Benchmarking Oakville’s Urban Forest

By Catherine Kavassalis April 21, 2007

Contents:

• Introduction
• Historical Background
• Statistics on Urban Forests

–        Oakville’s canopy and size distribution

–        Comparison of canopy cover and pollution benefits in various cities

• Statistic on Forestry Spending

–        Oakville’s Forestry Investment

–        Comparison to other cities

–        Comparison to Edmonton and Calgary

• Cost Benefit Analyses
• Setting Canopy Targets

Introduction

Although Oakville was once heavily forested, now only about 29% of the area is covered by tree or shrub canopy. This is not unusual for an eastern North American city, but below its potential and below the minimum 40% recommended by American Forests for metropolitan areas east of the Mississippi. 

While, Oakville has numerous trees, there are relatively few older, large trees.  This is due to the extensive land clearance that occurred in the 19^th century.  Comparative analysis with other communities shows that Oakville’s forest is currently storing less carbon than other cities with the same number of trees per acre, but has an actively growing forest with the potential for far greater storage.  Currently, Oakville has proportionally few large trees (75% have trunk diameters below 15cm or 6inches). Large trees provide the greatest benefits in terms of service to the community.

Overall, Oakville is spending more than the average North American city on forestry ($11.80 per capita CAD, 2007). However, it is far less than many cities like Milwaukee ($17.52 per capita CAD, 2004), which is widely regarded as a leader in urban forestry. In addition, many communities spend more per tree and more on tree maintenance and planting. Oakville has relatively few staff per acre (land area per staff: 7.72 km² vs. Toronto’s 3.52 km²) and could improve its investment in planting and maintenance. Such an investment would be well made.

Cost- benefit analyses of urban forest investment show that communities receive tremendous pay back for dollars spent.  Oakville has just recently joined the hundreds of North American cities that have performed some kind of urban forest assessment.  Oakville’s limited assessment estimated a $2.1 million benefit in terms of pollution mitigation, carbon sequestration, etc. Such valuations of the services trees perform have helped communities recognize the essential role trees play within a community.  When the contributions an average tree makes over its lifetime: $31,250 worth of oxygen production, $62,000 worth of air pollution control, $37,5000 worth of water management, $31, 250 worth of soil erosion control etc. are tallied, the benefits received from urban forests far outweigh the costs for their proper care. (Please view the Sacramento Tree Foundation short video: What is the value of a tree?)

Communities that have recognized the real value of their urban forests are working to ensure they can maintain and grow their forest canopies. Many have begun to set forest canopy targets. While American Forests has suggested setting a 40% minimum goal, many communities have analyzed their own plantable spaces and growth needs and set their own targets. Oakville has yet to take this important step.

There are many proactive initiatives being taken across North America to ensure the protection and enhancement of urban forests. Oakville’s Urban Forest report: Our Solution to Our Pollution, 2005, made many recommendations and proposed numerous Action Items to be pursued.  This is a proactive document which should be followed by the adoption of an Urban Forest Strategic Plan.

Urban forests add to the livability of cities. (Sacramento Government Commission. Livable Communities and Urban Forest). Many cities, like San Francisco, Seattle, Toronto and North Vancouver, that are like Oakville striving to become more livable communities, have developed strategic urban forest plans to sustain and enhance their urban canopies. A plan is needed for Oakville to secure the future of our urban forest and ensure that future generations will be able to enjoy its benefits.  A green community is a more livable community.

“Because of their proximity to people, urban forests can provide substantial benefits to environmental and recreational benefits to urban dwellers. Trees are a solar-powered technology that can help restore balance to dysfunctional urban ecosystems. Also, urban forests are strands in the urban fabric that connect people to nature and to each other. These strands weave through communities, and have the power to profoundly influence how people live at the scale of a family's yard and garden, the neighborhood, town, watershed, and region. Urban forestry is not a panacea for all the problems cities face, but it can make cities more livable.” (North American Forest Commission. 2000. Urban Forestry Issues in North America and Their Global Linkages. Twentieth Session New Brunswick, CA).

Historical Background

Oakville lies in the Carolinian Life Zone in what is called the Mixedwood Plains Ecozone. This area includes some of the most significant habitats and threatened plant and animal species that can be found in Canada. Historically rich hardwood conifer forests in the north of Halton transitioned into a mostly deciduous Carolinian forest at the warming shores of Lake Ontario. While the Carolinian zone makes up only 1% of Canada's total land area, it supports a greater variety of plants and animals than any other region in Canada.

Because of its hospitable climate and rich resources, our region was an early choice for settlement. Vast stretches of land were cleared as our forefathers harvested the bounty and prepared the land for homes, farming and business. You can see the massive oak logs that were harvested here in Halton during the 1800s, below.

According to the Ministry of Natural Resources, forest cover in our Carolinian Life Zone has been reduced from 80% to 11%. ”Less than a tenth of a percent (0.07%) of southern Ontario is now in old growth condition (that is - has trees over 120 years old).  Nearly all of the remaining ‘natural’ cover has been logged, irrigated, cleared, polluted or otherwise disturbed by human activities.” (Ontario Ministry of Natural Resources, The Big Picture project http://www.carolinian.org/ConservationPrograms_BigPictureMethodology2.htm )

The Current Picture

Since its early European settlement, Oakville has unquestionably increased forest canopy in some areas that were cleared by loggers and or used for agriculture. At the same time, Oakville has been loosing natural cover and regenerated cover as new developments unfold and infill and home expansion reduce potential growing space. While canopy cover is estimated to be at 29.1%, this figure will diminish unless growth is carefully managed, tree protection legislated, and planting and maintenance prioritized.

2005 Statistics on our urban forest canopy

• Canopy cover 29.1%
• 1.9 million trees and shrubs
• 53% (1.0 million) have trunk diameters below 7cm or 3 inches
• 75% (1.4 million) have trunk diameters below 15cm (6”). This includes:

–        6.1% Sumach (115,900) shrub or small tree

–        5.5% Hawthorn (104,500) shrub or small tree

–        2.0% European buckthorn (38,000) – exotic highly invasive shrub

• 10.6% Northern white cedar (200,100) mostly in hedgerows
• There are less than 200,000 trees with trunks over 15cm on private property
• Only 0.4% are large stature trees (8,500) with trunks above 76cm or 30inches, (5000 are on private property).

From Oakville’s Urban Forest: Our Solution to Our Pollution, 2005

“According to American Forests’ study—which analyzed 448 urban areas defined by the US Census—tree cover in these areas stands at an average 23 percent. Using Landsat satellite images, from a sample of 40 urban areas, American Forests calculated that urban areas have 21% less tree canopy today than they did 10 years earlier.” (American Forests . 2003. New Study Reveals Dramatic National Tree Loss http://www.americanforests.org/news/display.php?id=120 ).

“Based on tree canopy cover data from 26 cities in the United

States, we have derived a preliminary estimate of average urban canopy cover in the United States as 28%.” (Rowntree, R. Nowak, D. QUANTIFYING THE ROLE OF URBAN FORESTS IN REMOVING ATMOSPHERIC CARBON DIOXIDE. Journal of Arboriculture 17(10): October 1991 http://joa.isa-arbor.com/request.asp?JournalID=1&ArticleID=2457&Type=2)

Canopy cover comparisons can be problematic. There is no single standard for canopy cover determination.  Some measurements of urban forest canopy may include canopy-producing vegetation like shrubs or even vines and others may include only trees. Some may include only large extents of forested land and others may include individual trees. Part of the difference in assessment lies in the methods used to determine canopy cover. Canopy cover can be determined by compiling various field measurements or by analyzing aerial imagery, or by a combination of techniques. “These different techniques yield considerably different canopy cover estimates.” (Korhonen, L., Korhonen, K.T., Rautiainen, M. & Stenberg, P. 2006. Estimation of forest canopy cover: a comparison of field measurement techniques. Silva Fennica 40(4): 577–588)  For example, field data from Philadelphia and Baltimore  yielded15.7% and 21.0% tree canopy cover, respectively; whereas the National Land Cover Database landsat imagery analysis yielded 10.4% and 11.2% respectively, (Walton, J. 2005 An Investigation of National Tree Canopy Assessments Applied to Urban Forestry Doctoral Thesis State University of New York).  

That said, I would suggest that Oakville’s canopy coverage is typical of many urban communities across North America. Of course, not all communities across North American can or should have the same canopy coverage given the distinct differences say between the hot arid southern United States, the plains states and provinces, and those more temperate zones where forests are more typical.  This is why I began with a description of the pre European forest condition. Oakville can and should improve upon its current canopy cover.

 Just as there are some cautions that must be taken when comparing canopy coverage, so too are there problems comparing tree counts.  While the over 1.9 million trees reported for Oakville is on the surface a good number, it is important to note that this figure represents both trees and shrubs.  For the UFORE-based assessment of Oakville’s urban forest, a tree was defined as any woody vegetation with a diameter at chest level of 2.5 cm or 1 inch.  Another common definition of tree is a single or multi-trunked plant capable of attaining a height of at least 4.6 m or 15 feet. Oakville’s tree count includes many shrubs that would be excluded by the latter definition. Seattle, Washington for instance reports 1.4 million trees, but excludes shrubs. It becomes somewhat problematic to compare communities because there is a lack of agreement on definitions. Keep this in mind when reviewing the comparison tables that follow as I do not know the underlying assumptions of the various tree counts.

The first two tables that follow have been extracted from USDA city assessment reports. I have added data for Oakville to the tables for comparison purposes. The data was derived from Oakville’s urban forest report and units were converted to be consistent with the US reporting standard. To calculate per acre values for Table 2, I have assumed the area for Oakville to be 138.51 km² or 34,226.6 acres, (from the Town website).

Comparison of urban forests

“A common question asked in viewing data from a city is “how does this city compare to other cities?” Although comparison among cities should be made with caution as there are many attributes of a city that affect urban forest structure and functions, summary data are provided from other cities analyzed using the UFORE model.” USDA. 2005. San Francisco’s Urban Forest Assessing Urban Forest Effects and Values

Table 1. City Comparisons

Table 2. Total per acre for trees

Data collection group

a.        City personnel

b.        ACRT, Inc.

c.        University of Toronto

d.        US Forest Service & Institute of Tropical Forestry

e.        US Forest Service

f.         Casey Trees Endowment Fund

g.        New Jersey Department of Environmental Protection

h.        Davey Resource Group

i.          iWest Virginia University

j.          Oakville Area 138.51 km² 34,226.6 acres (from Town of Oakville Official Website)

k.        Carbon Storage at 133,000 tonnes 146,600 US tons  (2005. UFORE Report. p.1)

l.          Oakville’s forest removed 172 tonnes air pollutants or 379,195 pounds per year (2005. UFORE Report. p.1)

m.       Oakville trees sequester 22,000 tonnes of CO₂ or 48,501,697.7 pounds (2005. UFORE Report. p.1)

In comparison to these cities, Oakville would appear to fall somewhere in the middle on a variety of parameters. What is noticeable is the comparatively low numbers for carbon storage and high carbon sequestration figure. This may be do to an error on my part as I have just converted and inserted data without a full understanding of the data set. The anomalous figures may also be reflective of the size and species distribution of Oakville’s trees and shrubs

 “An urban forest is a living thing and it requires the same demographics as people (you need toddlers, teenagers, adults, and seniors, etc.)” 2004. Councillor Joe Pantalone, Deputy Mayor, City of Toronto City of Toronto, Tree Symposium: Healthy Trees for a Beautiful City

 
• Recommended distribution by size class: 40%,30%,20%,10%. (Richards, N.A. 1983. “Diversity and stability in street tree populations.” Urban Ecology 7:159-171 also Podol, 2004, “Species Diversity and Age Class Structure: University of Toronto’s Urban Forest” Master’s thesis http://www.forestry.utoronto.ca/pdfs/podol.pdf )
• Oakville distribution by size class: 86%,10%,3%,1%.

“The largest economic advantage of trees' ability to reduce building energy costs is for communities with many large-stature trees; for example, Eastlake's annual savings are valued at $280,539 with an average annual energy savings of $82 per residence unit.” (UFORE p. 1)

Oakville’s Current Forestry Spending

• Oakville Population 165, 613 (2006 Census); Area 138.51 km² (34K acres)
• 824,000 public trees  (5 trees and shrubs per capita)

–        83,000 street trees

–        300,000 open space trees

–        441,000 woodlot trees

• Planting statistics

–        3000 street trees per year (new development) (2000 spring 1000 fall)

–        187 street trees per year (replacement) (125 spring 62 fall)  Toronto (8000 – 4000 spring; 4000 fall)

–        225 park trees (7,000 parks and open spaces)

• Total 2007 Forestry Operating Budget $1,954,400 CAD

–        $2.37CAD per public trees “The five cities study $13–65 U.S. annually per tree [far fewer publicly managed trees], benefits returned for every dollar invested in management ranged from $1.37to $3.09 (0.1 to 0.35 trees per capita) McPherson, Greg et al. “Municipal Forest Benefits and Costs in Five US Cities.” Journal of Forestry. Dec. 2005: 411-416 http://www.fs.fed.us/psw/news/PSW_News/current/images/jof_Dec_2005.pdf

–        $11.80 per capita - On average, the per capita municipal forest budget in Canada was $4.55. (Alum, 2004. State of Canada’s Urban Forest)

• Planting budget (2007*) $215,000 from tax levy

–        $1.30 per capita (from tax levy) Canadian 2004 average: $1.16 (Alum, 2004. State of Canada’s Urban Forest)

•          $50,000 woodlot rehabilitation;

•          $90,000 replacement trees parks;

•          $600,000 new street trees in growth areas (not from tax levy);

•          $75,000 street trees (*2006 figure not given in 2007 budget)

• Maintenance budget $905,600 (2007**)

–         $5.74 per capita (from tax levy) Canadian 2004 average: $3.12 (Alum, 2004. State of Canada’s Urban Forest)

•          Large Trees $724,200

•          Small Trees $83,000 (net) (209,1000 gross)

•          Heritage Tree Protection $51,800 (net) ($81,800 gross)

•          Halton Region & Hydro $31,000 (net) (335,000 gross)

•          Forestry woodland stewardship $60,600 (**2006 figure, 2007 unknown)

• 18.5 FTE Forestry staff  - Land area per staff member: 7.7 km2  (Toronto 3.52 km2 in 2004)

–        3 management, 2 tree protection, 9 arborists, 2 temp, 10 students.

Spending on urban forestry across North America

• A 2000 national survey of U.S. cities with populations greater than 100,000 indicated that  per capita expenditure on trees ranged from $1.27 U.S to greater than $18.00 U.S. (see Table 9, next slide from: Seattle Urban Forest Assessment, 2000)
• Tree City USA communities average around $7 U.S. per capita for public tree maintenance.

•          Illinois  average $11.59 U.S. per capita. Chicago $5.32 U.S.

•          Michigan average $7.71 U.S. per capita. Detroit $13.00 U.S

•          Missouri average $8.02 U.S per capita. St. Louis $20.51 U.S

• In 2003, a national survey of Canadian cities indicated the average per capita municipal forest budget was $4.55 CAD ($4 U.S) (Alam, B. 2004. State of Canada’s Urban Forest)
• Toronto $6.20 CAD per capita
• Edmonton $5.83 CAD per capita for maintenance (see following slide for detail)
• Calgary $9.70 CAD per capita for maintenance (see following slide for detail)
• Oakville $11.80 CAD total budget;  $5.74 per capita for maintenance

The following table was extracted from 2000 Seattle Urban Forest Assessment: Sustainability Matrix. Oakville’s 2006 figures have been converted to current US dollars. One can assume that current forestry budgets in the communities listed have changed over time and that this is not an ideal comparison.

Table 3: Comparison of Forestry Operations for Cities over 100,000 population (2000) US dollars

Cities are ranked according to the Annual Expenditure per Capita.

*I do not know what is defined as “Street Tree”. Clearly Oakville’s budget is not simply for the 83,000 street trees. If one included the 300, 000 open space trees, the annual expenditure per tree would be $4.54. If all 824,000 public trees are used, the annual expenditure per tree would be $2.11.

Table 4: Per capita spending calculated by Edmonton and Calgary. (2006)

CALGARY / EDMONTON URBAN FORESTRY AND PLANT HEALTH CARE PROGRAM COMPARISON. Nov 2006.

http://www.edmonton.ca/OcctopusDocs/Public/Complete/Reports/UP/Elected-1995/2006-11-21/2006PW6655_Nov%2015%202006.doc

Looking over how Calgary and Edmonton determined their per capita spending, I think that they are spending more than the $5.74 per capita for maintenance than Oakville is spending. However, I do not know what assumptions are being made in budget inclusions: operating vs. capital; gross vs. figures, etc.

Cost Benefit Analysis of Urban Forest

The benefits of trees to a community are numerous. They include environmental, economic and social benefits. Potential benefits include:

• Environmental Benefits
  • Local Climate Control with Associated Energy Use Reduction
    • Shade Reduces Heat Island Effects
    • Improved Wind Control
    • Active Evaporation Cools Air
  • Carbon Sequestration
  • Air Quality
    • Oxygen Production
    • Pollution Reduction
    • Carbon Dioxide Reduction
  • Hydrological

§         Reduced Run-Off

§         Improved Water Quality

§         Erosion Prevention

§         Flood Mitigation

o       Noise Abatement

o       Glare Reduction

o       Animal Habitats

·        Economic Benefits

o       Improved Economic Stability and Sustainability

§         Increase attractiveness for business and tourists

§         Increased occupancy rates

o       Increased Property Values

o       Increased Productivity

o       Increased Shopping Rates

·        Social / Psychological Benefits

o       Architectural and Aesthetic Benefits

§         Beauty, Shape, Texture, Fragrance

§         Privacy and Visual Screening

§         Enhancing Architectural Form

o       Recreation

o       Health Improvements

§         Increased Recovery Times

§         Improved Air and Water Quality Reduces Associated Health Problems

o       Human Social Issues

§         Reduced Crime Rates

§         Increased Traffic Safety

§         Improved Learning (Particularly for Children with ADD)

While our urban forest provides direct economic benefit to a community in terms of increased property values and general economic stability. The environmental and social benefits have associated with them additional economic value. There are now numerous research studies that provide valuation of many of those benefits.

The Town’s urban forest report Our Solution to Our Pollution, 2005, examined some of the economic benefits Oakville’s urban forest provides in terms of air pollution control and provided some indication of the energy savings associated with our current tree distribution.  Looking at just those two parameters, it was estimated that Oakville’s forest provided $2.1 million in services to the community. This is consistent with valuations being done across North America.

Oakville has yet to assess the hydrological impact of trees and has only touched upon some of the energy savings they avail.

Cost benefit analysis in other communities suggest urban forest dollars are well spent.

“Washington stores 1,476 kilograms of carbon and removes 124 grams of sulfur dioxide from the atmosphere each year. To remove that same amount of pollution would otherwise cost society $5.44 annually. Multiply that by D.C.'s 1.9 million trees and the benefits add up.” (Gilsdorf, E. "What is the value of a tree?" Christian Science Monitor, April 26, 2006)

“The City of Portland estimates that each urban tree with a 50-year lifespan saves $273 a year in reduced costs for air conditioning, erosion and stormwater control, decreased air pollution, increased wildlife shelter and other infrastructure costs.” (2006. Neighborhood Trees Project Portland, OR)

“Factoring in the costs associated with planting and upkeep, New York City’s street trees provide an annual benefit of about $122 million, according to the Parks Department. The study concludes that New York receives $5.60 in benefits for every dollar spent on trees.” DAVID K. RANDALL "Maybe Only God Can Make a Tree, but Only People Can Put a Price on It" New York Times April 18, 2007  also see USDA NY Municipal Forest Resource Analysis

“The ability of Boulder ’s municipal trees to intercept rain, thereby reducing stormwater runoff, is …valued at $15 per tree.  Electricity saved annually in Boulder from shading and climate effects of trees equals 1,826 MWh ($104,074) and annual natural gas saved equals 11,403 MBtu ($72,022) for a total energy savings of $176,095 or $5 per tree.  Net annual air pollutants removed, released, and avoided average 0.47 lb per tree and are valued at $28,215 or $0.79 per tree.  The community is now receiving a substantial return on their investment of $3.67 in benefits for every $1 spent from city funds on the urban forest.”  (2005, CITY OF BOULDER, COLORADO MUNICIPAL TREE RESOURCE ANALYSIS www.ci.boulder.co.us/parks-recreation)

Setting Canopy Cover Targets

§         American Forests advocates that every city set a tree canopy goal for their community as an important step in ensuring that their valuable green infrastructure is maintained at minimum thresholds, even as the community continues to develop. Recommendations:

–        Average tree cover counting all zones 40%

–        Suburban residential zones 50%

–        Urban residential zones 25%

–        Central business districts 15%

§         Maryland Forest Conservation Act establishes targets for restoring forest cover in those urban areas deforested by development: Reforest to

–        25% of the pre-development forest for med. density res.

–        20% for high-density residential

–        15% for commercial, industrial or mixed use

§         Setting Canopy Target Guidelines

–        Guideline 1: The target should fit the characteristics of the local environment.

–        Guideline 2: Derive a value that is statistically appropriate for the data.

–        Guideline 3: Recognize potentials and constraints of various Urban Land Environments (ULEs).

–        Guideline 4: Maximize potential benefits by setting a high goal.

–        Guideline 5: Suggest a strategy for reaching the target.

–        Guideline 6: Be unambiguous and easily understood.

–        (URBAN FOREST CANOPY COVER IN PORTLAND)

§         Examples of City Targets

–        Milwaukee, WI  current 16% – target 40%

–        Vancouver, WA current 19.7% - target 28%.

–        Portland, OR 26.3% - goal for residential areas of 47% and for industrial/commercial areas of 12%.

–        Baltimore, MD current 19.8% - a goal to double (39.6%) canopy cover citywide within 30 years.

–        Seattle, WA current 18% - target 30% in 30 years (649,100 additional trees)

–        Toronto, ON current 18% - goal of 34% by 2020 citywide, 40% residential.

–        Syracuse, N.Y. increase street-tree stocking levels to a minimum of 60% to help attain an overall tree cover of 30%.

–        Annapolis, MD: 41% current adopt a 50% UTC goal to be attained by 2036

–        Montgomery County  current 42%: goals: Sub Res current 39% goal 50%; urban res current 25% goal 29% bus current 15% goal 20%

–        Roanoke, VA  current 32% goal 40% canopy in 10 years Increase the number of trees in Roanoke by 188,488 - shade trees that can achieve at least a 30 foot wide canopy at maturity

In the aerial photo (left), the white areas, mostly rooftops, are about 140 degrees Fahrenheit (60 degrees Celsius) and the dark areas, primarily vegetative areas or water, are approximately 85-96 degree Fahrenheit (29-36 degrees Celsius). The hottest spots are the buildings, seen as white rectangles of various sizes. In the thermal image (right), Sacramento's rail yard is the orange area east of the Sacramento River, which flows from top to bottom. Red and yellow areas indicate hot spots and generally correspond with urban development, while blue and green areas are cool and generally correspond to the natural environment. (Thermally Sensed Image of Sacremento http://www.epa.gov/heatisland/pilot/sacramento_thermal.html )

Many communities are setting canopy targets (or offering incentives to plant trees) explicitly to address heat island effects: (See EPA Heat Island Effect http://www.epa.gov/heatisland/regions/ and Trees and Vegetation http://www.epa.gov/heatisland/strategies/vegetation.html )

Cities with tree planting programs to increase urban forest:

§         Baton Rouge Green - Baton Rouge, LA

§         Trees Atlanta - Atlanta, GA

§         Treemendous Miami - Miami, FL

§         TreeUtah - Salt Lake City, UT

Cities with incentive programs to increase urban forest:

§         Roseville Urban Forest Foundation Shade Tree Program

§         Sacramento Municipal Utility District's Sacramento Shade Program