Lion Tailing
Lion tailing is over-thinning that strips out a tree’s interior branches and leaves most of the foliage at the ends of the limbs, like the tuft on a lion’s tail. The Kansas Forest Service calls it an improper pruning practice that ruins a tree’s structure, the way it moves and damps wind, and its overall health.
Source: Lion Tailing and its Impact on Tree Health (MF3551), Kansas Forest Service, K-State Research and Extension
What lion tailing looks like
Colorado State University Extension describes two versions. The extreme one is limbing up taken as far as it can go: all the lower branches come off, and only a few leaves are left at the tips of long, bare limbs. In milder cases only the interior branches are removed, so the foliage forms a shell around an empty center.
It often starts as a thinning job done badly. Colorado State notes that thinning is frequently done with too many branches removed from the interior of the canopy, with results that can resemble lion tailing.
Source: Pruning Mature Shade Trees
Why it harms trees
With most of the leaf weight at the branch ends, limbs are more exposed to wind, ice and other loads. The Kansas Forest Service adds that losing the interior leaves cuts photosynthesis, that the tree answers with a surge of poorly attached sprouts, and that newly exposed bark can suffer sunscald.
The USDA Forest Service guide How to Prune Trees lists similar results: sunscald, abundant epicormic sprouts, weak branch structure and breakage. Colorado State adds that removing the small twiggy wood inside the canopy lowers vigor, reduces the development of taper and makes wind damage more likely, because the tree is less able to dampen the wind.
Sources: Lion Tailing and its Impact on Tree Health (MF3551) ; How to Prune Trees (NA-FR-01-95, revised 2012) ; Pruning Mature Shade Trees
Why clients ask for it
The Kansas Forest Service says public demand largely drives lion tailing. Informal surveys suggest homeowners feel that the more branch material comes out, the more value they got for their money. They also wrongly believe the result looks good, protects against storm damage and lets light through to the lawn or beds, and the bulky brush pile seems to confirm it. Ironically, the Kansas Forest Service adds, a certified arborist’s good pruning job often goes unnoticed.
Thinning will not rescue a sun-loving lawn either. Colorado State says that thinning a middle-aged or mature tree will not do enough to help sun-loving plants such as Kentucky bluegrass grow in its shade.
Sources: Lion Tailing and its Impact on Tree Health (MF3551) ; Pruning Mature Shade Trees
Thinning without lion tailing
The Kansas Forest Service says proper thinning starts at the ends of the branches, removing branches that touch, cross or shade other branches, with cuts back to a lateral branch or the trunk and without overthinning the center. For most species and situations, it removes no more than 20 percent of the canopy in a single pruning.
Limits differ between publications: the USDA Forest Service guide allows at most a quarter of the living crown at a time, while Colorado State’s guide to mature trees puts the plant-health maximum at 10 percent of the foliage per pruning cycle and accepts a larger dose for a healthy tree when the objectives require it. When an exam question names a source, use its number.
Sources: Lion Tailing and its Impact on Tree Health (MF3551) ; How to Prune Trees (NA-FR-01-95, revised 2012) ; Pruning Mature Shade Trees
How the ISA arborist exam tests it
Lion tailing questions ask you to recognize the practice from a description and to respond to clients who want heavy interior thinning, whether for more sun on the lawn or a pruning job that looks bigger. Try 3 reviewed practice questions:
Which description matches the harmful practice called lion-tailing?
Show answer and explanation
Correct answer: C. Stripping interior branches so most foliage is left at the limb ends
The Kansas Forest Service describes lion-tailing as excessive thinning or removal of interior branches that leaves most of the foliage at the branch ends, like a lion's tail. With the weight concentrated at the ends, branches are more prone to wind and ice damage, and the tree may also suffer sunscald and a flush of poorly attached sprouts. The other choices describe a lost leader, tipping and shearing.
- A: Removing the leader leads to competing leaders, which is a different structural problem.
- B: Cutting laterals between nodes to narrow the crown is tipping, a different harmful practice.
- D: Shearing the outer crown is a different practice that produces dense surface growth.
Sources: Lion Tailing and its Impact on Tree Health (MF3551), Kansas Forest Service, K-State Research and Extension ; Lion Tailing and its Impact on Tree Health (MF3551), Kansas Forest Service, K-State Research and Extension
Report a problem with this question · ID prun-026
A homeowner asks for heavy thinning of a mature silver maple so the Kentucky bluegrass lawn beneath it will grow thick again. Based on Colorado State University Extension guidance, what is the best advice?
Show answer and explanation
Correct answer: B. Thinning a mature tree won't help a sun-loving lawn; use shade-tolerant plants
Colorado State University Extension notes that thinning can reduce shade enough for shade-tolerant plants, but on a middle-aged or mature tree it will not do enough to promote sun-loving plants, such as Kentucky bluegrass, that grow in the tree's shade. NC State Extension likewise says choosing plants that can survive dense shade is a better option than thinning an otherwise healthy tree. Stripping interior branches is lion-tailing, CSU says that in most cases the gains from thinning fade as the tree adds new growth, and CSU advises keeping the lowest branch in the bottom third of the tree.
- A: Stripping interior branches is lion-tailing, and even heavy thinning will not give a sun-loving lawn enough light.
- C: CSU says that in most cases the gains from thinning fade as the tree adds new growth, so repeating it does not build up more light.
- D: CSU advises that the lowest branch originate in the bottom third of the tree, so raising to half its height goes too far.
Sources: Pruning Mature Shade Trees (CMG GardenNotes #615), Colorado State University Extension ; Extension Gardener Handbook, Chapter 11: Woody Ornamentals, NC State Extension
Report a problem with this question · ID prun-036
After a crew prunes a client's maple to a written specification, the client complains that the tree barely looks different and the brush pile is small. What is the best response?
Show answer and explanation
Correct answer: C. Explain that good pruning often goes unnoticed and heavy cutting harms trees
The Kansas Forest Service observes that when a certified arborist prunes a tree well, the work often goes unnoticed, and that homeowners often wrongly judge value by the amount of branch material removed. What matters is a structurally sound, vigorous tree with only subtle changes. Removing extra interior branches would be lion-tailing, which reduces photosynthesis and concentrates weight at branch ends, and cutting back the top would be topping, which foresters have long discouraged.
- A: Stripping interior branches to make the work visible is lion-tailing, which harms the tree.
- B: The volume of brush removed is not a measure of a good pruning job.
- D: Shortening the top to make a visible change is topping, a practice foresters have long discouraged.
Sources: Lion Tailing and its Impact on Tree Health (MF3551), Kansas Forest Service, K-State Research and Extension ; Lion Tailing and its Impact on Tree Health (MF3551), Kansas Forest Service, K-State Research and Extension
Report a problem with this question · ID prun-037
0 of 3 correct
Common mistakes in the field
Cleaning out the interior
Thinning should take fairly small branches from the outer part of the canopy. Colorado State warns that removing large branches or many interior branches gives results similar to lion tailing, with lower vigor and a higher risk of wind damage, and the Kansas Forest Service says not to overthin the center.
Raising the crown too far
Stripping the lower limbs is the other road to lion tailing. Colorado State’s guide to pruning mature trees says to leave at least two-thirds of the tree’s height as canopy, with at most the lower third as bare trunk (its young-tree guide, covered on the structural pruning page, uses a live crown ratio of 60 percent), and the USDA Forest Service guide likewise wants live branches over at least two-thirds of total height.
Leaving the limits out of the specification
Colorado State says a pruning specification agreed by the owner and the arborist limits the room for misunderstanding and poor pruning. At a minimum it names the trees to be pruned, the kind of pruning and its objective, the most canopy that may be removed and the thickest live branch that may be cut. It can also rule out topping and lion tailing by name.
Sources
- Lion Tailing and its Impact on Tree Health (MF3551), Kansas Forest Service, K-State Research and Extension
- Pruning Mature Shade Trees, Colorado State University Extension
- How to Prune Trees (NA-FR-01-95, revised 2012), USDA Forest Service, Northeastern Area State and Private Forestry
- Structural Pruning of Young Shade Trees (CMG GardenNotes #613), Colorado State University Extension
Written in our own words from the public sources above, checked October 19, 2026. Arborist Practice Test is not affiliated with ISA.