Physical Dynamics

Fire in the Chaparral

Chaparral Ecology

The dominant native plant community in the Oakland-Berkeley Hills is called chaparral. Chaparral is the name given to this plant community in California. Generically, the ecosystem is know as Mediterranean scrub. The intensity of the Oakland-Berkeley Hills fire can partly be contributed to this native plant community.

The chaparral scrub ecosystem is a biological community of plants typical of vegetation in the five areas of the world with a Mediterranean climate. These areas are located on continents that are between 30° and 45° North or South latitudes and include California, central Chile, the Cape region of South Africa, southwestern Australia, and the Mediterranean area itself. The Mediterranean climate is characterized by hot, dry summers, and mild, rainy winters. These areas usually receive between 36 – 64 centimeters of rain per year. Day time temperatures during the summer can reach 43° C (115° F). During the winter, temperatures can drop below freezing.

    The lower elevation chaparral plant community is usually found between elevations of 350 and 900 meters and may grow alongside or into the coastal sage scrub ecosystem. The plants in chaparral ecosystems are adapted to surviving in hot, dry conditions. Whereas coastal sage scrub plants are drought deciduous and, therefore, lose their large, soft leaves in the summer, chaparral plants keep their leaves all year. During the hot, dry summers, many of the chaparral plants have hard, waxy leaves, which help the plants conserve moisture. In the winter, soft leaves replace the drought-adapted summer leaves.

    Common plants of the chaparral ecosystem include toyon (Heteromeles arbutifolia), sugarbush (Rhus ovata), yucca (Yucca spp.), coffeeberry (Rhamnus californica), California buckwheat (Eriogonum fasciculatum), scrub oak (Quercus dumosa), mountain mahogany (Cercocarpus montanus), and chamise (Adenstoma fasciculatum). Higher elevation chaparral is dominated by manzanita (Arctostaphylus spp.) and ceonothus (ceonothus spp.).

Chaparral Fire Cycle

Historically, fire swept through chaparral areas approximately every 20 to 30 years. Not only are most of the chaparral plants well adapted to resisting fire, but some of the species, such as laurel sumac (Rhus laurina), rely on fire for their persistence or rejuvenation. Some of the plants, such as toyon (Heteromeles arbutifolia), chamise (Adenstoma fasciculatum), and laurel sumac (Rhus laurina), have basal burls or root crowns from which branches resprout after a fire. Other chaparral plants have a seed bank underground in which seeds are deposited during non-fire years. After a fire, the parent plant is burned which results in the seeds receiving the water, space, light, and nutrients that they need in order to germinate and grow. Laurel sumac (Rhus laurina) seeds are thought to germinate only after being exposed to the heat from a fire (Vogl 1998).

Example of shrubs with features that help plants adapt to low-intensity fires:

Chamise (Adenstoma fasciculatum)	stump sprouting
Manzanita (Arctostaphylus spp.) Ceonothus (Ceonothus spp.)	heavy seed production in early stages
Manzanita (Arctostaphylus spp.)	reproduction by layering
Scrub Oak (Quercus dumosa) Laurel sumac (Rhus laurina)	basal spouting

Chaparral was the dominant native vegetation covering the hills where the Oakland-Berkeley fire occurred. To date, the cause of the fire has still not yet been determined. There is also still debate as to whether fire suppression is a key factor in the intensity of chaparral fires. In the early 1900's, fire suppression was the primary policy for fire prevention in the United States. This policy led to a large accumulation of fuels in America's wildlands. This fuel build-up is blamed for the intense wildfires occurring today. With each year that wildfires were suppressed, the situation worsened (Biswell 1989).

Although the Oakland-Berkeley fire has been attributed to the suppression of fires, new studies have argued that fire suppression is not a definitive contributing factor to the intensity of chaparral fires in general. Fire suppression has been effectively linked to fire intensity in forest ecosystems but this may not be the case according to new studies put out by the Western Ecological Research Center.

A study by the Western Ecological Research Center states that historically, the natural fire regime in Southern California shrublands, like the chaparral, included large high intensity fires and was not different from the contemporary regime (Keeley 2000). In a similar study, Keeley states that large fires are not dependent upon old age classes of fuels, but that the expansion of the urban-wild interface is the key factor for wildland fire destruction (Keeley 1999).

Oakland-Berkeley Firestorm

The Fire

    The Oakland-Berkeley Hills firestorm was the result of a flare up from a previously controlled fire which had started the Saturday prior. Although the fire had been suppressed, crews were still working to put out hot spots. When a firefighter’s digging threw sparks into an area of dry brush, the area exploded into flames.

    In order to better understand the terms used to describe the Oakland-Berkeley Hills fire, an understanding of fire terms and definitions is needed. Below are tables describing fire terms and definitions that pertain to the Oakland-Berkeley Hills fire.

FIRE TYPE:                                            DEFINITION

Brush fire	A fire burning in vegetation that is predominantly shrubs, brush, and scrub growth.
Crown fire	A fire that advances from top to top of trees or shrubs more or less independent of a surface fire.
Uncontrolled fire	Any fire which threatens to destroy life, property, or natural resources, and (a) is not burning within the confines of firebreaks, or (b) is burning with such intensity that it could not be readily extinguished with ordinary, commonly available tools.
Wildfire	An unplanned and uncontrolled fire spreading through vegetative fuels, at times involving structures.
Wildland fire	Any fire occurring on the wildlands, regardless of ignition source, damages or benefits.

FIRE TERM: DEFINITION

Conflagration	A raging, destructive fire. Often used to describe a fire burning under extreme fire weather. The term is also used when a wildland fire burns into a wildland/urban interface, destroying many structures.
Defensible space	An area, typically a width of 10 meters or more, between an improved property and a potential wildfire where the combusitbles have been removed or modified.
Firestorm	Violent convection caused by a large continuous area of intense fire. Often characterized by destructively violent surface indrafts, near and beyond the perimeter, and sometimes by tornado-like whirls.
Fire whirl	Spinning vortex column of ascending hot air and gases rising from a fire and carrying aloft smoke, debris, and flame. Fire whirls range in size from less than one meter to over 150 meters in diameter. Large fire whirls have the intensity of a small tornado.
I-zone	The line, area, or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels.
Wildland/Urban Interface	Any area where wildland fuels threaten to ignite combustible homes and structures

Both tables are adapted from the FIREWISE glossary.
URL: http://www.firewise.org/glossary/fwglossary.pdf

   During the first hour, the spread of the fire was unprecedented for an urban conflagration, including other wildland-interface fires. In fact the Federal Emergency Management Agency characterized it as the “ultimate” interface fire (Federal Emergency Management Agency 65). The fire began in a developed area and within 15 minutes of ignition, the fire had spread to the first structure. With strong winds, favorable topography and a dry fuel load the fire spread extremely fast. In those first 15 minutes the fire developed into a firestorm (National Fire Protection Association, 1992).

    Prior to reaching a firestorm level, a fire passes through another level. With the right wind and temperature, the fire develops into a conflagration. As the conflagration intensifies, it becomes a firestorm. The Oakland-Berkeley fire is commonly referred to as a conflagration, but at certain times and locations the fire intensified, such that, it became a raging firestorm (Federal Emergency Management Agency 66). Firestorms can create their own weather when the heat and motion of a fire builds up. These storms pull air into the fire and, similar to a thunderstorm, the storm feeds itself (National Fire Protection Association, 1992). This type of activity can also cause long-distance spotting, another characteristic of the Oakland-Berkeley Fire.

    Spotting occurs when brands or embers of vegetation are taken by the wind to another location and a new blaze erupts. Spotting contributed greatly to the spread of this fire and was a major reason crews could not contain the fire initially (National Fire Protection Association, 1992). Due to spotting, spot fires occurred almost a half a mile from the front of the fire. In the Oakland-Berkeley fire, spotting started fires in wildland areas and on top of structures (Federal Emergency Management Agency 15).

    The fire burned with great speed and intensity and the fire crews showed little sign of control. Cooler temperatures and a decrease in the wind slowed the fire naturally however, allowing the fire fighters to eventually contain the blaze. The exact cause of the fire still has not been determined (Federal Emergency Management Agency 16).

Click Here for Maps of Burn Area:
Extent of Burn Area
How the Fire Spread

Contributing Factors

Climate

There are three climatic factors that contributed to the Oakland-Berkeley fire. These conditions are low relative humidity, drought and Diablo winds. Temperature and relative humidity are inversely related. As the relative humidity falls, the temperature rises and vice versa. This inverse relationship had an effect on the fuel load on the ground. As the relative humidity fell and temperature rose, the fuel became drier and more flammable. Fuels with 20% moisture can readily catch fire and light fuels with 2% moisture can also ignite easily. These 2% fuels can burn like gasoline. The relative humidity on the day of the Oakland-Berkeley Hills fire was 16% and the temperature was 92o F (National Fire Protection Association, 1992).

   From 1986 – 1991 much of California experienced a significant drought. The drought also contributed to the lack of moisture and fuel load build up in the Oakland-Berkeley area. Accompanying the drought was an unusual freeze the December prior to the fire. This caused leaves on many eucalyptus trees in the area to either die or drop large amounts of bark on the ground. The litter caused by the dry leaves combined with the litter from the severe freeze added to the massive fuel load for the fire (Federal Emergency Management Agency 8).

    The most significant climatic factor was the Diablo winds that fueled the fire. Diablo winds occur when an inversion layer builds up in the Bay Area and forces air that is moving west from the San Joaquin Valley to speed up down the leeward side of the hills. The air then increases in temperature as it speeds up (National Fire Protection Association, 1992). According to the Federal Emergency Management Agency, most of the major wildland fires in California have occurred during wind conditions such as this. These winds caused the fire to become unmanageable. The erratic and turbulent pattern of the wind made it impossible for fire fighters to contain the blaze.

Vegetation

The Oakland-Berkeley Hills fire is classified as a wildland-urban interface fire. In his book World Fire (pg. 276), Stephen Pyne says, “build a city out of forest materials and it will burn like a forest.” In the Oakland-Berkeley area the fuel supply was an intimate mixture of vegetation surrounding human-made structures. It was the extreme example of a wildland-urban interface zone (Federal Emergency Management Agency 68).

   Not only were the buildings built right next to the wildland, but the materials used to build most of the structures acted as fuel for the fire. Most of the buildings had wood shingles. Virtually every interface fire has spread faster than it might have otherwise because of the use of wood shingles (National Fire Protection Association, 1992). The structures themselves were also enveloped with vegetation. The residents allowed for no defensible space between their homes and the vegetation around them. In some instances vegetation grew underneath over-hanging buildings. When the fire came through, it raced under the structures and completely overtook them (Federal Emergency Management Agency 15).

    Other human factors which contributed to the fire were the narrow roads and low water supply. Narrow switchback roads surrounded the canyon. Emergency vehicles were not able either to make the hairpin turns or climb the steep grade. The water supply in the area was very limited. Water tanks at different elevations were dependent upon electric pumps. This tank and pump system supplied not only the residential water but also the hydrants (Federal Emergency Management Agency 10).

Wildland-Urban Interface

   The role in which vegetation played in the fire varied among the species, vegetative type, and amount of vegetative land cover. The west face of the hills received more moisture than the east. This moisture encouraged the growth of trees and brush. The types of brush and trees on the Westside burned with great intensity. They spread the fire quickly and released large amounts of thermal energy (Federal Emergency Management Agency 9).

    The types of vegetation present were grassland, brushland, mixed broadleaf and eucalyptus and pine groves (Federal Emergency Management Agency 13). Efforts to remove the vegetative debris in the area were stopped by fiscal cutbacks. This allowed for a significant fuel build up. In normal conditions, the grassland would have contained the lowest fuel load. Due to this build up however, the grassland contained unusual amounts of fuel. Brushland covered most of the fire area, while the mixed broadleaf forest was not significant in the fuel load (Federal Emergency Management Agency 13).

    What was significant was the role that non-native plant species played in the fuel load and intensity of the fire. Eucalyptus (Eucalyptus spp.) groves intermixed with Monterey pine (Pinus radiata) covered much of the hills. Classified as a pyrophyte, eucalyptus was imported and planted to replace natives trees used for development in the late 1800’s and early 1900’s. The species was touted as a great hardwood replacement for the removed native oaks. By 1910 however, people began to realize that the trees were useless except for as a wind break (Pyne 1982). What were left behind were groves of closely stocked trees that were explosive in fires.