

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

buildings; 26.7 percent), and buildings (20.6 percent; Fig. 10). 

Benefi ts from trees are linked to the amount of healthy leaf surface area of the plant. In 

Toronto, trees that dominate in terms of leaf area are Norway maple, sugar maple, and 

Manitoba maple (Fig. 11).

Figure 10.—Percent of area covered by various ground-cover classes, by land-use class 

and city total, Toronto, 2008.

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

Open Space

Commercial

Industrial

MF residential

Unknown

Parks

SF residential

Utility & Trans

Institutional

Other

CITY TOTAL

Percent of Area 

Land-Use Category 

water bare soil

herbaceous duff/mulch cover

impervious surfaces (excluding buildings) buildings

Ground Cover Categories 

Figure 11.—Percent of total tree population and total leaf area for the 10 most common 

tree species, Toronto, 2008.

0

2

4

6

8

10

12

14

16

Percent 

Total leaf area

Tree population

-
10

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

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

are American elm (8.4 percent of its population greater than 76.2 cm d.b.h.), Norway 

maple (1.2 percent > 76.2 cm), and white oak (3.7 percent > 76.2 cm). A species must 

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

or small trees in the population. Silver maple comprises only about 0.9 percent of the 

population, but 15.6 percent of its population has a diameter greater than 76.2 cm.

Species with smaller individuals contributing to leaf area (species with percent of 

leaf area much less than their percent of total population) are Port-Orford-cedar 

(100 percent of population less than 7.6 cm d.b.h.), eastern white-cedar (70.3 percent 

< 7.6 cm), and European buckthorn (65.8 percent < 7.6 cm).

A species’ contribution to the urban forest can be described with an importance 

value (IV), which is calculated from a formula using the species’ relative leaf area and 

abundance (Fig. 11). Th e most important species in Toronto’s urban forest, according 

to calculated IVs, are sugar maple, Norway maple, and eastern white-cedar (Table 2).

Tree Cover Map

In addition to the photo-interpreted data (1999, 2005, and 2009), a high-resolution 

(0.6 m) map of tree and impervious cover was developed for Toronto using 2007 

imagery (Fig. 12).12 Th is map delimited eight land-cover classes (e.g., tree, impervious 

surfaces, etc.) and identifi ed potential locations to plant trees to be used by the City 

of Toronto for urban forest management. Th e data from this map cannot be directly 

compared to the photo-interpreted data to estimate change in cover due to the diff erences 

in methodology, but the results are similar. Tree cover from photo-interpreted data is 

estimated at 25.5 percent (SE = 0.4 percent) in 2005 and 26.6 percent (SE = 0.4 percent) 

in 2009. Th e tree cover estimate from the 2007 high-resolution map is 28.0 percent, 

but the error from the map estimation is unknown, though likely small.

Table 2.—Percent of population, percent of leaf area, and importance 

values of species with the greatest importance values, Toronto, 2008

Common Name %Popa %LAb IVc

Sugar maple 10.2 11.6 21.8

Norway maple 6.5 14.9 21.4

Eastern white-cedar 15.6 2.8 18.4

Manitoba maple 5.0 5.5 10.5

Green ash 3.6 5.0 8.6

White ash 5.3 2.7 8.0

White spruce 3.3 4.6 7.9

Eastern hophornbeam 3.2 2.4 5.6

Silver maple 0.9 4.5 5.4

American elm 1.5 3.7 5.2

a

 %Pop = percent of population

b

 %LA = percent of leaf area

c

 IV = %Pop + %LA

The most important 

species in Toronto's 

urban forest are sugar 

maple, Norway maple, 

and eastern whitecedar.
11

Tree Cover Change

To estimate tree and other surface cover changes in Toronto, photo-interpreted data 

from 1999 (leaf-off ), 2005 (leaf-off ) and 2009 (leaf-on) aerial photos were compared. 

Th is analysis of tree-cover change compared changes on a point-by-point basis using 

information from all images. Each point in each year was classifi ed into one of 

the following eight land-cover classes: tree/shrub, grass or herbaceous, agricultural 

(herbaceous or soil depending upon time of year), soil, water, buildings, roads, or 

other impervious materials.

Tree cover in Toronto increased 1.2 percent over the 10-year period (Table 3), from 

25.3 percent in 1999 to 26.6 percent in 2009. Th is change represents 2.7 percent 

(SE=0.16) in “new tree cover” off set by a 1.5 percent loss of previously existing tree 

cover. Th is 10-year net change is statistically signifi cant from zero (McNemars test; 

< 0.0001) and equates to an average annual increase of about 0.12 percent per year.

Figure 12.—Land cover based on 2007 imagery, Toronto.

Aerial view of a Toronto ravine.

Photo by Urban Forestry, City of Toronto, 

used with permission.

-
12

Impervious cover also increased from 45.6 percent in 1999 to 47.9 percent in 2009, a 

statistically signifi cant increase (McNemars test;  < 0.0001) (average annual increase 

of about 0.23 percent per year).

Past trends do not predict future conditions as environmental and management 

activities (e.g., development and tree planting trends) may change over time. Future 

monitoring is needed to track how current and future city activities will aff ect 

Toronto’s tree cover changes.

Surface Cover by Land Use (1999-2009)

Tree/shrub cover in 2009 was greatest on parks (56.9 percent of land), open space 

(31.8 percent) and single family residential land (31.4 percent; Table 4). Tree cover 

increased in all land uses between 1999 and 2009, except for multi-family residential 

where it decreased from 23.4 to 23.1 percent (Tables 4-5). Five land-use classes 

exhibited statistically signifi cant increases in tree cover ( <0.05): utility/transportation 

(3.3 percent), parks (3.1 percent), institutional (1.5 percent), industrial (1.1 percent) 

and single family residential (1.0 percent).

Impervious cover in 2009 was greatest on commercial (80.9 percent), industrial 

(76.4 percent) and multi-family residential (61.3 percent) land-use classes (Table 4). 

Impervious cover increased in all classes between 1999 and 2009 (Tables 4-5). Six landuse classes had statistically signifi cant increases in impervious cover ( <0.05): other (7.6 

percent), commercial (3.7 percent), industrial (3.4 percent), unknown (3.1 percent), 

multi-family residential (2.9 percent) and single family residential (2.0 percent).

Nearly half (49.9 percent) of Toronto’s tree cover is found on single family residential 

land, followed by parks (19.0 percent) and open space (7.3 percent) (Table 6). Single 

family residential land is the most common land use in Toronto (42.2 percent of area) 

Table 3.—Tree cover and impervious cover by land use, Toronto

Tree Cover (%) Impervious Cover (%)

Land Use 1999 2009 Sig.a 1999 2009 Sig.a

Commercial 8.5 8.9 77.2 80.9 **

Industrial 5.2 6.3 * 73.0 76.4 **

Institutional 19.0 20.5 * 49.7 50.1

MF residential 23.4 23.1 58.4 61.3 **

Parks 53.8 56.9 ** 9.9 10.1

Open Space 31.1 31.8 16.2 16.9

Other 20.0 21.4 24.1 31.7 **

SF residential 30.4 31.4 ** 47.7 49.7 **

Utility & Transportation 11.6 14.9 ** 38.2 39.4

Unknown 12.0 14.1 26.6 29.7 *

Toronto 25.3 26.6 ** 45.6 47.9 **

a Sig. = statistically significant difference in cover between 1999 and 2009 

where * =  < 0.05 and ** = < 0.01

Tree cover increased 

in all land uses 

between 1999 

and 2009, except 

for multi-family 

residential.
13

Table 4.—Land cover by land use (1999, 2005, and 2009), Toronto

1999 2005 2009

Land Use na Cover type % cover SEb % cover SEb % cover SEb

Commercial 684 Grass 12.9 1.3 10.4 1.2 10.2 1.2

Tree/Shrub 8.5 1.1 8.6 1.1 8.9 1.1

Building 26.9 1.7 27.6 1.7 28.4 1.7

Road 13.6 1.3 14.3 1.3 14.3 1.3

Impervious other 36.7 1.8 37.9 1.9 38.2 1.9

Water 0.0 0.0 0.0 0.0 0.0 0.0

Soil 1.5 0.5 1.2 0.4 0.0 0.0

Agriculture 0.0 0.0 0.0 0.0 0.0 0.0

Industrial 1,089 Grass 18.2 1.2 16.5 1.1 14.2 1.1

Tree/Shrub 5.2 0.7 5.0 0.7 6.3 0.7

Building 32.2 1.4 33.1 1.4 33.1 1.4

Road 6.7 0.8 6.8 0.8 6.8 0.8

Impervious other 34.1 1.4 35.6 1.5 36.5 1.5

Water 0.0 0.0 0.0 0.0 0.0 0.0

Soil 3.1 0.5 2.9 0.5 3.0 0.5

Agriculture 0.5 0.2 0.1 0.1 0.0 0.0

Institutional 664 Grass 29.7 1.8 27.9 1.7 26.7 1.7

Tree/Shrub 19.0 1.5 20.2 1.6 20.5 1.6

Building 17.5 1.5 17.5 1.5 17.9 1.5

Road 8.0 1.1 8.0 1.1 8.0 1.1

Impervious other 24.2 1.7 24.7 1.7 24.2 1.7

Water 0.0 0.0 0.0 0.0 0.0 0.0

Soil 1.7 0.5 1.8 0.5 2.7 0.6

Agriculture 0.0 0.0 0.0 0.0 0.0 0.0

MF residential 589 Grass 16.6 1.5 15.8 1.5 14.8 1.5

Tree/Shrub 23.4 1.7 22.4 1.7 23.1 1.7

Building 23.8 1.8 25.5 1.8 26.3 1.8

Road 13.4 1.4 13.6 1.4 13.2 1.4

Impervious other 21.2 1.7 21.4 1.7 21.7 1.7

Water 0.0 0.0 0.0 0.0 0.0 0.0

Soil 1.5 0.5 1.4 0.5 0.8 0.4

Agriculture 0.0 0.0 0.0 0.0 0.0 0.0

Parks 611 Grass 29.6 1.5 29.1 1.5 27.6 1.5

Tree/Shrub 53.8 1.7 54.7 1.7 56.9 1.7

Building 0.9 0.3 1.0 0.3 1.0 0.3

Road 4.7 0.7 4.8 0.7 5.0 0.7

Impervious other 4.3 0.7 4.1 0.7 4.1 0.7

Water 3.8 0.6 3.8 0.6 3.8 0.6

Soil 2.3 0.5 1.9 0.5 1.4 0.4

Agriculture 0.6 0.3 0.6 0.3 0.2 0.2

continued
14

Open Space 660 Grass 33.9 1.9 34.4 1.9 34.4 1.9

Tree/Shrub 31.1 1.9 31.3 1.9 31.8 1.9

Building 3.0 0.7 3.1 0.7 3.1 0.7

Road 5.2 0.9 5.2 0.9 5.2 0.9

Impervious other 8.0 1.1 8.0 1.1 8.5 1.1

Water 1.8 0.5 1.6 0.5 1.5 0.5

Soil 2.1 0.6 2.3 0.6 2.6 0.6

Agriculture 14.8 1.4 14.1 1.4 12.9 1.4

Other 192 Grass 34.5 1.9 32.0 1.8 28.5 1.8

Tree/Shrub 20.0 1.6 20.2 1.6 21.4 1.6

Building 2.3 0.6 2.3 0.6 5.8 0.9

Road 10.0 1.2 9.8 1.2 10.6 1.2

Impervious other 11.8 1.3 13.0 1.3 15.3 1.4

Water 8.3 1.1 8.3 1.1 8.2 1.1

Soil 5.8 0.9 9.1 1.1 5.9 0.9

Agriculture 7.3 1.0 5.3 0.9 4.4 0.8

SF residential 4,215 Grass 20.8 0.6 19.7 0.6 18.6 0.6

Tree/Shrub 30.4 0.7 30.4 0.7 31.4 0.7

Building 24.6 0.7 25.7 0.7 25.8 0.7

Road 10.0 0.5 10.2 0.5 10.2 0.5

Impervious other 13.1 0.5 13.5 0.5 13.6 0.5

Water 0.1 0.0 0.1 0.1 0.1 0.1

Soil 0.6 0.1 0.3 0.1 0.1 0.1

Agriculture 0.4 0.1 0.0 0.0 0.0 0.0

Utility & 409 Grass 43.8 2.5 40.6 2.4 38.9 2.4

Transportation Tree/Shrub 11.6 1.6 13.4 1.7 14.9 1.8

Building 1.5 0.6 1.5 0.6 1.5 0.6

Road 7.1 1.3 7.1 1.3 7.1 1.3

Impervious other 29.6 2.3 29.8 2.3 30.6 2.3

Water 0.5 0.3 0.5 0.3 0.5 0.3

Soil 0.7 0.4 1.7 0.6 1.2 0.5

Agriculture 5.2 1.1 5.4 1.1 5.4 1.1

Unknown 887 Grass 31.8 3.4 30.2 3.3 26.0 3.2

Tree/Shrub 12.0 2.3 12.5 2.4 14.1 2.5

Building 5.2 1.6 6.3 1.7 7.3 1.9

Road 9.9 2.2 10.9 2.3 11.5 2.3

Impervious other 11.5 2.3 10.4 2.2 10.9 2.3

Water 27.6 3.2 27.6 3.2 27.6 3.2

Soil 1.6 0.9 2.1 1.0 2.6 1.1

Agriculture 0.5 0.5 0.0 0.0 0.0 0.0

Toronto 10,000 Grass 24.0 0.4 22.6 0.4 21.3 0.4

Tree/Shrub 25.3 0.4 25.5 0.4 26.6 0.4

continued

Table 4.—continued

1999 2005 2009

Land Use na Cover type % cover SEb % cover SEb % cover SEb
15

Building 18.8 0.4 19.6 0.4 20.1 0.4

Road 9.1 0.3 9.3 0.3 9.3 0.3

Impervious other 17.7 0.4 18.2 0.4 18.5 0.4

Water 1.6 0.1 1.6 0.1 1.6 0.1

Soil 1.7 0.1 1.7 0.1 1.4 0.1

Agriculture 1.9 0.1 1.5 0.1 1.3 0.1

a n = sample size 

b SE = standard error

Table 5.—Matrix of change in land cover, Toronto, 1999 to 2009

1999 Land 

Cover Classes

2009 Land Cover Classes 1999

Grass/

herb

Tree/

shrub

Imp. 

Bldg.

Imp. 

Road

Imp. 

Other Water

Soil/Bare 

Ground Agri. Total SE

Grass/herb 19.4% 2.0% 0.7% 0.1% 1.4% 0.0% 0.4% 0.0% 24.0% 0.4%

Tree/shrub 0.7% 23.8% 0.2% 0.1% 0.4% 0.0% 0.1% 0.0% 25.3% 0.4%

Imp. Bldg. 0.1% 0.1% 18.5% 0.0% 0.2% 0.0% 0.1% 0.0% 18.8% 0.4%

Imp. Road 0.0% 0.1% 0.0% 8.9% 0.0% 0.0% 0.0% 0.0% 9.1% 0.3%

Imp. Other 0.4% 0.4% 0.4% 0.1% 16.2% 0.0% 0.2% 0.0% 17.7% 0.4%

Water 0.0% 0.0% 0.0% 0.0% 0.0% 1.6% 0.0% 0.0% 1.6% 0.1%

Soil/Bare Ground 0.3% 0.1% 0.2% 0.1% 0.4% 0.0% 0.5% 0.0% 1.7% 0.1%

Agriculture 0.3% 0.0% 0.1% 0.0% 0.1% 0.0% 0.1% 1.3% 1.9% 0.1%

2009 Total 21.3% 26.6% 20.1% 9.3% 18.5% 1.6% 1.4% 1.3%

2009 SE 0.4% 0.4% 0.4% 0.3% 0.4% 0.1% 0.1% 0.1%

Net Change 

(1999-2009) -2.7% 1.3% 1.3% 0.2% 0.8% 0.0% -0.3% -0.6%

Table 6.—Distribution of tree cover and available growing space by land use, Toronto, 2009

Tree Cover AGSa Tree Cover AGSa

Land Use % of City (% of Total Cover) (% of Total AGS) (% of City) (% of City)

Single family Residential 42.2 49.9 34.9 13.3 7.9

Parks 8.9 19.0 11.3 5.0 2.6

Open Space 6.1 7.3 10.0 1.9 2.3

Other 6.6 5.3 10.0 1.4 2.3

Institutional 6.6 5.1 8.6 1.4 2.0

Multi-family Residential 5.9 5.1 4.1 1.4 0.9

Industrial 10.9 2.6 8.3 0.7 1.9

Commercial 6.8 2.3 3.1 0.6 0.7

Utilities & Transportation 4.1 2.3 7.2 0.6 1.6

Unknown 1.9 1.0 2.4 0.3 0.6

Total 100.0 100.0 100.0 26.6 22.7

a AGS = potentially available growing space (non-agricultural soil or herbaceous cover) for tree planting 

Table 4.—continued

1999 2005 2009

Land Use na Cover type % cover SEb % cover SEb % cover SEb
16

but accounts for an even greater proportion of the city’s tree cover (49.9 percent). Two 

other land uses also contribute proportionally more tree cover than land area: parks 

and open space.

Land uses with greatest potentially available space to plant trees (defi ned as nonagricultural grass and soil space) are single family residential (34.9 percent of total 

available growing space in city), parks (11.3 percent), open space (10.0 percent), and 

other (10.0 percent). Th e available growing space (AGS) in single family residential 

land is about 7.9 percent of the total city area.

Increasing tree cover in pervious areas with existing available growing space is often 

cheaper than increasing tree cover over impervious surfaces. While tree canopy gains 

can be easily achieved on city property or rights-of way, this analysis of potentially 

available growing space does not take into account the potential limitations to tree 

planting in some grass and soil areas (e.g., sports fi elds, other land-use activities). 

Furthermore, achieving optimal tree growth along city streets and roads is challenging 

due to often diffi cult growing conditions and increased management costs. By 

recognizing potential available growing space and understanding the challenges to 

planting trees, Toronto offi cials can prioritize sites for expanding Toronto’s tree cover.

Contrasting Tree Cover Estimates

City offi cials in Toronto are interested in understanding tree canopy changes to help 

attain their goal of increasing tree cover to 30-40 percent.1

 A previously published 

report, “Every Tree Counts: A Portrait of Toronto’s Urban Forest”1

 used leaf-off aerial 

imagery to track canopy change from 1999 to 2005; the method showed a slight loss 

of tree cover (0.7 percent) in that period. Our study updates this earlier analysis with 

new tree-cover change estimates for the period of 1999-2009 (using imagery from 

1999, 2005, and 2009; see Tree Cover Change section) and shows a gain in tree cover 

of 1.3 percent between 1999 and 2009.

Th e diff erence between the two sets of estimates is likely due to two factors: 1) diff erent 

sets of random samples, and 2) diff erent tree conditions captured in the imagery.

Th e original sets of data (ortho-rectifi ed; 1999 and 2005) used leaf-off imagery, 

making it more diffi cult to detect some deciduous trees, thus underestimating the 

presence of some trees (Fig. 13). Th e current study used leaf-on imagery (2009) that 

provided information that helped interpretation in all three years (1999, 2005, 2009), 

as all three images were interpreted side-by-side.

Diff erences among estimates lead to the question: which method is best for 

determining tree cover or tree cover change. Both methods (photo-interpretation and 

high-resolution cover maps) can produce estimates with known accuracies, but both 

estimates have an inherent degree of uncertainty. Photo-interpretation uncertainty 

derives from the random sample itself, but is calculated in the standard error of the 

estimate. Photo-interpretation also relies on an accurate interpretation (by a human 

being) of the cover classes. In the case of the leaf-off imagery, some deciduous 
17

trees were likely misidentifi ed due to the diffi culty in assessing tree cover with leafoff imagery (e.g., some small deciduous trees could not be seen). Th us, leaf-off 

interpretation likely underestimates tree cover.

Estimates of tree and other land-cover types in the cover map also have errors due to 

cover being incorrectly classifi ed. Visual corrections were done to the map to reduce 

errors. However, misclassifi cation errors are inherent with most map products, but 

are considered to be low in the Toronto map due to the visual corrections. However, 

the accuracy of the Toronto map is unknown. Since 2007, when the Toronto canopy 

study was initiated, many cities within the greater Toronto area have done comparable 

studies. A review of the diff erences in results has provided useful information for 

Toronto’s Urban Forestry staff . Other cities in the Toronto area have used satellite 

imagery for estimating tree cover.

Both photo-interpretation and high-resolution cover maps can be used, and both have 

advantages and limitations. Limitations to both approaches relate to the accuracy of 

the estimate. In comparing detailed cover maps, changes between cover classes could 

be due to actual change or map misclassifi cation. Th e higher the accuracy of the cover 

maps, the less likely that misclassifi cation will lead to a false change. Misclassifi cation 

errors can be human-caused during the photo-interpretation process, but can be 

limited by using trained photo-interpreters and high-quality leaf-on imagery.

Th e advantages of the photo-interpretation method to detect tree cover change are: 

1) relatively quick and low cost; 2) images are compared side-by-side and the human 

interpreter can visually inspect and record change and detect issues of temporal change 

(e.g., agricultural fi elds that have soil or herbaceous cover depending upon time of 

year) or image parallax (apparent displacement of tall objects on images) that may 

lead to false change estimates using automated procedures; and 3) statistical estimates 

Figure 13.—Comparison of leaf off and leaf on imagery, Toronto. A) 1999 imagery with sample point; B) 2009 imagery 

with sample point.

A B
18

of sampling error can be produced. Th e advantage of the high-resolution cover map 

approach is that a detailed map of cover or change can be produced. Th ese cover 

maps can provide detailed spatial information that photo-interpretation cannot, 

but at a higher cost. If these cover maps are integrated into an urban forestry or city 

management program, then the maps are likely well worth the investment. However, 

if only general estimates of tree cover, or estimates of cover change are needed, then 

photo-interpretation of leaf-on imagery is likely the best and most cost-eff ective 

approach.

Th e comparison of the various cover estimation methods has been a useful process that 

has helped Toronto offi cials select an appropriate canopy cover methodology for future 

comparisons.

Sustaining Tree Cover

Tree cover will continue to change through time based on numerous factors, 

including annual tree mortality, growth of existing trees, and new tree establishment. 

To estimate a number of new trees needed annually to maintain current tree cover, 

Toronto’s tree population data were input into the i-Tree Forecast Prototype model.

i-Tree Forecast estimates annual tree canopy cover amounts and growth based on 

tree population data for an area of interest. For Toronto, the i-Tree Forecast model 

estimated the number of new trees to be established to maintain tree cover of 26.6 

percent or increase tree cover to 40 percent over 50 years. Several possible scenarios 

were entered into the i-Tree model: 1) average mortality rate of 3, 4, 5, or 6 percent, 

and 2) average mortality rate of 3, 4, 5, or 6 percent with an assumption that the 

entire ash population would die off in 10 years.

Tree cover expansion is predicted by the following tree characteristics: species (growth 

rate, longevity, height at maturity), diameter, crown light exposure, and dieback. 

Tree growth/annual diameter growth is based on the following: number of frost free 

days, crown light exposure, dieback, growth rate classifi cation, and median height 

at maturity. Individual tree mortality is predicted by dieback, diameter, and average 

height at maturity. Tree size classes based on average species height at maturity are 

used in calculations to determine species-specifi c mortality rates. Trees falling into a 

smaller size class have higher mortality rates at smaller diameters compared to trees in 

the larger size classes. See Appendix IV for more detailed information.

Th e estimated number of new trees needed annually to maintain tree cover, for each 

scenario, is given in Table 7.

Based on an average mortality of 4 percent, 380,000 trees need to be established 

annually to maintain the existing tree cover of 26.6 percent over 50 years. To increase 

the tree cover to 40 percent over 50 years, 780,000 trees need to be established. In the 

event that all ash trees die within 10 years, the number of new trees needed annually to 

maintain or increase tree cover becomes 470,000 and 900,000, respectively.

Based on an average 

mortality of 4 percent, 

380,000 new trees 

need to be established 

annually to maintain 

the existing tree cover 

of 26.6 percent over 

50 years.
19

Th e diff erent scenarios illustrate the natural variation in annual mortality and the 

infl uence of reduced mortality on annual planting rates. City eff orts to reduce tree 

mortality through tree maintenance and management has a positive eff ect on reducing 

the number of new trees needed to maintain or reach a desired tree cover.

In addition, natural regeneration and actions to promote it will reduce annual tree 

planting needs. About 46 percent of Toronto’s existing tree population was planted, 

with planting most common on residential lands and least common on parks and 

utility/transportation lands (Tables 8-9). Th is diff erence refl ects the role of human 

intervention in tree cover variations among land use type. Human activities in 

urban areas (development, mowing) often preclude the establishment of tree cover. 

Decreasing activities such as mowing and maintaining pervious surfaces can facilitate 

more natural regeneration.

An annual establishment rate of 380,000 trees per year to maintain existing tree 

cover equates to about six trees per hectare per year. Long-term monitoring data 

from Baltimore, MD, and Syracuse, NY,13 indicate that natural tree regeneration 

rates are around 4 to 8 trees/ha/yr. Th us, much of Toronto’s needs for sustaining 

tree cover could be accomplished via natural 

regeneration, but natural regeneration might 

not provide the desired species composition or 

mix to meet the desires of the city residents. 

Much of the regeneration in Syracuse is from 

the exotic invasive European buckthorn.14

Table 7.—Estimated number of new trees needed annually to sustain or reach 

desired tree cover level, Toronto

Maintain existing tree cover of 26.6%

No Additional Mortality Ash Kill in 10 Years

Mortality (%) Trees Planted Trees Planted

3 200,000 270,000

4 380,000 470,000

5 620,000 720,000

6 870,000 980,000

Increase tree cover to 40% 

No Additional Mortality Ash Kill in 10 Years

Mortality (%) Trees Planted Trees Planted

3 500,000 570,000

4 780,000 900,000

5 1,100,000 1,300,000

6 1,500,000 1,750,000

Community planting of large new 

naturalization within Toronto parkland system.

Photo by Urban Forestry, City of Toronto, used with 

permission.
20

Table 8.—Estimated percent of tree population 

planted, by land-use category, Toronto, 2008

Land Use Percent Planted na

MF Residential 94.4 54

SF Residential 73.5 1,322

Industrial 44.9 49

Institutional 36.5 74

Commercial 31.0 71

Other 15.2 191

Open Space 14.6 103

Parks 11.3 750

Utility & Transportation 3.6 55

Toronto 45.9 2,669 a n = sample size

Table 9.—Estimated percent of species population planted 

in Toronto (minimum sample size of 15 trees), 2008

Species Percent Planted na

Port-Orford-cedar 100.0 41

Norway spruce 100.0 32

Blue spruce 100.0 16

Red pine 96.3 27

Honeylocust 95.0 40

Common pear 94.7 19

Austrian pine 94.4 36

Eastern white-cedar 94.4 429

Sweet cherry 94.1 17

White spruce 89.0 91

Eastern redcedar 83.3 18

Silver maple 72.0 25

Norway maple 53.1 177

Siberian elm 50.7 75

European crab apple 45.0 60

Paper birch 44.7 38

Littleleaf linden 42.9 21

Green ash 41.1 95

White oak 34.6 26

Common chokecherry 32.7 52

Eastern white pine 22.9 35

American elm 22.5 40

Black cherry 21.3 61

Northern red oak 20.0 15

American basswood 16.7 36

Scotch pine 12.5 16

Boxelder 6.0 134

Sugar maple 5.7 263

Tree of heaven 5.6 18

American beech 5.6 18

European buckthorn 4.8 42

White ash 0.7 142

Eastern hophornbeam 0.0 82

Quaking aspen 0.0 60

Cockspur hawthorn 0.0 25

a n = sample size
21

Th e use of diff erent average annual mortality scenarios also refl ects the variation in 

planting program results. Many diff erent types of planting programs are currently 

underway on Toronto’s city-owned lands, primarily in parks and road rights-ofway. Th ese planting programs vary in funding, maintenance, and the conditions 

of the environments where they take place. Th erefore, annual mortality will likely 

vary among the diff erent planting programs. For example, the land parallel to the 

roads within Toronto’s downtown core produce a relatively inhospitable growing 

environment with constrained space for soil, limited nutrient inputs, salt loading, 

drought conditions, and soil compaction. To improve planting success, designs 

and planting methods are being modifi ed in these areas to use soil cell supports or 

continuous soil trenches to increase soil volume and quality.

Monitoring of Toronto’s urban 

forest will provide better data 

related to mortality, planting, 

and establishment rates to help 

guide urban foresters as they work 

toward a canopy goal of 30-40 

percent within 50 years. 

Based on a GIS analysis carried 

out by Toronto offi cials, the land 

ownership is 55 percent private 

and 45 percent public. Th e City 

of Toronto has been increasing 

planting programs since 2004 

and over the last 5 years the 

average number of trees planted 

is approximately 100,000 per 

year.1,15 At this rate, however, 

suitable planting areas on public 

land will likely be fully allocated 

with new planting in the next few 

decades. Implementing innovative 

private property planting through 

education campaigns or planting incentives would help disperse planting responsibility 

and make steps towards attaining canopy goals.

Th ough this study does not specifi cally analyze the costs versus benefi ts of trees, 

various studies have shown a positive net benefi t. For example, the average annual net 

benefi ts (benefi ts minus costs) for trees in New York City increase with mature tree 

size and diff er based on location: from US$5 (yard) to US$9 (public) for a small tree, 

from US$36 (yard) to US$52 (public) for a medium tree, and from US$85 (yard) to 

US$113 (public) for a large tree.16

Continous soil trench construction to provide Toronto 

street trees with increased soil volume.

Photo by Urban Forestry, City of Toronto, used with permission.
22

AIR POLLUTION REMOVAL BY URBAN TREES

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

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

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

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

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

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

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

reduced ozone formation.17

Pollution removal by trees and shrubs in Toronto was estimated using the i-Tree Eco 

model in conjunction with fi eld data and hourly pollution and weather data for the 

year 2007.18 Pollution removal was greatest for ozone (O3), followed by particulate 

matter less than 10 microns (PM10), nitrogen dioxide (NO2), sulfur dioxide (SO2), 

and carbon monoxide (CO). It is estimated that trees and shrubs remove 1,905 metric 

tons of air pollution (CO, NO2, O3, PM10, SO2) per year with an associated value of 

CAD$16.9 million CND (based on estimated 2007 national median externality costs 

associated with pollutants19) (Fig. 14). Trees remove more than four times more air 

pollution than shrubs in Toronto.

Th e average percentage of air pollution removed by trees during the daytime, leaf-on 

season was estimated to be:

• O3 2.3%

• PM10 2.2%

• SO2 2.4%

• NO2 1.5%

• CO 0.01%

The trees and 

shrubs in 

Toronto remove 

approximately 

1,905 metric tons of 

air pollution each 

year, with a societal 

value of CAD$16.9 

million/year.

General urban 

forest management 

recommendations 

to improve air 

quality are given in 

Appendix V.

Commercial streetscape (College Street) in Toronto.

Photo by Urban Forestry, City of Toronto, used with permission.
23

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

was estimated to be: 

• O3 16.4%

• PM10 14.1%

• SO2 16.2%

• NO2 9.0%

• CO 0.05%

Th e pollution removed by trees and shrubs was compared to facility emissions from 

Toronto (2006). Total pollution removed by trees (excluding ozone which is not 

emitted by facilities) is 22.3 percent of the total facilities emissions based on emissions 

data from Environment Canada’s National Pollution Release Inventory (Table 10).20

Th e greatest reduction compared to facility emission was for PM10 (61.0 percent). 

General recommendations to improve air quality with trees are given in Appendix V.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0

200

400

600

800

1,000

1,200

CO NO2 O3 PM10 SO2

Value (million CAN$/year) 

Pollution Removed (metric tons/year) 

Pollutant 

Pollution removed

Value

Figure 14.—Annual air pollution removed and value of removal by trees and shrubs, 

Toronto, 2008.

Table 10.—Comparison of pollutants removed by urban forest vs. emissions from 

facilities in Toronto

Pollutant 

Urban forest removal

(t/year)

Facility emissions

(t/year)

Urban forest effect

(%)

CO 10 894 1.1

NOx 297 1,576 18.8

O3 1180 n/a n/a

PM10 357 585 61.0

SO2 62 195 31.8

Total (w/o O3) 726 3,250 22.3
24

CARBON STORAGE AND SEQUESTRATION 

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

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

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

emissions from fossil-fuel based power plants.21

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

tissue growth every year. Th e amount of carbon annually sequestered is increased with 

healthier trees and larger diameter trees. Gross sequestration by trees in Toronto is 

about 46,700 metric tons of carbon per year with an associated value of CAD$1.1 

million.21 Net carbon sequestration in the urban forest is about 36,500 metric tons.

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

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

die and decay, they release much of the stored carbon back to the atmosphere. Th us, 

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

allowed to die and decompose. Trees in Toronto are estimated to store 1.1 million 

metric tons of carbon (CAD$25.0 million) (Fig. 15). Of all the species sampled, the 

Norway maple population stores the most carbon (12.3% of the total carbon stored), 

while the sugar maple population annually sequesters the most carbon (11.8% of all 

sequestered carbon) (Fig. 16).

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0

50,000

100,000

150,000

200,000

250,000

Total Sequestration (metric tons/year) 

Total Storage (metric tons) 

Diameter Class (d.b.h. in cm) 

Carbon storage

Carbon sequestration

Figure 15.—Total carbon storage and sequestration by diameter class, Toronto, 2008.

Urban forests may play 

important roles 

in capturing 

and storing 

carbon dioxide 

from the 

atmosphere. 

Net carbon 

sequestration is 

positive in healthy and 

actively growing trees, 

but can be negative 

if emission of carbon 

from decomposition 

is greater than 

sequestration by 

healthy trees.
25

TREES AFFECT ENERGY USE IN BUILDINGS

Trees aff ect energy consumption by shading buildings, providing evaporative cooling, 

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

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

months, depending on the location of trees around the building. Estimates of tree 

eff ects on energy use are based on fi eld measurements of tree distance and direction to 

space-conditioned residential buildings.10

Based on average energy costs in 2008,22 trees in Toronto reduce energy costs from 

residential buildings by an estimated CAD$9.7 million annually (Tables 11-12). Trees 

also provide an additional CAD$382,200 in value per year by reducing the amount of 

carbon released by fossil-fuel based power plants (a reduction of 17,000 metric tons of 

carbon emissions).

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

0

1,000

2,000

3,000

4,000

5,000

6,000

Value (CAN$/year) 

Sequestration (metric tons/year) 

Sequestration

Value

Figure 16.—Annual carbon sequestration and value for tree species with the greatest 

total sequestration, Toronto, 2008.

Table 11.—Annual energy savings due to trees near residential buildings, 

Toronto, 2008

Heating Cooling total

MBTUa 749,900 n/a 749,900

MWHb 6,400 34,800 41,200

Carbon avoided (t) 12,500 4,500 17,000

a MBTU = Million British Thermal Units

b MWH = Megawatt-hour

Table 12.—Annual savingsc (CAD$) in residential energy expenditures during 

heating and cooling seasons, Toronto, 2008

Heating Cooling Total

MBTUa 6,502,000 n/a 6,502,000

MWHb 499,000 2,709,000 3,208,000

Carbon avoided 281,700 100,500 382,200

a MBTU = Million British Thermal Units

b MWH = Megawatt-hour

c Based on 2008 energy costs22
26

STRUCTURAL AND FUNCTIONAL VALUES

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

a similar tree). Th e compensatory value11 of the urban forest in Toronto is about 

CAD$7.1 billion (Fig. 17). Th e structural value of an urban forest tends to increase 

with a rise in the number and size of healthy trees. Th e city has 

the following policy statement which supports the retention and 

planting of large stature trees: the City recognizes that long-lived, 

large-growing tree species are an important component of a healthy, 

diverse urban forest.

Urban forests also have functional values (either positive or 

negative) based on the functions the tree performs. Annual 

functional values also tend to increase with increased number and 

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

dollars per year. Th ere are many other functional values of the 

urban forest, though they are not quantifi ed here (e.g., reduction 

in air temperatures and ultraviolet radiation, improvements in 

water quality). Th rough proper care and management, urban forest 

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

amount of healthy tree cover declines.

Structural values (CAD$):

• Compensatory value: $7.1 billion

• Carbon storage: $25.0 million

Annual functional values (CAD$):

• Carbon sequestration: $1.1 million

• Pollution removal: $16.9 million 

• Lower energy costs and reduced carbon emissions: $10.1 million

Benefi ts such as these relate to a current initiative under way within Ontario for 

defi ning infrastructure to include trees and natural areas in an eff ort to protect and 

enhance these natural resources. Th e term “green infrastructure” is defi ned by the 

Ontario Coalition as the natural vegetation and vegetative technologies that are 

responsible for a variety of products and services to society. Green infrastructure 

promotes healthy living and can include things such as tree canopies, green roofs, and 

natural areas such as wetlands or meadows that are not dominated by trees. To learn 

more about the coalition’s initiatives visit: http://greeninfrastructureontario.org/.

More detailed information on the urban forest in Toronto can be found at http://

www.nrs.fs.fed.us/urban/data. Additionally, information on other urban forest values 

can be found in Appendix II and information comparing tree benefi ts to estimates 

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

household emissions can be found in Appendix VI.

House in Rosedale, Toronto, Ontario. 

Photo by WayneRay, Wikimedia Commons..
27

SPECIES RECOMMENDATIONS

To help sustain urban forest benefi ts in the future, proper species selection and 

landscape design will be essential. To aid in selecting tree species to maximize 

environmental benefi ts, the i-Tree species selector program was used.23 Th e program 

selected from the potential list of 1,585 tree species, eliminating trees not appropriate 

for Toronto’s hardiness zone (USDA zone 5b). Th e program then weighted various 

species function or benefi ts based on the following weights supplied by the city of 

Toronto. Functions are weighted on a scale of 0 to10, with a weight of 0 indicating no 

importance and a weight of 10 indicating highest importance.

• Air pollution removal = 10

• Stream fl ow reduction = 10

• Air temperature reduction = 10

• Ultraviolet radiation reduction = 9

• Building energy conservation = 9

• Wind reduction = 8

• Low volatile organic compound (VOC) emissions = 3

• Carbon storage = 2

• Pollen allergenicity = 1

Recommended species based on the weights provided are given in 10 percent grouping 

for the available species (e.g., top 10 percent, 10-20 percent, etc.) (Table 13). Th e 

recommended species list is designed to be only a beginning guide for species selection 

based on desired tree functions. Numerous other species attributes need to be 

considered in selecting species: invasiveness, native vs. exotic, pest or other problems, 

0

100

200

300

400

500

600

700

800

900

1,000

Compensatory Value (CAN$ millions) 

Figure 17.—Tree species with the greatest compensatory value, Toronto, 2008.

Urban forests 

have a structural 

value based on 

the characteristics 

of the trees 

themselves.

Urban forests also 

have functional 

values based on 

the ecosystem 

functions the trees 

perform.

Large, healthy, 

long-lived trees 

provide the greatest 

structural and 

functional values.
28

Table 13.—Top rated species for desired ecosystem services

Scientific name Common name

Species – top 10%

Abies concolor White fir

Abies holophylla Manchurian fir

Acer pseudoplatanus Sycamore maple

Acer rubrum Red maple

Acer saccharum Sugar maple

Acer x freemanii Freeman maple

Aesculus flava Yellow buckeye

Aesculus glabra Ohio buckeye

Aesculus hippocastanum Horsechestnut

Betula alleghaniensis Yellow birch

Betula papyrifera Paper birch

Celtis laevigata Sugarberry

Celtis occidentalis Northern hackberry

Corylus colurna Turkish hazelnut

Fagus grandifolia American beech

Juglans nigra Black walnut

Larix decidua European larch

Larix kaempferi Japanese larch

Larix laricina Tamarack

Larix leptolepis* Japanese larch

Liriodendron tulipifera Yellow-poplar or tuliptree

Magnolia acuminata Cucumbertree

Metasequoia glyptostroboides* Dawn redwood

Picea abies Norway spruce

Picea abies x asperata Norway x chinese spruce

Pinus jeffreyi Jeffery pine

Pinus monticola Western white pine

Pinus ponderosa Ponderosa pine

continued

maintenance requirements, life span, adapted to local site conditions, etc. In addition, 

some species that are hardy to the Toronto area are not in the species selection 

program23 (i.e., there are likely other good species candidates for planting). Consult 

local tree experts to determine a fi nal planting list.

City of Toronto Urban Forestry Staff have prepared two lists of recommended species. 

One list is relevant for street tree and urban applications and includes some of the 

most available urban tolerant species. It can be found at: http://www.toronto.ca/trees/

pdfs/FreeTree_Final.pdf. Th e second list details native species for naturalized areas and 

ravines and can be found at: http://www.toronto.ca/trees/pdfs/Tree_List.pdf.
29

Pinus strobus Eastern white pine

Pinus sylvestris Scotch pine

Platanus hybrida* London planetree

Platanus occidentalis American sycamore

Populus deltoides Eastern cottonwood

Pseudotsuga macrocarpa Bigcone douglas fir

Pseudotsuga menziesii Douglas fir

Quercus petraea Durmast oak

Tilia americana American basswood

Tilia cordata Littleleaf linden

Tilia platyphyllos Bigleaf linden

Tilia tomentosa Silver linden

Tsuga canadensis Eastern hemlock

Tsuga caroliniana Carolina hemlock

Tsuga mertensiana Mountain hemlock

Ulmus americana American elm

Ulmus glabra Wych elm

Ulmus serotina September elm

Zelkova serrata Japanese zelkova

Species – top 11-20%

Aesculus parviflora* Bottlebrush buckeye

Aesculus x hybrida* Hybrid chestnut

Betula lenta Black birch

Carpinus betulus European hornbeam

Chamaecyparis nootkatensis Alaska cedar

Fagus sylvatica European beech

Ginkgo biloba Ginkgo

Juglans cinerea Butternut

Juglans regia English walnut

Larix occidentalis Western larch

Magnolia macrophylla Bigleaf magnolia

Magnolia tripetala Umbrella magnolia

Morus rubra Red mulberry

Picea glehnii Sagholia spruce

Picea mariana Black spruce

Picea omorika Serbian spruce

Picea pungens Blue spruce

Pinus contorta Lodgepole pine

Table 13.—continued

Scientific name Common name

continued
30

Pinus densiflora Japanese red pine

Pinus parviflora Japanese white pine

Pinus radiata Monterey pine

Pinus resinosa Red pine

Pinus rigida Pitch pine

Pinus strobiformis Southwestern white pine

Prunus serotina Black cherry

Taxodium distichum Baldcypress

Taxus cuspidata Japanese yew

Tilia euchlora* Crimean linden

Tilia x vulgaris* Common linden

For methods – see i-Tree Species Selector (Beta) Utility at www.itreetools.

org.

* Some uncertainty to hardiness zone. As hardiness estimates or maps 

did not always exactly match USDA Plant Hardiness Zones, some 

extrapolations were made to the closest hardiness zone. Hardiness is 

based on USDA Plant Hardiness Zones. For hardiness zones with decimal 

(e.g., 4.5), values were rounded down for maximum hardiness (e.g., 4) 

and up for minimum hardiness zone (e.g., 5)

Species with hardiness zone uncertainty from genera or family averages 

were removed from the list.

Norway maple (Acer platanoides) and Siberian elm (Ulmus pumila) have 

been removed from the species recommendation lists because they are 

invasive species in the Toronto area.

White ash (Fraxinus americana), European ash (Fraxinus excelsior), 

green ash (Fraxinus pennsylvanica), and blue ash (Fraxinus 

quadrangulata) have been removed from the species recommendation list 

because they are common hosts to the plant pest the emerald ash borer.

Table 13.—continued

Scientific name Common name
31

POTENTIAL INSECT AND DISEASE IMPACTS

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

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

diff ering tree hosts, the potential damage or risk of each pest will diff er. Four exotic 

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

emerald ash borer, and Dutch elm disease (Fig. 18).

Th e Asian longhorned beetle (ALB)24 is an insect that bores into and kills a wide range 

of hardwood species. Th is beetle was discovered in 1996 in Brooklyn, NY, and has 

subsequently spread to Long Island, Queens, and Manhattan. In 1998, the beetle was 

discovered in the suburbs of Chicago, IL. Beetles have also been found in Jersey City, 

NJ (2002), Toronto/Vaughan, Ontario (2003) and Middlesex/Union counties, NJ 

(2004). In 2007, the beetle was found on Staten and Prall’s Island, NY. Most recently, 

beetles were detected in Worcester, MA (2008). Th is beetle represents a potential loss 

to the Toronto urban forest of CAD$4.0 billion in compensatory value (42.9 percent 

of the population).

Toronto and the Canadian Food Inspection Agency (CFIA) collaborated on an 

aggressive ALB eradication program when the beetle was fi rst found in Toronto in 

2003. Since then about 27,000 host trees have been removed in the Toronto and 

Vaughan areas as part of the eradication program. Tree replacement funded by the 

CFIA, Ministry of Natural Resources, and city of Toronto has mitigated this loss of 

tree canopy through replacement planting initiatives. Monitoring for ALB continues 

and no viable life stages of ALB have been detected since the summer of 2007.

Asian longhorned 

beetle

Photo by Kenneth R. Law 

USDA APHIS PPQ, www.invasive.org

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

4,500,000

ALB GM EAB DED

Compensatory Value (CA

'$ millions) 

Number of Trees at Risk 

Pest/Disease 

Number of trees at risk

Compensatory value

Figure 18.—Potential number of trees and value potentially affected by various insects and 

diseases, Toronto, 2008.
32

Th e gypsy moth (GM)25 is a defoliator that feeds on many species causing widespread 

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

potentially result in damage to or a loss of CAD$1.5 billion in compensatory value 

(16.2 percent of the population). In 2007 and 2008 Toronto successfully implemented 

a control program for the European gypsy moth. As part of the program, 320 ha (790 

acres) were sprayed with the biological control agent Bacillus thuringiensis subspecies

kurstaki (Btk) using a low-fl ying helicopter and egg masses were removed from over 

3,500 trees. Approximately 100 trees were treated with Btk from the ground. Th e 

result of this proactive integrated pest management approach was a drastic reduction 

of the European gypsy moth population to acceptable levels. Additional control 

measures have not been necessary since 2008.

Since being discovered in Detroit in 2002, emerald ash borer (EAB)26 has killed 

millions of ash trees in Illinois, Indiana, Kentucky, Maryland, Michigan, Minnesota, 

Missouri, New York, Ohio, Ontario, Pennsylvania, Tennessee, Quebec, Virginia, 

West Virginia, and Wisconsin. EAB has the potential to aff ect 8.4 percent of 

Toronto’s trees (CAD$570 million in compensatory value). Loss of ash trees in 

Toronto would reduce tree and shrub cover in the city from 26.6 % to about 24.4%. 

Th e city is monitoring emerald ash borer populations and aggressively removing trees 

from infested areas in an eff ort to manage the risk to the public (Figs. 19-20).

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

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

has killed more than 50 percent of the native elm population in the United States.27

Although some elm species have shown varying degrees of resistance, Toronto possibly 

could lose 1.6 percent of its trees to this disease (CAD$279 million in structural 

value).

Emerald ash borer

Photo by David Cappaert

Michigan State University,

www.invasive.org

An elm-lined street in St. Paul, MN, before most of the trees 

were killed by Dutch elm disease. Photo by Joseph O'Brien, U.S. 

Forest Service.

Symptoms of Dutch elm disease. 

Photo by Joseph O'Brien, U.S. Forest Service.
33

Figure 19.—Emerald ash borer infestation, Toronto, May 2011.

Image from Ruthanne Henry, Toronto Parks, Forestry and Recreation.

Figure 20.—Emerald ash borer infestation, Toronto, September 2011.

Image from Ruthanne Henry, Toronto Parks, Forestry and Recreation.

LESLIE ST

BATHURST ST

BAYVIEW AVE

WARDEN AVE

HIGHWAY 427 HIGHWAY 409

REXDALE BLVD

DIXON RD

HIGHWAY 401

EGLINTON AVE W

ROYAL YORK RD

THE QUEENSWAY

GARDINER EXPWY

LAKE SHORE BLVD W

BURNHAMTHORPE RD

CPR

CPR

DOVERCOURT RD

UNIVERSITY AVE

QUEEN ST

DVP

COXWELL AVE

LESL EI ST

CNR

HILL CRES

MORNINGSIDE AVE

CNR

LAWRENCE AVE E

HIGHWAY 401

ST CLAIR AVE E

SCR GLF CLB RD

ALLEN EXPY

BLOOR ST W

COLLEGE ST

AVENUE RD

SHERBOURNE ST

HIGHWAY 401

HIGHWAY 404

DON VALLEY PKWY

HIGHWAY 400

42

02

44

05

25

07 41

37

06

01 24

03

04

08

34

43

36

38

10 23

09

28

35

11

30

15

12

40

26

39

33

16

13

32

31

22

27

20

29

19

17

21

14

18

0 2,500 5,000 10,000 15,000 20,000

Meters

May 2011 EAB MONITORING UPDATE:

16 New subgrids observed with EAB, 4 of these with EAB mortality

1 subgrid has progressed from infestation to observed mortality

EAB infestation confirmed

Advanced infestation and ash mortality

Infestation observed or assumed based on branch sampling

Mortality observed
34

DON WATERSHED ANALYSIS

Toronto has designated approximately 11,000 ha (27,000 acres) or 17.5 percent of 

the city land area for the protection of natural features. Th is land buff ers watercourses 

within six major watersheds running through the city.

Th e Don Watershed (Fig. 21; 46,000 ha) in the Toronto area contains areas of 

ravines, which are common features in Toronto and cover about 17.5 percent of 

the city. Th e Don Watershed was analyzed using the i-Tree-Hydro model.28 i-TreeHydro is a semi-distributed, physical-based model created to simulate and study tree 

eff ects on urban hydrology. Th e model simulates the stream fl ow hydrograph using 

hourly precipitation data, digital elevation data, and cover parameters. Th e model 

fl ow is calibrated against actual stream fl ow values.

Th e precipitation data were collected from the Toronto City weather station 

(Ontario Climate Centre, climate ID: 6158355; WMO ID: 71508). Th e digital 

elevation model data were obtained from the Toronto Regional Conservation 

Authority. Tree, impervious, and other land cover parameters were derived from 

Figure 21.—Digital elevation map, Don Watershed.
35

photo-interpretation of Google Earth imagery (image dates circa 2005) using 500 

randomly located points. Watershed land cover was estimated as follows:

• Impervious cover = 47.8%

• Tree cover = 15.7%

• Grass and shrub cover = 27%

• Bare soil = 9%

In addition, fi eld data from Toronto were used to estimate the tree canopy leaf area 

index (5.1) and percent of impervious cover connected to the stream was estimated at 

40 percent. Th e model was calibrated using hourly stream fl ow data collected at the 

gauge at Don River at Tormorden (monitor ID: 02HC024) from April 1, 2007 to 

October 31, 2007. Model calibration indicated a reasonably good fi t to the measured 

fl ow data. Th e calibration coeffi cients of the model were (1.0 = perfect fi t):

• Peak fl ow weighted = 0.39

• Base fl ow weighted = 0.31

• Balance fl ow (peak and base) = 0.52

After calibration, the model was run a number of times under various conditions to 

see how the stream fl ow would respond given varying tree and impervious cover in 

the watershed. For tree cover simulations, impervious cover was held constant (47.8 

percent) with tree cover varying between 0 and 100 percent. Increasing tree cover 

was assumed to fi ll bare soil spaces fi rst, then grass and shrub covered areas, and then 

fi nally impervious covered land. At 100 percent tree cover, all impervious land is 

covered by trees. Th is assumption is unreasonable as all buildings, roads, and parking 

lots would be covered by trees. However the results illustrate the potential impact. 

Reductions in tree cover were assumed to be fi lled with grass and shrub cover. 

For impervious cover simulations, tree cover was held constant (15.7 percent) with 

impervious cover varying between 0 and 100 percent. Increasing impervious cover 

was assumed to fi ll bare soil spaces fi rst, then grass and shrub covered areas, and 

then fi nally under tree canopies. Th e assumption of 100 percent impervious cover is 

unreasonable, but the results illustrate the potential impact. In addition, as impervious 

increased from the current conditions, so did the percent of the impervious cover 

connected to the stream such that at 100 percent impervious cover, all (100 percent) 

impervious cover is connected to the stream. Reductions in impervious cover were 

assumed to be fi lled with grass and shrub cover.
36

Tree Cover Eff ects

Loss of current tree cover would increase total fl ow during the simulation period by an 

average of 2.1 percent (943,000 m3

) (Fig. 22). Doubling of tree cover would reduce 

fl ow by 2.5 percent (1.1 million m3

) during this 7-month period. Increasing tree cover 

reduces base fl ow, as well as fl ow regenerated from both pervious and impervious areas.

Impervious Cover Eff ects

Removal of current impervious cover would reduce total fl ow during the simulation 

period by an average of 23.8 percent (10.5 million m3

) (Fig. 23). Increasing 

impervious cover from 47.8 to 60 percent of the watershed would increase total 

fl ow another 30 percent (13.3 million m3

) during this 7-month period. Increasing 

impervious cover reduces base fl ow while signifi cantly increasing fl ow from impervious 

surfaces.

Increasing tree cover will reduce stream fl ow, but the dominant cover type infl uencing 

stream fl ow is impervious surfaces. Overall impervious cover had a 12-fold impact 

relative to tree cover. Increasing impervious cover by 1 percent averaged a 2.2 percent 

increase in stream fl ow, while increasing tree cover by 1 percent averaged only a 0.2 

percent decrease in stream fl ow.

Figure 22.—Change in stream flow by tree cover in Don Watershed.
37

During the simulation period, the total rainfall recorded at the Toronto City weather 

station was 315.1 mm. Since that amount is assumed to have fallen over the entire 460 

km2

 watershed, a total of 144.9 million m3 of rain fell on the watershed during the 

simulation time. Th e total fl ow in Don Watershed throughout the simulation time was 

43.9 million m3

. Th e total fl ow is made up of surface runoff and basefl ow (water that 

travels underground to the stream). Basefl ow and fl ow from impervious areas are the 

biggest contributors to stream fl ow with 47.5 percent and 47.3 percent of total fl ow 

generated from base and impervious surfaces, respectively. Flow from pervious areas 

was only estimated to generate 5.2 percent of total fl ow. Trees intercepted a little more 

than 17 percent of the precipitation that fell in their canopy areas, but since crowns 

only cover about 16 percent of the watershed, trees only intercepted about 2.7 percent 

of the total rainfall. Trees intercepted 24.9 million cubic meters of precipitation, and 

short vegetation, including shrubs, intercepted 8.4 million m3

. About 47 percent of 

total precipitation is estimated to re-enter the atmosphere through evaporation or 

evapotranspiration.

Figure 23.—Change in stream flow by impervious cover in Don Watershed
38

CONCLUSION

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

forest resource and the ecosystem services and values provided by Toronto’s urban 

forest. Managers and citizens can use these data to help develop improved longterm management plans and policies to sustain a healthy urban tree population and 

ecosystem services for future generations. Improved planning and management to 

sustain healthy tree populations can lead to improved environmental quality and 

quality of life for Toronto residents.

A key product of this study was the development of a digital land and forest cover 

map for the entire city. For the fi rst time, this map allows forest managers to assess 

the spatial distribution of the tree canopy and perform area-based analysis of forest 

and land cover for defi ned geographic areas. Th is map can assess both existing cover, 

but also potential space available for new tree cover. Th e map also provides a valuable 

communication tool for decision makers and residents who can use tree canopy maps 

to drive community interest in trees at a ward or neighbourhood level.

For additional information on estimating the costs of ecological benefi ts and ecosystem 

services, such as soil formation, nutrient cycling, pollination, natural regeneration, 

and habitat, there are a number of recent studies that are applicable to Ontario. 

One study in particular is the David Suzuki Foundation study, "Ontario’s Wealth, 

Canada’s Future: Appreciating the Value of the Greenbelt’s Eco-Services".29 Th is 

study references the 1.8 million acres of greenbelt that wraps the greater Toronto 

and Golden Horseshoe Areas, which contain the highest population density within 

Ontario. Another noteworthy study is the Ministry of Natural Resources’ publication 

"Estimating Ecosystem Services in Southern Ontario".30 In this study, the authors 

highlight the additional economic benefi ts of ecological services that are in proximity 

to higher populations often associated with urban areas that depend on these benefi ts. 

Th e Toronto and Region Conservation Authority (TRCA) has also published a "Peel 

Region Urban Forest Strategy".31 Th e work by the TRCA along with information 

in this Toronto publication are providing a consistent urban forest data collection 

strategy for the region to help guide urban forests in the future.

Improved planning and management to sustain healthy 

tree populations can lead to improved 

environmental quality and quality of life for 

Toronto residents.
39

By ownership type, it is Toronto’s residents and other private land owners 

(commercial/industrial) that control the majority (59.9 percent) of the city’s tree 

canopy. In addition, single family residential land contributed the most new tree cover 

(26,300 ha) between 1999 and 2009 and have the most potentially available space 

to plant trees. Th us, incentives to encourage tree planting on private properties and 

programs to engage residents and property owners in tree stewardship are potential 

actions that can signifi cantly support sustaining tree canopy in the long term. Th e city 

is interested in innovation and collaboration with private properties to continue to 

encourage growth, stewardship and conservation for the resource in private ownership. 

Th is study highlights the need for consistent tree cover assessment methodology. 

Recommendations for future methods for canopy assessment within Toronto will 

be explored in more detail in the context of a strategic forest management plan. Th is 

report on Toronto’s urban forest and tree cover provides valuable data that will help 

enrich the dialogue between decisionmakers, planners, forest managers, and residents 

regarding the future of Toronto’s urban forest.

More information on trees in Toronto can be found at: http://nrs.fs.fed.us/data/urban.

City arborist in a Toronto parkland tree. Photo by Urban Forestry, City of Toronto, used with permission.
40

APPENDIX I. LIST OF SPECIES

continued

Genus Species Common Name % Pop

% Leaf 

Area IVa

Abies balsamea Balsam fir 0.1 0.1 0.2

Abies concolor White fir 0.1 0.1 0.2

Acer campestre Hedge maple 0.1 0.1 0.2

Acer ginnala Amur maple 0.1 0.1 0.2

Acer negundo Manitoba maple 5.0 5.5 10.5

Acer nigrum Black maple 0.5 1.0 1.5

Acer palmatum Japanese maple 0.3 0.1 0.4

Acer platanoides Norway maple 6.5 14.9 21.4

Acer rubrum Red maple 0.2 0.8 1.0

Acer saccharinum Silver maple 0.9 4.5 5.4

Acer saccharum Sugar maple 10.2 11.6 21.8

Acer x freemanii Freeman maple 0.1 0.3 0.4

Aesculus hippocastanum Horsechestnut 0.1 0.2 0.3

Ailanthus altissima Tree-of-heaven 0.7 0.7 1.4

Alnus glutinosa European alder 0.2 0.1 0.3

Alnus incana Grey alder 0.4 0.1 0.5

Amelanchier alnifolia Western serviceberry 0.1 0.0 0.1

Amelanchier arborea Downy serviceberry 0.5 0.1 0.6

Amelanchier canadensis Eastern serviceberry 0.3 0.0 0.3

Amelanchier laevis Smooth serviceberry 0.0 0.0 0.0

Aralia spinosa Devils-walkingstick 0.1 0.0 0.1

Betula alleghaniensis Yellow birch 0.2 0.4 0.6

Betula nigra River birch 0.0 0.0 0.0

Betula papyrifera Paper birch 1.4 2.5 3.9

Carpinus caroliniana American hornbeam 0.2 0.1 0.3

Carya cordiformis Bitternut hickory 0.3 0.8 1.1

Catalpa speciosa Northern catalpa 0.3 0.3 0.6

Celtis occidentalis Common hackberry 0.0 0.1 0.1

Chamaecyparis lawsoniana Port-Orford-cedar 1.5 0.1 1.6

Cornus alternifolia Alternate-leaf dogwood 0.1 0.0 0.1

Cornus florida Flowering dogwood 0.0 0.0 0.0

Cornus mas Cornelian cherry 0.0 0.0 0.0

Crataegus calpodendron Pear hawthorn 0.3 0.0 0.3

Crataegus chrysocarpa Fireberry hawthorn 0.1 0.1 0.2

Crataegus crus-galli Cockspur hawthorn 1.0 0.4 1.4

Crataegus mollis Downy hawthorn 0.1 0.1 0.2

Cydonia oblonga Quince 0.0 0.0 0.0

Elaeagnus angustifolia Russian-olive 0.1 0.1 0.2

Euonymus atropurpureus Eastern wahoo 0.0 0.0 0.0

Euonymus europaea European spindle tree 0.0 0.0 0.0

Fagus grandifolia American beech 0.7 0.5 1.2

Fagus sylvatica European beech 0.2 0.2 0.4
41

Fraxinus americana White ash 5.3 2.7 8.0

Fraxinus excelsior European ash 0.1 0.2 0.3

Fraxinus pennsylvanica Green ash 3.6 5.0 8.6

Ginkgo biloba Ginkgo 0.0 0.0 0.0

Gleditsia triacanthos Honeylocust 1.5 1.2 2.7

Hamamelis virginiana Witch hazel 0.1 0.0 0.1

Hibiscus syriacus Rose-of-sharon 0.0 0.0 0.0

Juglans cinerea Butternut 0.2 0.6 0.8

Juglans nigra Black walnut 0.2 0.7 0.9

Juniperus chinensis Chinese juniper 0.0 0.0 0.0

Juniperus communis Common juniper 0.1 0.0 0.1

Juniperus pinchotii Pinchot juniper 0.0 0.0 0.0

Juniperus virginiana Eastern redcedar 0.7 0.2 0.9

Larix laricina Tamarack 0.0 0.1 0.1

Ligustrum lucidum Chinese privet 0.1 0.0 0.1

Magnolia acuminata Cucumbertree 0.2 0.1 0.3

Magnolia x soulangeana Saucer magnolia 0.1 0.0 0.1

Malus angustifolia Southern crab apple 0.0 0.0 0.0

Malus baccata Siberian crab apple 0.1 0.3 0.4

Malus coronaria Sweet crab apple 0.2 0.1 0.3

Malus sylvestris European crab apple 2.3 1.5 3.8

Malus tschonoskii Crabapple 0.2 0.2 0.4

Morus alba White mulberry 0.5 0.3 0.8

Morus nigra Black mulberry 0.2 0.2 0.4

Morus rubra Red mulberry 0.0 0.0 0.0

Ostrya virginiana Eastern hophornbeam 3.2 2.4 5.6

Other species Other species 0.8 0.4 1.2

Picea abies Norway spruce 1.2 1.0 2.2

Picea glauca White spruce 3.3 4.6 7.9

Picea pungens Blue spruce 0.6 1.4 2.0

Pinus nigra Austrian pine 1.4 2.7 4.1

Pinus resinosa Red pine 1.1 0.3 1.4

Pinus strobus Eastern white pine 1.5 0.9 2.4

Pinus sylvestris Scotch pine 0.6 0.4 1.0

Populus balsamifera Balsam poplar 0.4 0.0 0.4

Populus deltoides Eastern cottonwood 0.3 0.4 0.7

Populus grandidentata Bigtooth aspen 0.5 0.6 1.1

Populus tremuloides Quaking aspen 2.0 1.0 3.0

Populus x canadensis Carolina poplar 0.1 0.3 0.4

Prunus americana American plum 0.2 0.1 0.3

Prunus armeniaca Apricot 0.1 0.1 0.2

Prunus avium Sweet cherry 0.6 0.6 1.2

APPENDIX I.—CONTINUED

Genus Species Common Name % Pop

% Leaf 

Area IVa

continued
42

Prunus domestica Common plum 0.3 0.1 0.4

Prunus pensylvanica Pin cherry 0.1 0.0 0.1

Prunus persica Peach 0.0 0.0 0.0

Prunus sargentii Sargent cherry 0.0 0.1 0.1

Prunus serotina Black cherry 2.3 1.8 4.1

Prunus virginiana Common chokecherry 1.9 0.9 2.8

Pyrus communis Common pear 0.7 0.4 1.1

Quercus alba White oak 1.0 2.0 3.0

Quercus macrocarpa Bur oak 0.2 0.1 0.3

Quercus robur English oak 0.0 0.1 0.1

Quercus rubra Northern red oak 0.6 1.3 1.9

Rhamnus cathartica European buckthorn 1.6 0.5 2.1

Robinia pseudoacacia Black locust 0.2 0.9 1.1

Salix alba White willow 0.3 1.5 1.8

Salix babylonica Weeping willow 0.1 0.5 0.6

Salix discolor Pussy willow 0.1 0.0 0.1

Salix nigra Black willow 0.1 0.6 0.7

Sorbus americana American mountain-ash 0.1 0.0 0.1

Sorbus aucuparia European mountain-ash 0.0 0.0 0.0

Sorbus decora Showy mountain-ash 0.0 0.0 0.0

Syringa reticulata Japanese tree lilac 0.0 0.0 0.0

Syringa vulgaris Common lilac 0.2 0.1 0.3

Taxus baccata English yew 0.3 0.1 0.4

Taxus canadensis Canada yew 0.4 0.1 0.5

Thuja occidentalis Eastern white-cedar 15.6 2.8 18.4

Thuja plicata Western redcedar 0.0 0.0 0.0

Tilia americana American basswood 1.4 1.5 2.9

Tilia cordata Littleleaf linden 0.8 1.1 1.9

Tsuga canadensis Eastern hemlock 0.2 0.5 0.7

Ulmus americana American elm 1.5 3.7 5.2

Ulmus pumila Siberian elm 2.7 2.3 5.0

Ulmus rubra Slippery elm 0.2 0.3 0.5

APPENDIX I.—CONTINUED

Genus Species Common Name % Pop

% Leaf 

Area IVa

a

 IV = importance value (% population + % leaf area)
43

APPENDIX II. COMPARISON OF URBAN FORESTS

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

among cities should be made with caution as there are many attributes of a city that aff ect urban forest 

structure and functions, summary data are provided from other cities analyzed using the i-Tree Eco model.

City totals, trees only

City

% Tree 

cover

Number of 

trees

Carbon 

storage (t)

Carbon 

sequestration 

(t/yr)

Pollution 

removal 

(t/yr)†

Pollution 

value C

CAD$/yr‡

Calgary, Albertaa 7.2 11,889,000 404,000 19,400 296 2,329,000

Toronto, Ontarioa* 26.6 10,220,000 1,108,000 46,700 1,905 16,940,000

Atlanta, GAb 36.7 9,415,000 1,220,000 42,100 1,509 12,066,000

New York, NYb 20.9 5,212,000 1,225,000 38,400 1,521 11,692,000

London, Ontarioc 24.7 4,376,000 360,000 12,500 370 3,320,000 

Brampton, Ontarioe* 15.2 3,618,000 175,000 7,700 184 1,620,000

Baltimore, MDd 21.0 2,627,000 542,000 14,700 390 3,086,000

Philadelphia, PAb 15.7 2,113,000 481,000 14,600 522 4,100,000

Mississauga, Ontarioe* 19.0 2,104,000 203,000 10,000 336 2,973,000

Washington, DCf 28.6 1,928,000 477,000 14,700 379 2,824,000

Oakville, Ontarioc 29.1 1,908,000 133,000 6,000 172 1,404,000

Ajax, Ontarioe* 18.4 1,366,000 106,000 3,500 39 350,000

Boston, MAb 22.3 1,183,000 290,000 9,500 257 2,067,000

Woodbridge, NJg 29.5 986,000 145,000 5,000 191 1,507,000

Minneapolis, MNh 26.4 979,000 227,000 8,100 277 2,215,000

Syracuse, NYd 23.1 876,000 157,000 4,900 99 826,000

San Francisco, CAa 11.9 668,000 176,000 4,600 128 1,006,000

Moorestown, NJg 28.0 583,000 106,000 3,400 107 831,000

Morgantown, WVi 39.6 577,000 77,000 2,700 52 387,000

Jersey City, NJg 11.5 136,000 19,000 800 37 288,000

Casper, WYa 8.9 123,000 34,000 1,100 34 272,000

Freehold, NJg 34.4 48,000 18,000 500 20 160,000

Per hectare values of tree effects

City

No. of 

trees

(trees/ha)

Carbon 

Storage 

(t/ha)

Carbon 

sequestration 

(t/ha/yr)

Pollution 

removal 

(kg/ha/yr)†

Pollution 

value 

CAD$/ha/yr‡

Calgary, Albertaa 164.8 5.6 0.3 4.1 32.3

Toronto, Ontarioa 160.4 17.4 0.7 24.3 265.8

Atlanta, GAb 275.8 35.7 1.2 44.2 353.4

New York, NYb 65.2 15.3 0.5 19.0 146.3

London, Ontarioc 185.5 15.3 0.5 15.7 140.7

Brampton, Ontarioe 134.3 6.5 0.3 6.8 60.1

Baltimore, MDd 125.6 25.9 0.7 18.6 147.5

Philadelphia, PAb 61.9 14.1 0.4 15.3 120.1

Mississauga, Ontarioe 73.1 7.0 0.3 11.7 103.2

Washington, DCf 121.1 30.0 0.9 23.8 177.4

continued
44

Oakville, Ontarioc 192.9 13.4 0.6 17.4 101.0

Ajax, Ontarioe 202.5 15.7 0.5 5.8 51.9

Boston, MAb 82.9 20.3 0.7 18.0 144.8

Woodbridge, NJg 164.4 24.2 0.8 31.9 251.2

Minneapolis, MNh 64.8 15.0 0.5 18.3 146.6

Syracuse, NYd 134.7 24.2 0.8 15.2 127.0

San Francisco, CAa 55.7 14.7 0.4 10.7 83.9

Moorestown, NJg 153.4 27.9 0.9 28.1 218.4

Morgantown, WVi 258.1 34.6 1.2 23.4 173.3

Jersey City, NJg 35.5 5.0 0.2 9.6 75.3

Casper, WYa 22.5 6.2 0.2 6.2 49.8

Freehold, NJg 94.6 35.9 1.0 39.6 317.7

† Pollution removal and values are for carbon monoxide, sulfur and nitrogen dioxide, ozone, and particulate 

matter less than 10 microns (PM10), except for London, Ontario, where estimate includes particulate matter 

less than 2.5 microns (PM2.5) instead of PM10.

‡ Pollution values updated to 2007 values. Values are given in Canadian dollars (CAD = 0.988 USD)

*includes shrub cover in tree cover estimate based on photo-interpretation

Data collection group

a City personnel

b ACRT, Inc.

c City personnel, urban boundary of city

d U.S. Forest Service

e Toronto and Region Conservation Authority

f Casey Trees Endowment Fund

g New Jersey Department of Environmental Protection

h Davey Resource Group

i West Virginia University

APPENDIX II.—CONTINUED

Per hectare values of tree effects

City

No. of 

trees

(trees/ha)

Carbon 

Storage 

(t/ha)

Carbon 

sequestration 

(t/ha/yr)

Pollution 

removal 

(kg/ha/yr)†

Pollution 

value 

CAD$/ha/yr‡
45

APPENDIX III. TREE COVER BY NEIGHBORHOOD

Tree cover (percent) by Toronto neighborhood for 1999, 2005, and 2009

1999 2005 2009

Neighborhooda Tree Cover SEb Tree Cover SEb Tree Cover SEb nc

Agincourt North (129) 15.7 3.5 15.7 3.5 15.7 3.5 108

Agincourt South-Malvern West (128) 20.3 3.6 22.0 3.7 24.4 3.9 123

Alderwood (20) 22.4 4.5 21.2 4.4 24.7 4.7 85

Annex (95) 22.2 6.9 16.7 6.2 19.4 6.6 36

Banbury-Don Mills (42) 36.2 3.9 35.5 3.9 36.2 3.9 152

Bathurst Manor (34) 30.9 5.6 32.4 5.7 32.4 5.7 68

Bay Street Corridor (76) 6.7 4.6 6.7 4.6 6.7 4.6 30

Bayview Village (52) 35.6 5.6 39.7 5.7 43.8 5.8 73

Bayview Woods-Steeles (49) 39.1 6.1 39.1 6.1 37.5 6.1 64

Bedford Park-Nortown (39) 36.8 4.7 39.6 4.8 39.6 4.8 106

Beechborough-Greenbrook (112) 20.0 7.3 20.0 7.3 23.3 7.7 30

Bendale (127) 25.6 4.0 25.6 4.0 26.5 4.1 117

Birchcliffe-Cliffside (122) 29.9 4.9 32.2 5.0 31.0 5.0 87

Black Creek (24) 17.6 4.6 17.6 4.6 14.7 4.3 68

Blake-Jones (69) 20.0 7.3 23.3 7.7 26.7 8.1 30

Briar Hill-Belgravia (108) 8.3 4.6 8.3 4.6 11.1 5.2 36

Bridle Path-Sunnybrooke-York Mills (41) 56.3 4.1 55.6 4.1 55.6 4.1 144

Broadview North (57) 40.5 8.1 37.8 8.0 37.8 8.0 37

Brookhaven-Amesbury (30) 17.9 4.7 19.4 4.8 17.9 4.7 67

Cabbagetown-South St. Jamestown (71) 43.3 9.0 46.7 9.1 46.7 9.1 30

Caledonia-Fairbanks (109) 23.3 7.7 26.7 8.1 26.7 8.1 30

Casa Loma (96) 40.0 8.9 36.7 8.8 36.7 8.8 30

Centennial Scarborough (133) 19.5 4.3 21.8 4.4 23.0 4.5 87

Church-Yonge Corridor (75) 13.3 6.2 13.3 6.2 16.7 6.8 30

Clairlea-Birchmount (120) 15.0 3.6 16.0 3.7 15.0 3.6 100

Clanton Park (33) 11.1 3.7 9.7 3.5 11.1 3.7 72

Cliffcrest (123) 38.2 5.2 37.1 5.1 38.2 5.2 89

Corsa Italia-Davenport (92) 26.7 8.1 30.0 8.4 30.0 8.4 30

Crescent Town (61) 33.3 8.6 36.7 8.8 40.0 8.9 30

Danforth Village - East York (59) 17.6 6.5 20.6 6.9 23.5 7.3 34

Danforth Village - Toronto (66) 23.3 7.7 23.3 7.7 23.3 7.7 30

Don Valley Village (47) 25.6 4.7 25.6 4.7 30.2 5.0 86

Dorset Park (126) 11.1 3.3 10.0 3.2 12.2 3.5 90

Dovercourt-Wallace Emerson-Junction (93) 12.9 4.3 16.1 4.7 16.1 4.7 62

Downsview-Roding-CFB (26) 11.9 2.2 12.9 2.3 13.3 2.3 210

Dufferin Grove (83) 16.7 6.8 20.0 7.3 30.0 8.4 30

East End-Danforth (62) 34.3 8.0 37.1 8.2 37.1 8.2 35

Edenbridge-Humber Valley (9) 41.9 5.3 41.9 5.3 41.9 5.3 86

Eglinton East (138) 11.9 4.0 13.4 4.2 13.4 4.2 67

Elms-Old Rexdale (5) 27.8 7.5 27.8 7.5 30.6 7.7 36

Englemount-Lawrence (32) 26.5 6.3 30.6 6.6 32.7 6.7 49

continued
46

Eringate-Centennial-West Deane (11) 20.5 3.5 19.7 3.5 20.5 3.5 132

Etobicoke West Mall (13) 16.7 6.8 16.7 6.8 20.0 7.3 30

Flemington Park (44) 25.0 6.8 25.0 6.8 30.0 7.2 40

Forest Hill North (102) 50.0 9.1 50.0 9.1 50.0 9.1 30

Forest Hill South (101) 48.8 7.8 48.8 7.8 51.2 7.8 41

Glenfield-Jane Heights (25) 25.0 4.7 22.6 4.6 21.4 4.5 84

Greenwood-Coxwell (65) 23.3 7.7 26.7 8.1 30.0 8.4 30

Guildwood (140) 39.2 6.8 41.2 6.9 39.2 6.8 51

Henry Farm (53) 37.8 7.2 33.3 7.0 33.3 7.0 45

High Park North (88) 36.7 8.8 36.7 8.8 36.7 8.8 30

High Park-Swansea (87) 44.8 5.1 45.8 5.1 46.9 5.1 96

Highland Creek (134) 28.8 5.1 30.0 5.1 30.0 5.1 80

Hillcrest Village (48) 17.9 4.3 17.9 4.3 17.9 4.3 78

Humber Heights-Westmount (8) 25.6 7.0 25.6 7.0 28.2 7.2 39

Humber Summit (21) 7.7 2.8 7.7 2.8 8.8 3.0 91

Humbermede (22) 10.3 4.0 13.8 4.5 15.5 4.8 58

Humewood-Cedarvale (106) 34.4 8.4 37.5 8.6 34.4 8.4 32

Ionview (125) 25.0 7.7 21.9 7.3 21.9 7.3 32

Islington-City Centre West (14) 15.4 2.3 15.4 2.3 15.4 2.3 246

Junction Area (90) 6.7 4.6 6.7 4.6 6.7 4.6 30

Keelesdale-Eglinton West (110) 17.6 6.5 14.7 6.1 17.6 6.5 34

Kennedy Park (124) 37.8 8.0 37.8 8.0 35.1 7.8 37

Kensington-Chinatown (78) 20.0 7.3 20.0 7.3 20.0 7.3 30

Kingsview Village-The Westway (6) 24.3 5.0 25.7 5.1 25.7 5.1 74

Kingsway South (15) 40.8 7.0 44.9 7.1 46.9 7.1 49

Lambton Baby Point (114) 36.7 8.8 33.3 8.6 33.3 8.6 30

L’Amoureaux (117) 29.8 4.3 28.9 4.2 28.9 4.2 114

Lansing-Westgate (38) 44.4 5.5 44.4 5.5 48.1 5.6 81

Lawrence Park North (105) 37.5 7.7 37.5 7.7 37.5 7.7 40

Lawrence Park South (103) 37.5 7.0 39.6 7.1 39.6 7.1 48

Leaside-Bennington (56) 43.8 5.8 45.2 5.8 47.9 5.8 73

Little Portugal (84) 10.0 5.5 10.0 5.5 10.0 5.5 30

Long Branch (19) 26.5 7.6 26.5 7.6 26.5 7.6 34

Malvern (132) 23.1 3.5 23.1 3.5 25.9 3.7 143

Maple Leaf (29) 20.0 5.7 20.0 5.7 22.0 5.9 50

Markland Woods (12) 30.8 6.4 28.8 6.3 28.8 6.3 52

Milliken (130) 9.2 2.2 8.7 2.1 8.1 2.1 173

Mimico (17) 11.3 3.2 12.4 3.3 13.4 3.5 97

Morningside (135) 48.8 5.6 52.5 5.6 53.8 5.6 80

Moss Park (73) 13.3 6.2 13.3 6.2 13.3 6.2 30

Mount Dennis (115) 25.6 7.0 25.6 7.0 25.6 7.0 39

APPENDIX III.—CONTINUED

Tree cover (percent) by Toronto neighborhood for 1999, 2005, and 2009

1999 2005 2009

Neighborhooda Tree Cover SEb Tree Cover SEb Tree Cover SEb nc

continued
47

Mount Olive-Silverstone-Jamestown (2) 29.3 5.3 31.6 5.3 31.6 5.3 75

Mount Pleasant East (99) 54.8 7.7 52.4 7.7 54.8 7.7 42

Mount Pleasant West (104) 26.7 8.1 26.7 8.1 30.0 8.4 30

New Toronto (18) 15.2 5.3 8.7 4.2 8.7 4.2 46

Newtonbrook East (50) 23.8 5.4 23.8 5.4 28.6 5.7 63

Newtonbrook West (36) 24.7 4.6 24.7 4.6 24.7 4.6 89

Niagara (82) 14.8 4.8 14.8 4.8 16.7 5.1 54

North Riverdale (68) 20.6 6.9 20.6 6.9 26.5 7.6 34

North StJamestown (74) 20.0 7.3 16.7 6.8 13.3 6.2 30

Oakridge (121) 20.0 7.3 20.0 7.3 23.3 7.7 30

Oakwood-Vaughan (107) 10.0 5.5 16.7 6.8 16.7 6.8 30

O’Connor-Parkview (54) 33.8 5.3 35.0 5.3 35.0 5.3 80

Old East York (58) 23.3 6.4 23.3 6.4 23.3 6.4 43

Palmerston-Little Italy (80) 20.0 7.3 20.0 7.3 20.0 7.3 30

Parkwoods-Donalda (45) 34.0 4.7 34.0 4.7 35.9 4.7 103

Pelmo Park-Humberlea (23) 21.3 5.2 21.3 5.2 18.0 4.9 61

Playter Estates-Danforth (67) 36.7 8.8 36.7 8.8 36.7 8.8 30

Pleasant View (46) 26.3 7.1 26.3 7.1 26.3 7.1 38

Princess-Rosethorn (10) 37.1 6.1 35.5 6.1 38.7 6.2 62

Regent Park (72) 20.0 7.3 20.0 7.3 20.0 7.3 30

Rexdale-Kipling (4) 22.2 6.9 22.2 6.9 19.4 6.6 36

Rockcliffe-Smythe (111) 30.3 4.9 32.6 5.0 30.3 4.9 89

Roncesvalles (86) 10.0 5.5 10.0 5.5 13.3 6.2 30

Rosedale-Moore Park (98) 63.2 5.8 63.2 5.8 61.8 5.9 68

Rouge (131) 32.1 1.8 31.4 1.8 33.1 1.8 658

Runnymede-Bloor West Village (89) 23.3 7.7 23.3 7.7 26.7 8.1 30

Rustic (28) 30.0 8.4 30.0 8.4 30.0 8.4 30

Scarborough Village (139) 42.6 7.2 42.6 7.2 44.7 7.3 47

South Parkdale (85) 23.1 6.7 20.5 6.5 20.5 6.5 39

South Riverdale (70) 13.9 2.8 15.2 2.9 21.2 3.3 151

StAndrew-Windfields (40) 37.5 4.3 37.5 4.3 38.3 4.3 128

Steeles (116) 11.8 3.7 13.2 3.9 13.2 3.9 76

Stonegate-Queensway (16) 28.7 4.2 30.4 4.3 32.2 4.4 115

Tam O’Shanter-Sullivan (118) 26.1 4.7 23.9 4.5 28.4 4.8 88

The Beaches (63) 41.9 6.3 40.3 6.2 40.3 6.2 62

Thistletown-Beaumond Heights (3) 38.0 6.9 34.0 6.7 36.0 6.8 50

Thorncliffe Park (55) 16.3 5.3 16.3 5.3 18.4 5.5 49

Trinity-Bellwoods (81) 26.7 8.1 30.0 8.4 33.3 8.6 30

University (79) 30.0 8.4 30.0 8.4 30.0 8.4 30

Victoria Village (43) 17.7 4.3 20.3 4.5 21.5 4.6 79

Waterfront Communities-The Islands (77) 13.9 2.4 13.9 2.4 13.9 2.4 201

APPENDIX III.—CONTINUED

Tree cover (percent) by Toronto neighborhood for 1999, 2005, and 2009

1999 2005 2009

Neighborhooda Tree Cover SEb Tree Cover SEb Tree Cover SEb nc

continued
48

West Hill (136) 39.1 3.9 39.7 3.9 42.3 4.0 156

West Humber-Clairville (1) 10.1 1.4 10.3 1.4 10.3 1.4 475

Westminster-Branson (35) 15.4 5.0 15.4 5.0 21.2 5.7 52

Weston (113) 32.6 6.9 28.3 6.6 34.8 7.0 46

Weston-Pellam Park (91) 23.3 7.7 23.3 7.7 23.3 7.7 30

Wexford/Maryvale (119) 12.7 2.5 10.5 2.3 12.2 2.4 181

Willowdale East (51) 28.4 5.2 28.4 5.2 28.4 5.2 74

Willowdale West (37) 30.2 6.3 26.4 6.1 30.2 6.3 53

Willowridge-Martingrove-Richview (7) 33.7 5.1 36.0 5.2 37.2 5.2 86

Woburn (137) 26.3 3.2 25.8 3.2 25.8 3.2 186

Woodbine Corridor (64) 36.7 8.8 43.3 9.0 43.3 9.0 30

Woodbine-Lumsden (60) 23.3 7.7 23.3 7.7 23.3 7.7 30

Wychwood (94) 30.0 8.4 26.7 8.1 26.7 8.1 30

Yonge-Eglinton (100) 46.7 9.1 46.7 9.1 43.3 9.0 30

Yonge-StClair (97) 46.7 9.1 43.3 9.0 50.0 9.1 30

York University Heights (27) 11.2 2.1 12.1 2.2 13.5 2.3 223

Yorkdale-Glen Park (31) 7.3 2.9 8.5 3.1 11.0 3.5 82

a

 Number in parenthesis refers to number on Toronto neighborhood map

b

 SE = standard error

c

 n = sample size

APPENDIX III.—CONTINUED

Tree cover (percent) by Toronto neighborhood for 1999, 2005, and 2009

1999 2005 2009

Neighborhooda Tree Cover SEb Tree Cover SEb Tree Cover SEb nc
49

APPENDIX IV. I-TREE FORECAST PROTOTYPE MODEL 

METHODS

Th e i-Tree Forecast Prototype Model simulates future forest structure (e.g., number 

of trees and sizes) and various ecosystem services based on annual projections of the 

current forest structure data. Th ere are three main components of the model:

1) Tree growth—simulates tree growth to project annual increases in tree 

diameter, crown size, and leaf area for each tree

2) Tree mortality—removes trees from the projections based on user-defi ned tree 

mortality rates

3) Tree establishment—annually adds new trees to each projection. Th ese inputs 

can be used to illustrate the eff ect of the new trees or determine how many 

new trees need to be added annually to sustain a certain level of tree cover or 

benefi ts.

Tree Growth

Annual tree diameter growth is estimated for the region based on: 1) the length of 

growing season; 2) species average growth rates; 3) tree competition; 4) tree condition; 

and 5) current tree height relative to maximum tree height.

To determine a base growth rate based on length of growing season, urban street tree, 

park tree, and forest growth measurements were standardized to growth rates for 153 

frost-free days based on: Standardized growth = measured growth x (153/number 

of frost-free days of measurement).2

 Standardized growth rates of trees of the same 

species or genera were also compared to determine the average diff erence between 

standardized street tree growth and standardized park tree and forest tree growth rates. 

Park growth averaged 1.78 times less than street trees, and forest growth averaged 2.26 

times less than street tree growth.

Standardized growth rates are multiplied by Toronto’s number of frost-free days/153 

to estimate a base growth rate. For this study, the average base growth rates for opengrown trees was assumed to be 6.1 mm/yr for slow growing species, 10.2 mm/yr for 

moderate growing species, and 14.2 mm/yr for fast growing species. Th ere are limited 

measured data on urban tree growth for slow, moderate or fast-growing tree species, 

so the growth rates used here are estimates. Th ese growth rates by species growthrate class were estimated such that the entire population average growth rate was 

comparable to the estimated base growth rate for Toronto.

Crown light exposure (CLE) measurements of 0-1 were used to represent forest 

growth conditions; 2-3 for park conditions; and 4-5 for open-grown conditions. Th us, 

for: CLE 0-1: growth = base growth (BG)/2.26; CLE 2-3: growth = BG/1.78; and 

CLE 4-5: growth = BG. However, as the percent canopy cover increased or decreased, 

the CLE correction factors were adjusted proportionally to the amount of available 

greenspace (i.e., as tree cover decreased and available greenspace increased—the 
50

CLE adjustment factor decreased; as tree cover increased and available greenspace 

decreased—the CLE adjustment factor increased).

Growth rates are also adjusted based on tree condition. Th ese adjustments factors 

are based on percent crown dieback and the assumption that less than 25 percent 

crown dieback had a limited eff ect on diameter growth rates. For trees in fair to 

excellent condition (less than 25 percent dieback), growth rates are multiplied by 1 (no 

adjustment), trees in poor condition (crown dieback of 26-50 percent) by 0.76, critical 

trees (crown dieback of 51-75 percent) by 0.42, dying trees (crown dieback of 76-99 

percent) by 0.15, and dead trees (crown dieback of 100 percent) by 0.

As trees approach their estimated maximum height, growth rates are reduced. Th us the 

species growth rates as described above were adjusted based on the ratio between the 

current height of the tree and the average height at maturity for the species. When a 

tree’s height is over 80 percent of its average height at maturity, the annual diameter 

growth is proportionally reduced from full growth at 80 percent of height to one-half 

growth rate at height at maturity. Th e growth rate is maintained at one-half growth 

until the tree is 125 percent past maximum height, when the growth rate is then 

reduced to 0.

Tree height, crown width, crown height, and leaf area were then estimated based 

on tree diameter each year. Height, crown height, and crown width are calculated 

using species, genus, order and family specifi c equations that were derived from 

measurements from urban tree data (unpublished equations).

If there is no equation for a particular species, then the genus equation is used, 

followed by the family and order equations, if necessary. If no order equation is 

available, one average equation for all trees is used to estimate these parameters. Leaf 

area was calculated from the crown height, tree height, and crown width estimates 

based on i-Tree methods.2

Total tree cover was calculated by summing the two-dimensional crown area of each 

tree in the population. Th is calculated estimate of crown cover was adjusted to attain 

the actual tree cover of the study area based on photo-interpretation. Trees often have 

overlapping crowns, so the sum of the crown areas will often over-estimate total tree 

cover as determined by aerial estimates. Th us the crown overlap can be determined by 

comparing the two estimates:

% crown overlap = (sum of crown area - actual tree cover area)/sum of crown area

When future projections predicted an increase in percent tree cover, the percent 

crown overlap was held constant However, when 100% tree cover was attained all 

new canopy added was considered as overlapping canopy. When there was a projected 

decrease in percent tree cover, the percent crown overlap decreased in proportion to 

the increase in the amount of available greenspace (i.e., as tree cover dropped and 

available greenspace increased—the crown overlap decreased).
51

Tree Mortality Rate

Canopy dieback is the primary determinant of tree mortality. Trees with 50-75 percent 

crown dieback have an annual mortality rate of 13.1 percent; trees with 76-99 percent 

dieback have a 50 percent annual mortality rate; trees with 100 percent dieback have 

a 100 percent annual mortality rate.32 Trees with less than 50 percent dieback have a 

user-defi ned mortality rate that is adjusted to the tree size class and diameter.

Trees are assigned to species size classes: small trees have an average height at maturity 

of less than or equal to 40 ft (maximum diameter class = 20+ inches); medium trees 

have mature tree height of 41- 60 ft (maximum diameter = 30+ inches); large trees 

have a mature height of greater than 60 ft (maximum diameter = 40+ inches). Each 

size class has a unique set of seven diameter ranges to which base mortality rates are 

assigned based on measured tree mortality by diameter class (Fig. 24).29 Th e same 

distribution of mortality by diameter class was used for all tree size classes, but the 

range of the diameter classes diff ered by size class. Th e actual mortality rate for each 

diameter class was adjusted so that the overall average mortality rate for the base 

population equaled the mortality rates assigned by user. Th at is, the relative curve of 

mortality stayed the same among diameter classes, but the actual values changed based 

on the user-defi ned overall average rate.

Figure 24.—Mortality rate distribution by diameter class with range 

classified by maximum d.b.h. for the species (A) and for actual d.b.h. 

classes for small, medium, and large tree species (B)

0%

1%

2%

3%

4%

5%

6%

0 - 2 2 - 4 4 - 8 8 - 12 12 - 16 16 - 20 20 +

Mortality Rate (percent) 

Diameter Class (d.b.h inches) 

 0 - 3 3 - 6 6 - 12 12 - 18 18 - 24 24 - 30 30 + 

 0 - 4 4 - 8 8 - 16 16 - 24 24 - 32 32 - 40 40 + 

Small 

Medium 

Large 

0%

1%

2%

3%

4%

5%

6%

0-10% 10-20% 20-40% 40-60% 60-80% 80-100% Max.

Mortality Rate (percent) 

Diameter (percent of maximum d.b.h) (A)

(B)
52

Tree Establishment

Based on the desired tree cover and the number of years desired to reach that canopy 

goal, the model calculates the number of trees needing to be established annually to 

reach that canopy goal given the model growth and mortality rates. In adding new 

trees to the model each year, the species composition of new trees was assumed to 

be proportional to the current species composition. Crown light exposure of newly 

established trees was also assumed to be proportional to the current growth structure 

of the canopy. Newly established trees were input with a starting diameter (d.b.h.) of 

2.54 cm (1 inch). 

For ash mortality scenarios, the entire ash population was killed off in 10 years, with 

10 percent of the initial ash population killed off in each of the fi rst 10 years.

Th e following inputs were used for Toronto:

 Area: 64,158.37 ha/641.58 km2

 Number of Frost Free Days – 160

 Current tree cover: 26.6%

 Tree size classes

 Small trees – 10.9%

 Medium trees – 32.0%

 Large trees – 57.1%
53

APPENDIX V. GENERAL RECOMMENDATIONS FOR AIR QUALITY 

IMPROVEMENT

Urban vegetation can directly and indirectly aff ect local and regional air quality by altering the urban 

atmospheric environment. Four main ways that urban trees aff ect air quality are:

Temperature reduction and other microclimatic eff ects

Removal of air pollutants

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

Energy conservation on buildings and consequent power plant emissions

Th e cumulative and interactive eff ects of trees on climate, pollution removal, and VOC and power plant 

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

tree impacts on ozone have revealed that increased urban tree cover, particularly with low VOC emitting 

species, leads to reduced ozone concentrations in cities. Local urban forest management decisions also can 

help improve air quality.

Urban forest management strategies to help improve air quality include:

Strategy Reason

Increase the number of healthy trees Increase pollution removal

Sustain existing tree cover Maintain pollution removal levels

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

Sustain large, healthy trees Large trees have greatest per-tree eff ects

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

 and removal

Use low maintenance trees Reduce pollutants emissions from maintenance activities

Reduce fossil fuel use in maintaining vegetation Reduce pollutant emissions

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

Plant trees to shade parked cars Reduce vehicular VOC emissions

Supply ample water to vegetation Enhance pollution removal and temperature reduction

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

Avoid pollutant-sensitive species Improve tree health

Utilize evergreen trees for particulate matter Year-round removal of particles
54

APPENDIX VI. RELATIVE TREE EFFECTS

Th e urban forest in Toronto provides benefi ts that include carbon storage and sequestration, and 

air pollutant removal. To estimate a relative value of these benefi ts, tree benefi ts were compared to 

estimates of average carbon emissions in the city33, average passenger automobile emissions34, and 

average household emissions.35

General tree information:

Average tree diameter (d.b.h.) = 16.3 cm

Median tree diameter (d.b.h.) = 10.2 cm

Average number of trees per person = 4.1

Number of trees sampled = 2,674

Number of species sampled = 115

Average tree effects by tree diameter

D.b.h.

Class (cm)

Carbon storage Carbon sequestration Pollution removal

(kg) (CAD$) (km)a (kg/yr) (CAD$/yr) (km)a (kg) (CAD$)

2.5-7.6 2.7 0.08 32 0.7 0.02 10 0.0 0.29

7.7-15.2 15.9 0.45 210 2.2 0.06 29 0.1 0.77

15.3-22.9 58.7 1.67 758 4.5 0.13 60 0.2 1.88

23.0-30.5 118.7 3.38 1,548 7.1 0.20 92 0.3 3.08

30.6-38.1 218.0 6.21 2,839 10.0 0.28 131 0.4 4.67

38.2-45.7 348.6 9.93 4,532 13.0 0.37 169 0.5 5.77

45.8-53.3 523.5 14.92 6,823 16.7 0.47 216 0.6 6.76

53.4-61.0 786.5 22.42 10,242 21.3 0.61 277 0.8 9.04

61.1-68.6 985.0 28.07 12,823 24.8 0.71 323 0.9 10.55

68.7-76.2 1,366.7 38.95 17,790 34.0 0.97 444 1.0 11.72

76.2+ 2,708.6 77.20 35,258 52.4 1.49 682 1.8 19.91

a km = number of automobile kilometers driven that produces emissions equivalent to tree effect

Th e Toronto urban forest provides:

Carbon storage equivalent to:

Amount of carbon (C) emitted in city in 29 days or

Annual carbon emissions from 733,000 automobiles or 

Annual C emissions from 367,900 single family houses 

Carbon monoxide removal equivalent to:

Annual carbon monoxide emissions from 44 automobiles or

Annual carbon monoxide emissions from 180 single family 

houses 

Nitrogen dioxide removal equivalent to:

Annual nitrogen dioxide emissions from 20,700 automobiles 

or

Annual nitrogen dioxide emissions from 13,800 single family 

houses 

Sulfur dioxide removal equivalent to:

Annual sulfur dioxide emissions from 99,900 automobiles or

Annual sulfur dioxide emissions from 1,700 single family 

houses 

Particulate matter less than 10 micron (PM10) removal 

equivalent to:

Annual PM10 emissions from 1,047,000 automobiles or

Annual PM10 emissions from 101,100 single family houses 

Annual C sequestration equivalent to:

Amount of C emitted in city in 1.2 days or

Annual C emissions from 30,900 automobiles or

Annual C emissions from 15,500 single family houses
55

REFERENCES

1 City of Toronto, Parks, Forestry and Recreation. 2010. Every tree counts: A portrait 

of Toronto’s urban forest. Toronto, ON: City of Toronto. 63 p. http://www.toronto.

ca/trees/every_tree_counts.htm

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

2008. A ground-based method of assessing urban forest structure and ecosystem 

services. Arboriculture and Urban Forestry. 34(6): 347-358.

3 Nowak, D.J.; Crane, D.E.; Stevens, J.C.; Hoehn, R.E. 2005. Th e urban forest eff ects 

(UFORE) model: fi eld data collection manual. V1b. [Newtown Square, PA]: U.S. 

Department of Agriculture, Forest Service, Northeastern Research Station. 34 p.

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

4 Nowak, D.J. 1994. Atmospheric carbon dioxide reduction by Chicago’s urban 

forest. In: McPherson, E.G.; Nowak, D.J.; Rowntree, R.A., eds. Chicago’s urban 

forest ecosystem: results of the Chicago urban forest climate project. Gen. Tech. Rep. 

NE-186. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station: 83-94.

5 Baldocchi, D. 1988. A multi-layer model for estimating sulfur dioxide deposition 

to a deciduous oak forest canopy. Atmospheric Environment. 22: 869-884.

6 Baldocchi, D.D.; Hicks, B.B.; Camara, P. 1987. A canopy stomatal resistance model 

for gaseous deposition to vegetated surfaces. Atmospheric Environment. 21: 91-101.

7 Bidwell, R.G.S.; Fraser, D.E. 1972. Carbon monoxide uptake and metabolism by 

leaves. Canadian Journal of Botany. 50: 1435-1439.

8 Lovett, G.M. 1994. Atmospheric deposition of nutrients and pollutants in North 

America: an ecological perspective. Ecological Applications. 4: 629-650.

9 Zinke, P.J. 1967. Forest interception studies in the United States. In: Sopper, W.E.; 

Lull, H.W., eds. Forest hydrology. Oxford, UK: Pergamon Press: 137-161.

10 McPherson, E.G.; Simpson, J.R. 1999. Carbon dioxide reduction through urban 

forestry: guidelines for professional and volunteer tree planters. Gen. Tech. Rep. 

PSW-171. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacifi c 

Southwest Research Station. 237 p. 

11 Nowak, D.J.; Crane, D.E.; Dwyer, J.F. 2002.Compensatory value of urban trees 

in the United States. Journal of Arboriculture. 28(4): 194-199. Species values and 

replacements costs based on ISA Ontario Chapter values.
56

12 Forest and land cover imagery and data was derived from the city of Toronto’s data 

catalog. http://www1.toronto.ca/wps/portal/open_data/open_data_item_details?vgnex

toid=1b30790e6f21d210VgnVCM1000003dd60f89RCRD&vgnextchannel=6e886aa

8cc819210VgnVCM10000067d60f89RCRD

13 Nowak, D.J. 2012. Contrasting natural regeneration and tree planting in cities. 

Urban Forestry and Urban Greening. doi:10.1016/j.ufug.2012.02.005

14 Nowak, D.J.; Greenfi eld, E.J. 2012. Tree and impervious cover change in U.S. 

cities. Urban Forestry and Urban Greening. 11:21-30.

15 City of Toronto. Urban Forestry, Policies and Standards staff . Personal 

communication.

16 McPherson, E. Gregory; Simpson, James R.; Peper, Paula J.; Gardner, Shelley L.; 

Vargas, Kelaine E.; Xiao, Qingfu. 2007. Northeast community tree guide: benefi ts, 

costs, and strategic planting. Gen. Tech. Rep. PSW-202. Albany, CA: U.S. 

Department of Agriculture, Forest Service, Pacifi c Southwest Research Station. 106 p.

17 Nowak D.J.; Dwyer, J.F. 2000. Understanding the benefi ts and costs of urban 

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

forestry in the northeast. New York, NY: Kluwer Academics/Plenum: 11-22.

18 Based on boundary layer height data from Buff alo, NY, and pollution and weather 

data from Toronto.

19 Murray, F.J.; Marsh L.; Bradford, P.A. 1994. New York state energy plan, vol. II: 

issue reports. Albany, NY: New York State Energy Offi ce. 

Th ese values were updated to 2007 dollars based on the producer price index from U.S 

Department of Labor, Bureau of Labor Statistics. n.d. www.bls.gov/ppi 

Values were adjusted to Canadian dollars with a conversion rate of 0.988 Canadian 

dollars per U.S. dollar.

20 Environment Canada. National pollution release inventory. Gatineau, QC: 

Environment Canada. http://www.ec.gc.ca/pdb/npri/npri_home_e.cfm.

21 Abdollahi, K.K.; Ning, Z.H.; Appeaning, A., eds. 2000. Global climate change and 

the urban forest. Baton Rouge, LA: GCRCC and Franklin Press. 77 p. Carbon values 

based on estimated social cost of carbon (2000-2010) of US$22.8 from Fankhauser, 

S. 1996. Th e social cost of greenhouse gas emissions: an expected value approach. 

Th e Energy Journal. 1(2): 157-184. Values were adjusted to Canadian dollars with a 

conversion rate of 0.988 Canadian dollars per U.S. dollar.
57

22 Based on 2008 electricity costs (7.79 cents/kWh) from Canada Energy (http://www.

energyshop.com/electricity-prices-Toronto-residential.cfm) and 2008 MBTU costs 

from Natural gas ($8.67 per MBTU) (www.oeb.gov.on.ca/OEB). Most of Canada’s 

non-electrical heating comes from natural gas (www.nrcan.gc.ca/eneene/sources/pripri/

reprap/2008-10-24/supsup-eng.php)

23 i-Tree Species Selector (Beta) Utility methods documentation. http://www.itreetools.

org/applications/SpeciesSelector.shtm

24 USDA Animal and Plant Health Inspection Service. 2012. Plant health – Asian 

longhorned beetle. Washington, DC: U.S. Department of Agriculture, Animal and 

Plant Health Inspection Service. http://www.aphis.usda.gov/plant_health/plant_pest_

info/asian_lhb/index.shtml

Natural Resources Canada. 2011. Trees, insects, and diseases of Canada’s forests - 

Asian longhorned beetle. https://tidcf.nrcan.gc.ca/insects/factsheet/1000095

25 Northeastern Area State and Private Forestry. 2005. Gypsy moth digest. Newtown 

Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Area State 

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

26 USDA Forest Service et al. 2010. Emerald ash borer. East Lansing, MI: Michigan 

State University. http://www.emeraldashborer.info/

27 Stack, R.W.; McBride, D.K.; Lamey, H.A. 1996. Dutch elm disease. PP-324 

(revised). Fargo, ND: North Dakota State University, Cooperative Extension Service. 

http://www.ext.nodak.edu/extpubs/plantsci/trees/pp324w.htm 

28 Wang, J.; Endreny, T.A.; Nowak, D.J. 2008. Mechanistic simulation of urban 

tree eff ects in an urban water balance model. Journal of American Water Resource 

Association. 44(1): 75-85.

29. Wilson, S. 2008. Ontario’s wealth, Canada’s future: appreciating the value of the 

greenbelt’s eco-services. Vancouver, BC: David Suzuki Foundation. 61 p.

30. Troy, A.; Bagstad, K. 2009. Estimating ecosystem services in southern Ontario. A 

report prepared for Ontario Ministry of Natural Resources. Pleasanton, CA: Spatial 

Informatics Group. 70 p. Available at http://www.ontla.on.ca/library/repository/

mon/23011/296833.pdf (Accessed Apri 18, 2013).

31. Toronto and Region Conservation Authority. 2011. Peel Region urban forest 

strategy. [Publisher unknown]. 83 p. http://www.peelregion.ca/planning/

climatechange/reports/pdf/peel-urban-forest-strategy-july25-2011.pdf (Accessed April 

18, 2013).
58

32 Nowak, D.J.; Kuroda, M.; Crane, D.E. 2004. Tree mortality rates and tree 

population projections in Baltimore, Maryland, USA. Urban Forestry and Urban 

Greening. 2: 139-147.

Explanation of Calculations of Appendix VI

33 Total city carbon emissions were based on 2003 U.S. per capita carbon emissions, 

calculated as total U.S. carbon emissions (Energy Information Administration, 2003, 

Emissions of Greenhouse Gases in the United States 2003. http://www.eia.doe.gov/

oiaf/1605/1605aold.html) divided by U.S. population, 2003 (www.census.gov). Per 

capita emissions were multiplied by Minneapolis population to estimate total city 

carbon emissions.

34 Average passenger automobile emissions per mile were based on dividing total 2002 

pollutant emissions from light-duty gasoline vehicles (National Emission Trends 

http://www.epa.gov/ttn/chief/trends/index.html) by total miles driven in 2002 by 

passenger cars (National Transportation Statistics http://www.bts.gov/publications/

national_transportation_statistics/2004/).

Average annual passenger automobile emissions per vehicle were based on dividing 

total 2002 pollutant emissions from light-duty gas vehicles by total number of 

passenger cars in 2002 (National Transportation Statistics http://www.bts.gov/

publications/national_transportation_statistics/2004/).

Carbon dioxide emissions from automobiles assumed 6 pounds of carbon per gallon of 

gasoline with energy costs of refi nement and transportation included (Graham, R.L.; 

Wright, L.L.; Turhollow, A.F. 1992. Th e potential for short-rotation woody crops to 

reduce U.S. CO2 emissions. Climatic Change. 22: 223-238.)

35 Average household emissions based on average electricity kWh usage, natural gas Btu 

usage, fuel oil Btu usage, kerosene Btu usage, LPG Btu usage, and wood Btu usage per 

household from: 

Energy Information Administration. Total energy consumption in U.S. households 

by type of housing unit, 2001 Washington, DC: U.S. Department of Energy, Energy 

Information Administration. www.eia.doe.gov/emeu/recs/recs2001/detailcetbls.html.

CO2, SO2, and NOx power plant emission per KWh from:

U.S. Environmental Protection Agency. U.S. power plant emissions total by year 

www.epa.gov/cleanenergy/egrid/samples.htm.CO emission per kWh assumes onethird of 1 percent of C emissions is CO based on:
59

 Energy Information Administration. 1994. Energy use and carbon emissions: nonOECD countries. DOE/EIA-0579(94). Washington, DC: Department of Energy, 

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

 PM10 emission per kWh from: 

Layton, M. 2004. 2005 Electricity environmental performance report: electricity 

generation and air emissions. Sacramento, CA: California Energy Commission. 

http://www.energy.ca.gov/2005_energypolicy/documents/2004-11-15_

workshop/2004-11-15_03- A_LAYTON.PDF

CO2, NOx, SO2, PM10, and CO emission per Btu for natural gas, propane and butane 

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

kerosene) from:

Abraxas energy consulting. http://www.abraxasenergy.com/emissions/

CO2 and fi ne particle emissions per Btu of wood from:

Houck, J.E.; Tiegs, P.E.; McCrillis, R.C.; Keithley, C.; Crouch, J. 1998. Air emissions 

from residential heating: the wood heating option put into environmental perspective. 

In: Proceedings of U.S. EPA and Air and Waste Management Association conference: 

living in a global environment, V.1. Research Triangle Park, NC: U.S. Environmental 

Protection Agency: 373-384.

CO, NOx and SOx emission per Btu of wood based on total emissions from wood 

burning (tonnes) from:

Residential wood burning emissions in British Columbia. 2005. http://www.env.gov.

bc.ca/air/airquality/pdfs/wood_emissions.pdf.

Emissions per dry tonne of wood converted to emissions per Btu based on average dry 

weight per cord of wood and average Btu per cord from:

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

volumes I. NebGuide G-88-881-A. Lincoln, NE: University of Nebraska, Institute of 

Agriculture and Natural Resources, Cooperative Extension.
Autumn view of Queen's Park in Toronto, Ontario. Photo by MarcusObal, Wikimedia Commons.
Printed on Recycled Paper

Nowak, David J.; Hoehn, Robert E. III; Bodine, Allison R.; Greenfield, Eric J.; Ellis, 

Alexis; Endreny, Theodore A.; Yang, Yang; Zhou, Tian; Henry, Ruthanne. 2013. 

Assessing urban forest effects and values: Toronto’s urban forest. Resour. 

Bull. NRS-79. Newtown Square, PA: U.S. Department of Agriculture, Forest 

Service, Northern Research Station. 59 p.

An analysis of trees in Toronto, Ontario, reveals that this city has about 10.2 million 

trees with a tree and shrub canopy that covers approximately 26.6 percent of the 

city. The most common tree species are eastern white-cedar, sugar maple, and 

Norway maple. The urban forest currently stores an estimated 1.1 million metric 

tons of carbon valued at CAD$25.0 million. In addition, these trees remove about 

46,700 metric tons of carbon per year (CAD$1.1 million per year) and about 1,905 

metric tons of air pollution per year (CAD$16.9 million per year). Trees in Toronto are 

estimated to reduce annual residential energy costs by CAD$9.7 million per year. The 

compensatory value is estimated at CAD$7.1 billion. Information on the structure and 

functions of the urban forest can be used to improve and augment support for urban 

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

environmental quality in the Toronto area.

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

sequestration, tree value

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 alternate 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 to 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. 
Northern Research Station

www.nrs.fs.fed.us