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April 16, 2024

PORT OF SEATTLE
RESOLUTION NO. 3821
A RESOLUTION of the Port of Seattle Commission adopting SEA Tree
Replacement Standards for Airport Activities Area and SEA
Land Stewardship Plan for Seattle-Tacoma International
Airport.
WHEREAS, the Port of Seattle is a special purpose government with a mission to
promote economic opportunities and quality of life in the region by advancing trade, travel,
commerce and job creation in an equitable, accountable and environmentally responsible
manner; and
WHEREAS, the Port operates essential transportation infrastructure at Seattle-Tacoma
International Airport (SEA), to ensure the efficient movement of people and goods in the
region, and must utilize land for development and operations; and
WHEREAS, the Port is committed to responsible management of its natural resources
because trees, forests, and other habitat are incredibly important to the environment and
provide tremendous benefits to our neighboring communities and the public; and
WHEREAS, the Port continues to ensure that all its operations and development
activities are in compliance with city, state, and federal development standards; and
WHEREAS, the Port continually strives to go beyond the minimum regulatory
requirements to address environmental justice, improve environmental health, increase
climate resilience, and improve habitat for fish and wildlife; and
WHEREAS, the Port Commission, through Resolution No. 3741, adopted the Interlocal
Agreement with the City of SeaTac defining the “Airport Activity Area” inside which Port
capital development activities are subject to compliance with the Airport Building Department
development standards; and
WHEREAS, Burien, Des Moines, and SeaTac municipal code all include tree
replacement standards for development, while no tree replacement standards are currently in
effect for the Airport Activity Area; and

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WHEREAS, the Port Commission, through Order No. 2023-10, adopted Environmental
Land Stewardship Principles and Strategies to guide development of Port environmental land
stewardship efforts around trees, forest, and other habitat to further improve the livability,
accessibility, and environmental health of the region; and
WHEREAS, the Environmental Land Stewardship Principles recommend a holistic
ecological approach, ensuring development and other land use projects replace the ecological
function and community benefits of any cleared trees; and
WHEREAS, the SEA Tree Replacement Standards for Airport Activity Area and SEA Land
Stewardship Plan emphasize healthy and self-sustaining forests in harmony with the
Commission values recommended in the Environmental Land Stewardship Principles; and
WHEREAS, the Land Stewardship Plan is a living, operational document used as a
framework to steward trees, forests, and other habitats that will be updated administratively
on a periodic basis to reflect new and changing conditions.
NOW, THEREFORE, BE IT RESOLVED by the Port of Seattle Commission as follows:
SECTION 1. Port of Seattle Commission adopts the Tree Replacement Standards
policy directive, attached as Exhibit A to this resolution in alignment with the Commission Order
No. 2023-10: Port-wide Environmental Land Stewardship Principles and Strategies.
SECTION 2. Port of Seattle Commission adopts the SEA Land Stewardship Plan,
attached as Exhibit B to this resolution, in alignment with the Commission Order No. 2023-10:
Port-wide Environmental Land Stewardship Principles and Strategies. The Plan will be updated
administratively, as needed.
ADOPTED by the Port of Seattle Commission at a duly noticed public meeting thereof,
held this 16 day of April, 2024, and duly authenticated in open session by the signatures of the
commissioners voting in favor thereof and the seal of the commission.

Port of Seattle Commission
Resolution No. 3821, SEA Land Stewardship Plan

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EXHIBIT A to Resolution 3821
SEA Tree Replacement Standards For Airport Activity Area
SECTION 1.

Purpose.

Port-owned properties are subject to tree replacement standards established by the local
jurisdictions in which the properties are located. Certain Port-owned properties within the SEA
airport boundary, the “Airport Activity Area” as defined in the 2018 Port-SeaTac Interlocal
Agreement, attachment to Resolution 3741, are not subject to City of SeaTac tree replacement
standards.
The purpose of this policy directive is to offer tree replacement standards for the “Airport
Activity Area”, that may be impacted by Port operational and development purposes,
consistent with the Port-wide Environmental Land Stewardship Principles.
Tree replacement standards include components for retention of existing trees on the
development site and replacing trees permitted to be cleared. The retention requirement
recognizes the intensive industrial and commercial land use that typifies Port development.
The replacement standard relies on a holistic ecological approach that gives credit for planting
trees and for taking actions to improve forest health at off-site locations, including protecting
the life of existing high-value trees and restoring areas infested with invasive plants to native
vegetation.
This approach is consistent with the Environmental Land Stewardship Principles, which
recommends using holistic ecological methods and practices, as well as the SEA Land
Stewardship Plan (Exhibit B), which includes site resource documentation that informs project
planning and design, including tree replacement.
SECTION 2.

Definitions

When used in this policy directive, the following words and phrases shall have the meanings
given below unless the context in which they are included clearly indicates otherwise:
A. Adjacent location. Port-owned property contiguous to and easily and directly accessible
from the development footprint.
B. Airport Activity Area (AAA). The area defined in the 2018 Port-SeaTac Interlocal
Agreement, attachment to Resolution No. 3741, as being within Airport Building
Department jurisdiction and subject to the tree replacement standards herein.
C. Forest. An area with predominant tree canopy cover.

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D. Forest cover. The proportion of tree canopy in a given area. Includes trees in forested
areas and tree groves as well as individual trees.
E. High-value tree. A tree providing significant ecological function due to size, maturity,
species, or location in a tree grove. In general, trees greater than 30 inches diameter at
breast height (30 inches DBH) are considered high-value due to their size. All regulated
native conifers occurring within a tree grove that contains at least three trees greater
than 30” DBH are considered to be high-value trees.
F. Invasive species. Non-native plant species that aggressively colonize areas, threating
native plants and habitat as well as infrastructure. Invasive species cause environmental
and economic harm. Invasive species prioritized for management are listed on King
County’s Noxious Weeds List.
G. Off-site location. Distant from and not directly associated with a proposed development
footprint.
H. On-site location. Within the development footprint, which includes the building and
supporting infrastructure (e.g., parking areas, landscaping; exterior fencing and
lighting).
I. Portwide Environmental Land Stewardship Principles. Refers to Order 2023-10,
approved by the Commission on July 11, 2023.
J. Regulated Tree. A tree that is subject to replacement according to the development
standards herein.
K. Tree. A woody perennial plant with a single stem growing to more than 30 feet at
maturity and bearing lateral branches beginning some distance above the ground.
L. Tree Grove. A group of trees that grow close together, generally without many bushes
or other plants underneath, and anchored by at least three high-value trees.
SECTION 3.

Scope and Applicability.

These standards pertains to the “Airport Activity Area”, as defined in the 2018 Port-SeaTac
Interlocal Agreement, attachment to Resolution No. 3741.
SECTION 4.

Responsibilities.

The Port’s Executive Director, or a delegate, shall ensure the Tree Replacement Standards
Policy Directive is implemented and adequately funded, and that the Policy Directive is
integrated into capital project plans and key operational decisions in the Airport Activity Area,
as defined in the 2018 Port-SeaTac Interlocal Agreement, attachment to Resolution 3741. The
Executive Director shall also ensure that outcomes associated with the application of the Tree
Replacement Standard Policy Directive are transparently documented and publicly exhibited so
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that the Port of Seattle Commission can review, in public, how projects are meeting its Tree
Replacement Standards. The Executive Director shall also ensure that the program evaluation
meets the purpose and timeliness identified in Section 6 of this policy.
SECTION 5.

Policy.

A. Tree Replacement Standards.
(1)

Regulated Tree. A regulated tree must be replaced according to the
standards herein. Regulated trees meet one of the following criteria:

a. equal to or greater than six inches diameter at breast height (6” DBH); or
b. any tree planted by design as part of landscaping for existing development.
(2)

Tree Retention. The intensive industrial/commercial land use supporting
airport operations provides limited opportunity for retaining existing trees on
development sites. Therefore, projects with clearing impacts will not be
subject to a minimum retention requirement but shall retain existing trees to
the extent practicable.

(3)

Tree Replacement. If a Regulated Tree is to be cleared:

a. It must be replaced at a 4:1 ratio.
b. Replacement uses a “stewardship credit” approach for which a replacement
credit can be generated the following ways:
i.
ii.

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iii.

Tree Planting. Plant one tree in an on-site or off-site location, or
Invasive removal. Remove 200 square feet of invasive vegetation
from an off-site location and replanting the area with native
understory vegetation, or
Tree Protection. Protect the life of one tree using one of the following
means:
a. Retain one regulated tree within the development footprint
through project design and construction methods, or
b. Protect the life of one high-value tree in an off-site location from
invasive threats (e.g., removing English ivy from the tree trunk
and vicinity).

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B. The tree replacement standards shall be supplemented by specific design criteria, to be
applied as part of capital project planning and design. The criteria ensure that tree
replacement concepts and designs are consistent with Environmental Land
Stewardship Principles, operational requirements, and equity policy.
(1)

Tree replacement requirements are to be evaluated using site inventories for
the development site and potential adjacent and off-site planting areas. Site
inventories are required to be completed as part of the project planning and
design.

(2)

Stewardship credits generated by tree planting shall account for greater than
50% of the replacement requirement.

(3)

Tree replacement shall be prioritized and maximized first on-site, then adjacent
to the development footprint before utilizing off-site locations.

(4)

For tree replacement that occurs on-site or at adjacent locations, projects shall
consider the potential for employee access to tree replacement areas to
improve project equity and employee wellness benefits.

(5)

Designed tree replacement shall be consistent with rules for safe aviation,
including the Wildlife Hazard Management Plan; Flight Corridor Safety Program
vegetation height limits and regulatory requirements; and all applicable
environmental laws and regulations.

SECTION 6.

Program Evaluation.

The Executive Director, or a delegate, shall monitor and evaluate progress towards achieving
the policy directive. This monitoring and evaluation shall include but not be limited to the
following:
A. Documentation. In alignment with the Airport Building Department permitting, capital

projects are required to inventory and documents all trees in the development
footprint and trees that are planned for clearing. Projects that clear trees must create
a tree replacement plan documenting how trees will be replaced and complete an
accounting worksheet demonstrating tree replacement requirements are achieved.

A comprehensive database will be developed and maintained documenting the
location and extent of all tree clearing impacts and replacement actions (tree
planting, tree protection, invasive restoration).
B. Reporting. Documented tree replacement pursuant to the SEA Tree Replacement

Policy Directive will be reported annually in the Environment and Sustainability Center
of Expertise’s Key Performance Indicators. Staff will present a summary of Key

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Performance Indicators annually to the Sustainability, Environment, and Climate
Committee.
C. When substantive administrative updates to the SEA Land Stewardship Plan are made,

Commissioners will be notified through the Sustainability, Environment, and Climate
Committee.

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