1. The natural fire return interval for chaparral is 30 to 150 years or more. 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 by first reducing its biodiversity through the loss of fire-sensitive species, then by converting it to non-native weedlands (called type-conversion).
3. Being dense, impenetrable, and prone to infrequent, large, high-intensity wildfires is the natural condition of chaparral. It's not the fault of past fire suppression, poor land management, "unnatural" amounts of vegetation, or environmental laws as some claim.
4. The age and density of chaparral has little to do with the occurrence of large fires. Large fires in California shrublands are driven primarily by weather, such as Santa Ana and sundowner winds, and multi-year droughts.
5. Chaparral has a high-intensity, crown fire regime, meaning when a fire burns, it burns everything, frequently leaving behind an ashen landscape. This is in contrast to a mixed-severity fire regime found in dry Ponderosa pine forests in the American Southwest where fires burn in large and small patches, where trees are either completely burned in a crown fire or only scorched as the understory burns.
6. Native Americans did burn the landscape for various purposes in the past. Some of their burning practices likely eliminated native shrublands along the coast through type-conversion (see #2 above). However, their burning activity did not prevent the occurrence of large, infrequent, high-intensity chaparral fires. Such fires have always been a natural and inevitable part of the landscape.
Too learn more about the basics of wildfires and how they behave, please see our Fire Page.
Most threats to chaparral have to do with too much fire.
Adult, perennial shrubs, like most manzanitas and about half of Ceanothus species, are killed by the flames and depend on seedlings to replace their populations.
These obligate seeders depend on some fire cue (heat or the chemicals from charred wood/smoke) to germinate. Conifers like Tecate cypress (Cupressus forbesii), one of the rare trees found in chaparral, are also obligate seeders and deal with fire through serotiny, the tendency for cones to remain on the tree and closed until the heat of a fire opens them, releasing their seeds. This does not mean obligate seeders "need" fire, but rather are adapted to a particular fire pattern.
The seedlings of the obligate seeder Ceanothus tomentosus emerge from the soil after the 2007 Witch Creek Fire in San Diego County, California.
2. Obligate Resprouters
Adult, perennial shrubs, like toyon (Heteromeles arbutifolia) depend on resprouting from their underground root systems or burls to help create the new, pyrogenic habitat after a fire. Their usually large seeds are not helpful because they are either burned in the fire or have been previously eaten by herbivores.
This obligate resprouting toyon is sending up new shoots from its underground burl in response to the fire.
3. Facultative Seeders
A few shrub species resprout AND germinate after a fire. About half the Ceanothus species and a few manzanita species are facultative seeders.
Chamise (Adenostoma fasciculatum) is a facultative seeder. The species resprouts and its seeds are stimulated by the chemicals in wood/smoke to germinate.
4. Fire Followers
One of the most spectacular responses Nature has to fire is the explosive display of wildflowers several months after the flames. Most of the annual wildflowers and short-lived perennials seen in the post-fire, pyrogenic habitat are stimulated to germinate by the chemicals from charred wood/smoke. Some species, endemic fire followers, are especially dependent on fire as they are only seen within the first year or two after a fire. Whispering bells (Emmenanthe penduliflora) and Phalcelia grandiflora are endemic fire followers.
California poppy (background) and Parry's phacelia (foreground) are fire-following wildflowers.
Whispering bells (Emmenanthe penduliflora), an endemic fire follower.
Phalcelia grandiflora, an endemic fire folllower.
Geophytes (perennials with fleshy, underground structures like bulbs or tubers) are obligate resprouters, but have a unique after-fire response. The enhanced sunlight from the lack of cover stimulates geophytes to produce explosive flower displays that can cover hillsides.
Brodiaea (Dichelostemma capitatum) is a common wildflower that emerges post-fire.
- A CRITICAL DIFFERENCE -
FOREST FIRES VS. SHRUBLAND FIRES
Something you have likely heard over and over is that past fire suppression has caused an unnatural overabundance of vegetation, creating dangerous levels of "fuel" in California's wildlands.
This is not true for California's chaparral ecosystems (or for many forests). In fact, California chaparral is suffering from too much fire.
Fortunately, firefighters have been able to suppress most of the non-wind driven wildfires in chaparral country, despite the fact that fire frequencies have increased dramatically over the past century, especially in southern California.
If the fires had been allowed to burn, as some have suggested, it is likely much more of the native chaparral habitat that makes California so special would have been type converted from shrubland to non-native weedlands. This conversion would result in creating a more flammable environment due to the presence of flashy fuels (weeds and grasses), higher rates of soil erosion (and, thus, greater landslide risks), a substantial loss of biodiversity across the state, a reduction in carbon absorption, and the further deterioration of unique habitats.
Next time you hear someone claim your local habitat is supposed to burn every 5-10 years or so, or when someone uses the pine forests in the Southeast or Arizona/New Mexico as a model of what is supposed to happen in California fire wise, share this map with them.
The highest lightning frequencies in the United States occur in the Southeast and the Southwestern regions. Both of these areas have forests that have short fire return intervals - long leaf pine in the Southeast, ponderosa pine in the Southwest.
The lightning frequency in California is extremely low. For much of the state it borders on being non-existent. This is a good proxy for natural fire return intervals - extremely long for most of the state, to a bit more in the Sierra Nevada Mountains.
Lightning flashes per square mile per year.
The hotter the cooler, the more lightning. Notice California. Other than the desert and the Sierra Nevada, lightning is a rare event in California when compared to the rest of the country. This data can be used to help determine the natural fire return interval for a particular area. The less lightning, generally the longer the fire return interval. Click on image to enlarge.