An interview with Mike Ellison – founder of QTRA

qtra tree risk assessment team

Can you tell us about your background and what inspired you to develop QTRA

Mike: In the early 1990’s, I won a contract with Commission for the New Towns (now English Partnerships) to deliver tree inspections and safety advice across their projects in the North West of England from Deeside to the north of Preston. I was frustrated by the tree industry’s risk aversion when it came to providing advice on the management of tree safety and had been involved in bringing Jim Clark and Nelda Matheny over from the United States to deliver seminars on their recently published book Evaluation of Hazard Trees in Urban Areas. I started to apply their method, but it didn’t work for that project because I needed to provide some kind of safety threshold beyond which a risk would usually be mitigated. I came across an article by the tree and woodland specialist Rodney Helliwell, who had used quantification to assess the likelihood of moving vehicles being struck by trees. Having discussed tree risk with Rodney, it was clear that quantification was the approach I should take and his method was the catalyst for QTRA, which also incorporated elements of the Matheny and Clark approach.

How does QTRA address the balance between preserving trees and mitigating risks to public safety?

Mike: A tree might have gross defects and a high chance of falling or shedding a branch, but where human occupation is low or there is little or nothing to be  damaged or lost as a consequence of tree or branch failure, QTRA enables the user to communicate clearly that risk is low and the tree asset can be retained. As trees age and become increasingly susceptible to failure, they often provide enhanced values of habitat and amenity, shade and shelter, and QTRA enables the user to compare and balance the level of risk with the level of benefits provided by the tree. When benefits from trees are lost to risk mitigation, we should always consider the loss as one of the costs of controlling the risk.

Can you share any case studies or success stories where QTRA has been particularly effective?

Mike: That’s a difficult one. I can’t talk about specific cases. I think the greatest value is that it enables us to more clearly communicate levels of risks and benefits from trees in a way that tree owners and duty holders can make more proportionate and reasonable decisions. It also helps us to question when unreasonable decisions are being made.

What are some common misconceptions or challenges associated with implementing QTRA?

Mike: That applying QTRA can be onerous and that you must apply it to every tree. It isn’t because you don’t. In fact, for large tree populations, it often removes substantial areas of trees from the need to carry out any inspections at all, solely based on levels of land-use. It can also guide the levels of inspection that are required based on the general characteristics of the tree population and its relationship with land-use.

How has QTRA evolved since its inception, and what developments do you foresee in the future?

Mike: I have had my critics and I have listened to them. The way the risk is represented in our outputs has become less precise over the years. The outputs are colour-coded, which simplifies risk communication and aligns with other risk models such as weather and fire danger warnings.

What are your hopes for the future of tree risk assessment, and how do you see QTRA contributing to that vision?

Mike: I hope that training in the tree industry will follow the QTRA model of proportionality and balance in risk decision making and continue to move away from hazard-based decisions where the tree inspector passes the liability back to the duty holder by specifying often unnecessary risk-reduction work.

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