Standards Reference
ANSI A300 arboricultural standards, ANSI Z133 safety requirements, and ISA Best Management Practices — the authoritative references behind every ISA exam question.
Pruning
- Crown cleaning: selective removal of dead, dying, diseased, detached, or crossing branches that cause structural defects
- Crown reduction: decreases height or spread using reduction cuts to lateral branches that are at least 1/3 the diameter of the cut stem
- No topping — reduces tree to stubs or lateral branches too small to assume terminal dominance, leading to decay, epicormic growth, and hazard
- Remove no more than 25% of live crown in a single growing season to avoid stressing the tree
- Make cuts at branch collars — never flush cuts; the branch collar contains tissue that seals wounds
- Use the 3-cut method on limbs over 1 inch in diameter to prevent bark tearing: undercut, relief cut, final collar cut
Exam Tip
A300 Part 1 is the most tested standard. Know the four pruning types: crown cleaning, thinning, raising, and reduction — and the difference between reduction cuts and topping.
Soil Management
- Aeration: vertical mulching, air excavation (air spade), and radial trenching improve oxygen diffusion in compacted soils
- Optimal soil pH for most trees is 6.0–7.0; pH affects nutrient availability, particularly iron, manganese, and phosphorus
- Organic mulch applied 2–4 inches deep, kept 6 inches away from the trunk, reduces compaction and moderates soil temperature
- Soil amendments should be based on soil test results — avoid adding amendments to backfill unless specific deficiencies are identified
- Critical root zone (CRZ): minimum protection area equal to 1 foot radius per inch DBH, never less than 8 feet radius
- Compaction raises bulk density and reduces macropore space, limiting root growth and gas exchange
Exam Tip
Know the difference between CRZ (protection area, 1 ft/inch DBH) and root zone (total rooting area). Aeration methods and their appropriate applications are frequently tested.
Supplemental Support Systems
- Cabling installs flexible steel or synthetic rope in the upper crown to limit the range of motion of a defective union or co-dominant stem
- Bracing uses threaded steel rods through a split or cracked crotch to reduce the chance of overloading the union
- High-strength steel cables are typically installed at 2/3 of the distance from the crotch to the branch tips
- Hardware must be inspected annually; cables can cause included-bark tissue to grow around anchors, reducing effectiveness over time
- Supplemental support is not a cure — it manages risk while the tree may continue to decline; removal may still be necessary
- Dynamic (synthetic) systems allow more natural movement and may be preferred for trees with moderate defects
Exam Tip
Know where to install a cable (2/3 up from the defective crotch to branch tips) and the difference between cabling (flexible, crown) vs. bracing (rigid, crotch/split).
Lightning Protection Systems
- Lightning protection systems (LPS) provide a low-resistance path from air terminals at the tree's apex to ground rods in the soil
- Copper cable conductors are most common; minimum conductor size specified by the standard (typically No. 4 AWG or heavier)
- Ground rods must be driven at least 8 feet deep, beyond the root zone to minimize root damage
- Air terminals (tips) are installed at the highest point of the crown and on tall lateral branches
- LPS does not prevent a lightning strike — it conducts current safely around the tree to protect the tree and nearby structures
- Inspections are required annually; LPS must be repaired as the tree grows to maintain continuity
Exam Tip
High-value specimen trees and trees near structures are priority candidates for LPS. Know the path: air terminal → conductor → ground rod, and that copper is the standard conductor material.
Management of Trees During Site Planning and Construction
- Tree protection zones (TPZ) must be established before grading or excavation begins — typically 1 ft radius per inch DBH, minimum 8 ft
- TPZ fencing should be rigid, at least 4 feet tall, and located at or beyond the drip line whenever possible
- Grade changes within the TPZ — filling or cutting — can kill trees by suffocating roots or severing root structure
- Tunnel or bridge over critical roots rather than cut through; use air excavation tools when roots must be exposed near the tree
- Retain healthy, well-structured trees; removal of poor-quality trees before development reduces liability
- Pre-construction tree assessments should document condition, structural integrity, and species tolerance of site disturbance
Exam Tip
Construction is a leading cause of tree death — often delayed by 3–7 years. Know TPZ sizing (1 ft/inch DBH) and that grade changes (fill or cut) within the TPZ are the most damaging activities.
Planting and Transplanting
- Plant at the correct depth: root flare must be at or slightly above grade — burying the root flare is a primary cause of decline
- Planting hole should be 2–3× the width of the root ball and no deeper than the root ball height
- Backfill with native soil unless a soil test indicates specific amendments are needed
- Staking is only needed if the tree cannot stand upright on its own; remove stakes after one growing season to prevent girdling
- Balled-and-burlapped (B&B) trees must have wire baskets and burlap removed or cut back from the top third of the root ball
- Container-bound or girdling roots must be corrected at planting time — circling roots left uncorrected will girdle the trunk
Exam Tip
Planting depth is the most tested topic here. The root flare must be at or above grade. Wide, shallow holes are always better than deep, narrow holes.
Integrated Vegetation Management in Utility Rights-of-Way
- IVM uses a combination of mechanical, biological, cultural, and chemical methods to manage vegetation in a right-of-way (ROW)
- The goal is to maintain a stable, low-growing plant community that resists invasion by tall-growing species
- Selective treatment targets incompatible species while retaining compatible low-growing plants that stabilize the ROW
- Herbicide use in IVM must follow label requirements; basal bark, cut-stump, and foliar methods are common
- IVM programs must consider environmental factors, wildlife habitat, endangered species, and adjacent landowner concerns
- Directional pruning shapes tree growth away from conductors while maintaining biological function and reducing re-treatment frequency
Exam Tip
IVM is the preferred approach in utility ROWs because it creates a self-sustaining compatible plant community — reducing long-term costs and the need for repeated cutting.
Root Management
- Root pruning cuts must be clean and straight; ragged or torn roots heal more slowly and are more susceptible to decay pathogens
- Roots should be pruned no closer than 5× the trunk diameter (5× DBH) from the trunk to minimize structural destabilization
- Root barriers can redirect roots away from hardscape; flexible panels must extend at least 18–24 inches deep
- Root excavation with air spade is the preferred method for exposing roots without mechanical damage
- Avoid root pruning during drought or when the tree is already stressed — stress compounds the impact of root loss
- After significant root pruning, a proportional crown reduction may be needed to balance the reduced root system capacity
Exam Tip
Root pruning too close to the trunk destabilizes the tree structurally and stresses it physiologically. The 5× DBH minimum distance rule is a common exam question.
Tree Risk Assessment
- Risk = likelihood of failure × likelihood of impact × consequences of failure (a 3-part equation)
- Qualitative risk categories: low, moderate, high, extreme — assessed using the ISA Tree Risk Assessment Qualification (TRAQ) framework
- Structural defects assessed include dead wood, cracks, root problems, canopy dieback, decay, co-dominant stems, and poor architecture
- Tree Risk Assessment must document findings, target identification, and recommended mitigation options
- Targets are people, property, or high-use areas within the distance a tree or its parts could strike if it fails
- Level 1: limited visual assessment; Level 2: basic assessment; Level 3: advanced assessment using tools (increment borer, resistograph, tomography)
Exam Tip
Know the three-part risk equation and the three assessment levels. TRAQ qualification is required to perform professional tree risk assessments using this standard.
Integrated Pest Management (IPM)
- IPM is a decision-based approach that integrates multiple pest management tactics to minimize economic, health, and environmental risks
- Action thresholds: pest or damage levels at which action is warranted — preventing treatment when pest populations are below damaging levels
- The four IPM tactics: cultural (site/species selection), mechanical (traps, removal), biological (natural enemies), and chemical (pesticides as last resort)
- Monitoring and correct pest identification are foundational — misidentification leads to ineffective or harmful treatments
- Pesticide selection follows a hierarchy: least toxic, most target-specific product is always preferred
- Documentation of pest, treatment, timing, and outcomes is required for a defensible IPM program
Exam Tip
IPM is a framework, not a single method. Know the action threshold concept and the four control tactics in order of preference: cultural → mechanical → biological → chemical.