Certified Arborist Test Tree Pruning Principles 1 — Questions and Answers
Question 1: According to ISA Best Management Practices, what is the maximum percentage of live crown generally recommended to remove during a single pruning session?
- 10%
- 25% (Correct answer)
- 40%
- 50%
Correct answer: 25%
Removing more than 25% of a tree's live crown in one session can stress the tree by reducing its photosynthetic capacity below the level needed to sustain roots and defend against pests and pathogens. Repeated conservative pruning over multiple seasons is safer than aggressive one-time removal.
Question 2: What is 'lion's-tailing' and why is it considered poor arboricultural practice?
- Shaping the canopy into a rounded silhouette by heading all branch tips
- Removing interior lateral branches so foliage is concentrated only at branch ends (Correct answer)
- Elevating the crown by removing the lowest scaffold branches
- Selectively thinning the upper canopy to admit more light to the interior
Correct answer: Removing interior lateral branches so foliage is concentrated only at branch ends
Lion's-tailing strips interior foliage and shifts weight to the ends of long lever-arm branches, increasing the risk of failure. It also removes the interior sprouts that shade the branch wood and help distribute wind load throughout the canopy, and frequently triggers heavy epicormic sprouting.
Question 3: A reduction cut is valid only when the retained lateral branch meets what minimum size requirement relative to the removed portion?
- At least one-half the diameter of the removed branch
- At least one-third the diameter of the removed branch (Correct answer)
- At least one-quarter the diameter of the removed branch
- Any size lateral is acceptable as long as it is live
Correct answer: At least one-third the diameter of the removed branch
A lateral that is at least one-third the diameter of the branch being removed is large enough to take over the apical role, maintain adequate sap flow, and produce a suitably sized wound that can close efficiently. A smaller lateral cannot assume dominance and the result functionally resembles a stub.
Question 4: What does current research indicate about the use of wound dressings (pruning paint or sealants) on fresh pruning cuts?
- They significantly accelerate wound closure by locking in cambial moisture
- They are beneficial when applied within 15 minutes of making the cut
- They generally provide no measurable benefit to wound closure and may inhibit compartmentalization (Correct answer)
- They are recommended on all cuts larger than 5 cm during the growing season
Correct answer: They generally provide no measurable benefit to wound closure and may inhibit compartmentalization
Decades of research, including work by Dr. Alex Shigo, demonstrated that trees compartmentalize wounds through internal chemical and anatomical barriers — wound dressings do not enhance this process. Some sealants can actually trap moisture and pathogens beneath the surface, potentially making decay worse.
Question 5: What distinguishes a 'heading cut' from a 'thinning cut'?
- A heading cut removes a branch at its point of attachment; a thinning cut shortens a branch to a lateral
- A thinning cut removes a branch at its point of attachment; a heading cut removes a branch at a point other than its attachment, leaving a stub or cutting to a very small lateral (Correct answer)
- A heading cut is used only on dead branches; a thinning cut is used only on live branches
- Both cuts are identical — the terms are interchangeable in ISA standards
Correct answer: A thinning cut removes a branch at its point of attachment; a heading cut removes a branch at a point other than its attachment, leaving a stub or cutting to a very small lateral
Thinning cuts remove branches entirely at their origin, maintaining the natural branching architecture and producing little regrowth. Heading cuts sever branches at arbitrary points between nodes or to undersized laterals, destroying apical dominance and triggering clusters of vigorous, weakly attached epicormic shoots at the wound site.
Certified Arborist Test Tree Pruning Principles 1
According to ISA Best Management Practices, what is the maximum percentage of live crown generally recommended to remove during a single pruning session?