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Trees Withstand the Firestorm

November 14, 2010

Today, we visited the site of the fire in San Bruno that destroyed 37 homes, damaged many others and killed 8 people on September 8, 2010.  The fire occurred because a 30 inch natural gas pipeline exploded, sending a 200 to 300 foot fireball into the sky, according to the San Francisco Chronicle.  A federal investigation reported that it took the responsible utility company 1-1/2 hours to shut the supply valves to the burning gas line, so the fireball persisted for sometime, producing intense heat.

San Bruno blast destroyed this home, but the Monterey pines did not burn

Although trees in the immediate area of the blast burned, along with the homes, the fire did not spread into surrounding trees. 

Eucalypts on the ridgeline did not burn

The area of the blast is a small valley.  The ridgeline of that valley is lined with eucalypts.  The fire did not spread into those trees.  The eucalypts did not explode nor did they “loft embers” from one side of the ridge to the other, as we are often told they will by those who want us to believe that they are highly flammable and must be destroyed.

Trees adjacent to the blast did not burn

The San Bruno fire is therefore the most recent example of the fire resistance of trees.  There are many other examples.  An entire neighborhood of homes in San Diego burned in 2003, but the surrounding eucalypts just a few feet away did not ignite.

NY Times reported that 150 homes burned in this wind-driven fire in San Diego in 2003, but the eucalyptus did not burn. NY Times photo

The fire on Angel Island   in 2008, twelve years after most eucalypts were destroyed, stopped at the edge of the remaining 6 acres of eucalypts.  The eucalypts did not ignite during the fire in the Tamalpais Valley in 2006, according to the National Park Service, which continues to destroy eucalypts anyway, based on a bogus claim that they are highly flammable.

How much more evidence do we need to debunk the myth that eucalyptus and Monterey pine are highly flammable?  Since those making this claim don’t seem to be influenced by actual experience, let’s subject their myth to some laboratory science.

The predominant species of eucalyptus in California, the Blue Gum eucalyptus (E. globulus) is native to Tasmania.  Scientists at the University of Tasmania conducted laboratory experiments on the plants and trees in the Tasmanian forest to determine the relative flammability of their native species.  The Blue Gum eucalyptus (E. globulus) is included in this study.  The study reports that, E. globulus leaves, both juvenile and adult, presented the greatest resistance [to ignition] of all the eucalypts studied.  In this case, leaf thickness was important as well as the presence of a waxy cuticle.”  Also, in a table entitled “Rate of flame front movement,” the comment for E. globulus leaves is “resistant to combustion.”*  In other words, despite the oil content in the leaf, its physical properties protect the leaf from ignition.

Although local native plant advocates still maintain that non-native trees are highly flammable, we are encouraged by the comments of the Environmental Protection Agency (EPA) regarding the FEMA grant applications in the East Bay Hills.  These and many other comments submitted to FEMA to identify the environmental issues are now available on FEMA’s website (scroll down to Appendix F). Although the projects propose to clear-cut non-native trees in most areas, the EPA does not consider this necessary for fire safety:

“Include a commitment to leave trees greater than a specific DBH [trunk diameter at breast height] in size, and identify how this should be implemented.  Diameter and height are, in effect, measures of tree resistance to fire damage.  Large diameter trees are generally more able to withstand wildfire, assuming that surface and ladder fuels have been reduced and the severity of the fire is not extreme.  By leaving the largest trees and treating surface and ladder fuels, fire tolerant forest conditions can be created.”

This sensible fire safety policy is finally emerging from the highest levels of government.  Surely it is only a matter of time before this common sense approach to fire safety penetrates local levels of government.  We can only hope that it does so before our trees are destroyed.


* Dickinson, K.J.M. and Kirkpatrick, J.B., “The flammability and energy content of some important plant species and fuel components in the forests of southeastern Tasmania,” Journal of Biogeography, 1985, 12:  121-134.

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