Agenda Item - 2022-12-20 - Number 9.01 - State of the Urban Forest Report Update503-635-0215 380 A AVENUE PO BOX 369 LAKE OSWEGO, OR 97034 WWW.LAKEOSWEGO.CITY
Subject: State of the Urban Forest Report Update
Meeting Date: December 20, 2020 Staff Member: Scot Siegel, Director
Department: Community Development
Action Required Advisory Board/Commission Recommendation ☐Motion ☐Approval☐Public Hearing ☐Denial☐Ordinance ☐None Forwarded
☐Resolution ☒Not Applicable
☒Information Only Comments:
☐Council Direction☐Consent Agenda
Staff Recommendation: No action requested. The item is informational only.
Recommended Language for Motion: NA
Project / Issue Relates To: Climate action and urban forestry
Issue before Council:
☒City Council Goal: “Combat climate change by reducing greenhouse gas emissions and
strengthening the community’s resilience to climate impact.” Initiative: “Update the Urban
and Community Forest Plan by evaluating the 2022 State of the Urban Forest Report.”
EXECUTIVE SUMMARY
On December 20, staff and project consultant Parametrix will present the results of the State of
the Urban Forest Report Update. The Report (Attachment 1) provides data that will help inform
updates to the Urban and Community Forestry Plan, consistent with City Council goals and the
City’s Climate and Sustainability Action Plan. Staff in Planning, Parks, Engineering, Public Works,
and the Sustainability Program contributed to the Report, which should be updated on a 5-year
cycle to coincide with regional plans to fly high-resolution aerial imagery and Lidar.
9.1
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503-635-0215 380 A AVENUE PO BOX 369 LAKE OSWEGO, OR 97034 WWW.LAKEOSWEGO.CITY
DISCUSSION
The urban forest, made up of all trees within Lake Oswego, is a defining characteristic of the
city. The trees that line streets, neighborhoods, parks, and natural areas, and shade streams
contribute to the environmental, economic, and social sustainability of Lake Oswego. Trees are
part of the City’s infrastructure, along with roads, utilities, parks, and cultural services, and the
City recognizes the urban forest as a critical asset that must be managed to realize its benefits.
The State of the Urban Forest Report Update (Attachment 1) provides data that will help
inform the City’s Urban and Community Forestry Program, including updates to the Urban and
Community Forestry Plan consistent with the 2022 City Council initiative. The update also fulfills
a work plan item in the City’s Sustainability and Climate Action Plan. The Report’s qualitative
and quantitative analysis may also be used to help planners and managers prioritize projects
and funding to maintain and enhance the community’s urban forest and inform discussions
about the City’s tree code and other policies.
The Report findings include:
• Citywide tree canopy increased from 48.6 percent to 53.4 percent from 2014–2019.
(The City also lost canopy in the 2021 ice storm, though this has not been quantified.)
• Lake Oswego has the highest tree canopy cover in the Portland region among cities of
comparable size.
• Canopy cover is well distributed with all neighborhoods achieving over 40 percent
canopy and all having increased canopy during the study period.
• The ecosystem services of Lake Oswego’s urban forest are immense, including nearly
270 thousand pounds of air pollutants removed annually, 155 million gallons of avoided
stormwater runoff, and storage of 467 megagrams of carbon.
• The urban tree canopy is a valuable community resource. Threats include climate
change, extreme weather, wildfire, insects and disease, urban development, and
invasive species.
• Lake Oswego has a diverse mix of trees of varying sizes with an abundant stock of
smaller trees, only some of which will eventually replace larger trees.
• Planting large stature tree species, where appropriate, will help replace larger trees as
they decline or are otherwise removed. The loss of larger trees negatively impacts
carbon storage as well as other important community benefits.
• Urban forestry policies and practices will need to be balanced with other community
goals including housing, energy conservation, and renewable energy.
Staff presented the initial findings of the Urban Tree Canopy Analysis to the Parks and Natural
Resources Advisory Board and Sustainability Advisory Board in September 2022. However, the
Report was not developed through a participatory public process because it is not a “plan”. It is
a technical study. Any updates to the Urban and Community Forestry Plan will have public and
stakeholder engagement.
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503-635-0215 380 A AVENUE PO BOX 369 LAKE OSWEGO, OR 97034 WWW.LAKEOSWEGO.CITY
The Report should be updated on a 5-year cycle to coincide with regional plans to fly high-
resolution aerial imagery and Lidar, which are tools that form the basis for the urban tree
canopy (UTC) assessment. The UTC assessment is a critical component to the report that
provides detailed canopy cover and change analysis statistics city-wide, within road right-of-
way, and across various land classifications. The analysis provides information that will help the
City manage the urban forest, conserve natural resources, and plan for climate resilience.
Preceded by the 2007 Urban and Community Forestry Plan, the original State of the Urban
Forest was published in 2009.
RECOMMENDATION
Address Urban and Community Forestry during 2023 goalsetting and the budget process.
FISCAL IMPACT
An update to the Urban and Community Forestry Plan, including policy and programmatic
updates that could follow, is major undertaking that will require significant staff time and other
resources. This work might span over two years and it could require as much as 0.5 FTE in
Planning in addition to staff resources from Parks, Engineering, Public Works, and Sustainability.
Based on the State of the Urban Forest Report Update costs, consultant fees for updating the
plan could be $100,000 or more. Long-Range Planning staff currently does not have capacity for
this work due to State planning mandates (HB 2003), annexations, neighborhood planning
projects, and other ongoing work.
ATTACHMENTS
1. State of the Urban Forest Report Update
CITY OF LAKE OSWEGO
State of the Urban Forest
December 2022
State of the Urban Forest Report | December 2022ii
Contributors
City Staff
Scot Siegel, Community Development Director/City Project Manager
Megan Big-John, Parks Manager
Daphne Cissell, Associate Planner
Sonja Johnson, Associate Engineer
Jessica Numanoglu, Deputy Community Development Director
Erik Olson, Long-Range Planning Manager
Pam Peterson, City Beautification Specialist
Amanda Watson, Sustainability Program Manager
Morgan Holen & Associates
Morgan Holen, City Consulting Arborist
Parametrix
Chad Tinsley, Consultant Project Manager
Clara Olson, Surface Water Quality
Taya Maclean, Natural Resources
Colton Kyro, Habitat
Sarah Hale, Editing/Graphic Design
Todd Prager & Associates
Todd Prager, Consulting Arborist
Cascadia-Partners
Sachi Arakawa, Carbon Sequestration
Oswego Lake Watershed Council
Jack Halsey, Executive Director
(Mountain Park Wildfire Management Project Contributor)
Heritage Tree #37, a Pacific dogwood located at Oswego Pioneer Cemetery
State of the Urban Forest Report | December 2022iii
Contents
EXECUTIVE SUMMARY ..............................................1
Purpose of this Report ..................................................................1
Acknowledgement of Previous Efforts .................................2
1 // URBAN FOREST BENEFITS .................................4
Environmental ....................................................................................4
Social......................................................................................................6
Economic ...............................................................................................7
i-Tree – Tree Benefits .......................................................................8
2 // URBAN FOREST THREATS ................................10
Insects and Diseases .......................................................................10
Air Temperature and Aridity ........................................................11
Development .......................................................................................11
Ice Storms ............................................................................................11
Wildfire ................................................................................................12
Invasive Plants ...................................................................................13
3 // CITY TREE STEWARDSHIP AND
REGULATORY EFFORTS ..........................................14
Tree Stewardship and Conservation Efforts .....................14
Regulatory Efforts ........................................................................17
4 // URBAN TREE CANOPY ASSESSMENT ............24
Urban Tree
Canopy Models ...............................................................................25
Regional Canopy Analysis ...........................................................26
Citywide Canopy Analysis............................................................28
Neighborhoods ...............................................................................35
Zoning ..................................................................................................37
Business Districts ..........................................................................40
Outdoor Recreation and Conservation Areas ................42
Road Right-of-Way / Street Trees ..........................................44
Street Tree Equity—Census Block Groups .........................47
Watersheds ........................................................................................49
Sensitive Lands ..................................................................................51
Effective Stream Shade ...............................................................53
5 // CARBON SEQUESTRATION .............................55
Explanation of Carbon Sequestration ................................55
The Carbon Sequestration Tool .............................................56
Summary and Future Scenario Planning ............................62
6 // COMMUNITY PROGRAMS ..............................63
Tree City USA .....................................................................................63
Arbor Month Events.....................................................................63
Forestry at the Farmers’ Market ............................................65
Urban & Community Forestry Workshops .........................65
Tree Care and Maintenance Website ......................................66
CONCLUSION ...........................................................67
APPENDIX ....................................................................1
i-Tree Benefits......................................................................................1
Tree Code Amendments .................................................................3
Street Tree Equity .............................................................................8
Urban Tree Canopy Model Methodology ............................11
Carbon Sequestration Tool Methodology .......................16
State of the Urban Forest Report | December 20221
The urban forest, made up of
all trees within Lake Oswego, is
a defining characteristic of the
city. The trees that line streets,
neighborhoods, parks, and
natural areas, and shade streams
contribute to the environmental,
economic, and social sustainability
of Lake Oswego. Trees are part of
the City’s infrastructure, along with
roads, utilities, parks, and cultural
services, and the City recognizes
the urban forest as a critical asset
that must be managed to realize
the benefits that it provides.
Purpose of this Report
This report provides data that will help
inform updates to the City’s Urban and
Community Forestry Plan, consistent with
the 2022 City Council initiative by the
same name. This report is also a work
plan item in the City’s Sustainability and
Climate Action Plan. This qualitative and
quantitative analysis may be used to help
planners and managers prioritize projects
and funding to maintain and enhance
the community’s urban forest resource
and inform discussions about the City’s
tree code and policies. The report also
sets the framework for future updates to
the report on a 5-year cycle. The 5-year
cycle correlates with regional plans to fly
high-resolution aerial imagery and Lidar,
which are tools that form the basis for the
urban tree canopy (UTC) assessment. The
UTC assessment is a critical component to
the report that provides detailed canopy
cover and change analysis statistics city-
wide, within road right-of-way, and across
various land classifications. The analysis
provides information that will help the City
manage the urban forest, conserve natural
resources, and plan for climate resilience.
The urban forest, as defined in the
vision statement of the City’s Urban and
Community Forest Plan in 2007,
“is a thriving and sustainable mix of tree
species and age classes that contribute
to a healthy ecosystem. The forest is
valued and cared for by the community
as an essential environmental, economic,
and cultural asset.”
Executive Summary MAJOR KEY FINDINGS
»Citywide tree canopy increased from 48.6 percent
to 53.4 percent from 2014–2019.
»Lake Oswego has the highest tree canopy cover in
the Portland region among cities of comparable size.
»Canopy cover is well distributed with all
neighborhoods achieving over 40 percent canopy
cover and all having increased canopy during the
study period.
»The ecosystem services of Lake Oswego’s urban
forest are immense, including nearly 270 thousand
pounds of air pollutants removed annually, 155
million gallons of avoided annual stormwater runoff,
and storage of 201,732 megagrams of carbon.
»Lake Oswego must manage multiple ongoing
threats to the urban forest, including climate
change, extreme weather, wildfire, insects and
disease, urban development, and invasive species.
»Lake Oswego has a diverse mix of trees of varying
sizes with an abundant stock of smaller trees, only
some of which will eventually replace larger trees.
»Replanting large stature tree species, where
appropriate, will help replace larger trees as they
decline or are otherwise removed. The loss of
larger trees negatively impacts carbon storage as
well as other important community benefits.
»Urban forestry policies will need to be balanced with
other community goals, including housing, energy
conservation, and renewable energy.
2 State of the Urban Forest Report | December 2022
Executive Summary
This report builds on previous efforts,
including the 2007 Urban and Community
Forestry Plan and the 2009 State of the
Urban Forest Report. A brief synopsis of
each of these efforts is included below.
2007 Urban
and Community
Forestry Plan
The 2007 Urban and
Community Forestry
Plan (2007 Plan)
established goals
and recommended
actions related
to urban forest
management, with an overall goal to
“create a comprehensive, sustainable, and
integrated approach to tree management
on both public and private property.” The
plan prioritized stewardship collaboration
between the City, community groups,
and residents. Another goal of the 2007
Plan was to support public outreach and
education about urban forest health and
management. A comprehensive list of
specific goals was developed in the 2007
Report that were organized in six categories
of emphasis with the following intentions:
• Stewardship and Education goals to
promote public engagement in forest
stewardship through education and
outreach.
• Forest Health goals to ensure that the
forest remains healthy and diverse with
respect to size, age, and species.
• Forest Size goals to increase canopy
cover by planting trees that are likely to
succeed (right tree in the right place).
• Tree Maintenance goals to establish
maintenance and assessment
standards needed for publicly owned
or cared-for trees.
• Invasive Species Management goals to
focus on eradicating plants that kill trees.
• Integration goals to ensure that
community forest principles are
implemented across all City
departments.
Significant progress has been made
toward many of the goals identified in the
2007 Plan. Some of the specific actions
taken by the City and community groups
are highlighted throughout this report.
State of the
Urban Forest
Report 2009
The State of the Urban
Forest Report 2009
(2009 Report) provided
analysis on forest
benefits, canopy cover,
and forest structure.
The report summarizes
baseline data about the urban forest which
has been the basis of plans, goals, and
actions by the City and community groups
since 2009.
The canopy cover chapter of the 2009
Report produced a forest canopy estimate
of 44.4 percent based on a GIS analysis
of 2007 aerial imagery. In addition to
the city-wide statistics of canopy cover,
the report detailed breakouts by road
right-of-way, public lands, single-family
residential zoning, neighborhoods, and
stream corridors. The 2009 Report also
provided details on the economic benefits
of the urban forest based on the US Forest
Service’s i-Tree tool. The 2022 Report
provides updates to each of these analyses
based on the latest available data.
Acknowledgement of Previous Efforts
3 State of the Urban Forest Report | December 2022
Executive Summary
The 2009 Report also made some urban
forest management recommendations on
removing invasive species like English ivy,
using best practices for maintaining existing
trees, encouraging tree diversity, and
planting the right tree in the right place.
Below are some of the key findings that
were highlighted in the 2009 Report:
• The urban tree canopy provides
economic benefits worth more than
10 times the money spent on trees
throughout the city.
• Planting the right tree in the right place
is key to maintaining species diversity,
minimizing maintenance costs, and
ensuring tree health, especially within
the right-of-way.
• Canopy cover near streams is high, but
decreases at larger distances from the
stream. The City has since implemented
the current Sensitive Lands protections
that extend beyond the 100-foot buffers
that were used in the 2009 analysis.
• English ivy is a major threat to
the health of the urban forest in
Lake Oswego. Comprehensive
management and regulations to
eradicate ivy should be a priority for
the City and Community Groups.
• Continued tracking of urban forest
changes over time is necessary
to better understand the benefits
provided by the urban forest and the
effects of forest management practices.
Southwood youth stewardship ivy removal event
State of the Urban Forest Report | December 20224
Trees provide a wide range
of environmental, social, and
economic benefits for the
community.
Environmental
The urban forest is a defining feature of the
city. It provides many ecosystem services
that we all rely on and that influence
how we interact with the environment.
Individual trees and the collective urban
forest provide visible benefits such as shade
and landscape beautification, but they
also provide other less visible benefits that
promote clean air and water, and healthy
ecosystems. By sequestering carbon and
reducing the urban heat island effect, the
urban forest also helps to mitigate the
impacts of climate change. Consideration
of these environmental benefits is integral to
managing this resource.
Air Quality
The impact of pollutants and ozone-
forming chemicals on air quality is
temperature dependent. Shading
from trees and transpiration of water
from leaf surfaces can lower local air
temperatures, prevent heat storage
and radiation absorption, lower wind
speeds, and improve local air quality.
Pollutants that trees can remove include
particulate matter, ozone, sulfur dioxide,
nitrogen dioxide, and carbon monoxide.
Trees can also have indirect air quality
benefits through the shading of buildings
in summer and decreasing wind speeds
in the winter, which decrease heating and
cooling demands. This results in lower
energy usage and decreased power plant
emissions.1
However, trees can also have negative
effects on air quality through the emission
of volatile organic compounds (VOCs)
which contribute to the formation of
ozone and carbon monoxide. Different
species vary in the level of VOC emissions,
so species composition can have a
cumulative effect on VOC emissions in
urban areas.
Maintenance activities including pruning,
tree removal, and leaf cleanup can
negatively affect air quality and must be
factored into the overall benefits trees
provide. Also, the placement of trees can
negatively impact energy usage through
1 Nowak, David J. 2000. The Effects of Urban Trees on Air
Quality. USDA Forest Service, Syracuse, NY. https://www.
nrs.fs.fed.us/units/urban/local-resources/downloads/
Tree_Air_Qual.pdf
excessive shading in the winter or blocking
summer breezes or solar energy.1
Since trees can have both positive and
negative effects on local air quality,
the urban forest should be managed
thoughtfully to maximize benefits and
minimize costs.
2 The Roll of Urban Trees in Stormwater Management.
(2017). Center for Watershed Protection, (66), 2. Retrieved
from https://cwp.org/wp-content/uploads/2017/01/
cwp_rr_jan17.7.pdf
Water Quality
Trees reduce stormwater runoff through
rainfall interception by the tree canopy, by
releasing clean water into the atmosphere
through evapotranspiration, and by
promoting infiltration of water through
the soil and storage of water in the soil
and forest litter (includes leaves and other
organic matter).2 In the absence of tree
canopy, rain falling on urban surfaces
such as roads, parking lots, buildings,
and driveways picks up various pollutants
as it runs off the landscape. The tree
canopy temporarily detains some of
the rainfall and gradually releases it,
regulating the flow of stormwater runoff
downstream and thereby preventing some
of the pollutants in rainfall and on urban
1 // Urban Forest Benefits
5 State of the Urban Forest Report | December 2022
1 // Urban Forest Benefits
surfaces from being transported to local
waterways.
Solar radiation is also a significant
pollutant that trees help to reduce. The
Willamette River and Tryon Creek are
impaired waterbodies with regards
to temperature. Nettle Creek, the city’s
primary tributary to Tryon Creek, exceeds
the current maximum temperature
standards. These standards were designed
to protect threatened and endangered fish
species during critical periods when they
use rivers for spawning, rearing, migration,
or other life stages.
Trees reduce solar radiation in two ways.
First, tree canopy over impervious surfaces
reduces pavement temperature. During a
rainfall event, thermal energy is transferred
from impervious surfaces to stormwater
runoff, causing the runoff to become
warmer. This high temperature runoff
can be harmful to coldwater habitat in
receiving waters. Second, canopy cover
over streams increases shade and reduces
direct heat gain by streams from solar
radiation.
Habitat
Urban forests and trees support a wide
diversity of habitats across parks and
natural areas, wildlife corridors, and even
in neighborhoods and urban centers. The
diversity of trees and their varied sizes and
arrangement in the landscape supplies a
unique variety of habitats and resources
that are used by various mammals, birds,
insects, amphibians, and fish.
Diverse forested habitats found within the
city include oak and conifer woodlands
and forests, riparian habitats, and the
mixed urban forest. Animals use trees
within these habitats as food resources,
shelter, nesting, and for places from
which to hunt. Key wildlife, including
strategy species designated by Oregon
Department of Fish and Wildlife, and over
100 species of migratory birds, are known
to occur in forested habitats across the city.
Habitat fragmentation can block wildlife
from accessing and utilizing the full array
of resources available on the landscape.
Urban forests in the City of Lake Oswego
serve to connect the larger habitat
areas of the Willamette River shoreline,
Tryon Creek State Park, and surrounding
underdeveloped lands to one another.
A pair of nesting Western screech-owls in the Palisades Neighborhood, photo by Linda Hoagland and Harvey Tucker
6 State of the Urban Forest Report | December 2022
1 // Urban Forest Benefits
Social
Trees provide a range of social benefits
that can increase public health, safety, and
sense of community.3
3 Turner-Skoff JB, Cavender N. The benefits of trees for
livable and sustainable communities. Plants, People,
Planet. 2019; 1: 323–335. https://doi.org/10.1002/ppp3.39
Health
By reducing air pollution, trees can also
help to reduce lung disease, glaucoma,
heart attacks, and blood pressure, as
well as improve cognitive development
in children. Reduced temperature in
urban areas from tree shading also helps
mitigate the risk of heat-related illnesses by
reducing the urban heat island effect.
The presence of trees is strongly linked
to mental and emotional health benefits
including reduced negative thoughts,
reduced rates of depression, and
increased life satisfaction. Views of trees
have been shown to improve the recovery
time of hospital patients as well.3
4 Naderi, Jody & Kweon, Byoung-Suk & Maghelal,
Praveen. (2008). The street tree effect and driver safety.
ITE Journal on the Web. 78. 69-73.
Safety
Trees are linked with reduced violence
and aggression in households, reduced
criminal activity in neighborhoods, and
increased perception of safety and
security.3 Tree-lined streets are also
perceived as safer in both urban and
suburban communities, and driving
speeds are shown to be significantly
reduced on suburban tree-lined streets.4
Sense of Community
5 Elmendorf, William. (2008). The Importance of Trees
and Nature in Community: A Review of the Relative
Literature. Arboriculture and Urban Forestry. 34.
10.48044/jauf.2008.020.
6 Sullivan, William. (2007). Landscapes of 20th Century
Chicago Public Housing.
Trees can increase a sense of community
in urban and suburban neighborhoods.
Scientific literature provides evidence
that neighborhood trees are a critical
component of personal and community
pride. Environmental projects, including
community tree plantings, increase
social interactions, build community
capacity, and support the development
of community itself.5 Green spaces with
trees and landscaping increase informal
community surveillance, neighbor
interactions, and stronger social ties, which
ultimately lead to decreases in crime.6
Heritage Tree Bike Ride, 2014
7 State of the Urban Forest Report | December 2022
1 // Urban Forest Benefits
Economic
Trees also provide a range of tangible economic benefits including
increased property values, increased business activity, and reduced
public infrastructure costs.
Property Values
A study published in 2010 found that one street tree in Portland can
increase the sales price of a home by $8,870 on average and can
reduce time on market by 1.7 days.7 2011 study also found that a
single tree on a lot can increase a house’s monthly rental income
by $5.62, and a single street tree can increase monthly rental
income by $21 on average.8
However, tree canopy contribution to property value does not
increase exponentially. A 2010 study in Minnesota found that the
sale price of homes increased until canopy cover reached 40 to
60 percent. Additional canopy cover beyond 60 percent resulted in
lower sales prices.9
7 Donovan, Geoffrey & Butry, David. (2010). Trees in the city: Valuing street trees in Portland,
Oregon. Landscape and Urban Planning. 94. 77-83. 10.1016/j. landurbplan.2009.07.019.
8 Donovan, Geoffrey H.; Butry, David T. 2011. The effect of urban trees on the rental price of
single-family homes in Portland, Oregon. Urban Forestry & Urban Greening. 10: 163-168.
9 Sander, Heather & Polasky, Stephen & Haight, Robert. (2010). The value of urban tree
cover: A hedonic property price model in Ramsey and Dakota Counties, Minnesota, USA.
Ecological Economics. 69. 1646-1656. 10.1016/j.ecolecon.2010.03.011.
Business Activity
It is well established through published research that quality urban
forest canopy in business districts and commercial areas results
in positive shopping perceptions and behavior. On average,
consumers are willing to pay 12 percent more in large cities and 9
percent more in small cities for similar products when quality tree
canopy is present.10
A study of strip malls in Seattle, Washington; Tacoma, Washington;
and Portland, Oregon, found that the presence of roadside trees
and landscaping contributed to positive shopping behavior,
including a willingness to pay 8.8 percent more for goods and
services.11
10 Wolf, K.L. 2014. City Trees and Consumer Response in Retail Business Districts (pp.
152-172). In: F. Musso, & E. Druica (eds.) Handbook of Research on Retailer- Consumer
Relationship Development. Hershey, PA: IGI Global.
11 Wolf, K.L. 2009. Strip Malls, City Trees, and Community Values. Arboriculture & Urban
Forestry. 35 (1): 33-40.
12 McPherson, E.G.; Maco, S.E.; Simpson, J.R.; Peper, P.J.; Xiao, Q.; VanDerZanden, A.; Bell,
N. 2002. Western Washington and Oregon Community Tree Guide: Benefits, Costs and
Strategic Planting. International Society of Arboriculture, Pacific Northwest Chapter. 58 p.
Ecosystem Service Benefits
Ecosystem service values provided by trees can be calculated using
pricing derived from factors such as energy costs, emission control
costs, and stormwater management costs.12 There are a variety of
methodologies for calculating benefits, including the i-Tree suite of
tools discussed in the next section.
8 State of the Urban Forest Report | December 2022
1 // Urban Forest Benefits
i-Tree – Tree Benefits
The USDA Forest Service provides the
peer-reviewed tool i-Tree for estimated tree
benefits based on best available science.
The i-Tree Canopy tool was used to estimate
tree benefits in Lake Oswego based on the
city-wide acreage of UTC from the 2014
and 2019 models that are described in the
Urban Tree Canopy Assessment chapter
of this report. i-Tree quantifies many of
the environmental benefits previously
described and applies monetary values to
them. The monetary values are based on
extensive peer reviewed research on costs
associated with items such as healthcare
expenses, productivity losses, and mortality
(for air pollutants), stormwater control and
treatment costs (for hydrological costs), and
the social costs of carbon as determined by
the US EPA.13
The results of this analysis (Figure 1.1) were
confirmed with i-Tree staff, which helped
calibrate the tool to match typical urban
canopy conditions within urban Clackamas
County. Complete results from the i-Tree
tool for 2014 and 2019 are included in the
appendix.
13 Nowak, David J. 2021. Understanding i-Tree: 2021 summary
of programs and methods. General Technical Report NRS-
200-2021. Madison, WI: U.S. Department of Agriculture,
Forest Service, Northern Research Station. 100 p. [plus 14
appendixes]. https://doi.org/10.2737/NRS-GTR-200-2021
Figure 1.1 2019 annual environmental tree benefits based on urban tree canopy assessment.
2019 Urban Tree Canopy: 4,265 acres
Carbon Carbon Stored in Trees
201,732
$34,405,392.60
CARBON STORAGE 1
MONETARY VALUE
STORED (MGC)
Carbon price: $170.55/MgC
AVRO Avoided Runoff E Evaporation I Interception T Transpiration PE Potential Evaporation
PET Potential Evapotranspiration
155 million 770 million 774 million 329 million 2.1 billion 1.8 billion
HYDROLOGICAL
$1,380,125 saved by trees in avoided runoff
REMOVAL RATE (GAL/YR)
CO Carbon Monoxide
NO2 Nitrogen Dioxide
O3 Ozone PM10 Particulate Matter (2.5–10 microns)
PM2.5 Particulate Matter (<2.5 microns)
SO2 Sulfur Dioxide
4,517 31,906 165,102 34,743 22,826 10,709
$3,011 $5,463 $277,869 $108,891 $2,197,416 $536
AIR QUALITY
MONETARY VALUE ($/T/YR)
REMOVAL RATE (LBS/YR)
$2,593,186 total value of air quality benefits
1 The values for carbon storage were
calculated using the baseline
methods described in chapter 5
on carbon sequestration. The tool
uses i-Tree calculations for carbon
storage, but has been calibrated
based on the typical tree species
mix and tree canopy height
categories found in Lake Oswego.
(not an annual rate)
9 State of the Urban Forest Report | December 2022
1 // Urban Forest Benefits
It is important to also consider costs associated with managing trees, which
include planting, watering, pruning, removal, infrastructure damage, liability,
management, and energy usage from maintenance activities.14 However,
research comparing tree costs with tree benefits consistently shows that
trees provide net benefits over costs. For example, a 2002 study in the Pacific
Northwest found that the annual net benefits provided by street or park
trees ranged from $1 for small stature trees to $48 for large stature trees.
These annual net benefits were even greater for well-placed residential
yard trees that screened a west-facing building wall, ranging from $8 to
$53.11.14 This underscores the importance of appropriate planting design
and management considerations for items including shading, infrastructure
protection (e.g., sidewalks and paved surfaces), stormwater management,
and selecting large stature trees when planting space is available.
14 McPherson, E.G.; Maco, S.E.; Simpson, J.R.; Peper, P.J.; Xiao, Q.; VanDerZanden, A.; Bell, N. 2002. Western
Washington and Oregon Community Tree Guide: Benefits, Costs and Strategic Planting. International
Society of Arboriculture, Pacific Northwest Chapter. 58 p.
KEY FINDINGS
»Trees provide a wide range of environmental, social,
and economic benefits that have been thoroughly
documented through peer-reviewed scientific research.
»Many of these benefits are quantifiable and are
based on items such as healthcare expenses,
stormwater control and treatment costs, and the
social costs of carbon. For example, Lake Oswego’s
urban forest provides 154,860,785 gallons of avoided
runoff annually. This is equivalent to the water held
by over 230 Olympic-sized swimming pools.
»Trees also tend to increase property values, rental
income, and business activity. However, too much tree
canopy may result in a decline in value.
»Research has shown trees provide a range of social
benefits including improved health outcomes, safer
neighborhoods, reduced vehicle speeds, and stronger
bonds between neighbors.
Cherry trees at Millennium Plaza
State of the Urban Forest Report | December 202210
There are a variety of threats to
the short- and long-term health
and sustainability of Lake Oswego’s
Urban Forest.
According to a USDA Forest Service study
of forests completed in July of 2022 for the
continental US, the primary threats for
urban Clackamas County (Figure 2.1) are
insects and disease, air temperature and
aridity increases, and decreases in urban
tree cover due to development.1 In addition
to these threats, invasive plants are a
major threat to trees in Lake Oswego.
Insects and Diseases
There are a variety of native and
non-native pests and diseases that affect
trees in the Lake Oswego area. They
are a natural part of the ecosystem and
contribute to ongoing forest succession,
regeneration, and renewal. However, at
times, exotic pests can gain a foothold
where they lack natural predators to keep
their numbers in check, which can result
in devastating impacts to trees. Insects
1 David J Nowak, Eric J Greenfield, Alexis Ellis, Assessing
Urban Forest Threats across the Conterminous United
States, Journal of Forestry, 2022;, fvac019, https://doi.
org/10.1093/jofore/fvac019
and diseases have been identified as the
most significant threat to urban Clackamas
County by the USDA Forest Service.
The most recent example of this threat type
is emerald ash borer (Agrilus planipennis)
which was discovered for the first time in
Oregon in June 2022. Emerald ash borer
has been found to be fatal to all ash
species in other parts of North America,
so its arrival in Oregon is of significant
concern. Ash species are found throughout
Lake Oswego, including native trees in
riparian and wetland areas along with
non-native street trees and trees within
ornamental landscapes.2
2 Oregon Department of Forestry. (2022). Forest Facts:
Emerald Ash Borer (EAB) Agrilus planipennis Fairmaire
[Fact sheet]. https://www.portland.gov/sites/default/
files/2022/fact-sheet-emerald-ash-borer_0.pdf
2 // Urban Forest Threats
Figure 2.1 Projected urban forest threats (2010-2060) in urban Clackamas County
11 State of the Urban Forest Report | December 2022
2 // Urban Forest Threats
Air Temperature
and Aridity
Increased air temperature and aridity,
as a result of climate change, have been
identified as the second biggest threat
to trees in urban Clackamas County.
Oregon has been in drought since 2012.
Trees that are stressed due to increased
temperatures and drought are more
susceptible to secondary pests and
diseases, often leading to overall decline
and mortality. Examples of trees suspected
as particularly vulnerable to increased
temperatures and aridity in the Lake
Oswego area include bigleaf maple and
western redcedar.3 4
In response to a changing climate, many
communities are evaluating tree species
that may be better adapted to future
growing conditions.5
3 Oregon Department of Forestry. (2019). Why is my tree
dying? Western redcedar (Thuja plicata) [Fact sheet].
https://www.oregon.gov/odf/Documents/forestbenefits/
TreeDeclinesRedcedar.pdf
4 Oregon Department of Forestry. (2019). Why is my tree
dying? Bigleaf maple (Acer macrophyllum) [Fact sheet].
https://www.oregon.gov/odf/Documents/forestbenefits/
tree-declines-bigleaf-maple.pdf
5 City of Seattle. 2022. Urban Forest Management Plan.
Seattle, WA, City of Seattle Urban Forestry Core Team. 41p.
Development
Development is another major threat to
tree canopy and is projected to cause
a 10 percent decline in tree cover in
urban Clackamas County by the year
2060. Losses in tree cover are a result
of urban expansion into the rural and
unincorporated fringes of urban areas,
along with infill and increasingly dense
urban development within city limits.
Ice Storms
Ice storms are projected to be an increased
threat in the future.6 The February 2021 ice
storm illustrates the devastating impacts
ice can have on existing tree canopy.
Tree damage, including whole tree and
branch failures, caused significant property
damage, service disruptions, blocked
roadways, and caused park closures in Lake
Oswego. Although ice storms are relatively
infrequent weather events, their impacts to
tree canopy can be severe and long lasting.7
The City of Lake Oswego may be able to
monitor any long- term impacts from the
2021 ice storm using Lidar data in 2024-2025.
6 Campbell, John L.; Rustad, Lindsey E.; Driscoll, Charles
T.; Halm, Ian; Fahey, Timothy J.; Fakhraei, Habibollah;
Groffman, Peter M.; Hawley, Gary J.; Leuenberger, Wendy;
Schaberg, Paul G. 2020. Simulating Impacts of Ice Storms
on Forest Ecosystems. Journal of Visualized Experiments.
160: e61492. 15p. https://doi.org/10.3791/61492
7 City of Salem. 2022. Salem Tree Report. City of Salem,
OR, Public Works Department. 68p
Clearing downed trees after the 2021 ice storm
12 State of the Urban Forest Report | December 2022
2 // Urban Forest Threats
Wildfire
Wildfire is also projected to be an
increased future threat for Lake Oswego’s
urban forest. Lake Oswego has been
identified by the Oregon Department of
Forestry as a Community at Risk (CAR) due
in part to fuel loads in the forested areas
surrounding and within Lake Oswego.8
Historically, fire was a natural component
of Oregon’s forest ecosystems with more
frequent, lower intensity fires in the forest
understory. With fire suppression, fuels
build up in the understory and can result
in catastrophic fires that can burn and kill
entire trees and forests. Increased aridity
is also contributing to increased wildfire
risk. The Lake Oswego Fire Department
offers recommendations to reduce fuel
loads and create defensible space around
structures.9
8 The Oregon Department of Forestry and State Fire
Marshall’s Office are currently preparing updated
wildfire risk maps and risk prevention strategies under
SB 762 (2021).
9 Clackamas County. 2018. Clackamas County Community
Wildfire Protection Plan. Clackamas County, OR, Wildfire
Planning Executive Committee. 128p
Mountain Park Fuel Reduction and Land Resilience Project
In 2022, Oswego Lake Watershed Council
(OLWC), Mountain Park Homeowners Association
(MPHOA), and Oregon Department of Forestry
(ODF) began working to reduce the risk of
catastrophic wildfire and improve healthy forest
successional processes on 120 acres of private
urban forest in Lake Oswego. Other partners
include Clackamas Soil and Water Conservation
District, Lake Oswego Fire Department, and the
City of Lake Oswego.
Mountain Park is a local example of the Wildland
Urban Interface, where the intersection between greenspaces and residential property presents the
potential for ignition and spread of wildfire. Over $300,000 will be invested over the course of the
project to reduce hazardous fuel loads, address deferred maintenance issues, and improve forest
health. In a novel urban forest environment, woody invasive species such as holly, laurel, English
hawthorn, and sweet cherry can form a dense non-native understory. By removing weedy trees,
shrubs, and invasive vines such as ivy and clematis, the project reduces the risk of catastrophic
wildfire while also creating space for native species to thrive. Because the vegetation management
is selective and intentional, the project will reduce fuel loads and ladder fuels while improving the
health of our urban forest, habitat for wildlife, and ecosystem functions.
With support from community volunteers and natural resource professionals, native tree and
shrub species will be planted and managed to realize the vision of a healthy urban forest that
supports biodiversity, soil health, watershed health, and carbon sequestration. Visit the OLWC
and MPHOA websites to learn more about the Mountain Park Fuel Reduction and Land Resilience
Project and how you can get involved.
ODF crew removing invasive trees from a Mt. Park HOA natural area
13 State of the Urban Forest Report | December 2022
2 // Urban Forest Threats
Invasive Plants
Invasive plants include non-native trees,
shrubs, and vines with the capacity to
self-propagate and out-compete native
and other desirable plant species. English
ivy (Hedera helix), was identified in both
the 2007 Plan and 2009 Report as a major
threat to the City’s urban forest health. The
2007 report established goals specific to
eradicating English ivy. Since that time,
outreach, education, and volunteer efforts
have taken place through Arbor Month
events , Neighborhood Friends Groups,
Oswego Lake Watershed Council, and
public information including brochures on
the City’s website.
Other examples of invasive plants in the
Lake Oswego area include Himalayan
blackberry (Rubus armeniacus) and the
12 species of trees on the City’s invasive
tree list. Invasive plants are a threat to Lake
Oswego’s urban forest in two main ways:
1) directly by growing and smothering
the branches, leaves, and canopies of
desirable trees such as when English ivy
grows unmanaged on trees or in forests;
or 2) indirectly after invasive plants gain
a foothold in an area and prevent the
propagation and regeneration of diverse
natural forested ecosystems and replace
them with one or just a few species of
invasive plants.
Oswego Lake Watershed Council ivy removal Ivy growing up tree trunks
State of the Urban Forest Report | December 202214
This chapter summarizes the efforts that the City is taking to
promote tree stewardship and conservation, and the regulatory
programs related to urban forest management and the tracking of
tree removal and mitigation activities.
Tree Stewardship and Conservation Efforts
City Tree Activities in Parks and Public Right-of-Way (2017–2021)
The City is committed to planting trees in its parks and public right-of-way to
mitigate some of the urban forest threats and help maintain a healthy urban forest.
Lake Oswego Parks Department has nine recognized Friends Groups that lead
habitat restoration work parties throughout the year in coordination with Parks staff.
The Friends Groups are dedicated volunteers that support the City’s restoration
efforts in designated park natural areas by removing invasive species and planting
native species. From 2018 to 2022, more than 4,650 volunteers provided over 14,250
hours of habitat restoration and service in Lake Oswego’s park natural areas.
The number of trees planted by the City far exceeds the number of park and
street trees removed since the City started tracking this data in 2017 (Figure 3.1).
The appendix includes details on the permit type for tree removals and additional
information on forest management activities.
KEY FINDINGS
»The ratio of planted trees to removed trees by the City from 2017 to 2021 was about
18 to 1. 27,356 trees were planted and 1,535 trees were removed during that period.
»From 2017 to 2021, an average of 330 acres of park natural area were in active
restoration each year, with 327,661 native plants planted during that time.
3 // City Tree Stewardship and Regulatory Efforts
Figure 3.1 City tree planting and removal activity in public parks and rights-of-way, 2017-2021
15 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
Stewardship of Natural Areas
Healthy ecosystems support the health,
wellness, and safety of Lake Oswego
residents. The City has recognized this
and has a long history of planning for
projects that enhance parks and natural
areas. In 2011, the City Council directed
Lake Oswego Parks & Recreation (LOPR) to
prioritize English ivy removal from natural
area parks. LOPR was asked to redirect
$70,000 of general funding to support
ivy removal annually, which became the
Invasive Removal Program. This funding
was used to hire restoration contractors to
treat and remove ivy and other prioritized
invasive species. Through the LOPR 2025
Master Plan, the City’s natural areas were
evaluated and ranked on the basis of
condition and resource values. The Master
Plan established the initial framework to
guide City staff, contractors, and volunteer
restoration priorities.
In 2014 the City developed an updated
Sensitive Lands Ordinance in coordination
with Metro. Sensitive Lands regulated by
the City include wetlands, streams, riparian
areas, and upland forest stands. Updates
to the Sensitive Lands Ordinance reduced
regulations on private landowners with
upland tree groves, and increased riparian
area protections, with the promise that the
City would also increase restoration efforts
and protections on City-owned land. The
City Council directed $250,000 in annual
funding to support and expand ongoing
restoration efforts. This funding created the
Habitat Enhancement Program (HEP). The
HEP continued invasive removal efforts,
added native species planting projects,
and provided for ongoing maintenance.
Currently, HEP funds are used in the
following ways:
• City natural areas restoration
• Grant funding for local watershed
councils to support restoration work on
private land, often adjoining public land
• Use as matching funds for restoration
grant applications (leveraged to gain
grant funding)
• Purchase of plants for volunteer work
parties.
To date, Invasive Removal Program and
HEP funds have been used to enhance
31 public natural areas, including more
than 370 of the 460 acres of natural area
parks managed by the City. Funding has
also supported all three local watershed
councils with annual support for various
watershed restoration projects on private
lands. It should be noted that natural
areas management efforts are iterative
and often require several site visits over
2015 Dedication of Heritage Tree Number 34
16 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
several years to control noxious weeds and
establish native plant communities.
LOPR has also been instrumental in
developing master plans and restoration/
maintenance plans for several of the
natural area park properties (e.g., Iron
Mountain Park Master Plan [2017]; George
Rogers Park Master Plan [2002]; Cooks
Butte Park Management Plan [2008]; and
Woodmont Natural Park Master Plan [2017]).
In 2021, Lake Oswego voters passed Citizen’s
Initiative 3-568 to amend the City Charter
to include additional protections of natural
areas within the City. This initiative was a
grassroots effort to protect natural areas.
Backyard Habitat Program
The City contracts with the Backyard
Habitat Certification Program (BHCP), a
partnership between Portland Audubon
and Columbia Land Trust. The program
currently works on sites smaller than one
acre throughout much of urban and
suburban Clackamas, Clark, Multnomah,
and Washington counties. Technical
assistance and incentives are provided to
participating Lake Oswego residents and
organizations such as schools and HOAs
who wish to restore native wildlife habitat
in their backyards.
The BHCP focuses on the removal of
aggressive weeds, naturescaping with
native plants, stormwater management,
and wildlife stewardship. The latest Lake
Oswego BHCP report, published June 2022,
showed there are over 9,400 enrolled
properties, spanning nearly 2,100 acres
region wide, including 200 acres in Lake
Oswego. These properties are mostly
single-family residential lots, but also
include several multi-family dwellings and
public demonstration sites at schools and
places of worship.
Heritage Tree Program
The City’s Heritage Tree Program
was established in November 1997 to
recognize trees considered important
to the community because of unique
characteristics or values. The 2007 Report
included the celebration of heritage trees
as a goal for stewardship and education.
Since that time additional emphasis
has been placed on the Heritage Tree
Program, especially during Arbor Month
when dedication celebrations are held
for newly designated trees. Anyone can
nominate a tree or group of trees for
designation as long as the nomination
form is signed by the property owner. Lake
Oswego Code Chapter 55 states that the
Parks, Recreation and Natural Resources
Advisory Board is responsible for reviewing
all Heritage Tree nominations at a public
meeting and shall vote to designate trees
complying with designation requirements.
Nominations are reviewed by the board
annually in February or March and new
Heritage Trees are announced during April,
Arbor Month.
There are two main designation criteria:
1. The tree or tree grove is of landmark
importance due to age, size, species,
horticultural quality or historic
importance; and,
2. The tree is not irreparably damaged,
diseased, hazardous or unsafe, or
the applicant is willing to have the
tree treated by an arborist and the
treatment will alleviate the concern.
Here are some statistics as of April 2022:
• There are currently 41 designated trees
and groups of trees, including 27 located
on private properties and 14 located
on City-owned parks or the public
right-of-way. This includes two Heritage
Trees that have been cut down due to
catastrophic failures: an American elm
on 1st Street between B & C Avenues
and a redwood at 785 9th Street. Wood
from both trees was salvaged and is
being dried for future use.
17 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
• Of the 41 designated trees and groups of
trees, 20 distinct species are represented.
Douglas-fir, Oregon white oak, and
giant sequoia are most common. A
zelkova was designated in 2021.
The Heritage Tree Story Map was
published in 2019. It includes an interactive
map and listing of all the Heritage Trees
along with photographs, suggested
walking tours, a bike route, and more.
A goal of the 2007 Plan was to create
incentives for homeowners and builders
to protect trees. To support the long-term
preservation of designated Heritage
Trees, the City began offering grants from
the Tree Fund in 2022 to assist property
owners with costs of Heritage Tree care
and maintenance services performed by
qualified tree care specialists. Heritage
Tree Preservation Grant funding may be
used to diagnose, treat, manage and
care for designated Heritage Trees. Seven
grants have been awarded since the
program began, totaling $14,367.
Regulatory Efforts
Tree Code
The purpose of the Tree Code is to
regulate the removal of trees, encourage
and assist property owners in managing
large forested properties, and prescribe
preventative protection measures to avoid
damage to trees during site development
in order to preserve the wooded character
of the City of Lake Oswego and to protect
trees as a natural resource of the City.
Maintenance of the Tree Code is an
ongoing process, and the code has
been amended numerous times since its
adoption in 1971 to refine and expand the
regulations and processes as directed by
the City Council in response to community
concerns and values.
Since the first State of the Urban Forest
Report was published in 2009, some
significant amendments to the Tree Code
have been made. Most notably, in 2015
the City Council held an Urban Forestry
Summit with the public as well as focus
group discussions with arboricultural and
development professionals in order to
convene a community dialog on the Tree
Code and how it might be improved.
That effort resulted in the appointment
of an Ad Hoc Tree Committee charged
with reviewing the Tree Code and making
recommendations to the City Council.
In 2016, the Council adopted most of
the code amendments recommended
by the Ad Hoc Committee, which were
aimed at reducing the regulatory burden
of the Tree Code on residential property
owners, clarifying criteria, and streamlining
processes. Beyond code amendments, staff
also implemented recommendations from
the committee to improve public access to
pending Type II tree removal applications
and to provide resources on tree care and
maintenance, planting, and protection.
Other amendments to the Tree Code that
have been made since 2009 include the
addition of a Forest Management permit
type, which provides property owners
of large forested tracts a more flexible
process to manage their property in
accordance with urban forestry principles,
but still maintain the wooded character of
the city, and to strengthen and clarify tree
protection regulations. The appendix lists
and summarizes the major amendments
that have been made to the Tree Code
since the first State of the Urban Forest
Report was published in 2009.
Sensitive Lands Regulations
The City has taken steps to protect the
urban forest through implementation
of sensitive lands overlay districts (LOC
50.05.010) which delineate Resource
Protection (streams, wetlands, riparian
forest) and Resource Conservation (upland
forests) districts to protect and conserve
wildlife habitat and water quality. These
18 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
districts limit the development and
removal of canopy within them to ensure
these ecosystems function and provide
ecosystems services. In addition, Habitat
Benefit Area districts were created to
promote habitat-friendly development
through voluntary development incentives.
The City ensures that development
standards within these districts:
1. Protect and conserve wildlife habitat;
2. Protect and improve water quality;
3. Control and prevent water pollution
for the protection of public health and
safety;
4. Comply with federal laws including the
Clean Water Act and the Endangered
Species Act;
5. Comply with State Land Use Goal 5; and
6. Comply with Metro’s Urban Growth
Management Functional Plan.
The Sensitive Lands and Effective Stream
Shade sections of Chapter 4 (Urban Tree
Canopy Assessment) provide details on
the canopy cover within the Sensitive
Lands and the importance of preserving
and enhancing canopy to provide stream
shade for water quality.
Tree Removals
The City has been tracking tree removal
permit applications since 2014. Since 2017 the
City has also been tracking the number of
tree removals and mitigation trees planted.
Tree Removal Permit Applications by Type (2014–2021)
The number of permit applications
received, approved, and denied by
permit type have been tracked by the
City since 2014. It is important to note
that the number of permits is not a direct
correlation with the number of trees
that are removed. Multiple trees can be
removed from a single permit depending
on permit type. The number of permits is
telling of the types and quantity of activity
that are occurring throughout the City that
are triggering tree removal. The list below
details the activities that are associated
with each of the permit application types.
Type I: Up to two trees up to 15-inch trunk
diameter per year on residentially zoned
lots occupied by a single-family dwelling.
No limits on fruit tree removals. Special
restrictions apply, such as for trees in
sensitive lands.
Type II: Trees that do not qualify for other
tree removal permit types being removed
for landscaping or development purposes.
Hazard Tree: For trees that are high or
extreme risk according to an International
Society of Arboriculture Qualified Tree Risk
Assessor. Trees damaging private services
or public facilities may also be considered
hazard trees. Snag creation may be
required in Sensitive Lands to provide
wildlife habitat.
Emergency Permits: For emergency
situations such as a tree actively failing or
interrupting a utility service.
Invasive Permit: For the removal of trees on
the City’s Invasive Tree List.
Verification Permit: For trees previously
approved for removal through a land use
decision such as a subdivision or partition.
Topping Permit: Issued to utility providers to
allow pruning of trees to prevent conflicts
with overhead utilities.
Forest Management Permit: Allows tree
removal for the purposes of improving
forest health such as preventing
overcrowding of trees in a forested area.
Applies in a variety of contexts including
residential, recreational, and open space
properties.
19 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
Figure 3.2 shows the number of permit applications by type since 2014 in addition to the
percentage for each permit type. Note that all Type II permit applications are included in
the table, regardless of approval status. A complete table showing permit applications by
type including approved, denied, and withdrawn permits is available in the appendix.
Figure 3.2 Number of tree removal permit applications by type
KEY FINDINGS
»Type I tree removal applications
increased the most significantly, likely
based on the increase in the size
threshold for Type I trees. Hazard and
Emergency permit types increased
significantly in 2021 likely due to extreme
weather events including the President’s
Day ice storm.
»From 2014 to 2021, 90 percent of the
Type II permit applications were
approved or approved after being
modified, 1 percent were denied, and 9
percent were withdrawn.
»2021 had the highest number of permit
applications since tracking began in
2014. However, the following section
shows that the number of trees actually
removed was lower in 2021 than in 2017
or 2019.
20 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
Number of Trees Removed (2017–2021)
The City has been tracking the number of trees
removed since 2017 by permit type. Unlike the
previous section, these values represent the
number of trees, rather than just the number of
permits. Figure 3.3 shows the number of trees
removed per year including the percentage by
application type. For Type II applications, the
City also tracks the species of trees permitted
for removal. The number of trees removed per
year by application permit type is available
in the appendix (Table A.5). Table 3.1 displays
the top five tree species removed from 2017 to
2021 through Type II permits.
The count of trees permitted for removal is
not exact, and the actual number of trees
permitted for removal is slightly lower than
reported. This is because the City’s Type II
tree tracking software does not account for
partial approval of a tree permit when one
or more trees were withdrawn or denied
and the remaining trees were approved. For
these partial approvals, the original quantity
of trees listed in the application is counted
as being removed even if some trees in
the application were not approved. Partial
approvals are not uncommon, and staff
estimates that approximately 100 trees were
withdrawn or denied from partially approved
Type II applications between 2017-2021. This
estimate is based on the difference between
the number of trees removed and the number
Figure 3.3 Number of trees removed by permit application type, 2017-2021
Species Total trees removed from 2017–2021 Percent of total trees removed, 2017–2021
Douglas-fir 655 24%
Bigleaf maple 268 10%
Pine 153 6%
Other maple 139 5%
Cedar 89 3%
Other (94 other species)1,392 52%
TOTAL TREES REMOVED 2,696
Table 3.1 Top five species of trees removed through Type II permits, 2017–2021
21 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
of mitigation trees required during this time period, but also takes
into consideration that some trees permitted for removal required
increased mitigation that was not accounted for as described in the
next section.
KEY FINDINGS
»From 2017-2021, a total of 15,600 trees were permitted for removal,
of which 20 percent were Type I trees smaller than 15-inch
diameter, 24 percent were dead, 12 percent were hazardous or
emergency, 16 percent were invasive species, 17 percent were
Type IIs for landscaping or development, and 10 percent were
Forest Management, Verification or Topping permits.
»Douglas-fir was the most removed species each year, accounting
for 24 percent (655 trees removed) of the total 2,696 Type II permit
tree removals from 2017 to 2021.
Mitigation Tree Plantings for Type II
Tree Removals, 2017-2021
Type II tree removal applications require one or two new trees to
be planted as mitigation for each tree permitted for removal and
removal of native species trees requires native mitigation. Payment
into the City’s Tree Fund in lieu of planting is allowed only when staff
determines there is insufficient space on site to replant. From 2017 to
2021 the annual percentage of applicants allowed to pay into the
tree fund in lieu of planting was 9.6 percent. For the mitigation trees
planted, the City tracks species and whether the trees were native
or non-native species. The breakdown of mitigation trees from 2017
to 2021 is shown in Figure 3.4 on the next page. The top species by
mitigation type are shown in Table 3.2.
Species Total trees planted Percent of total trees planted
Dogwood 705 30%
Cedar/Cypress 421 18%
Maple 238 10%
Douglas-fir 193 8%
Oak 84 4%
Cascara 74 3%
Hemlock 60 3%
Fruit 58 2%
Pine 48 2%
Ash 28 1%
Magnolia 19 1%
Willow 17 1%
Alder 14 1%
Other 407 17%
TOTAL TREES PLANTED 2,373
Table 3.2 Top species of Type II permit mitigation trees planted, 2017-2021.
Species are grouped (e.g., all dogwood types grouped together).
The mitigation counts are not exact, and the actual number of
mitigation trees required is slightly higher than reported. This is
because removal of a tree identified as a “significant tree”1 for
development purposes requires two mitigation trees, but the City’s
Type II tree tracking software does not account for the additional
tree. City staff began tracking 2:1 mitigation manually in 2022 to
provide more accurate data in the future.
1 Significant Tree means a healthy, noninvasive tree over 15 in. DBH that is considered
significant to the neighborhood due to size, species, or distinctive character, or that is the
only remaining tree on a property.
22 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
Figure 3.4 Breakdown of mitigation trees planted, 2017-2021
23 State of the Urban Forest Report | December 2022
3 // City Tree Stewardship Efforts
KEY FINDINGS
»2,373 mitigation trees were planted between 2017-2021, of
which 65% were native species trees.
»Large stature trees such as Douglas-fir are being replaced by
smaller stature trees, primarily disease-resistant varieties of
native Pacific dogwood, likely due to lack of available planting
space with increased development density and limited species
options for small stature native trees. Large stature trees provide
greater economic and environmental benefits compared with
smaller stature trees when adequate growing space is available.
»Only 18 dogwoods (less than 1 percent of total trees removed)
were removed from 2017-2021 with Type II permits, but it was
the most popular mitigation tree planted. 705 dogwoods were
planted during this time, equivalent to 30 percent of all Type II
mitigation trees. The City should monitor mitigation tree species
mix to ensure adequate species diversity and consider expanding
the mitigation tree list to support a diverse urban forest.
»Payments were made to the City’s Tree Fund to mitigate the
removal of 229 trees that could not be planted on-site from
2017 to 2021 , or about 9.6 percent of total Type II mitigation
trees planted in this period.
CARBON DIOXIDE UPTAKE
$8.28
CARBON DIOXIDE UPTAKE
$2.05 1
Carbon Sequestered
97.1 lbs
Carbon Sequestered
24.06 lbs
Carbon Stored
2,170.74 lbs2
Carbon Stored
4,350.97 lbs2
STORMWATER MITIGATION
$4.94
STORMWATER MITIGATION
$11.01
Runoff Avoided
552.28 gal
Runoff Avoided
1,232.59 gal
AIR POLLUTION REMOVAL
$2.07
AIR POLLUTION REMOVAL
$7.62
Carbon Monoxide
0.36 oz
Carbon Monoxide
0.85 oz
Nitrogen Monoxide
1.83 oz
Nitrogen Monoxide
4.2 oz
Sulfur Monoxide
0.21 oz
Sulfur Monoxide
0.5 oz
1 As large trees mature, their rate of sequestration slows even though the amount of
carbon they store is higher than smaller trees.2 Total amount of carbon stored at full maturity.
Figure 3.5 i-Tree annual benefits comparison of a mature Pacific Dogwood versus a mature Douglas-fir.
Pacific Dogwood
Cornus nutlallii
40 feet tall 24-inch diameter
Douglas-fir
Pseudotsuga menziesii
200 feet tall 50-inch diameter
State of the Urban Forest Report | December 202224
This chapter summarizes the
Urban Tree Canopy (UTC) cover
assessment, regionally and
citywide, and within a series of
eight land classifications shown
in Figure 4.1. The purpose of this
assessment is to provide a snapshot
of the existing UTC cover to serve
as baseline information to inform
planning, management, and policy
decisions, and help the City monitor
change of the UTC over time.
4 // Urban Tree Canopy Assessment
Figure 4.1 Focus areas for UTC assessment, including metro region, citywide, and eight land classifications
CITYWIDE
METRO REGION
WATERSHEDS
BUSINESS DISTRICTS
NEIGHBORHOOD
ASSOCIATIONS
ROAD RIGHT-OF-WAY
(STREET TREES)
OUTDOOR
RECREATION AREAS
ZONING
CENSUS BLOCK GROUPS
(STREET TREE EQUITY)
SENSITIVE LANDS
25 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Urban Tree
Canopy Models
The City of Lake Oswego has been
developing a UTC model every 5 years
since 2009 using Lidar and aerial imagery.
A UTC height model is a map layer that
represents tree canopy location and height.
The City tracks canopy growth using the
UTC height model to understand this aspect
of urban forest health. The UTC models
discussed in this chapter were developed
using the latest Lidar flown in the region
from 2014 and 2019. The next regional Lidar
acquisition is expected in 2024, and an
update to this report would likely occur in
2025 or 2026 after the data is processed
and a new UTC model is developed.
This chapter makes use of UTC models
created by the City of Lake Oswego as
well as a regional UTC model developed
by Metro. Due to differing methodologies,
there are some variances in the percent
canopy cover reported in the Metro regional
model and the Lake Oswego UTC model
within the incorporated City Limits of Lake
Oswego. Both models used 10 feet as a
minimum height threshold to be included
in the UTC, and both reported an overall
accuracy of about 97 percent based on a
random sampling of points. All numbers
reported for acreage and percent UTC Figure 4.2 City-wide UTC Model. The 2019 UTC Model is depicted within the City including unincorporated areas within the USB that are included the analysis in this chapter. The map also shows the waterbodies that are excluded for area calculations.
cover in this chapter have the large waterbody areas removed so that the assessment is
based on coverage over land. The major waterbodies in Lake Oswego are the Willamette
River, Tualatin River, and Oswego Lake. The Metro model was only used for comparing
canopy to other cities in the region and was not used in any of the other assessments in this
chapter. Additional details about the methodology for developing the models in GIS and the
differences between the models can be found in the appendix. Figure 4.2 depicts the most
recent city-wide 2019 UTC model developed by the City of Lake Oswego and highlights the
level of detail captured in the model over the 2019 aerial imagery.
26 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Regional Canopy Analysis
The regional canopy analysis uses Metro’s UTC model from 2019 that spans three counties
and 24 incorporated cities within the Metro Planning Area. The region-wide model allows
for comparison amongst neighboring cities in the Portland-Metro area. It is important
to note that the regional model based on Metro’s 2019 UTC analysis reports a different
canopy cover than the City model for areas in the City of Lake Oswego. In the following
section of this report, the numbers reported in the Lake Oswego UTC model indicate a
higher percent canopy cover due to the aforementioned difference in modeling.
Figure 4.3 shows the canopy cover percent within the incorporated city boundaries based
on the 2019 Metro UTC model. The cities are arranged from left to right based on the highest
to lowest percent canopy cover. The map in Figure 4.4 shows the same values as the chart,
providing a visual on where the more densely canopied cities are situated across the metro
region. Lake Oswego, Durham, Rivergrove, and West Linn are the only four cities with over
40 percent UTC cover based on the Metro model and they are all neighbors. Portland has a
canopy cover of 32 percent which includes some very urbanized areas with minimal forested
areas along with some large dense canopy areas like Forest Park.
KEY FINDINGS
»Lake Oswego ranks second amongst
cities in the Portland Metro area for
percent canopy cover, and it leads cities
that are of comparable size.
Figure 4.3 Percent UTC cover for incorporated cities in the Metro area. 2019.
27 State of the Urban Forest Report | December 2022
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Figure 4.4 Map showing percent UTC cover for cities across the metro region, 2019.
28 State of the Urban Forest Report | December 2022
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Citywide Canopy Analysis
The Citywide Canopy Analysis examines UTC cover in the incorporated city limits of Lake
Oswego and the unincorporated areas within the Urban Services Boundary (USB) as
depicted Figure 4.6. The model excludes the large waterbodies including Oswego Lake, the
Willamette River, and the Tualatin River. Excluding the large waterbodies results in a more
accurate measurement of percent canopy cover and potential canopy cover.
Designation 2014 UTC Acres 2014 % UTC 2019 UTC Acres 2019 % UTC Total Land Acres
Incorporated City Limits 3,368 48.7%3,703 53.5%6,916
Unincorporated USB 508 47.7%561 52.7%1,066
TOTAL
(Incorporated + Unincorporated)3,876 48.6%4,264 53.4%7,982
Table 4.1 Acreage and percent UTC cover in incorporated and unincorporated areas of Lake Oswego, 2019.
Figure 4.5 Comparison of 2014 and 2019 UTC acreage and percent cover within the combined city limits and USB.
KEY FINDINGS
»The total acreage of UTC increased from
3,876 acres in 2014 to 4,264 acres in 2019.
Based on a total city-wide land area of
7,982 acres, that equates to a percent
canopy cover change from 48.6 percent
in 2014 to 53.4 percent in 2019, a 4.8
percent increase.
»There was a small difference between
the percent canopy cover within
the incorporated city limits and the
unincorporated areas within the USB.
29 State of the Urban Forest Report | December 2022
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Figure 4.6 Lake Oswego city limits and urban services boundary (USB).
30 State of the Urban Forest Report | December 2022
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UTC Height Classes
In addition to UTC cover, the city-wide
analysis also evaluated the UTC height
groups (Table 4.2 and Figure 4.7) based on
guidance provided in the City’s Right Tree in
the Right Place publication. The publication
identifies short, medium, and tall zones that
correlate with planting guidance for mature
tree height and distance from power lines.
The document further provides a list of
tree species organized by approximate
mature height and spread, tree shape,
recommended planting area needed,
and other useful information for choosing
the right species. By creating height
classifications in the UTC model based on
Right Tree in the Right Place, future analysis
can quantify potential planting capacity
in Lake Oswego and identify potential
locations for planting the right type of tree
based on space available. For the purposes
of the analysis, the Tall Zone identified in
the Right Tree in the Right Place report
was broken down into three separate tall
categories for UTC height analysis to also
highlight where the tallest canopy stands
are distributed throughout the city.
Figure 4.7 Acreage of canopy based on 2014 and 2019 UTC height classes.
UTC Height Class 2014 UTC Acres 2019 UTC Acres 2014 to 2019 change in acres 2014 to 2019 percent change
Combined Tall Zones (over 50 ft)2,384 2,440 56 2%
Very Tall Zone (over 120 ft)213 252 38 18%
Tall Zone (80-120 ft)958 996 38 4%
Medium-Tall Zone (50-80 ft)1,212 1,192 -20 -2%
Medium Zone (25-50 ft)970 1,037 67 7%
Short Zone (10-25 ft)523 787 265 51%
TOTAL UTC 3,876 4,264 388 10%
Table 4.2 Height classes for the UTC analysis
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4 // Urban Tree Canopy Assessment
Tree Size Distribution
Looking at the distribution of canopy height
classes raises the question, “What is the
ideal distribution of tree sizes?” While there
is no single answer to this question, research
studies generally recommend a distribution
with most trees in the young (short) size class
and the fewest trees in the mature (very
tall) size class. The purpose of a distribution
skewed towards the young size class is for
managing forest succession over time. This
allows young trees to replace mature trees
as they decline, die, or are removed due to
hazard risk potential. Table 4.3 includes an
“ideal” size class distribution from a widely
cited research study that recommends a five
percent distribution in the largest size class
and 40 percent distribution in the smallest
size class. Lake Oswego’s tree canopy study
measured tree height rather than trunk
diameter (DBH), which was the metric used
for size class distribution in the cited research
study. Therefore, the authors converted
tree height to DBH in the table as further
explained in the footnotes.
Size Classes (DBH)1
Canopy Height Class Rough Fit using Author’s Estimate2
Ideal % Distr. 2014 2019
over 35 inches Very Tall Zone (over 120 feet)5%5.5%5.9%
24 inches to 35 inches Tall Zone (80-120 feet)25%24.7%23.3%
Up to 24 inches3 Short to Tall Zone: (10-80 feet)70%69.8%70.8%
6 inches to 24 inches Medium to Tall Zone: (25–80 feet)30%56.3%52.3%
below 6 inches Short Zone (10-25 feet)40%13.5%18.5%
1 Millward, A.A.; Sabir, S. Structure of a forested urban park: Implications for strategic management. J. Environ. Manag.
2010, 91, 2215–2224.
2 This is a rough fit of the DBH size class distribution discussed in Millward and Sabir converted to the Lidar tree heights
measured in this canopy analysis by the project team ISA-certified arborists. DBH to tree height conversions were based
on Douglas-fir species, which is estimated by the ISA-certified arborists to be the dominant species in the study area.
3 As an alternative, the short to tall zones are combined since Lidar tree heights below 10 feet were not measured in this
canopy analysis and therefore likely did not capture a significant percentage of trees below 6” DBH.
Table 4.3 Size class (DBH) and rough fit UTC height class with recommended ideal distribution and
actual percent UTC from 2014 and 2019 models.
KEY FINDING
»In terms of tree height correlated
to diameter, the City's size class
distribution closely matches
recommended ideal size class
distributions. However, in order to
maintain the ideal distribution over time,
it is important to plant a diverse mix of
tree species, including species capable
of becoming tall and very tall trees
where growing space allows.
The results of this analysis indicate that
Lake Oswego currently has a mix of tree
sizes that closely correlates to the ideal size
class distribution. However, this analysis
assumes that trees in the smaller sizes
classes have the capacity to become
trees in the larger size classes, which may
not be the case if small stature trees such
as dogwood species are relied upon as
replacement species for large stature trees
such as Douglas-fir.
32 State of the Urban Forest Report | December 2022
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Figure 4.8 City-wide 2019 UTC height class map.
33 State of the Urban Forest Report | December 2022
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Evergreen and Deciduous
Distribution
1 Santamour, Frank S., Jr. 1990. Trees for Urban Planting:
Diversity ,Uniformity , and Common Sense. Proc. 7th Conf.
Metropolitan Tree Improvement Alliance (METRIA) 7:5765.
In addition to citywide canopy cover and
height, this report shows the distribution of
canopy by evergreen and deciduous type.
This analysis is based on Metro’s 2014 UTC
model, which classified leaf-off and leaf-on
imagery from 2012 and 2014. Metro has not
been completed the analysis for more recent
versions of UTC models at the city or regional
levels. Figure 4.9 displays the percent
canopy by classification and the spatial
distribution across the city. Historically, urban
forest managers have strived for a diverse
urban forest that meets the “10-20-30” rule.1
The goals of the “10-20-30” rule are that no
more than 10 percent of the urban forest is
represented by any one species, 20 percent
by any one genus, and 30 percent by any
one family. The goals for having a diverse
urban forest include resilience to pests and
disease outbreaks, resistance to losses from
climate change, as well as aesthetic reasons
including visual interest. The evergreen and
deciduous distribution provides limited
information on species diversity, so a future
study with field sampling would be required
to evaluate the diversity and species mix
of the urban forest. The evergreen and
deciduous mix may be useful in drawing
inferences as to relative maturity of certain
upland forest types and the location of
certain forest types such as oak woodlands
and forested wetlands. A future study would
be needed to more accurately categorize
forest types and maturity throughout
the city, but it could be useful in ongoing
management including appropriate tree
mitigation and planting based on forest
conditions. Native forest types in the Lake
Oswego area typically include:
Douglas-fir forest: Dominated by coniferous
species at maturity, including Douglas-fir,
western redcedar, western hemlock, and
grand fir. Earlier successional species
including red alder and bigleaf maple
dominate in more recently disturbed areas
impacted by logging, development, or
fires.2 An example of a mature Douglas-fir
forest includes the lower portion of Iron
Mountain Park. An early successional
example is Springbrook Park which is
dominated by red alder and bigleaf maple.
Mixed coniferous/deciduous riparian forests: Located along streams with
periodic flooding. Species adapted to these
conditions include western redcedar, red
2 City of Portland. 2016. Portland Plant List. City of Portland,
OR, Bureau of Planning and Sustainability. 202p
alder, bigleaf maple, black cottonwood,
Oregon ash, and willows. Springbrook
Creek includes riparian forest types
throughout its corridor.
Mixed deciduous forests: Located along
dry slopes dominated by species such
as Oregon white oak and bigleaf maple.
The upper bluffs along Iron Mountain
Park include mixed deciduous forests with
Oregon white oak that thrive along the dry,
south-facing slopes.
Deciduous forested wetlands and floodplains: Soils are saturated for much
of year and support species including
Oregon ash, black cottonwood, red alder,
and willows in the more frequently flooded
areas. Slightly drier areas on higher ground
support Oregon white oak, bigleaf maple,
and western redcedar. Examples of this
forest type can be found at Bryant Woods
Nature Park and within natural areas in the
Westlake Neighborhood.
34 State of the Urban Forest Report | December 2022
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Figure 4.9 City-wide distribution of UTC by Type (2014 Metro UTC Model). Model accuracy of 88% was reported by Metro.
KEY FINDINGS
»The urban forest has a
relatively even mix of
evergreen and deciduous
canopy cover. Future studies
would be required to map
and assess species and age
class diversity.
»This type of information
may be valuable for
future successional forest
management planning
to maintain and enhance
canopy cover and urban
forest benefits.
35 State of the Urban Forest Report | December 2022
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Neighborhoods
The Tree Canopy Height model was assessed for 29
neighborhoods in Lake Oswego. Canopy cover change was
assessed from 2014 to 2019 within the canopy height classes.
Mapping the distribution and change of UTC across the height
classes provides the ability to identify:
• Where are more small trees being planted and how quickly
are those trees growing?
• Where is the loss of tall trees occurring?
Table 4.4 Neighborhood association percent UTC cover from 2014 and 2019 within height classes.
Table 4.4 lists the neighborhoods in order based on greatest
percent UTC cover in 2019 to lowest percent UTC cover. The table
also highlights the overall total UTC percent in 2014 and 2019 and
the percent cover and change within each height zone. Several
neighborhoods experienced a decrease in canopy cover in the
medium-tall zone and the tall zone. The decrease in canopy cover
may be due to tree removal or loss in some cases, but there is also
movement between height zones from year to year as trees grow
into a new height class. The City can use canopy change maps
from 2014 to 2019 to determine where canopy loss is occurring.
36 State of the Urban Forest Report | December 2022
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Figure 4.10 Percent UTC from the 2019 model by neighborhood association. Darker green areas indicate higher percent UTC cover.
KEY FINDINGS
»Overall canopy cover
increased in all neighborhoods
from 2014 to 2019.
»A substantial portion of the UTC
increase across neighborhoods
occurred in the Short Zone
(10- to 25-foot) canopy height
class. This is largely the result
of younger trees reaching the
10-foot height minimum to
be included in the UTC model
sometime between 2014 and
2019, and also horizontal crown
growth of individual trees
especially street trees and
parking lot trees.
»Five neighborhoods showed a
decrease in canopy across the
tall zones representing trees
over 50 feet. The largest loss in
canopy over 50 feet occurred
in First Addition-Forest Hills,
Birdshill, and Forest Highlands.
37 State of the Urban Forest Report | December 2022
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Zoning
The City can look at UTC cover across zoning classes
to understand how land use and development type
impact the urban forest. For the purposes of this study,
zoning codes were grouped into generalized zoning
classes reflective of land use function.
Figure 4.11 Percent 2014 and 2019 UTC cover by zoning class.
KEY FINDINGS
»An overall increase in canopy cover occurred across
each zoning class from 2014 to 2019.
»The highest percent increase was in the Residential-
Medium Density Zones.
»Public functions zoning had the lowest percent
of cover. This zone is intended for public uses
such as government services, education, and
similar activities. One major function of the zone
is to support recreational uses, so large areas are
dedicated to school sports fields without tree canopy.
»The greatest increase in canopy in the residential
zones was within the short height category. See Table
4.6 on the following page.
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Table 4.6 UTC by zoning class across UTC height classes. The tall classes have all been combined into a single class for trees over 50 feet.
Table 4.5 Zoning class and 2019 percent UTC cover. Note that the sum of the total land acres is not equal to the total land acres of the incorporated city limits. This is because
there are small tracts of land throughout the city that are not part of the zoning layer
Zoning Class Zoning Code Total Land Acres 2014 UTC Acres 2019 UTC Acres 2014 % UTC 2019 % UTC
Commercial CI, GC, HC, NC 277 97 105 35.1%37.8%
Industrial I, IP 147 42 46 28.8%31.6%
Mixed Use CR&D, EC, MC, NC, OC, WLG,
other combined zone codes 403 120 143 29.7%35.5%
Park and Natural Area PNA 727 583 599 80.1%82.4%
Public Functions PF 236 54 60 23.0%25.2%
Residential Low Density R-7.5, R-10, R-15 4,046 2,018 2,231 49.9%55.1%
Residential Medium Density R-5,R-6, R-DD 670 277 320 41.4%47.8%
Residential High Density R-0, R-2, R-3, R-W 396 174 195 43.8%49.2%
39 State of the Urban Forest Report | December 2022
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Figure 4.12 Zoning class and 2019 percent UTC cover.
40 State of the Urban Forest Report | December 2022
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Business Districts
The business districts in this analysis are based on employment centers, town
centers, neighborhood villages, and commercial corners that were defined in the
Vision 2035 community visioning process that supported the City of Lake Oswego
Comprehensive Plan 2013. According to the Comprehensive Plan, these mixed-use
areas were identified to accommodate future growth based on existing zoning
while maintaining Lake Oswego’s character and design quality.
Figure 4.13 Percent 2014 and 2019 UTC cover by business district.
KEY FINDINGS
»A net increase in canopy occurred across the
business districts while still accommodating
development and densification.
»The UTC percent canopy across the business
districts was 32.9% in 2014 and 37.6% in 2019.
41 State of the Urban Forest Report | December 2022
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Figure 4.14 Business district and 2019 percent UTC cover.
42 State of the Urban Forest Report | December 2022
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Outdoor Recreation
and Conservation Areas
Metro maintains GIS data for Outdoor
Recreation and Conservation Areas
(ORCA) across the region. These areas
can be either public or private lands
and are classified by Metro based on
general use. The map in Figure 4.16
displays the types of sites that are
included in the dataset. Typically, there
is a lot of potential in these areas to
protect existing canopy or make use of
these areas for canopy enhancement.
Data on City Parks and Natural Areas
within the Urban Services Boundary
(USB) is also provided for comparison.
Figure 4.15 2014 and 2019 UTC acreages by ORCA land type. Includes City-managed parks and natural areas.
ORCA Classification Total Land Acres 2014 UTC Acres 2019 UTC Acres Change in UTC Acres 2014 % UTC 2019 % UTC Change in % UTC Cover
Cemetery 7.9 1.8 2.2 0.4 23.1%28.1%4.9%
Golf Course 157.9 38.9 37.4 -1.5 24.6%23.7%-0.9%
Home Owner
Association 256.0 196.2 206.5 10.3 76.6%80.7%4.0%
Other1 104.5 71.0 74.6 3.6 68.0%71.4%3.4%
School 235.1 56.5 62.5 6.0 24.0%26.6%2.5%
Park and/or
Natural Area 695.6 570.8 584.7 13.8 82.1%84.1%2.0%
City-Managed
Park/Natural Area2 440.0 343.2 356.4 13.2 78.0%81.0%3.0%
Table 4.7 2014 and 2019 UTC by ORCA Classification and
City Managed Parks and Natural Areas.
1 “Other” category in the ORCA layer includes vacant
parcels not specifically designated for any other type
or unknown. These include privately owned plats,
transportation corridor buffers, and trail/path parcels
not large enough to be part of a park or natural area.
2 The CIty-managed Parks and Natural Areas does not
include lands outside of the USB that the City manages.
Examples are Lusher Farm, Stevens Meadows Natural
Area, and Sunny Slope Open Space. The public golf
course is included under Golf Course, not City-Managed
Parks/Natural Areas.
43 State of the Urban Forest Report | December 2022
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Figure 4.16 ORCA land type and 2019 percent UTC cover. Hatched areas display the City-managed Parks and Natural Areas. City-managed parks outside of the USB are not included.
KEY FINDINGS
»An increase in UTC occurred in
each of the categories except for
golf courses.
»The ORCA Parks and Natural
Areas category has a greater
percent UTC and total acreage
compared to the City-managed
Parks and Natural Areas due to
the inclusion of Tryon Creek State
Natural Area.
»The Parks and Natural Areas
managed by the City showed
an increase of 13 acres and an
increase of 3 percent in UTC Cover.
The efforts of the City within parks
are highlighted under City Tree
Planting Activities.
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Road Right-of-Way / Street Trees
Tracking UTC cover within the road right-of-way is an efficient way to quantify street
trees city-wide and track change over time. The earlier chapter on Urban Forest Benefits
summarized the positive environmental, social, and economic functions that trees
provide city-wide. To help quantify the coverage of street trees, this analysis looks at
UTC cover within the road right-of-way and the percent cover overhanging paved road
surfaces based on a GIS land cover layer. The UTC within the road right-of-way is used
to approximate the overall cover of street trees and measure change over time. UTC
overhanging paved road surfaces includes tree canopy that is directly over the road
surface, which provides some of the benefits like reducing heat island effects, encouraging
trips by walking where pathways exist, and intercepting rainfall.
Lake Oswego street trees include all trees located within public rights-of-way. The
increase in canopy cover within the road right-of-way is attributed to planting new street
trees, as well as canopy and height growth of existing street trees over time. The image
in Figure 4.20 on page 46 shows the UTC change model from 2014 to 2019 with two
example locations that represent canopy and height growth. This location highlights the
potential for increased canopy cover within the right-of-way between natural growth and
planting of new street trees.
KEY FINDINGS
»The canopy increased by 53 acres within
the street right-of-way city-wide from
2014 to 2019.
»Research shows that an attainable goal
for coverage overhanging paved roads
and sidewalks is 25 percent for typical
cities.1 The City is meeting that mark
based on the 2019 UTC cover over road
surfaces of 25.5 percent.
1 Maco, S.E.; McPherson, E.G. 2002. Assessing canopy
cover over streets and sidewalks in street tree
populations. Journal of Arboriculture. 28(6): 270-276.
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Figure 4.17 Detailed view of the 2019 UTC model within the road right-of-way and the portion
of the UTC overhanging the paved road surface
Figure 4.18 2014 and 2019 UTC city-wide cover distribution of UTC
across height classes within the road rights-of-way city-wide.
Figure 4.19 2014 and 2019 UTC acres and percent UTC overhanging
paved road surfaces.
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Figure 4.20 Location 1 - At the location within the red circle, crowns of existing trees have grown outward, producing more shade and mitigating more stormwater runoff. Location 2 - At the location on the right in the red box, existing trees have reached the 10-foot minimum to be captured in the model. The callout box shows the trees at that specific location in Google Street View from 2012 and 2019. Trees that have been planted since 2014 that meet the 10-foot minimum height requirement would also have this contribution in the model.
47 State of the Urban Forest Report | December 2022
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Street Tree Equity—Census Block Groups
By measuring street tree density at the US Census block group level, we can understand
some of the socioeconomic, health, and climate implications of street tree canopy
distribution. In many cities, a map of tree canopy deficit correlates closely with a map
of historically underserved populations, including racial minorities and low-income
households. The City was interested in understanding whether similar inequities existed
in Lake Oswego and adapted the American Forests “Tree Equity Score” tool3 to map tree
equity based on total UTC cover within the road right-of-way.
The result of the tool is a Tree Equity Score, which can range from a score of 1 to 100. A lower
Tree Equity Score indicates a greater priority for closing the tree canopy gap, and a score of
100 indicates that tree equity has been achieved based on a benchmark UTC percent cover
of 40 percent within the right-of-way. It should be noted that the 40 percent benchmark
is typically established as the overall goal for a block group, not specific to the road right-
of-way. The City chose to focus on mapping tree equity based on street trees because of
the social and economic benefits they provide to a community. The score is based on the
relationship between the UTC percent cover and an Equity Priority Score based on the
following characteristics:
Low Income: Less than two times the federal poverty level
Employment: Unemployment rate
Race: Percentage of people who are not white non-Hispanic
Age: Ratio of seniors and children to working-age adults
Climate: Urban heat island severity
Health: Prevalence of poor mental, physical, respiratory, and cardiac health (composite
index)
Details on the methodology and the full block group level results within the city can be
found in the appendix. The map in Figure 4.21 shows the Tree Equity Score for the block
groups city-wide based on canopy within the road rights-of-way.
3 Tree Equity Score. American Forests, 2021. https://www.treeequityscore.org/
KEY FINDINGS
»50% of the census block groups in the
City have achieved Street Tree Equity
based on the 40% benchmark UTC.
»The majority of the block groups
with the lowest tree equity score are
located along the west side of the city
and have significant portions that are
unincorporated.
»The block groups with a 100 Tree Equity
Score match up with low-density
residential zoning and parks and natural
areas.
48 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Figure 4.21 Tree Equity Score based on Equity Priority and 2019 UTC within the road rights-of-way. A score of 100 indicates that Tree Equity has been achieved based on a benchmark UTC percent cover of 40% within the right-of-way.
49 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Watersheds
Tree canopy is analyzed within watersheds to identify the distribution of tree canopy as
it relates to stormwater mitigation and water quality. Watersheds are delineations of the
areas that drain to the major waterbodies in Lake Oswego. The tree canopy improves
stream quality and watershed health primarily by decreasing the amount of stormwater
runoff and solar radiation that reach these waterbodies. By looking at UTC cover within
the city’s watersheds and identifying gaps in canopy coverage, the City can begin to
identify potential areas for forest restoration for improving water quality.
Watershed Total Land Acres 2014 UTCAcres 2019 UTCAcres
Increase in UTC Acres from 2014 to 2019 2014 % UTC 2019 % UTC
Oswego Lake 2,738 1,323 1,481 158 48.3%54.1%
Springbrook Creek 1,242 663 720 57 53.4%58.0%
Tryon Creek 1,241 676 694 18 54.4%55.9%
Tualatin River 1,722 718 814 97 41.7%47.3%
Willamette River 1,036 495 553 58 47.8%53.4%
Totals1 7,979 3,874 4,262 388 48.6%53.4%
Table 4.8 2014 and 2019 UTC acreage and percent cover by watershed.
1 Totals shown in this table do not align exactly with Table 4.1 which shows the total incorporated and unincorporated areas
due to minor inconsistencies in the delineation of Oswego Lake.
KEY FINDINGS
»Each of Lake Oswego’s five watersheds
showed an increase in canopy cover from
2014 to 2019.
»The Tualatin River Watershed has the
lowest percent canopy cover, although it
showed a 5 percent increase from 2014 to
2019.
50 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Figure 4.22 Watersheds in Lake Oswego.
51 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Sensitive Lands
Figure 4.23 and Figure 4.24 show the
UTC within the City’s Sensitive Lands
districts. The Regulatory Efforts section of
Chapter 3 highlights the importance of the
UTC within Sensitive Lands for supporting
habitat and shading streams to keep
water temperatures cool for fish and other
aquatic species.
Figure 4.23 2019 UTC distribution across height classes for Sensitive Lands city-wide. The chart shows the acreage within each height category and above the bar the total acreage and percent UTC by year.
KEY FINDINGS
»UTC cover increased across all Sensitive
Lands from 87 percent in 2014 to 89
percent in 2019.
»Within the Riparian Protection (RP)
areas, UTC increased 20 acres.
»Within the Resource Conservation (RC)
areas, UTC increased 2.8 acres. Nearly
98% of RC areas are covered by canopy
and about 88% of the RC zone’s total area
is covered by canopy over 50 feet tall.
»Within the Habitat Benefit Areas (HBA).
UTC increased overall by 0.5 acres.
However, canopy over 50 feet tall
decreased by 0.5 acres.
52 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Figure 4.24 Sensitive Lands and 2019 Percent UTC cover. Canopy within the RP areas provide shade for the streams
53 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Effective Stream Shade
Canopy within the Sensitive Lands areas, particularly the Resource
Protection areas, is important for shading streams and cooling
the water. As part of the City’s Total Maximum Daily Load (TMDL)
Implementation Plan and stormwater permitting requirements,
the City measured effective shade for all streams city-wide using
the 2014 and 2019 UTC models and used an Oregon Department
of Environmental Quality (DEQ) program called HeatSource to
determine compliance with effective shade targets. Elevated
stream temperatures negatively impact salmonid species and
have detrimental consequences to riparian habitat and watershed
health. DEQ determined that increased solar radiation from
disturbed or removed riparian vegetation, including trees, is the
largest contributor to elevated temperatures in small streams
without a point source discharge.
Figure 4.25 shows the average effective stream shade by
watershed based on the 2014 and 2019 UTC in comparison with
shade targets that are established by DEQ based on stream
channel width and orientation. (Note that the chart is displaying
percent effective shade, rather than percent UTC cover.) The results
show that improvement has been made toward achieving the
shade target goals in all watersheds except Tryon Creek, which
already exceeds the shade target standard. The map in Figure 4.26
shows which stream segments in the City are meeting shade
targets and which have a shade target deficit. This information is
useful for the City in determining stream-adjacent areas that would
most benefit from canopy protection or restoration. The City’s TMDL
Implementation Plan provides greater detail on the stream shade
analysis, technical process, and results.
Figure 4.25 Average effective shade by watershed based on 2014 and 2019 UTC and the effective shade target determined by DEQ based on stream width and orientation.
54 State of the Urban Forest Report | December 2022
4 // Urban Tree Canopy Assessment
Figure 4.26 Effective stream shade target deficit for all streams and open channels city-wide based on the 2019 UTC HeatSource results. The point colors, as defined in the map legend, show the degree to which segments of streams are meeting shade targets.
State of the Urban Forest Report | December 202255
This section describes how
much carbon Lake Oswego’s
greenspaces, including trees,
are storing and how much more
carbon might be stored if the urban
forest is expanded. The Carbon
Sequestration Tool (CST) models
the carbon sequestration benefits
in a simple map-and-spreadsheet
based tool.
Explanation of Carbon Sequestration
Trees play an important role in capturing and storing (also described as sequestering)
carbon dioxide (CO2). CO2 is the primary greenhouse gas (GHG) emitted through human
activities such as burning fossil fuels for transportation and energy that contribute to
climate change. Healthy urban forests, including trees and soil, absorb and sequester
carbon and provide significant and cost-effective opportunities to reduce GHG emissions.
Trees are considered resilient carbon sinks—meaning they sequester carbon through
photosynthesis and store it in their leaves, trunks, branches, and roots for long periods of
time so that it is not released into the atmosphere. Carbon is sequestered in soil by plants
through photosynthesis and can be stored as soil organic carbon (SOC).
5 // Carbon Sequestration
56 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
The Carbon Sequestration Tool
Using carbon sequestration modeling, we can estimate how much
carbon Lake Oswego’s greenspaces including trees are storing, and how
much more carbon we might be able to sequester through tree planting
strategies. In order to estimate this, a carbon sequestration tool (CST) was
created using a GIS-based map and a spreadsheet model that estimates
how much more carbon could be sequestered through tree planting on
public land.
The CST measures Lake Oswego’s existing carbon—the carbon currently
sequestered both below ground (in the soil) and above ground (in
organic matter such as grasses, shrubs, and trees)—and the future carbon
sequestration potential of planting trees.
A mature live tree can absorb more than 48 pounds of carbon dioxide,
which is permanently stored in its fibers until a physical event like fire or
decomposition releases it back into the atmosphere. Maintenance and
preservation of existing trees will ensure this carbon storage into the future.
KEY FINDINGS
»The City of Lake Oswego is currently storing approximately
202,291 MgC above ground and 327,809 MgC below
ground, for a gross total of 530,100 MgC in the soils and
plants of Lake Oswego.
»The amount of carbon currently being stored in the plants
and soils of Lake Oswego is equivalent to:
▶The GHG emissions from 418,808 gasoline-powered
vehicles driven for one year, or
▶The CO2 emissions from 378,195 homes’ electricity
use for one year
»By the acre, the model estimates that Lake Oswego’s trees
are currently storing approximately 27.5 MgC per acre.
By comparison, in a study of tree benefits by the City of
Seattle, it was estimated that trees in Seattle on average
are storing 9.9 MgC of carbon per acre based on the
city-wide average canopy density and species mix.1
»An acre of land with 50% canopy cover (the approximate
city-wide average) sequesters:
▶The equivalent to the GHG emissions from 21.7
gasoline-powered passenger vehicles for one year, or
▶The equivalent to CO2 emissions from 19.6 homes’
electricity use for one year.
1 Seattle’s Forest Ecosystem Value Report. 2012. https://www.seattle.gov/
documents/Departments/Trees/Mangement/EcoSystem/Seattles_Forest_
Ecosystem_Values_Report.pdf
Source
Total Acres of Cover Type
Average Megagrams of Carbon (MgC) Stored per Acre Total MgC Stored
Below Ground (Soil)7,336 44.7 327,809
Above Ground (Plants)4,920 41.1 202,291
Grasses 763 0.2 157
Shrubs 451 0.9 402
Small Trees 1,592 33.5 53,326
Large Trees 2,113 70.2 148,406
CITY-WIDE TOTAL N/A N/A 530,100
Table 5.1 Lake Oswego’s existing carbon storage profile for plants and soil. Totals and averages are based on the existing carbon storage of each land cover type. Small trees are considered 10 to 50 feet and large trees are taller than 50 feet. Total acres and average MgC are not quantified city-wide because mapped areas of soil and plants are overlapping.
57 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
Figure 5.1 Megagrams of above-ground carbon per acre by parcel for the City of Lake Oswego.
58 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
Figure 5.2 Megagrams of below-ground (soil) carbon per acre by parcel for the City of Lake Oswego.
59 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
Test Scenarios
Test scenarios were used to measure the future carbon
sequestration potential of planting trees. Two tree planting strategies
were modeled using the CST to estimate their carbon sequestration
potential: Urban Forest Expansion and Street Tree Planting.
The Urban Forest Expansion strategy focuses on increasing tree
canopy outside of the public right-of-way in areas such as parks
and open spaces. The trees that can be planted in these areas
generally have fewer constraints (such as narrow planting strips
and overhead high voltage wires) than street trees in terms of the
size and species of tree that can be planted. Two levels of intensity
of this strategy were modeled: one at a planting rate of 30 trees per
acre, which represents an area with a lower density of trees that
might have other uses like sports or other recreation; and one at a
planting rate of 60 trees per acre, which represents an area with a
higher density of trees that would function more like a natural area.
The Street Tree Planting strategy explores planting street trees
that are primarily in the public right-of-way, such as parking
strips and medians, or adjacent to a street in unimproved rights-
of-way. This type of planting is generally more constrained than
Urban Forest Expansion.
URBAN FOREST EXPANSION
ON A 4.69 ACRE CITY-OWNED LOT
These scenarios explore the carbon sequestration benefits of tree
planting on publicly owned land. The test lot is a 4.69-acre parcel
that is owned by the City of Lake Oswego. The current use is a
park, River Run Park. The park was identified in a recent analysis
as having a stream shade target deficit (lack of trees) along a
small tributary to the Tualatin River that runs through the park and
could benefit from tree planting.
The Urban Forest Expansion strategy includes two rates of
application to reflect two different levels of tree density: one more
dense (Scenario 1) that would function as a forested natural area;
and one less dense (Scenario 2) which would be applied in areas
that are used frequently for sports or other recreation. The high
application rate for Scenario 1 of planting 60 trees per acre is
estimated to sequester 9.43 MgC/acre/year until peak sequestration
is reached. The lower application rate for Scenario 2 of planting 30
trees per acre is estimated to sequester 4.72 MgC/acre/year.
Figure 5.3 Aerial image of 4.69-acre lot
60 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
–SEQUESTRATION BENEFITS–
SCENARIO 1 // Dense Planting Rate: If all 4.69 acres of this lot were
planted at a rate of 60 trees per acre over a 10-year period, the
carbon sequestration benefit would be:
143.7 MgC by 2040
1,413.7 MgC by 2070
1,745.5 MgC by 2150
By 2040, the trees planted would sequester the equivalent to:
▶Emissions from 114 gasoline-powered passenger vehicles
driven for one year, or
▶The CO2 emissions from 103 homes’ electricity use for one year.
SCENARIO 2 // Less Dense Planting Rate: If all 4.69 acres of this lot
were planted at a rate of 30 trees per acre over a 10-year period,
the carbon sequestration benefit would be:
71.8 MgC by 2040
706.9 MgC by 2070
872.7 MgC by 2150
By 2040, the trees planted would sequester the equivalent to:
▶Emissions from 57 gasoline-powered passenger vehicles
driven for one year, or
▶The CO2 emissions from 51.4 homes’ electricity use for one year.
Costs
Trees provide many ecosystem services and social benefits that can
translate into an economic benefit for cities and their communities.
However, planting and maintaining trees also costs money. To
understand the fiscal costs of any Urban Forest Expansion strategy,
the cost of implementation must be considered. Cost estimates are
broken down into two types of costs: initial costs per acre to plant
and annual costs per acre to maintain trees as they establish. Cost
of pruning of mature trees or tree removal was not included in the
cost estimate. Scenario 1 does not include the cost of maintenance
because it is considered a natural area planting.
SCENARIO 1 // Dense Planting Rate:
• $4,221 for planting small stock saplings (less than 1” caliper)
• $84,420 for planting large stock saplings (1”-2” caliper)
Trees planted in this scenario will be treated as a natural area so
no maintenance costs will be incurred.
SCENARIO 2 // Less Dense Planting Rate:
• $2,110 for planting small stock saplings (less than 1” caliper)
• $42,210 for planting large stock saplings (1”-2” caliper)
• $30,391 maintenance, including watering during summer months
for the first 3 years and structural pruning of young trees
61 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
STREET TREE PLANTING ALONG A ONE-MILE STRETCH
OF RIGHT-OF-WAY, BOONES FERRY RD.
This scenario explores the carbon sequestration benefits of a
recent street tree planting project on Boones Ferry Road from
Madrona Drive to Oakridge/Reese Road, approximately one mile.
While 150 existing trees had to be removed, 182 new trees were
planted with a net gain of 32 trees.
–SEQUESTRATION BENEFITS–
The Street Tree Planting strategy can sequester approximately
0.13 MgC/tree/year. Assuming the new trees were planted over a
5-year period, the carbon sequestration benefit for planting all 182
new trees is estimated to be:
116.5 MgC by 2040
817.2 MgC by 2070
1,552.3 MgC by 2150
By 2040, the trees planted would sequester the equivalent to:
▶The emissions from 92 gasoline-powered passenger vehicles
driven for one year, or
▶The CO2 emissions from 83.1 homes’ electricity use for one year.
Even taking into account the fact that 150 existing trees needed to
be removed and only accounting for the net gain of 32 trees, the
carbon sequestration benefit for those 32 trees is estimated to be:
27.7 MgC by 2040
152.0 MgC by 2070
272.9 MgC by 2150
By 2040, the trees planted would sequester the equivalent to:
▶The emissions from 21 gasoline-powered passenger vehicles
driven for one year, or
▶The CO2 emissions from 19.8 homes’ electricity use for one year.
Figure 5.4 Newly planted trees on Boones Ferry Road
It is important to note that many of the trees removed for the road project
were not suitable as street trees. Several were growing under powerlines
and had been topped. The new trees should be better suited.
62 State of the Urban Forest Report | December 2022
5 // Carbon Sequestration Analysis
Costs
Street trees provide many ecosystem services and social benefits
that can translate into an economic benefit for cities and their
communities. However, planting and maintaining street trees
also costs money. In order to understand the fiscal costs of our
proposed Street Tree Planting strategy, we include the cost of
implementation. Cost estimates are broken down into two types
of costs: initial costs per acre to plant and annual costs per acre to
maintain trees. These represent the total cost to plant and maintain
the trees over their lifespan. Cost of pruning of mature trees or tree
removal was not included in the cost estimate.
Total estimated costs for tree planting and maintenance for 182
street trees are:
• $54,600 to $72,800 for coordination and planting of a large
stock street trees (1-2-in caliper).
• $39,312 for maintenance, including watering during summer
months for the first 3 years, and structural pruning of young trees.
Summary and Future Scenario Planning
Today, Lake Oswego’s trees are an essential reservoir for carbon.
Through the existing canopy alone, 202,291 MgC are being stored,
which is about 38 percent of the total carbon stored in Lake
Oswego’s plants and soil. Through City-led actions to preserve
and increase the urban forest, they can further reduce carbon
dioxide in the atmosphere.
The Urban Forest Expansion strategy can increase carbon
sequestration by 9.43 MgC/acre/year, and if applied on as
little as 4.69 acres of land, and factoring in 10 years’ time to full
implementation, by 2040 it could increase Lake Oswego’s carbon
storage by an additional 143.7 MgC if trees are planted as a dense
natural area and 71.8 MgC if planted as a less dense recreational
area. The Street Tree Planting strategy can increase carbon
sequestration by 0.13 MgC/tree/ year, and if applied on as little as
one mile of right-of-way planted over 5 years, could increase Lake
Oswego’s carbon storage by an additional 116.5 MgC by 2040.
If these two strategies were applied in one park and one mile of
right-of-way, by 2040 these tree planting efforts could sequester
the equivalent of:
▶The emissions from 206 gasoline-powered passenger vehicles
driven for one year, or
▶The CO2 emissions from 186 homes’ electricity use for one year.
The CST may be used to estimate the carbon sequestration
benefits and fiscal costs of applying a variety of strategies, to help
the City make decisions about how and where to plant trees.
State of the Urban Forest Report | December 202263
The City has a variety of different
tree-related programs that support
urban forest health and shape the
identity of the city, as summarized
below.
Tree City USA
In 2022, the City of Lake Oswego
celebrated 33 years as a Tree City USA
(TCUSA), a National Arbor Day Foundation
program that recognizes cities for
demonstrating a strong commitment to
managing and caring for trees. Cities earn
TCUSA status by meeting four standards:
maintaining a tree board (the Parks,
Recreation and Natural Resources Advisory
Board), having a tree ordinance, spending
a minimum $2 per capita on urban forest
management, and proclaiming and
celebrating Arbor Day annually.
In 2018, the Oregon Department of
Forestry (ODF) in partnership with Oregon
Community Trees (OCT) named Lake
Oswego the 2018 Oregon Tree City of
the Year. Each year, ODF and OCT select
one of Oregon’s TCUSA communities to
recognize their commitment to urban
and community forestry. Some cities are
recognized for grant efforts or projects they
have undertaken in a given year.
In recognizing Lake Oswego with this
distinction, ODF noted, “Lake Oswego
has consistently exemplified what a great
Tree City should be with good planning
and citizen engagement.” Lake Oswego
received the award during an Arbor Week
event at Stafford Grove.
There are currently 69 TCUSA communities
across Oregon. Visit www.arborday.org/
programs/treecityusa to learn more.
Arbor Month Events
A goal identified in 2007 was to expand
and foster Arbor Week events as an
education and outreach opportunity. For
many years, the City of Lake Oswego
celebrated Lake Oswego Arbor Week
during the first full week of April. Since the
Governor first proclaimed Oregon Arbor
Month in 2021, the City began celebrating
Lake Oswego Arbor Month throughout
the month of April. Arbor Month events
and activities and Urban and Community
Forestry events were postponed in 2020
and 2021 due to the COVID-19 pandemic.
The City publishes an annual Urban &
Community Forestry Newsletter as an insert
in the April Hello LO, which is mailed to all
Lake Oswego residents. This publication
announces Arbor Month events, annual
workshops, and Heritage Trees; provides
summaries of recent tree code and policy
changes; and includes educational and
informational articles on a variety of urban
forestry topics.
Arbor Month celebrations are organized
by the Planning Department in
collaboration with Parks and Recreation,
the Lake Oswego Library, Luscher Farm,
and the Oswego Lake Watershed Council.
6 // Community Programs
2018 Oregon Tree City of the Year Award–Brian French from OCT with City Councilors
64 State of the Urban Forest Report | December 2022
6 // Community Programs
Some typical Arbor Month activities
include:
• Neighborhood Stewardship Work
Parties
• Heritage Tree Dedications
• Friends of Springbrook Park Preschool
Nature Walks
• Promote the Trillium Festival at Tryon
Creek State Natural Area and Oswego
Lake Watershed Council events
including the LOTree Inventory Project,
Soil Your Undies, and invasive ivy
removal
Highlights from past years include:
• The Hiroshima Peace Tree planting in
Foothills Park in 2019
• Forest Hills Elementary School Second
Graders tree planting at Stafford Grove
in 2018
• Heritage Tree Bike Ride 2013, 2016
• Arbor Week Festival 2014, 2016
• Arbor Day Coloring Contest 2013, 2014
• Tree-Themed Poetry Contest 2015, 2016
• Arbor Week/Month Art Contest (themes
listed below by year)
»2017: Trees of Lake Oswego
»2018: Oregon Tree City of the Year
»2019: All About Douglas-firs
»2022: Wildlife in the Urban Forest
TREE OF LIFE
The trees near my house
Are bursting with lives.
They have branches, trunks and leaves,
Filled with bugs, birds and bees.
Those trees are very generous.
Because of all the things they give us.
They give us air, they give us wood.
They give us paper, they give us food.
Without them we would die,
I love trees, I cannot lie.
–SYLVAN SCHOENHEIT
Westridge Elementary School, 1st Grade
First Place
ARBOR DAY
A new planted tree with a
Rainbow behind,
Begins with a seed full
Of pride.
Rain gives it water.
Day gives it light.
A person gives it love.
Your tree is so bright.
.
–ADDISON FINNEY
Forest Hills Elementary School, 2nd Grade
Second Place
2016 Arbor Day Poetry Contest Winners
65 State of the Urban Forest Report | December 2022
6 // Community Programs
Forestry at the
Farmers’ Market
In recent years (except for 2020 and 2021),
the City has celebrated forestry at the
Farmers’ Market with Urban & Community
Forestry booths and activities for children
and adults during the first or second week
of the market opening. The booths have
included a nature-themed prize wheel for
kids and teens, nature-themed crafts for
kids, tree pruning demonstrations, free tree
seedling giveaways, opportunities to talk
with an ISA Certified Arborist, tree trivia and
raffles, and information on the City’s tree
code, Heritage Tree Program, native and
invasive species, habitat restoration, and
neighborhood stewardship workshops. In
addition, Arbor Month Art Contest winners
are announced on the main stage and
prizes are awarded by the mayor. This
event is an annual collaboration between
the City’s Planning and Parks & Recreation
Departments.
Urban & Community
Forestry Workshops
For at least 14 years, the City has offered a
series of free Urban & Community Forestry
workshops for the public. One of the
goals identified in the 2007 plan was the
promotion of urban forestry stewardship in
the community through education events.
The annual workshop series have included
Tree Protection and Removal workshops
for builders, landscapers, arborists, and
other professions. Other workshops have
been held to educate the general public.
Below is a list of some of the most popular
workshops held over the years:
• Invasive Plant Management 2013, 2014
• Landscaping for Conservation 2016,
2017, 2018, 2019
• Right Tree in the Right Place 2013, 2014
• Tree Species Identification Walking Tour
2016, 2017, 2018, 2019, 2022
• Tree Pruning 2014, 2015, 2016, 2017, 2018,
2019, 2022
• Understanding the Tree Code 2013,
2014, 2015, 2016, 2017, 2018, 2019
• Understanding Your Tree: Basics of Tree
Biology and Structure 2013
2018 Tree Pruning Workshop
2013 Tree Climbing Demonstration
66 State of the Urban Forest Report | December 2022
6 // Community Programs
Tree Care and
Maintenance Website
The City’s Tree Care and Maintenance
webpage, featuring seasonal articles on
a wide variety of topics, kicked off in 2016.
Since then, 22 articles have been published,
and they are all available at https://www.
ci.oswego.or.us/trees/tree-care-and-
maintenance. The website publishes content
that helps address a number of the goals
from the 2007 Plan. Each article provides
a concise summary of the topic and offers
links to credible references to learn more.
The list of topics currently available include:
• Emerald Ash Borer 2022, 2018
(pre- arrival)
• Healthy Trees are Defended Trees
• After the Storm
• What is an Arborist?
• Soil Management
• Retaining and Creating Snags for Wildlife
• Mulch: Numerous Benefits and
Easy Application
• Tree Planting: To Stake or Not to Stake?
• Insects and Diseases
• Drought Stress Revisited
• Trees and Construction
• Topped Tree
• Autumn Leaves
• Pruning Young Trees
• Tree Related Storm Damage
• New Tree Selection and Planting
• Trees and Turfgrasses
• English Ivy Removal
• Recognizing Tree Risk
• Drought Stress
• Preparing Trees for Winter
2022 Tree Identification Workshop
2018 Tree City of the Year Art Contest
State of the Urban Forest Report | December 202267
Lake Oswego’s urban forest canopy
is widespread and well distributed
with over 40 percent canopy cover
in all neighborhoods. In addition, all
neighborhoods have experienced canopy
increases during the study period. Lake
Oswego is unique in that while many
communities in the region have set goals
to reach 40 percent canopy, Lake Oswego
has an astounding 53.4 percent canopy.
Based on the current state of Lake
Oswego’s trees, urban forest management
should focus on preserving and
maintaining the resource, rather than
significantly expanding tree canopy
citywide. Particular attention will need to
be paid to the many threats to the urban
forest which include climate change,
extreme weather events, wildfire, insects
and disease, urban development, and
invasive species.
The City has been proactive in updating
its codes, policies, procedures, and
education/outreach materials in recent
years in response to economic, social,
and environmental conditions that impact
the urban forest. The City should continue
its adaptive management approach
to address the many threats facing the
urban forest.
Lake Oswego has a diverse mix of trees
of varying size classes with an abundant
stock of smaller trees. Replanting with large
stature tree species, where growing space
is adequate, is important for replacing
larger trees as they decline or are
otherwise removed. This mix is important
to maintain for combating climate change
at a local level as large trees are important
for carbon storage while smaller, rapidly
growing trees are more efficient at
sequestering (removing) carbon from the
atmosphere.
Five neighborhoods experienced small
losses of canopy in the 50-foot to 120-
foot height range over the study period.
Although overall canopy increased in
these neighborhoods, the loss of larger
trees negatively impacts carbon storage in
addition to the other environmental, social,
and economic benefits large trees provide.
While Lake Oswego should be proud of the
current state of the urban forest, ongoing
management will be required to preserve,
protect, and enhance this valuable
resource so its benefits can continue to be
provided for generations to come.
Conclusion
Heritage Tree #37, a Pacific dogwood located at Oswego Pioneer Cemetery
State of the Urban Forest Report | December 2022A-1
i-Tree Benefits
Table A.1–Table A.3 detail the full findings of the i-Tree canopy tool
based on the reported acreages of 2014 (3,877 acres) and 2019
canopy (4,265 acres) from the UTC models. The following are used
in the tables:
• ac = acres
• gal = gallons
• lbs = pounds
• T = tons
• yr = year
• yd3 = cubic yard
Appendix
Table A.1 Annual air quality benefits
Air Quality Description Removal Rate (lbs/ac/yr) Monetary Value ($/T/yr) Lake Oswego 2014 lbs/yr Lake Oswego 2014 Monetary Value Lake Oswego 2019 lbs/yr Lake Oswego 2019 Monetary Value
CO Carbon Monoxide
removed annually 1.059 $1,334 4,106 $2,738 4,517 $3,011
NO2 Nitrogen Dioxide
removed annually 7.481 $342 29,004 $4,966 31,906 $5,463
O3 Ozone removed annually 38.711 $3,366 150,083 $252,590 165,102 $277,869
PM10
Particulate Matter greater than
2.5 microns and less than 10
microns removed annually
8.146 $6,268 31,582 $98,985 34,743 $108,891
PM2.5 Particulate Matter less than 2.5
microns removed annually 5.352 $192,534 20,750 $1,997,511 22,826 $2,197,416
SO2 Sulfur Dioxide removed annually 2.511 $100 9,735 $487 10,709 $536
TOTAL 245,259 $2,357,276 269,804 $2,593,187
A-2 State of the Urban Forest Report | December 2022
Appendix
Table A.3 Hydrologic benefits
Description Tree Effects (gal/yd²/yr) Monetary Value ($/yd³/yr) Lake Oswego 2014 gal/yr Lake Oswego 2014 Monetary Value Lake Oswego 2019 gal/yr Lake Oswego 2019 Monetary Value
Avoided Runoff 8 $1.80 140,772,629 $1,254,570 154,860,785 $1,380,125
Evaporation 37 699,847,505 769,886,410
Interception 38 704,013,264 774,469,067
Transpiration 16 298,865,058 328,774,690
Potential Evaporation 101 1,897,090,383 2,086,946,217
Potential Evapotranspiration 88 1,652,811,779 1,818,220,851
Description Carbon Rate (T/ac/yr)
Lake Oswego 2014 Carbon Sequestration Rate (T/yr)
Lake Oswego 2014 Carbon Sequestration Monetary Value
Lake Oswego 2019 Carbon Sequestration Rate (T/yr)
Lake Oswego 2019 Carbon Sequestration Monetary Value
Carbon Sequestered annually in trees 1.08 4,187 $714,120 4,606 $785,587
Carbon Stored in trees (Note: this
benefit is not an annual rate) 34.281 132,907 $22,667,363 146,208 $24,935,854
Table A.2 Carbon storage benefits. Based on carbon price of $170.55 per ton. Note that the carbon results in i-Tree are provided for reference. Base
level carbon is calculated separately in the Carbon Sequestration chapter of the report based on the more detailed approach.
A-3 State of the Urban Forest Report | December 2022
Appendix
In November 2019, tree code amendments
in LOC Article 55.08 became effective
that strengthen and clarify requirements
for tree protection primarily associated
with building and plumbing permits. A
summary of the changes is provided
below:
1. Defined “Development”/“Development
Activities” to include: tree removal;
grading; excavation; parking,
storage, or movement of construction
equipment/materials in the
development area; removal or
placement of soil; demolition; and
construction;
2. Defined the “development area” of a
Tree Protection Plan to include staging
areas, off-site utility work, construction
parking and other construction related
activities that may injure or damage a
protected tree;
3. Expanded the definition of “Tree
Protection Zone” to be based on either
a tree’s dripline or a one-foot radius
of protection for each inch of trunk
diameter, whichever is greater;
4. Clarified what pre-construction
activities (brush clearing for tree
protection fencing/erosion control,
debris removal, etc.) are allowed prior
to the issuance of a Tree Protection
Plan and required a Certified Arborist
be present for such activities;
5. Created an “enhanced enforcement
fee” for damaging trees that are one
of the following: 36” diameter or larger;
designated as a Heritage Tree; located
in the Willamette River Greenway; or,
located on the public right-of-way,
city-owned or dedicated property,
public or private open space area or
conservation easement;
6. Clarified tree protection fencing shall
remain in place until after installation of
utilities and stormwater improvements;
construction of the driveway/access
lane; and completion of exterior
building walls (siding, painting, etc.);
7. Expanded the situations when a
violation letter with enforcement fee
can be issued due to tree damage or
injury;
8. Created a cover sheet for building
permit applications and plumbing
applications to better explain to
applicants the requirements for a Tree
Protection Plan;
9. Created a summary sheet of
information to include in an arborist
report;
10. Reorganized the Type II Native
Mitigation Tree List (Appendix 55.02-1)
for clarity and added Eddie’s White
Wonder as an acceptable substitute to
native Pacific dogwood; and,
11. Added a provision in the Tree Code
that tree removal cannot conflict with
other sections of the Lake Oswego
Code (for example, tree removal
restrictions in LOC Chapter 50.05.010,
Sensitive Lands).
In October 2019, code amendments
added new conditions to Tree Protection
Plans in a format that makes it clearer
for the Builder to know when a certified
arborist is required on a construction site
and what information the arborist should
report to the City. Examples of the new Tree
Protection Plan conditions include:
1. Arborist’s Supervision: The arborist
shall stop construction activities under
a protected tree’s dripline when the
activities become detrimental to the
health and long-term viability of the
tree;
Recent Tree Code Amendments
A-4 State of the Urban Forest Report | December 2022
Appendix
a. Any tree roots damaged within the
protection zone will be a violation of
the Tree Code and fees of at least
$595/violation will be assessed;
2. Arborist Inspections and Status Reports
required:
a. Arborist Inspections: A certified
arborist shall visit the site:
i. On-call as indicated in the
Arborist report;
ii. When opening or adjusting tree
protection fencing; and,
iii. Twice monthly at a minimum to
inspect tree protection measures
during periods of development
activity. The arborist may modify
the frequency of inspections by
documenting periods of inactivity
near a protected tree;
b. Status Reports:
i. The arborist shall document
each site visit in an inspection
report and submit within 7
days of observation to the City,
contractor, and owner which
contains:
1. Description of the condition of
the tree protection measures;
2. Photographs to document
observations and findings;
3. Recommendations for
remedial actions and if they
were followed;
4. Periods of inactivity if the
frequency of site inspections
were reduced;
City Resolution 19-59: Policy on Natural
Resource Protection Prior to Annexation
(Policy Adopted May 2004; Updated
December 2019). The purpose of this policy
is to encourage property owners interested
in petitioning the City for annexation to
preserve and protect natural resources
and significant trees prior to annexation.
The policy is intended to minimize erosion
and protect water quality, wildlife habitat,
and the wooded character of Lake
Oswego and allows the City to decline
or delay requests for annexation for up
to 3 years from property owners who
violate the policy, and require payment of
significant restoration fees and completion
of mitigation plantings, if resources or
significant trees are removed or degraded
within 10 years of the annexation request.
Not all tree removal or work within natural
resource areas on unincorporated lots is
subject to the policy and the City offers
a process that allows a property owner
in unincorporated areas within the City’s
Urban Services Boundary to apply for
certification that tree removal prior to
annexation does not violate this policy.
In Summer 2016, the City Council adopted
amendments to the Tree Code to
help ease tree removal restrictions for
developed single family residential lots
and improve the review and processing
of permits. Some of the key improvements
that were implemented include:
1. Increasing the size of trees eligible for
a Type I “over the counter” permit from
10” in diameter to 15” in diameter and
including any size of fruit-bearing trees.
Type I permits allow the removal of up
to two 15” diameter trees per calendar
year, or any size or number of fruit-
bearing trees, on developed single-
family lots (other restrictions apply).
2. Expanding eligibility for “over the
counter” dead tree permits to include
trees that, while not completely lifeless,
are in a “progressive and irreversible
state of decline.”
3. Creation of a new website with easy
access to application forms, FAQs,
seasonal tree care tips, and other
helpful tree-related information. In
addition, the public can search and
view pending Type II tree removal
applications in the City, track the status
A-5 State of the Urban Forest Report | December 2022
Appendix
of these applications, and submit
comments.
4. Improved noticing of Type II tree
removal applications. Automated
notices are emailed to neighborhood
associations when a Type II application
is received in their neighborhood and
when a tentative staff decision is made
on the application, it is also emailed
to the applicant, neighborhood
association, and anyone that submitted
comments during the comment period.
In March 2015, the City Council tentatively
approved Ordinance 2664, amending
the Tree Code (LOC 55) to provide a
more flexible permit process for large,
forested parcels that is focused on urban
forestry principles rather than individual
tree regulations while still maintaining
the wooded character of the city. The
primary objective is to encourage and
assist owners of large, forested tracts in
managing their property, while providing
safeguards for neighborhood character,
protection of water quality, and erosion
control. The code amendment created
separate permitting processes for forested
properties of one acre or larger, leaving
intact the existing Tree Code for residential
lots and new development. The Minor
Forest Management Permit provides for
removal of a small number of trees with
a simple, over-the-counter permit process
that is scalable (e.g., based on forested
acres) and uses objective criteria. The
Major Forest Management Permit, subject
to approval of a forest management plan
prepared by a qualified professional,
allows for tree removal for the purposes of
forest management, including managing
for tree health and sustainability, as well as
minimizing the risk of catastrophic events
such as wildfire, drought, infestations, storm
damage, and landslides.
A-6 State of the Urban Forest Report | December 2022
Appendix
Metric 2014 2015 20161 2017 2018 2019 2020 2021
# tree removal apps (total) 1,327 1,286 1,522 1,653 1,490 1,651 1,534 1,797
# dead apps 246 309 393 261 392 491 404 380
# hazard apps 312 304 215 260 176 174 152 295
# emergency apps 10 15 15 55 17 22 20 58
# forest management apps N/A 2 1 1 4 0 0 0 1
# Type I apps 209 209 319 509 425 428 467 448
# invasive apps 152 171 160 166 130 181 171 188
# Type II apps 374 264 395 380 324 340 311 415
# verification apps 24 13 24 18 26 15 9 12
# Type II apps approved 360 245 374 343 292 294 281 346
# Type II apps denied3 1 0 5 5 2 7 4 2
# Type II apps withdrawn4 13 19 16 32 30 39 26 67
# Type II apps appealed
2 4
1 withdrawn
2
1 withdrawn
4
1 withdrawn
2 4 9
4 withdrawn
3
2 withdrawn
Table A.4 Tree application details by permit type, 2014-2021.
1 Tree Code Amendments became effective on 8/18/2016 (Ordinance 2721).
2 Forest Management Permit added as a new permit type on 5/7/2015 (Ordinance 2664).
3 Indicates when an entire tree removal application was denied. More commonly, one or more individual trees from an
application is or would be denied, rather than the entire application. (Note: if staff finds a tree cannot be approved, the
applicant is given the option to withdraw the tree and get a partial refund in lieu of staff issuing a denial; in these instances,
most applicants elect to withdraw the tree from the application.) Staff will begin tracking the number of individual trees
withdrawn or denied starting in 2022.
4 Indicates when an entire tree removal application was withdrawn. More commonly, an applicant will withdraw one or more
individual trees from an application rather than the entire application (also see Footnote 5). Staff will begin tracking the
number of trees withdrawn starting in 2022.
A-7 State of the Urban Forest Report | December 2022
Appendix
Permit Application Type 2017 2018 2019 2020 2021 Total 2017-2021
Dead 714 686 889 727 665 3,681
Hazard 565 227 271 247 431 1,741
Emergency 67 24 23 27 65 206
Forest Management 81 0 0 0 16 97
Type I 712 607 605 614 640 3,178
Invasive 404 311 8381 466 528 2,547
Type II 764 564 460 344 564 2,696
Verification 290 174 297 506 187 1,454
TOTAL NUMBER OF
TREES REMOVED 3,597 2,593 3,383 2,931 3,096 15,600
Table A.5 Number of trees removed by permit application type, 2017-2021.
1 Includes 298 English hawthorns removed for
Woodmont Park redevelopment.
A-8 State of the Urban Forest Report | December 2022
Appendix
City Tree Activities1 2017 2018 2019 2020 2021
TOTAL NUMBER OF
TREES PLANTED 1,252 3,548 4,115 5,887 12,554
In Public Right-of-Way 247 195 155 175 136
Park Lands 1,005 3,353 3,960 5,712 12,418
TOTAL NUMBER OF
TREES REMOVED 225 134 166 132 878
Total Removed by Public Works
(permit type unknown) 195 95 115 100 350
Total Removed by Parks
(by permit type below) 41 46 50 32 528
Invasive Permit 18 5 8 0 298
Dead Permit 1 12 38 19 11
Hazardous Permit 20 18 4 8 15
Emergency Permit 0 6 0 5 93
Type II (Iron Mountain and
Woodmont Parks) in 2021 2 5 0 0 111
Forest Management
Acres in restoration (Data
based on fiscal year)
285.81
(FY 16-17)
270.73
(FY 17-18)
356.41
(FY 18-19)
361.74
(FY 19-20)
373.84
(FY 20-21)
Total number of native
plants planted 100,114 40,727 50,640 21,680 114,500
(11,000 trees)
Per capita spending on trees2 $10.16 $10.98 $11.48 $12.52 $15.44
1 From Parks and Public Works.
2 From annual Tree City USA application.
Table A.6 City tree removal and mitigation planting in public parks and rights-of-way, 2017-2021.
A-9 State of the Urban Forest Report | December 2022
Appendix
Street Tree Equity
The methodology for creating the Tree
Equity Score based on UTC within the road
right-of-way was derived from American
Forests Tree Equity Score tool. Lake
Oswego adjusted the methodology to use
their own UTC model only within the road
rights-of-way to measure street Tree Equity
and identify priority census block groups.
1. Right-of-Way Target UTC Goal
The ROW target UTC goal is meant to be
equitable, aspirational and achievable
and is developed using the following data:
• Tree canopy cover
• Census American Community Survey
(ACS) 2018 5-year Block Group
population estimates
• Census ACS 2018 5-year city and block
group Median Income estimates
The UTC goal is selected based on the
generalized biome baseline targets in
conjunction with the USDA Forest Service.
The options are:
• Forest: 40%
• Grassland: 20%
• Desert: 15%
Lake Oswego is in the forest biome so the
analysis uses a baseline target of 40% UTC.
2. Canopy Gap
The canopy gap, GAP, is calculated by
subtracting the existing canopy from the
density adjusted target, that is: GAP =
GOAL – EC, where EC is % existing canopy
for that neighborhood. The canopy gap is
then normalized to a score from 0-100.
• GAPScore = 100 * GAP / GAPmax ,
where:
»GAPmax is the maximum GAP value
citywide for that indicator
Notes: If the GAP is negative (i.e., existing
canopy is greater than the neighborhood
goal), it is adjusted to 0 before normalizing
to create the gap score. Also, if GAPmax =
0, then GapScore is set to 0 as well.
3. Equity Priority Score
The Priority Score is developed to help
prioritize the need for planting to achieve
Tree Equity. The priority score includes the
following equally weighted characteristics:
Income: Less than two times the federal
poverty level.
Employment: Unemployment rate
Race: Percentage of people who are not
white non-Hispanic
Age: Ratio of seniors and children to
working-age adults
Climate: Urban Heat Island severity
Health: Prevalence of poor mental,
physical, respiratory, and cardiac health
(composite index)
These measures are normalized and
combined to create a simple priority index
from 0 to 1, where 1 indicates a greater
amount of inequity. The indices, N, are
calculated as follows:
• Ni = (xi - xi,min ) / (xi,max - xi,min) ,
where, for each indicator, Ni,
»xi is the value for that neighborhood
for that indicator, i;
»xi,max is the maximum value
citywide for that indicator, i; and
»xi,min is the minimum value citywide
for that indicator, i.
The Equity Priority score, E, is then
calculated as follows:
• E = (N1 + N2 + N3 + N4 + N5 + N6) / 6 ,
where Ni refers to each indicator value
(income, employment, race, age, or
climate)
4. Tree Equity Priority Score
The Tree Equity Priority Score, TES, is
calculated by multiplying the UTC Target
Gap Score by the Equity Priority Score,
simply:
• TES = 100 (1 - GAPScore E)
A lower TES indicates a greater priority for
closing the tree canopy gap.
A-10 State of the Urban Forest Report | December 2022
Appendix
Table A.7 Census block group table showing socioeconomic attributes, right-of-way percent UTC cover, and the resulting equity priority rankings.
1 Number of children + seniors
divided by number of 18-64 adults
2 Hot summery dayBlock Group ID CountyTotal PopulationLow Income (%)Unemployment Rate (%)People of Color (%)Dependency Ratio1Average Temperature2Normalized Health Index (%)Equity Priority ScoreRight-of-way UTC Cover (%)Right-of-Way UTC Gap ScoreTree Equity Priority Score410050203041 Clackamas 2271 10%6%26%70%79.9 28%47 28%12%53
410670320051 Washington 241 10%7%37%2%86.7 75%45 31%9%65
410050204012 Clackamas 953 12%3%29%48%82.4 74%55 33%7%67
410050203022 Clackamas 3162 12%7%22%53%79.1 54%50 33%7%70
410050205041 Clackamas 1100 1%5%16%84%79.6 36%54 35%5%76
410050203021 Clackamas 1042 12%4%23%44%79.7 54%44 34%6%77
410050201003 Clackamas 871 17%0%24%51%82.4 40%43 35%5%81
410510064041 Multnomah 1930 14%6%27%64%76.9 90%53 36%4%82
410050204013 Clackamas 1458 17%4%5%67%79.4 74%44 35%5%82
410510064022 Multnomah 2560 8%1%11%56%75.1 33%19 29%11%83
410050203042 Clackamas 1221 5%0%21%58%81.0 28%30 34%6%85
410050204032 Clackamas 984 10%8%21%52%75.9 34%41 36%4%87
410050203043 Clackamas 2045 18%7%24%47%81.2 28%54 38%2%89
410050202005 Clackamas 1042 24%3%7%111%77.1 36%41 37%3%89
410050205051 Clackamas 1432 29%0%20%232%77.6 35%55 39%1%97
410050205031 Clackamas 1263 9%4%9%62%78.0 44%32 39%1%98
410050204042 Clackamas 1784 8%5%10%94%78.1 31%34 40%0%100
410050201001 Clackamas 2248 12%3%15%81%75.6 40%31 43%0%100
410050201002 Clackamas 1011 11%3%13%78%75.3 40%30 44%0%100
410050202001 Clackamas 1205 10%3%16%40%77.2 36%29 46%0%100
A-11 State of the Urban Forest Report | December 2022
Appendix
Block Group ID CountyTotal PopulationLow Income (%)Unemployment Rate (%)People of Color (%)Dependency Ratio1Average Temperature2Normalized Health Index (%)Equity Priority ScoreRight-of-way UTC Cover (%)Right-of-Way UTC Gap ScoreTree Equity Priority Score410050202002 Clackamas 1348 7% 3% 8% 74% 75.9 36% 24 52% 0% 100
410050202003 Clackamas 653 18% 6% 3% 103% 78.7 36% 42 42% 0% 100
410050202004 Clackamas 1963 8% 2% 6% 55% 74.2 36% 16 46% 0% 100
410050203031 Clackamas 2513 15% 0% 21% 35% 77.9 39% 30 40% 0% 100
410050203032 Clackamas 929 13% 0% 10% 68% 78.2 39% 27 47% 0% 100
410050203033 Clackamas 2241 12% 0% 27% 83% 79.6 39% 39 41% 0% 100
410050204011 Clackamas 1705 4% 6% 38% 49% 78.1 74% 51 42% 0% 100
410050204014 Clackamas 1756 14% 5% 12% 103% 76.5 74% 45 41% 0% 100
410050204031 Clackamas 2656 13% 6% 10% 97% 76.0 34% 36 42% 0% 100
410050204041 Clackamas 1966 7% 2% 10% 77% 73.8 31% 18 49% 0% 100
410050205032 Clackamas 1130 13% 3% 5% 81% 75.4 44% 27 53% 0% 100
410510064042 Multnomah 1881 20% 6% 12% 49% 77.8 36% 26 42% 0% 100
A-12 State of the Urban Forest Report | December 2022
Appendix
The UTC models developed by the City and Metro were derived
using GIS software with image analysis capabilities using Lidar
and multispectral imagery. The Lake Oswego models from 2014
and 2019 are used to analyze UTC cover and height distribution
across various land cover classifications within the city. The Lake
Oswego UTC model assesses canopy cover at various heights and
uses 10 feet as the minimum height threshold based on the Lidar
data. The 10-foot minimum height for inclusion in the UTC model
was chosen to support an earlier analysis to determine effective
stream shade in support of the City’s Temperature TMDL. Ten feet
is the threshold for classification as tree canopy for the analysis in
DEQ modelling tools. The 10-foot cutoff also matches what is used
by Metro in its regional UTC model. While the argument could
be made that a 10-foot hedge or small yard tree should not be
considered part of the urban forest canopy, it is important that
the City’s analysis is consistent with the data used by state and
regional agencies. Additionally, smaller stature trees and large
shrubs do in fact contribute to many of the positive environmental
impacts discussed in the earlier chapter on urban forest benefits.
The UTC model developed by Metro based on the 2019 Lidar
and aerial imagery is used for a regional comparison of Lake
Oswego to other cities with regards to percent canopy cover.
Metro’s UTC model was created independently of Lake Oswego’s
based on the same data inputs. However, the Metro model was
created using different analytical processes, which resulted in
slightly different results. Figure A.1 depicts some of the differences
between the two models in one area of the city. The 2019 Lake
Oswego UTC model had an overall accuracy of 97 percent based
on a assessment of 200 randomly generated points across the
City. Metro’s UTC model had a very similar accuracy reported
at 96.4 percent. Based on the model metadata from Metro and
canopy results shared in this chapter on Lake Oswego city-wide
UTC percent cover, the tendency for the Metro UTC model is to
underestimate canopy cover (by up to 3 percent) by missing some
trees in the cover. The City’s model tends to overestimate canopy
cover by up to 3 percent, sometimes misclassifying tall objects
from Lidar that have spectral characteristics similar to vegetation,
like edges of buildings that are heavily shadowed in the aerial
or sections of vegetation under overhead wires. Lake Oswego’s
model relies more heavily on the Lidar, and the Metro model
relies more heavily on the aerial for classification of canopy. These
observations are evident in the images below showing both the
Lake Oswego UTC model and the Metro UTC model overlaid with
the 2019 Lidar height surface and the aerial imagery.
Urban Tree Canopy Model Methodology
Comparing the Lake Oswego and Metro UTC Models
A-13 State of the Urban Forest Report | December 2022
Appendix
Large trees missed
in Metro model
Overhead wires over
grass classified as
canopy in LO model
Tree missed in
Metro model
Figure A.1 Left—2019 Lidar Height Surface. Right—2019 Aerial Imagery. Cyan lines depict the 2019 Lake Oswego UTC Model and the red lines depict the 2019 Metro Regional UTC Model. Similar overall accuracies are reported for the two models. The tendency of the Lake Oswego model is to over-estimate the canopy cover in some areas, and the tendency of the Metro Model is to under-estimate the canopy cover.
A-14 State of the Urban Forest Report | December 2022
Appendix
UTC Analysis Process in GIS
The following steps provide an overview
of the methodology for creating the UTC
height model performed in GIS software. It is
important to note that large waterbody areas
like Oswego Lake, the Willamette River, and the
Tualatin River were removed for the analyses
since there is no potential for canopy cover in
these areas.
Step 1. Aerial Imagery Processing
Infrared cameras are used to collect
multispectral imagery that includes a near-
infrared band that GIS software can make use
of to create a Normalized Difference Vegetation
Index (NDVI), as shown in Figure A.2. The NDVI
is calculated using values from the red and
near-infrared bands from the imagery and is a
great indicator of vegetation that can be used
to isolate tree canopy cover.
Step 2. Lidar Processing
The Lidar point cloud for the City of Lake
Oswego is made up of over 2 billion points
that represent individual pulses from aerial
Lidar collection. Each point is populated with
important information such as elevation,
classification, return number, color, and
intensity. Some of these Lidar point cloud
attributes are depicted in Figure A.3. The Lidar
point clouds are used to generate surfaces.
Figure A.2 Creation of the NDVI Layer using multispectral imagery.
Figure A.3 Lidar point cloud with the various attributes used for visualizations and feature extractions.
A-15 State of the Urban Forest Report | December 2022
Appendix
Step 3. Isolating the
UTC Height Model
An automated process was developed
in the ArcGIS Pro environment to derive
the UTC model from the aerial and Lidar
input datasets. From the Lidar point cloud
information, a Normalized Digital Surface
Model (nDSM) is first created. The nDSM
represents the height above ground of
all objects. The UTC model is extracted
by combining the object height from the
nDSM (features of at least 10 feet) with
the spectral information from the NDVI.
Manual desktop cleanup is performed
on the UTC model after the automated
extraction of the canopy to clean up errors
until the goal UTC model accuracy of 97
percent is achieved.Figure A.4 Canopy Height Model derived in ArcGIS Pro using information from the Lidar and multispectral imagery
A-16 State of the Urban Forest Report | December 2022
Appendix
Understanding Canopy Change
By overlaying the 2014 and 2019 UTC models, a visual is produced that highlights locations of new or
lost canopy cover across the City. In the map below, the bright green areas represent new canopy in the
model. Much of the growth from 2014 to 2019 is attributed to horizontal (outward) growth of tree crowns.
There are also existing trees that reached the minimum height of 10 feet to be included in the model.
Orange areas represent canopy loss or tree removal. The model includes all types of trees including
native, nonnative, and invasive species.
Figure A.5 Typical canopy change from 2014 to 2019. Cyan areas show new canopy in the 2019 model and orange areas show canopy loss from 2014 to 2019.
A-17 State of the Urban Forest Report | December 2022
Appendix
The CST demonstrates how much carbon Lake Oswego’s
greenspaces including trees are storing, and how much more
carbon might be able to sequestered if the urban forest is
expanded. The tool uses a GIS-based map that measures
the amount of carbon that is being sequestered today in Lake
Oswego and a spreadsheet model that estimates how much
more carbon could be sequestered through tree planting on
public land.
Inputs
The following inputs and assumptions are necessary to run the CST.
Existing Carbon
To fully understand the carbon sequestration benefits of future tree
planting, it is necessary to have a full accounting of existing carbon
sequestered both below ground (in the soil) and above ground (in
organic matter like grasses, shrubs, and trees).
Existing above-ground carbon was modeled using multiple data
sources to develop an appropriate representation of land cover.
Land cover designations were then related to above-ground
carbon densities (carbon per acre) for grasses, shrubs, small
trees, and large trees based on calculations from the national
tree benefits calculator and cross referenced with estimates from
the California-based carbon sequestration model TerraCount.
A representative tree and shrub mix for Lake Oswego was used,
gathered from interviews with City staff and review of the City’s
2009 State of the Forest Report. An estimated tree-density-per-
acre of 40 for shrubs and small trees and 20 for large trees was
applied.Below-ground carbon was estimated using USDA-NRCS
Soil Survey Geographic data. Among other things, SSURGO
estimates measure the existing soil organic carbon in soil types
detailed in the soil polygon map. Soil organic carbon from 0-100
centimeters below ground was included in the analysis. Total
existing carbon estimates were then assigned to each taxlot parcel
in Lake Oswego to get a lot-by-lot snapshot of existing carbon to
which additional tree planting could be applied and the carbon
sequestration benefits measured.
DATA SOURCES:
• National Tree Benefits Calculator: tree carbon sequestration rates
• TerraCount: carbon sequestration rates for grasses
• Soil Survey Geographic Database: carbon sequestration rates
for soils
• Metro’s Regional Land Information System: taxlot parcel data
• Parametrix: Landcover classifications, digital terrain and digital
surface models, tree canopy height models
Data Used Year Application
Taxlot Parcels 2020 Above-Ground Carbon,
Below-Ground Carbon
Landcover classifications 2020 Above-Ground Carbon
Tree Canopy Height Model 2014, 2019 Above-Ground Carbon
Digital Surface Model 2019 Above-Ground Carbon
Digital Terrain Model 2019 Above-Ground Carbon
Soil Survey Geographic
Database 2021 Below-Ground Carbon
Table A.8 Data used for existing carbon calculations.
Carbon Sequestration Tool Methodology
A-18 State of the Urban Forest Report | December 2022
Appendix
Strategies for Future
Tree Planting
Two tree planting strategies were
calibrated in the model—Urban Forest
Expansion and Street Tree Planting.
URBAN FOREST EXPANSION
Urban Forest Expansion focuses on
increasing tree canopy outside of the
public right-of-way (trees in the right-of-
way are considered “street trees”), in areas
such as parks and open spaces. The trees
that can be planted in this area generally
have fewer constraints (such as narrow
planting strips and overhead high voltage
wires) than street trees in terms of the size
and species of tree that can be planted.
The Urban Forest Expansion strategy
involves pairing an assessment of the
carbon in existing trees, from iTree and the
National Tree Benefit Calculator, with an
assessment within the spreadsheet model
of the carbon potential of planting new
trees. The annual carbon sequestration
rate assumed for this strategy is based
on a blended average of a variety
of frequently planted and climate
appropriate native and non-native tree
species selected from Lake Oswego’s
Right Tree Right Place guide. Trees
selected represent a variety of functional types (large-medium-small form, evergreen
and deciduous dormancy) though focused on trees and larger tree types that sequester
the greatest amounts of carbon. Total carbon sequestration in any future year is based on
the number of trees planted each year, and growth curves applied to estimate the total
carbon sequestration potential in any year for that mix of species and ages.
Sequestration Benefits
The Urban Forest Expansion strategy includes two rates of application. A high application
rate of planting 60 trees per acre is estimated to sequester 9.43 MgC/acre/year until peak
sequestration is reached. A lower application rate of planting 30 trees per acre is estimated
to sequester 4.72 MgC/acre/year.
Species Mix Calibration % Species Rate MgC/yr/tree Rate MgC/yr/ac* Age at Peak Sequestration DBH at Peak Growth
10% Oregon White Oak 0.064 3.84 150 50
10% Ponderosa Pine 0.125 7.5 200 40
10% Douglas-fir 0.083 4.98 100 40
10% Southern Magnolia 0.28 16.8 80 20
10% Incense Cedar 0.09 3 100 40
10% Bigleaf Maple 0.13 7.8 80 50
10% American Linden 0.26 15.6 100 20
10% Accolade Elm 0.24 14.4 80 20
10% Red Maple 0.21 12.6 80 20
10% Cascara 0.09 5.4 60 10
Table A.9 Tree species mix inputted into the model for the Urban Forest Expansion strategy.
A-19 State of the Urban Forest Report | December 2022
Appendix
Urban Forest Expansion Strategy Costs
Trees provide many ecosystem services and social benefits that can translate into an
economic benefit for cities and their communities. However planting and maintaining trees
also costs money. In order to understand the fiscal costs of any Urban Forest Expansion
strategy, the cost of implementation must be considered.
Cost estimates are broken down into two types of costs: initial costs per acre to plant and
annual costs per acre to maintain trees as they establish. Cost of pruning of mature trees or
tree removal was not included in the cost estimate.
• Low Density Plantings for Higher Recreational Use Areas
»$450/acre for planting small stock saplings (less than 1” caliper) - $9,000/ acre for
planting large stock saplings 1-2” caliper) at a density of 30 trees/acre.
»$6,480/acre maintenance, including watering during summer months for the first 3
years, and structural pruning of young trees.
• High Density Plantings for Open Space and Natural Areas with Low Recreational Use
»$900/acre for planting small stock saplings (less than 1” caliper) - $18,000/ acre for
planting large stock saplings 1-2” caliper) at a density of 60 trees/acre
»No maintenance costs will be incurred because trees planted will be treated as a
natural area.
A-20 State of the Urban Forest Report | December 2022
Appendix
STREET TREE PLANTING
The Street Tree Planting strategy explores
planting street trees that are primarily in
the public right-of-way such as parking
strips and medians, or adjacent to a street
in unimproved rights-of-way. This type
of planting is generally more constrained
than Urban Forest Expansion.
The carbon sequestration potential of
planting new street trees is assessed
by applying an average of a mix of
tree species. The tree mix was chosen
from frequently planted and climate
appropriate tree species of a variety
of functional types (large-medium-
small form, evergreen and deciduous
dormancy) and will be counted on a
per tree basis. If data is available, the
model will consider the limitations and
opportunities of the range of available
potential planting locations. Total carbon
sequestration in any future year is based
on the number of trees planted each year,
and growth curves applied to estimate the
total carbon sequestration potential in any
year for that mix of species and ages.
Sequestration Benefits
Application of the Street Tree strategy will
sequester 0.13 MgC/Tree/Year until peak
sequestration is reached.
Street Tree Planting Strategy Costs
Street trees provide many ecosystem services and social benefits that can translate
into an economic benefit for cities and their communities. However, planting and
maintaining street trees also costs money. In order to understand the fiscal costs of
our proposed Street Tree Planting strategy, we include the cost of implementation.
Cost estimates are broken down into two types of costs: initial costs per acre to
plant and annual costs per acre to maintain trees. These represent the total cost to
plant and maintain the trees over their lifespan. Cost of pruning of mature trees or
tree removal was not included in the cost estimate.
• $300-400/tree for coordination and planting of a large stock tree (1-2” caliper).
• $216/tree for maintenance, including watering during summer months for the
first 3 years, and structural pruning of young trees.
Species Mix Calibration % Species Rate MgC/yr/tree Age at Peak Sequestration DBH at Peak
10% Douglas-fir 0.083 100 40
10% Accolade Elm 0.24 100 20
10% Zelkova 0.14 80 20
10% Black Tupelo 0.12 80 20
10% Red Maple 0.21 80 20
10% American Hornbeam 0.03 60 10
10% Persian Ironwood 0.05 60 15
10% Paperbark Maple 0.08 60 10
10% Southern Magnolia 0.28 80 20
10% Japanese Snowbell 0.07 60 8
Table A.10 Tree species mix inputted into the model for the Street Tree Planting strateg.