ISA TRAQ cheat sheet

Risk is defined as the combination of likelihood of failure, likelihood of impact, and consequences of the failure; all three components must be evaluated, not failure likelihood alone.

Likelihood of failure uses a five-level scale (improbable, possible, likely, probable, imminent) based on the tree's condition, species characteristics, and site factors.

Likelihood of impact uses four levels (very low, low, medium, high) derived from occupancy rate and the target's value and use.

Consequences are rated negligible, minor, significant, or severe according to potential injury, property damage, and disruption of use.

Risk rating matrix combines likelihood of failure x likelihood of impact to yield a risk category from negligible to extreme; the matrix is qualitative and ordinal, not a numeric probability.

Target definition: a person, property, or activity that could be struck; a tree with no target has no risk regardless of defect severity, though the defect still warrants monitoring.

Occupancy rate is the proportion of time a target is present (e.g., 8 hours/day, 5 days/week = roughly 24% occupancy) and directly scales the likelihood of impact.

Inspection levels: Level 1 limited visual (drive-by), Level 2 basic (360-degree walk-around with binoculars), Level 3 advanced (aerial, climbing, or aerial lift), and Level 4 detailed/advanced diagnostic testing.

Site factors that raise failure likelihood include soil compaction, grade changes, root cutting, excavation within the critical root zone, wind exposure, and recent construction disturbance.

CODIT: compartmentalization of decay in trees describes four walls - wall 1 (plugging of vessels), wall 2 (toughened latewood), wall 3 (ray cells), wall 4 (new wood) - that resist spread of decay.

Reaction wood: tension wood forms on the upper side of leaning stems in angiosperms; compression wood forms on the lower side in gymnosperms; both indicate a corrective growth response to lean or load.

A sound shell of wood is the primary strength element in hollow trees; the ratio of sound wood thickness to radius (t/R) below about 0.3 is commonly used as a threshold warranting advanced assessment.

Included bark (bark-to-bark contact at a union) is a structural defect that creates a weak attachment; look for a V-shaped union, bark ridge turning inward, and swelling.

Cracks: shear cracks run longitudinally and indicate torsional failure; radial cracks run across the stem; check for separation of the crack faces, which signals active failure.

Root defects: girdling roots, root plate lifting, soil mounding or cracking on the tension side of a lean, and fungal fruiting bodies at the root collar indicate instability.

Lean assessment: a recent increase in lean, soil heave at the base, or exposure of the root plate on the tension side indicates active root failure and imminent risk.

Fungal decay indicators: conks, brackets, and mushrooms identify the decay organism; brown rot leaves cubical brittle residue, white rot leaves spongy fibrous residue.

Branch unions: a branch with a smaller diameter relative to the trunk (less than about one-third) and a wide U-shaped union is stronger than a codominant union with included bark.

Resistograph measures drilling resistance through wood; a drill resistance profile can detect density changes and internal decay but is a relative, not absolute, measure of wood strength.

Sonic and ultrasonic tomography measures the velocity of stress waves through wood; lower velocity indicates decay, cavities, or cracks because sound travels slower through less dense or discontinuous material.

Tomography devices (e.g., multi-sensor arrays) produce a two-dimensional cross-sectional image of relative velocity; results are qualitative and should be confirmed with other methods.

Increment borer extracts a core to verify decay extent, ring width, and growth history; it is invasive and leaves a wound that can serve as an entry point for pathogens.

Static load testing applies a controlled pulling force to the stem and measures trunk deflection and root plate movement to evaluate anchorage and stem stiffness.

Dynamic/elastometer testing measures stem deflection under a known load to estimate modulus of elasticity; useful for comparing trees and detecting changes over time.

Visual tree assessment (VSA) is the first-line method: identify symptoms such as swelling, ribs, seams, and hollows that indicate internal defects before deploying instruments.

No single tool measures strength directly; advanced diagnostics estimate the presence and extent of defects, and results must be interpreted with the visual assessment and species biology.

Risk categories in the TRAQ matrix run from negligible to low, moderate, high, and extreme; only high and extreme typically justify immediate action, and moderate warrants mitigation or monitoring.

Mitigation options include target removal or relocation, pruning, cabling and bracing, root collar excavation, soil management, and tree removal; the least intrusive effective option is preferred.

Residual risk is the risk remaining after mitigation; the assessor should document it and communicate that mitigation reduces but does not eliminate risk.

Risk tolerance is set by the tree owner or manager, not the assessor; the assessor provides the rating and options, and the owner decides whether to accept the residual risk.

A written report should include the tree location and species, inspection level and date, observed defects, targets, likelihood ratings, consequences, risk category, and recommended mitigation with a timeframe.

Re-inspection intervals are set based on risk category and tree growth rate; high-risk trees require shorter intervals (often 6-12 months) than low-risk trees (multi-year).

Client communication: explain the difference between tree health and tree risk; a healthy tree can still present high risk, and a declining tree may present low risk if no target exists.

Documentation should note limitations of the inspection (e.g., limited visibility, no aerial inspection, no diagnostic testing) so the client understands the basis of the rating.

Emergency response: imminent-failure trees with high-value targets require immediate action, which may include temporary exclusion of the target area before physical mitigation is completed.