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Urban Tree Risk Assessment – Perceptions, Reality, and Reliability

2013 | Dr. Andrew Koeser, University of Florida

This project will address three aspects of risk assessment: 1.) Factors driving homeowner and professional risk perceptions; 2.) Impact of individual arborist on common risk assessment method outcomes; and 3.) Relationship between target rating and actual site occupancy given time of assessment. These efforts represent the beginning of a larger research program to assess the reliability of commonly used risk assessment methods (ISA Tree Hazard Evaluation Method, USDA FS Community Tree Risk Evaluation Method, and ISA Tree Risk Assessment BMP Method) and improve tree risk prediction models. Results from the risk perception aspect of this project are intended to identify areas were risk perception and risk reality are misaligned – offering guidance for industry and public education efforts. The remaining aspects of this project are intended to be an independent assessment of past and emerging risk assessment methods.

Study Results

Risk assessment is a very personal thing. Every tree has a real risk and a perceived risk to people and property. While we try to make the process more consistent with structured methods like the ISA Best Management Practices (BMP), in all of our studies we found rating biases among our participants. While the research is ongoing, we do see that when arborists assess tree risk, as much of 55% of their risk rating decision lies with the severity of the defect they see.

In contrast, much less weight is given to target (approx. 24%) supporting assumptions made by Ellison (2007), that arborists fixate on defects when target may be more important. In gauging likelihood that a target could be impacted by a falling tree, we found that arborists were better able to rate target occupancy when traffic count data was made available to them. Without this data, target occupancy ratings fluctuated significantly depending on the time of day the site was visited (peak times vs non peak time). Finally, we expanded our original plan of study (thanks to matching funds from Florida-ISA) to look at how level of assessment (i.e., limited visual, basic, and advanced) impacted assessments of likelihood of failure. While limited visual assessments were significantly different from the basic and advanced assessments, the ratings differed less significantly among the other assessment (visual, visual with mallet, resistance-recording drill, and sonic tomograph).

The funding from the TREE Fund helped turn these three ideas into real studies that now serve as the basis for my research program. With the project funded, I had a ready-made master’s thesis for Ryan when he approached me about graduate school. With this project and a great student in place, my center director found the funds to pay for his tuition and part of his stipend (which I was able to leverage to get the remaining stipend from a college-level fellowship). The Florida ISA matched the project with $5,000 in share money which I was able to use to expand my research in risk assessment and tree failure prediction. Finally, after hearing about my work from a mutual colleague, a senior risk expert and researcher (Tom Smiley) asked if I would be willing to work on a project that expands on this proposed work. In short, these funds set off a chain reaction which gave my program a core focus, provided a young professional with a graduate education, and spurred a new and exciting collaboration.

Year: 2013

Funding Duration: 1-3 years

Grant Program: Jack Kimmel International Grant

Grant Title: Urban Tree Risk Assessment – Perceptions, Reality, and Reliability

Researcher: Dr. Andrew Koeser

Key words: 

Peer Reviewed Publications from Grant:

General Audience/Trade Publications:

Presentations:

Categories 2013, Grant Archive, Jack Kimmel International Grant

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