Fire scientist says, “…eucalyptus did not burn with high intensities leading to home destruction”

We have the pleasure of publishing a guest post by a member of the team that is trying to prevent the pointless destruction of the urban forest in the East Bay Hills.  This article is an example of the expertise and dedication of our team.  It also makes another contribution to the considerable body of evidence that eucalyptus has been inappropriately blamed for the 1991 Oakland fire and that destroying our urban forest will not reduce fire hazards.  (emphasis added)

April 24, 2016

Jack Cohen is a fire scientist at the US Forest Service fire lab in Missoula Montana.  For decades he has researched fire behavior in the Wildland Urban Interface areas (WUI). His research includes scores of post-fire investigations, as well as controlled experiments in the only forest fire lab in this country.  WUI fire poses a unique set of challenges to local fire departments. Mr Cohen’s research has informed nationwide strategies on how to prevent and manage fire in the WUI setting.

He concludes that it is neither desirable nor realistic to attempt complete suppression of catastrophic fires, or to expect fire departments to fully defend WUI areas. We live, after all, in a fire dependent natural environment, and have over the years constructed many combustible structures within heavily vegetated and dry areas. He does believe it is possible to construct and maintain buildings to resist ignition, (by addressing the Home Ignition Zones) and that this effort will do much more towards preserving human life and property than remote fuel treatment, or poorly focused fire suppression efforts.

As part of my work as a building inspector and engineer, I spent 18 years studying, developing and enforcing building codes in the East Bay, including the WUI areas of Berkeley. In years following the 1991 Oakland hills fire, both local and national bodies incorporated the findings of Mr. Cohen’s ground-breaking research into building regulations for new construction.  “…destruction in the WUI is primarily the result of the flammability of the residential areas themselves, rather than the flammability of the adjacent wildlands…Research has shown that a home’s characteristic and its immediate surroundings principally determine the WUI ignition potential during extreme wildfire behavior.” (1)

It’s my opinion that the removal of eucalyptus trees from the hills will not advance, and may even worsen, fire hazard mitigation. The trees are not the problem. As for firebrands emitted during a fire, they are generated in all vegetation types. The best strategy to save homes is to harden structures to prevent ignition and maintain surrounding defensible space. Still, I wondered about the often-repeated claim by local officials that these eucalyptus trees are to blame for the 1991 fire, and that they present a major threat to fire safety. So, I asked Jack. Here’s his private email response. He included some photos, worth taking a look at. His website follows, including links to his extensive research:
Marg Hall
Berkeley, Ca

  1. Elizabeth Reinhardt, Robert Keane, David Calkin, Jack Cohen, “Objectives and considerations for wildland fuel treatment in forested ecosystems of the interior western United States,” Forest Ecology and Management, 256 (2008) 1997-2006.

(Here attach emails, but remove our addresses)

From: “Cohen, Jack -FS”
Date: March 25, 2016 3:38:38 PM PDT
To: Margaret Hall
Subject: RE: 1991 Oakland Hills fire


Thank you for your generous words of support for the research I’ve done!

I did a quick analysis of Oakland Hills as part of an internal effort to better understand the contribution of firebrand ignitions. I used video footage as my window to the event and did not do a site examination. This effort did not generate a written report. However, it became abundantly clear the Oakland residential fire disaster was similar to more recent disasters where eucalyptus is significantly present. I have attached 5 photos (poor quality) showing that the “gasoline” tree remains unconsumed adjacent to/surrounding destroyed houses as with all the other disasters I’ve examined (refer to my reports). The first 2 photos are from the 2009 Melbourne, Victoria fires that destroyed many structures with 173 civilian fatalities in Kinglake and Marysville in the hills north of Melbourne (I did a site visit but these are not my photos). The unconsumed tree vegetation is eucalyptus. The next 3 photos (not mine) are from the 2003 San Diego County fires. All of the destroyed homes and the burning wood roof home have adjacent eucalyptus – not burning in the tree canopy with high intensities. This is consistent with all the disaster examinations I’ve done (internal reports and published) regardless of the tree species. The common characteristics initiating the disastrous losses in high density residential development are extreme wildfire conditions in surrounding wildlands producing firebrand showers that ignite homes directly and surface fuels within the community to produce significant firebrands from burning homes/structures and adjacent trees that were ignited by the burning homes. This indicates that the eucalyptus trees did not burn with high intensities (or any intensity) leading to home destruction. This strongly suggests that eliminating eucalyptus and replacing it with some other vegetation would not prevent future WU fire disasters because the problem was inappropriately defined as a eucalyptus vegetation problem and not a home ignition-home ignition zone problem.

This is my perspective in answer to your question. Hope that helps. If you have further questions please feel free to ask.



Melbourne, Victoria, Australia, 2009
Melbourne, Victoria, Australia, 2009
Melbourne, Victoria, Australia, 2009
Melbourne, Victoria, Australia, 2009
San Diego County, California, 2003
San Diego County, California, 2003
San Diego County, California 2003
San Diego County, California 2003
San Diego County, California, 2003
San Diego County, California, 2003

From: Margaret Hall
Sent: Sunday, March 13, 2016 3:09 PM
To: Cohen, Jack -FS
Subject: 1991 Oakland Hills fire

Dear Mr. Cohen,

I am a retired building inspector/civil engineer in the SF Bay Area and am familiar with your work on home ignition zones. After the 1991 fire, we (City of Berkeley) adopted a building code ordinance which focused on hardening structures against wild land/urban interface fire. When I began to learn of your research, I realized retrospectively how very helpful that information was in developing our code. Thanks for all your great work!

There is a debate in our community about a plan to remove large quantities of eucalyptus stands in the East Bay hills. Some firefighters remember that the many wood shingle roofs were the primary contributor to the spread of that fire. Other folks remember events quite differently and blame the trees. I’ve got two questions:

  1. Did you study the1991 Oakland HIlls fire? If so, can I have a copy of your report? (if it’s not in electronic form, I’m happy to pay for copying/mailing as needed)
  1.  Do you have any fire-science based information on the dangers represented by a specific tree species (in this case E globulus) as compared to other vegetation types? Is there any basis in science for calling eucalyptus trees “gasoline trees”?

Full disclosure: I am opposed to this plan. I don’t think it will reduce the fire danger, especially as the goal of this plan is to replace forested areas with very dry ignitable “grasslands and shrubs”. Also, I’m not happy about the prospect of escalating the use of herbicides in heavily used regional parks, herbicides required to prevent the trees from re-sprouting and suppress unwanted vegetation.

Please let me know if I need to file a formal public records request, and if so, in what format you need that. Again, thanks for your great research. I love watching your videos and the way you are able to make geeky fire science accessible to firefighters and to the public.

Marg Hall
Berkeley, Ca


8 thoughts on “Fire scientist says, “…eucalyptus did not burn with high intensities leading to home destruction””

  1. Cohen’s work is spot on. He is part of the modern band of wildfire scientists that work on the cutting edges of reality instead of fantasy. I am extremely grateful to him not only for his excellent work but that he gets to have it noticed. If it were not for the successful efforts of certain powers that be, there would be hundreds more like him thus the public’s understanding of the essential place that wildfire has in a healthy world would be far greater, and perhaps that trend would have spilled over into other aspects of ecosystem awareness, lessening Million Trees’ uphill climb.

    Cohen works at “the only forest fire lab in this country” because vested interests combined to de-fund any research that threatened to produce information that might impede the justifications to convert natural resources into profits. Saint Reagan, for instance, wanted to accelerate federal timber receipts in order to mask the extent of the public debt he was creating with militarism, and to assist the enrichment of private timber companies from the public stash – only one of many threads of “privatization” sold as a political ideology to mask that it is a hoarding of the Commons for relatively greater personal advantage. Fire Suppression is BIG business. It opens the spigots on the Treasury drains just like other fears of other ‘terrorists’ do.

    The manifestations of this world view are countless. Virtually all of us (myself included) participate, and drive it via our collective personal choices.

    We admirably decry the removal of vegetation by citing the benefits of that vegetation to countless species, our aesthetics, and the existing ecosystems of our civilized habitations and beyond. But we largely ignore that those civilized habitations supplanted pre-existing ecosystems. One may wish to excuse that by viewing the landscape that pre-dated Golden Gate Park as a “wasteland”. Be careful: that was once the same argument used to describe deserts, but later we learned that they teem with life and ecosystem processes. And it was once the argument that justified total suppression of wildfire – ‘all fires create wastelands’—and now we know that (although many have not yet gotten the memo) that wildfire is an essential ecosystem process that powers the multitudes of what we value about ecosystems. (And, btw, while coastal Chaparral is, indeed, a different animal than are treed forests, wildfire IS a natural part of them – in the form of stand-replacing fires on long return intervals. Why would we think that it must be harmful in that context?)

    And we largely ignore the reality that to maintain and expand our civilized habitations, we continue to degrade ecosystems elsewhere. Where do we think that the lumber to build our houses comes from? By cutting down the trees in some other environment. And if anyone thinks that building their house out of, say, stone or concrete or steel, instead of wood, does not degrade ecosystems, they ought to think again. Mining is not pretty, and the toxicity it and the processing of its extracts leaves in its wake is abominable. Do our roads precipitate from Heaven, or do they gobble up gravel bars, hillsides, and petroleum (via a processing/handling system hardly environmentally benign?) And don’t get me started about the elements of computer and cell phone manufacture.

    I am sorry you live in a part of the world that so-robustly converted its native ecosystems into merchantable goods and ways of living in attempts to be protected from evil Mother Nature. It leaves you little choice but to now struggle with paradoxes. I wish your plight would motivate people in more “rural” areas to think not twice, but hundreds of times, about proliferating the urban model, but it rarely does and when it does, it does not last long. The seduction is overwhelming.

    1. Thank you. I now have a better understanding of where you are coming from. Usually you take pot shots at my articles. This more positive explanation of what you know about natural ecosystems and how they deserve to be treated, is much more effective to make your case.

      1. I have rarely had the intersection of time, clarity, and hook to write thusly here. If I did, my writings would have become essays, not comments. In my first draft, I had begun “I have been waiting for to open this door.”

        You may have missed some of this same character in my early comments years ago? Regardless, glad I finally was able to get my point across to you. I now may be able to stop trying to, which has always robbed from other responsibilities and sleep.

  2. This is a wonderful blog entry. We might never have known Mr. Cohen’s perspective on the 1991 Oakland fire if Marg Hall had not written to him, and shared his response with readers of the Million Trees blog. I always read every article posted by the person who does Million Trees. Many of us who care about trees and want to save as many as possible depend on the commitment and research skills that the Million Trees webmaster has demonstrated over and over again. I especially appreciate the webmaster’s consistent and painstaking attention to detail that has uncovered a great deal of important information that might otherwise never have been daylighted.

    1. And I appreciate equally the work done by the Hills Conservation Network. If there is anything I can do to accommodate the needs of the Hills Conservation Network, please let me know. I gather the leadership is somehow disappointed in the collaboration with Million Trees. However, the leadership has not been explicit enough for me to understand why they are disappointed.

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