Guide to Arborist Reports

The following guide outlines the minimum requirements for Arborist Reports submitted to the City of Kirkland. The City recommends following these guides to avoid delays and/or corrections to submitted Tree Removal Permit applications or Tree Retention Plans.

Arborist Reports for Tree Removal Permits


Factual data such as tree species, trunk size (DBH), and overall health/structure. Observations may indicate the presence of pests/disease and structural defects and the location of the tree relative to adjacent targets in the event of failure. For nuisance trees, photos documenting any property damages should be included. Examples of defects may include, but are not limited to, the following:

  • Dead, diseased, or broken branches, stems, and roots
  • Weakly attached branches and weak codominant unions
  • Mechanical damage and deep cracks
  • Abnormal growth such as swelling, flat/sunken areas, or seams
  • Positive indicators of decay and cankers
  • Root plate shifting, abnormal trunk flare, lack of trunk flare, soil cracks, grade changes, or restricted or undermined roots
  • Unusual tree form and architecture, such as an uncorrected lean, low live crown ratio, or poor taper

Arborists may be asked to verify findings with an advanced assessment, such as a Level 3 Assessment, when there is unsubstantial information provided in the Arborist Report. This may include using decay testing equipment (i.e., core sampling, micro-resistance drill, sonic tomography), conducting an aerial climbing assessment, and/or conducting a root crown excavation using hand tools or air excavation.


An arborist’s professional assessment based on observations. For hazard trees, the ISA has developed a standardized process for assessing tree risk and requires arborists to hold the Tree Risk Assessment Qualification (TRAQ) to assess risk. This approach evaluates the likelihood of whole tree or tree part failure and the associated consequences, based on what is visible during the time of the inspection and what is likely to occur under normal weather conditions, over a reasonable time frame, typically 1 to 5 years. This assessment should include an explanation of structural defects as they relate to overall risk, including the following:

1) An explanation of how the tree or tree parts meet the definition of a hazard pursuant to KZC 95.10(15)(b); and

2) Overall tree risk rating with correlating mitigation measures as follows:

  • If a potential target does not exist, recommendations for routine pruning and maintenance to abate the tree issue;
  • If a tree/tree part is found to have a Low or Moderate Overall Risk Rating, potential mitigation measures to reduce the risk; or
  • If a tree/tree part is found to have a High or Extreme Overall Risk Rating and mitigation of the risk through pruning or moving potential targets is not feasible, recommendations to remove the tree as a hazard tree and suggestions for replacement tree species.

These are the reasonable and proper arboricultural practices that apply, which may include tree removal. Arborists should first consider alternate options for managing trees before recommending removal, such as: pruning, cabling, mulching, irrigation, treatments, regular monitoring, and/or Level 3 Assessments.

Please note the following:

  • An ISA Tree Hazard Evaluation Form is not a substitute for an Arborist Report, as conclusions and recommendations are not within this format. The City will not accept a Hazard Tree Assessment that only includes this form.
  • An invoice or bid for tree work is NOT an arborist report and will not be accepted.

Arborist Reports for Tree Retention Plans Related to Development

The following is intended to be a guide to Arborist Reports prepared for development projects where a Tree Retention Plan is required pursuant to KZC 95.30. The City recommends including all of the following components to avoid corrections and revisions.  Please note that Arborist Reports will not be accepted if the most recent site plans have not been reviewed.


The Summary Section of the arborist report should include the total number of trees assessed and of those trees, the number of trees proposed for retention versus removal. The number of 'Not Viable' trees should also be mentioned. If development plans were not reviewed this should be noted as well.

Observations & Discussion of Development Impacts

Existing Site Conditions: This section should describe existing site conditions such as the site address, square footage of the lot, existing conditions/structures, level of invasive species, and/or existence of critical areas.

Proposed Plans: Reference to the plans reviewed during the evaluation, including the title, author, and date of the plans reviewed.

Tree Information: This section should include all relative tree information and required components per KZC 95.30(3). It should also include a discussion of how the proposed development impacts existing trees located on the subject property, in the public right-of-way, and on neighboring properties.  A summary of these requirements is included below. 

Tree Inventory: Include a Tree Inventory (or reference to attached Tree Table). See Example Tree Inventory Table(PDF, 292KB) . The following information must be included, either in the body of the report or in the associated attachments:

1)  All existing regulated trees on the subject property identified by a numbering system that is consistent throughout the Arborist Report, site plan and onsite tree tags. The inventory must also include regulated trees that are on adjacent properties that appear to have CRZs extending onto the subject property;

2)  Identification of all existing trees in the public right-of-way adjacent to the subject property, regardless of tree size;

3)  The CRZ and the proposed TPZ of all existing regulated trees specified in feet from the face of each tree trunk. The inventory must also include the approximate CRZ and proposed TPZ of regulated trees on adjoining properties that appear to have CRZs extending onto the subject property;

4)  DBH of all existing regulated trees;

5)  Proposed tree removals;

6)  Viability status of each regulated tree based on the combined condition ratings pursuant to KZC 95.30(3)(c);

7)  Tree species and/or common name; and

8)  Potential Landmark Trees and Groves.

9) Tree Density Credits (TDC) for all Viable and Retained trees per KZC 95.34

Tree Viability: A combined overall viability status based on the condition ratings of both health and structure for each regulated tree, including regulated trees on adjoining properties that appear to have CRZs extending onto the subject property. The condition ratings for each regulated tree shall be assessed using the criteria in KZC 95.30(3)(c).

When a tree is determined to be Not Viable, a description of the reason(s) for this rating must be provided.

Tree Protection Zone (TPZ): A description of the method(s) used to determine TPZs (i.e., CRZ formula, trunk multiplication method, dripline, exploratory root excavations, or a case-by-case basis description for individual trees).

Tree Protection Specifications: Any special instructions specifically outlining any work proposed within the CRZ of retained trees (i.e., additional protection from soil compaction, hand-digging, tunneling or boring, root pruning, mitigating any grade changes, monitoring during development activity, watering during summer and aftercare), including potentially impacted trees on adjacent properties,

High Retention Value Trees: If development proposals result in the retention and/or removal of High Retention Value Trees (including Landmark Trees and Groves) provide an explanation of how tree retention was prioritized based on retention feasibility and proposed construction impacts,

Tree Protection Measures: A discussion of timing and installation of tree protection measures that must include fencing in accordance with the tree protection standards in KZC 95.32, including any anticipated changes to tree protection fence location or other activity within the CRZ of retained trees during project construction (e.g., material delivery, equipment access, landscaping),

Tree Removal Impacts: Describe the impact of necessary tree removal on the trees to be retained, including those on adjacent properties,

Supplemental/Replacement Trees: The suggested location and species of replacement trees to be planted. The report shall include planting and maintenance specifications pursuant to KZC 95.50, 95.51, and 95.52.


Qualified Professional Arborist Credentials


The City of Kirkland requires that all Arborist Reports are prepared by a Qualified Professional Arborist with at least two of the following credentials:

  • International Society of Arboriculture (ISA) Certified Arborist
  • Tree Risk Assessment Qualification (TRAQ) as established by the Pacific Northwest Chapter of ISA (or equivalent)
  • American Society of Consulting Arborists (ASCA) registered Consulting Arborist
  • Society of American Foresters (SAF) Certified Forester for Forest Management Plans

For the submittal of Hazard Tree Removal Permits, the arborist must hold an up-to-date TRAQ credential.