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Coast redwoods increasingly susceptible to fire damage

Fire consumes a once-healthy California redwood tree. (photo: USFS)
California’s renowned coast redwood trees, previously believed to be fireproof, are now more than four times more susceptible to wildfire injury in coastal forest areas infested with the sudden oak death pathogen. These redwoods are now as susceptible to wildfires as other trees.

Millions of trees, including tanoaks, coast live oak, California bay laurels, and many other forest species have been killed by sudden oak death in coastal areas of central and northern California, and Oregon. The pathogen, Phytophthora ramorum, was first linked to the massive tree death in the mid-1990s.

David Rizzo, professor in the Department of Plant Pathology at UC Davis, and his research team are studying how the coastal forest ecology is changing since sudden oak death appeared, and why coast redwoods (Sequoia sempervirens) are subsequently so much more susceptible to fire.

It is the presence of the sudden oak death pathogen in forests that poses heavier fire risks for redwoods.

“If redwoods didn’t live in forests affected by the disease, they could withstand fires just fine,” says Margaret Metz, a postdoctoral research scholar working with Rizzo.

Professor David Rizzo, UC Davis.
An initial explanation for the higher redwood mortality following wildfires is heavier fuel loads (such as fallen, dead branches from tanoaks) in forests affected by sudden oak death. Tanoak, Notholithocarpus densiflorus, is the primary host dying from sudden oak death and the main source of pathogen inoculum.

According to Rizzo, “The disease likely created more fuel for wildfires as dead tanoak branches fell. The loss of the oaks also would have decreased the amount of shade, drying out the forest and turning it into a tinder box, one not even redwoods could survive.”

A real key, though, is the finding that dead tanoaks, still standing, carry flames high into tree canopies, scorching the crowns of adjacent redwood trees. It’s this crown injury that is believed to have caused so many redwood trees to die in a number of fires that occurred in 2008.

Dead tanoaks in a redwood forest in the scientists’ California study area, pre-fire. (photo: Kerri Frangioso/UC Davis)
“Humans are causing widespread changes throughout our world, including greater wildfires related to changing climate and from increasing infectious disease due to more modes of transportation,” said Sam Scheiner of the National Science Foundation, which funded some of this research.

Rizzo, noting that an increase in fire severity is resulting from climate change and global movement of species, says, “There may be all sorts of consequences, among them, dead and dying coast redwoods.”

Additional information:

  • California's iconic redwoods in danger from fire and infectious disease. National Science Foundation report on Rizzo group’s work, August 2013
  • The effects of sudden oak death and wildfire on forest composition and dynamics in the Big Sur ecoregion of coastal California. General technical report
  • Ecology research article, Ecological Society of America
  • California Oak Mortality Task Force website
Posted on Wednesday, September 4, 2013 at 7:21 AM


As someone living in the Navarro watershed, I can attest to the appearance of increased stress on the redwoods in the Mendocino Redwood Company forest stands. Now, the concern is all the dead tan oak killed through hack and squirt that have been left standing in remote areas if MRC land. It is one thing to worry about sudden oak death syndrome, without having to also contend with the industrial motivation for killing yet more such trees.

Posted by Franklin Graham on October 7, 2013 at 8:57 PM

I performed an under 3 acre conversion in a third @50-60 yo growth redwood/doug fir/tanoak/bay forrest to establish a 75 foot clearance defensible perimeter on a homesite with outbuildings (1 mile from the coastline) on top of a mountain(moderate marine influence), juxtaposed to a saddle with slope gradients 30-50%. This was performed with an RPF, biologist, F&G, Calfire, etc. and I followed their recommendations. There is a high fuel load due to previous logging, fire suppression (duff up to 3+' at the base) and high sods death rate. I have been challenged by those passionate to save all redwoods (not local or my neighbors) that my clearing of the 50 yo redwoods was unnecessary and I should left the redwoods since they can't transmit wildfire crown to crown and would not have been a hazard. The head of Calfire for our region who visited my property five times said that is a partial truth and that I did not want to chance the experience the part that was not as true and that was part of the prescription for establishing the defensible perimeter at least 75 feet clearance with selective removal from 75-150' as opposed to 150'+ clearance that would have been normally recommended with a severe risk and then additional circumstances that contribute to a very severe risk. I am just having some second thoughts (or else I would not be researching this after the fact) and at the same time feeling guilty second guessing those who helped me (and I feel are my friends) in asking "Did I do the right thing removing the redwoods which I actually do care about". If you cannot respond, please help me by sending me in the right direction to rest my mind.  
ps-I want to share my appreciation for all the great work you do and Dr. Metz (who I believe is working under you & I researched a couple days ago), it allows me to be an informed steward of 300 acres on our precious coast and to fulfill my own passions through your scientific endeavors.

Posted by John J. McGovern, MD on July 19, 2014 at 10:28 PM

Thank you for this wonderful information. It's true that fire can kill our forests there are cases of wild fires everywhere. It says sometimes by human error or sometimes it's just by nature.

Posted by Loic Brun on October 24, 2014 at 8:11 AM

The top photo is typical of any redwood park in the north where fires over centuries burned out goose pens, commonly seen.  
But I find the articles interesting anyway. Common sense alone suggests that greater fuel from disease in the understory would increase fire intensity.  
If the extra info provides the age of redwoods where the studies are being done, that will be a useful bit of insight, whether its old or new growth.  
M. D. Vaden /

Posted by M. D. Vaden on April 20, 2016 at 8:34 AM

I am astonished to see no mention of forestry practices (logging and fire suppresion) anywhere in this entire article. Those are far more responsible for the increased fuel loading. P. ramorum is simply an opportunist, thriving in the overcrowded forest created by mismanagement.

Posted by T. Bray on May 9, 2016 at 6:58 PM

Thanks for sharing.

Posted by Kavi raj on September 20, 2018 at 9:41 AM

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