How to Read an Arborist Report

An arborist report is a written assessment of a tree, a group of trees, or a tree-related condition on a property. It is prepared by an ISA-certified arborist or equivalent professional, and it is used as the technical record on which permitting decisions, real-estate transactions, insurance claims, litigation, and TPZ plans are made.

Most readers get one of these documents in one of three ways: a property owner ordering a tree risk assessment in advance of a sale or development; an attorney, claims adjuster, or subrogation counsel receiving a report commissioned by the other side; or a developer or applicant submitting one to a permitting agency and needing to know whether it will hold up to review.

This article walks through what a well-formed arborist report contains, in the order a reader encounters it — and signals the parts that determine whether it is defensible if it gets pulled into a deposition, a denial letter, or a hearing.

Related: For the segment-specific deep dives, see our Tree-Protection Ordinance FAQ for North Bay Property Owners and our Permits service page for developer- and applicant-facing guidance.

Section 1 — Cover and Administrative Information

Every defensible arborist report begins with administrative metadata that establishes who wrote it, when, for whom, and under what authority. This is not boilerplate — the cover sheet is what the reader uses to assess credibility before opening the technical body.

The cover page should contain, at minimum:

• Property identification: Address, APN, and a clear site description sufficient to locate the trees without ambiguity.
• Engagement scope: A one-paragraph statement of what was inspected and what was not. A report that says "general tree risk assessment" is weaker than one that says "Level 2 TRAQ assessment of trees 1–6 at the rear easement" because the second sets the methodology standard explicitly.
• Date of inspection and date of report: These are separate fields. A report dated months after the inspection raises a chain-of-custody question; a report dated before the inspection is meaningless.
• Author credentials: ISA certification number, TRAQ qualification status, and any specialty credentials (QAL, CTSP, Utility Specialist). The certification number is what a reader uses to verify the credential against the ISA international registry — if it is missing, the report cannot be verified.
• Standards referenced: The specific framework under which the inspection was performed. Acceptable references include ISA TRAQ (the Tree Risk Assessment Qualification), ANSI A300 (tree care operations), and CTLA (the Council of Tree and Landscape Appraisers). Reports that cite none of these are essentially unlabeled assessments.

What the reader should check: Does the cover page answer "who, what, when, under which standard" in four lines or fewer? If any of those four questions is unanswered, the rest of the report is operating from unclear premises.

If the cover page raises more questions than it answers — a missing credential, an unverifiable certification number, or a vendor-authored conflict — request a consultation and we will walk through the cover sheet with you and flag what an opposing reviewer will pull on first.

Section 2 — Tree Inventory and Site Description

The tree inventory is the body of the report that lists each tree individually, with measurements and condition notes. It is the part that anchors every opinion that follows to a specific physical object on the property.

A complete inventory entry contains:

• Tree number / ID: A consistent reference scheme (T-1, T-2, etc.) used throughout the report.
• Species: Confirmed by a qualified arborist, not a contractor. Species misidentification is one of the most common errors — a native oak miscalled as a non-protected species can invalidate an entire permit process. For property owners, see our heritage-tree FAQ for what the species identification actually triggers in North Bay permitting.
• DBH (diameter at breast height): The measurement that drives every TPZ calculation and almost every threshold test in local ordinances.
• Height and canopy spread: Used in target identification (who or what could be struck if the tree fails).
• Condition notes: Observable defects — deadwood, cavities, leaning, root exposure, fungal conks, included bark. Each defect is described specifically, not generally.
• Location on site: With a reference to a site map. Reports without a corresponding map force the reader to guess which tree the report is discussing.

For each protected tree flagged for permit review, the inventory should include the calculated TPZ radius. For full background on how that radius is calculated and what counts as a protected tree under each North Bay jurisdiction's ordinance, see the property owner FAQ linked above and the Permits service page for the developer-facing side of the same process. For the other half of the reader population — attorneys, claims professionals, and opposing-party reviewers weighing the inventory as evidence — our litigation support work often begins with an inventory review like this one, and the same completeness checks are what determine whether the inventory will hold up under cross-examination.

What the reader should check: Does each tree have a number, a species, a measurement, and a location? Does the count match what is on the site map? Missing entries are a sign the inspection was rushed, and they are the first thing a city arborist, an opposing attorney, or a claims reviewer will look for.

Section 3 — The Risk Matrix: Reading Likelihood × Consequence

The risk matrix is the centerpiece of any TRAQ-based arborist report. It translates the arborist's observations into a numerical risk rating that the reader can compare across trees and across reports. It is also the section most commonly misread.

Under ISA TRAQ, the risk rating is the product of two independent judgments:

The combination of Likelihood (rows) and Consequence (columns) yields the risk rating — typically Low, Moderate, High, or Extreme. The arborist assigns each tree a specific rating based on the observed defects and the targets within the tree's fall zone.

What the reader should check: Two things matter most. First, that the matrix is shown explicitly — a TRAQ report that does not include a Likelihood and Consequence rating is operating outside the standard. Second, that the consequence rating accounts for the actual targets on the site: a tree that overhangs a playground, a parking area, or a structure is a different risk than the same tree in an open meadow. If the consequence column is "moderate" but there is a school across the property line, the rating is wrong.

Section 4 — Methodology References: TRAQ, ANSI A300, and CTLA

The methodology section tells the reader what standard the inspection followed. If this section is missing or generic, the rest of the report is technically unsupported — no expert witness can defend a methodology section that does not name the framework under which they worked.

Three framework references appear in North Bay arborist reports, often in combination:

• ISA TRAQ (Tree Risk Assessment Qualification): The standard applicable to tree risk assessments performed for permit, real-estate, and litigation purposes. TRAQ defines the four-step process — site assessment, tree assessment, risk assessment, and risk mitigation — and requires the explicit Likelihood × Consequence matrix discussed in the previous section.
• ANSI A300 (Tree Care Operations): The American National Standards Institute standard for tree care work, covering pruning, fertilization, bracing, and removal specifications. ANSI A300 is referenced when the report describes tree care recommendations or assesses work that has already been performed on the tree.
• CTLA (Council of Tree and Landscape Appraisers): The appraisal methodology used when the report assigns a dollar value to a tree — most commonly in property-damage claims, replacement-cost disputes, and eminent-domain contexts. The CTLA "species rating × condition rating × location rating" framework produces a numeric appraised value.

What the reader should check: For a tree risk assessment, TRAQ should be referenced. For a report that includes a recommendation to prune or remove, ANSI A300 should appear. For a report that values a tree in dollar terms, CTLA should appear. If the framework is named but not applied — i.e., the report says "TRAQ methodology" but does not produce a risk matrix — the standard is invoked in name only.

Section 5 — Limitations and Re-Inspection Cadence

The limitations section is the most underestimated part of the report. It tells the reader what the report does not cover, what conditions constrained the inspection, and when the assessment expires. Every TRAQ report must include this section; reports that omit it are operating outside the standard.

A complete limitations section addresses:

• Inspection constraints: Trees or parts of trees not accessible due to terrain, vegetation, neighboring structures, or weather; roots not visible without excavation; cavities or decay not detectable without resistograph or sonic tomography.
• Scope exclusions: What the inspection did not address — soil analysis unless specifically commissioned, structural engineering opinions outside the arborist's credentials, subsurface utilities unless marked, neighboring trees not on the subject property.
• Time horizon: A TRAQ assessment is a snapshot. Conditions change. The reader should know how long the conclusions remain reliable — typical recommendations are 12 months for routine risk assessments, 6 months for trees at the upper end of the Moderate risk rating, and immediate for trees rated High or Extreme.
• Re-inspection triggers: Specific conditions that would require a new inspection before the regular cadence — significant storm event, construction activity within the TPZ, observed change in canopy condition, root disturbance from utility work.
• Forward-looking disclaimer: A clear statement that the arborist's opinion reflects the conditions observed on the date of inspection and that no opinion is made about future events outside the inspection scope.

What the reader should check: The limitations section is where the report tells you its expiration date. For a North Bay property owner, this is the part that determines whether the report can be relied on for the next year's permitting cycle or whether a new inspection will be required before any further work begins. For an attorney or claims professional, this section is what bounds the expert's testimony — it is also the section the opposing counsel will focus on at deposition.

CanopyMetrics produces reports designed to be read at this level of detail. Shawn McIntyre holds ISA Certified Arborist #WE-12351AU, is TRAQ Qualified, QAL-licensed, and CTSP-certified. Reports are formatted for direct use as California Rule of Court 26 expert disclosures.

Related Reading

• Anatomy of a Tree Risk Assessment Report — A deeper walkthrough of every section in an ISA TRAQ Level 2 report, with sample lines and a color-coded risk matrix
• Tree-Protection Ordinance FAQ — North Bay Property Owners — Plain-language answers about permits, heritage trees, and what to do with a report you have already received
• Permits services — Developer- and applicant-facing permitting support across Marin, Sonoma, and Napa
• Litigation Support services — Pre-litigation inspections, expert declarations, deposition, and trial testimony
• Insurance & Subrogation support — Adjuster-facing overview of scope, SLAs, and engagement model
• What Insurance Adjusters Actually Need from an Arborist Report — Subrogation-ready report requirements and California Rule 26 compliance
• Tree Service Case Results North Bay — Anonymized case-result blurbs from independent arborist engagements