Arborist Reports & Tree Risk Assessments in Mercer Island, WA

An arborist report should answer a specific question.

Do you need documentation for a Mercer Island permit? Are you concerned about a leaning or damaged tree? Are you buying a property with mature trees, planning construction, or trying to prioritize tree work across a shared property?

We provide arborist reports and tree risk assessments for Mercer Island property owners, buyers, HOAs, and project teams. Our team includes Alexander Lasko, ISA Certified Arborist PN-7704A (TRAQ).

The first step is telling us why the report is needed. That determines what we inspect, what we document, and how detailed the written report needs to be.

Call (425) 369-8733 or request an arborist assessment.

What Kind of Arborist Report Do You Need?

The right report depends on the decision it needs to support.

Some assignments overlap. A permit report may include risk findings, while a property evaluation may identify a tree that needs a more formal tree risk assessment.

We define the scope before the visit so you are not paying for a larger report than the situation requires.

What Is an Arborist Report?

An arborist report is a written professional evaluation of one or more trees that documents their condition, relevant defects, site factors, and recommendations.

Depending on the purpose, the report may include species, diameter, photographs, tree condition, risk findings, construction impacts, root-zone information, and recommended action.

What Is a Tree Risk Assessment?

A tree risk assessment evaluates what part of a tree could fail, the likelihood of that failure, what could be struck, and the consequences if failure occurs.

The result helps determine whether monitoring, pruning, further investigation, restricting the target area, or removal is appropriate.

The International Society of Arboriculture’s credentialing program includes the ISA Tree Risk Assessment Qualification, or TRAQ, for professionals trained in standardized tree-risk assessment.

When Does Mercer Island Require an Arborist Report?

Mercer Island may require an arborist report when tree work is connected to development, critical areas, tree removal, or another permit condition. A report isn’t automatically required for every tree-related project.

The exact documentation depends on where the tree is located and why it is being evaluated.

The City’s tree permit guidance is the starting point for current requirements.

Residential Construction and Remodeling

For small residential additions and remodels, Mercer Island currently requires an arborist report as a supplemental document when the project involves removing or working within the drip line of one or more trees.

See the City’s small residential additions and remodels requirements.

That can make early arborist involvement useful for projects involving:

• Additions
• Driveways
• Retaining walls
• Grading
• Utility work
• Excavation
• Other construction close to existing trees

The tree question is easier to solve before the design is final than after excavation limits and building footprints have already been fixed.

Development Reports Have Additional Qualification Rules

Development-related arborist work on Mercer Island has stricter qualification requirements than a normal residential tree consultation.

For development reviews, the City requires additional construction-tree-protection experience alongside TRAQ and an accepted professional credential.

The City can also require peer review or a replacement arborist when it believes a conflict of interest exists, including when an arborist employed by a tree-removal company prepares a development report.

Because we also perform tree work, we review the City’s request before accepting a development-report assignment. Send us the permit comments, checklist, or project documents first so we can confirm whether the scope fits our role or requires an independent consulting arborist.

Trees in Critical Areas

Tree removal in a Mercer Island critical area follows a separate process.

For non-development removal, the City requires qualified-arborist documentation showing that an applicable criterion has been met, such as the tree being hazardous, diseased, in decline, or not viable for retention.

See the City’s tree removal requirements for critical areas.

A critical-area report should therefore address the specific City criterion rather than simply state that the owner wants the tree removed.

What Does Mercer Island Expect in a Development Arborist Report?

A development arborist report can require much more than a statement that a tree is healthy or should be removed.

Depending on the project, Mercer Island can require documentation of:

• Arborist qualifications
• Tree species and diameter
• Critical root zones
• Limits of allowable disturbance
• Tree health, condition, and viability
• Methods used to establish disturbance limits
• Proposed work within tree-protection areas
• Reasons a tree isn’t viable for retention
• Effects of tree removal on remaining or neighboring trees
• Tree-protection measures
• Replacement recommendations
• A numbered tree inventory

The City’s current residential building submittal forms include the Tree Submittal Checklist and related tree documentation used during development review.

The report also needs to correspond with the actual project.

If a foundation, driveway, utility trench, or retaining wall enters the protected area around a retained tree, the important question isn’t simply whether the tree looks healthy today. The arborist may need to evaluate excavation, grading, access, root disturbance, and whether retaining the tree is realistic.

What Is Included in a Tree Risk Assessment?

A tree risk assessment looks at the tree, the site, and what could be affected if part of the tree fails.

Depending on the assignment, we may evaluate:

• Tree species and size
• Roots and visible root-plate condition
• Trunk defects
• Cracks and cavities
• Decay indicators
• Branch unions
• Dead or broken limbs
• Canopy condition
• Changes in lean
• Nearby structures, roads, driveways, or occupied areas
• Recent excavation or root disturbance
• Storm damage
• Site exposure and surrounding conditions

Labelling every imperfect tree as dangerous isn’t the goal.

A mature tree can have defects without requiring removal. The assessment should identify the relevant defect, what could fail, what could be affected, and what action is proportionate to the actual risk.

Level 1, Level 2, and Level 3 Tree Risk Assessments

Level 1 is a limited visual assessment. It is primarily used to screen trees and identify which ones may need closer inspection.

Level 2 is a basic assessment. It involves a detailed ground-based inspection of the tree and surrounding site and is appropriate for many residential risk questions.

Level 3 is an advanced assessment. It is used when a basic inspection cannot adequately answer an important question and may involve specialized diagnostic techniques.

Not every tree needs advanced testing.

If a Level 2 assessment provides enough information to make a reasonable recommendation, additional investigation may not change the decision. When specialized diagnostics are warranted, we confirm that scope separately rather than automatically adding them to every assessment.

How Do We Prepare an Arborist Report?

We start with the reason for the report rather than forcing every property into the same template.

1. Tell Us Why You Need the Report

Let us know whether the assessment concerns:

• A Mercer Island permit
• A leaning or damaged tree
• A property purchase
• An HOA or shared property
• A remodel or construction project
• Another specific tree concern

2. Send the Documents You Already Have

Useful material can include:

• City notices or correction letters
• Permit checklists
• Site plans
• Surveys
• Architectural drawings
• HOA requests
• Photographs
• Previous arborist reports
• Relevant tree history

You do not need to create documents that do not already exist. We mainly want to understand who requested the report and what they expect it to answer.

3. We Inspect the Tree and Site

The site visit may include tree measurements, photographs, condition observations, surrounding targets, and other information required by the assignment.

For permit or project work, we also review the relevant plans or City documentation you provided.

4. We Prepare the Written Findings

The report detail should match the purpose.

A written report for one residential tree does not need to become a full construction tree-management plan. A multi-tree, permit, HOA, or development assignment may require substantially more documentation.

5. You Receive the Report and Recommendations

The final report documents the findings, recommendations, relevant photographs or supporting information, and arborist credentials appropriate to the scope.

If the City, HOA, buyer, or another recipient requests additional information, we can determine whether it falls within the original assignment or requires additional work.

For broader consulting needs, see our professional arborist consultations.

Should a Leaning or Damaged Tree Be Removed?

A leaning tree does not automatically need to be removed. A new or increasing lean combined with root movement, soil cracking, structural damage, or other recent changes deserves prompt assessment.

Warning signs worth evaluating include:

• A new or increasing lean
• Soil lifting or cracking near the base
• Exposed or newly lifted roots
• Fresh trunk cracks
• Major branch-union cracks
• A broken top or large limb
• Significant decay indicators
• Recent excavation near the tree
• Storm damage
• Movement toward a home, road, driveway, or occupied area

A tree risk assessment may lead to monitoring, pruning, further investigation, managing the area beneath the tree, or removal.

If removal is ultimately appropriate, we also provide tree removal services.

If pruning can reasonably address the problem, see our tree trimming and pruning services.

Arborist Assessments for Home Buyers, HOAs, and Property Owners

A standard home inspection isn’t a detailed arboricultural assessment.

If a Mercer Island property has mature trees close to the house, driveway, retaining wall, neighboring property, or proposed future construction, a separate arborist evaluation can identify conditions worth understanding before closing.

A buyer assessment can document:

• Visible tree condition
• Major structural concerns
• Damaged or declining trees
• Obvious root or soil problems
• Trees likely to need near-term attention
• Tree locations that could affect planned remodeling

The goal is not to predict every future tree expense. It is to identify significant conditions you would rather understand before buying the property.

HOA and Shared-Property Assessments

For an HOA or shared property, the more useful question is often which trees need action first.

A multi-tree assessment can help:

• Identify trees needing closer evaluation
• Prioritize pruning, monitoring, or removal
• Document observed condition at the time of inspection
• Separate immediate concerns from lower-priority maintenance
• Create a clearer basis for tree-care budgeting
• Track recommendations across later inspections

For larger properties, numbered trees or a basic inventory can also make future work orders and reassessments easier to follow.

How Much Does an Arborist Report Cost on Mercer Island?

A single-tree written arborist report on Mercer Island typically costs $200 to $400 through MTS Tree and Landscape, while a formal single-tree TRAQ risk assessment typically costs $250 to $500. Multi-tree written reports generally run $500 to $1,000 or more, and pre-construction assessments typically run $500 to $2,000 or more.

Our current regional pricing is:

These are our current regional service ranges, not independent Mercer Island market averages.

Price increases mainly come from:

• More trees
• A written report instead of a verbal consultation
• Formal risk-assessment requirements
• Tree inventories or mapping
• Construction-plan review
• Extensive photography or supporting documentation
• Site access
• Specialized diagnostic work

A written report for one tree is a much smaller assignment than documenting multiple trees around a construction project.

Tell us how many trees are involved and why the report is needed so we can quote the correct scope.

Request an arborist report quote or call (425) 369-8733.

Why Work With MTS Tree and Landscape?

We’ve served the Eastside and Seattle since 2005 and provide arborist consultations, written reports, tree risk assessments, and related tree-care services throughout the region.

We are licensed, bonded, and insured in Washington under contractor registration SOUNDPL826DZ and UBI 603554491. Our team includes Alexander Lasko, ISA Certified Arborist PN-7704A (TRAQ).

The recommendation should follow what we find.

Depending on the tree and the reason for the assessment, the appropriate next step may be:

• Monitoring
• Selective pruning
• Additional investigation
• Changes to the project or target area
• Removal where the tree cannot reasonably be retained

For development work, we also recognize Mercer Island’s additional qualification and conflict-of-interest requirements and confirm the appropriate report path before accepting the assignment.

For our other local services, see our tree and landscape services on Mercer Island.

Book an Arborist Assessment on Mercer Island

You do not need to know the technical name of the report before you contact us.

Tell us what prompted the assessment, how many trees are involved, who needs the documentation, and what decision the report needs to support.

We can determine whether the appropriate next step is a written condition report, tree risk assessment, permit-support report, property evaluation, or another arborist service.

Mercer Island Arborist Report and Tree Risk Assessment FAQs