Chapter 19.10


19.10.005    Purpose.

19.10.010    Tree code – Overview.

19.10.020    Applicability and permit required.

19.10.030    Exemptions.

19.10.040    General provisions.

19.10.050    Tree removal – Not associated with a development proposal.

19.10.060    Tree removal – Associated with a development proposal.

19.10.070    Tree replacement.

19.10.080    Tree protection standards.

19.10.090    Application requirements.

19.10.100    Trees on public property.

19.10.110    Seasonal development limitations.

19.10.120    Rounding.

19.10.130    Bald eagle and other federal and state requirements.

19.10.140    Nuisance abatement.

19.10.150    Appeals.

19.10.160    Enforcement.

19.10.005 Purpose.

Protecting, enhancing, and maintaining trees are key community values expressed in the Mercer Island comprehensive plan. The purpose of this chapter is to encourage building and site design to minimize tree removal, and to establish standards and procedures that will result in the retention of trees on Mercer Island.

The city recognizes that trees:

A. Contribute to the residential character on Mercer Island;

B. Provide a public health benefit;

C. Provide wind protection, ecological benefits to wetlands and watercourses, and aid in the stabilization of geologically hazardous areas;

D. Improve surface water quality and control and benefit Lake Washington; and

E. Reduce noise and air pollution.

The city further acknowledges that the value of protecting, enhancing, and maintaining trees should be balanced with the other community goals of:

F. Reasonable enjoyment and use of private property by the property owner; and

G. Providing delivery of reliable utility service. (Ord. 17C-15 § 1 (Att. A)).

19.10.010 Tree code – Overview.

This section is intended to provide an overview of the tree regulations contained in this chapter.

A. Generally, a permit is required to remove any tree with a diameter of greater than 10 inches (see MICC 19.10.020 and 19.10.030 for details).

B. Nondevelopment Tree Removal. If the tree is being removed for reasons other than development (for example, if the tree is coming out because a property owner is landscaping their yard), then:

1. A simple application is required. The application shows the location of trees on the property, the tree(s) to be removed, and where replanting will occur (see MICC 19.10.090(A), General Information, for details).

2. Replacement trees are required for the tree(s) removed, typically between October 1 and April 1 following removal (see MICC 19.10.070 for details).

C. Development Tree Removal. If the tree is being removed as part of a development (for example, to allow for construction of a new home), then:

1. A full application is required. The application provides details on the trees on site, the removed trees, and the proposed protection measures for trees that will remain (see MICC 19.10.090 for details).

2. Retention of some trees is required. At a minimum, 30 percent of the trees will need to be retained. Trees that are exceptional, are large, and have a high likelihood for long-term survival are prioritized for retention (see MICC 19.10.060 for details).

3. Replacement trees are required for the tree(s) removed, typically between October 1 and April 1 following removal (see MICC 19.10.070 for details). (Ord. 17C-15 § 1 (Att. A)).

19.10.020 Applicability and permit required.

A. Applicability. The provisions of this chapter shall apply to all property and public rights-of-way in the city.

B. Permit Required. A permit approval is required prior to removing any tree, except for trees that are exempt pursuant to MICC 19.10.030.

1. Permit approval to remove one or more nonhazardous trees may take the form of a tree removal permit or other construction permit approval.

2. Permit approval to remove one or more trees that pose an imminent threat to life or property, such as tree limbs or trunks that are demonstrably cracked, leaning toward overhead utility lines or structures, or are uprooted by flooding, heavy winds or storm events, in which event the permit must be applied for within 14 days of the removal. Permit applications shall be accompanied by documentation of the imminent threat to life or property, ideally in the form of a report by a qualified arborist, but at least in the form of photographs that clearly depict the threat. Prior notice of the impending tree removal should be provided to the city.

3. For the purposes of this section, tree removal includes the cutting or removing directly or indirectly through site grading of any tree, or root destruction that will result in a tree ultimately becoming a hazardous tree. (Ord. 17C-15 § 1 (Att. A)).

19.10.030 Exemptions.

Except where undertaken within critical areas and associated buffers, or on public property, the following activities are exempt from the permitting, replacement, retention, and protection provisions of this chapter:

A. Small Tree Removal. Removal of trees with a diameter of less than 10 inches that meet the definition of small trees, except if the small tree is an exceptional tree, as defined, or was previously planted as a replacement tree.

B. Removal of species identified in the weeds of concern, noxious, or invasive weed lists established by Washington State or King County, as amended.

C. Tree Pruning. Tree pruning, as defined in MICC 19.16.010, on private property. (Ord. 17C-15 § 1 (Att. A)).

19.10.040 General provisions.

A. Relationship with Other Mercer Island Codes and Ordinances. In addition to any requirements under this chapter, the removal or pruning of any tree located within a critical area, critical area buffer or the shoreline jurisdiction shall comply with the requirements of Chapter 19.07 MICC. The city arborist may require additional information in order to confirm compliance with those requirements.

B. Public Property.

1. A private property owner may apply for a tree permit to prune or cut trees on any city street, pursuant to MICC 19.10.100.

2. Pruning or cutting of trees within a public park by a private property owner is prohibited.

C. Private Utility Companies. A tree permit will be issued to private utility companies to cut trees located on public or private property if necessary for public safety, removal of hazardous trees, removal of diseased or dead trees, as part of any private utility tree maintenance program approved by the city, or for construction work. Regardless of whether or not a permit is required, all cutting or pruning of trees by private utility companies shall be performed under the supervision of a certified arborist and at the sole cost and expense of the utility company. (Ord. 17C-15 § 1 (Att. A)).

19.10.050 Tree removal – Not associated with a development proposal.

A. Tree removal that is not associated with a development proposal shall provide replacement trees (MICC 19.10.070), but is exempt from tree retention (MICC 19.10.060).

B. An application for tree removal that is not associated with a development proposal shall provide the application information described under MICC 19.10.090(A) – General Information.

C. This section shall not be construed as an exemption to the tree retention and replacement requirements of Chapter 19.07 MICC. (Ord. 17C-15 § 1 (Att. A)).

19.10.060 Tree removal – Associated with a development proposal.

A. Single-Family Zoning Designations.

1. In the R-8.4, R-9.6, R-12, and R-15 zoning designations, tree retention is required for the following development proposals:

a. An addition or remodel to an existing single-family dwelling that will result in the addition of more than 500 square feet of gross floor area on a lot with a net lot area of 6,000 square feet or more;

b. A new single-family dwelling on a lot with a net lot area of 6,000 square feet or more;

c. A subdivision or short subdivision.

2. Retention Requirement. Development proposals specified under subsection (A)(1) of this section shall retain trees as follows:

a. A minimum of 30 percent of trees with a diameter of 10 inches or greater, or that otherwise meet the definition of large tree, shall be retained over a rolling five-year period.

b. In addition to the retention required in subsection (A)(2)(a) of this section, the development proposal shall be designed to further minimize the removal of large trees and maximize on-site tree retention as follows:

i. Site improvements, including but not limited to new single-family homes, additions to a single-family home, appurtenances, accessory structures, utilities, and driveways, shall be designed and located to minimize tree removal during and following construction.

ii. The following trees shall be prioritized for retention:

(a) Exceptional trees;

(b) Trees with a diameter of more than 24 inches;

(c) Trees that have a greater likelihood of longevity; and

(d) Trees that are part of a healthy grove.

iii. Trees shall not be removed outside the area of land disturbance except where necessary to install site improvements (e.g., driveways, utilities, etc.).

iv. Tree removal for the purposes of site landscaping should be limited to those trees that will pose a future safety hazard to existing or proposed site improvements.

c. Provide tree replacement pursuant to MICC 19.10.070.

3. Retention of Exceptional Trees. Development proposals specified under subsection (A)(1) of this section shall retain exceptional trees with a diameter of 24 inches or more. Exceptional trees with a diameter of 24 inches or more that are retained shall be credited towards compliance with the retention requirements of subsection (A)(2) of this section. Removal of exceptional trees with a diameter of 24 inches or more, shall be limited to the following circumstances:

a. Retention of an exceptional tree(s) with a diameter of 24 inches or more will result in an unavoidable hazardous situation; or

b. Retention of an exceptional tree(s) with a diameter of 24 inches or more will limit the constructable gross floor area to less than 85 percent of the maximum gross floor area allowed under Chapter 19.02 MICC; or,

c. Retention of an exceptional tree(s) with a diameter of 24 inches or more will prevent creation of a residential lot through a subdivision or short subdivision that is otherwise allowed by this title.

4. Calculation of Rolling Five-Year Period. For the purposes of this section, the rolling five-year period begins five years prior to the date of application for a development approval that is subject to tree retention.

5. Compliance Required. Development proposals on lots that have removed more than 70 percent of large trees within the rolling five-year period, such that the 30 percent tree retention requirement under subsection (A)(2) of this section cannot be met, shall not receive approval unless and until compliance has been achieved. For example, a lot that has removed all of the trees in year “one” may not receive a preliminary subdivision approval in year “four.” However, the preliminary subdivision approval may be granted in year “six,” such that the rolling five-year period does not include the tree removal in year “one.”

B. Commercial or Multifamily Zoning Designations – Tree Removal.

1. In the P, B, C-0, PBZ, TC, MF-2, MF-2L, and MF-3 zoning designations a tree permit is required and will be granted if it meets any of the following criteria:

a. It is necessary for public safety, removal of hazardous trees, or removal of diseased or dead trees;

b. It is necessary to enable construction work on the property to proceed and the owner has used reasonable best efforts to design and locate any improvements and perform the construction work in a manner consistent with the purposes set forth in MICC 19.10.005;

c. It is necessary to enable any person to satisfy the terms and conditions of any covenant, condition, view easement or other easement, or other restriction encumbering the lot that was recorded on or before July 31, 2001; and subject to MICC 19.10.090(B);

d. It is part of the city’s forest management program or regular tree maintenance program and the city is the applicant;

e. It is desirable for the enhancement of the ecosystem or slope stability based upon professional reports in form and content acceptable to the city arborist.

2. Design Commission Review Required in Commercial Zones. A tree permit for a development proposal, resulting in regulated improvements located in a commercial zone, that has previously received design commission approval must first be reviewed and approved by the city’s design commission prior to permit issuance by the city. (Ord. 17C-15 § 1 (Att. A)).

19.10.070 Tree replacement.

Trees that are cut pursuant to a tree permit shall be replaced as specified in subsections A and B of this section, or a fee in lieu shall be paid as specified in subsection C of this section.

A. Tree Replacement Ratio. Removed trees shall have the following base replacement ratio:

Diameter of removed tree

Number of replacement trees required

Less than 10 inches


10 inches up to 24 inches


24 inches up to 36 inches


More than 36 inches and any exceptional tree(s)


B. Replacement Trees.

1. Location. Replacement trees shall be located in the following order of priority from most important to least important:

a. On-site replacement adjacent to or within critical tree areas as defined in Chapter 19.16 MICC;

b. On-site replacement outside of critical tree areas adjacent to other retained trees making up a grove or stand of trees;

c. On-site replacement outside of critical tree areas; and

d. Off-site in adjacent public right-of-way where explicitly authorized by the city.

2. Species. Replacement trees shall primarily be those species native to the Pacific Northwest. In making a determination regarding the species of replacement trees, the city arborist shall defer to the species selected by the property owner unless the city arborist determines that the species selected is unlikely to survive for a period of at least 10 years, represents a danger or nuisance, would threaten overhead or underground utilities or would fail to provide adequate protection to any critical tree area.

3. Size.

a. Coniferous trees shall be at least six feet tall; and

b. Deciduous trees shall be at least one and one-half inches in caliper.

The city arborist may authorize the planting of smaller-sized replacement trees if the applicant can demonstrate that smaller trees are more suited to the species, the site conditions, neighborhood character, and the purposes of this section, and that such replacement trees will be planted in sufficient quantities to meet the intent of this section. The city arborist shall not authorize the planting of shrubs or bushes in lieu of required replacement trees.

4. Reduction. The city arborist may reduce the number of replacement trees as follows, where other measures designed to mitigate the tree loss by restoring the tree canopy coverage and its associated benefits are considered to be effective and consistent with the purposes of this chapter. The city arborist may consider, but is not limited to, the following measures:

a. Replacement of hazardous, undesired, or short-lived trees with healthy new trees that have a greater chance of long-term survival;

b. Restoration of critical tree areas with native vegetation; and

c. Protection of small trees to provide for successional stages of tree canopy.

5. Timing. Replacement trees shall be planted in the wet season (October 1 through April 1), following the applicable tree removal or, in the case of a development proposal, completion of the development work, provided the city arborist may authorize an extension to ensure optimal planting conditions for tree survival.

C. Fee-in-Lieu. If the city arborist determines there is insufficient area to replant on the site or within the adjacent public right-of-way, the city arborist may authorize payment of a fee-in-lieu provided:

1. There is insufficient area on the lot or adjacent right-of-way for proposed on-site tree replacement to meet the tree replacement requirements of this chapter; or

2. Tree replacement or management provided within public right-of-way or a city park in the vicinity will be of greater benefit to the community.

3. Fees provided in lieu of on-site tree replacement shall be determined based upon:

a. The expected tree replacement cost including labor, materials, and maintenance for each replacement tree; and

b. The most current Council of Tree and Landscaper Appraisers Guide for Plant Appraisal.

4. Any fee-in-lieu is also optional for the applicant and requires an explicit written agreement.

D. Maintenance of Replacement Trees. The applicant shall maintain all replacement trees in a healthy condition for a period of five years after planting. The applicant shall be obligated to replant any replacement tree that dies, becomes diseased, or is removed during this five-year time period.

E. Private Utility Company. If the permit is granted to a private utility company and the property owner is unwilling to place any replacement trees on the owner’s property, the private utility company shall pay to the city the amount necessary to purchase and plant replacement trees on public property necessary to mitigate the impact of the removed trees based upon arborist industry standards. Monies paid to the city for replacement trees shall be used for that purpose. (Ord. 17C-15 § 1 (Att. A)).

19.10.080 Tree protection standards.

A. To ensure long-term viability of trees identified for protection, permit plans and construction activities shall comply with the then-existing Best Management Practices (BMP) – Managing Trees During Construction, published by the International Society of Arboriculture, adopted by reference. The tree protection plan shall be prepared by a qualified arborist and the plan shall be reviewed for adequacy by the city arborist. All minimum required tree protection measures shall be shown on the development plan set and tree replanting/restoration/protection plan.

B. Alternative Methods. The city arborist may approve construction-related activity or work within the tree protection barriers if the city arborist concludes:

1. That such activity or work will not threaten the long-term health of the retained tree(s); and

2. That such activity or work complies with the protective methods and best building practices established by the International Society of Arboriculture. (Ord. 17C-15 § 1 (Att. A)).

19.10.090 Application requirements.

The city shall establish and maintain a tree removal permit application form to allow property owners to request city review of tree removal for compliance with applicable city regulations. The application shall include at a minimum, the following:

A. General Information.

1. The name, address, telephone number of the applicant, the name, address, telephone number of the property owner, and the street address of the property.

2. The proposed location, species, diameter, and number of trees proposed to be cut or public tree proposed to be pruned.

3. The proposed location and number of any required replacement trees.

4. A site plan reflecting the location of large trees and the relative location of structures, driveways, and buildings.

5. Additional information required by the city to confirm compliance with this Chapter or Chapter 19.07 MICC.

B. Critical Tree Area. An application covering a tree located in a critical tree area, as defined in Chapter 19.16 MICC, shall include a proposed time schedule for the cutting, land restoration, implementation of erosion control and other measures that will be taken in order to prevent damage to the critical tree area.

C. Development Plan Set. An application for a development proposal that requires tree retention, and that will result in the removal of one or more trees and as a result of construction work, shall include the following:

1. Detailed Site Plan. The site plan shall include the following information at a minimum:

a. Location of all proposed improvements, including building footprint, access, utilities, applicable setbacks, buffers, and required landscaped areas clearly identified. If a short plat or subdivision is being proposed and the location of all proposed improvements cannot be established, a phased tree retention plan review is required as described below;

b. Accurate location of large trees on the subject property (surveyed locations may be required). The site plan must also include the trunk location and critical root zone of large trees that are on adjacent property with driplines extending over the subject property line;

c. Trees labeled corresponding to the tree inventory numbering system;

d. Location of tree protection measures;

e. Indicate limits of disturbance (LOD) drawn to scale around all trees potentially impacted by site disturbances resulting from grading, demolition, or construction activities (including approximate LOD of off-site trees with overhanging driplines);

f. Proposed tree status (trees to be removed or retained) noted by an ‘X’ or by ghosting out;

g. Proposed locations of any required replacement trees.

2. A Tree Retention Plan and Arborist Report. The tree retention plan shall contain the following information:

a. A tree inventory containing the following:

i. A numbering system of all existing large trees on the subject property (with corresponding tags on trees); the inventory shall also include large trees on adjacent property with driplines or critical root zones extending into the development proposal site;

ii. Size (diameter);

iii. Proposed tree status (retained or removed);

iv. Tree type or species;

v. Brief general health or condition rating of these trees (i.e., poor, fair, good, etc.).

b. An arborist report, prepared by a qualified arborist, containing the following:

i. A complete description of each tree’s diameter, species, critical root zone, limits of allowable disturbance, health, condition, and viability;

ii. A description of the method(s) used to determine the limits of allowable disturbance (i.e., critical root zone, root plate diameter, or a case-by-case basis description for individual trees);

iii. Any special instructions specifically outlining any work proposed within the limits of the disturbance protection area (i.e., hand-digging, air spade, tunneling, root pruning, any grade changes, clearing, monitoring, and aftercare);

iv. For trees not viable for retention, a description of the reason(s) for removal based on poor health, high risk of failure due to structure, defects, unavoidable isolation (windfirmness), or unsuitability of species, etc., and for which no reasonable alternative action is possible must be given (pruning, cabling, etc.);

v. Describe the impact of necessary tree removal to the remaining trees, including those in a grove or on adjacent properties;

vi. For development applications, a discussion of timing and installation of tree protection measures. Such measures must include fencing and be in accordance with the tree protection standards as outlined in this chapter; and

vii. The suggested location and species of supplemental trees to be used when required. The report shall include planting and maintenance specifications to ensure long-term survival.

3. Additional Information. The city arborist or code official may require additional documentation, plans, or information as needed to ensure compliance with applicable city regulations.

D. Peer Review and Conflict of Interest.

1. The city may require peer review of the tree permit application by a qualified arborist to verify the adequacy of the information and analysis. The applicant shall bear the cost of the peer review.

2. The code official may require the applicant to retain a replacement qualified arborist or may require a peer review where the code official believes a conflict of interest exists. For example, if an otherwise qualified arborist is employed by a tree removal company and prepares the arborist report for a development proposal, a replacement qualified arborist or a peer review may be required. (Ord. 17C-15 § 1 (Att. A)).

19.10.100 Trees on public property.

An application for a tree permit to cut a tree on public property or a request to have the city prune a public tree located on a city street shall be reviewed by the city arborist based upon the following conditions and criteria:

A. By the City. An annual tree permit will be issued to the city to cut any public trees necessary for public safety, removal of hazardous trees, removal of diseased or dead trees, as part of the city’s forest management program or regular tree maintenance program or for construction work on public property.

B. By Private Property Owners in City Street. A private property owner may apply for a tree permit to cut or prune a public tree located on any city street if the owner demonstrates in the following order that all of the criteria are satisfied:

1. The owner establishes that the tree is located on a city street;

2. The city arborist determines that the proposed pruning or cutting can be performed without adversely affecting any critical tree areas;

3. Tree Cutting. The city arborist determines that proposed tree removal is:

a. Necessary for access to private property;

b. Necessary for installation of required public improvements (e.g., sidewalk, public utilities, etc.);

4. Tree Pruning. The city arborist determines that proposed tree pruning is:

a. Required to resolve a possible hazard to public or private health or safety; or

b. Requested by a valid petition executed by at least 60 percent of the property owners located within a 300-foot radius of the subject tree in favor of the proposed pruning of the tree; and

5. Additional information prepared by a qualified arborist, if required by the city arborist, is provided to ensure the long-term health and viability of trees that will remain following pruning or removal;

6. In the case of tree cutting, the private property owner provides tree replacement consistent with MICC 19.10.070;

7. The owner pays a fee to cover all costs associated with reviewing the pruning or cutting request;

8. The pruning or cutting is performed at the sole cost and expense of the private property owner; and

9. Tree topping is prohibited.

C. Pruning or cutting of trees within a public park by a private property owner is prohibited. (Ord. 17C-15 § 1 (Att. A)).

19.10.110 Seasonal development limitations.

No cutting of trees located in geologic hazard areas or protected slope areas is allowed between October 1 and April 1 unless: (A) a tree permit with explicit authorization for removal between October 1 and April 1 has been granted; or (B) removal is required due to an emergency situation involving immediate danger to life or property. The city arborist may authorize tree removal between October 1 and April 1 if the city arborist determines that such environmentally critical areas will not be adversely impacted by the proposed cutting and the applicant demonstrates compelling justification based on a geotechnical evaluation of the site. The city arborist may require hydrology, soils and storm water studies, erosion control measures, restoration plans, and/or an indemnification/release agreement. (Ord. 17C-15 § 1 (Att. A)).

19.10.120 Rounding.

When the retention or replacement calculations results in a fraction, the fraction shall be rounded to the nearest whole number as follows:

A. Fractions of 0.50 or above shall be rounded up to the closest whole number; and

B. Fractions below 0.50 shall be rounded down to the closest whole number. (Ord. 17C-15 § 1 (Att. A)).

19.10.130 Bald eagle and other federal and state requirements.

In addition to any requirement of this chapter, persons must comply with all applicable federal and state laws, rules and regulations including without limitation the Endangered Species Act, the Bald Eagle Protection Act and the Migratory Bird Treaty Act, as now existing or hereinafter adopted or amended. (Ord. 17C-15 § 1 (Att. A)).

19.10.140 Nuisance abatement.

A. In addition to the requirements of this chapter, trees and vegetation which meet the definition of a nuisance shall be subject to the provisions of Chapter 8.24 MICC, Nuisance Control Code.

B. In addition to the provisions of Chapter 8.24 MICC, Nuisance Control Code, the following requirements shall apply to trees and vegetation:

1. Branches over roads shall be trimmed to a minimum of 12 feet above the road surface (see Figure 1).

2. Branches over sidewalks shall be trimmed to a minimum of eight feet above the sidewalk and one foot behind the sidewalk (see Figure 1).

3. Street trees and other vegetation will be spaced according to the following spacing requirements to facilitate the safe flow of traffic (see Figure 2):

a. No tree plantings are allowed within a 30-foot sight triangle at any street intersection.

b. Shrubs shall not exceed 36 inches in height above the street level within this triangle.

c. Ten-foot minimum spacing shall be observed for small trees.

d. Hedges are not allowed between the sidewalk and the curb, and must be planted at least five feet behind the sidewalk.

e. Hedges must be trimmed at least three feet behind the sidewalk.

f. Plantings of trees, shrubs or hedges are not allowed between the street/road edge and a ditch.

Figure 1

Figure 2

(Ord. 17C-15 § 1 (Att. A)).

19.10.150 Appeals.

Any person or persons aggrieved by any action or decision of city staff made pursuant to any section of this chapter may appeal such action or decision in accordance with the appeal procedure set forth in Chapter 19.15 MICC. (Ord. 17C-15 § 1 (Att. A)).

19.10.160 Enforcement.

A. Violation. It is a violation of this chapter for any person to fail to comply with the requirements of this chapter.

B. Civil Penalty and Remediation.

1. Civil Penalty. The penalty for violating this chapter shall be a fine equal to up to three times the value of the damaged or cut tree or removed vegetative cover, plus the cost of reasonable remediation. Trees and other vegetation shall be appraised according to the method specified by the Council of Landscape and Tree Appraisers, most current edition.

2. Remediation. Remediation for trees removed in violation of this chapter shall include, but is not limited to, the following:

a. Removal of the remaining plant parts or debris;

b. Preparation of a replanting plan in a form approved by the code official for replanting the area where trees were removed in violation of this chapter;

c. Payment of the costs to review, approve, and administer the remediation process;

d. Installation of the required replantings as reflected on the replanting plan; and

e. Maintenance of the required replantings for a period of five years.

C. Tree Retention Enforcement. Trees identified for retention through the approval of a development proposal that are subsequently removed, or are damaged to the extent that removal is required, with prior written approval by the city arborist, whether the removal or damage is intentional or unintentional, shall result in a civil penalty pursuant to subsection B of this section, in addition to required replanting and remediation. The code official may waive the civil penalty if the code official determines that appropriate tree protection standards were in place and maintained and natural disaster or events entirely outside the knowledge and control of the property owner resulted in the tree loss. (Ord. 17C-15 § 1 (Att. A)).