8.4 Pruning Tools, Sanitation & Writing Enforceable Pruning Specifications
Key Takeaways
- The current ANSI A300 pruning standard requires the pruning amount to be specified rather than imposing a fixed percentage cap.
- A complete pruning specification names location, objectives, system, part types, amount, location in crown, cut types, size range, debris disposal, and time frame.
- Bypass tools make a scissor cut that leaves a clean surface; anvil tools crush tissue against a flat jaw and should not be used on live wood.
- Tool disinfection between trees is warranted for wound-transmitted pathogens such as fire blight and the vascular wilts, and matters most when pruning susceptible taxa during periods of active transmission.
- Specifying an objective without specifying an amount, or an amount without an objective, produces a document that cannot be enforced.
Two of the four tasks under Pruning are about tools and about specifications. Both are frequently under-studied because they feel like trade knowledge rather than science, and both are heavily represented in scenario questions where the arborist is acting as specifier or inspector rather than as operator.
Cutting Tools and What They Do to Tissue
The biological requirement is fixed: a pruning cut must leave a clean surface with the adjacent bark firmly attached, because a crushed or torn surface enlarges the wound, delays woundwood formation, and provides a larger colonization front.
| Tool | Mechanism | Appropriate use | Failure mode |
|---|---|---|---|
| Bypass hand pruner | Two curved blades pass each other in a scissor action | Live wood up to roughly 2 cm | Twisting the tool to force an oversized cut tears bark |
| Anvil hand pruner | One blade closes onto a flat anvil | Dead wood only | Crushes and splits live tissue against the anvil |
| Ratchet pruner | Anvil action with mechanical advantage | Dead wood; low-strength operators | Same crushing failure as anvil |
| Bypass lopper | Long-handled bypass action | Live wood up to roughly 4–5 cm | Overreaching capacity; tearing |
| Hand pruning saw | Curved blade, usually cutting on the pull stroke | Live and dead wood beyond lopper capacity | Failure to precut heavy limbs causes bark tearing |
| Pole saw / pole pruner | Extends reach from the ground | Small-diameter cuts out of reach | Poor cut placement and poor visibility of the collar; never near conductors unless dielectric and the operator is qualified |
| Chain saw | Powered chain | Larger removal and reduction cuts | Cannot make precise small cuts; kickback hazard; overuse leads to oversized cuts |
| Hedge shears / powered shears | Indiscriminate shearing to a plane | Formal hedges, topiary, espalier | Never a substitute for selective pruning on a tree |
Two operational habits govern quality more than tool choice:
- Precut heavy limbs. The three-cut method — an undercut, a top cut beyond it to drop the weight, then the final cut at the collar — prevents the bark tearing that occurs when a limb's weight peels the stem as it falls. The current standard makes precutting a requirement where it is needed to avoid splitting or tearing.
- Match the tool to the cut, not the cut to the tool. The standard's preference for the smallest diameter cut that meets the objective, and its instruction to minimize cuts that expose heartwood, are both undermined when a crew reaches for a chain saw because it is in hand.
Sharpness and Maintenance
A dull blade compresses before it severs. Practical maintenance:
- Sharpen bypass blades on the bevelled side only, maintaining the original angle; the flat side is trued only to remove burrs.
- Keep saw teeth clean; most modern arboricultural hand saws have hardened impulse-set teeth and are replaced rather than resharpened.
- Clean sap and pitch from blades; residue increases friction and holds pathogen-bearing material.
- Maintain chain saw chain sharpness and depth gauge settings — a dull chain produces sawdust rather than chips and increases kickback risk and operator fatigue.
Sanitation Between Cuts and Between Trees
Tool disinfection is not universally required, and blanket recommendations reduce the credibility of the ones that matter. It is warranted where the pathogen is transmitted through wounds and is present on the tool.
High-priority situations:
- Fire blight (Erwinia amylovora) on rosaceous hosts during active infection — disinfect between cuts, not merely between trees.
- Vascular wilts — oak wilt, Dutch elm disease, Verticillium — when pruning known or suspected infected material.
- Cankers with abundant surface inoculum on susceptible taxa.
- Any time visibly infected tissue has been cut.
Common agents include 70 percent isopropyl or ethyl alcohol (immediate contact action, evaporates, no rinse), dilute household bleach solutions (effective but corrosive to metal and requiring rinse and drying), and commercial quaternary ammonium disinfectants. Contact time matters: a wipe that evaporates instantly has not disinfected.
The stronger control for wilt pathogens is timing, not disinfection. Not wounding oaks during the vector's spring flight period prevents infection far more reliably than sterilizing a saw. Where a specification governs oaks in an oak wilt region, the timing restriction belongs in the specification.
Writing the Specification
The pruning standard treats the specification as the operative document. It requires one or more objectives to be specified, and it lists what a specification should contain.
The specification checklist
| Element | What to write | Why it is enforceable |
|---|---|---|
| Physical location of the plants | Address, plan reference, tag numbers, or a marked plan | Removes ambiguity about which trees |
| Pruning objectives | Manage risk, manage health, develop structure, provide clearance, manage size or shape | The objective bounds every other decision |
| Pruning system | Natural, pollarding, topiary, espalier, pleaching | Sets the long-term form |
| Type of parts to be removed | Living branches, dead branches, fruit, mistletoe, epicormic shoots | Distinguishes cleaning from reduction |
| Pruning amount | Percent of foliage or crown, or number of branches | The dosage — this is where the number goes |
| Location in crown | Upper, lower, interior, outer, specific aspect, over a target | Prevents lion-tailing and interior stripping |
| Cut types | Removal, reduction, heading, shearing | Removal versus reduction is the core distinction |
| Size range of parts | Minimum and maximum diameter or length to be removed | Prevents both oversized cuts and pointless twig work |
| Debris disposal / repurposing | Chip on site, haul, cord, leave habitat material | A real cost line the contractor must price |
| Time frame | Season, dates, restrictions | Carries phenological and regulatory restrictions |
| Other information as necessary | Topiary shape, clearance distances, lines of sight, desired views | Captures what the general terms cannot |
The dosage question, stated correctly
The current standard does not impose a numeric percentage cap. It requires three things instead: the amount shall be specified; operations should remove no more living material than necessary to achieve the specified objectives; and species, size, age, condition, and site shall be considered when specifying the location and amount of live branches removed. The familiar "not more than 25 percent in an annual growing season" was in the 2001 and 2008 editions and was removed in the 2017 revision.
The professional consequence is that the arborist owns the number. Writing "prune per ANSI A300" and expecting the standard to supply a dose is a defective specification. Writing "reduce live foliage by no more than 10 percent, distributed across the outer crown, by reduction cuts to laterals at least one third the diameter of the parent, on limbs 25 to 100 mm in diameter, over the west aspect only" is enforceable.
Two failure modes to recognize
- Objective without amount. "Clean and reduce for clearance over the driveway" gives the contractor no dosage boundary and gives the inspector no criterion.
- Amount without objective. "Remove 20 percent of the canopy" invites indiscriminate removal, most easily achieved by stripping interior and lower branches — producing lion-tailing, the precise outcome the standard's location-in-crown element exists to prevent.
Inspecting Against the Specification
An inspection is a comparison, not an opinion. Walk the job with the specification and check: were cuts made at the correct location relative to the collar and branch bark ridge; were flush cuts avoided; are reduction cuts made to laterals large enough to assume the terminal role; were heading cuts used where reduction cuts were specified; is the removal distributed as specified or concentrated in the interior; is the actual amount within the specified dose; were size limits observed; was the debris handled as specified; and were timing restrictions met. Document with photographs at the same locations before and after.
Utility and Clearance Work
Line-clearance pruning follows directional pruning principles: remove branches growing toward the conductor at their point of origin rather than heading them back, so regrowth is directed away from the facility. Specifications for clearance work state the clearance distance to be achieved, the cycle length, and the treatment of unacceptable candidates for pruning. Growth regulators may be specified as an adjunct where regrowth rates make the cycle uneconomic. All such work is governed by the electrical safety requirements covered in the safety chapter, and only qualified line-clearance arborists may perform it inside the minimum approach distance.
A municipality's pruning contract states only: "Prune all street trees on Elm Avenue in accordance with ANSI A300." A dispute arises when the contractor removes an amount the city considers excessive. What is the fundamental defect in the specification?
A crew is pruning a row of ornamental pears during an active fire blight outbreak. What sanitation practice is warranted, and why?
Why should an anvil-type pruner not be used on live wood?
A specification reads: "Remove 20 percent of the canopy." A crew satisfies it by stripping interior and lower branches, leaving foliage only at the branch tips. Which specification element would have prevented this outcome?