Case Study: News Story - Douglas Fir
This property owner is concerned that the two Douglas firs (Pseudotsuga menziesii) in front of her property might fall over and cause damage to her home or neighboring houses. A news story about a failed Douglas fir recently aired (Kamb, 2016), and the sensationalization of the damage caused created a misperception that the trees at her site were likely to fail in the same manner.
The north tree is 31 inches in diameter at standard height, and approximately 110 feet tall. The south tree is 27 inches in diameter at standard height, and approximately 95 feet tall. The subject trees have no visible trunk defects, a sounding mallet produced no concerning noises, and a climbing inspection and an exploratory root flare excavation revealed nothing notable. Evidence of previous branch failures is present, but the property owner acknowledged that they had happened when the trees were loaded with snow and ice several winters earlier.
There are high value targets within 1x tree height of both trees, but the lack of any defect which would suggest a likelihood of whole tree failure means that no mitigation work is necessary. The only target within the dripline is the homeowner’s car, so the recommendation is to park her car between the two trees during weather events where it was unlikely to be struck by a falling branch.
While these specific trees require no intervention beyond temporary target relocation (Dunster, et al., 2017, pg. 141), the common misunderstanding of the risk trees present (Klein, et al., 2019) is a worthwhile discussion in its own right. Trees are often perceived as a liability (Mortimer and Kane, 2004) and ethical arborists are tasked with discussing both the risks and benefits that trees provide to help a property owner make an informed decision (Dunster, et al., 2017, pg. 144).
Arborists are trained early in their careers to follow a standardized method of assessing risk and then communicating that information to their client (ISA, 2022), and the benefits are presented as a contextual baseline for tree risk management (Dunster, et al., 2017, pg. 3; VALID, n.d.). On the other hand, most additional training about the benefits of trees is offered in the form of one-off classes through a regional ISA chapter or local extension college (personal experience; PNW ISA, n.d.; Western Chapter ISA, n.d.). Entry- to mid-level training and many online resources tend to use inconsistent methods and ambiguous language (personal experience), and advanced training and academic work tends to be highly quantitative (Council of Tree and Landscape Appraisers, 2019, pg. 7) and may not be accessible to the average arborist for a variety of reasons including education level (American Society of Consulting Arborists, n.d.) employer buy-in, or time available.
This creates a mismatch in the style and quality of communication tools available to an arborist when speaking about risks and benefits. Tree risk assessment and communication as taught by the ISA is qualitative (Dunster, et al., 2017, pg. 6-7) with clearly defined ranges which can be understood intuitively. Benefits, however, are frequently less immediately visible (The Nature Conservancy, 2020) which in combination with a poor vocabulary (loose and general on the one end, and extremely numbers-oriented and cumbersome to relate on the other, but minimal middle ground) naturally leads to a greater emphasis being placed on risks.
On the client’s end, loss aversion plays heavily into decision-making. Loss aversion is a well documented psychological phenomenon that people are more likely to fixate on the loss potential of a situation rather than equivalent gains (Sokol-Hessner and Rutledge, 2018). A structured process for assessing both risks and benefits would create a more credible platform for discussion, while minimizing playing into the loss averse predisposition of the client (and the arborist!).
The language used around trees and tree risk management plays a role in the outcome, even when delivered by a well-meaning ethically minded arborist. Understanding of the pathogens, defects, and management strategies for different species of trees is unarguably a foundational need for sound risk management, but competence and confidence in assessing benefits, the soft skills to deliver a balanced recommendation, and a basic understanding human psychology are all important components of the total skill set required to advise on tree risk.
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This project was built as an assignment for the Tree Risk Management module within the MSc Arboriculture and Urban Forestry course at Myerscough College. All photos and content are my own unless otherwise attributed or cited. All names, addresses, and dates are made up, but accurately reflect season and site conditions at the time of assessment.
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