ISA Tree Risk Assessment Questions and Answers — Questions and Answers
Question 1: An arborist performs a detailed, 360-degree visual inspection of a tree from the ground, using a mallet to sound the trunk and a probe to investigate a potential cavity. According to ISA standards, this type of on-site evaluation is best described as which level of assessment?
- Level 1 (Limited Visual)
- Level 3 (Advanced)
- Level 2 (Basic) (Correct answer)
- Preliminary Hazard Survey
Correct answer: Level 2 (Basic)
A Level 2 (Basic) Tree Risk Assessment involves a comprehensive, 360-degree visual inspection of the tree and its site from the ground. It often includes the use of simple tools like mallets, probes, and binoculars. A Level 1 assessment is a more limited, 'walk-by' or 'drive-by' inspection, while a Level 3 assessment involves advanced diagnostic tools and techniques like sonic tomography or aerial inspection.
Question 2: In the ISA Tree Risk Assessment Qualification (TRAQ) methodology, the final risk rating is determined by combining three primary components. Which of the following correctly identifies these components?
- Defect severity, tree species, and site conditions
- Likelihood of failure, likelihood of impacting a target, and consequences of failure (Correct answer)
- Tree height, canopy spread, and proximity to structures
- Load factors, tree health, and soil stability
Correct answer: Likelihood of failure, likelihood of impacting a target, and consequences of failure
The ISA TRAQ methodology defines risk as the combination of the likelihood of a tree or part failing, the likelihood of that part impacting a target, and the severity of the consequences if it does. The other options list important factors that are considered during an assessment, but they are not the three core components of the final risk calculation itself.
Question 3: An arborist identifies a mature tree with a significant structural defect. However, the tree is located in a remote, fenced-off wildlife preserve with no trails or public access. Despite the defect, the arborist assigns a low overall risk rating. What is the most likely justification for this low rating?
- The tree has excellent adaptive growth around the defect
- The species is known to compartmentalize decay effectively
- The likelihood of the tree or its parts impacting a target is negligible (Correct answer)
- The arborist plans to mitigate the defect with cabling
Correct answer: The likelihood of the tree or its parts impacting a target is negligible
In tree risk assessment, risk only exists when a tree failure has the potential to impact a target (people, property, or activity). In a location with no targets, even a tree with a high likelihood of failure will have a low overall risk rating because the 'likelihood of impacting a target' and 'consequences' components of the risk equation are negligible.
Question 4: When assessing codominant stems, the presence of included bark in the union is a significant concern primarily because it:
- Attracts wood-boring insects that further weaken the tree.
- Creates a weak attachment by preventing strong, interlocking wood tissue from forming. (Correct answer)
- Restricts the flow of water and nutrients to the competing stems.
- Is a definitive sign of an aggressive fungal pathogen.
Correct answer: Creates a weak attachment by preventing strong, interlocking wood tissue from forming.
Included bark is bark that becomes embedded in the junction between two stems, preventing the formation of a normal, strong branch union. Instead of being connected by continuous, overlapping wood grain, the stems are pushed apart as they grow, creating a weak point that is significantly more prone to failure under load.
Question 5: A Level 2 assessment of a high-value historic oak reveals suspected internal decay, but the extent cannot be determined visually. To gather more detailed, quantitative data about the amount of solid wood remaining, which of the following would be the most appropriate next step?
- Immediately recommend removal to eliminate all risk.
- Proceed with a Level 3 assessment using sonic tomography. (Correct answer)
- Use an increment borer to extract multiple core samples for visual review.
- Prescribe a heavy crown reduction to reduce weight on the trunk.
Correct answer: Proceed with a Level 3 assessment using sonic tomography.
When a Level 2 (Basic) assessment identifies a potential issue that requires more detailed information, a Level 3 (Advanced) assessment is recommended. Sonic tomography is a common Level 3 technique that uses sound waves to create a map of internal decay without significantly wounding the tree, making it ideal for gathering quantitative data on high-value trees.
Question 6: Which of the following is an example of 'target management' as a tree risk mitigation strategy?
- Pruning a heavy limb to reduce its weight.
- Installing a dynamic cable system to support weak branches.
- Relocating a park bench from underneath a tree's dripline. (Correct answer)
- Applying a fungicide to treat a root rot pathogen.
Correct answer: Relocating a park bench from underneath a tree's dripline.
Target management involves reducing risk by moving or restricting access to the target, rather than altering the tree itself. Relocating a park bench removes the target from the potential impact zone, effectively mitigating the risk to people using the bench. The other options are valid mitigation techniques, but they involve treating the tree itself.
ISA Tree Risk Assessment Questions and Answers
An arborist performs a detailed, 360-degree visual inspection of a tree from the ground, using a mallet to sound the trunk and a probe to investigate a potential cavity.
According to ISA standards, this type of on-site evaluation is best described as which level of assessment?