Tumwater commission recommends keeping Davis-Meeker Oak on historical register

The risk rating matrix was used incorrectly to generate an artificially inflated rating.”

Beowulf Brower, arborist

The Tumwater Historic Preservation Commission unanimously voted on Thursday, April 18, to recommend keeping the Davis-Meeker Oak on the city’s historical register.

City staff is currently considering the removal of the 400-year-old Oregon White Oak tree (Quercus garryana) along Old Highway 99 as the analysis of the city’s consultant arborist, Kevin McFarland of Sound Urban Forestry, found that the tree poses a high risk. An 18-inch diameter branch already fell from the tree from a height of 50 feet in June last year, which McFarland attributed to decay in the tree.

The tree would have to be removed from the city’s historic register before the city can proceed with removal.

“The public's input is overwhelmingly not to delist the tree or take it down and try to do what we can to save it as long as we possibly can until it's just going to fall. Like we all do,” said commission member Don Trosper before voting to keep the tree.

“The historical value, I think, outweighs the legal financial liability, in a historic sense to me. The council has to weigh that. That's their decision, of course,” he continued.

Commission Chair David Shipley added that the commission has yet to have the final say on the matter and that the city council can either accept or reject their recommendation.

The Tumwater Historic Preservation Commission unanimously voted to keep the tree on the city’s historic register.

Arborist claims McFarland made errors in assessing the risk of tree

The commission came to its decision after a series of inquiries towards McFarland about the tree's condition, his techniques, and most importantly, the way he evaluated the risk rating of the tree.

In assessing the risk rating of the tree, McFarland used the International Society of Arboriculture’s (ISA) basic tree risk assessment form.

Arborist Beowulf Brower, who works for but does not represent the State Parks and Recreation Commission, wrote a report claiming that McFarland made errors in using the form.

For the analysis, McFarland considered four conditions should the tree fail: a large scaffold branch falls on either the highway or a nearby parking lot, a co-dominant term falls on the hangar, and a branch falls on the power lines.

An appendix from McFarland’s report shows how he evaluated the tree’s risk rating.

For each condition, three factors are to be considered according to ISA’s manual: the likelihood of failure, the likelihood of impact, and the consequence of tree failure. The manual also contains a matrix that represents the risk rating for every combination of these three factors.

Brower claimed that in three instances, McFarland incorrectly labeled the likelihood of failure and impact (LFI) as “likely” when it was only supposed to be “somewhat likely.” These errors eventually led to McFarland’s decision to have a “high” risk rating for the three conditions.

In his analysis, McFarland noted that either the scaffold branch or the co-dominant stem is likely to fail. Should these three parts fail, he labeled the likelihood of impact as “high.”

The matrix in the ISA manual shows that a “possible” likelihood of failure and a “high” likelihood of impact should result in an LFI of “somewhat likely” instead of “likely,” as McFarland put in the form.

Due to the incorrect categorization, the risk rating of these conditions should range from “low” to “moderate,” depending on how harsh the consequence of failure is rated. Even with a “severe” consequence of failure, the risk rating of these conditions would only be “moderate.”

As McFarland tagged the risk rating of these conditions as “high,” the final risk rating of the entire tree was labeled as “high.” The only condition in which the risk rating wasn’t high was if a branch fell on the powerlines.

“The risk rating matrix was used incorrectly to generate an artificially inflated rating. This tree, at most, would present a ‘Moderate’ risk. The errors present here make the assessment of the tree as being a ‘High’ risk are the result for a series of mistakes,” Brower stated in his report.

Further errors on categorization

Brower also argued that McFarland made errors in assessing the likelihood of impact on two conditions, which would further result in lower risk ratings.

Brower claimed that if a large scaffold branch were to fall on the highway, the likelihood of impact should be “medium” instead of “high.”

According to the manual, a medium likelihood means that “the failed tree or tree part could impact the target but is not expected to do so.” The manual explicitly states an example of this condition, which is when the target of the impact could be “passengers in a car traveling on an arterial street.”

According to Brower, McFarland also mislabeled the likelihood of impact when he categorized the likelihood of the scaffold branch falling to the parking area as “low” instead of “high.”

According to the manual, a “high” likelihood means that “there is a constant target with no protection factors, and the direction of fall is toward the target.” Brower claims that the tree’s branches do not overhang the parking lot and would, therefore, not directly fall on it.

McFarland’s risk rating remains despite admitting to certain errors

In response to the alleged errors, McFarland admitted to making certain errors with the form but not in the way Brower reported.

McFarland said that in evaluating the likelihood of failure of the three conditions in question, he incorrectly shaded “possible” instead of “probable.”

“This is probably going to make a lot of people go ‘aha.’ I should have had; it was, I guess you could say, a typo for condition number one, two, and three. They actually should be ‘probable,’ not ‘possible,’” McFarland said.

According to the ISA manual, a “possible” likelihood of failure means “failure may be expected in extreme weather conditions but is unlikely during normal weather conditions.”

In contrast to “probable” which McFarland noted it should be, such category means “failure may be expected under normal weather conditions.”

McFarland noted that even with the error he made, the risk rating would remain as “high.” 

According to the manual, a “probable” likelihood of failure and a “high” likelihood of impact yields a “somewhat likely” LFI.

This LFI returns a risk rating of “low” to “high” depending on how the consequence of failure was rated. As McFarland noted that the consequence of failure would be “severe,” the risk remains at “high.”

McFarland justifies techniques used to assess decay in the tree

McFarland also justified the techniques he used to assess the extent of the decay in the tree.

In his report, McFarland stated that due to the significant presence of decay in the tree, structural concerns existed with the base and lower main stem, as well as one of the co-codominant stems up to the large scaffold branches.

To determine how far the decay extended, McFarland employed sounding which involved striking the tree with a mallet to listen for tones indicating cavities or cracks inside the tree.

McFarland told the commission that sounding can be very accurate, especially if the person using the technique is familiar with how different tree species sound when struck.

The city also hired another consultant to conduct tomographic tests to visualize the tree's interior.

McFarland affirmed that the tomographic test could pick up the content of the tree vertically, in contrast to Brower’s report, which claimed that the tree's tomograph is only a 2D representation and does not show how the decay progressed up the tree.

The city’s arborist also assuaged misconceptions about his intent on working on the tree.

“I don't take this lightly. As I mentioned before, and the other commission meeting prior, I have been working in and assessing and doing different things with that oak tree for 27 years,” McFarland said.

“I've actually talked with friends and some of their colleagues, there's a lot of misunderstanding and misconceptions about my intent. I don't want the tree for firewood, I don't want it for furniture, I don't have an agreement with the city to, you know, funnel off some of that wood for growing shitake mushrooms. I don't have any other ulterior motive but to just work and do my best on assessing a tree like this.”

Decay on tree not new

International Society of Arboriculture’s manual for its tree risk assessment form shows a matrix to determine the risk rating of a tree.

Brower also wrote in his report that the decay on the tree is not new and that the tree has survived several years despite its condition. In his report, Brower showed an email from the late 1990s by a certain Neal Wolbert to the granddaughter of Jack Davis.

Davis's efforts in the 1980s led to the tree's inclusion in the city’s historic register and the rerouting of Old Highway 99.

The old email showed that the highway construction left three feet of soil over the tree’s root crown, which provided the ideal conditions for the Armillaria fungus to propagate.

Brower’s report also stated that a vehicle struck the tree in 2008. He argued that if the tree were not in good health, it would not have been able to seal the wound it sustained from the accident.

“The decay in the tree is not new, nor is it the worst the tree has endured over a long lifetime. Were the stem weakened to the point of imminent failure, it would have fractured from the impact that wounded it,” Brower wrote.

“In no small part, the tree survives because the community cares. From Jack Davis getting a highway moved, the city listing it as its first heritage tree, and efforts by arborists over the years, its history is punctuated by care and devotion,” he added.

In concluding his report, Brower recommended that the city contract a neutral third-party arborist for a new report. He also advised the city to supply the tree with soil amendments for now, as this would be an inexpensive solution to improve the tree’s condition in the absence of a long-term management plan.