More Fire Factors: Fire Ladders and Embers

Recently, a local news program broadcast an interview about the legal suit filed by the Hills Conservation Network (HCN) against the “Wildfire Hazard Reduction and Resource Management Plan” of the East Bay Regional Park District (EBRPD).  Although both HCN and EBRPD are committed to reducing fire hazard, they disagree about how to achieve that goal.  The spokesperson for HCN said there is no “scientific or factual evidence” that eliminating the canopy of non-native trees will reduce fire hazard.  The spokesperson for EBRPD said the trees will be removed because they “burn intensely” and “loft embers into the wind, causing spot fires downwind” when their crowns begin to burn.  

Is there scientific or factual evidence to support the claims of EBRPD?  Are non-native trees more likely to burn than native trees and if so do they burn more intensely than native trees?  Are non-native trees more likely to loft embers than native trees?  This post will document the answers to these questions:  NO, NO, and NO!

When fire spreads on the ground, through fine fuels such as grass, it bypasses trees unless there is a fire ladder to their canopy.  The fire ladder is composed of low branches that extend from the ground, into the canopy of the tree.  Tall eucalyptus trees usually do not provide such a fire ladder to their canopy.

We see a few of the eucalypts in the distance that EBRPD intends to destroy in Lake Chabot park. We notice that they are very tall and there is no fuel ladder to their canopy. In the foreground, on the right, we see some of the native bay laurels that EBPRD plans as replacements for the eucalypts. We notice that the bays are close to the road and that they grow to the ground, providing a fuel ladder to adjacent vegetation.

When tall trees, such as eucalypts have a fire ladder to their canopy, their lower limbs can be removed without harming the tree.  This method of reducing fire hazard has been used effectively in the Mountain View Cemetery in Oakland.  Obviously, this method of reducing fire hazard is cheaper and less destructive than destroying the trees and then killing their roots with poison.  This was one of the strategies suggested by the Hills Conservation Network during negotiations with EBRPD before they filed suit after negotiations failed.

The fire ladders on these eucalypts have been removed in the Mountain View Cemetery.

In a wind-driven firestorm the fire may rapidly spread high above the ground.  In that case, how likely is the canopy of eucalypts to ignite compared to other trees?  The firestorm of 1991 in the Oakland/Berkeley hills is an example of such a fire.  In our posts “FIRE!!! The Cover Story” and “The Power of a Legend” we have reviewed two official documents and one book about the 1991 fire which contain no evidence that eucalypts were responsible for that fire.   

Please click here to see a picture of an entire neighborhood of homes destroyed by a wildfire in the Scripps Ranch in 2003..  The burned homes are entirely surrounded by tall eucalyptus trees that are untouched by the fire.  Despite this obvious evidence that the eucalypts were blameless in this fire, native plant advocates seized upon this fire to demand that the eucalypts be destroyed.  The residents of Scripps Ranch fought back and for the moment, they have succeeded in preventing the destruction of their eucalyptus forest. 

The National Park Service is one of many managers of public lands that are engaged in massive restorations of native plants that frequently result in the destruction of non-native trees.  And as most managers of public lands, it attempts to justify the destruction of the trees by claiming that they are a fire hazard.  Reading the fine print of its literature about eucalyptus,  we find that their claims are not supported by the evidence.  Studying the table comparing the fuel loads of eucalyptus with native oaks and bays, we find that the table has been carefully constructed to support their case.  If logs–which would take 1,000 hours to ignite*–are removed from this table, the available fuel load of eucalyptus is not greater than that of native oaks.  Also, deeply embedded in the fine print, you find that the park service admits that the leaves of the eucalyptus are resistant to fire (“The live foliage [of the eucalypts] proved fire resistant, so a potentially catastrophic crown fire was avoided.”) 

We conclude that all evidence from past fires indicates that eucalypts are unlikely to ignite in a wildfire.  If they don’t ignite, they obviously will not “loft embers” to spread the fire.  The final question is, in the unlikely event that there is a crown fire in eucalyptus, how likely is it that embers will be produced that spread the fire downwind?  Although we don’t know the answer to that question, we have both scientific and experiential evidence that native trees are also capable of producing embers.

In “Ignition Behavior of Live California Chaparral Leaves,”  Steven Smith, Joshua Engstrom, Jordan Butler, Thomas Fletcher (Brigham Young University, Provo, Utah) and David Wiese (USDA, Forest Service) report the results of laboratory tests on four species of native plants and trees, including oaks.  They find that both native chamise and oaks loft embers absent any wind.  In the case of oaks, they report that “Many of the oak leaves had sharp points (i.e., spines) around the outer edge.  The oak leaves would ignite at these points, sometimes accompanied by small explosions of the points that led to the ejection of small brands.” 

The Marin Independent Journal in its report of the Angel Island Fire of 2008 tells us that embers from the burning oaks were responsible for nearly igniting the historic buildings on the island:  “’All the oaks up there were burning,” said the 28-year veteran of the department. “It was an ember shower that just rained on the entire building, and all the vegetation around us was burning.’”  As we reported in our post about the Angel Island Fire, most of the eucalyptus had been removed from the island about 12 years before the fire in 2008.  The fire stopped at the edge of the remaining 6 acres of eucalyptus.

There is overwhelming evidence that eucalyptus is not more flammable than native trees and has not played a role in the many wildfires in California.  The myth that eucalypts are responsible for wildfires is propagated by native plant advocates who use the fear of fire to justify the destruction of eucalypts.  Those who are willing to look closely at the evidence will see through this carefully constructed myth to the reality that destroying non-native trees will not reduce fire hazard.

*For a technical explanation of timelag, we quote from Sugihara’s Fire in California Ecosystems:  “The proportion of a fuel particle that contains moisture is a primary determinant of fire behavior…Timelag is the amount of time necessary for a fuel component to reach 63% of its equilibrium moisture content at a given temperature and relative humidity……1,000-hour fuels reflect seasonal changes in moisture.  The firewood analogy applies here as well.  Your large logs would take several months to dry if left out in the rain for the winter, yet kindling, if brought inside, would dry in a few hours.”