ISA Tree Risk & Management 2 — Questions and Answers
Question 1: Which term describes the probability that a specific tree failure will occur within a defined time period?
- Likelihood of failure (Correct answer)
- Likelihood of impact
- Consequences of failure
- Risk rating
Correct answer: Likelihood of failure
Likelihood of failure is the probability that a tree part or whole tree will fail under a given set of conditions.
Question 2: A 'target' in tree risk assessment refers to:
- The tree being evaluated
- People, property, or activities that could be harmed by tree failure (Correct answer)
- The zone of failure around a tree
- The root zone radius
Correct answer: People, property, or activities that could be harmed by tree failure
A target is any person, property, or activity in the vicinity of the tree that could be injured or damaged if the tree or a part of it fails.
Question 3: When assessing tree risk, 'occupancy rate' refers to:
- The percentage of the crown that is alive
- How often a target is present in the impact zone (Correct answer)
- The density of wood in the trunk
- The rate at which decay is spreading
Correct answer: How often a target is present in the impact zone
Occupancy rate describes how frequently a target (person, vehicle, etc.) is present in the area where it could be struck by a failing tree part.
Question 4: Which of the following best describes 'residual risk' in tree risk management?
- Risk before any mitigation actions are taken
- Risk that remains after mitigation measures are implemented (Correct answer)
- The probability of root failure specifically
- Risk posed by dead branches only
Correct answer: Risk that remains after mitigation measures are implemented
Residual risk is the level of risk that remains after risk mitigation treatments or actions have been applied to a tree.
Question 5: A tree with a large stem cavity but no visible crown symptoms would best be evaluated using:
- Aerial inspection only
- Advanced assessment tools such as resistograph or sonic tomography (Correct answer)
- Visual ground-level inspection alone
- Increment borer to confirm decay
Correct answer: Advanced assessment tools such as resistograph or sonic tomography
Advanced assessment tools like resistographs and sonic tomography help quantify internal decay that may not be apparent from external visual inspection.
Question 6: The 'wind-sail effect' is most relevant when evaluating which tree defect?
- Root decay
- Excessive crown size relative to root system (Correct answer)
- Bark inclusions
- Chlorotic foliage
Correct answer: Excessive crown size relative to root system
A large crown relative to the root plate creates a high wind-sail effect, increasing the mechanical load on potentially compromised roots.
Question 7: Under ISA BMP guidelines, which action is appropriate when a tree is rated as 'extreme' risk?
- Schedule annual monitoring
- Prune dead branches only
- Take immediate action such as removal or crown reduction before next use (Correct answer)
- Apply fungicide to the root zone
Correct answer: Take immediate action such as removal or crown reduction before next use
An extreme risk rating requires immediate action, typically removal or significant risk mitigation, before the target area is used again.
ISA Tree Risk & Management 2
Which term describes the probability that a specific tree failure will occur within a defined time period?