ISA Certified Arborist Study Guide

Learn the stem from the outside in: outer bark, phloem, vascular cambium, xylem, pith. Know which tissue carries water up from the roots and which carries sugars from the leaves to the rest of the tree, why trees wall off decay instead of healing it (CODIT), and how energy reserves drive recovery after stress or heavy pruning.

Get fluent with twig and leaf vocabulary (buds, leaf scars, opposite versus alternate arrangement, simple versus compound leaves) and with writing scientific names correctly. For selection questions, run the same checklist every time: space above and below ground, soil, drainage, light, hardiness, pests and maintenance.

Separate soil texture (particle sizes) from soil structure (how particles aggregate), and understand how compaction destroys pore space. Know what pH and cation exchange capacity tell you, why organic matter and mycorrhizae matter, and why fertilizer should follow a soil test or a diagnosed need.

Most planting questions come back to depth: find the root flare and keep it at or slightly above grade. Know the trade-offs of each nursery stock type, how to deal with circling roots and packaging, and the basics of aftercare: water, a wide ring of mulch kept off the trunk, and staking only when needed.

Picture every cut. Removal cuts go just outside the branch collar, reduction cuts go back to a lateral large enough to take over, and topping is never an acceptable practice. Learn the pruning types by objective, the three-cut method for heavy limbs, and how to manage codominant stems in young trees.

Diagnose before you treat: identify the tree, separate signs (the agent itself) from symptoms (the tree's response), and look for patterns that point to living or non-living causes. Know the plant health care and integrated pest management mindset: monitor, set thresholds, favor the least disruptive control, keep records.

Most construction damage is to roots you cannot see. Know how tree protection zones are set and enforced, why compaction, trenching and grade changes are so harmful, what alternatives to open trenching exist, and why the arborist should join the project at the planning stage, not after damage is done.

Risk needs a target. Practice separating the likelihood of failure, the likelihood of hitting a target and the consequences. Know the common defects, the three levels of assessment (limited visual, basic, advanced) and the mitigation options from pruning to moving the target.

The heaviest domain. Learn the job briefing, PPE head to toe, who may work near energized lines and why, chainsaw kickback and safe handling, chipper hazards, climbing system inspection, rigging basics and the felling sequence: plan the fall, clear an escape route, cut the notch, then make the back cut while leaving a proper hinge.

Know the benefits of community trees by category (environmental, economic, social, health) with one example each, why species diversity protects a city from pests, what a tree inventory records, and the basic idea behind tree appraisal and tree ordinances.