ISA Pruning & Tree Maintenance 2 — Questions and Answers

Question 1: What is crown cleaning and what types of branches are targeted?

Removing all branches below 15 feet for clearance
Selective removal of dead, dying, diseased, crowded, weakly attached, and broken branches from the crown (Correct answer)
Power washing the trunk and branches to remove algae
Removing the entire inner crown to improve air circulation

Correct answer: Selective removal of dead, dying, diseased, crowded, weakly attached, and broken branches from the crown

Crown cleaning is the selective removal of dead, dying, diseased, broken, and weakly attached branches from the tree's crown. It is the most basic and commonly performed pruning operation.

Crown cleaning is defined by ANSI A300 as the selective removal of specific branch categories: dead branches (which pose falling hazards and harbor decay organisms), dying branches (those in progressive decline), diseased branches (to reduce inoculum and prevent spread), broken or damaged branches (hanging hazards), and weakly attached branches (those with included bark or poor structure). Crown cleaning is often the first pruning operation performed on neglected trees and is appropriate for trees of any age. Unlike crown thinning, it does not target healthy, well-attached branches for removal. It improves safety, appearance, and tree health while minimizing stress, since most removed branches contribute little to the tree's photosynthetic capacity.

Question 2: What is the appropriate maintenance schedule for inspecting and adjusting supplemental support systems (cables and braces) installed in trees?

Only when visible damage occurs
At least annually, and after every major storm event (Correct answer)
Every 5 years or at the next scheduled pruning
No maintenance is needed once properly installed

Correct answer: At least annually, and after every major storm event

Supplemental support systems require annual inspection to check hardware condition, cable tension, tree growth around hardware, and any new defects. Additional inspections should follow any major storm event.

Supplemental support systems (cables, braces, guy wires) are installed in living, growing organisms, which means the relationship between the hardware and the tree changes over time. Annual inspections should verify: cable tension is appropriate (not too tight or slack), termination hardware is secure and not pulling out, the tree has not grown around or engulfed hardware (creating girdling), the structural condition of the supported branch or stem has not deteriorated, the tree has not grown asymmetrically to shift loading, and all components are free of corrosion or fatigue. After major storms, additional inspection is critical because the system may have been loaded to capacity, potentially stretching cables, loosening hardware, or revealing that the supported defect has progressed beyond what the system can mitigate.

Question 3: When raising the crown of a mature tree for clearance, what guideline helps maintain tree health and structural stability?

Remove all branches below the desired clearance height in one session
Remove no more than one-third of the live crown height, and maintain at least two-thirds of the total tree height in live crown (Correct answer)
Only remove branches on the side facing the road or path
Crown raising should only be done on trees under 6 inches in diameter

Correct answer: Remove no more than one-third of the live crown height, and maintain at least two-thirds of the total tree height in live crown

To maintain tree health and structural stability, crown raising should preserve at least two-thirds of the total tree height in live crown. Removing too many lower branches reduces photosynthetic capacity and can create a top-heavy crown.

Crown raising (also called crown lifting) involves removing lower branches to provide clearance for pedestrians, vehicles, buildings, or sight lines. The key guideline is maintaining a live crown ratio of at least 60-66% (two-thirds) of the total tree height. For example, a 30-foot tree should retain at least 20 feet of live crown. Removing too many lower branches reduces the tree's photosynthetic capacity, creates a top-heavy crown more vulnerable to wind, and can stress the tree. For large or mature trees, crown raising should be done gradually over multiple pruning cycles. Lower trunk branches also contribute to trunk taper development — removing them causes the lower trunk to grow more slowly in diameter, potentially creating a structurally weaker form.

Question 4: What is the purpose of crown thinning and how does it differ from lion-tailing?

Both terms describe the same practice of removing interior branches
Crown thinning selectively removes branches throughout the crown to reduce density while maintaining even distribution; lion-tailing removes only interior branches, leaving tufts at branch ends (Correct answer)
Crown thinning removes branches from the outside; lion-tailing removes from the inside
There is no practical difference between the two techniques

Correct answer: Crown thinning selectively removes branches throughout the crown to reduce density while maintaining even distribution; lion-tailing removes only interior branches, leaving tufts at branch ends

Crown thinning removes select branches evenly throughout the crown to reduce density while maintaining the tree's shape and balanced branch distribution. Lion-tailing strips interior foliage, concentrating weight and wind load at branch tips — a harmful practice.

Crown thinning, as defined by ANSI A300, is the selective removal of branches to reduce crown density while maintaining the tree's natural form. Proper thinning removes branches throughout the crown — not just from the interior — so that remaining foliage is evenly distributed. This improves light penetration and air circulation, reduces wind resistance uniformly, and maintains balanced branch loading. Lion-tailing, by contrast, strips interior and lateral branches from limbs, leaving foliage only at the ends. This shifts the center of gravity outward on each limb, concentrates wind loading at the tips, reduces the branch's structural taper, and removes interior foliage that dampens sway energy. Lion-tailing dramatically increases the risk of branch failure and is universally condemned by professional arboricultural organizations.

Question 5: At what stage of development is structural pruning most effective and why?

After the tree reaches full maturity and defects become visible
During the young, actively growing stage when developing branches are small and the tree can quickly close pruning wounds (Correct answer)
Only during the first year after transplanting
Structural pruning is equally effective at any age

Correct answer: During the young, actively growing stage when developing branches are small and the tree can quickly close pruning wounds

Structural pruning is most effective on young trees because defects are corrected while branches are small (wounds close quickly), the tree's natural form can be directed, and the energy cost of pruning is minimal relative to the tree's growth capacity.

Structural (or training) pruning during a tree's establishment and early development years is the most cost-effective arboricultural investment. When a tree is young, structural issues like codominant stems, included bark unions, crossing branches, and excessive branch density can be corrected by removing small-diameter branches that produce small wounds — often closing within one growing season. The young tree's vigorous growth quickly compartmentalizes these small wounds. If the same defects are addressed in a mature tree, the required pruning cuts are dramatically larger, creating extensive wounds that take years to close and provide significant entry points for decay. Many structural failures in mature trees originate from defects that could have been prevented with proper training pruning during the first 5-10 years after planting.

Question 6: What is the recommended approach for managing water sprouts (epicormic growth) that develop after heavy pruning?

Remove all water sprouts immediately and completely each time they appear
Selectively thin water sprouts, retaining some well-positioned ones to rebuild the crown while removing the weakest and most poorly attached (Correct answer)
Apply herbicide to the sprout bases to prevent regrowth
Leave all water sprouts to grow naturally without intervention

Correct answer: Selectively thin water sprouts, retaining some well-positioned ones to rebuild the crown while removing the weakest and most poorly attached

Rather than removing all water sprouts (which stimulates more sprouting) or leaving them all (which creates a dense, weakly attached mass), selective thinning retains the best-positioned sprouts to eventually become permanent replacement branches.

Epicormic sprouts (water sprouts) commonly develop after heavy pruning, storm damage, or topping. These sprouts originate from dormant or adventitious buds and initially have weak attachment to the parent branch because they arise from surface tissue rather than the branch's structural wood. Removing all sprouts triggers another wave of even more prolific sprouting because the tree desperately needs to restore leaf area. The recommended management approach is selective thinning: remove crowded, poorly positioned, and competing sprouts while retaining the most vigorous, best-positioned ones that can serve as replacement branches. Over time, retained sprouts develop stronger attachment as they are incorporated into the parent branch's annual growth rings. This process may require several pruning cycles over 3-5 years to gradually restore a functional crown.

ISA Pruning & Tree Maintenance 2

What is crown cleaning and what types of branches are targeted?