Sources and Studies

Why clients ask for what they ask for

The topping surveys are small, regional, and 25 to 27 years old. They are the best I found.

Fazio and Krumpe 1999. Underlying beliefs and attitudes about topping trees. Journal of Arboriculture 25(4):193-199. Read it
Close, Groninger, Mangun, Roth 2001. Homeowners' opinions on the practice and effects of topping trees. Journal of Arboriculture 27(3):160-165. Read it 13.6 percent response rate.
Kuhns and Reiter 2009. Tree care and topping beliefs, knowledge, and practices in six western US cities. Arboriculture and Urban Forestry 35(3):122-128. Read it
Kuhns and Reiter 2007. Knowledge of and attitudes about utility pruning. Arboriculture and Urban Forestry 33(4):264. Read it
Koeser, Klein, Hasing, Northrop 2015. Factors driving professional and public urban tree risk perception. Urban Forestry and Urban Greening 14(4):968-974. Read it I read the university's news release, not the paper.

Risk, in proportion

Schmidlin 2009. Human fatalities from wind-related tree failures in the United States, 1995-2007. Natural Hazards 50:13-25. Read it 407 deaths over 13 years, about 31 a year.
Klein, Koeser, Hauer, Hansen, Escobedo 2019. Risk assessment and risk perception of trees. Arboriculture and Urban Forestry 45(1):26-38. Read it Where the one in 9.7 million figure comes from.
ISA Basic Tree Risk Assessment Form. Read it

Pruning, wind and storms

Both wind trials used planted live oaks about 20 feet tall. Nobody has run this on a mature oak.

Gilman, Masters, Grabosky 2008. Pruning affects tree movement in hurricane force wind. Arboriculture and Urban Forestry 34(1):20-28. Read it
Gilman, Grabosky, Jones, Harchick 2008. Effects of pruning dose and type on trunk movement in tropical storm winds. Arboriculture and Urban Forestry 34(1):13-19. Read it
Smiley and Kane 2006. The effects of pruning type on wind loading of Acer rubrum. Arboriculture and Urban Forestry 32(1):33-40. Read it Lion tailing took 19 percent of tree weight and did not change the center of wind pressure.
Gilman, Miesbauer, Masters 2015. Structural pruning effects on stem and trunk strain in wind. Arboriculture and Urban Forestry 41(1):3-10. Read it About 20 percent of a stem's mass off cut strain 38 percent.
Pavlis, Kane, Harris, Seiler 2008. The effects of pruning on drag and bending moment of shade trees. Arboriculture and Urban Forestry 34(4):207-215. Read it
Duryea, Kampf, Littell 2007. Hurricanes and the urban forest, part one. Arboriculture and Urban Forestry 33(2):83-97. Read it Florida Panhandle neighborhoods after Ivan.
Duryea and Kampf. Wind and trees, lessons learned from hurricanes. UF/IFAS FR173. Read it
Duryea and Kampf. Selecting Coastal Plain species for wind resistance. UF/IFAS FR174. Read it
McDonnell. Lion tailing and its impact on tree health. Kansas State MF3551, 2021. Read it

Cuts, wounds and dose

Eisner, Gilman, Grabosky 2002. Branch morphology impacts compartmentalization of pruning wounds. Journal of Arboriculture 28(2):99-105. Read it Small branches, four months.
Gilman and Bisson 2007. Developing a preventive pruning program. UF/IFAS ENH 1062 and ENH 1063. Read it Cut size 1 to 3 inches on decay-prone trees. Mature tree dose under 10 percent.
ISA. Why topping hurts trees. Read it
ISA. Pruning mature trees. Read it Still prints the 25 percent figure that left A300 in 2017.

Roots

Smiley 2008. Root pruning and stability of young willow oak. Arboriculture and Urban Forestry 34(2):123-128. Read it Young willow oaks, so treat three trunk diameters as a floor and not a clearance.
Miesbauer, Koeser, Kane 2025. Impact of trenching on root loss and tree stability. Arboriculture and Urban Forestry 51(1):94-102. Read it Red maple. Cutting at three diameters cost about as much stability as one.
Koeser, Grabosky, Benson, Morgenroth 2025. Quercus virginiana root regrowth following linear trenching. Arboriculture and Urban Forestry 51(1):3-13. Read it 22 percent of the original cross-section back after five years.
UF/IFAS root pruning guidelines. Read it

Palms

Broschat 2011, reviewed 2020. Pruning palms. UF/IFAS ENH1182. Read it The hurricane-cut observation is field experience, not a trial.
ISA. Palms. Read it

Standards and ethics

ANSI A300 is a paid document. Everything below comes through TCIA and ISA summaries, so check a clause against the printed standard before you quote a number from it.

ISA Code of Ethics. Read it
ANSI A300 Tree Care Standards, Tree Care Industry Association. Read it
TCIA on Part 1, pruning. Read it
Kempter 2016. A300 pruning standard changes in public review. TCIA. Read it Where the 25 percent figure came out.
Rasmussen 2026. Stop pruning malpractice with a prescription. TCI Magazine. Read it Performance standards, not work specifications.
American Society of Consulting Arborists. What is a consulting arborist? Read it

Utility and municipal

The regrowth and strength studies are northern species with small samples. There is no live oak data.

Goodfellow, Blumreich, Nowacki 1987. Tree growth response to line clearance pruning. Journal of Arboriculture 13(8):196-200. Read it Six species, Green Bay.
Dahle and others 2006. Branch strength loss implications for silver maple. Arboriculture and Urban Forestry 32(4):148. Read it Six trees.
Browning and Wiant 1997. The economic impacts of deferring electric utility tree maintenance. Journal of Arboriculture 23(3):106-112. Read it
Pizza 1984. What can be done about trim refusals. Journal of Arboriculture 10(7):209. Read it A practitioner article, not a study.
Arbor Day Foundation. Tree City USA Bulletin 3, resolving tree and sidewalk conflicts. Read it
Arbor Day Foundation. Tree City USA Bulletin 8, do not top trees. Read it
Grand Forks Park District tree removal policy, 2021. Read it A published list of what a city will not remove a tree for.
ISA Utility Specialist exam outline, 2021. Read it Customer relations is 20 percent of it.
ISA Certified Urban Forest Professional exam outline, 2024. Read it Communication and public education is 21 percent.
City of Orange Beach zoning ordinance, Article 16, tree protection. Read it

Explaining things so they stick

Borrowed from medicine, where people have studied this far longer than we have.

Agency for Healthcare Research and Quality. Health literacy universal precautions toolkit, tools 4 and 5. Read it One to three key points, and teach-back.
Elwyn and others 2012. Shared decision making, a model for clinical practice. Journal of General Internal Medicine 27(10):1361-1367. Read it Choice talk, option talk, decision talk.
Miller and Rollnick, motivational interviewing, as summarized in SAMHSA TIP 35, chapter 3. Read it Asking permission before giving advice.
Rubak and others 2005. Motivational interviewing, a systematic review and meta-analysis. British Journal of General Practice 55:305-312. Read it Health settings, not sales.
Kessels 2003. Patients' memory for medical information. Journal of the Royal Society of Medicine 96(5):219-222. Read it The 40 to 80 percent forgetting figure, resting on older small studies.
Federal Trade Commission. How to avoid a home improvement scam. Read it Do not automatically choose the lowest bidder.

Three things worth saying plainly

The 25 percent pruning limit is not in the current standard. It was in A300 in 1995 and 2001, and the 2017 revision took it out in favor of the objective and the tree. ISA's homeowner brochure still prints it.

Thinning is not settled. One trial cut upper trunk movement at 110 miles an hour; another found thinning the outer edge among the least effective types. Both used planted oaks about 20 feet tall. Neither tested stripping the inside of a mature tree.

Three trunk diameters is a floor, not a clearance. The number came from young willow oaks, and a 2025 trial found cutting at three diameters cost about as much stability as cutting at one.

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