Some Thoughts on Tree Risk

Early in January, two strong winter storms passed through Snoqualmie, where I work full-time. The second of these storms lasted about 20 hours, and at its peak, winds were 40-45 mph sustained with gusts in the mid 50’s. Beyond cleaning up tree failures and doing follow-up risk assessments, I spent a lot of time talking with scared residents. Many were concerned about the risk that trees pose to their families, and were convinced that swaying trunks were an indication that trees were about to fail.

In storms like these, there is a perceived high risk of trees. The actual risk for people (outside of our industry) is quite low, even during storms. As a juxtaposition to this, the perceived risk of driving a car or being on roads is low, whereas the actual risk is quite high.

Let me backup these assertions. A study by Thomas Schmidlin: “Human fatalities from wind-related tree failures in the United States, 1995–2007” discovered in that period, 407 deaths were caused by trees. By comparison, in the same time period, 416,268 fatalities were recorded on US roads by the National Highway Traffic Safety Administration. In other words, it seems that the average person is 1000 times more likely to die in a traffic accident than by a tree falling on them. However, I don’t think many of us think when we get behind the wheel: “Wow, I’m about to do a really risky thing”.

This is leading me to an ethics-check, and some questions I ask myself, that I’ll ask you too:

1) Do you communicate the benefits of trees, as much as the risks, to clients?

2) Do you have any way to put the risk of trees in perspective for the average person?

3) Are you focused solely on the trees when you risk-assess, or do other considerations creep in and affect your judgement?  Examples: The risk-tolerance of the client, the possibility that you may get paid to remove the tree, your own fear about being wrong in assigning a risk rating.

Culturally, we have accepted the risks that come from driving.  I think it’s part of our job as Arborists to help people understand the risk of trees, in balance with the benefits, and make sure there is a similar cultural acceptance of trees.

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Phil Bennett Phil Bennett
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