1. Crown fires: where large, high-intensity fires take out all of the above-ground living material. Chaparral and many forest types, like the lodgepole pine forests in Yellowstone, are characterized by high-severity crown fires. This is a perfectly natural event.
2. Surface fires: where mixed-severity fires burn forests and create low, moderate, and high-severity burn patches. Low-severity fire burns just the understory vegetation, leaving larger trees unharmed. High-severity fire burns off nearly all the above ground living material like a crown fire. Dry forests like some mixed-conifer and ponderosa pine dominated forests in western Sierra are characterized by mixed-severity surface fires.
The important thing to remember about forests characterized by surface fires is that the size of the burn patches varies depending on weather and climatic conditions. Long-term drought and low humidity plus wind can create conditions where a huge, high-severity fire "patch" can take out hundreds of acres of trees, burning through both dense and sparsely forested areas. Conventional wisdom claims such large high-severity patches are unnatural and a product of past fire suppression efforts. This idea is being seriously challenged. Learn more by going to our Forest Fires page.
A Crown Fire Regime where everything is taken out, setting the stage for a new, post-fire habitat.
A Surface Fire Regime with low to moderate intensity burning. A high-intensity patch is not shown.
The Basics on Fire in the Chaparral
1. The natural fire return interval for chaparral is 30 to 130 years plus (today, there are more fires than the chaparral ecosystem can tolerate - see #2 below).
2. Fires more than once every 20 years, or during the cool season by prescribed fire, can eliminate chaparral and convert it to non-native weedlands (called type-conversion).
3. Being dense, impenetrable, and prone to infrequent, huge wildfires is the natural condition of chaparral (it's not the fault of past fire suppression, "unnatural" amounts of vegetation, or environmental laws).
4. The age and density of chaparral has little to do with the occurrence of such large fires (large fires in southern California shrublands are driven primarily by weather, such as Santa Ana winds and drought).
5. Chaparral has a crown fire regime, meaning when a fire burns it burns everything, frequently leaving behind an ashen moonscape. This is in contrast to a "surface fire regime" found in dry Ponderosa pine forests in the southwest where fires typically burn at mixed-severity, frequently leaving patches of trees with only surface fire scars.
Whispering Bells (Emmenanthe penduliflora), an obligate seeding annual
Fire as a Disruptive Force
Is fire a good thing for chaparral as many people claim? The answer is no because such a statement is overly simplistic and based on misunderstandings about the role of fire in the chaparral ecosystem.
Fire in the chaparral is a disruptive force leading to the selection of fire survival strategies. Since fire has been a recurring, although infrequent event, for millions of years in the chaparral, only those species that have adaptations that allow them recover after the flames will persist. Consequently, many chaparral plant species depend on some fire cue or post-fire environmental condition for maximal reproductive success. Does this mean the chaparral "needs" to burn? In the current environment, absolutely not. Before humans arrived on the scene, the fire return interval for chaparral was on the order of 30 to 150 years plus. But over the past century fires have increased dramatically because of human activity, in excess of what the chaparral can tolerate, especially in Southern California.
Old-growth chaparral (50 years old +) remains a vigorous plant community, continues to add biomass over time, and supports a dynamic population of animals. Chaparral plants have evolved fire-related adaptations in order to survive and carry on AFTER a fire, not because they "need" to burn. So it is better to think of chaparral plants as not "fire-adapted" per se, but rather adapted to particular fire regimes or patterns (involving season of burn, frequency, intensity, etc.).
Toyon (Heteromeles arbutifolia) resprouting after a fire.
There are three basic strategies plants use to respond to fire in the chaparral.
1. Obligate resprouters like toyon (Heteromeles arbutifolia) depend on resprouting from their underground root systems or burls to survive after a fire. Geophytes (perennials with fleshy, underground structures like bulbs or tubers) are obligate resprouters as well, but have a unique after-fire response. The enhanced light from the lack of cover stimulates many geophytes to produce large numbers of flowers.
2. Obligate seeders that are perennial shrubs, like many Ceanothus species, are destroyed in the flames and depend on seedlings to replace their populations. Their seeds require some fire cue (heat, charred wood, smoke) to germinate. Conifers like Tecate cypress (Cupressus forbesii) are also obligate seeders and deal with fire through serotiny, the tendency for cones to remain closed and on the tree until the heat of a fire opens them up, releasing its seeds. Most of the wildflowers that are seen in the post-fire environment are obligate seeding annuals or short-lived perennials. Again, this does not mean obligate seeders "need" fire, but rather are adapted to particular fire patterns.
3. Facultative seeders like chamise (Adenostoma fasciculatum) resprout AND germinate after a fire. A few Ceanothus and manzanita species are faculative seeders as well (most are obligate seeders as explained above).
A list of many chaparral plant species and how they respond to fire can be found in, "Fire, Chaparral, and Survival in Southern California." Further details can be found on our Book Excerpts page.
For the most part, California has been able to avoid the "catastrophic" forest fires that have plagued much of the western United States over the past few years.
If all these fires that occur in California on a regular basis aren't forest fires, what are they? California wildfires are typically shrubland fires and have nothing to with trees. Surprising to many is the fact that forests only comprised about 5 percent of the total acreage burned during the 2003 firestorm in Southern California.
The paradigm that has been repeated over and over is that fire suppression has caused an unnatural overabundance of vegetation, creating dangerous levels of "fuel" in California's wildlands. While this may be an accurate description for some forests, such as dry ponderosa pine forests in the southwest, it is not true for California chaparral.
Instead of blaming the fire suppression efforts of firefighters for causing a problem, we should be thanking them for holding back the flames. Despite the fact that fire frequencies in Southern California have increased dramatically over the past century, firefighters have been able to prevent those fires from destroying the kinds of natural resources we all enjoy so much. If the fires had been allowed to burn, as some have suggested, it is likely much more of the chaparral habitat that makes California so special would have been converted into large tracts of invasive, non-native weeds.
For more details on this subject, please see our Threats to Chaparral page. See our Forest Fires page for more information on forest fires and how best to deal with them.