Tree risk assessment

Why a risk assessment takes longer than a condition report

You are not really paying for the inspection. You are paying for a document that has to hold up when somebody questions it, which might be years later and might be somebody with a reason to want it wrong.

So the report names the method, shows the reasoning at each step rather than jumping to a rating, and stops short of a conclusion the evidence will not carry. It takes longer to write than a condition report and it costs more.

The method

Tree Risk Assessment Qualification is one of the two structured risk methods in common use here, the other being QTRA, the Quantified Tree Risk Assessment system. When I last looked, very few consulting arborists advertising in metropolitan Melbourne published a risk qualification of either kind on their website.

The assessment works through three things separately rather than collapsing them into a single impression:

• Likelihood of failure. What could fail, how likely is it, over what timeframe
• Likelihood of impacting a target. What is beneath it, how often, for how long
• Consequences. What happens if it does, and to what

Those three combine into a risk rating, with the working shown at each step so you can see how it was reached.

What is in the report

• Tree identification, dimensions and condition
• Site context and target occupancy, assessed rather than assumed
• Defects described specifically, with photographs
• Likelihood of failure and of impact, stated separately
• Consequences and the resulting risk rating
• Mitigation options with the residual risk after each, so removal becomes a choice rather than a default
• A recommended reinspection interval
• The matrix used, reproduced, so the rating can be checked against the method