Tree Risk Assessments

Tree Risk Assessments

Arborist Reports on Risk

A consultant with AQF Level 5 (or higher) qualifications in arboriculture will conduct all risk assessments. Your consultant will hold an International Society of Arboriculture (ISA) Tree Risk Assessment Qualification and Quantified Tree Risk Assessment license. Your arborist will be ISA certified and a Registered Consulting ArboristTM.
Your family and your home are the most important things in your life, so it makes perfect sense to occasionally have a risk assessment done on the trees around your home.

Basic Tree Risk Assessment (BTRA)

The risk associated with the tree will be qualitatively assessed using the ISA’s Basic Tree Risk Assessment (BTRA) following the method outlined in the Tree Risk Assessment Training and the ISA’s Best Management Practice.

There are issues with using a qualitative system is assessing risk. Some criticisms have been levelled at the inferred mathematics behind the BTRA, and as a result, the use of a quantified system or improved benchmarking seems prudent. 

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Quantified Tree Risk Assessment (QTRA)

The QTRA process gives you a statistical number so you and your arborist can compare the risk of harm associated with your trees to that of other daily activities such as driving. All QTRA users must hold a current license. Our QTRA licensees participate in continuing education and training related to risk assessment to keep current with this rapidly changing field of arboriculture.

Every QTRA inspection comes with a set of notes from your arborist for your records. If your neighbours are concerned about your trees, you may find it useful to provide them with a copy of the assessment.

Tree Risk Assessments for Schools

One of our AQF 5 (or higher) consulting arborists will visit the site. The consultant will consider the area within the target zone, and ask for a site sketch or plan where one exists. The consultant may need to ask a number of questions about student and staff numbers, particular areas, and student movement patterns.

Once the use of the target zone is understood, the consultant will inspect the trees using a Visual Tree Assessment (VTA). This first stage involves looking for defects or indicators of defects from the ground. Where concerns exist about a tree or a particular defect and the tree falls in the region of an unacceptable or the upper end of tolerable risk, further testing will be recommended.

The interim risk of these trees will be calculated, and where required, further diagnostic testing may be recommended. Unless there is a sound arboricultural reason to believe otherwise, where further testing is recommended, the tree will be assumed to pose an unacceptable risk until the test results are available.

Where a tree is found to pose an unacceptable Risk of Harm, an Interim Action Plan will be issued within 24 hours of the inspection. Where a tree is found to pose a risk in the tolerable range, consideration will be given to reducing the risk where practicable. Where such options exist, a set of Recommended Works will be provided within 10 days of the site inspection.

Where aerial inspections are recommended, and it seems likely that pruning will sufficiently reduce the risk, the aerial inspection will usually be done at the same time the pruning work is performed.

A Tree Risk Assessment Report will be produced and will include the above documentation and will usually be issued about 4-6 weeks after the site inspection and any further testing has been completed. The report will indicate the inspection cycle based on the health and structural condition of the trees that will remain.

A Tree Risk Assessment does not include plotting, identifying, and collecting specific details about each tree. The purpose is to identify trees that pose an unacceptable level of risk. These trees will generally be photographed and roughly plotted on a plan to allow for their identification by staff and others.

Sometimes when decay and/or basal wounds are present, a resistograph or ultrasound may need to be undertaken to assess the extent of the decay/wound.

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