Tree Risk Assessment Basics (ISA TRAQ)

Understanding tree risk assessment helps you make informed recommendations to customers.


ISA TRAQ assessment levels:

  • Level 1 (Limited Visual): Walk-by or drive-by assessment of large populations
  • Level 2 (Basic): Detailed visual inspection of individual trees — the most common level
  • Level 3 (Advanced): Uses diagnostic tools (resistograph, sonic tomography, root excavation)

    • What to assess:

  • Crown: Density, dieback percentage, epicormic sprouting, branch attachment
  • Trunk: Cavities, cracks (shear cracks are critical), cankers, fungal fruiting bodies, lean
  • Root zone: Soil heaving, girdling roots, severed roots, decay fungi at root flare
  • Targets: What could be damaged if the tree or branch fails (people, structures, vehicles)

    • Risk rating: Combines likelihood of failure, likelihood of impacting a target, and consequences. Ratings range from Low to Extreme. Extreme means recommend immediate action.


    Key indicators of imminent failure:

  • Recent lean with soil heaving (root plate failure)
  • Shear cracks in trunk (not frost cracks)
  • Large fungal fruiting bodies (Ganoderma, Armillaria) at base
  • Crown dieback exceeding 50%

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