Understanding Wildfire in the Chaparral of Southern California

Toyon, or California Holly (Heteromeles arbutifolia) re-sprouts following a fire.

Whether naturally ignited or caused by man, fires are an inevitable part of life in Southern California. California’s history is dotted with wildfires, many severe and engulfing large tracts of the landscape. The 2009 Santa Barbara Fire, October 2007 wildfires, Cedar Fire of 2003, and 1993 Malibu Fire, among others, are recent memories of particularly devastating events. Undoubtedly, more wildfires will occur in the future.

As with Earthquakes, the question is not if the next wildfire will occur, but when. Records indicate that infrequent wildfires are a natural part of the ecology of the region we live in, although the interval between fires has shortened in recent times. In the Chaparral biome, the scrubland community that encompasses much of the Coast Ranges and foothills of several interior mountain ranges, the average fire interval is thirty to forty years. In certain areas the typical interval between fires can drop as low as ten to fifteen years, and span up to one hundred years in others. It has been estimated that the fire regime was much less frequent before human settlement: between thirty and one hundred fifty years. It has only been within the past century that the interval has shortened dramatically.

The Chaparral is a biome characterized by extended hot, dry periods in the summer and mild, wet winters. In order to withstand the harsh, dry summer conditions, many plant species in the Chaparral have adapted drought-tolerant qualities. Small, waxy, and often oily leaves help these plants conserve water. Consequently, the oil in the leaves that help these plants survive drought also contributes to their flammability.

Certain habitat types such as redwood forests require periodic fire to maintain ecosystem health. In redwood forests, fairly frequent fire aids in nutrient cycling, clearing the understory, preparing the soil for seed germination, and controlling insect populations and disease.

Protected by their thick bark, which acts as a heat shield, redwood trees survive most fires. The Chaparral, on the other hand, does not rely on fire to remain healthy; instead, it is adapted to surviving and recovering from fairly infrequent fires. Chaparral plant species employ several strategies to recover from fires. Certain species germinate following a fire cue such as smoke, heat, charred wood, or chemical changes in the soil. Others, including Toyon, Scrub Oak, and Manzanita, re-sprout from their underground root systems, or burls, after a fire. Chamise, an attractive evergreen flowering shrub, re-sprouts and germinates following a fire. However, if fires occur too frequently (less than 10-15 years between fires), several plant species are eliminated from the Chaparral, and weedy, often invasive species take over. This often results in a conversion of Chaparral habitat to annual grassland.

The much sought-after, warm and sunny climate of Southern California has attracted people from all over to settle in this area. Enticed by the picturesque canyons of the Santa Monica Mountains and Santa Ynez Mountains, many have built large homes and estates in the midst of the Chaparral. The alluring qualities of the Chaparral ecoregion have in fact resulted in more and more people putting themselves and their properties in direct fire threat.

Chamise (Adenostoma fasciculatum), an evergreen shrub native to the Chaparral, re-srouts and germinates following a fire

Following a hot, dry summer, the notorious Santa Ana winds begin appearing in the fall. By this time, the parched landscape is especially vulnerable to fire. Lightning strikes are a natural ignition source, and tend to occur at higher frequencies in interior mountain ranges. Some of these lightning-induced fires continue slowly for months, or can be “held over” in logs (when the majority of the fire burns out). These fires can spread or be reignited with the arrival of the Santa Ana winds and the often associated low relative humidity. Human activity has led to several accidental as well as intentional fires, both of which can increase dramatically in size and spread quickly to other areas via the Santa Ana winds.

Although we cannot prevent a wildfire from occurring, there are steps we can take to protect our property and ourselves. Clearing brush within one hundred feet of a home that borders a natural area is one of the easiest preventative measures. This creates a buffer zone and allows fire fighters room to work when a wildfire is advancing. Any home within one mile of a natural area is defined as “in the ember zone”, and in danger of catching fire from windborne embers. Homes can be retrofitted with certain features to protect from embers. Materials that can present a hazard, such as woodpiles and propane tanks, should be kept away from the home, garage, or shed, and trees should not be near power lines. One of the best defenses is education and preparedness. The Ventura County Fire Department has a comprehensive and detailed wildfire action plan available on their website.

Works Cited:

-Chronology of Southern California Wildfires. University of California Agriculture and Natural Resources. http://ucanr.org/sites/SAFELandscapes/files/79451.pdf. Accessed 9/10/12.

-Fire and Nature. California Chaparral Institute. http://www.californiachaparral.com/firenature.html. Accessed 9/4/12.

-Fire in the Chaparral. Santa Barbara City College Biological Sciences. http://www.biosbcc.net/b100plant/htm/fire.htm. Accessed 9/4/12.

-Jebens, B. 1999. The Biogeography of Sequoia sempervirens. San Francisco State University Department of Geography.http://bss.sfsu.edu/holzman/courses/Fall99Projects/redwood.htm. Accessed 9/17/12.

-Keeley, J., and Fotheringham, C. 2000. Historic Fire Regime in Southern California Shrublands. Conservation Biology 15(6): pp 1536-1548.

-Philpot, C.W. 1979. Fire Dynamics in Chaparral. California-Nevada Wildlife Transactions. http://www.tws-west.org/transactions/Philpot.pdf. Accessed 9/5/12.

-Ready, Set, Go! Prepare Yourself and Your Home Against Wildfires. Ventura County Fire Department.

http://fire.countyofventura.org/Prevention/WildfirePreparedness/tabid/23 1/Default.aspx. Accessed 8/31/12.

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