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Urban Tree Risk Assessment- Perceptions, Reality, and Reliability. (Part 1)
Dr. Andrew Koeser
University of Florida
I first became interested in tree risk assessment 14 years ago while working as one of the junior technical experts at the International Society of Arboriculture’s headquarters. In this role, I often fielded calls from the public and the media. One day, my phone rang repeatedly with calls from news agencies requesting information on the risks trees pose. I soon discovered that a branch had fallen at the Central Park Zoo in New York, striking a mother and her 6-month-old child. Sadly, the child did not survive the incident.
At the time, my oldest daughter was also 6 months old. The thought of such a tragedy happening to her led me to declare that I would dedicate my future research career to studying tree risk in an effort to prevent accidents like this from happening again. Nearly a decade and a half later, experience and data have shown me what so many other experienced experts have come to realize: trees have much more to fear from us than we have from them.
One of my first funded studies along this journey was, “Urban Tree Risk Assessment - Perceptions, Reality & Reliability.” I am extremely grateful for the opportunity provided by the TREE Fund as it helped kick off a trail of research that I will attempt to summarize below.
Lesson One: Some Arborists are able to Predict Tree Failure
Following Hurricane Matthew's impact on the East Coast, the Bartlett Tree Expert Company had the opportunity to re-evaluate tree populations they had previously risk-assessed on institutional properties across Savannah, Georgia, and Charleston, South Carolina. The study involved three experienced consulting arborists with multiple industry credentials. While attempting to predict tree failure using the collected data, we identified a strong correlation between the arborists' estimates of failure likelihood and actual failures. Additionally, a pattern common to many datasets emerged: the vast majority of assessed trees were classified as low risk. Furthermore, the number of trees decreased with increasing risk ratings, with very few trees categorized as extreme risk.
These findings are encouraging, as they demonstrate that arborists have the potential to accurately assess tree risk. However, translating the knowledge they acquired through their credentials and personal experience remains a challenge. This is because personal experience, inherent biases, and differing levels of risk perception can significantly influence both risk ratings and mitigation recommendations.
See Part 2 in next month's TREE Press.
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