Your FREE Certified Arborist Flashcards 2026 – 250+ Cards

The process where leaves use light energy, water, and CO₂ to make sugars (food) and release oxygen.

The process that breaks down sugars to release energy for growth and maintenance, using oxygen and releasing CO₂.

Water loss as vapor, mostly through leaf stomata; it drives water movement up from the roots.

Conducts water and minerals upward from roots to leaves; older xylem becomes the structural wood.

Transports sugars (food) made in the leaves down and throughout the tree; it lies just inside the bark.

A thin layer of dividing cells between xylem and phloem that produces new wood and bark, increasing trunk diameter.

Tiny pores, mostly on leaf undersides, that open and close to exchange gases and release water vapor.

The older, central, non-conducting wood that provides structural support; often darker than sapwood.

The younger, outer, living wood that actively conducts water and minerals (functional xylem).

Undifferentiated tissue where cell division occurs, allowing growth (apical and lateral meristems).

Growing tip tissue at shoot and root ends responsible for primary (length) growth.

Root hairs greatly increase surface area for the absorption of water and nutrients.

Beneficial fungi that form a symbiosis with roots, extending their reach for water and nutrients.

The green pigment in leaves that captures light energy for photosynthesis.

Severing bark/phloem around the trunk; it stops downward sugar flow and eventually kills the tree.

The ground area beneath the outer edge of the crown; a rough guide to root spread, though roots extend beyond it.

In the top 6–18 inches (about 15–45 cm) of soil, often extending well past the dripline.

A tree that sheds its leaves seasonally, typically in autumn.

A tree, usually cone-bearing with needles, that keeps foliage year-round.

Yearly layers of xylem; earlywood and latewood form one ring, allowing age and growth-rate estimation.

The sugars produced by photosynthesis, transported by phloem to fuel growth and stored as starch.

A period of suspended growth (often winter) that lets trees survive cold or drought.

Water pressure inside plant cells that keeps tissues firm; its loss causes wilting.

The upper leaf cells packed with chloroplasts where most photosynthesis occurs.

Excess photosynthate is stored as starch in roots, stems, and branches for use during dormancy and flush.

Primary growth lengthens shoots/roots (apical meristems); secondary growth thickens them (cambium).

Pores in bark and stems that allow gas exchange between internal tissues and the air.

A node is where leaves/buds attach; the internode is the stem segment between nodes.

Plant responses to day length, triggering events like dormancy, flowering, and leaf drop.

Transpiration pulls a continuous water column up the xylem, held together by water's cohesion.

It produces xylem (wood) toward the inside and phloem (inner bark) toward the outside.

One leaf per node, staggered along the stem — a key ID feature distinguishing many genera.

Two leaves per node directly across from each other (e.g., maple, ash, dogwood — 'MAD' families).

A leaf with a single, undivided blade attached to the petiole.

A leaf blade divided into multiple leaflets along a common stalk (rachis).

A bud is found at the base of a true leaf (petiole), but not at the base of a leaflet.

Scientific (binomial) name: capitalized Genus + lowercase species, both italicized (e.g., Quercus rubra).

They are precise and universal, avoiding the confusion of multiple common names for one tree.

Matching a species' mature size, form, and site needs to the planting location to reduce future conflicts.

Selecting species that fit the space (above and below ground) to avoid utility, structure, and root conflicts.

Choosing species adapted to the site's climate (cold/heat tolerance) for long-term survival.

Over-planting one species makes the urban forest vulnerable to a single pest or disease (e.g., elm, ash).

Aim for no more than 10% one species, 20% one genus, 30% one family in the urban forest.

A species that occurs naturally in a region; often well-adapted and supportive of local wildlife.

A non-native species that spreads aggressively and harms ecosystems, economy, or health.

A cultivated variety selected for desirable traits (form, flower, disease resistance); named in 'single quotes'.

Deciduous gives summer shade and winter sun; evergreens give year-round screening and windbreaks.

Its characteristic shape (columnar, round, vase, pyramidal) — a key selection and ID trait.

The edge of a leaf (entire, toothed/serrate, lobed) used as an identification feature.

An ID feature, especially in winter — smooth, furrowed, plated, or peeling bark distinguishes species.

An ID tool of paired either/or choices that narrows down to a species step by step.

Three or more leaves arising at a single node.

Leaflets arranged along both sides of a central rachis, like a feather (e.g., ash, walnut).

Leaflets radiating from a single point, like fingers from a palm (e.g., buckeye, horsechestnut).

The pattern of veins in a leaf (pinnate, palmate, parallel) used in identification.

A winged dry fruit (e.g., maple 'helicopter', ash) — an ID clue.

Selecting species tolerant of the site's soil, pH, and moisture greatly improves survival.

Choosing species that withstand de-icing or coastal salt for roadside and seaside sites.

Fast-growing trees establish quickly but often have weaker wood and shorter lives than slow growers.

A balanced soil of sand, silt, and clay — good drainage, aeration, and water/nutrient holding for trees.

The proportion of sand, silt, and clay particles in soil, which affects drainage, aeration, and nutrients.

How soil particles clump into aggregates, creating pore space for air, water, and roots.

It reduces pore space, limiting oxygen and water to roots — a leading cause of urban tree decline.

Slightly acidic to neutral, roughly 6.0–7.0, where most nutrients are available.

Yellowing of leaves (often between veins) from nutrient deficiency, frequently iron or manganese at high pH.

Nitrogen — needed in the largest amounts and the most common deficiency in landscapes.

Nitrogen (leaf/shoot growth), Phosphorus (roots/energy), Potassium (overall vigor/stress) — the three macronutrients.

It identifies pH and actual nutrient needs so you apply only what's deficient, avoiding waste and harm.

Organic material over the root zone that conserves moisture, moderates temperature, reduces weeds, and adds organic matter.

Mulch piled against the trunk; it traps moisture, invites decay and pests, and can girdle the tree.

About 2–4 inches (5–10 cm), kept a few inches away from the trunk flare.

A soil's ability to hold and supply nutrient cations; clays and organic matter raise CEC.

Techniques that loosen compacted soil and add air/organic matter to improve root health.

The amount of water soil holds after drainage by gravity — the ideal moisture range for roots.

The soil moisture level below which a plant cannot extract water and wilts irreversibly.

It improves structure, water holding, nutrient supply, and feeds beneficial soil organisms.

High soil salts (e.g., de-icing salt) that draw water from roots and cause leaf scorch and decline.

Generally, backfill with native soil; broad amendment of the hole is not recommended for landscape trees.

Nitrogen that releases gradually, reducing burn risk and leaching and feeding over a longer period.

Poor drainage and aeration but high nutrient/water holding; prone to compaction.

Excellent drainage and aeration but low water and nutrient retention.

The zone of soil around roots influenced by root activity and rich in microbial life.

Lab testing of foliage to diagnose nutrient deficiencies more precisely than soil tests alone.

They cycle nutrients, improve structure, and protect roots — supported by organic matter and mulch.

Waterlogged, low-oxygen soil suffocates roots and promotes root-rot pathogens.

Measuring how fast water drains from a hole to assess soil drainage before planting.

2–3 times the width of the root ball, with sloping sides; only as deep as the root ball.

With the trunk flare (root flare) at or slightly above grade — never buried too deep.

The widening at the base where the trunk meets the roots; it must be visible at the soil line.

Deep planting suffocates roots and promotes stem-girdling roots and decline.

Remove/fold down the top of the basket and burlap after setting the ball to free the roots.

Tease apart, straighten, or cut circling/girdling roots so they grow outward.

Only when needed for stability or vandalism; stake low and loosely, and remove after about one year.

Trees develop stronger trunk taper and roots when allowed to flex; long-term staking weakens them.

Deep, regular watering during establishment (often the first 1–3 years) to keep the root ball moist, not soggy.

Stress and reduced growth after planting from root loss; minimized by proper handling, planting, and watering.

Balled-and-burlapped: field-grown trees dug with a soil ball wrapped in burlap.

Trees sold with soil removed from roots; lightweight, best planted dormant with roots kept moist.

Trees grown in pots; check for and correct circling roots before planting.

Roughly one year per inch of trunk diameter before a tree is fully established.

Generally no nitrogen at planting; focus on proper depth, mulch, and water for root establishment.

Dormant season — fall or early spring — to reduce stress and allow root growth before heat.

A root that grows around and compresses the trunk, restricting flow and slowly killing the tree.

Disturbing the ball breaks remaining roots and worsens transplant shock.

By the root ball, never by the trunk, to avoid breaking roots and loosening the ball.

It encourages deep, drought-resistant roots rather than shallow ones from frequent light watering.

A spray sometimes used on evergreens to reduce winter water loss after transplanting.

Treated/synthetic burlap does not decompose and can girdle roots; remove it at planting.

Gradually acclimating nursery stock to outdoor conditions before or after planting to reduce shock.

No — grass competes for water/nutrients; a mulch ring reduces competition and mower/trimmer damage.

Guards or wraps that prevent sunscald, rodent damage, and string-trimmer wounds.

Compartmentalization Of Decay In Trees — how trees wall off decay behind four protective boundaries (Shigo).

The swollen base of a branch where it joins the stem; pruning cuts must be made just outside it, never flush.

An improper cut that removes the branch collar, damaging the stem and preventing proper compartmentalization.

Leaving too long a branch stub; it dies back, decays, and delays wound closure — improper pruning.

A pruning technique for heavy branches: undercut, top cut to remove weight, then a final cut at the collar to avoid bark tearing.

The raised line of bark in a branch union that, with the branch collar, marks where a proper pruning cut is made.

A pruning type that removes dead, dying, diseased, broken, and weakly attached branches from the crown.

Selective removal of live branches to reduce density, improving light and air movement while keeping the natural form.

Removing lower branches to provide clearance for traffic, pedestrians, buildings, or sightlines.

Decreasing the height or spread of a crown using reduction cuts back to a live lateral large enough to assume the terminal role.

Removing a larger branch back to a living lateral at least one-third its diameter (the 1/3 rule), able to assume apical dominance.

Cutting a branch back to its point of origin at the parent stem or trunk, just outside the branch collar.

Cutting between buds or nodes (or to a too-small lateral); causes weak, dense regrowth — generally avoided.

An unacceptable practice of cutting branches to stubs or small laterals; causes decay, weak sprouts, and stress.

Over-thinning that strips inner foliage and leaves growth at branch ends; increases breakage risk — avoid it.

Less stress and disease spread, clearer structure to see, and vigorous spring growth; ideal for most structural pruning.

During the growing season in oak-wilt regions; prune in dormancy to avoid attracting beetles that spread oak wilt.

Reducing competing leaders and co-dominant stems early to develop one dominant trunk and strong scaffold branches.

Two or more similarly sized upright stems competing for dominance; often weakly attached and a structural concern.

Bark trapped between a branch and stem (or two stems); creates a weak union prone to splitting.

Generally no more than about 25% in a single pruning, and less for mature or stressed trees.

No — wound dressings are not recommended; they do not prevent decay and can interfere with compartmentalization.

Reduction cuts to a lateral that redirect growth away from a target like a utility line.

The terminal bud's suppression of lateral buds; pruning the leader releases laterals to grow.

A vigorous, upright epicormic shoot arising on a branch or trunk, often after heavy pruning or stress.

An epicormic shoot arising from the root system or below the graft union; usually removed.

To prevent spreading pathogens (e.g., fire blight) between cuts and between trees.

Training a tree to grow flat against a support in a pattern through selective pruning and tying.

U.S. industry standards for tree care operations — pruning, and other practices — that define proper techniques.

A pruning system that repeatedly cuts back to the same points (pollard heads) to maintain a small, formal crown.

Selective pruning over several years to improve the structure of a topped, vandalized, or storm-damaged tree.

Selective branch removal to open a view through a tree without harming its health or form.

Dead, diseased, and hazardous branches can be removed at any time of year.

Cutting just outside the branch collar/bark ridge so the tree's natural defenses close the wound (Shigo).

It needs its full leaf area to make food and establish roots; limit early pruning to defects only.

Specialized pruning to keep trees a safe distance from power lines, using directional reduction cuts.

The larger stem or limb from which a smaller branch arises; removal cuts return to it at the collar.

A holistic program of monitoring and maintaining tree health using cultural, preventive, and least-toxic methods.

A strategy that prioritizes monitoring, prevention, and cultural/biological controls, using pesticides only as a last resort.

Correctly identify the pest/problem and monitor; intervention follows only when thresholds are exceeded.

The pest level at which control action is justified to prevent unacceptable damage.

A problem caused by a living agent — insect, fungus, bacterium, virus, or nematode.

A non-living cause of stress — drought, compaction, salt, mechanical injury, or improper planting.

Biotic spreads progressively and is often species-specific; abiotic is usually uniform and non-spreading.

Disease requires a susceptible host, a virulent pathogen, and a favorable environment together.

Anthracnose, powdery mildew, or root rots (e.g., Armillaria) caused by fungi.

Signs are the pathogen itself (fungal fruiting bodies); symptoms are the host's response (wilting, cankers).

An insect whose larvae tunnel under bark or in wood (e.g., emerald ash borer), disrupting transport.

An invasive beetle whose larvae kill ash trees by tunneling and girdling the cambium.

Browning of leaf margins from water stress, heat, salt, or root problems — often abiotic.

A localized dead area of bark and cambium, often from fungal or bacterial infection at a wound.

Using natural enemies (predators, parasitoids, pathogens) to suppress pest populations.

Pests like aphids and scale that feed on sap, causing distortion, honeydew, and sooty mold.

Sugary excretion from sap-feeders (honeydew) that grows black sooty mold fungus on leaves.

An insect that eats leaves (e.g., caterpillars); repeated defoliation stresses and can kill trees.

Treating the wrong cause wastes resources and can harm the tree; identify the agent first.

Identify the plant, define normal, examine symptoms/signs, consider history and site, then diagnose.

Phytophthora and Armillaria root rots that attack roots and the root collar.

A pathogen (e.g., Dutch elm disease, oak wilt, Verticillium) that plugs the water-conducting xylem.

A fungal vascular wilt spread by elm bark beetles and root grafts that kills American elms.

A lethal fungal vascular disease of oaks spread by beetles and root grafts; avoid wounding oaks in season.

Damage limited to one species or genus often points to a biotic (living) cause.

Choose cultural, mechanical, and biological controls first; use targeted pesticides only when justified.

Delivering a pesticide or nutrient directly into the vascular system for certain pests/diseases.

Regularly inspecting trees to detect pests/problems early before they exceed action thresholds.

A fenced area around a tree, often based on trunk size or dripline, that excludes construction impacts.

The soil/root area essential to a tree's survival, commonly estimated from trunk diameter (e.g., ~1 ft radius per inch DBH).

Soil compaction and root severance in the root zone — often unseen until decline appears later.

To keep equipment, materials, and traffic out of the root zone and prevent compaction and damage.

Adding or removing soil over roots; fill suffocates roots and cuts reduce them, both causing decline.

Diameter at Breast Height — trunk diameter measured at 4.5 ft (1.4 m), used for sizing CRZ/TPZ and risk work.

Cutting through roots for utilities; severs major roots, reducing stability and water uptake.

Boring under the root zone instead of trenching to install utilities with minimal root loss.

Early planning protects trees through design, fencing, and specifications rather than reacting to damage.

Documenting species, condition, and value of trees to decide which to preserve and how.

Reduces oxygen and water infiltration to roots; use permeable surfaces or suspended pavement where possible.

Mulch, plywood/ground protection mats over root zones, and limiting equipment access.

An engineered load-bearing soil that supports pavement while allowing root growth in urban sites.

A retaining structure around a trunk when grade is raised, intended to keep soil off the root flare.

Root loss and compaction cause a slow decline; symptoms can lag the injury by several years.

Using compressed air to excavate soil without cutting roots, exposing them for inspection or utility work.

Estimating a tree's monetary value (e.g., trunk-formula method) for loss, insurance, or planning.

Healthy trees compartmentalize a wound; repeated or large wounds plus root loss cause decline.

Even a few inches of fill can reduce oxygen to roots and cause gradual decline.

Written requirements (fencing, no-storage, pruning, monitoring) protecting trees during a project.

Protect the root zone first; root and soil damage is harder to fix than canopy pruning.

Fuel, oil, and concrete washout are toxic to roots and soil — keep them out of the root zone.

Likelihood of failure × likelihood of impacting a target × consequences of that impact.

People, property, or activities that could be struck if a tree or part fails.

Level 1 (limited visual), Level 2 (basic walk-around), and Level 3 (advanced, with tools).

A 360° ground inspection of the whole tree and site — the standard arborist assessment.

A weak union prone to splitting; a common structural defect raising failure likelihood.

Internal or open decay that reduces sound wood and load-bearing capacity, raising failure risk.

A broken, detached branch lodged in the crown that can fall — an immediate risk.

A recent or progressive lean (especially with soil heaving/cracking) suggests possible root or stability failure.

Loss of structural roots reduces anchorage and increases whole-tree (uprooting) failure likelihood.

A tool combining likelihood of failure-and-impact with consequences to assign Low/Moderate/High/Extreme risk.

Pruning, cabling/bracing, moving the target, reducing use, or removing the tree.

Hardware that supplements weak unions/limbs to reduce failure risk; cables (flexible) and rods/braces (rigid).

A hazard is a defect with potential to cause harm; risk also considers the likelihood and the consequences.

A categorical (Low–Extreme) judgment of risk, the most common method in ISA's TRAQ approach.

Tree Risk Assessment Qualification — ISA's standardized methodology for assessing tree risk.

The risk that remains after mitigation actions are taken.

Action is recommended urgently — the failure is likely and a target is present.

Improbable, Possible, Probable, or Imminent — describing how likely a part is to fail.

Checking the trunk base and root flare for decay, cavities, fungi, and girdling roots affecting stability.

Possible internal wood decay; a sign to investigate structural soundness.

How often a target is present in the strike zone; it affects the likelihood-of-impact rating.

Decayed wood loses load-bearing strength; the amount and location of remaining sound wood matter for stability.

A rough rule that risk rises when sound shell thickness is small relative to trunk radius (interpret with judgment).

A separation in wood (e.g., from included bark or stress) that can indicate impending failure.

An evaluation of how exposed people/property are to a potential failure (occupancy and value).

To document findings, risk rating, and recommended mitigation so the owner can make informed decisions.

Resistance drills, sonic tomography, or pull tests to assess internal decay or root anchorage.

Past failures, weather events, and recent site changes inform the likelihood of future failure.

Head, eye, and hearing protection, cut-resistant leg protection (chaps), gloves, and proper boots.

The closest a worker may get to energized power lines; only qualified line-clearance arborists may work near them.

Only qualified line-clearance arborists, trained and authorized — never untrained ground workers.

ANSI Z133 — the safety standard for arboricultural operations.

The area where cut limbs or debris may fall; it must be kept clear of people and verbally controlled.

To monitor the climber, manage the drop zone, handle ropes, and respond to emergencies — never work alone aloft.

A planned procedure to bring down an injured climber; ground crew must be trained to perform it.

A sudden upward/backward thrust when the upper bar nose contacts wood; a major cause of saw injuries.

Chain brake, reduced-kickback chain, avoiding the bar-nose 'kickback zone', and proper technique.

A climber must be tied in with a proper climbing line/saddle; ANSI Z133 requires being secured while aloft.

Using a separate secondary attachment so a climber is never reliant on a single point during certain operations.

Never reach into the feed; feed butt-first, stand to the side, and keep loose clothing away.

Cones, signs, and flaggers to protect workers and the public around roadside tree work.

Identifying nearby conductors and assuming all lines are energized until verified otherwise.

A crew discussion of hazards, the work plan, the drop zone, communication, and emergency procedures.

Controlling the descent of cut limbs with ropes/blocks to protect targets and workers below.

Reduced control and higher kickback injury risk; use a pole saw or reposition instead.

Continuous tie-in with a climbing system; never disconnect from all attachment points while in the tree.

One trained and knowledgeable in tree work and associated hazards to perform the task safely.

Stay clear, keep others back, call for help/utility; do not touch the victim or equipment in contact.

Inspecting saws, ropes, saddles, and lanyards before use and removing damaged gear from service.

Fatigue and heat impair judgment and reaction time, raising the chance of serious tree-work accidents.

Maintain a safe minimum distance from energized lines; treat all conductors as energized.

Hardware (blocks, friction devices) that controls rope load when lowering heavy limbs.

On the ground or firmly braced with the chain brake engaged — never 'drop starting'.

Out of the drop zone, in clear view of the climber, with planned escape routes.

No one can perform aerial rescue or manage hazards; a trained ground person is required.

To make workers visible to traffic and equipment operators in and near roadways.

Inspect before each use for cuts, glazing, and wear; retire any rope that fails inspection.

The management of trees and forests in cities for environmental, social, and economic benefits.

Cities are hotter than surrounding areas; tree canopy cools them through shade and transpiration.

Stormwater interception, air-quality improvement, cooling, carbon storage, wildlife habitat, and property value.

The percentage of ground shaded by tree crowns; a key metric of urban forest extent and benefit.

Canopies intercept rain and roots increase infiltration, reducing runoff and flooding.

They capture particulates and absorb some gaseous pollutants, while shade reduces ozone-forming heat.

A record of a community's trees (species, size, location, condition) used to plan and manage the urban forest.

A long-term strategy for planting, maintenance, diversity, and budgeting of community trees.

It limits catastrophic loss from a single pest/disease and stabilizes the urban canopy over time.

Public support and stewardship (e.g., volunteer planting, care) sustain the urban forest.

Trees near utilities and roads requiring clearance pruning and careful species selection.

Trees absorb and store atmospheric carbon in wood and soil, offsetting some emissions.

Large, healthy mature trees provide far greater benefits than many small ones, so preserving them is high priority.

A suite of tools that quantifies the benefits and value of trees (canopy, stormwater, air, carbon).

A mix of tree ages and sizes so the canopy is sustained as old trees decline.

Evaluating space, soil, utilities, and use to choose the right tree for each location.

Compacted, limited soil, heat, drought, salt, and damage shorten city tree life versus forest trees.

Higher property values, business district appeal, and reduced energy costs from shade.