Standards Australia published AS 4970:2025 Protection of trees on development sites on 30 May 2025, replacing the 2009 edition. If you commission arboricultural reports for planning applications, the changes are worth knowing about because some online comments are wrong, and those errors can cost you at the assessment stage.
A report prepared to AS 4970:2025 should show four things: the Notional Root Zone (NRZ) calculation, the Tree Protection Zone the arborist has derived from it, the encroachment classified against the standard's thresholds, and the protection controls split into a plan (TPP) and a specification (TPS). A report that still uses the 2009 approach reads as out of date, and a Council arborist or planner will notice.
NRZ and TPZ are now two separate terms
The most repeated mistake is that the new Notional Root Zone (NRZ) "replaces" the Tree Protection Zone (TPZ). It doesn't. The 2009 standard used the TPZ for both the calculated root area and the fenced area on site. The 2025 edition splits that: the NRZ is the calculation, providing the on-paper area to consider, and the TPZ is the on-ground zone the project arborist determines from it (AS 4970:2025 cl. 3.2). A report should show both, and the reasoning that moves from one to the other.
The formulas, the considerations the arborist weighs, and the SRZ sit in the companion piece, TPZ and NRZ under AS 4970:2025: what changed, what didn't. This piece covers the remaining changes.
The measurement label changed, not the method
The NRZ input is now Diameter at Standard Height (DSH) rather than Diameter at Breast Height (DBH). The measurement point hasn't moved. It's still 1.4 metres above ground. The label was changed to align with how the rest of the world measures trees (AS 4970:2025 cl. 3.2, Appendix A). Some online summaries claim the calculation itself changed, or invent new names for the zone. It didn't, and you can disregard those commentaries.
Encroachment thresholds are triggers, not verdicts
The 2025 standard classifies a proposed incursion into the root zone as minor (10% or less of the NRZ), moderate (more than 10%, up to 20%), or major (more than 20%, or any incursion into the Structural Root Zone) (AS 4970:2025 cl. 3.3.4 to 3.3.6). These need to be read as 'triggers' only, not a determination of a permit or a refusal of one. A moderate or major encroachment doesn't mean a design is refused. It means the standard requires the arborist to investigate and justify rather than wave it through. For you, that's useful: it shows early where a design needs root investigation or a redesign, before it reaches a planner's desk.
The plan and the specification are now separate deliverables
This is the change most likely to show in the documents Council are provided. The 2025 edition moves away from the older catch-all management plan and names two outputs (AS 4970:2025 cl. 2.2.6).
The Tree Protection Plan (TPP) is the drawing: a scaled plan showing the trees to be retained (or removed), the TPZ for each retained tree, and the protection devices (AS 4970:2025 cl. 1.3.20). The Tree Protection Specification (TPS) is the written document that sets out the instructions to protect the trees, and it includes the TPP (AS 4970:2025 cl. 1.3.21). Both are prepared by the project arborist, and the current version of each is included in the construction documentation (AS 4970:2025 cl. 2.2.6).
The practical effect: protection is now a drawing plus a written method, not a single combined plan. Victorian Councils are already asking for the controls shown this way.
Definite language is built into the standard
AS 4970:2025 sets out how to read its own wording. "Shall" marks a requirement; "should" marks a recommendation ("How to read this Standard"). The specification carries that through: the TPS shall specify the measures by which the trees will be protected, shall state any prohibitions, and shall document the critical stages (AS 4970:2025 cl. 2.2.6).
That matters because ambiguous wording in a protection requirement is what gets exploited on-site when a builder decides the fencing was optional. A specification written in the standard's mandatory terms removes that wriggle room, which protects the tree and protects you from a non-compliance argument later.
One thing the standard is not
AS 4970:2025 provides guidance on the principles for protecting trees on development sites. It isn't a regulation, and it isn't a condition of development in its own right. Some commentary frames the new edition as "enforceable" in a way the 2009 version wasn't. That overstates it. What gives the standard force in Victoria is a planning permit condition or a scheme provision that requires its application, not the standard itself.
What this means for you
If a report you're handed shows the NRZ calculation, the TPZ derived from it, the encroachment classified against the new thresholds, and protection split into a TPP and a TPS, it's working to the current standard. If it gives a single zone figure called the TPZ with no NRZ behind it, and one combined management plan, it's working to the 2009 edition, and a Council reviewer will see that straight away.
Sources
- AS 4970:2025 Protection of trees on development sites: cl. 3.2 (NRZ = DSH x 12, minimum 2 m, maximum 15 m; DSH measured at 1.4 m), cl. 3.3.4 to 3.3.6 (minor, moderate, major encroachment), cl. 1.3.20 (Tree Protection Plan), cl. 1.3.21 (Tree Protection Specification), cl. 2.2.6 (TPS and TPP prepared by the project arborist; the TPS shall specify measures, state prohibitions, document critical stages), "How to read this Standard" ("shall" a requirement, "should" a recommendation), Appendix A (Diameter at standard height).
- AS 4970-2009 Protection of trees on development sites: cl. 3.2 (superseded single-zone TPZ = DBH x 12).
- Planning and Environment Act 1987: a standard takes effect where a permit condition or planning scheme provision requires it.
Note. This article is general information, not site-specific advice.