Tree Risk Assessment: The TRAQ Method

The Tree Risk Assessment Qualification (TRAQ) is an ISA program that provides a standardized method for evaluating tree risk. Understanding and applying this framework is essential for arborists who assess trees for safety, write reports, or testify as expert witnesses.

The Three Components of Risk

TRAQ defines tree risk as the combination of three factors:

1. Likelihood of failure: How likely is it that the tree or part of the tree will fail?
2. Likelihood of impact: If it fails, how likely is it to hit a target (person, structure, car)?
3. Consequences of impact: If it hits the target, how severe would the damage be?

All three components must be present for risk to exist. A dead tree in the middle of an empty field has a high likelihood of failure but no target, so the risk is low. A dead tree over a playground has high failure likelihood, high impact likelihood, and severe potential consequences.

Assessment Levels

TRAQ defines three levels of assessment:

• Level 1 - Limited Visual: A walk-by or drive-by assessment covering many trees quickly. Used for municipal inventories, neighborhood surveys, and post-storm triage.
• Level 2 - Basic: A detailed visual inspection of an individual tree, including the crown, trunk, root flare, and surrounding site. This is the standard assessment for most residential tree evaluations.
• Level 3 - Advanced: Uses specialized equipment (resistograph, sonic tomography, aerial inspection, root excavation) to investigate defects that cannot be fully evaluated visually. Used when Level 2 findings indicate possible internal decay or root issues.

Identifying Defects

Common structural defects to look for during a Level 2 assessment:

• Dead branches and deadwood in the crown
• Cracks in the trunk or major branches
• Decay indicators: conks, mushrooms, soft or punky wood, cavities
• Included bark at branch unions (codominant stems growing together with bark trapped between them)
• Root plate issues: severed roots, girdling roots, soil heaving, exposed roots
• Leaning: recent lean (with root plate movement) vs. natural lean (stable)
• Canopy dieback exceeding 25%

Assigning Risk Ratings

TRAQ uses a matrix to combine the three risk components into an overall rating: Low, Moderate, High, or Extreme. The rating drives the recommended action, from "no action needed" (Low) to "immediate mitigation required" (Extreme).

Document everything. Take photos, sketch the tree, note the defects, record the assessment level, and clearly state your recommendation. Your report may be referenced by insurance adjusters, attorneys, or municipal officials years later.

Sources and Further Reading

• • International Society of Arboriculture (ISA): Provides the official Tree Risk Assessment Qualification (TRAQ) certification program and comprehensive training materials on standardized risk assessment protocols
• • USDA Forest Service: Offers research publications and technical guidelines on urban forest management and tree hazard evaluation methodologies used by municipal arborists
• • American National Standards Institute (ANSI): Publishes the A300 Part 9 standard for tree risk assessment which establishes industry best practices and safety protocols for professional arborists
• • Tree Care Industry Association (TCIA): Provides continuing education resources and safety standards for tree risk management practices in commercial arboriculture operations

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