ISA Certified Arborist Exam Flashcards

Q: What is the ISA Certified Arborist exam pass rate?

ISA does not publish an aggregate pass rate for the Certified Arborist credential. The exam has a 76% passing score (roughly 152 of 200 questions), 200 multiple-choice questions including 20 unscored pretest items, and a 3.5-hour time limit.

Q: What are the highest-weighted domains on the exam?

Safe Work Practices (15%), Pruning (14%), Tree Biology (11%), and Tree Risk (11%) together make up 51% of the scored exam per the 2022 Job Task Analysis — the highest-value domains to master first.

Q: What experience do I need to sit for the exam?

ISA requires a minimum of three years of full-time eligible arboriculture experience (about 5,385 hours), or a qualifying degree/education pathway combined with related experience.

Q: How long is the Certified Arborist credential valid?

The credential is valid for 3 years. Recertification requires 30 Continuing Education Units (CEUs) earned during that period, or retaking the exam.

Q: What happens if I fail the exam?

Candidates may retake the exam 30 days after the most recent attempt; a $120 retake fee applies for each retake attempt.

Q: What are the two most heavily tested standards?

ANSI A300 (tree pruning standards) and ANSI Z133 (arboricultural safety requirements, current edition 2017) are the two industry standards referenced most often across exam scenarios.

Question 1

CODIT (Compartmentalization Of Decay In Trees)

Accepted Answer

Shigo's model showing trees do NOT heal wounds by replacing damaged tissue like animals do; they wall off (compartmentalize) injured wood behind chemical/physical boundaries while new growth forms outside the wound. Closing over a wound does not mean internal decay is gone.

Question 2

CODIT's four walls

Accepted Answer

Wall 1 blocks vertical spread (weakest); Wall 2 blocks inward spread toward the center; Wall 3 blocks lateral spread via rays; Wall 4 (the barrier zone) blocks outward spread into wood formed after the injury and is the strongest of the four.

Question 3

Cohesion-tension mechanism

Accepted Answer

The force that pulls water up a tree: evaporation from leaves (transpiration) creates negative pressure (tension) that pulls a continuous water column upward through the xylem, held together by cohesion between water molecules.

Question 4

Xylem vs. phloem

Accepted Answer

Xylem (sapwood) conducts water and dissolved minerals upward and forms structural wood. Phloem (inner bark) carries sugars and signaling compounds from source tissue (mature leaves) to sink tissue (roots, buds, fruit, wounds).

Question 5

Vascular cambium

Accepted Answer

A thin living layer between xylem and phloem that produces new xylem inward and new phloem outward each growing season; a girdling wound that severs the cambium interrupts both water transport and sugar transport.

Question 6

Reaction wood: tension wood vs. compression wood

Accepted Answer

Hardwoods (angiosperms) form tension wood on the UPPER side of a leaning stem to pull it upright. Conifers (gymnosperms) form compression wood on the LOWER side to push the stem up — a frequently confused exam distinction.

Question 7

Binomial nomenclature format

Accepted Answer

A species name pairs a capitalized, italicized genus with a lowercase, italicized specific epithet (e.g., Quercus rubra). Cultivar names follow in single quotes, not italicized (e.g., Acer rubrum 'October Glory'); varieties use 'var.'; hybrids use a multiplication sign (x).

Question 8

MAD-Cap-Horse mnemonic

Accepted Answer

Memory aid for the few common tree genera with OPPOSITE leaf/bud arrangement: Maple (Acer), Ash (Fraxinus), Dogwood (Cornus), Caprifoliaceae (viburnum/honeysuckle relatives), and Horsechestnut/buckeye (Aesculus). Nearly everything else woody is alternate.

Question 9

Distinguishing a leaf from a leaflet

Accepted Answer

Look for the axillary bud: it sits in the axil where a whole (true) leaf meets the twig, but is never found at the base of an individual leaflet. A compound leaf with many leaflets (e.g., hickory) is still one leaf.

Question 10

Compound leaf types

Accepted Answer

Pinnately compound: leaflets arranged along a central axis (e.g., ash). Palmately compound: leaflets radiate from one point (e.g., buckeye). Bipinnately (twice) compound: leaflets divided again off a secondary axis (e.g., honeylocust).

Question 11

"Right tree, right place"

Accepted Answer

The core species-selection principle: match mature size, hardiness zone, above/below-ground space, soil/drainage tolerance, and pest pressure to the site BEFORE planting, rather than fighting a mismatch with maintenance later (e.g., avoid a large-maturing shade tree under low overhead utility lines).

Question 12

Soil texture vs. soil structure

Accepted Answer

Texture is the fixed mineral particle-size mix (sand/silt/clay) and cannot be changed by management. Structure is how particles aggregate into peds and pore space, and CAN be protected, degraded by compaction, or rebuilt with organic matter. Roughly 40% sand/40% silt/20% clay is a loam, often the most favorable texture for trees.

Question 13

Root-limiting bulk density

Accepted Answer

Compacted soil becomes root-limiting at roughly 1.4-1.6 g/cm3 in clay soils and about 1.7-1.8 g/cm3 in sandy soils (sand tolerates more because particles already pack with larger gaps). Compaction destroys macropores first, cutting oxygen and water infiltration before total porosity changes much.

Question 14

High-pH (lime-induced) chlorosis

Accepted Answer

As soil pH climbs above about 7.5, availability of iron, manganese, and zinc plummets, producing interveinal chlorosis (yellow tissue, green veins) worst on the newest leaves — classic on pin oak and river birch in calcareous or over-limed urban soils. Most landscape trees prefer pH 6.0-7.0.

Question 15

Correct planting depth

Accepted Answer

The root collar (trunk flare) must be located before planting and set at or slightly above finished grade — never buried. Burying the flare restricts gas exchange, invites girdling roots and stem-rot, and hides defects; it is the single most common installation error.

Question 16

Planting hole width guideline

Accepted Answer

Dig the hole no deeper than the root-ball height (resting on firm, undisturbed soil) but 2-3 times as wide as the root ball, with sides roughened to break a glazed clay interface and encourage lateral root growth.

Question 17

Correct mulch application

Accepted Answer

Apply mulch 2-4 inches deep in a broad, shallow ring, pulled back 2-3 inches from the trunk. "Volcano mulching" (mulch piled against the trunk) is a defect, not extra care — it keeps bark chronically moist and invites decay and girdling roots.

Question 18

Establishment period rule of thumb

Accepted Answer

A common field estimate budgets roughly one growing season of establishment per inch of trunk caliper before a newly planted tree is self-sufficient (e.g., a 2-inch caliper tree needs about two years) — the period during which roots grow out into surrounding soil.

Question 19

ANSI A300 pruning philosophy

Accepted Answer

ANSI A300 (Part 1) requires the pruning OBJECTIVE to be defined before the method — e.g., clearance, young-tree structure, risk reduction, or deadwood removal — with measurable specifications (branch-size limits, clearance dimensions, a live-crown removal limit) that a second qualified arborist could reproduce.

Question 20

Correct pruning cut location

Accepted Answer

A proper branch-removal cut is made just OUTSIDE the branch collar and branch bark ridge, leaving the collar intact so it can compartmentalize the wound and grow woundwood. Never make a flush cut (removes the collar, injures trunk tissue) or leave a stub (delays closure, invites decay).

Question 21

Maximum live-crown removal (pruning dose)

Accepted Answer

As a general guideline, avoid removing more than about 25% of a tree's live crown in a single growing season — and use a lower limit on stressed, declining, or mature trees.

Question 22

The three-cut pruning method

Accepted Answer

For removing heavy limbs: (1) an undercut a short distance out to stop bark from tearing downward, (2) a top cut farther out to remove the bulk of the limb's weight, then (3) the final cut just outside the branch collar to leave a clean wound.

Question 23

Codominant stems and included bark

Accepted Answer

Codominant stems are two or more upright stems of nearly equal diameter arising from one point; when the union is narrow, bark gets trapped between them (included bark), which is not a wood-to-wood bond and is prone to splitting. The fix on a young tree is to SUBORDINATE the weaker stem (reduce, don't remove outright) rather than wait until it becomes a large removal.

Question 24

Structural pruning timing for young trees

Accepted Answer

Most ISA Best Management Practices recommend beginning structural/training pruning about 2-3 years after planting (once root function re-establishes), then repeating on a roughly 2- to 5-year cycle through the establishment years.

Question 25

Half-diameter rule for scaffold branches

Accepted Answer

A branch whose attachment diameter exceeds roughly half the trunk diameter at that point is competing for dominance and should be subordinated; permanent scaffolds on large-maturing trees should also be spaced vertically about 18 inches or more apart.

Question 26

Biotic vs. abiotic disorders

Accepted Answer

Biotic disorders are caused by living organisms (insects, mites, fungi, bacteria, viruses, phytoplasmas, nematodes, animals). Abiotic disorders are caused by non-living site/environmental factors (drought, compaction, salt, mechanical injury, nutrient imbalance, temperature extremes).

Question 27

IPM control hierarchy

Accepted Answer

Integrated Pest Management applies controls in this order of preference: (1) cultural — fix site/health causes first, (2) mechanical/physical — pruning out, sanitation, barriers, (3) biological — natural enemies, (4) chemical — used only when justified, targeted, correctly timed, and legal. IPM does not forbid pesticides; it prevents automatic spraying.

Question 28

Insect feeding styles and signatures

Accepted Answer

Chewing insects (caterpillars, beetles) remove tissue, leaving holes or skeletonized leaves. Sucking insects (aphids, scales, lace bugs) pierce tissue, causing stippling and honeydew/sooty mold. Boring insects (bark beetles, emerald ash borer) feed under bark/wood, leaving exit holes, frass, and galleries.

Question 29

Primary vs. secondary pests

Accepted Answer

Many biotic agents (borers, canker fungi, decay organisms) are SECONDARY — they typically attack trees already weakened by drought, deep planting, root injury, or compaction. Treating the organism while ignoring the underlying stress gives poor, short-lived results.

Question 30

Tree Protection Zone (TPZ) sizing

Accepted Answer

A common North American rule of thumb sizes an optimal TPZ radius at about 1-1.5 feet per inch of trunk DBH (diameter at breast height, measured at 4.5 ft above grade), with 1 foot per inch as a minimum — not simply the drip line.

Question 31

Root zone depth and spread

Accepted Answer

Most absorbing roots sit in the upper 6-18 inches of soil, and the root system commonly spreads 2-3 times beyond the branch/drip line in open soils — which is why the drip line alone is an unreliable protection boundary.

Question 32

Tree protection fencing requirements

Accepted Answer

Protection fencing must be visible and durable (chain link or sturdy panel, not flagging tape alone), installed BEFORE demolition or grading begins, and maintained as a true exclusion boundary — excluding parking, equipment travel, material stockpiles, washout, and grade change.

Question 33

Delayed construction-damage symptoms

Accepted Answer

Crown symptoms from root severance, soil compaction, or construction injury often do NOT appear until the next season or two — the tree can look fine immediately after construction while decline is already underway below ground.

Question 34

Definition of tree risk

Accepted Answer

Tree risk is the combination of (1) the likelihood that a tree or tree part will fail, (2) the likelihood that the failed part impacts a target, and (3) the consequences of that impact. A defect over an empty field is lower risk than the same defect over a busy entrance.

Question 35

ISA risk rating categories

Accepted Answer

The final risk rating is one of four categories: low, moderate, high, or extreme — produced by combining likelihood of failure, likelihood of impact, and consequences of failure.

Question 36

The two-matrix risk rating logic

Accepted Answer

Matrix 1 combines likelihood of failure with likelihood of impact to yield a combined likelihood (unlikely, somewhat likely, likely, very likely). Matrix 2 combines that combined likelihood with consequences (negligible, minor, significant, severe) to produce the final risk rating.

Question 37

ISA's three tree risk assessment levels

Accepted Answer

Level 1 (Limited): a focused screening such as a drive-by or walk-by. Level 2 (Basic): a systematic 360-degree visual inspection from the ground — the default for most routine decisions. Level 3 (Advanced): specialized tools, climbing/aerial access, root collar excavation, or decay testing.

Question 38

Tree risk assessment period

Accepted Answer

A risk rating applies only over a stated assessment period agreed with the owner, after which conditions are presumed to have changed. It is a structured judgment under current conditions, not a forecast of whether failure will or will not happen.

Question 39

Defensible tree risk communication

Accepted Answer

Avoid declaring a tree "safe" — no inspection eliminates all risk. A defensible report states what was observed, which defects were found, which targets were present, and what action is recommended, clearly noting the scope and limitations of the assessment.

Question 40

ANSI Z133

Accepted Answer

The American National Standard for Arboricultural Operations — Safety Requirements; the consensus safety standard for tree work (current edition 2017, revised on roughly a five-year cycle). It governs electrical approach distances, PPE, rigging, and work practices.

Question 41

Minimum approach distance (MAD) for untrained workers

Accepted Answer

Under ANSI Z133, a worker who is NOT a trained, qualified, or trainee line-clearance arborist must stay at least 10 feet from energized conductors up to 50,000 volts (50 kV); the required distance increases above 50 kV.

Question 42

Treating conductors as energized

Accepted Answer

The safe starting assumption is that ALL conductors are energized until the responsible utility or authority confirms otherwise — never rely on insulation appearance, wire size, weather, or a quiet line to judge safety.

Question 43

Hierarchy of controls (PPE's place)

Accepted Answer

Controls rank, in order of effectiveness: eliminate, substitute, engineer, administrate, then PPE. PPE is the LAST layer — it reduces injury severity but never removes the hazard, so it must be paired with proper hazard control and safe work method.

Question 44

Chainsaw kickback

Accepted Answer

Kickback is the sudden upward/backward rotation of the bar when the upper tip (kickback zone) contacts wood or the chain pinches in the cut — the leading chainsaw injury mechanism. Defenses: keep the nose clear, maintain a firm two-handed grip, keep a stable stance and escape path, and rely on the chain brake.

Question 45

Climbing system attachment rule

Accepted Answer

Climbing systems require two means of attachment when a climber is repositioning aloft, along with a pre-use inspection, compatible components, and a workable aerial-rescue plan; damaged or questionable life-support gear is removed from service immediately.

Question 46

Job briefing and stop-work authority

Accepted Answer

A job briefing precedes every operation and covers the objective, hazards, equipment, assignments, traffic/electrical exposure, weather, access, and rescue plan. Any crew member has stop-work authority — when conditions change, the correct response is to pause and reassess, not push to meet the schedule.

Question 47

Step potential

Accepted Answer

The voltage gradient across the ground near an energized object (e.g., a downed power line, or a fence/tree in contact with one); a bystander can be electrocuted simply by walking toward it, even without direct contact, because current flows through the ground and up through the legs.

Question 48

ISA credential vs. municipal authority

Accepted Answer

The Certified Arborist credential is a voluntary professional certification, NOT a municipal permit or contractor license. Public-tree work (planting, pruning, removal) on the public right-of-way is governed by local tree ordinances, permits, and the tree board/city forester — the arborist usually advises rather than authorizes.

Question 49

Tree inventory purpose

Accepted Answer

A systematic record of trees in a defined area (location, species, diameter class, condition, maintenance need, site restrictions) used to PRIORITIZE work by risk and benefit — not decoration. Stale or uncalibrated data should be field-verified before issuing high-consequence work orders.

Question 50

Urban forest canopy goal

Accepted Answer

A community's target percentage of land area covered by tree crowns; species selection, planting, and maintenance choices should support this long-term canopy plan rather than being driven by whichever complaint is loudest.

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