By Mary McAllister
FEMA’s recent decision to cancel grants to UC Berkeley and the city of Oakland to destroy tens of thousands of trees was a fitting commemoration of the 25th anniversary of the 1991 fire in the East Bay Hills.
FEMA’s decision reminds us that the 1991 fire was not caused by trees and that destroying them would not reduce fire hazards. Like most fires in California, the 1991 Oakland fire started in grasses, the very sort of vegetation that would colonize the hills if the trees were destroyed.
In 1908, the University of California funded a study that concluded that eucalyptus trees help reduce the risk of fire. It specifically noted that the denser the trees, the lower the risk. It cautioned against thinning the trees, noting that when they are thinned, “their crowns are unable to form a canopy that will shade the ground enough” to stop the spread of highly flammable grasses. Shade is the most benign method of controlling weeds, far less damaging to the environment than the herbicides that are commonly used.
The U.S. Forest Service evaluation of the FEMA projects said that the resulting landscape would be more flammable than the existing landscape: “Removal of the eucalyptus overstory would reduce the amount of shading on surface fuels, increase the wind speeds to the forest floor, reduce the relative humidity at the forest floor, increase the fuel temperature and reduce fuel moisture. These factors may increase the probability of ignition over current conditions.”
The U.S. Fire Administration Technical Report on the 1991 fire concluded that removal of the trees would lead to growth of highly flammable brush species, noting that “brush fuel types played a significant role in the progression of the fire” and that brushland made up “a large portion of the available fuel.”
A Forest Service fire scientist studied wildfires in which homes were destroyed but eucalyptus trees surrounding the homes were unconsumed by the fire and concluded that, “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 Wildland/Urban fire disasters because the problem was inappropriately defined as a eucalyptus vegetation problem and not a home ignition-home ignition zone problem.”
Scientists at the U.S. Forest Service fire science laboratory in Montana advise us to focus on methods of fire hazard mitigation that are appropriate in the Wildland-Urban Interface (WUI): “ … 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 characteristics and its immediate surroundings principally determine the WUI ignition potential during extreme wildfire behavior.”
Let’s commemorate the 1991 fire by cleaning up flammable debris and trimming shrubbery around our homes, cleaning our roof gutters, putting screens on the vents to our attics and replacing our wooden roofs. There are many useful things we can do to keep our community safe. Destroying trees is not one of them.
Mary McAllister is an Oakland resident and the webmaster of the Million Trees blog (milliontrees.me).