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I spent all of January 5th, 2019 in north Seattle pulling a tree out of a house. I arrived on-scene that morning at 4am and worked till 7:30pm that night. I got home to my house in Kent, Washington and passed out only to be awoken at 1:30am by very intense gusting winds. I spend the next hour or so watching transformers blow out and the trees in my neighborhood violently sway back and forth.
I have lived in that house for almost four years and had never experienced stronger winds than those I experienced that night. I seriously thought one of my well cared for trees was going to fall onto my neighbor’s house. My brother who is also an Arborist and lives a couple miles from me was also awoken by the wind. While watching the wind’s effect on the trees in his neighborhood, he saw a large hemlock tree sway back and forth and then fall on a house. It was a pretty intense night.
The morning after the storm my neighborhood was eerily quiet and littered with Douglas fir branches. Our power was out but work was calling so I left my son and wife at home and headed back in. That day I worked until 5pm clearing trees from roads and from on top of various things. It was a big overtime weekend for me. A few days later I sifted through the tree failure reports the Pacific North-West Tree Failure Database (PNWTFD) had received.
The day of the storm, January 6th, the PNWTFD received 82 tree failure reports. All came from King County in Washington State. Acer macrophyllum was the species with the most reported failures. But from what I saw in the field, conifer root and lower stem failures were the most destructive failures and what I will focus on for a little bit.
The PNWTFD received 15 conifer root failure reports on January 6th, 2019. Many of these failures damaged private property. We received reports of 6 hemlocks, 4 Douglas firs, 2 Chamecyparis, one grand fir, one incense cedar and one spruce root failures. The average DBH of these root failed trees was 23 inches and the average height was 82 feet. Six of the 15 failures had root decay organisms present, all six were listed as being Armillaria sp.
We received 12 reports of conifer stem failures (6 Douglas fir, 5 hemlocks, and 1 Western white pine). Six of these stem failures had one or more decay organisms listed as being a contributing factor to the failure (6 Phaeolus schweinitzii, 1 Armillaria sp., 1 Heterobasidion occidentale, and 1 Phellinus hartigii). The average height of these trees was 92 feet and the average DBH was 30 inches.
Now, flash forward to January 20th. I am doing some trail running with my lovely wife through Saltwater State Park in Des Moines, Washington. I am doing my best to keep up, but I keep getting distracted by tree failures that we keep coming across. I apologize to my wife and abandon our run to start collecting tree failure data, what a great date I am.
At the end of my run/data collection adventure, I had entered 13 trees into the database that had most likely failed during the January 6th storm.
I thought this information was comprehensive and interesting but before I can get into the tree failure data, I should tell you all about the site and the storm. Saltwater state Park is in the lowland Puget Sound area of Washington State. It is bordered by houses on all sides except the west where it is adjacent to Puget Sound. Topography wise, it is basically a figure 8 with two a-bowls pushed together and a creek running down the center. There is a mixture of conifer and hardwood trees in the park with a diverse collection of native understory. A trail runs around the upper edge of the park. There are also a few campsites down near the creek.
When the trees at Saltwater State Park failed on January 6th, southerly wind gusts were clocked in at Seatac Airport at 60mph. These speeds were likely higher nearer to the Saltwater State Park as it is near to the Puget Sound where unlike at the Airport, the southwesterly winds were not impeded and dissipated by any type of objects. Wind speeds were also higher in places like my house which are higher in elevation than Seatac Airport.
Now that you understand the site and winds, here are some interesting things that I noted about the specific tree failures at the park.
Tree Failures in Saltwater State Park in Des Moines. Red lines indicate the direction the trees failed.
The grand fir (10) which failed was in great pre-failure condition. I think this tree was a pure wind-thrown tree. It was in an open area and I think a perfect placed wind gust pushed it over. This was the only tree that didn’t have obvious defects that would put a tree at an elevated risk of failing.
All of the hemlocks which failed had extensive heart rot. The largest hemlock to failed also had extensive root rot. The organisms which caused this rot are native and can spread by root to root contact.
I came back on my bike the day after my run to take better pictures of tree 2, the large Tsuga heterophylla, Western hemlock root failure.
Tree 13, the large big leaf maple failure had a tree of similar size fail just to the south of it the previous year. This tree was likely blocking some wind force for this tree and without that protection, this tree failed.
Tree 12 is in an area which has experienced tree failures ever year since I started visiting this park in 2016. Because of this, Tree 12 was likely exposed to new wind forces and failed as a result.
I found evidence in the form of fungal fruiting bodies of several tree destabilizing organisms while entering the tree failure data at the park. Many of these organisms can spread via root contact so lots of trees in this park are likely affected. This is not uncommon in our area where stress from drought and soil compaction from trails are increasing the prevalence of these organisms.
Lastly, This data should emphasize two things: all trees eventually fail and tree failures are hard to predict. This data shows a wind range of pre-failure health conditions, tree sizes, decay organisms infections, tree species and directions of failure. Please know your trees and perform an industry standard tree risk assessment when assessing trees for related risk.