International Tree Care Standards: Why are they so different?

The UK’s tree care standard BS3998 has been in force since 1966.  Germany’s ZTV  since 1981, and the US’s A300 Part 1 since 1991.   British and German cultures have a longer history of managing mature trees than the US.  The regions and legal systems and the trees themselves are similar, and the tree care standards also have some similarities.   A brief comparison on pruning mature trees might indicate more opportunities for harmonization:


US:ANSI A300 Part 1 Germany:  ZTV UK:  BS3998
Informative text (not normative/’standard’) included for clarity Excluded from the body; in annexes or saved for ISA BMP Included in the body, italicized Included in the body, italicized
Guidance on reduction pruning 6 lines Several pages (example below) Several pages (example below)
“Regeneration” aka

“Retrenchment” ?

No “Promote secondary (reiterative) crown” … “Main solution to prevent failure”…
“Heading cut” used? Yes, with 3 definitions No No
Size of reduction cuts: Required,  recommended, or suggested? Suggested:Small cuts “should be preferred” Recommended

Should not exceed 4”

Required with exceptions; exceed 4” only under specialcircumstances


German Normative Guidance

“On young trees, the goal of pruning is to direct their outward growth and development. On mature trees, pruning preserves health, safety, and function for as long as possible.


To regenerate a tree’s crown, trees that are showing dieback should be cut back to an inner crown. Individual branches should be reduced. When reducing the entire crown don’t go over 20%.  Heavy sprouting after damage should be thinned or reduced.  Make the cuts above the old pruning wounds.  Develop a secondary crown using reiterations.


Maintain features that are characteristic to the individual tree.

Branches greater than 4 inch diameter should not be removed.  Large cuts less than 4 inches on poorly compartmentalizing species should also be avoided.  Consider reducing the limb.


British Normative Guidance BS3998

After crown reduction, there should be a strong framework of healthy small-diameter branches and twigs (leaf-bearing structure), capable of producing dense leaf cover during  the following growing season. Each tree should first be assessed to decide how much and where to cut

A crown should normally be reduced in proportion to its original shape, so as to avoid altering the balance of the tree as a whole… The  shape of the crown can be changed if there is a specific need to do so, e.g. for biomechanical integrity.  During crown reduction, unlike topping, the cuts should not exceed 4” diameter except on very large trees.  Etc…


According to the ISA, the ANSI A300 standard fits with its “special companion Best Management Practices booklets. The ANSI A300 standards represent the industry consensus on performing tree care operations.”   A300 may be the dominant standard for the US industry, but it seems to leave out common practices in the international industry.  


ANSI directs the A300 group to incorporate an international perspective:  “Standards… Developers are encouraged to consult any relevant international or regional guides that may impact the proposed standard.”


The A300 group only agreed “To review and incorporate changes in industry standard practices, as appropriate, since the approval of the current standard. Harmonization with related industry standards will be considered.”  

This wording does not align with A300’s assigned responsibility to be a global partner, and limits A300’s usefulness as a reference for an international BMP.

ANSI does not encourage the A300 group to consider harmonization, but to actively harmonize.


Are operations other than pruning incorporated? No, 10 other Parts are separated into different publications Support, Contracting, Habitat, Diagnosis, Root and Soil Care… Support, Contracting, Habitat, Diagnosis, Root and Soil Care…


The 11 separate-but-overlapping volumes of A300 make this difficult, and the need for combining these should be acted upon sooner rather than later.  But with the deadline for comment October 2nd, the more urgent action is to comment on the draft and encourage A300 to consult and harmonize with relevant international standards.


“Scope summary: A300 (Part 1) Pruning standards provide acceptable industry performance parameters and an industry standard specification writing guide for pruning of trees, shrubs, and other woody plants. ..”  

By consulting international standards, the A300 group can “provide acceptable industry performance parameters and an industry standard specification writing guide.”  Without a wider perspective, Part 1’s parameters restrict the performance and competitiveness of a growing number of experienced arborists in the US.

Practices that are proven by long experience to be acceptable elsewhere in the world and compatible with tree health, value and stability are put at a significant disadvantage in the US.  This disadvantage is worsened when they are omitted from the ISA BMP.


Tree workers and managers who communicate or travel between the US and other countries lose time and effectiveness while adapting to different tree care standards.  Technology transfer across borders is inhibited.  With more consistency among tree care standards and practices, the international arboricultural industry can advance.


If the A300 group chooses not to harmonize with international guidance, the wording in their standard should reflect that limitation, such as:  1 ANSI A300 standards 1.1 Scope ANSI A300 performance standards cover the care and management of trees, shrubs, palms and other woody landscape plants **in the USA**. 1.2 Purpose ANSI A300 standards are intended for the development of work practices, written specifications, best practices, regulations and other measures of performance **in the USA**. ..

1.3 Application ANSI A300 standards shall apply to any person or entity engaged in the management of trees, shrubs, palms, or other woody plants **in the USA**, including federal, state or local agencies, utilities, arborists, consultants, arboricultural or landscape firms, and managers or owners of property.”


Added language to the next draft that includes common practices like mature tree reduction, vine and shrub care, etc. is not only possible, but necessary to meet A300’s aspirations to represent industry consensus.  So comment today to Bob Rouse,


Author: Guy Meilleur


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