ISA Tree Risk Practice Questions and Study Guide: Defects, Targets, Likelihood, and Mitigation

What Tree Risk covers on the ISA exam

ISA lists Tree Risk as one of the ten domains on the Certified Arborist exam, which has 200 multiple-choice questions and a 3.5-hour time limit. ISA controls the outline and can change it, so treat the ISA Certified Arborist credential page and the exam outline PDF as the source of truth for current domain wording and exam details. The exam domains guide shows how Tree Risk fits the full blueprint.

Most risk decisions start from a tree condition, a site use, and several possible actions. The right action depends on the relationship between the defect and the target. Six skills carry most of that reasoning:

• Inspection limits: knowing when the information is not enough for a final recommendation.
• Defects: dead branches, cracks, decay, cavities, conks, included bark, weak unions, root damage, and new lean.
• Targets: the people, property, utilities, roads, structures, or site uses that could be hit, and how often they are occupied.
• Likelihood: separating likelihood of failure from likelihood of impact.
• Consequences: why part size, occupancy, and target value change priority.
• Mitigation: an action that fits the risk without under-reacting or over-treating, plus the risk that remains.

Tree Risk misses can hide inside pruning, diagnosis, construction, and safe work questions, so treat it as its own domain before trusting a full mock score. Do not study it as a list of scary defects. A cavity, crack, dead branch, or included bark union matters because of what could fail and what it could hit.

Key Tree Risk concepts

Start with the target

A target is a person, structure, vehicle, utility, trail, bench, playground, road, or other valued object that could be struck if a tree or tree part fails. Without a target, the risk rating changes.

This is easy to miss. The same defect can call for different actions depending on site use:

• A large dead limb over a school pickup area calls for faster action than a similar limb over an unused woodland edge.
• A cracked stem near a busy sidewalk has a different consequence profile than one inside a closed conservation area.
• A tree leaning toward a house after recent root disturbance is not the same as a tree with a long-standing phototropic lean away from targets.

Read the site description before choosing a mitigation answer. If you skip the target, you will over-treat some questions and under-treat others.

Likelihood of failure vs. likelihood of impact

Tree risk assessment separates two ideas that are easy to blur together.

Likelihood of failure asks whether the tree or tree part is likely to fail during the assessment period. It depends on defects, load, decay, root condition, species traits, site exposure, and recent changes.

Likelihood of impact asks whether the failed part is likely to hit a target. It depends on target location, occupancy, direction of fall, distance, and whether the target can be moved or excluded.

A branch can have a high likelihood of failure and a low likelihood of impact if nobody uses the area below it. Another branch can have a lower likelihood of failure but still deserve action because the target is occupied all day. Fencing off the area under a cracked limb does not repair the crack; it lowers the likelihood of impact. If you keep mixing these up, the Likelihood and consequences questions isolate the pattern.

Consequences complete the risk picture

Consequences describe what happens if failure and impact occur. Even without full assessment-form language, the reasoning is the same: a small dead twig over mulch is not the same as a large scaffold limb over a playground. Two limbs with the same likelihood of failure can carry very different priorities when target occupancy and potential harm differ.

When you read a question, ask:

• What part could fail?
• How large is it?
• What target could it hit?
• How often is that target occupied?
• What would the likely damage or injury be?
• Can the target be moved, protected, or excluded?

The best answer usually connects those pieces. An answer that names a defect but ignores target use is incomplete.

Defects that show up in risk scenarios

Know common defects well enough to explain why they matter, not just to recognize the words. If defect recognition is your repeated miss, drill the defect scenarios in the 15 questions below, then the Tree defects questions on cracks and conks.

Dead branches. Dead branches lose strength and can fail without the same warning signs as living branches. Priority usually turns on size, height, and target occupancy. Removing small deadwood in an unused area may be low priority; large deadwood over a path is different.

Cracks. Cracks can indicate separation of wood fibers and reduced structural integrity. Watch for wording about fresh cracks, cracks extending through the stem, cracks associated with included bark, or cracks after storm loading.

Included bark and weak unions. Included bark prevents normal wood connection between stems or branches, and the union can become weaker as the stems grow and loading increases. It often comes up with codominant stems, narrow branch angles, and structural pruning. The codominant stems and included bark practice questions cover the pruning side of that pattern.

Decay, cavities, and conks. The word "cavity" alone rarely settles a decay concern. What matters is the extent and location of decay, fungal fruiting bodies, remaining sound wood, species response, and target exposure. Do not assume every cavity means removal, and do not assume every cavity is harmless. A conk is a significant sign, but a single close-up photo of one is not a risk assessment.

Root damage and soil movement. Anchorage depends on roots and soil. Recent trenching, grade changes, construction damage, saturated soil, lifting root plates, or soil cracking near a leaning tree should get your attention. Root loss can affect stability as well as health. Construction-related root injury gets fuller treatment in the Trees and Construction practice questions.

Lean. A lean is not automatically a defect. A long-standing lean with adaptive growth can be stable. A recent lean with soil heaving, root plate movement, cracks, or new target exposure is more concerning.

Mitigation: match the action to the risk

Mitigation reduces risk. Several choices can sound reasonable at once; pick the one that addresses the actual risk with the least unnecessary harm.

Common mitigation options include:

• pruning dead, broken, or weak branches
• reducing end weight where appropriate
• cabling or bracing when the objective and structure fit
• restricting access or moving the target
• changing site use below the tree
• monitoring at a defined interval
• further assessment by a qualified professional
• removal when risk cannot be reduced enough by other means

Removal is sometimes the right answer, especially where the defect is severe and the target cannot be moved. But if a question describes a manageable branch defect over a target, pruning or target control may be the better answer. Target control also works as temporary mitigation: closing or rerouting a trail under a cracked limb keeps people out of the strike zone until the limb can be addressed.

Support systems are their own trap. Cabling, bracing, guying, and propping are one mitigation option with inspection requirements and residual risk, not an automatic guarantee. The Tree support systems questions cover that topic, including lightning protection and post-installation inspection.

Inspection process and its limits

Sometimes the right call is the next step, not the final prescription. The best answer may be to inspect more carefully, collect history, or escalate the assessment before recommending work.

Watch for:

• limited visual information
• hidden root or trunk conditions
• conflict between symptoms and site history
• recent construction, excavation, or grade change
• targets with high occupancy
• defects that need closer inspection before a rating is defensible

If the question says you do not have enough information, the best answer may not be treatment. It may be a more appropriate level of inspection. Professional judgment also includes communicating limits: when targets are present and a basic visual inspection cannot settle the question, managing obvious exposure and recommending a higher level of assessment beats a premature yes-or-no answer.

15 ISA Tree Risk practice questions

These are original practice questions written for study, not real ISA exam questions. Treat the set as a scenario-reading check, not a score prediction:

1. Give yourself 20 minutes for all 15 questions.
2. Mark each answer as confident, uncertain, or guessed.
3. For every miss, label the reasoning gap: defect, target, likelihood of failure, likelihood of impact, consequence, inspection level, or mitigation.
4. Write why the tempting wrong answer was too aggressive, too passive, or not supported by the facts.
5. Retest weak categories before taking another full mock.

Score guide

Use the score to choose the next study action:

• 13-15 correct: Tree Risk probably is not your main leak. Review uncertain answers and try the Tree support systems questions, a topic the 15 questions skip, then test adjacent domains like Safe Work Practices, Trees and Construction, and Diagnosis and Treatment.
• 9-12 correct: You understand the general pattern but still miss scenario details. Check whether your misses came from ignoring targets, overreacting to defects, or choosing unsupported mitigation, then work the matching section: Targets and occupancy, Tree defects or Tree support systems.
• 0-8 correct: Pause mixed mocks. Relearn targets, likelihood of failure, likelihood of impact, consequences, defects, mitigation, and inspection limits, then work the topic sections from Targets and occupancy through Tree support systems before continuing.

A short quiz cannot predict your real exam score. The useful signal is the pattern: missing three target questions is different from missing three defect-identification questions.

How Tree Risk questions are phrased and common traps

Most questions on this page combine a tree condition, a site use, and a range of actions from doing nothing to removing the tree. Some ask for the final mitigation. Others ask what changed, what matters most, or what should happen first, and the answer to those is often exposure control or a better inspection rather than a prescription. Read the target and the timeline before you react to the defect.

The traps repeat:

1. Ignoring the target. The biggest trap: seeing a defect and jumping to removal or treatment without asking what it could hit, how often the target is occupied, and what the consequences would be.
2. Over-treating. Whole-tree removal or heavy crown reduction sounds safe but is not proportional to a small defect over a low-use area.
3. Under-reacting. Waiting for symptoms, fertilizing, or checking again next year is too passive when a recent lean or a cracked limb sits over an occupied target.
4. Blurring failure and impact. Moving or excluding the target changes impact, not the condition of the wood.
5. Treating one clue as a full assessment. A lean, a cavity, or a conk is context, not a verdict.
6. Answering from thin information. When decay extent, targets, or history are missing, the best answer may be further assessment, with interim exposure control if targets are present.
7. Missing the safety overlap. When the target is a road, a sidewalk, or the crew itself, work-zone or traffic control may come before the cut. The Safe Work Practices practice questions cover that side.

If an answer ignores the target, treats every defect as automatic removal, or delays action when exposure is obvious, be skeptical.

How to study Tree Risk

Use scenario loops instead of vocabulary lists:

1. Pick one defect: dead limb, crack, included bark, decay, root damage, or lean.
2. Write what could fail.
3. Add a target: sidewalk, road, house, playground, low-use woodland, or utility line.
4. Decide whether the target changes the priority.
5. Pick a mitigation option.
6. Explain why two tempting alternatives are wrong.

That last step matters. If you can explain why removal is excessive, why monitoring is too slow, or why target restriction is the first move, you are studying the right way.

Then put the reasoning under test conditions:

1. Review the Tree Risk section in your study material.
2. Drill 25 to 50 Tree Risk questions.
3. Log every miss by category: defect, target, likelihood, consequence, or mitigation.
4. Retest the weakest category.
5. Return to mixed quizzes and a timed 200-question practice exam only after Tree Risk stops dragging down your total.

Arborist Practice is built for that second loop: focused Tree Risk sets, mixed domain quizzes, explanations for wrong and guessed-right answers, bookmarks for scenarios that confuse you, an AI tutor you can ask why a mitigation choice fits the described target, and timed mock exams. Official ISA materials remain the source for credential rules and exam policies.

Targets and occupancy

ISA's exam outline lists target analysis and target-based mitigation (relocation, restricting access) under Tree Risk. A target is any person or property a failed tree or tree part could strike: pedestrians, parked cars, structures, roads, utility lines and the work crew itself.

The questions turn on the target sentence: what sits in the strike zone, how often it is occupied, and whether it can be moved, closed or rerouted until the tree work is done. Two traps recur: counting only people as targets, and treating a closed area as if the defect no longer needs work.

Tree defects

ISA's exam outline lists tree analysis under Tree Risk: identifying defects and conditions that could increase the likelihood of failure. A defect matters because of what could fail and what it could hit, not because the word sounds serious.

The 15-question set above already covers dead limbs, lean, included bark, cavities and root damage. The two questions here turn on cracks and conks. A fresh crack through a loaded union over a busy area is more concerning than an old wound with good woundwood. A conk is possible evidence of decay: judge its extent and the target instead of stopping at the fungus name.

Likelihood and consequences

These questions keep three parts of risk apart: likelihood of failure, likelihood of impact if the part fails, and consequences, meaning the harm an impact would do. Only likelihood of failure appears in the Tree Risk part of ISA's exam outline; likelihood of impact and consequences come from ISA's Tree Risk Assessment best management practices.

Likelihood of impact follows occupancy over time: a lot that fills every weekday is a regular target even if empty at night. Consequence can differ when both likelihoods match, since an empty shed is not a bus stop. A defect that is not imminent can still matter over a playground used daily.

Tree support systems

ISA's exam outline lists pruning and structural support systems as tree-based mitigation measures under Tree Risk, and support for newly planted trees under Installation and Establishment. Cabling, bracing, guying, propping and lightning protection can each reduce a specific risk when the objective is clear and the system is properly specified, installed and inspected.

The questions turn on fit and limits. Reduction pruning may solve end weight before hardware does. A cable may not be enough for advanced decay over a busy target. Hardware needs periodic inspection as the tree grows, and no system replaces explaining the risk that remains.