Free ISA Certified Arborist Exam Questions

Correct answer: A. Level with or slightly above the surrounding grade

Planting depth is set by the trunk flare, where the topmost roots spread out from the trunk, and it should finish level with or just above the surrounding grade. Following the container's soil line is the tempting wrong answer, because nursery soil often already covers the flare, sometimes by an inch or more. Burying the flare, whether to keep roots moist or to steady the tree, invites stem-girdling roots and bark problems.

• B: The container soil line often already buries the flare; the flare, not the container, sets the depth.
• C: Even an inch or two of soil over the flare counts as planting too deep.
• D: Deep planting does not make a tree more stable; it leads to girdling roots and decline.

Sources: What is the proper planting depth for a tree?, Iowa State University Extension and Outreach (Yard and Garden) ; Tree Installation: Process and Practices (FNR-433-W), Purdue Extension

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Correct answer: D. Fungal fruiting structures on the lower trunk

A sign is physical evidence of the damaging organism itself, such as the insect, its frass, or a fungus's fruiting structures. A symptom is the plant's response to injury. Wilting, discolored foliage, and dieback are all symptoms, and each can have many different causes, so none of them points to a specific agent the way a sign can.

• A: Wilting is a symptom, the plant's response to injury, and it has many possible causes.
• B: Yellowing and browning are discoloration symptoms, not evidence of the organism itself.
• C: Dieback is a symptom; it shows the tree's response but not what caused it.

Source: Overview of Plant Diagnostics, Penn State Extension

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Correct answer: B. At the start of planning, before the site design is set

Purdue Extension and the Texas A&M Forest Service both say the arborist should be involved from the very beginning of the planning phase, because small changes in where a building, driveway or utility line goes can decide whether a tree survives. Waiting until fences go up is the tempting answer, but by then the site design is fixed and many conflicts can no longer be designed out. Arriving after clearing or after construction usually means the damage is already done.

• A: By the time clearing is finished, the layout is set and root zones may already be disturbed.
• C: Fencing comes after design decisions that the arborist should already have helped shape.
• D: After construction the arborist can only assess and treat damage that planning might have prevented.

Sources: Construction and Trees: Guidelines for Protection (FNR-463-W), Purdue Extension ; Protect Tree Roots During Construction, Texas A&M Forest Service

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Correct answer: B. Less pore space, which can restrict roots and air and water flow

Bulk density is found by dividing a soil's dry weight by its volume, so it rises as traffic squeezes out pore space. High bulk density is a standard indicator of compaction and low porosity, conditions that can restrict root growth and slow the movement of air and water. Loose, organic-rich soils have lower bulk density, and trampling packs particles together without changing the soil's texture.

• A: Loose, organic-rich soils have lower bulk density, not higher.
• C: Foot traffic does not change soil texture; it packs the existing particles closer together.
• D: Traffic raises bulk density by packing the soil, which NRCS treats as a sign of compaction and impaired function, not of a livelier soil.

Source: Soil Quality Indicators: Bulk Density, USDA Natural Resources Conservation Service

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Correct answer: B. Leaves evaporate water drawn up from the roots, using heat from the air

EPA describes evapotranspiration as trees taking up water through their roots and evaporating it through their leaves. The energy needed to evaporate that water is drawn from the surrounding air, so the air cools; shade is a separate cooling effect. Reflecting sunlight is how light-colored cool roofs and pavements work, not evapotranspiration, and the oxygen released in photosynthesis does not cool the air.

• A: Reflecting sunlight describes cool roofs and pavements, not evapotranspiration.
• C: Trees do not store daytime heat in the trunk; the cooling comes from evaporating water.
• D: Oxygen given off in photosynthesis has no meaningful cooling effect.

Source: Benefits of Trees and Vegetation (Heat Islands), U.S. Environmental Protection Agency

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