Pruning standards by country: what A300, BS 3998 and AS 4373 cover

A pruning standard is a document that says what pruning work is, what to call each type, and which practices it does not accept. This page describes what the publishers and official summaries say. It is a map to the documents, not advice on how to prune. The full texts are sold.

United States

ANSI A300

ANSI A300 is the American national standard for tree care. The Tree Care Industry Association (TCIA) acts as secretariat for it. Pruning used to be A300 Part 1. TCIA's store now lists a consolidated ANSI A300 Tree Care Standards book with 15 clauses. Pruning is Clause 5, tree risk assessment is Clause 13 and industry definitions are Clause 15.

ISA sells the same book as ANSI A300 Tree Care Standards (2023). Its page says the book replaces ten separate publications and also gives guidelines for writing tree care work specifications. The price is US$105.79 for ISA members and US$158.69 for everyone else. TCIA lists the same two prices.

TCIA's page says the standards are used as the final authority in US civil court. That is TCIA's wording, not a ruling.

Pruning types and terms

The public page of ISA's Trees Are Good site lists the pruning types in plain words.

Cleaning is the removal of dead, dying, diseased, weakly attached and low-vigor branches from the crown.
Raising removes the lower branches to give clearance for buildings, vehicles, pedestrians and vistas.
Reduction reduces the size of a tree, often for utility line clearance. The page says that compared to topping, reduction helps keep the tree's form and structural integrity.
Thinning reduces the density of foliage at the edge of the crown.

An older edition, A300 Part 1 from 2001, is hosted by the town of Sullivan's Island, South Carolina. In it, topping is defined as reducing a tree's size with heading cuts that shorten limbs back to a set crown limit. It says topping and lion's tailing are unacceptable pruning practices. It also defines restoration as selective pruning to improve the structure, form and appearance of trees that have been severely headed, vandalized or damaged. The text is on the Sullivan's Island copy.

What changed in 2023

TCI Magazine reports that the 2023 revision of Clause 5 allows mechanical pruning outside areas defined as remote or rural. It also quotes the standard saying that mastication, the indiscriminate grinding of tree and shrub parts by heavy equipment, is not an acceptable branch cutting practice. See the TCI Magazine article, dated June 5, 2024. It adds that A300 pruning was first published in 1995.

ISA Best Management Practices

ISA also sells a series of Best Management Practices booklets. The Pruning booklet, third edition (2019) explains pruning types and pruning cuts and reviews sample pruning specifications. ISA calls it a companion publication for A300. It costs US$19.95 for ISA members and US$25.95 for everyone else.

Canada

No Canadian standards body page or official Canadian city page linked here names A300 as the pruning standard. A300 and the ISA booklets above are American publications. A job spec or a bylaw that names a standard states which one.

United Kingdom

The British standard is BS 3998:2010, Tree work: Recommendations. The British Standards Institution (BSI) lists it as current, published December 31, 2010. The BSI page shows £306.00 for non-members and £153.00 for members.

BSI says the standard gives general recommendations for tree work. It covers management options for established trees, including soil care and tree felling, and overgrown hedges. BSI calls the 2010 edition a full revision, updated and expanded for changes in the law and working practice. It adds that the standard looks at the effect of work on one tree in relation to its neighbours but does not cover the overall management of tree populations. See the BSI Knowledge page.

BSI's page does not list the pruning terms. For those, see a council guide, the High Peak Borough Council tree work guide, which says it refers to BS 3998:2010. That guide describes these terms in its own words.

Crown lifting is the selective reduction and removal of the lower branches.
Crown thinning is the removal of a proportion of secondary and small live branch growth throughout the crown, to leave an even density of foliage.
Crown reduction, or shaping, is the systematic reduction of peripheral branches to decrease the height or spread of the crown.
Topping is hard pruning that removes nearly all of a mature or semi-mature tree's branches and foliage. The guide calls it nearly always unacceptable and says it should not be confused with pollarding.

The same guide says usually 15 to 20 percent of crown volume is removed at one time, and in some justified cases a maximum of 25 percent. That is a council's description of its own approach, not a quote from BSI.

Australia

The Australian standard is AS 4373-2007, Pruning of amenity trees. Standards Australia published it on March 14, 2007. It runs to 14 pages. The Standards Australia store lists it at AU$114.35 with the status Pending Revision. The store also shows it superseded AS 4373-1996 and carries a reconfirmation marked REC:2020. No revised edition is listed.

A free sample of the first pages is hosted by a tree care association, the AS 4373-2007 preview. It says three things.

The scope includes removal of deadwood, crown lifting, formative pruning, reduction pruning (including line clearance), selective pruning, crown thinning and remedial or restorative pruning.
Lopping, topping and flush cutting are unacceptable practices.
An arborist, for the purposes of the standard, is someone trained to AQF Level 3 in Arboriculture or above, or with equivalent recognized and relevant experience.

Councils can write the standard into their rules. The Newcastle City Council manual for private trees, updated February 2018, says all tree pruning is to be done in accordance with AS 4373-2007. It asks for a pruning specification from a person with at least AQF Level 3 in arboriculture, and says the pruning itself should be done by a suitably qualified person with at least AQF Level 2. It notes that topping and lopping are not forms or classes of pruning in AS 4373-2007. That rule is Newcastle's. Other councils write their own.

New Zealand

New Zealand has no pruning standard of its own. The New Zealand Arboricultural Association says that in the absence of NZ specific standards it supports and recommends three international ones for tree pruning: AS 4373-2007, BS 3998:2010 and ANSI A300 (Part 1)-2017. It also says its own Amenity Tree Pruning Guide is under review. See the NZ Arb safety and guidelines page. The page names the 2017 edition of A300 Part 1.

At a glance

Country	Standard	Price listed
US	ANSI A300, 2023 book	US$158.69 (US$105.79 ISA members)
Canada	None named here	Not applicable
UK	BS 3998:2010	£306.00 (£153.00 BSI members)
Australia	AS 4373-2007, Pending Revision	AU$114.35
New Zealand	Uses the three above	Not applicable

The guide on safety rules country by country covers the safety side of the same trade. For the words themselves, see the tree work glossary.