19 Tree Risk Assessment Practice Questions & Answers

1. 1. A large tree with a severe structural defect stands deep inside a nature preserve, with no trails, buildings, or utilities anywhere within several tree lengths. How should the arborist describe this tree in risk terms?

   • A.The risk is high, because a severe structural defect by itself defines a high rating.
   • B.The risk is negligible, because no person or property occupies the area the tree could strike.✓ Answer
   • C.The risk is moderate, because every mature tree carries a basic risk wherever it grows.
   • D.The risk cannot be defined until the owner places a target within striking distance.

   Risk combines the likelihood that a tree or part fails with the consequences of that failure to a target. With no people or property in the area the tree could reach, there is no consequence to weigh, so the risk rating stays negligible even though the defect is real and failure may well occur.

   Source: ISA Best Management Practices, Tree Risk Assessment — risk defined as likelihood of failure combined with consequences to a targetReport a problem with this question

2. 2. A picnic shelter sits directly beneath a tree's crown. It is crowded every weekend but almost empty on weekdays. Which part of the risk assessment does this usage pattern belong to?

   • A.Estimating the risk that would remain after the recommended mitigation is carried out.
   • B.Estimating how much of the stated period the target occupies the zone below the tree.✓ Answer
   • C.Estimating how likely the defective union is to break within the stated time frame.
   • D.Estimating the severity of the injury or property damage that a falling part would cause.

   How often and how long a target sits in the zone the tree could strike is the occupancy rate, a separate step from judging failure or consequences. Occupancy feeds into the likelihood that a failed part actually impacts something, together with protection and likely fall direction.

   Source: ISA Best Management Practices, Tree Risk Assessment — target zone and occupancy rateReport a problem with this question

3. 3. A codominant leader with included bark overhangs a driveway that is used briefly twice a day. Why must the arborist rate the likelihood of failure and the likelihood of impacting the target as two separate judgments?

   • A.They are separate because impact is judged only after a failure has occurred.
   • B.They are split so the assessor rates failure and the owner rates the impact.
   • C.They ask different things: does the part break, and does it then reach the target?✓ Answer
   • D.They differ because failure applies only to branches and impact to whole-tree events.

   Whether a defective part breaks is a question about the tree and its loading; whether the broken part reaches a target is a question about geometry, protection, and how often the target is there. Because a very weak part over an empty space and a sound part over a crowded space give opposite answers, the two judgments are made independently and only then combined.

   Source: ISA Best Management Practices, Tree Risk Assessment — likelihood of failure and likelihood of impacting the target rated separatelyReport a problem with this question

4. 4. An arborist writes that a large limb is 'probable to fail' but states no time period. Why is that statement incomplete?

   • A.Likelihood of failure describes whole trees only and cannot be assigned to one limb.
   • B.Likelihood of failure only has meaning when a specific time period is stated.✓ Answer
   • C.Likelihood of failure guarantees the limb will stay attached through the coming season.
   • D.Likelihood of failure should be given as a numerical probability, not a category word.

   Likelihood of failure is always rated against a stated time frame, commonly the interval until the next planned inspection, because a defect that is unlikely to fail this year may be quite likely to fail over a decade. Without that period the rating cannot be interpreted, and it is never a guarantee of performance.

   Source: ANSI A300 Part 9, Tree Risk Assessment — likelihood of failure rated over a specified time frameReport a problem with this question

5. 5. A city asks for a rapid screening of street trees along a busy corridor, carried out from a slowly moving vehicle, to flag obvious defects for later follow-up. Which description matches this assignment?

   • A.An advanced assessment using decay-detection instruments on every tree along the corridor.
   • B.A detailed inventory recording the health condition and species of each tree on the street.
   • C.A basic assessment, which requires walking around each tree and inspecting it from all sides.
   • D.A limited visual assessment from a specified perspective, aimed at finding obvious defects.✓ Answer

   A limited visual assessment looks at a tree or a population of trees near specified targets from a stated perspective, such as a vehicle patrol, and is designed only to catch obvious conditions. It is fast and cheap, but it cannot rule out defects hidden on the unseen side of the tree, which is why flagged trees go on for closer inspection.

   Source: ANSI A300 Part 9, Tree Risk Assessment — limited visual (Level 1) assessmentReport a problem with this question

6. 6. During a ground-based inspection from all sides, an arborist finds a large fungal conk on the trunk and a hollow tone when the trunk is struck with a mallet, but cannot judge how much sound wood remains. What is the appropriate next step?

   • A.Remove the tree at once, since a fungal conk proves the trunk has already failed.
   • B.Record the tree as sound, because the sounding did not expose any open cavity.
   • C.Recommend an advanced assessment able to estimate the extent of the internal decay.✓ Answer
   • D.Assume that one third of the shell is gone and rate the tree on that basis.

   A conk is a reliable sign that decay is present, and a hollow tone suggests a void, but neither tells the assessor how thick the remaining sound shell is. When the extent or severity of a defect cannot be determined from the ground, the correct response is to recommend advanced assessment rather than guess in either direction.

   Source: ANSI A300 Part 9, Tree Risk Assessment — advanced assessment when defect extent cannot be determined from the groundReport a problem with this question

7. 7. Which statement best describes what advanced assessment tools such as resistance drilling or sonic tomography contribute to a tree risk assessment?

   • A.They must be applied to every tree in the population before any risk rating is assigned.
   • B.They measure the likelihood that a target will be present at the moment the tree fails.
   • C.They deliver an exact numerical probability that the trunk will break in the coming decade.
   • D.They estimate the extent of a defect already found, without replacing visual inspection.✓ Answer

   Advanced tools are used after a visual inspection has located something that cannot be characterized from the outside, and they answer a narrow question about the extent or severity of that defect. They do not produce a risk rating on their own, because risk still depends on targets, occupancy, and consequences, none of which a drill or a scan can measure.

   Source: ISA Best Management Practices, Tree Risk Assessment — role of advanced assessment toolsReport a problem with this question

8. 8. Why does a union between codominant stems with included bark carry a higher likelihood of failure than a well-formed branch attachment?

   • A.The embedded bark blocks water movement, so the smaller stem dies back and snaps off.
   • B.The embedded bark attracts decay fungi that always hollow the stems out from inside.
   • C.The embedded bark makes the union heavier than the wood beneath it is able to support.
   • D.The embedded bark keeps the stems from joining with wood, so the union stays weak.✓ Answer

   In a normal branch attachment the tissues of branch and stem interlock as successive layers of wood are laid down. Where bark is trapped in the union it never fuses, so the two stems are pressed together rather than joined, and as they grow the wedge of bark acts to split them apart under load.

   Source: ISA Arborists' Certification Study Guide — included bark and codominant stem unionsReport a problem with this question

9. 9. An arborist finds a vertical crack running along a main stem, with fresh edges that have separated. What does this finding indicate about failure?

   • A.The crack affects only the bark and has no bearing on the strength of the stem.
   • B.The crack closes over each growing season and gains strength as woundwood covers it.
   • C.The crack shows wood already separating, so failure is nearer than in a sound stem.✓ Answer
   • D.The crack is old damage and shows the stem has fully adapted to its present loading.

   A crack is a separation of wood fibres, which means part of the failure process has already begun rather than merely being possible. Fresh, open edges show the separation is active, and a stem that is already splitting resists bending far less than an intact one.

   Source: ISA Best Management Practices, Tree Risk Assessment — cracks as indicators of failure in progressReport a problem with this question

10. 10. Why does an arborist compare the thickness of the remaining sound wood shell with the radius of the stem when evaluating a column of decay?

    • A.A hollow stem carries load at its centre, so the missing heartwood sets its strength.
    • B.The comparison replaces the need to weigh loading, species, and any response growth.
    • C.A hollow stem carries bending load mainly in its outer shell, so shell thickness matters most.✓ Answer
    • D.The comparison gives a fixed cutoff below which a tree must always be removed at once.

    When a stem bends, the stress is greatest at the outside and near zero at the centre, so a hollow tube of sound wood can still be surprisingly strong. Comparing shell thickness with stem radius is therefore a useful indicator of how much of the load-bearing outer material is left, but it is a guideline that must be read alongside species, loading, and any response growth rather than as a pass-or-fail test.

    Source: ISA Best Management Practices, Tree Risk Assessment — sound wood shell thickness relative to stem radiusReport a problem with this question

11. 11. Two leaning trees are compared. The first has a swollen, well-developed root flare and undisturbed soil around it; the second shows cracked, mounded soil on the side opposite the lean. What is the sound interpretation?

    • A.The first has adapted to its lean over time, while the second shows recent root plate movement.✓ Answer
    • B.The second has adapted, because disturbed soil shows that its roots are actively growing.
    • C.Both leans mean the same thing, since the angle of lean is what determines the risk.
    • D.The first is more dangerous, since swelling at the base always signals internal decay.

    A lean that a tree has grown with is usually accompanied by adaptive wood and a broad, thickened flare, evidence that the tree has already built structure to carry the load. Cracked or mounded soil, by contrast, means the root plate is lifting now, so the lean is recent and the likelihood of failure is much higher.

    Source: ISA Best Management Practices, Tree Risk Assessment — lean, response growth, and root plate movementReport a problem with this question

12. 12. How does a large dead branch retained in a crown differ from a live branch of the same size in the way it fails?

    • A.Dead wood carries the same load as live wood, but with less foliage it catches less wind.
    • B.Dead wood holds more water than live wood, so it bends much further before it breaks.
    • C.Dead wood loses flexibility and strength, so it breaks under less load and can shatter.✓ Answer
    • D.Dead wood stays attached until the trunk supporting it fails beneath it in high wind.

    Living wood is moist and flexible and can bend considerably before it breaks, while dead wood dries, becomes brittle, and is progressively degraded by decay organisms. A dead branch therefore fails at lower loads, often without warning and even on a calm day, and brittle pieces can break apart and travel some distance from the tree.

    Source: ISA Arborists' Certification Study Guide — dead branches and wood propertiesReport a problem with this question

13. 13. A long branch shows very little change in diameter from its base to its tip. Why is poor taper treated as a structural concern?

    • A.Poor taper reduces the foliage the branch carries, which lowers the load it has to bear.
    • B.Poor taper indicates the branch grew too fast and is therefore full of included bark.
    • C.Poor taper means the branch is dead, because living branches always narrow toward the tip.
    • D.Poor taper leaves bending stress concentrated at one point instead of spread along the part.✓ Answer

    A tapered part is thickest where bending moment is greatest, which spreads stress fairly evenly along its length. When diameter barely changes, the outer end is relatively over-built and the inner end relatively under-built for the load it carries, so stress piles up at one section and failure becomes more likely there.

    Source: ISA Best Management Practices, Tree Risk Assessment — taper as a structural characteristicReport a problem with this question

14. 14. A tree topped several years ago now carries dense sprouts on the old cut stubs. What does this history imply about failure?

    • A.The sprouts are anchored deep in the old stubs and are stronger than normal branches.
    • B.The sprouts lower the risk, because a shortened crown catches far less wind than before.
    • C.The sprouts attach only to outer wood over decaying stubs, so they come off easily.✓ Answer
    • D.The sprouts prove the tree is vigorous, so decay in the old cuts can be ruled out.

    Sprouts that arise after topping grow from buds just under the bark and are held by wood laid down only after the cut, while the stub beneath them decays from the exposed end. The result is a heavy, fast-growing limb attached to a decaying base by a shallow union, which is why previously topped trees are watched for branch failure.

    Source: ANSI A300 Part 1 and ISA guidance on topping — epicormic sprouts on decaying stubsReport a problem with this question

15. 15. A tree now stands alone in an open field after the surrounding stand was cleared. Why does the arborist raise the loading expected on this tree?

    • A.It now receives more sunlight, which makes its wood permanently weaker.
    • B.It is now fully exposed to wind that the neighbouring trees used to intercept.✓ Answer
    • C.Its roots grow more slowly in open ground, which lowers its anchorage.
    • D.Its crown becomes denser after the clearing, so less wind passes through the canopy.

    Trees grown within a stand develop under mutual shelter, so their stems and roots are built for the reduced wind they have always experienced. Removing the neighbours exposes the full crown to wind at once, greatly increasing the load without giving the tree time to add the wood such loading requires.

    Source: ISA Best Management Practices, Tree Risk Assessment — wind exposure and site changesReport a problem with this question

16. 16. How do accumulations of ice and wet snow change the loading on a tree?

    • A.They add weight to branches, raising bending stress on long, poorly tapered limbs.✓ Answer
    • B.They compress the crown into a narrower shape, which lowers stress at the unions.
    • C.They insulate the branches, so the wood becomes more flexible and breaks less often.
    • D.They add weight only to the trunk, so branch attachments are not affected by them.

    Ice and wet snow coat twigs and foliage and add static weight that acts through the whole length of every branch, so the bending moment at each attachment rises sharply. Long, over-extended limbs with little taper gain the most added weight furthest from their support, which is why they fail first under these loads.

    Source: ISA Best Management Practices, Tree Risk Assessment — ice and snow loadingReport a problem with this question

17. 17. An owner asks whether installing a cable will 'fix' a weak codominant union. What is the most accurate response?

    • A.A cable can limit movement between the stems, but the defect and some risk remain.✓ Answer
    • B.A cable removes any need for further inspection of the union in the years ahead.
    • C.A cable makes reduction pruning unnecessary, because the load transfers to the hardware.
    • D.A cable restores the union's strength to that of a normal, well-attached branch.

    Supplemental support is intended to limit the movement of weakly attached stems, not to rebuild the union or make the tree sound. The defect stays where it is, the hardware itself can corrode, loosen, or damage the tree, and so a cabled tree carries residual risk and needs periodic reinspection of both the system and the union.

    Source: ANSI A300 Part 3, Supplemental Support Systems — objectives and limits of cablingReport a problem with this question

18. 18. A structurally poor but ecologically valuable tree stands beside a seldom-used bench in a park, and the owner wants to keep the tree. Which mitigation reduces risk without touching the tree?

    • A.Relocate the bench and fence off the area beneath the crown so nobody enters it.✓ Answer
    • B.Remove the deadwood and thin the crown so that wind passes through it more freely.
    • C.Install a brace rod through the weakest union and add a support cable above it.
    • D.Reduce the length of the heaviest scaffold limbs in order to lower their end weight.

    Mitigation falls into two families: changing the tree, or changing the target. Moving the bench and restricting access removes or reduces what could be struck, which lowers the risk while leaving the tree's habitat value intact; the other three options all alter the tree itself.

    Source: ISA Best Management Practices, Tree Risk Assessment — target-based mitigation optionsReport a problem with this question

19. 19. After recommending reduction pruning on a defective limb, what must the arborist communicate to the owner?

    • A.That the recommended pruning will eliminate the risk associated with that limb.
    • B.That risk remains after the work, and the owner judges whether it is acceptable.✓ Answer
    • C.That no further inspection will be needed once the recommended work is complete.
    • D.That the arborist, as the qualified expert, decides what level of risk is acceptable.

    Any mitigation short of removing the tree leaves residual risk, and the assessor's job is to state plainly what that remaining risk is along with a monitoring interval. The decision on whether that level of risk is acceptable belongs to the owner, manager, or controlling authority, because they bear the consequences and set the tolerance.

    Source: ISA Best Management Practices, Tree Risk Assessment — residual risk and the owner's role in setting acceptable riskReport a problem with this question

Practice questions based on the published knowledge domains of the ISA Certified Arborist examination outline and on standard arboriculture references. ISA and Certified Arborist are marks of the International Society of Arboriculture; this site is not affiliated with or endorsed by ISA. Answers here deliberately avoid pesticide products and rates, standard clause numbers and the dimensions recalled from them, regional species recommendations and local ordinances, all of which change and vary by place — always follow the pesticide label and your jurisdiction's applicator licensing, the tree-care safety standards in force, and the requirements of the authority having jurisdiction. Confirm current exam requirements with ISA before testing. About the ISA Certified Arborist credential →