Navigating the New AS 4970-2025: What Australian Arborists and Developers Need to Know
Understanding the Evolution of Tree Protection on Development Sites
For anyone working in land development, construction, or arboriculture in Australia, the protection of trees on development sites is a critical consideration. These guidelines not only safeguard our valuable urban canopy but also ensure compliance with environmental regulations and contribute to sustainable development practices.
The recent publication of AS 4970-2025: Protection of Trees on Development Sites marks a significant milestone, superseding the long-standing AS 4970-2009. This updated standard brings crucial refinements and clarifications that will impact how arborists, developers, planners, and land managers approach tree retention and protection.
At Arbor Australis, we are dedicated to staying at the forefront of industry best practices and delivering our clients the most current knowledge and services. This comprehensive review examines the core changes introduced by AS 4970-2025, providing key insights to ensure your projects are compliant, sustainable, and environmentally friendly.
The Foundation: Why AS 4970 Matters
Before we explore the changes, it’s essential to reiterate the fundamental purpose of AS 4970. This standard provides the framework for assessing, managing, and protecting trees that are to be retained on development sites. It acknowledges the immense ecological, aesthetic, health and economic value that trees bring to our urban and regional landscapes. By establishing clear principles and processes, AS 4970 aims to minimise the adverse impacts of development on trees, promoting their long-term health and viability.
The standard guides practitioners through various stages of development, from initial planning and design to construction and post-construction management. It is a vital tool for ensuring that tree protection is integrated into the development process, rather than being an afterthought.
Key Shifts: AS 4970-2025 vs. AS 4970-2009
The 2025 revision is not a complete overhaul, but rather a refinement of the principles established in the 2009 version. These changes are designed to provide greater clarity, address practical challenges encountered over the past 15 years, and align with the evolving field of arboriculture and industry best practices.
One of the most notable changes is the introduction and clarification of terminology, particularly concerning the critical zones around trees.
Redefined Root Zone Terminology: Notional Root Zone (NRZ) and Tree Protection Zone (TPZ)
Perhaps the most significant update in AS 4970-2025 is the refined terminology for root protection areas.
- Notional Root Zone (NRZ): The 2025 standard introduces the term Notional Root Zone (NRZ). This term replaces what was previously largely understood as the Tree Protection Zone (TPZ) in the 2009 standard, in terms of its theoretical calculation. The NRZ represents the theoretical area required to sustain a tree’s health and long-term viability. Importantly, the calculation method for the NRZ remains the same as the previous TPZ calculation (Diameter at Breast Height (DBH) x 12). This area is considered essential for the tree’s physiological processes, including the uptake of water and nutrients to sustain its health.
- Tree Protection Zone (TPZ) Refined: With the introduction of the NRZ, the term Tree Protection Zone (TPZ) now specifically refers to the physical area on a development site that is protected during development activities. This protection is typically achieved through physical barriers, site management measures, and specific construction controls. Essentially, the NRZ is the calculated ideal area, while the TPZ is the practical, implemented protected area on site. This clarification aims to avoid ambiguity in planning and on-site implementation. It emphasises that while the NRZ is the biological requirement, the TPZ is the actionable zone of protection.
The existing Structural Root Zone (SRZ) remains an integral component of the standard. The SRZ is the innermost zone critical for tree stability, encompassing the woody roots and associated soil cohesion necessary to support the tree. Any encroachment into the SRZ is generally considered highly impactful and requires rigorous assessment and mitigation strategies.
Changes from DBH to DSH
Another departure from the 2009 terminology is Diameter at Standard Height (DSH): This new term replaces Diameter at Breast Height (DBH). The calculation and measurement method are the same (1.4m from the ground).
Enhanced Encroachment Classifications and Responses
The 2025 standard provides a more detailed and structured approach to classifying and responding to encroachments into the Notional Root Zone (NRZ). This aims to provide more precise guidance for arborists and decision-makers. The previous standard broadly discussed minor and major encroachments, but AS 4970-2025 now formalises three distinct levels:
- Minor Encroachment: This category applies to encroachments of 10% or less of the NRZ area, provided they are outside the SRZ and there have been no recent NRZ encroachments. Such encroachments are generally considered low-risk. If standard tree protection measures are implemented diligently, significant impacts on tree health, structure, or longevity are deemed unlikely.
- Moderate Encroachment: This is defined as greater than 10% and up to 20% of the NRZ area, when outside the SRZ, and with no recent NRZ encroachments. For moderate encroachments, the Project Arborist is now explicitly required to review the proposal and demonstrate whether the tree’s viability can be maintained. This may necessitate site-specific mitigation strategies and appropriate design or construction controls, such as non-destructive digging or alternative foundation designs.
- Major Encroachment: This classification is triggered by more than 20% of the NRZ area, and/or any encroachment into the SRZ. For major encroachments, the Project Arborist must be engaged to investigate alternative designs or demonstrate conclusively whether the tree can remain viable. This level of encroachment requires a detailed assessment of the tree and site, which may involve non-destructive root investigations to understand the root architecture and potential impacts thoroughly. This stricter definition highlights the risk of adverse impact resulting from this level of encroachment into the NRZ.
This refined classification system provides a more nuanced framework for assessing impacts and determining appropriate mitigation, moving beyond a simple “minor” or “major” distinction.
Emphasis on Clear and Definitive Language in Documentation
The shift from “Tree Management Plan” to “Tree Protection Plan (TPP)” and “Tree Protection Specifications (TPS)” in AS 4970:2025 is a crucial change that adds much-needed clarity.
The term “Tree Management Plan” in the 2009 standard was often ambiguous. It was used to describe both the written document outlining the protection measures and the physical site plan or drawing. This led to confusion for arborists, developers, and council planners.
AS 4970:2025 separates these two components into clearly defined, distinct terms.
- Tree Protection Plan (TPP): This is the drawing or site plan. Its purpose is to visually show the location of the Tree Protection Zone (TPZ), fencing, and other on-site protective measures. It’s the “blueprint” for where and how protection will be implemented on the site.
- Tree Protection Specifications (TPS): This is the written documentation. It contains all the detailed instructions, a schedule of works, and compliance requirements for protecting the trees. It specifies the type of fencing to be used, the timing of different works, the role of a project arborist, and other critical details.
While AS 4970-2025 provides technical guidance, this revision reinforces its connection with broader planning and environmental legislation in Australia. In fact, many external documents now explicitly require this integration.
Arboricultural Impact Assessments and Tree Management Plans (as termed in the 2009 version) are often mandatory for Development Applications (DAs) or other work permits. The updated standard helps ensure a more consistent and robust application of tree protection principles across Australia’s regulatory landscape.
For example, some jurisdictions are already incorporating the new AS 4970 definitions into their planning guidelines. A prime example is the ACT’s Urban Forest (Tree Management Plans) Guidelines 2025 (No 1), which directly references the updated standard.
While implicitly encouraged in the 2009 standard, AS 4970-2025 places a stronger emphasis on the use of clear and definitive language in all arboricultural reports. The standard explicitly states that critical tree protection specifications containing ambiguous language such as “should” or “may” will not be accepted where a firm requirement is intended. For instance, stating “TPZ fencing may be erected prior to works” is now unacceptable if the intention is for it to be a mandatory pre-commencement activity. The expectation is for “will” or “must” to be used for prescriptive requirements. This level of clarity aims to reduce misinterpretation, improve compliance, and ensure that protection measures are implemented effectively on site.
Integration with Broader Planning and Environmental Legislation
While AS 4970:2025 provides technical guidance, this revision reinforces its connection with broader planning and environmental legislation in Australia. In fact, many external documents now explicitly require this integration.
Arboricultural Impact Assessments and Tree Protection Specifications are often mandatory for Development Applications (DAs) or other work permits. The updated standard helps ensure a more consistent and robust application of tree protection principles across Australia’s regulatory landscape.
Focus on Long-Term Tree Viability
Throughout the 2025 standard, there’s a reinforced emphasis on not just the survival of trees during construction, but their long-term viability. The assessments and recommended protection measures are geared towards ensuring that retained trees can continue to thrive and provide their intended benefits for many years post-development. This holistic view is intended to encourage more thoughtful design and construction practices that consider the tree’s entire lifecycle.
What This Means for You
The updated AS 4970-2025 has significant implications for various stakeholders:
- Developers and Builders: You must ensure your project designs and construction methodologies adhere to the new definitions and requirements, particularly regarding the NRZ, TPZ, and the stricter encroachment classifications.
Engaging a qualified Project Arborist early in the planning process is more critical than ever to identify potential conflicts and design effective mitigation strategies. Non-compliance could lead to project delays, costly rework, or enforcement actions.
- Arborists and Consulting Arborists: The standard provides more straightforward guidelines for undertaking Arboricultural Impact Assessments (AIAs) and preparing Tree Protection Specifications (TPS). The distinction between NRZ and TPZ, along with the refined encroachment categories, demands precision in reporting and recommendations. A minimum Diploma in Arboriculture (AQF Level 5) remains the expected qualification for those preparing AIAs in accordance with AS 4970.
- Planners and Council Authorities: The updated standard offers a more robust framework for assessing development applications in relation to tree retention. The clarified terminology and encroachment guidelines will assist in consistent decision-making and the enforcement of tree protection conditions.
- Property Owners: If you’re undertaking renovations or new builds near existing trees, understanding these standards is crucial to protecting your valuable tree assets and avoiding potential issues with local council approvals.
Embracing the Future of Tree Protection
AS 4970-2025 can be considered a progressive step forward in the protection of trees on Australian development sites. By adopting more precise definitions, more detailed encroachment classifications, and a stronger emphasis on definitive language, the standard aims to improve consistency, reduce ambiguity, and ultimately enhance the effectiveness of tree protection measures nationwide.
It’s essential to note that the standard is advisory, not regulatory. Nore is it a specification to be used as a condition for development. Instead, it provides an improved framework for assessing the long-term impacts of development on the health and structure of trees, thereby demonstrating the effects of proposed work.
The updated definitions for Moderate and Major encroachments are simply triggers to initiate further investigation rather than being an acceptable or unacceptable outcome on their own. Nor should these encroachments be weaponised to promote the removal of trees without a thorough justification of impacts.
At Arbor Australis Consulting, we are fully equipped to assist you in navigating these changes. Our team of experienced consulting arborists can provide comprehensive Arboricultural Impact Assessments, Tree Protection Plans, and expert advice to ensure your projects meet the requirements of AS 4970-2025 and contribute to a healthier, greener urban environment.
Contact Arbor Australis today for a consultation and let us help you integrate best-practice tree protection into your next development.
