Certified Arborist Test Tree Risk Assessment 2

Question 1

In the ISA Tree Risk Assessment Qualification (TRAQ) framework, what are the three components of tree risk?

Accepted Answer

Probability of failure, target occupancy, and consequence of failure

Answer

ISA's TRAQ framework defines risk as the combination of three components: the probability that a part will fail, the likelihood that it will strike a target (target occupancy), and the severity of the consequences if it does (consequence of failure).

Question 2

What is a 'target' in tree risk assessment terminology, and how does target occupancy affect overall risk rating?

Accepted Answer

People, property, or other valued objects that could be struck if a tree part fails

Answer

In TRAQ, a target is any person, property, or structure that could be struck by a failing tree part. Target occupancy — how frequently and for how long the target is present in the impact zone — directly scales the likelihood component of risk, since failure causes harm only when something is present to be struck.

Question 3

What is 'trunk flare inspection' and what does its absence or deformity potentially indicate?

Accepted Answer

Examination of the base of the trunk to detect buried root flare, girdling roots, or basal decay that indicates structural or root system problems

Answer

Trunk flare inspection examines the tree base for the natural widening where trunk transitions to roots. Absence of visible flare (buried or compressed) can indicate deep planting, fill soil, girdling roots, or basal decay — all potentially serious structural or health issues.

Question 4

What does 'failure mode' refer to in tree risk assessment, and what are the primary structural failure modes assessed?

Accepted Answer

The mechanism by which a tree or tree part fails — including stem failure, branch failure, root failure, and whole tree failure

Answer

Failure mode describes how a tree or part fails mechanically — the primary modes are branch failure, stem failure, root failure (overturning), and whole tree failure. Each mode has different defect indicators, risk assessment methods, and mitigation strategies.

Question 5

What is the purpose of resistance drilling in tree risk assessment and what does the instrument measure?

Accepted Answer

It measures the drilling resistance of a small probe as it penetrates the wood, creating a profile that reveals density variations indicating decay, cracks, or voids

Answer

Resistance drilling (e.g., IML Resistograph) inserts a thin needle into the wood and continuously records the torque required to drill through successive layers — healthy dense wood produces high resistance, while decayed wood, voids, and cracks produce characteristic low-resistance profiles.

Certified Arborist Test Practice Test

Certified Arborist Test Practice Test

Certified Arborist Test Tree Risk Assessment 2