The Quantified Tree Risk Assessment Method
Updated: Oct 18, 2021
Accomplished Tree Management is QTRA certified. What does that mean to you?
Safety is the one word that is undoubtedly paramount to all of us, no matter what part of our daily lives it relates to. It is something that extends to virtually everything we do, be it at home, work, school, while travelling or even to the surrounding natural environment.
Residents of Australia are fortunate to be surrounded by a bountiful array of natural wonders and beauty, with an extensive range of majestic native trees just one example – however, how many of us truly consider tree safety as a topic?
The Quantified Tree Risk Assessment (QTRA) enables tree safety management
It very much is a topic and a system has been developed around it. The Quantified Tree Risk Assessment (QTRA) system, developed by Mike Ellison at Cheshire Woodlands in the UK, applies established and accepted risk management principles to tree safety management.
As the QTRA website states itself, tree safety management entails limiting the risk of harm from tree failure while maintaining the benefits that trees provide. It is not just a case of classifying trees as safe or unsafe, however, as the QTRA system quantifies the risk of significant harm from tree failure in a way that enables tree managers to balance safety with tree values and operate to predetermined limits of tolerable or acceptable risk.
By quantifying the risk from tree failure as a probability, QTRA enables a tree owner or manager to manage the risk in accordance with widely applied and internationally recognised levels of risk tolerance. QTRA further provides a decision-making framework which considers the balance between the benefits provided by trees, levels of risk they pose, and costs of risk management.
Although it may seem counterintuitive, the condition of trees should not be the first consideration. Instead, tree managers should consider first the usage of the land on which the trees stand, and in turn this will inform the process of assessing the trees.
Using QTRA, the land-use (Target) upon which trees could fail is assessed first. By valuing the Target first, the tree owner and the risk assessor are able to determine whether or not, and to what degree of rigour, a survey or inspection of the trees is required.
Where necessary, the tree is then evaluated in terms of its size and probability of failure. Ranges of value for Target, Size, and Probability of Failure are entered into a QTRA calculator which generates a traffic light colour-coded risk of harm. The tree owner can then compared the risk to advisory levels for risk tolerance.
By taking a QTRA approach, tree owners commonly find they spend substantially less resources on assessing and managing tree risk than they did previously, whilst maximising the many benefits their trees provide. Moreover, in the event of a 'tolerable' or 'acceptable' risk being realised, they are in a position to demonstrate the risk has been managed reasonably and proportionately.
Accomplished Tree Management is QTRA certified
Port Macquarie-based Accomplished Tree Management has recently received QTRA accreditation. How does this benefit clients within the local area?
“It’s a qualification for quantifying risk for owners/managers of trees within locations such as schools, daycare centres, businesses, public lands and residential locations alike whilst assisting in the allocation of budget by applying straightforward mathematical equations,” explained Rhys.
“It does this by placing a value on the target, whether it be a statistical life or the cost of repairs to the building/structure; this is done by calculating the probability of harm as a fraction which can then be applied to the statistical life/costs of repair to the structure (target). For example: If the statistical life in AUD is $3 600 000 and the risk of harm is less than 1/10 000 (i.e. 1/10 000 - 1/1 000 000) then the allocation of funds is $360 per year or in the case of costs to repair a structure being $36,000, the figure would be reduced to $3.60. Conversely where the risk is greater than 1/10 000 (i.e. 1/1000 - 1/10 000) the annual budget would be $3 600 or $36 respectively.”
“This gives the manager a real figure for budgeting and they can plan for future work accordingly.”
“The QTRA method demystifies risk in a way that should be reassuring to the tree owner/manager, considering the risks most of us take for granted such as commuting on our roads. A risk which attracts a risk threshold several thousand times greater than the comparable likelihood of coming to harm from a tree. Greener, more densely canopied metropolitan areas are happier, healthier places and the QTRA method does much to preserve this resource.”
For further information on how the QTRA method can benefit you please contact Accomplished Tree Management directly.
About Accomplished Tree Management: Tel 0411 443 535
Accomplished Tree Management is based in Port Macquarie and services the Mid North Coast. With over 16 years of experience, we employ safe work methods and are certified with Australian AS 4373-2007-Pruning of Amenity Trees standards. We're fully insured with $20 million Public Liability and $5 million Professional Indemnity Insurance. We provide the following tree services -
Tree management - tree removals, palm tree services, council permits
Tree and garden maintenance - hedging, pruning, deadwooding, stump grinding
Tree consultation - arboricultural reports, hazard assessment
"The Quantified Tree Risk Assessment Method"is written by Vermilion Pinstripes, a sales marketing and communications agency based in Port Macquarie helping businesses thrive with brand confidence.