FACT #1: Old-growth chaparral is a beautiful, healthy ecosystem. It does NOT need fire to "renew" or clean out "built-up" or "over-grown" vegetation.
FACT #2: Past fire suppression efforts have protected the chaparral. It has NOT led to an "unnatural" accumulation of vegetation.
The natural fire return interval for chaparral is between 30 to 150 years or more. Careful, objective statistical analyses by scientists at UC Berkeley and the US Geological Survey have found no significant change in the probability of chaparral burning as it ages except a slight reduction in risk in stands less than 5 years old. Slight tendencies don’t provide much solace in the face of our inevitable Santa Ana firestorms, which sweep through all vegetation age classes. The notion that a mosaic (patches of different aged chaparral) will prevent large firestorms is not supported by data collected over the past two decades and has been rejected by the scientific community. Please see our Naturally Large & Intense Fire page for more details. The following articles, and graph, are excellent resources to help cultivating a better understanding about the underlying scientific truths concerning shrubland wildfire ecology: Moritz, M., Keeley, J., Johnson, E., & Schaffner, A. (2004). Testing a Basic Assumption of Shrubland Fire Management: How Important Is Fuel Age? Frontiers in Ecology and the Environment, 2(2), 67-72.
FACT #3: Large, infrequent chaparral wildfires are natural and inevitable in California.
"During the past three or four days destructive fires have been raging in San Bernardino, Orange, and San Diego...It is a year of disaster, wide-spread destruction of life and property - and well, a year of horrors."- The Daily Courier, San Bernardino
The best ways to prevent loss of life and property are to retrofit existing structures to make them more fire safe, plan communities so they are not built in high fire risk areas, and maintain proper fuel management (which includes wooden fences, wood piles, ornamental vegetation, and native vegetation) directly around structures. Please see our Protecting Your Home page for more information.
FACT #4: Chaparral has adapted to particular fire patterns, NOT to fire per se; today, fire occurs too often in chaparral.
FACT #5: Chaparral plant species have adapted to survive drought and disturbances like fire; they are not "born to burn."
*The dramatic "oozing" quote came from the July 2008 issue of National Geographic. Being "born to burn" was a comment made by a member of the San Diego Board of Supervisors when justifying the need to conduct large scale prescribed burn programs in the backcountry.
See the paper below for additional details on fire and chaparral shrubs:Alessio, G.A., et. al 2008. Influence of water and terpenes on flammability in some dominant Mediterranean species. International Journal of Wildland Fire 17: 274-286.
FACT #6: Infrequent, hot, intense wildfires are a normal part of chaparral ecosystems. Such fires do NOT "sterilize" the soil.
For more information see: Halsey, R.W. and A.D. Syphard. 2015. High-severity fire in chaparral: cognitive dissonance in the shrublands. In D. A. DellaSala and C.T. Hanson, The Ecological Importance of Mixed-Severity Fires: Nature's Phoenix. Elsevier Publications, Inc.
Keeley, J.E., T. Brennan, and A.H. Pfaff. 2008. Fire severity and ecosystem responses following crown fires in California shrublands. Ecological Applications 18: 1530-1546.
Keeley, J.E., A.H. Pfaff, and H.D. Safford. 2005. Fire suppression impacts on postfire recovery of Sierra Nevada chaparral shrublands. International Journal of Wildland Fire 14: 255-265.
A related issue to fire severity impacts has to do with "hydrophobic soils." It is often suggested that fire creates some kind of water repellant layer under the soil like a sheet of wax paper because of the "waxy" chemicals that burned off the plants' leaves (see #5 above). It is then concluded that unless we "do something", rains will cause massive erosion and debris flows as the top soil surface washes away. However, hydrophobic soil conditions are not particularly important in post-fire chaparral environments. In fact, whatever "hydrophobic" condition occurs post fire usually disappears after the first light rain. See page 193-194 in High Severity Fire in the Chaparral.
FACT #7: Seeds of most chaparral plant species are naturally dormant. Chemicals from chaparral shrubs do NOT suppress seed germination or growth of plants beneath the chaparral canopy.
This lack of scientific verification, however, has not prevented the concept from being presented as a well-understood and accepted phenomenon in science texts. Dramatic explanations are seductive, especially if they provide interesting answers to intriguing problems. If repeated often enough, they become dogma and influence thinking for decades.
C.H. Muller, an accomplished botanist from the University of California, Santa Barbara, suggested allelopathy explained the lack of plant growth under the canopy of mature chaparral stands in Southern California (Muller, et.al. 1968). According to his hypothesis, chemicals washed off the leaves of chamise and manzanita shrubs, suppressing the germination of seeds in the ground below. When the chaparral burned, flames denatured the toxic substances releasing the seeds from inhibition. This resulted in the remarkable number of shrub seedlings and wildflowers emerging in post-fire environments. The problem with this explanation is that the soil chemicals suspected of suppressing growth actually increase after a fire. In addition, the dormancy found in chaparral plant seeds is innate, not caused by some outside, environmental factor. The seeds are dormant before they hit the ground. Chaparral seed dormancy evolved because poor growing conditions under mature shrubs selected for seed traits postponing germination until those conditions improved. Under xeric (dry) conditions, germinating under a shady canopy with hungry herbivores scurrying around is not a recipe for success. Fire quickly removes those problems and sets the stage for chaparral renewal. The post-fire seedling response in chaparral can be easily explained without invoking the notion of chemical inhibition.
Muller also suggested allelopathy was the cause for bare zones often found around purple sage (Salvia leucophylla) and California sagebrush (Artemisia californica) (Muller, et.al. 1964) in the coastal sage scrub community. Later investigations revealed these bare zones are primarily the work of herbivores (Bartholomew 1971), not volatile substances from the plants themselves. To little furry rodents like the California mouse (Peromyscus californicus) and the pacific kangaroo rat (Dipodomys agilis) the world is a dangerous place. Cover is critical to their survival since they are on the dietary preference list of local carnivores like coyotes, snakes, and hawks. Consequently, they have a tendency to remain under shrubbery with only occasional, quick forays into surrounding grassland to nibble on available seeds or new growth. They will stray only as far as they can quickly leap back to safety. Bare zones, therefore, can be viewed as “calculated-risk terrain” where rodents have a fair chance of grabbing food without getting caught. Bare zones are bare because herbivores exploit the space to grab available snacks.
Do volatile compounds in certain coastal sage scrub plants ever play a role significant enough to make a difference in naturally occurring vegetation patterns? “As far as I know, the question of why grasses grow within bare zones during wet years, despite animal activity, has never been adequately addressed,” Bob Muller said when reflecting upon his father’s work. “Why don’t animals always eliminate seedlings, regardless of the level of moisture?
The explanation favored by C.H. Muller provides a reasonable hypothesis for this phenomenon; heavy rains leach toxins from the soil, removing inhibitory chemicals and permitting seedling success. However, without further investigation the question remains unresolved.
“The critical issue,” John Harper (1975), a prominent plant population biologist from England explained, “is to determine whether such toxicity plays a role in the interactions between plants in the field. Demonstrating this has proved extraordinarily difficult – it is logically impossible to prove that it doesn’t happen and perhaps nearly impossible to prove absolutely that it does.”
-From "Fire, Chaparral, and Survival in Southern California." See the Book Excerpts page for more details.
The full paper dealing with allelopathy has been published in the Journal of the Torrey Botanical Society 131(4), 2004, pp. 343-367, "In search of allelopathy: an eco-historical view of the investigation of chemical inhibition in California coastal sage scrub and chamise chaparral." If you are interested in obtaining an electronic copy, please request one by writing us an EMAIL.