Many of us who love the chaparral often find ourselves involved in conversations where we hear the tired, old paradigm that chaparral "needs" to burn, that large chaparral fires are "unnatural," and that large fires can be prevented if we could just burn off large patches of chaparral on a regular basis (known as the Baja/Southern California fire mosaic hypothesis). Below is an example cited by the WildlandFireLessonsLearnedCenter (a consortium of fire agencies in the United States) that adds to the growing list of scientists and firefighters who challenge this hypothesis. This is a powerful reference to cite in our continuing efforts to help spread the truth about the chaparral:
"For decades, land-management policy in the region has been based on the idea that landscape-level fuel management can ultimately limit the size of these massive fires. A growing body of research has called that paradigm into question, and the results have big implications for land and fire management."
A sample of some of the research referenced above:
“Early studies characterizing differences in fire size north and south of the United States border invoked fire suppression as the primary explanation for these patterns (Minnich 1983, Minnich and Chou 1997). However, recent analyses show no evidence that 20th-century fire suppression has diminished fire activity on these landscapes.”
“The fire regime in this region is dominated by human-caused ignitions, and fire suppression has played a critical role in preventing the ever increasing anthropogenic ignitions from driving the system wildly outside the historical fire return interval. Because the net result has been relatively little change in overall fire regimes, there has not been fuel accumulation in excess of the historical range of variability, and as a result, fuel accumulation or changes in fuel continuity do not explain wildfire patterns.”
It is a common misconception that wildlands are unnaturally "overgrown" with a half-century's worth of highly combustible shrubs and small trees because of successful firefighting efforts since the 1950s. In addition, environmental groups and government regulations are often blamed for preventing thinning and prescribed burns to help alleviate this hypothesized buildup. Such oversimplifications of a very complex problem are not helpful in finding solutions. They also have nothing to do with California's most characteristic wildland, the chaparral.
It does appear that some, but certainly not all, of our nation's forests have "unnatural fuel loads," a consequence of past logging and grazing practices as well as fire suppression efforts. However, without understanding the dramatic differences between forests and the chaparral-covered hillsides in California, some are promoting a single solution to deal with the threat of wildfire everywhere. This will not only lead to a waste of tax-payer money and damage valuable natural resources, but will do little to prevent the kind of firestorms Southern California continually experiences.
The notion of performing prescribed burns to create different-aged patches of backcountry chaparral as a way to prevent wildfires is the basic tenet of the Baja-Southern California fire mosaic hypothesis first elaborated by Richard Minnich of UC Riverside in 1983. The hypothesis suggests that the size of wildfires north of the Mexican-Californian border are larger than those in Baja because of dramatically different fire management strategies.
According to the hypothesis, a century of fire suppression in Southern California has caused an "unnatural" accumulation of "fuel" that has consequently led to large, destructive chaparral fires. A map showing small fire perimeters south of the border and large ones to the north is often used as supporting evidence.
At first, the map is convincing and the logic appears reasonable. However, after being tested by a diversified group of scientists over the past ten years, the fire mosaic hypothesis fails for a simple reason. It ignores a significant number of important variables.
Scientifically, the comparison between southern California and Baja is problematic because of variations between the two regions as well as how the data was collected. Baja is much drier, has different soil types, and is not subject to the same Santa Ana wind conditions as Southern California. In addition, the Baja landscape has been heavily damaged by ranchers who consistently burn back natural vegetation in order to increase grasslands. It is difficult to find an area south of the border that does not show signs of grazing activity.
The other important factor to consider in the Baja comparison is how fire perimeters were determined. In California, offical fire perimeter data from state agencies was used in the study. Such detailed records do not exist in Baja. Instead, fire perimeters in Baja were estimated by using LANDSTAT satellite images and subjective, on the ground measurements. These create two completely different data sets which are consequently difficult to use for any comparative analysis. In addition, smaller fires that were extinguished by firefighters in California before they became large ones were left out of Baja/California comparisons.
Extensive research by J.E. Keeley and C.J. Fotheringham has shown that burn patterns have not changed significantly in Southern California since 1878. The California Statewide Fire History Database clearly indicates that since 1910, the mean size of fires in San Luis Obispo, Santa Barbara, Ventura, Los Angeles, San Bernardino, Riverside and San Diego counties has remained constant. The timing of fires is equally consistent, with most igniting June through November with September representing the most flammable period (reference #1 below).
In a study by S.A. Mensing and others, seabed charcoal deposits off the coast of Santa Barbara County have shown that the frequency of large, Santa Ana driven fires has not changed over the past 500 years (reference #2). Similar results are produced even when comparing years before and after 1950 when advanced fire suppression technology was developed and utilized on a massive scale. The only important change revealed by these studies has been an increase in fire frequency during modern times, not a decrease.
One of the more indefensible assumptions of the Baja hypothesis is that large fires never existed in Southen California prior to the influence of fire suppression activitives (usually identified as starting after 1910) - presumably because "mixed-aged mosaics" would naturally prevent the spread of fire. A 2009 paper by Keeley and Zedler has put to rest the false claim that large fires did not occur prior to 1910. And while fires will sometimes stop in younger vegetation, firefighter experience refutes the notion that mosaics can be depended upon to naturally constrain a fire, especially during extreme weather conditions (see Halsey, et al. 2009).
Infrequent fire in chaparral is a natural, unpreventable event. Despite all our efforts to control them, large chaparral fires have continued unabated since our arrival in California. The assumption that old stands with an "unnatural accumulation of old brush" encourage fires to spread and become more dangerous is inaccurate. Studies by M. Moritz and others have shown that fuel age does not significantly affect the probability of burning. These findings analyzed some of the same data used in the Baja Model (reference #3).
P. Zedler examined the same question through mathematical modeling and arrived at the same conclusion. Under Santa Ana conditions, fire rapidly sweeps through all chaparral stands, regardless of age. Once the flames start, everything can burn (see reference #4).
Years of fire suppression have not been successful in excluding fire in chaparral landscapes. Relying on non-strategic prescribed burning in the backcountry in order to create mosaics of "mixed-aged stands" will likely prove to be equally frustrating (reference #5).
What is the solution then?
The first task is to objectively examine the research. Unfortunately, fire management has become increasingly politicized. Instead of scientifically analyzing the data, some have the tendency to personalize the discussion and assign names or labels to particular positions. This is not only counterproductive, but confuses the public about how science is supposed to work. There are no positions. There are only collections of observations and facts with conclusions being derived from such data. By looking at the methods, the scientific design, and underlying assumptions, it becomes relatively easy to determine whether or not ignored variables or biases have influenced the results.
Another challenge is to implement fire-safe community planning and long term education programs to help maintain the public's fire vigilance. Unfortunately, developers will continue to be allowed to push farther into the backcountry as the population continues to grow. Homeowners will become complacent again as time goes on and allow fire-prone materials to slowly accumulate around their homes.
The best way to reduce the risk of wildfire is to allocate scarce fire management resources at the wildland-urban interface (called the WUI - where homes meet wildland areas) and enforce fire-safe building/planning codes. This includes new regulations encouraging retrofitting older, flammable homes with such things as ember-resistent vents and non-combustible roofing, emphasizing strategic (and rational) fuel management directly around communities, and restricting development in extremely high fire hazard areas.
Below are seven seminal papers addressing Baja California fuel mosaic hypothesis. The original paper describing the hypothesis in 1983 is listed first. Then a detailed analysis with responses published in the December 2001 issue of Conservation Biology follow. The final three papers demonstrate that large fires are a natural part of Southern California's landscape (and not an artifact of past fire suppression).
When discussing an idea, it is usually best to ignore personalities and stick to the data. This is how science is supposed to work.
Well, there comes a time when a viewpoint becomes so disconnected from the accepted body of scientific knowledge that it distracts from constructive dialogue. At times it can even delay or alter important policy decisions. Such delays create negative consequences for future generations by creating unproductive, "my expert" vs. "your expert" politicized debates in the press. Although each of the experts are assumed to have equally valid viewpoints supported by objective data, one or more are often only interested in promoting their own individual cause or agenda regardless of the facts. Sometimes these causes are pushed by narrow, special interests in a consciously dishonest manner. Or alternatively, the promoter honestly believes his or her own view of the world so strongly that he or she is unable to objectively evaluate contrary data. Instead, everything is seen in light of a favored theory and seemingly obvious contradictions are dismissed (often unconsciously). Consequently, when the cause is continually taken to the popular media instead of being objectively discussed within the framework of science, it becomes impossible to ignore the messenger. This is why a number of well-know fire scientists spoke out in 2006 about Thomas Bonnicksen who was disregarding scientific fact to promote politically motivated policies dealing with wildland fire.
The June 16, 2007, San Bernardino County Sun news article "Forests Need to Burn" was a signal to many of us in the wildland fire and fire science communities that the time had come to directly address individuals who continually promote incorrect and potentially damaging notions about wildland fire management.
In summary:
In their insistence on focusing on only one variable (chaparral age), promoters of the Baja/Southern California fire moasic hypothesis do not appear to have a clear understanding of wildland fire. Wildland fire risk in California is not the fault of the fire service, or the result of old stands of chaparral, it is an inherent part of the landscape. Laying more fire on the ground on a landscape level or allowing fires to run is unacceptable in Southern California for both safety and ecological reasons. The fire mosaic hypothesis described in 1983 and elaborated further in 1997 is not applicable to the region. The best and most efficient way to reduce wildland fire risk is through proper community design, fire-safe building construction, adequate vegetation management around structures and strategically placed fuel treatment projects.