Tree Risk Assessment (QTRA)
Trees provide enormous value to properties, communities and the environment. They also carry inherent risk. When something goes wrong, the consequences can be serious. For property owners, managers and organisations with trees in their care, understanding and managing that risk is a legal obligation.
At Asset Tree Care, we provide professional tree risk assessments using the Quantified Tree Risk Assessment (QTRA) methodology. As a qualified tree risk assessors operating across Mandurah, the South West and regional WA, we work directly with clients to deliver clear, defensible risk assessment reports that support informed decision making and demonstrate duty of care.
What Is a QTRA Tree Risk Assessment?
The Quantified Tree Risk Assessment (QTRA) is a systematic, evidence-based methodology used by qualified arborists to evaluate the risk posed by trees to people and property. It is one of the most widely recognised tree risk assessment frameworks in Australia and provides a consistent, defensible basis for risk management decisions.
A QTRA report quantifies risk by evaluating three key parameters for each tree assessed:
- Probability of failure: the likelihood that the tree or a part of it will fail, based on observed structural condition, defects, species characteristics and site factors
- Probability of impact: the likelihood that a failure would strike a person or target, based on how frequently the area beneath the tree is occupied
- Consequences of impact: the likely outcome if a person or target were struck, taking into account the size of the tree or the part most likely to fail
Together, these three parameters produce a quantified risk rating that allows property managers, councils and organisations to make informed, documented decisions about tree retention, remediation or removal.
When Is a Tree Risk Assessment Required?
A formal tree risk assessment is commonly required or strongly recommended in the following situations:
- Concerns about the structural condition or stability of a tree
- Following storm damage or observed tree failure on or near the property
- Prior to events, markets or gatherings where trees are located near attendees
- As part of an ongoing tree management program for councils, schools or community facilities
- When a tree is the subject of a complaint or insurance claim
- Prior to development works where trees are to be retained near construction activity
- As part of due diligence when purchasing or managing a property with significant trees
- When a council or insurer requests documented evidence of tree risk management
Property owners, strata managers, schools, local councils and commercial operators all have a duty of care to manage trees under their control and reduce unreasonable risks to people and property. A professional tree risk assessment provides documented evidence that hazards have been identified, assessed and appropriate management recommendations have been made. For organisations responsible for multiple trees or sites, regular inspections form an important part of a proactive tree management program.
If you are unsure whether a formal assessment is needed, Hamish is available to discuss your situation and recommend the most appropriate approach.
Formal tree impact assessments for development applications, prepared in compliance with AS 4970-2025.
Assessments for trees meeting regulated size thresholds under local council planning policy.
“Hamish and his team did a fabulous job removing some trees in our yard, including a very large and challenging tree. They were friendly, helpful, and thorough. Communication was always very prompt. We were very pleased with what a great job they did and how tidy they left the yard after they had completed the job. We would highly recommend them to anyone needing tree pruning or removal.”
Sydney Roberts
Tree Removal
Frequently Asked Questions
QTRA stands for Quantified Tree Risk Assessment. It is a structured methodology used by qualified arborists to evaluate the risk posed by trees, based on three parameters:
- the probability of failure
- the probability of impact on a person or target
- the likely consequences of that impact
The result is a quantified risk rating that supports documented, defensible risk management decisions.
Tree risk assessments are relevant to anyone with a duty of care over trees, including homeowners with large trees near structures, strata managers, schools, councils, commercial property owners and event organisers. A formal assessment is particularly important where trees show signs of structural decline, following storm damage, or where trees are located near frequently occupied areas.
QTRA (Quantified Tree Risk Assessment) and TRAQ (Tree Risk Assessment Qualification) are two different frameworks used for tree risk assessment.
- TRAQ is a qualification and methodology developed by the International Society of Arboriculture (ISA) and is widely used in North America.
- QTRA is the methodology used by Asset Tree Care and is the approach most commonly adopted by arborists in Australia and the UK.
Both aim to produce consistent, evidence-based risk ratings, though they differ in their methodology and scoring systems.
Yes. A QTRA report prepared by a qualified tree risk assessor provides documented, evidence-based findings that demonstrate a property has been professionally assessed and that identified risks have been acted upon. This documentation is important in the context of insurance claims, legal proceedings and council compliance.
The ISA TRAQ (Tree Risk Assessment Qualification) is a certification offered by the International Society of Arboriculture that recognises arborists trained in the ISA tree risk assessment methodology. While this qualification is common in North America, Asset Tree Care uses the QTRA methodology, which is the standard approach in Australian arboricultural practice.
Assessment frequency depends on the tree species, condition, location and the level of risk to people and property. Low-risk trees in low-occupancy areas may only require inspection every few years, while high-value or structurally compromised trees in high-traffic areas may warrant annual assessment. Hamish can advise on an appropriate monitoring schedule as part of your risk assessment report.
Asset Tree Care is based in Mandurah and provides tree risk assessments across the Peel region, South West WA and regional Western Australia. Contact us to discuss your location and we will confirm availability and scheduling.
Ready To Get Started?
Concerned about the risk posed by a tree on your property? Contact Asset Tree Care today for a qualified QTRA tree risk assessment across Mandurah, the South West and regional WA.
Call Hamish on 0490 762 201
Or Request Your Free Consultation
Asset Tree Care | Mandurah’s trusted arboricultural specialists.
Fully qualified. Fully insured. Always reliable.