2012-10-04 / Columns
Intervals between wildfires are shorter
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.
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 coastal ranges and foothills of several interior mountain ranges, the average fire interval is 30 to 40 years. In certain areas the typical interval between fires can drop as low as 10 to 15 years and span up to 100 in others.
It has been estimated that the fire regime was much less frequent before human settlement—between 30 and 150 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. The oil in the leaves that helps 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 after a fire cue such as smoke, heat, charred wood or chemical changes in the soil. Others, including toyon, scrub oak and manzanita, resprout from their underground root systems, or burls, after a fire. Chamise, an attractive evergreen flowering shrub, resprouts and germinates after a fire.
However, if fires occur too frequently—less than 10 to 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 can- yons 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 eco region have, in fact, resulted in more and more people putting themselves and their properties in direct fire threat.
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.
Although we cannot always prevent a wildfire from occurring, we can take steps to protect our property and ourselves. Clearing brush within 100 feet of a home that borders a natural area is one of the easiest preventive measures.
Any home within one mile of a natural area is in danger of catching fire from wind-borne embers. Homes can be fitted with certain features to protect from embers.
One of the best defenses is education and preparedness. The Ventura County Fire Department has a comprehensive and detailed wildfire action plan available on its website.
Madison Most works with the Agoura Hills-based Havasi Wilderness Foundation. Visit www.havasiwf.org. This article is reprinted with permission.