ISA Arborist Practice Questions (2026) — Free Sample Questions with Answers

Answer: C

Heavy thinning to stimulate new vigor: Removing much live foliage drains the limited energy of an old tree and does not rejuvenate it.

Raising the crown by removing the low growth: The new lower growth is the crown the veteran tree is retrenching into; removing it strips the foliage that keeps the tree alive.

Phased reduction, keeping lower growth: Correct. Veteran trees often retrench naturally. Gradual, phased reduction that keeps the lower crown and retains habitat where safe follows this process with minimal stress.

Structural pruning to restore one leader: Establishing a dominant leader is a young-tree objective, not appropriate for a retrenching veteran.

Pruning goals change with age: structure for young trees, minimal and phased work for veteran trees.

Answer: C

Wall 1, plugging of vessels above and below: Wall 1 resists vertical spread along the stem; it does not separate old wood from new wood.

Wall 2, the latewood of each growth ring: Wall 2 resists inward spread toward the pith; it does not protect wood formed after the wound.

Wall 4, the cambium-formed barrier zone: Correct. CODIT wall 4 is the barrier zone produced by the cambium after wounding. It separates wood present at wounding from new wood and is the strongest wall.

Wall 3, the ray cells around the stem: Wall 3 resists lateral (tangential) spread around the stem, not outward spread into new wood.

In CODIT, wall 4 (the barrier zone) is formed by the cambium after wounding and keeps decay out of new wood.

Answer: B

Juglans (walnut): Walnut leaves are pinnately compound but alternate.

Fraxinus (ash): Correct. Ash has opposite, pinnately compound leaves, a combination shared by few large trees in temperate regions.

Carya (hickory): Hickory leaves are pinnately compound but alternate.

Gleditsia (honeylocust): Honeylocust leaves are alternate and often bipinnately compound.

Leaf arrangement (opposite vs. alternate) combined with leaf type quickly narrows an identification.

Answer: C

Loam has larger pores than gravel, so it drains slowly: Loam has smaller pores than gravel; that difference in pore size is what holds the water above the interface.

The gravel wicks water back up into the loam: Coarse gravel has very weak capillary pull; it does not draw water upward into finer soil.

Loam must near saturation before water enters gravel: Correct. Water moves from fine pores into coarse ones only when the fine layer is close to saturation, so a perched water table forms in the loam above the gravel.

The gravel compacted the loam above it: Gravel beneath a soil layer does not compact it; the wetness comes from the textural interface.

Any abrupt change in texture (fine over coarse or coarse over fine) slows water movement; fine-over-coarse layers create perched water.

Answer: A

Water slowly over the root ball itself, often: Correct. Roots are still confined to the ball, and coarse potting media dries faster than the surrounding clay, so water must be applied directly to the ball frequently until roots grow out.

Wait until the surrounding soil dries, then water: The ball will stay dry because water does not move readily from clay into coarse media.

Run the lawn sprinklers once a week: Light, infrequent sprinkling does not wet the ball enough or often enough during establishment.

Water only at the hole edge to draw roots out: Watering beyond the ball leaves the roots in the dry ball without water.

During establishment, water where the roots are: the root ball, which can be dry when the surrounding soil is moist.

Answer: C

Use the 50:50 compost mix as requested: Heavily amended backfill creates an interface with the clay, holding water like a bathtub and keeping roots in the hole.

Backfill with sand to improve drainage: Sand in a clay hole also forms an interface that collects water around the roots.

Backfill with the native soil, broken up: Correct. Native soil broken up and returned to the hole avoids a sharp textural interface; roots grow from the hole into the surrounding soil more readily.

Add gypsum to the backfill to loosen the clay: Gypsum does not improve the structure of most non-sodic clays, and amending only the hole still forms an interface.

Backfill is normally the excavated native soil; site-wide soil improvement, not hole amendment, is used when the soil itself is poor.

Answer: B

Back to a 2 cm lateral growing outward: Heading cut: a 2 cm lateral is far too small (about 1/6 of the stem) to take over the terminal role, so the cut acts like a stub with weak sprouting.

Back to a 5 cm lateral growing upward: Correct. ANSI A300 (pruning): a reduction cut goes back to a lateral large enough to assume the terminal role; ISA guidance commonly cites at least one-third of the removed stem's diameter (5 of 12 cm qualifies).

Just above a cluster of dormant buds: Heading cut: cutting to buds leaves no lateral to take over and produces a cluster of weakly attached sprouts.

Halfway between two laterals for even length: Heading cut to a stub (internodal cut): the stub dies back and decays, and sprouts form below it.

Reduction cuts end at a lateral that can take over as the new leader; cuts to buds, stubs or small laterals are heading cuts.

Answer: D

It removes most of the limb's weight before the final cut: This describes the second (top) cut, made just beyond the undercut, which drops the limb and its weight.

It marks where the final cut will be placed at the collar: The final cut location is set by the branch bark ridge and collar, not by the undercut, which is made farther out.

It keeps the saw from binding as the top cut is made: Near-miss: an undercut is not made to stop pinching of the top cut; its job is to stop the bark tearing as the limb drops.

It stops bark from stripping back toward the trunk: Correct. In the three-cut sequence the undercut stops a tear in the bark from running along the underside and down the trunk when the limb falls.

Three-cut sequence: undercut, top cut to drop the limb, then a final cut outside the branch bark ridge and collar, so the bark does not tear on heavy limbs.

Answer: B

A vascular wilt pathogen spreading along the street: Incorrect; wilt pathogens are usually host-specific and spread over time, not across three genera in one week.

Leaf scorch from water loss exceeding uptake: Correct. Sudden onset on several unrelated species, concentrated on the most exposed side, points to an abiotic cause: leaf scorch from transpiration outpacing water supply.

Anthracnose favored by the warm weather: Incorrect; anthracnose is favored by cool, wet weather and is largely host-specific.

Defoliating insects feeding on the leaf margins: Incorrect; insect feeding removes tissue and leaves frass or insects as signs, and rarely hits several genera on one side at once.

Damage on many species at once, with a uniform or exposure-related pattern, suggests an abiotic cause; biotic problems tend to be host-specific and spread over time.

Answer: A

Water in dry spells, mulch and monitor: Correct. Supplemental water, a mulch layer over the root zone and regular monitoring support root regrowth with the least added stress.

Apply a balanced fertilizer right away: Incorrect; fertilize only if a soil test shows a need; pushing growth adds demand on a reduced root system.

Deep-till the root zone to loosen the soil: Incorrect; tilling cuts more of the remaining roots, adding to the injury.

Apply a root stimulant on a fixed schedule: Incorrect; calendar product applications are not based on need and do not replace care that supports root regrowth.

Post-construction care: water, mulch, protect the soil, monitor for decline and secondary pests, and avoid adding stress such as high-N fertilizer or heavy pruning.

Answer: C

A narrow trench cut with a chain trencher: Incorrect; a narrow trench still severs every root crossing its path, even if the cuts are cleaner.

An open trench that is backfilled the same day: Incorrect; quick backfilling limits drying, but the roots in the trench line are already cut.

Boring or tunneling under the root zone: Correct. Tunneling or boring at depth passes under most roots, which are in the upper soil, so far fewer roots are severed than with any open trench.

An open trench followed by a root stimulant: Incorrect; products applied afterward do not replace severed roots or prevent the loss.

Near trees, tunneling or boring under the root zone is preferred to trenching; if a trench is unavoidable, route it outside the TPZ.

Answer: C

Monitor the lean at the next annual inspection: Treats an active root plate failure like a stable, long-standing lean.

Cable the trunk to a neighboring tree: Cabling does not restore anchorage and can load the second tree; it is not a fix for root plate failure.

Restrict access and recommend prompt removal: Correct. A new lean with soil heaving on the side away from the lean indicates the root plate has already partly failed; the likelihood of failure is imminent.

Backfill the lifted roots and water heavily: Covering the heave hides the defect, and wetter soil further reduces anchorage.

A recent lean with root plate heave signals whole-tree failure in progress; protect targets immediately.

Answer: D

Installing a cable to support the limb: Support systems are tree-based mitigation.

Reducing the end weight of the limb: Pruning is tree-based mitigation.

Removing the limb back to the trunk: Branch removal is tree-based mitigation.

Moving the picnic table elsewhere: Correct. Target-based mitigation changes the target (relocate it or restrict access) rather than the tree.

Tree-based: pruning, support systems, removal. Target-based: move the target or restrict access.

Answer: D

A conventional notch of about 45°: A 45° notch closes partway through the fall; the hinge then breaks and control is lost.

A Humboldt notch cut from below: A Humboldt also closes at about 45° and loses hinge control early.

A notch whose cuts cross past each other: Overlapping cuts (a Dutchman) close the notch early and can turn or split the tree.

An open-face notch of about 70° or more: Correct. A wide open-face notch stays open longer, so the hinge keeps steering the tree until it is close to the ground.

The wider the notch, the longer the hinge holds and steers; open-face notches of 70° or more give the most control.

Answer: A

As energized and uninsulated, despite the covering: Correct. Coverings on many conductors are weatherproofing, not rated insulation, and can be damaged unseen; all conductors are treated as energized and uninsulated.

As insulated for brief brushing contact only: Weatherproof covering is not rated insulation; even brief contact can cause a shock.

As safe once the house’s main breaker is off: The main breaker shuts power on the house side only; the service drop from the utility stays energized.

As harmless, since service drops carry low voltage only: Service-drop voltages are lethal; low voltage does not mean safe.

Treat every conductor, covered or bare, as energized and uninsulated unless the utility has de-energized and grounded it.

Answer: A

Indirect contact: Correct. Indirect contact is contact with an energized conductor through a conductive object such as a branch, rope or tool; it is as dangerous as direct contact.

Step potential: Step potential is voltage between the feet as current spreads through the ground.

Direct contact: Direct contact means a body part touches the energized conductor itself.

Electrical induction: Induction is voltage created in a nearby conductor by a field, not current through a held rope.

Ropes, branches and tools can conduct electricity; touching anything in contact with a conductor is indirect contact.

Answer: A

1. BCR = total benefits ÷ total costs.
2. $725,000 ÷ $250,000 = 2.9.
3. So each $1 spent returns about $2.90 in benefits.

2.9 : 1: Correct. BCR = benefits ÷ costs = $725,000 ÷ $250,000 = 2.9.

1.9 : 1: This is net benefit ÷ cost ($475,000 ÷ $250,000), the return on investment, not the BCR.

0.34 : 1: Inverted: costs ÷ benefits.

0.66 : 1: Divides net benefit by total benefits rather than benefits by costs.

BCR divides benefits by costs; ROI uses net benefit (benefits minus costs) divided by costs.