Tree Removal Permits in Mercer Island, WA (2026 Guide)

January 4, 2026

arborist in red hard hat with face shield smiling outside near trees.

Written By: Eric Ledford

ISA Certified Arborist – PN-9290A

ISA Qualified Tree Risk Assessor (TRAQ)

Everything Mercer Island homeowners, HOAs, and contractors need to know about tree removal permits, significant tree regulations, Environmentally Critical Areas (ECAs), Tree Protection Zones (TPZs), and replanting requirements (2026)

If you’re planning to remove or prune a tree on Mercer Island in 2026, it’s critical to understand how the city’s tree protection ordinance and land-use regulations apply to your property. Mercer Island enforces some of the strictest tree and environmental protections in the region, particularly for significant trees, shoreline areas, steep slopes, and Environmentally Critical Areas (ECAs).

Tree removal on Mercer Island is closely regulated, and permits are often required even for trees located on private residential property. Missteps—such as removing a regulated tree without approval or disturbing a Tree Protection Zone (TPZ)—can result in project delays, fines, mitigation requirements, or stop-work orders.

This guide explains when a tree removal permit is required on Mercer Island, what qualifies as a significant or regulated tree, how ECAs and TPZs affect development and landscaping, and how working with an ISA Certified Arborist helps ensure your project remains compliant in 2026.

💡 Need help navigating Mercer Island’s tree code? Our team prepares permit-ready arborist reports, tree inventories, risk assessments, and code-compliant removal plans for homeowners, HOAs, and contractors across Mercer Island.

✅ When You Need a Tree Removal Permit in Mercer Island (2026)

In 2026, Mercer Island typically requires review or permitting when any of the following apply:

🌳 Significant Trees

Trees that meet Mercer Island’s size thresholds (measured at DBH — diameter at breast height) may be regulated, particularly when removal affects canopy coverage, site layout, or redevelopment plans.

🏗️ Construction or Development Activity

Tree removal associated with building permits, grading or land clearing, utility installation, or new construction/redevelopment almost always triggers City review.

Building permits
Grading or land clearing
Utility installation
New construction or redevelopment

🌿 Environmentally Critical Areas (ECAs)

Trees located within or adjacent to protected areas often require additional review, protections, and mitigation.

Steep slopes
Wetlands and buffers
Streams and riparian corridors

🌐 Street & Right-of-Way Trees

Trees in the planting strip or public right-of-way require City approval and often must be handled by a properly licensed and insured tree service.

⚠️ Not sure if a permit is required?

An ISA Certified Arborist assessment can determine tree status, document hazards, and clarify permitting requirements before work begins.

📜 Key Highlights of Mercer Island’s 2026 Tree & Land Use Rules

🌱 Tree Replacement & Canopy Requirements

Removal of regulated trees typically requires 1:1 or 2:1 replanting
Replacement trees must meet minimum caliper sizes (commonly 1.5″–2″)
Approved species emphasize long-term canopy value and climate adaptability

🛑 Tree Protection Zones (TPZs)

Trees approved for retention must be protected during construction
TPZ fencing is required to safeguard critical root zones
Encroachment typically requires written justification and mitigation

👉 Tree Protection Zones (TPZ) Explained

⚠️ Hazard Trees

Dead, diseased, or structurally compromised trees may qualify for expedited removal
Mercer Island generally requires a written arborist report
Documentation must address defects, targets, and overall risk level

🌲 Significant, Landmark & Street Trees in Mercer Island

🌲 Significant Trees

Trees meeting Mercer Island’s size thresholds or site-impact standards may be regulated, especially during permitting or redevelopment.

🏗️ Designated / Retained Trees

Trees preserved as part of development approvals. These often come with protection requirements and limits on disturbance.

🛣️ Street Trees

Trees located in the City right-of-way or planting strips. Removal typically requires City approval and the right process.

🚫 Important

Removing protected trees without approval can result in fines, mitigation requirements, and project delays.

🛠️ Working in ECAs & Steep Slopes

If your Mercer Island property is located in an Environmentally Critical Area additional codes apply,

🛠️ What is an Environmentally Critical Area (ECA)?: ECAs can include steep slopes, wetlands and buffers, streams and riparian corridors, and other regulated sensitive areas. If your tree work is within or near an ECA, Mercer Island may require additional review before removal or pruning.
✅ Critical area review (before removal): A critical area review or approval may be required prior to tree removal, especially when work is tied to grading, redevelopment, or site changes.
📋 Tree Inventory & Protection Plan: The City may require a Tree Inventory and Protection Plan prepared by an ISA Certified Arborist to document regulated trees, retention targets, and protection measures.
🛑 TPZ reductions must be justified: If Tree Protection Zones (TPZs) need to be reduced due to lot constraints, existing pavement, or structures, Mercer Island typically expects written justification and mitigation.

📌 2026 Reminder

ECA sites face higher scrutiny and often have stricter replanting and mitigation requirements in 2026.

📝 Documents Commonly Required for Mercer Island Tree Permits

📝 Core Permit Documents

Arborist Report — prepared by an ISA Certified Arborist to document tree condition, defects, and compliance findings
Tree Inventory Table — species, DBH, canopy spread, and health condition for each regulated tree
Site Plan with TPZ Fencing — shows driplines, critical root zones, and required protection measures
Tree Risk Assessment — required when claiming hazard tree status or expedited removal

🌱 Canopy & Mitigation Documents

Tree Credit Calculation Worksheet — used by Mercer Island to evaluate canopy loss, retention, and required mitigation.
Replanting / Mitigation Plan — identifies replacement tree species, caliper size, spacing, and planting locations to meet canopy requirements.
Replacement Ratios — Mercer Island typically requires 1:1 or 2:1 replacement when regulated trees are removed.
Minimum Planting Sizes — replacement trees usually must meet 1.5″–2″ caliper requirements.
Approved & Native Species — ECAs often require native-only species. Commonly approved options may include Douglas fir, western red cedar, vine maple, shore pine, and other regionally appropriate trees.

📄 Our Mercer Island Tree Services include TRAQ risk assessments, arborist reports, site plans, TPZ documentation, and canopy calculations to help streamline the permitting process.

💸 Penalties for Unpermitted Tree Removal in Mercer Island

Fines up to the appraised value of the tree 🌳
Stop-work orders and inspection delays
Increased mitigation and replanting requirements, especially in ECAs

Mercer Island enforces tree regulations strictly. Removing or damaging protected trees without approval can result in costly delays and additional compliance requirements.

Need help with tree permits?
Tree removal and pruning rules vary by city across Washington State. View our Tree Permits by City guide →

🔗 Related Guides for Mercer Island Property Owners

🔗 Related Guides

👷 How Sound Tree Care Helps Mercer Island Property Owners

Our team of ISA Certified Arborists specializes in navigating Mercer Island’s tree code, permitting process, and canopy requirements for residential, HOA, and commercial properties.

📋

Permit-Ready Arborist Reports

Tree inventories, canopy documentation, and City-ready narratives prepared for Mercer Island permit review.

🌳⚠️

TRAQ Hazard Tree Evaluations

Risk assessments supporting expedited or emergency removals under Mercer Island’s tree code.

🪓

Tree Removal & Stump Grinding

Safe, code-compliant removals aligned with permit conditions and inspection requirements.

🛑

TPZ Planning & Construction Support

Tree protection fencing, monitoring, and on-site coordination during construction.

🌱

Replanting & Mitigation Services

Native and approved species selected to meet Mercer Island’s canopy coverage and ECA requirements.

🌲 Tree Removal Permits & Tree Code in Mercer Island (2026)

Your complete guide to Mercer Island’s tree removal permits, significant tree rules, ECAs, canopy requirements, and compliance in 2026.

Planning to remove or work near a tree in Mercer Island, WA? 🏡🌳
Mercer Island’s tree code can be complex — especially when significant trees, Environmentally Critical Areas (ECAs), canopy coverage rules, or construction permits are involved.

This 2026 guide explains when a tree removal permit is required in Mercer Island, how canopy and mitigation are calculated, and what documentation the city typically expects. Whether you’re a homeowner, HOA, or contractor, understanding the rules upfront can help you avoid delays, fines, and stop-work orders.

✅ What This Mercer Island Tree Permit Guide Covers

✔ When a tree removal permit is required in Mercer Island
✔ How significant, retained, and street trees are regulated
✔ ECA & steep slope rules that affect tree work
✔ Tree Protection Zones (TPZs) and construction requirements
✔ Canopy coverage & Tree Credit Calculation Worksheets
✔ Replanting, mitigation, and native species requirements in 2026

🌟 ISA Certified Arborists | TRAQ-Qualified
🌟 5-Star Reviews on Google, Yelp & Facebook
🌟 Licensed, Insured & City-Compliant
🌟 Trusted by Homeowners Throughout Mercer Island

📞 Call us now at 206-486-7790– Speak with a Mercer Island arborist!
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📍 Serving all Mercer Island Neighborhoods

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