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Exam reference

The ISA Certified Arborist® exam: the ten domains and what each one is worth

ISA publishes the weight of every domain on the exam, but it does so inside a PDF that most candidates never open. This page sets out all ten — the percentage, how many of the 200 questions that comes to, what sits inside each one, and where the marks are most easily won and lost.

Last reviewed 17 September 2026 against the ISA Certified Arborist Program Guide (rev. August 2025) and the Examination Content Outline (2022 Job Task Analysis).

The exam at a glance

Questions
200
180 scored + 20 pretest
Time
210 min
3 hours 30 minutes
Pass mark
76%
≈ 137/180 at face value
Options
4
single best answer

Twenty of the 200 questions are unscored pretest items that ISA is trialling for future papers. They are not marked on the exam and you cannot tell which they are, so there is nothing to do about them except answer all 200 as though they count. At 210 minutes for 200 questions you have about 63 seconds per question — comfortable, provided you do not spend five minutes on any single one.

All ten domains and their weights

These percentages come from ISA's published examination content outline. The question counts are ours: the weight applied to a 200-question paper, rounded to the nearest whole question.

DomainWeightQuestions
Safe Work Practices15%≈ 30
Pruning14%≈ 28
Tree Biology11%≈ 22
Tree Risk11%≈ 22
Tree Identification and Selection9%≈ 18
Installation and Establishment9%≈ 18
Diagnosis and Treatment9%≈ 18
Trees and Construction9%≈ 18
Soil Management7%≈ 14
Urban Forestry6%≈ 12
Total100%200

The pass mark is a whole-paper mark

You need 76% overall. There is no minimum per domain, so a weak domain can be carried by strong ones — and a domain worth 6% cannot sink you on its own. That is an argument for shoring up Safe Work Practices and Pruning before polishing Urban Forestry, not for ignoring anything entirely: at 76% you can be wrong on about a quarter of the scored questions and no more, which is less slack than most candidates assume. ISA publishes the pass mark as a percentage only and notes that the domain figures on your score report will not average out to your overall score, so treat any raw "number correct" you see quoted — including the arithmetic above — as an approximation.

Dividing your study time by weight

The simplest defensible study plan is to give each domain the share of your time that it has of the paper. Here is what that looks like for a 40-hour and an 80-hour preparation.

Domain40 hours80 hours
Safe Work Practices6 h12 h
Pruning5.6 h11.2 h
Tree Biology4.4 h8.8 h
Tree Risk4.4 h8.8 h
Tree Identification and Selection3.6 h7.2 h
Installation and Establishment3.6 h7.2 h
Diagnosis and Treatment3.6 h7.2 h
Trees and Construction3.6 h7.2 h
Soil Management2.8 h5.6 h
Urban Forestry2.4 h4.8 h

Adjust it once, after a full-length timed mock, using your actual per-domain result rather than your impression of which topics feel hard. The two are rarely the same.

What is inside each domain

Heaviest first. The contents below summarise ISA's published outline in our own words — the outline itself is ISA's document and is worth reading in full; it is a free download. The study notes are ours.

Safe Work Practices

15% · about 30 questions

The largest domain — close to one question in six. It is also the one place where the exam rewards straight memorisation over reasoning: cut names, knot names, approach distances, PPE categories.

What it covers

  • ANSI Z133 and the local laws that sit alongside it
  • Electrical hazards: line types, minimum approach distances, insulating PPE
  • Choosing, inspecting, fitting and looking after PPE — head, eye, ear, leg, foot and hand
  • Powered equipment: aerial lifts and cranes, stump grinders, chippers, chainsaws
  • Climbing systems, knots, tie-in, ascent, descent and work positioning
  • Rigging: lowering devices, blocks and pulleys, and the load an anchor point actually sees
  • Felling and aerial dismantling — directional notch and back cut, plus the spear, snap and drop cuts
  • Job briefings, emergency action plans, first aid and aerial rescue

Where marks get lost

Candidates who inspect and assess trees rather than climb them lose more marks here than anywhere else, because the climbing and rigging vocabulary has no shortcut. Learn each knot and each cut by what it does, not by what it looks like, and the recall questions stop being guesswork.

Pruning

14% · about 28 questions

The most predictable domain in the exam. Cut placement, the branch collar and the consequences of topping appear in essentially every recalled paper, and the rules are short enough to learn completely.

What it covers

  • ANSI A300 Part 1 and the ISA pruning Best Management Practices
  • Pruning objectives: structural, clearance, reduction, restoration, size management
  • The four cuts — removal, reduction, heading, shearing — and where each belongs
  • Branch collar, branch bark ridge and correct cut placement
  • CODIT, wound response and what dictates how a tree walls off damage
  • Timing and dose: species, season, age and proportion of live crown
  • Harmful practice: topping, lion-tailing, over-thinning, flush cuts
  • Tool selection, sharpening and disinfection; root and utility pruning

Where marks get lost

Reduction cut versus heading cut. A reduction cut goes back to a lateral large enough to assume the terminal role — at least one-third the diameter of the stem being removed; a heading cut does not. That one-third figure is worth memorising outright.

Tree Biology

11% · about 22 questions

Everything else rests on this. A question in Pruning or Diagnosis is very often a biology question wearing different clothes, so time spent here pays out three times over.

What it covers

  • Root, trunk, branch, twig and leaf anatomy, and what each part does
  • Photosynthesis, respiration, and how a tree allocates and stores energy
  • Water uptake, transport and transpiration
  • CODIT: the walls, and what strengthens or defeats them
  • Response growth to mechanical stress; reaction and tension wood
  • Growth stages, phenology, dormancy, senescence and the decline spiral
  • Reproduction and propagation: cuttings, layering, grafting

Where marks get lost

Where stored energy sits and what happens when it is spent — and, under time pressure, which direction moves in xylem and which in phloem.

Tree Risk

11% · about 22 questions

Learn the vocabulary exactly as ISA defines it. 'Hazard' and 'risk' are not interchangeable here, and a good share of the questions turn on holding the definitions apart.

What it covers

  • The three levels of assessment: limited visual, basic, advanced
  • Targets, target zones and occupancy rate
  • Likelihood of failure, likelihood of impact, and consequences of failure
  • Defects: cracks, cavities, decay, included bark, lean, root plate problems
  • Mitigation, both tree-based (pruning, support systems) and target-based
  • Inspection intervals and how they are set
  • Who is responsible for what: owner, manager, assessor, arborist

Where marks get lost

Consequences are rated from the value of the target and the severity of the harm — not from how likely the failure is. Candidates who blur the two lose marks on several questions at once, because the same confusion recurs across the domain.

Tree Identification and Selection

9% · about 18 questions

Half identification vocabulary, half right-tree-right-place judgement. The vocabulary half is pure memorisation and is the fastest set of marks available anywhere in the paper.

What it covers

  • Leaf type, arrangement, margin, apex and base; simple versus compound
  • Reading a bare twig: bud position and shape, leaf scars, lenticels, node spacing
  • Bark, flower, inflorescence, fruit and seed characteristics
  • Form, growth habit and silhouette; tropical and desert adaptations
  • Binomial nomenclature; gymnosperm and angiosperm, monocot and eudicot
  • Dichotomous keys, field guides, apps and sample collection
  • Right tree, right place: mature size, soil, exposure, water, rooting volume
  • Invasiveness, species diversity and long-term maintenance cost

Where marks get lost

Opposite versus alternate arrangement, and simple versus compound leaves, asked in words with no picture in front of you. Practise reading those descriptions as text rather than recognising them in the field.

Installation and Establishment

9% · about 18 questions

The most rule-based domain in the exam, which makes it the most examinable: depths, widths, ratios and durations that are either right or wrong.

What it covers

  • Nursery stock types; inspecting a root ball before you buy
  • Planting depth, hole width, and finding the trunk flare
  • Getting the packaging off: containers and crates, and the wire and fabric around a balled root ball
  • Backfill, berms, and mulch depth and placement
  • Staking, guying and trunk wrap: when, how, and for how long
  • Watering through establishment, and how long establishment takes
  • Structural pruning of young trees; correcting circling and girdling roots
  • Season and timing, including moving trees while dormant

Where marks get lost

Establishment-period rules of thumb are climate-specific, and the one the exam uses is the temperate one: roughly a year per inch of trunk caliper. Published establishment rates run considerably faster in warm humid zones and can run slower in arid ones, so if you work outside the temperate range, answer with the rule as the study guide states it and keep your local experience for the job site.

Diagnosis and Treatment

9% · about 18 questions

Process over encyclopaedia. You are not expected to know every pest in the world; you are expected to know the order in which a competent arborist rules things out.

What it covers

  • Signs versus symptoms, and biotic versus abiotic disorders
  • A diagnostic process: what is affected, where, when, and in what pattern
  • The main biotic agents — fungal and bacterial disease, insects and mites, nematodes, and the vectors that carry them
  • The disease cycle, and what has to line up for an infection to take hold
  • Abiotic injury: compaction, drought, chemical damage, wounding, bad planting
  • Stress that compounds — telling the opportunist that moved in from the thing that actually weakened the tree
  • Plant health care and integrated pest management: thresholds, monitoring, records
  • Choosing a treatment, and the rules that govern chemical use

Where marks get lost

Sign versus symptom. A fungal fruiting body is a sign — evidence of the agent itself; wilting is a symptom — the tree's response. Several questions turn on that single word.

Trees and Construction

9% · about 18 questions

Nine per cent of the paper — around eighteen questions, more than Soil Management — and consistently the domain candidates skip. It is under-studied rather than hard.

What it covers

  • ANSI A300 Part 5 and BS 5837; what a tree protection plan contains
  • Tree protection zone and critical root zone, and how each is set
  • Reading a site plan and locating trees on it
  • The construction phases and what the arborist does in each
  • Impacts: compaction, root severance, grade change, drainage, trunk wounds
  • Protective fencing, signage, access control and material storage
  • Post-construction care, and recognising when removal is the honest answer
  • Working with developers and contractors, and checking the plan holds

Where marks get lost

Treating the critical root zone and the tree protection zone as the same thing. They are related but set differently, and questions exploit the overlap. One careful read of the A300 Part 5 BMP repays the hour.

Soil Management

7% · about 14 questions

A small domain that feeds two larger ones. Know the soil texture triangle and what pH does to nutrient availability, and Diagnosis and Installation both get easier.

What it covers

  • Texture, structure, bulk density and compaction
  • pH, cation exchange capacity and buffering
  • Organic matter, mycorrhizae, the rhizosphere and soil fauna
  • Sampling soil properly and reading a soil test report
  • Water movement, drainage, water-holding capacity and water budgets
  • Irrigation, scheduling and recycled water
  • Macro- and micronutrients, deficiency symptoms, fertiliser types and timing
  • Fixing a poor soil: amendments and biochar, decompaction and vertical mulching, and engineered rooting volume under paving

Where marks get lost

Reaching for fertiliser when the tree is short of water, root space or air rather than nutrients. The exam tests that judgement at least as often as it tests the nutrient list.

Urban Forestry

6% · about 12 questions

The smallest domain and the easiest to revise in a single evening — roughly twelve questions for a couple of hours of reading.

What it covers

  • Environmental, economic, social, health and aesthetic benefits of urban trees
  • Benefit–cost ratio and return on investment
  • Plant appraisal approaches and the data you record to value a tree
  • Inventories, canopy-cover goals and urban forest management plans
  • Species diversity, invasive species, pest and maintenance cycles
  • Ordinances, preservation orders, permits and wildlife law
  • Communicating tree care to owners, officials and the public

Where marks get lost

Appraisal terminology. Know what the recognised approaches are called and roughly when each applies; the questions ask for the name far more often than for a calculation.

Sitting the exam: eligibility, fees and results

Eligibility
Three years of full-time practical experience in arboriculture, or a shorter period paired with formal study — a two-year degree plus two arboriculture courses and two years' experience, a four-year degree plus four courses and one year, or assessed training hours substituting for part of the experience. The program guide sets out each route precisely; check which one you fall under before you pay anything.
Fees
A non-refundable application fee of US$40 for members and credential holders or US$50 for everyone else, plus an exam enrolment fee of US$295 for members or US$396 standard; a retake is US$120 and recertification is US$220. On those numbers ISA membership pays for most of itself at the point of enrolment. Taken from ISA's fee table on 17 September 2026. The downloadable program guide still shows US$369 for standard enrolment — the fee table is the current one. Confirm before you apply.
How and where you sit it
Most candidates take it by computer at a Pearson VUE test centre; some ISA chapters also arrange paper-based sittings. The content outline, the question count and the pass mark are identical either way, and the exam is offered in several languages.
Results
A computer-based sitting tells you whether you passed as soon as you finish, and the test centre prints a score report showing how you did domain by domain — the document worth keeping, because it tells you exactly where you were strong and weak. The official result is posted to your ISA account and mailed to you separately: the program guide says within four weeks, ISA's FAQ page says four to six.
Keeping the credential
Thirty continuing education units within each three-year recertification cycle, plus the recertification fee — or sit the exam again.

One thing ISA does not publish: a pass rate

We looked for one in the program guide, the credential pages and the FAQ, and it is not there. Pass-rate figures circulating on forums and test-prep sites are estimates, not ISA numbers, and we would not plan around any of them. What you can control is measurable: your score on a full-length timed paper, broken down by domain.

A note on study materials

The current Arborists' Certification Study Guide is the fourth edition, published in 2022. Plenty of second-hand third editions (2010) are still in circulation and they are cheap for a reason: they pre-date the current content outline. We took a 200-question set written down from memory by a recent candidate and tried to ground every item in the third edition; around one in ten could not be traced to it at all, and those clustered in tree risk assessment and in modern climbing and rigging systems — the areas the fourth edition reworked most. That is one candidate's recollection rather than a controlled study, but the direction is clear enough: if you are buying one book, buy the current edition. If you already own the third, put ISA's Best Management Practice volumes for tree risk assessment and for pruning alongside it.

Common questions

How many questions are on the ISA Certified Arborist exam?

200 multiple-choice questions with four options each. Only 180 are scored; the other 20 are unscored pretest items being trialled for future exams, and they are not identified on the paper. The time limit is 210 minutes.

What score do you need to pass the ISA Certified Arborist exam?

76 percent. ISA publishes the pass mark only as a percentage. Taken at face value across the 180 scored questions that is about 137 correct, but ISA does not publish a raw number and cautions that the domain percentages on your score report will not average out to your overall score.

Which domain is worth the most marks?

Safe Work Practices, at 15 percent — about 30 questions on a 200-question paper. Pruning is next at 14 percent, then Tree Biology and Tree Risk at 11 percent each.

How long does it take to get ISA exam results?

A computer-based exam tells you the result as soon as you finish, and the Pearson VUE test centre prints a score report showing how you performed domain by domain. The official result is posted to your ISA account and mailed to you separately: ISA's program guide says within four weeks, while its FAQ page says four to six.

Does ISA publish a pass rate for the Certified Arborist exam?

No. ISA does not publish a pass rate for this exam anywhere in its program guide, its FAQ or its credential pages. Any percentage you see quoted online is someone's estimate, not an ISA figure.

What are the eligibility requirements?

Three years of full-time practical experience in arboriculture, or a shorter period combined with formal study: a two-year degree plus two arboriculture courses and two years' experience, a four-year degree plus four courses and one year, or assessed training hours in place of part of the experience. The current program guide sets out each route in full.

What does the exam cost?

ISA's current fee table lists a non-refundable application fee of US$40 for members and credential holders or US$50 for everyone else, plus an exam enrolment fee of US$295 for members and US$396 standard. A retake is US$120 and recertification is US$220. The downloadable program guide still shows US$369 for standard enrolment, so trust the fee table on ISA's site — and confirm it before you apply, because these change.

How do you keep the credential once you have it?

Thirty continuing education units within each three-year recertification cycle, together with the recertification fee, or retake the exam.

Which study guide edition should I use?

The Arborists' Certification Study Guide, fourth edition, published in 2022. The third edition dates from 2010 and predates the current exam content outline; several topics on today's exam — particularly in tree risk, climbing systems and response growth — are not covered in it at all.

Is the exam the same everywhere in the world?

The content outline, the number of questions and the 76 percent pass mark are the same wherever you sit it. Most candidates take it by computer at a Pearson VUE test centre; some ISA chapters also arrange paper-based sittings. The exam is offered in several languages.

Sources

Reviewed 17 September 2026. Where this page and an ISA document disagree, ISA is right — tell us at nwtech.hk@gmail.com and we will correct it.

See where you actually stand across the ten domains

CanopyPrep builds timed papers to the weights on this page and returns a score report broken down domain by domain, with every wrong answer explained. The 50-question sample is free.

Try the free sampleHow the full mock works