Tree Risk Assessments (TRA)
A detailed analysis of the risk posed by a single tree or group of trees within a specific site.
Tree risk assessments are often carried out at schools, universities, holiday resorts, parks, and other public spaces where trees have the potential to cause harm to the persons who occupy that space. There are three components to calculating the risk posed by a tree:
The first stage of a tree risk assessment comprises a visual tree assessment of all trees within the site. The visual tree assessment comprises a walkover risk assessment in accordance with the Quantified Tree Risk Assessment (QTRA) method. Where the walkover risk assessment identifies conditions or defects that present an increased risk of tree failure, the identified tree will be assessed using the full QTRA method and a stage one Visual Tree Assessment (VTA) as formulated by Mattheck & Breloer (1994).
Trees identified as posing an increased risk of harm are spatially located, tagged, and allocated an identification number. Following the site inspection, a comprehensive report is prepared to detail the overall structure of each identified tree, the subsequent likelihood of tree failure, and the potential risk of harm posed by that individual tree. General information for each individual tree will include:
Our tree risk assessment includes management/mitigation options to reduce or eliminate the risk posed by each of the identified trees and a tree location plan prepared using AutoCAD or ArcGIS drafting software. The tree location plan displays the location of each identified tree, its allocated number, and its risk rating. A photo of each identified tree is provided and included in the report to allow for identification and verification purposes.
Frequently Asked Questions
A tree risk assessment is a detailed analysis of the risk posed by a single tree or group of trees within a specific site. Although it may seem counterintuitive, the condition of the trees should not be the first consideration. The first consideration should be the usage of land on which the trees are located. The risk from falling trees/branches only exists if there is potential for tree failure, and potential for harm to result. The risks from falling trees are usually very low and high risks will only be encountered in areas with high levels of human occupancy or with valuable property/assets.
There are three components to calculating the risk posed by a tree:
- Target: The persons, property, or asset at risk and the likelihood of that target being present/impacted in the event of partial or whole tree failure.
- Size: The size of the tree or branch most likely to impact the target. The size of the failure determines the likely force exerted upon impact.
- Probability: The likelihood of a failure occurring within the assessment period based on the structure and condition of the tree.
The first stage of a Tree Risk Assessment usually comprises tagging (numbering) all trees within the subject site. A visual tree assessment of all trees within the site is carried out to identify any trees that pose an increased risk of failure. Following the site inspection, a comprehensive report will be prepared detailing the overall structure of each identified tree, the subsequent likelihood of tree failure, and the potential risk of harm posed by that individual tree.
Only an AQF level 5 arborist with qualifications in a recognised tree risk assessment method is suitably qualified. Recognised tree risk assessment methods include the Tree Risk Assessment Qualification (TRAQ – ISA) and Quantified Tree Risk Assessment (QTRA – M. Ellison).
Tree risk assessments should be carried out annually or following a significant change to the subject tree(s) or surrounding environment, including catastrophic storm/wind events. Tree risk assessments are often carried out at primary schools, high schools, universities, holiday resorts, parks, and other public spaces where trees have the potential to cause harm to the persons who occupy that space. Tree risk assessments are usually commissioned by property owners or managers as part of their duty of care to the public or people who occupy that space.
A tree risk assessment report includes detailed information on any trees within the site that pose an increased risk of harm. This information will include the overall health and condition of the trees, as well as any significant/visible defects that may be present. The technical report should include a tree location map prepared using CAD or ArcGIS software showing each of the identified trees, their allocated number, and risk rating. The report must also provide management/mitigation options to reduce or eliminate the risk posed by the identified trees.
Tree Survey will carry out the site inspection and prepare the tree risk assessment within 14 days following acceptance of the quote. This timeframe can be reduced to 7 days (priority service) for a +25% increase in the quoted fee.
Tree Survey provide practical, cost-effective, and reliable tree risk assessments for a variety of organisations, institutions, and landowners. Our AQF level 5 consulting arborists have previously worked to develop and implement the very first risk management program for trees within the M2 Motorway corridor. Subsequently, our consultants have since been engaged by Sydney Trains to review and further develop the “At Risk” Tree Program for trees adjacent to the high voltage feeders (powerlines) and rail network (rail corridor).
Our current projects include large-scale tree risk assessments for Sydney Trains throughout the entire rail network and include the following regions:
- City South and South Coast Territories: Shoalhaven, Kiama, Shellharbour, Wollongong, Sutherland Shire, Georges River and Bayside.
- West and South West Territories: Lithgow, Blue Mountains, Hawksbury, Penrith, Blacktown, City of Parramatta, Cumberland, Fairfield, Liverpool, Campbelltown, Camden and Wollondilly.
- City East and City West: Canterbury-Bankstown, Cumberland, City of Parramatta, Strathfield, Burwood, Inner West, Sydney City and North Sydney.
- City North and Central Coast: North Sydney, Lane Cove, Ku-ring-gai, Canada Bay, Ryde, City of Parramatta, Hornsby, Central Coast, Lake Macquarie and Newcastle.