The Oakland Hills Fire may have started on the ground, but the Eucalyptus trees surrounding people’s homes in the Oakland-Berkeley Hills helped it burn more and spread even further. The highly flammable non-native species accounted for 70 percent of the energy released through combustion of vegetation during the fire, according to the National Park Service. Twenty years after the fire, Eucalyptus trees still surround many homes and live in many of Oakland’s parks, while residents debate whether they should be saved or removed as fire hazards.
When Eucalyptus catch fire, said John Swanson, assistant fire chief for the East Bay Regional Parks District Fire Department, they can go through a process called “crowning out” in which a 100-foot tree can burst into flames within two to ten seconds. The tree can produce flames as tall as its height, so 100-foot trees are capable of creating 100-foot flames. “It’s like a major torch exploding—like a huge Roman candle going off,” Swanson said. “There’s a definite roaring noise and you get the sight of it and feel this strong wind that can just pull your hat right off your head.”
During the 1991 fire, the inland dry-hot Diablo Winds stirred up burning embers of leaf and bark on the ground—“like throwing matches out of your car window driving down the road,” Swanson said. According to Swanson, Eucalyptus are coated in a flammable and fragrant oil that collects at high concentrations at the base and junctions of the trees. So from the forest floor, the flames quickly spread to the trees’ stems, and eventually crowned out at the top of tree. Exploding embers were carried westward by winds that gusted up to 65 miles per hour, spreading the fire further. Many of the fiery particles then landed on wood shake roofs, setting hundreds of homes ablaze.
Following the 1991 fire, the East Bay Regional Parks District removed tens of thousands of Eucalyptus in Claremont Canyon, Sibley Preserve, Anthony Chabot Regional Park, and Tilden Park, Swanson said. Herbicides were used in all areas to remove the trees, and in some clear-cutting was also used—a process which involves uprooting of all the trees in one area with a tractor as well.
Because of public concern about herbicide use and tree removal, today the East Bay Regional Parks is making greater efforts to minimize the change to the landscape by using a “thinning out” process instead, said Swanson. According to Swanson, thinning out is the process of removing younger Eucalyptus trees that have trunks less than 12 inches in diameter and spacing the largest trees about 20 to 30 feet apart from one another in an effort to slow down the spread of a potential wildfire from tree to tree.
According to Swanson, spacing out the trees also provides areas of sunlight where native vegetation can re-grow in areas that were once shaded by the taller Eucalyptus canopies. At the same time, it doesn’t allow enough sunlight for undesirable weeds—like Poison Hemlock and Scotch Broom shrub—to spread. Swanson said that thanks to thinning out Eucalyptus, parks staffers have been seeing successful comebacks of native species like the native Coast Live Oak, Blue Oak, Valley Oak, and bay laurel and, along with them, a greater resurgence of native wildlife.
“Deer thrive on acorn mast produced by oaks. We also see, because of a wider spacing, other raptors and other birds using the area more,” Swanson said. “When there’s a really dense stand of trees the prey base do not enter the stand and even if they did raptors couldn’t enter them because the trees are so dense.”
Some environmental groups have expressed concern that overzealous vegetation clearing efforts—both by homeowners and through official channels—would threaten endangered hillside species, like the pallid manzanita. The pallid manzanita, found almost exclusively in Alameda and Contra Costa Counties, is a large shrub with reddish or grayish bark that produces white blossoms. “The city has been more aggressive in clearing any kind of vegetation after the fire, especially by roads, and it’s pushed residents to be clearing around their homes,” Ralph Kanz, conservation director for the Alameda Creeks Alliance. “Frankly not many people know what a pallid manzanita is and with all good intention they will go and cut own down without knowing it is a rare species with only 1,200 or 1,300 left in the world.”
Oakland resident Kanz said that removing the Eucalyptus would allow for more native species like the pallid manzanita to grow, but he is in favor of doing it in a gradual way, rather than clear-cutting. “Arguably the best way to do it would be to go through and take a few every couple of years out, and in 10 or 20 years you will have cleared out all the non-native and be back to natural restoration of the native environment,” Kanz said. “The reality is that it’s cost-ineffective. It’s much easier to go through and log all Eucalyptus trees. They tend to be in a cluster, especially in Claremont Canyon. You get them out of there and you’re done and working on restoring native species, if possible.”
The Hills Conservation Network is a small group of concerned Oakland Hills residents who do not want to see the Eucalyptus cut down. Director Dan Grassetti says the parks service should better manage the undergrowth beneath Eucalyptus, Monterey Pine, and acacia trees to prevent fires from spreading up the trees, but should not remove the trees.
Grassetti worries that the plan to eradicate Eucalyptus is about favoring native plants and not so much about fire safety. “For a number of us, we lost homes in the fire. One of us lost a family member, so we take this very seriously. With the 20th anniversary there has been a tendency to vilify these trees rather than deal with the real causes of the 1991 fire,” Grassetti said. He cites human error and technical problems—like narrow roads, radio failure, and the inability to shut off natural gas lines as factors that lead to the fire’s spread. “There are problems that could be fixed without cutting down millions of trees,” he said.
In May 2010 the Hills Conservation Network sued the East Bay Parks District over Measure CC, approved by voters in 2004, which called for wildfire mitigation work ranging from Miller Knox Regional Park to Chabot Regional Park, including Claremont Canyon. The Hills Conservation Network raised concerns about the greenhouse gas effect of removing so many trees, which absorb carbon, as well as the use of the herbicide Garlon 4 in removing Eucalyptus. “There are a lot of concerns about the health impact of Garlon reaching to the soil and getting into aqueducts,” Grassetti said.
But according to Swanson, herbicides are the only proven technique to effectively remove Eucalyptus, which can easily sprout back up from a base of a chopped-down or burnt tree. Swanson said that herbicides are only administered by licensed applicators on days when it is not raining, so as not to contaminate to waterways, and that the status of the treated trees is checked on an almost daily basis. The application process of Garlon 4 also involves applying an additional oil to help Garlon 4 be absorbed into the stump and the tree’s root system. A blue or green dye is also applied to show when the herbicide reaches the core of the stump, so that park staffers don’t apply more Garlon 4 than necessary, he said.
As for the greenhouse impact, Swanson says parks staffers leave standing the largest trees that often do the best job of storing carbon, and encourage the growth of other trees that serve the same purpose but are less flammable.
The lawsuit was settled in August 2011. “Of the 3,000 acres in which we were managing vegetation, there were about 250 acres that the lawsuit was over and on this we agreed to modify treatment on 75 acres, which are principally occupied by Eucalyptus,” Swanson said. “Modifications are miniscule, in my perspective, although they were agreed to by both parties and that’s very important.”
The Parks District is current moving ahead with plans to remove trees around Lake Chabot, Stonewall Road, and the Environmental Education Center in Tilden Park. Swanson said that due to the lawsuit they will be “thinning out” 60 acres of trees, rather than removing all of them. According to Swanson, this modification will not reduce the plan’s fire prevention effectiveness. The plan will continue to be discussed this year and removal is set to begin in 2012.
Swanson said that thinning out highly flammable trees is the best method to prevent a future fire from spreading as quickly as the 1991 fire. And as he points out, the question is not if another wildfire will happen, but when. “We’ve known for a couple of hundred years that what influences fire management is fuels, weather, and topography. We can’t do much about the weather and the topography is not changing much at all. The only factor of the triad we can influence are the fuels,” Swanson said. “This area of the Oakland Hills has a history of burning every 15 to 25 years and the last one was in 1991. It would not be a surprise to anyone that there would be one in the coming future.”