I was asked a surprising question while at the 16,800 acre Horse fire in eastern San Diego County (July 2006). In a conversation with several people about how another fire near the desert town of Yucca Valley had been fueled primarily by alien grasses, I expressed concern over the transformation of many native landscapes to non-native grasslands, a process also known as type-conversion. Afterwards I was asked, “Has type-conversion of chaparral really been proven to occur?”
I pointed up to a nearby hillside covered with weeds. “It’s happening up there,” I said. “Areas that have been repeatedly burned lose nearly all their native species and end up a monoculture of alien, weedy annuals; lots of fine fuels ready to carry a fire nearly every year. It becomes a self-perpetuating process.”
Although I knew the question was a sincere one, it was also very troubling. How could such a significant threat to native landscapes not be as well known and understood as other environmental problems?
Poor attention by the press and lack of awareness of the issue by traditional conservation organizations provides part of the answer. But I fear another reason why the threat of type-conversion is grossly underestimated is due to a select group of individuals who have chosen to dismiss the problem in favor of promoting favored theories and specialized agendas. A helpful way to think of these individuals is as “denialists.” It is important to note, however, that denialists are not the same as skeptics. Skepticism is a crucial and healthy part of analyzing theories and ideas. Denialists, on the other hand, confuse the process by either consciously or unconsciously denying verifiable scientific truth because it does not fit into their personal view of the world.
The problem with denialists is that regardless of the quality of their data, they are frequently viewed as equals to others who actually know what they are talking about. Denialists use this to their advantage whenever their favored theory is challenged. The resulting “debate” is seen by the public as simply one of expert vs. expert without any objective analysis of what is being said. The media fosters this approach because it provides personal drama to what the public might otherwise view as boring science.
Classic forums for denialists are government hearings held by federal or state legislative committees. One would think a balanced group of individuals would be called to testify in order to inform those listening. However, the participants of these hearings are often selected by the majority party in order to slant the discussion in one direction or the other.
Why would anyone want to ignore or minimize the threat of type-conversion in native ecosystems due to increased fire frequency? Wildfire and how to deal with it is fraught with politics, economics, and strong opinions. Any issue complicating land management decisions under such conditions is hotly debated and prone to denialist rhetoric. The “wildflower/grass controversy” revolving around the Sawtooth Complex fire near Yucca Valley may provide one such example.
It was reported in the July 13, 2006 Desert Sun newspaper that a geographer from the University of California said native wildflowers carried the fire’s sweep across the desert. In addition, he predicted the area would not burn again for “another century or so, depending on heavy rainfall.”
These statements led to a whirlwind of emails and conversations over the following week because those familiar with the area knew that alien weeds, mainly cheatgrass and red brome, had created a dangerous fuel bed throughout the desert. Attributing the fire to native wildflowers was not only contrary to what was known, but it fostered two unfortunate misconceptions; the fire was an unusual event caused by record rainfall and that native plants were once again the responsible agents of a destructive inferno. The geographer’s statements were so unbelievable to some that they questioned the accuracy of the quotes. However, both the accuracy and emphasis of the quotes were later confirmed by the reporter and the geographer himself.
After assembling information from multiple on-site visits, interviewing or hearing from numerous individuals who were either on the fire or have an intimate knowledge of the area (including local ecologists, land managers, and firefighters), and studying official post-fire reports from the US Forest Service and the California Department of Forestry, there is no question that the geographer’s perceptions and predictions were wrong.
Post-fire inspections of unburned islands within the fire perimeter (caused by fire suppression activity or topological features) revealed the remains of very few native wildflowers. In fact, it was difficult to find any at all in most locations. Instead, the overwhelming fine fuel component was cheatgrass and red brome. Fuel conditions within the burned area prior to the fire were similar based on interviews with local residents and scientists. Native wildflowers were not responsible for carrying the flames.
The only way the low desert portion of the Sawtooth Complex fire could have carried the way it did was because alien grasses created a continuous fine fuel bed in many areas, with especially dense concentrations under trees and shrubs. Coupled with high winds and record temperatures, this unnatural fuel bed facilitated the rapid movement of embers and heat, quickly igniting one shrub after another. Although it is extremely difficult to know exactly what the historical fire regime was in such desert regions, the scientific consensus is that desert fires in the past were limited in size because there was not a continuous fuel bed to carry the flames.
The suggestion that the fire was only made possible by heavy rains stimulating abundant native wildflower growth fails to consider the flammable mix of invasive species and how they have altered both fire behavior and frequency (one wonders how the alien grasses responded to all the extra rain!). Desert fires are becoming more common and are increasing in size not because of increased rainfall, but because of increased volumes of weedy annuals.
Why would anyone ignore the impact of alien weeds on fire frequency and focus instead on native wildflowers?...
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Additional information on Sahara mustard, an alien weed having serious impacts in the Sonoran Desert, can be found at the Arizona-Sonoran Desert Musuem.
Some excellent references:
1. Haines, DF., T.C. Esque, L.A. DeFalco, S.J. Scoles, M.L. Brooks, and R.H. Webb. 2003. Fire and exotics in the Mojave Desert: An irreversible change? A state-transition model for blackbrush (Coleogyne ramosissima) habitat. P. 31 in R.K. Livingston (ed.). Third U.S. Geological Survey Wildland Fire-Science Workshop, Denver, Colorado, November 12-15, 2002. U.S. Geological Survey Scientific Investigations Report 2004-5005, 67pp [Proceedings]
2. Esque, T.C., C.R. Schwalbe, L.A. DeFalco, R.B. Duncan, and T.J. Hughes. 2003. Effects of desert wildfires on desert tortoise (Gopherus agassizii) and other small vertebrates. The Southwestern Naturalist 48: 103-110. [Journal Article]
3. Brooks, M.L., T.C. Esque, and T. Duck. 2003. Fuels and fire regimes in creosostebush, blackbrush, and interior chaparral shrublands. Technical Report for the Southern Utah Demonstration Fuels Project, USDA, Forest Service, Rocky Mountain Research Station, Fire Science Lab, Missoula, Montana. 17pp. [Technical Report]
4. Brooks, M.L. and T.C. Esque. 2001. Non-native grass invasions and fire in the Mojave Desert. USGS Fact Sheet.
5. Brooks, M.L. and T. Esque. 2000. Alien grasses in the Mojave and Sonoran deserts. Proceedings of the 1999 California Exotic Pest Plant Council Symposium 6:39-44. [Proceedings]
