Post-fire tree mortality study

I came across a 2017 USFS paper about mortality on Doug-fir and ponderosa pine after wildfires.

Brief excerpts:

Only 8% of Ponderosa pine and 14% of Douglas-fir died within 3 years after fire. The amount of crown volume consumed, the number of bole quadrants with dead cambium and the presence of beetles were variables that classified most accurately,
but surviving trees in our sample displayed a wide range of fire injury making the accurate classification of dead trees difficult.

Injury to trees from wildfire and prescribed fire can produce mortality that is not immediately apparent and environmental
stress before and after a fire may also contribute to tree mortality in years after a fire

9 thoughts on “Post-fire tree mortality study”

  1. I am not surprised by this paper…in the late ’80s, I was a tree marker armed with a 1950s FS research paper that described how to predict tree mortality after a wildfire (this paper was the ‘best available science’ at the time). Its prediction factors also discussed crown mortality as well as % circumference adversely affected by the wildfire’s combustion/radiant heat. According to the paper, true fir trees are the most susceptible to mortality; Douglas-fir and ponderosa/white pine are the most durable, especially if no crown mortality is evident. The primary defense DF/PP/WP have against fire is their bark thickness and their ability to sustain larger percentages of circumference burned.

    BUT, I did not work on that National Forest long enough to verify whether my predictions as a tree marker were accurate. I believe that same area that I worked in has burned at least 2 times since I left in 1990.

    • In my experience, younger DF and WP have much thinner bark than PP, at the same age. That makes the cambium kill worse, for sure. We used to be directed to determine cambium kill…. with hatchets! I’m sure a great many survivors were killed off by this ‘destructive testing’ method.

      I worked on a salvage project where we used the brand new wildfire mortality guidelines put out by the Forest Service, in response to litigation that didn’t allow us to cut trees with any green limbs. The new guidelines were so confusing that even the plaintiff’s ‘expert’ could not decipher them, in court. The court case was lost in the Ninth Circuit Court, partly because ‘the guidelines were confusing’. A settlement was arranged.

  2. I don’t have access to the full paper, but as always the devil is in the details and mortality rate is not just some measure based on existing forests, but rather mortality directly correlates to land use history. As in the more recent a forest has been cleared the higher the mortality rate. So without knowing the management history, as well as fire history the context of mortality rates don’t make much sense.

    for example in undisturbed forest stands with 500 year old trees (once quite common a few centuries ago) there is 5 centuries of adaptation to periodic fires, which includes thick bark and no ladder fuels, as well as advantageous locations in relation to how prevailing winds normally carry a fire through an area.

    And while the younger trees in a 500 year old forest will have high mortality rates in a fire, the mature trees that have survived many fires will be able to quickly replenish the lost younger trees and keep the forest going. Of course if the land use history indicates all those 500 year old trees were long ago logged off then it’s not just mortality of existing thin bark trees with ladder fuels that’s higher, but the regeneration of future trees is also more problematic.

  3. I also learned that in Douglas-fir stands, by age 80 most of the original trees at stand initiation had fallen over. I’ve often wondered why foresters don’t fear walking through green forests [sarcasm intended].

    • Andy, if a fire killed all of the trees around your house (assuming you have a house with tall trees around it), trees within striking distance, would you cut any of them for safety’s sake?

      FWIW, last year I had a 28-inch DBH, 160-foot DF cut, since it has Schweinitzii root rot and was within striking distance on my house and a neighbor’s.

      • Jack Cohen’s research on home protection zone counsels strongly for treating vegetation near homes. Needless to say, what is appropriate for the home ignition/safety zone is inappropriate for the middle of the Mt. Jefferson wilderness or an almost-never-used Level 2 logging road. So I’m not sure what your point is.

        As to my personal experience with trees falling . . . Several years ago my father was almost killed when wind blew out one of three green and healthy boles of a 150′ coast redwood located about 50 feet from his house. The 3′ diameter 100′ long chunk demolished his attached deck and ripped off the front of his house, missing his sleeping self by about 6 feet. I persuaded him to remove the rest of the healthy redwood (this was its third assault in 60 years), which was sawn on-site into planks used to rebuild his deck. Karma is a bitch.

        When the on-going drought started killing 2nd-growth D-firs around my home, I asked my brother-in-law to remove them (my own tree falling skills are rusty), leaving in place the ponderosa pine and Oregon white oak native to the Willamette Valley. This was done primarily for fuels reduction, i.e., Firewise. My neighbors have yet to remove their dead trees, which are within striking distance of my house. However, their odds of hitting my property or loved ones are about the same whether the trees are dead or alive, so I’m not sweating it.

        The only time I’ve been hit by standing wood is when, as a Forest Service tree faller, I was cutting it down. I’ve the scar to remember the incident and always wear a hard hat when logging and a helmet when riding my bicycle.

      • PS: I’ve been having a running battle with the City of Eugene over its burdensome tree-cutting rules, which create a significant barrier to Firewise practices. The irony that Eugene manages residential housing properties like they are wilderness and the Forest Service wants to manage the backcountry like it’s suburbia has not been lost on me.


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