Large Douglas Fir Failure in Lowland Puget Sound

Our subject tree; an old growth Pseudotsuga menziesii, Douglas fir.

The following is the first of many articles which I will be writing for this newsletter. These will be stories of tree failures and will include the possible contributing factors involved in these failures. My articles will include data from the Pacific North-West Tree Failure Database (PNWTFD). This article and the information from the PNWTFD is for informational use only. All trees and their locations are individual. A tree risk assessment which meets industry standards should be performed to assess risk related to any tree. Do not ruin the PWNTFD or my good graces in writing this by suing me. Now, let us continue…

This tree failure occurred February 18th, 2018 in the Lowland Puget Sound area of Washington State. During the days leading up to this event, an inch of rain had fallen in the area. In the early morning of the 18th, southwesterly wind gusts were recorded near the tree at 57 mph.

The day this tree fell, the PWNTFD received an unprecedented 44 tree reports. This included 23 stem failures, 19 root failures, and 5 branch failures. Twenty of these trees were conifer trees. I believe many conifer trees failed because evergreen conifer trees experienced more wind force then their deciduous counterparts.

The location of our subject tree was a forested bluff very near to the Puget Sound. Here the storm winds were higher than the reported 57mph. This is because the winds that slammed into this tree came directly off the Puget Sound where nothing had dissipated their force.

Our subject tree was a Pseudotsuga menziesii, Douglas fir tree. This specimen was probably a few hundred years old. This tree was one of the largest in the area and its canopy was taller than the trees surrounding it. It was in an area which I considered to be unmaintained open space. This space was developed with an infrequently used trail about 60’ from the subject tree.

The mature Phaelous schweinitzii, Velvet Top Fungus conk is circled in red

The subject tree was roughly 86 inches in diameter and around 125 feet tall. The tree failed in the direction of the prevailing wind in what I considered to be a basal torsion failure. This meant that the tree rotated side-to-side right before it failed. Evidence of this can be seen, as one side of the trunk failed at ground level and the other side of the trunk remained as a ten-foot-tall splinter.

The heartwood of this tree was extensively decayed. There was a one-foot tall clump of Phaelous schweinitzii, Velvet Top Fungus a few feet away from the side of the tree which failed at ground level. Phaelous schweinitzii is a native wood decaying fungus that effects many PNW trees but most commonly associated with Douglas fir. This fungus is soil borne and causes a lower trunk or butt rot. While P. schweinitzii can attribute to tree failures, it is also beneficial in the long-term health of our forested lands. This is because it helps to bring down large mature trees where they land on the forest floor and decay. This decaying tree creates living space called “nurse logs” for wildlife and as returns nutrients back to the soil for other trees to grow.

P. schweinitzii can be identified by its emerging yellow conks which can be seen in late summer or by its mature conks which resemble cow patties and remain near the base of infected trees year-round. It can also be identified by the bottling effect which it causes in the trunk of infected trees. Unlike this failure, tree failures associated with P. schweinitzii generally occur around the top of the trunk bottling which is usually around 10-15 feet up on the trees stem.

So, what caused this tree to fail? There are many short term and long-term factors to should be considered. The wind forces did contribute to this failure, but would they have caused this tree to fail if the base was not as decayed? What factors contributed to the decayed wood? Would the P. schweinitzii have been as successful at decaying the trees wood if the stress from the trail and our recent drought weather patterns not occurred? Maybe, but to what extent? I don’t know.

In the end, like most tree failures we are left with several obvious contributing factors and some unanswered questions. But it was an amazing tree. I was so impressed by its size and stature. I hope this article intrigues the reader and this tree is honored by the advancement of your knowledge of trees and why they fail.

Christopher Rippey, Co-Founder of the PNWTFD

A typical old Phaelous schweinitzii failure
Trunk bottling effect

Article By:

Christopher Rippey Christopher Rippey
PNW-ISA Secretary and Co-Founder of the PNWTFD
Learn more about Christopher Rippey.