CHAPTER 3

FIRE

FIRE IS KEY to understanding chaparral communities. While most of the vegetation types of California are prone to fire, chaparral is particularly so. It is the large chaparral wildfires near urban areas that capture public attention, as they are experienced directly by those who live near the chaparral and indirectly by others who watch footage on television or read the news.

Though seemingly cruel and destructive from our perspective, fire is a natural and an essential part of the life cycle of the chaparral community. Fire recycles and rejuvenates, and without fire many of the commonly observed chaparral plants and animals would die out. There is a tremendous diversity of plants and animals in the chaparral, including many endemic species. These organisms depend on the heterogeneous environment and the shifting mosaic of habitats created by repeated fires (pl. 21). Chaparral vegetation and some of its botanical antecedents have existed for millions of years in California, and fire has always been an integral part of this community. In short, where there is chaparral there is fire.

Plate 21. Wildfires driven by erratic winds create a mosaic of burned and unburned chaparral, as shown in this photo from the city of Santa Barbara.

The Fire Cycle

The repeating pattern of fire followed by renewal and recovery of the chaparral community is called the fire cycle. This cycle and the resiliency of chaparral to fire are most obvious in the plants. Plant populations grow back and persist in the same place through repeated turns of the fire cycle, and they dominate the physical structure of the chaparral ecosystem. Animals track the plants' reestablishment and growth, waxing and waning in abundance with time in accordance with the changing structure of the vegetation (fig. 6).

Recovery of the chaparral shrubs after fire takes five to 10 years in most areas of the state. Initially, fire leaves behind exposed hillsides with blackened skeletons of shrubs protruding here and there, and with ash and charcoal on the surface of the soil (pl. 22). Most chaparral wildfires occur at the driest time of the year, late summer and early fall. Despite the dry conditions, recovery of the woody vegetation often begins immediately. Within just a few weeks after fire, green shoots can be seen at the base of burned trunks and stems (pl. 23).

The shrubs resprout after fire from reserves held in the root systems and burls. Burls, enlarged areas at the base of the stems, contain water and stored energy to produce new shoots and maintain the plant during the early phases of recovery. As a consequence, resprouting shrubs grow quickly, forming distinct clumps of stems one to three feet tall within a year (pls. 24, 25). All species of chaparral shrubs, with the notable exception of some species of ceanothus (Ceanothus spp.) and manzanitas (Arctostaphylos spp.), have a burl. Some burls, such as those of chamise (Adenostoma fasciculatum), are almost spherical, while others, such as those of silk tassels (Garrya spp.), are more like woody platforms. Even though burls lack a common anatomy, they all contain tissues capable of generating new shoots. Shoots arise from folds and recesses of the burl that are shallowly buried beneath the soil and protected from the fire's heat. As shrubs grow older and survive repeated fires, the burls become progressively larger, and resprouting takes the form of a ring of shoots around the outer edge of the burl. Old burls can be as much as six feet across and are undoubtedly several centuries old. Some chaparral shrubs, such as laurel sumac (Malosma laurina), resprout not only from the burl, but also directly from roots (pl. 26). Not all individual shrubs capable of resprouting survive every chaparral fire, however. The proportion that does survive depends on the species, intensity of the fire, season of the burn, and health of the plants at the time of the fire.

Figure 6. The fire cycle of the California chaparral. Fire destroys the dense shrub cover leaving hillsides blackened, but within a few weeks shrubs begin to resprout from burls or roots. The blackened branches make good perches for lizards to sun themselves and take advantage of the many insects that appear soon after fire (right). Spring produces an abundant growth of flowering plants and resprouts, providing food and habitat for animals such as this Brush Mouse (bottom). For the next several years, subshrubs and recovering shrubs dominate, and Brush Rabbits and other small mammals become common (left). The shrubs grow to full size within a about a decade, returning the chaparral to its prefire appearance and providing habitat for wood rats and other animals of dense chaparral (top). Chamise is illustrated here at various stages of recovery from immediately after fire (right) to a mature shrub (top).

Plate 22. A hillside blackened by a recent chaparral fire in the San Gabriel Mountains, Los Angeles County. The light patches on the dead branches of laurel sumac are caused by dead, peeling bark.

In the first several months following a fire, the recovery of the chaparral vegetation accelerates. Winter rains dampen the soil, and the seeds of the fire annuals germinate, roused by the fire from years of dormancy. These short-lived plants sprout in winter, gradually transforming the stark black hillsides to a soft green (pl. 27). As spring progresses, these annual plants often form dense stands producing spectacular displays of white, blue, yellow, purple, red, and orange flowers. The first spring after a chaparral fire is the most obvious manifestation of the regenerative power of the fire cycle and one well worth seeing (pl. 28).

Plate 23. One season's growth of chamise sprouts from the basal burl, following fire.

After the initial display of the first spring after fire, the annuals begin to diminish in numbers and are replaced by low growing plants with woody bases and soft stems that are knee to waist high. These are called subshrubs. Subshrubs remain vigorous for roughly four or five years after fire, until the shrubs overtop them. Some of these plants are also brightly flowered and add to the beauty of the chaparral even after the annuals have faded.

Peeking out among the annuals and subshrubs, resprouting chaparral shrubs such as chamise, toyon (Heteromeles arbutifolia), and scrub oaks (Quercus spp.) appear as bright green tufts the first year. They darken with time, forming multistemmed clumps that steadily increase in size. Also, initially hidden by the annuals and subshrubs are the newly germinated seedlings of the shrubs. These shrub seedlings may remain concealed beneath the taller subshrubs and resprouts until they are several years old. Since reliably obtaining water is essential for a young shrub to become established, much of the initial growth goes into establishing the root system. Shrub seedlings grow down faster than they grow up. Most mature chaparral shrubs have deep and extensive root systems, so that what is seen above ground is a relatively small part of the plant (fig. 1, pl. 29). These deep roots hold the soil in place and on slopes are important in preventing erosion and landslides.

Plate 24. Resprouting shrubs such as this toyon, or California holly, can reach a large size within two to three years after fire.

Plate 25. A two-year-old burn site showing resprouting chamise along with interspersed subshrubs and sparse annual flowering plants.

Plate 26. Laurel sumac resprouts vigorously from its roots within a few weeks after fire in fall. Note that the surrounding ground remains bare, because of insufficient rainfall to stimulate germination of seeds.

Plate 27. Herbaceous plants grow quickly after a chaparral fire. The large flowering plant is Fremont's star lily, and the vine sprawling on the ground is wild cucumber. At the top of the photo, a coast live oak tree has new sprouts emerging from burned branches.

Plate 28. The first spring following a fall fire is one of the most spectacular sights in the chaparral, as California poppies and other colorful fire annuals flourish.

Growth slows when the shrubs become large enough to entirely cover the ground beneath, shading and crowding out the subshrubs and herbaceous plants that may have persisted. After approximately five to seven years the chaparral is once again dense shrub vegetation. Then for long and indeterminate periods the shrubs continue to gradually increase in size, storing reserves in their burls and roots and producing seeds that then lay dormant in the soil until the cycle turns over again with the next fire. Since few chaparral shrub seeds germinate between fires, open patches may develop where large shrubs have died (pl. 30). This phenomenon is most common in chaparral dominated by ceanothus and along the lower margins of chaparral where it borders other types of shrublands or grasslands.

Plate 29. Chaparral shrubs are deeply rooted and hold the soil in place. The root of the laurel sumac to the right of the black and white measuring stick is 18 feet long from the base of the shrub to the point at which it disappears into the excavation hole. The complete root is considerably longer.

Animals also respond to the cycle of periodic destruction and renewal by fire. The time elapsed since fire is closely correlated with the composition of the species of animals that inhabit a particular stand of chaparral, because the age of a shrub stand governs key elements of habitat characteristics. The quantity and quality of plant cover, the quality and variety of plant food, and even the potential locations and building materials for nests are all related to the time elapsed since the last fire. The open ground, newly available after fire, provides an opportunity for animals to exploit foods that were not destroyed by heat and flame. For example, kangaroo rats (Dipodomys spp.) depend on seeds buried in the soil before the fire. Other species, such as the harvester ants (Pogonomyrmex spp.), search for seeds blown in from beyond the perimeter of the burn. The Western Fence Lizard (Sceloporus occidentalis) uses newly available resources as it snatches up passing insects from its sunny resting place between burned stems of chamise (pl. 31). Mule Deer and Black-tailed Deer (Odocoileus hemionus) are also attracted to recently burned areas of chaparral, particularly when fires have been patchy, since this leaves open areas with lush vegetative growth adjacent to dense shrubs. Deer feed on the new growth of both herbaceous plants and chaparral shrubs while using the nearby dense vegetation for cover. Deer reproduction and survival are relatively high when burned and unburned areas are juxtaposed, and deer populations can increase tenfold in a few years time. As the recovering plant community generates a diverse and abundant mixture of succulent leaves, flowers, fruits, and seeds, the variety and density of insects, birds, mammals, and reptiles in chaparral increases very rapidly, reaching a peak two to five years after the fire. After two or three decades of postfire growth, the chaparral plant community becomes a structurally homogeneous habitat that supports fewer species of animals and excludes some that were present when the community was younger.

Plate 30. Shrubs of old chaparral stands may appear more variable and open than in younger stands as some individuals reach great size while others die back.

Plate 31. A Western Fence Lizard sunning on a rock among the burned stems of chamise.

The Fire Regime

The overall pattern of recurrent fires in a particular place is called the fire regime. Four main elements contribute to the fire regime: frequency, intensity, seasonality, and spatial pattern. These elements are highly variable in many respects, contributing to the heterogeneity of chaparral in time and space.

Fire Frequency

Although the true natural frequency of fire is difficult to know, it is clear that fires are a periodic and inevitable feature of chaparral. The data on natural fire frequency are gathered from a number of different sources and they do not always agree. Fires have been observed to burn every five to 40 years in some areas, whereas they may occur only once a century in others. Chaparral grows in many settings, so that fire frequencies will always vary from place to place. Some factors that are important in natural fire frequency are species of shrubs present, elevation, latitude, proximity to other types of vegetation, frequency of ignition, wind patterns, topography, and time since last fire. Modern fire frequencies in many areas are affected by human actions (see chapter 6).

Fire-free periods of a century or more in chaparral watersheds are suggested by information obtained from charcoal varves in the Santa Barbara Channel. These varves are layers of sediment deposited annually on the sea floor from soil carried in the seasonal runoff of streams and rivers from the nearby Santa Ynez mountains. These layers contain charcoal if there has been a recent fire. Occasional years with large floods produce thicker varves than years with normal rainfall and runoff. Thick varves are also associated with floods that come from hillsides that have been denuded of chaparral by a recent fire, and these layers also contain charcoal. Consequently, vertical cores taken through the annual deposits can reveal patterns of fires and floods that go back for several centuries. The Santa Barbara Channel varves showed that in the Santa Ynez mountains there were two very large fire-flood episodes in the period between the years 1400 and 1550, and large fires somewhere in the area about once every 65 years over the past 600 years. Between episodes of large fires were quiet periods with few or no detectable fires. Similarly, records from soil profiles and tree-ring scars from Santa Cruz County in northern California indicate that large fires occurred there regularly prior to the European colonial period, at intervals from one to several hundred years.

Studies of fire frequency in San Diego County looked at the reproductive success of chaparral shrubs and trees with different intervals between fires. It was shown that short fire intervals could cause local extinction of chaparral plants. For example, a pair of fires a year apart wiped out the local chamise population. The first fire killed the tops of these shrubs, after which the population followed the usual pattern of quickly beginning to regenerate by resprouting and germination of seeds. A second fire the following year killed nearly all the seedlings and most of the resprouts along with their root systems. In another case, a fire interval of 30 years was also shown to be too short for the long-term survival of the Tecate cypress (Cupressus forbesii), a small tree that grows among chaparral shrubs near the border with Mexico. Tecate cypress has cones that persist on the tree for years, remaining closed to protect the seeds within (a condition referred to as serotiny). Wildfires kill the mature trees but also cause the cones to open up within days, dropping the seeds onto the soil, where they germinate. Trees must be more than 30 years old to accumulate sufficient seeds stored within cones to produce seedlings at densities necessary for stand replacement after a fire. Similar work on seedling production by big-berry and Eastwood manzanitas (Arctostaphylos glauca and A. glandulosa) showed that more seeds were produced on 90-year-old plants than on nearby 25-year-old plants. The conclusion from these studies of shrubs and trees was that a fire-return interval of many decades, or even a century, is the optimum cycle for these plants. Long fire-free intervals pose no particular risk to chaparral shrubs and trees, but much shorter fire intervals could be very damaging. The death of some shrubs after several decades does not necessarily indicate that those particular species need fires at closer intervals. For example, populations of the shrub Ceanothus tomentosus that had largely died after 80 years in a chaparral stand were found to have left a sufficient store of viable seeds in the soil to produce a new population of seedlings after fire.

Studies suggesting more frequent chaparral fires in historical times come from newspaper accounts during early settlement days in Los Angeles, and more recent observations comparing fire frequencies between San Diego County and adjacent Baja California. Both of these studies concluded that in earlier times small chaparral fires in southern California were frequent and patchy. This pattern appears to have resulted from fires that burned until they were naturally extinguished. The Baja California study suggests that in the absence of fire suppression, the frequency of smaller fires in San Diego County would be higher than it is today, while the frequency of large fires would be less than it is now. This conclusion is not universally accepted. Both of these studies are described in greater detail later in this chapter.

Frequent chaparral wildfires are the rule in many areas now, although not from natural causes. People living and working close to chaparral are the ignition source of the majority of today's fires. According to U.S. Forest Service statistics, the most common cause of wildfires is children playing with matches. Other common causes are sparks from motorcycles without spark arresters, sparks from campfires, discarded cigarettes, downed power lines, accidents with vehicles and motorized equipment, structural fires, and careless burning. Events as seemingly unlikely as plane crashes, locomotive sparks, and birds electrocuted on power lines have started disastrous chaparral wildfires. These accidental sources are sometimes compounded by deliberate ignition, in other words, arson.

Fire Intensity

Fire intensity, another aspect of the fire regime, is also important in chaparral. A fire burning ferociously in a hot, dry windstorm will release much more heat in a minute or an hour than a fire burning the same vegetation under calm conditions and lower temperatures. Aluminum objects are frequently reduced to puddles in wildfires, and the melting point of aluminum is 1,150 degrees F. Under some extreme conditions even glass bottles are melted, requiring a temperature of 3,000 degrees F! These are peak temperatures, but even so, most chaparral wildfires have recorded temperatures at the surface from 350 to 800 degrees F. Although fire temperatures above the ground can be extreme, just a few inches below the soil surface it is much cooler. Seeds shallowly buried are protected from heat death by the insulating soil. Kangaroo rats and other animals with deep burrows are also very little affected by the fire burning above them (see chapter 5).

The intensity of the fire affects the microbiology of the soil, the amount of standing charred and uncharred wood, the amount of ash and remaining nutrients, and many other community characteristics. Very hot fires may reduce all the vegetation to ash, turning the soil surface to a loose powder devoid of organic matter and internal cohesion, so that it is directly exposed to the erosive forces of wind and rain. A cooler fire may leave many charred stems and living roots in place, slowing erosion and reducing the hillside slippage. Very hot chaparral fires turn much of the nitrogen from the plants and leaf litter into ammonia and other gases that escape to the atmosphere, so that less of this important nutrient remains in the soil to support the growth of new vegetation. Within the boundaries of a given fire, intensity varies greatly from point to point, depending on the distribution and quantity of fuel, wind patterns, topography, and other physical variables. In general, north-facing slopes burn more slowly and less intensely than exposed south- and west-facing slopes. Uneven combustibility of the shrubs may also add to differences in intensity.

Seasonality

The season of a chaparral wildfire is important. As summer wears on, chaparral shrubs become progressively drier and more flammable. The water content of the shrubs' leaves is depleted, and the roots are no longer able to extract water from the dry soil. The fine, dead branches inside mature shrubs become crisp, dry kindling. All it takes is a small source of fire, such as a match or spark, to set off an explosive blaze. Lightning strikes, the natural source of ignition, are most common in late summer and fall, making fires from this source more likely at this time than at other times of the year. The likelihood of a fire becoming large is also increased by gusty seasonal winds, such as Santa Anas, that are common in fall. High fire danger can continue until winter rains begin days to months later (see chapter 2).

Fires that burn between September and November, the most typical time for catastrophic wildfires, occur when shrub growth is minimal, and when few animals are engaged in reproduction. In spring, on the other hand, shrubs are actively growing and have moved most of their reserves of energy and nutrients from root systems to stems, leaves, and flowers. Fires during spring sometimes kill a substantial fraction of the shrubs that might have readily survived a fire in fall. This is because fewer reserves remain in the burl and the root system that the plant can use to regroup and begin growing again, and because of the lethal effect of steam in growing tissues. Many animals are building nests and raising their offspring in springtime, as well, so that the eggs and young of vertebrates and invertebrates are likely to be at their most vulnerable at this time. The soil is also likely to contain moisture at or near the surface where a fire's heat can turn water into life-destroying steam that sterilizes the uppermost layer of soil. For all of these reasons a spring fire, started by humans, can be much more damaging to chaparral plants, animals, and soil than even very hot fires that occur in fall.

Spatial Pattern

Pattern, another aspect of the fire regime, is created by the confluence of frequency, intensity, and season, plus topographic differences, local microclimates, the individual characteristics of shrub species, and the weather at the time. Fire burns differently in different vegetation types, and the chaparral varies as to the dominant species of shrubs in different regions. Each species of shrub burns in its own way. Shrubs do not gradually ignite and burn smoothly, but rather the shrubs burn one by one as the halo of hot gases volatilized from heated resins and waxes in the leaves suddenly causes the entire shrub to explode into flames (pl. 32). Since each species of shrub has its own particular characteristics of burning, chances are good that some individual plants on a hillside will be only singed while others will be incinerated right down to the soil. As mentioned earlier, cooler and moister north-facing slopes often burn incompletely, whereas hot, dry south-facing slopes are more likely to burn entirely. Furthermore, topographic features such as cliffs, canyons, and rock outcroppings can redirect the path and change the intensity of a fire. Chaparral areas also frequently border ravines and stream areas, and this, too, may cause different patterns of burning. For example, a fire that burns everything in its path when moving through chaparral shrubs may become a much less intense ground fire as it travels beneath a stand of live oak trees and may altogether skip the moist canyon bottom. Working together, all of these variables often result in islands of unburned shrubs next to areas that are completely blackened. Looked at on a large scale, we see a mosaic of different ages and sizes of chaparral stands across the state. Today, the mosaic of recently burned and long-unburned chaparral in California is made up mostly of big pieces. Largely, this is due to the size of modern wildfires. For more information see Fire Patterns in the Twentieth Century later in this chapter.

Plate 32. Chaparral shrubs burst into flame from explosively ignited gases.

Sources of Ignition

The natural cause of fire in chaparral is lightning. In California, lightning strikes are most common in the interior mountains and foothills above 5,000 feet, where there are open forests and low, patchy chaparral. Consequently, fires started by lightning usually begin away from the coast but may spread in that direction if pushed by winds or storms. The peak of lightning activity is mid-July through September. Many of these naturally ignited fires burn out in a short time, leaving small, irregular patches. However, sometimes a fire does not go out, but continues to burn for weeks, depending on the weather and the fuels. Smoldering logs and litter can be a latent source of fire. During the nights following wildfires, the woody bases of large, burning chaparral shrubs can be seen glowing like jack-o-lanterns set out on blackened hillsides. If the weather turns dry and windy, flames can spring up anew from embers, igniting what may become a large and uncontrollable wildfire. Since gusty winds are a common feature of late summer and fall in many parts of the state, it is mostly during this part of the year that fires spread away from their initial source area and turn into large wildfires. In August 1977 a low-pressure area that stretched the length of California generated lightning without rain statewide. The lightning strikes ignited nearly a thousand wildfires in one night. One of them became the Marble Cone fire, which burned for weeks through much of the very old chaparral of the Central Coast Ranges and grew to be the third largest wildfire in the history of California. Very similar circumstances occurred again in August 1999, when several very large wildfires ignited by lightning burned until October in central and northern California.

Under most circumstances today, lightning is a minor factor in predicting the probability of chaparral wildfires. The millions of people in California provide a steady supply of ignition sources in and around chaparral, so that people have become the leading cause of chaparral wildfires. These human-initiated events are unlike those sparked naturally by lightning. Human-caused fires most often begin at low elevations near urban areas and along highway corridors rather than up in the mountains, where lightning is most common. In addition, there is little seasonal pattern to fires caused by humans, which may burn through the same area of chaparral more frequently than at intervals of decades or centuries, as happens from fires caused by lightning.

Aboriginal Burning

As an evolutionary force, fire has shaped chaparral over millions of years, and for most of this time period humans were absent. For example, charcoal fragments of chaparral plants have been discovered in sedimentary rocks of the Santa Monica Mountains that are 20 million years old—long before humans arrived in North America. Across this expanse of time, populations of organisms that were unable to survive periodic wildfires were eliminated from ancestral chaparral, while those that possessed or evolved adaptations to survive wildfires persisted. The arrival of humans approximately 11,000 years ago brought about important changes in the fire regime by providing a new ignition source that could be applied any time the vegetation was flammable. Humans everywhere use fire in ways that modify the landscape, and the vegetation of fire-prone California was particularly susceptible to this kind of manipulation. It is hard to escape the conclusion that burning by humans has exerted a profound effect on the nature of chaparral and all the other fire-prone plant communities of California.

There is no doubt that the original inhabitants of California caused fires in many plant communities, including chaparral. Anthropologists and historians have made inferences about the influence of California Indians on the fire regime by examining the records made around the time of first European settlement in the second half of the eighteenth century. There is evidence of intentional burning of vegetation by Indians in both northern and southern California. A diary from 1774 by Fernando Rivera y Moncada, the Spanish commander of Alta California, noted regular burning to increase grass seed yield, and a 1793 account by naturalist José Longinos Martinez observed that Indians throughout Alta California were in the habit of burning brush to drive out rabbits, and to produce the edible vegetation that followed. The first law regulating fire in California was a proclamation in 1792 by Spanish Governor José Joaquin de Arrillaga, which prohibited deliberate burning of vegetation. He declared that he was acting against “the widespread damage which results to the public from the burning of the fields, customary up to now among both Christian and Gentile Indians in this country (Alta California)” (Clar 1959, 8-10). Some wildfires from this early period evidently were quite large.

Nineteenth-Century Fire

Written records from the nineteenth century also indicate the continued importance of fire as part of both the pristine and the inhabited portions of the state. For example, after a visit to Santa Barbara in 1831, Alfred Robinson wrote the following:

A great fire had originated in the mountains to the south, which spread to the environs of the pueblo, endangering the fields of grain and gardens. It approached the low hills…close to town and favored by a strong wind kept traveling along the mountain range. The sight was magnificent but terrible at night when the fire reached the rear of the town. Large cinders fell in every direction, even the very vessels in the harbor having their decks covered with burning ashes. The air was too hot to breathe. People fled from their houses to the beach…. When the fire came to the vicinity of the mission vineyard, its path was checked because of the green state of the vegetation but it continued its course to the mountains northward where everything was destroyed and for months afterwards the bare and blackened hills marked the course of the raging fire. (Robinson 1925,130–131)

In 1836 Richard Henry Dana commented on the same fire, writing in Two Years Before the Mast:

The town is certainly finely situated, with a bay in front and an amphitheater of hills behind. The only thing which diminishes its beauty is that the hills have no large trees upon them, they having been all burned by a great fire which swept them off about a dozen years before, and they had not yet grown up again. The fire was described to me by an inhabitant as having been a very terrible and magnificent sight. The air of the whole valley was so heated that the people were obliged to leave the town and take up their quarters for several days on the beach. (Dana 1949,55)

The New Englander Dana made the same error as did many others who came to California later on. He assumed that fire was an unnatural event, and that were it not for fire, the surrounding hillsides would carry a forest resembling that which he had grown up with in Massachusetts. Dana undoubtedly saw the chaparral shrubs that would have covered the hillsides 12 years after the fire, but these stirred no further comment. He was, in fact, within sight of chaparral most of the time as he sailed up and down the California coast, although it is never mentioned in his famous journal.

Studies of the fire regime of the late nineteenth century on the chaparral-covered slopes of the San Gabriel Mountains, facing the Los Angeles Basin, show a different pattern of burning than we see today. An analysis of early newspaper accounts and descriptions from the first stewards of the newly created Federal Forest Reserves paint a picture of a landscape that was broken up by many small fires into patches of chaparral of different age classes. Fires started by summer lightning burned for weeks, or even months, sometimes until they were extinguished by rain in late fall. Most of the time these fires were scarcely noticed in the valleys because they were kept alive only by smoldering in the trunks and stumps of burned trees or by slowly creeping along the ground. Occasionally, these fires would flare into intense blazes like those that make dramatic television footage today. These bursts of flames occurred when smoldering fires were suddenly whipped into conspicuous blazes by the first Santa Ana winds of the season. A large fire that burns over many days and weeks, as these did, is actually many fires that are connected together in a time sequence by a common source of ignition. Such fires burned through many plant communities and many age classes of vegetation. As discussed in the following section, our current pattern of occasional large wildfires in chaparral and many smaller fires that are quickly suppressed may or may not be like that of the past, with or without aboriginal burning. The current regime is influenced by frequent ignitions and successful suppression of almost all fires shortly after they begin. Neither circumstance existed before the twentieth century.

Fire Patterns in the Twentieth Century

A study by Richard Minnich, comparing contemporary fire patterns in the chaparral of Baja California Norte, Republic of Mexico, with patterns in the same sort of chaparral just north of the international border in San Diego County, gives us one view of what the natural fire pattern might be even now in extreme southern California were it not for fire suppression policies (see chapter 6 for more explanation). The mean interval between fires was the same in both countries—approximately 70 years—but the burning patterns were quite different. In Mexico, most fires were relatively small and burned at moderate intensities, mostly in mature chaparral. These fires seldom burned very far, because they almost invariably stopped when they encountered nearby patches of chaparral that were younger and consequently less flammable. In contrast, during the same period in next-door southern California, there were far fewer fires, but a few of these were very large and burned with great intensity. This striking contrast between the behaviors of fires on opposite sides of the border was attributed to differences in fire suppression practices between the two countries. In Mexico there is little or no attempt to put out most chaparral wildfires, and they therefore burn until they go out naturally. These fires are usually small because the patches of older, highly flammable chaparral are relatively small and fire simply stops when it burns up against younger patches of chaparral. The patches are small because the numerous fires divide the chaparral up into small pieces.

North of the border in the United States, most fires are quickly extinguished, and large areas remain free of fire for several decades. This long period without fire allows extensive, contiguous areas to accumulate so much fuel that once ignited the fires are difficult to stop. Thus the fire regime in the chaparral of southern California appears to have been changed by fire suppression and with the resulting pattern of the chaparral across large areas. The mosaic of chaparral age classes created by fires in the United States is made of a few large pieces, while the mosaic in Mexico has a much finer texture of relatively small, numerous pieces.

An analysis of 90 years of fire records from the nine California counties between Monterey and San Diego with extensive shrublands by Jon Keeley and coworkers paints a different picture of the historical fire regime. Their study of fire records concludes that overall fire frequency increased during the twentieth century, as did the total area of chaparral and related vegetation burned in Riverside, Orange, and San Diego Counties. Contrary to prevailing opinion, the size of fires did not increase in this area that contains most of California's chaparral. An accompanying analysis of large shrubland wildfires driven by Santa Ana winds across the Santa Monica Mountains of Los Angeles and Ventura Counties showed that these fires burned through chaparral of all ages, not just older vegetation. They concluded that in extreme fire weather conditions, chaparral burns without regard to the age of the vegetation, so that managing fire hazards through chaparral fuel reduction is likely to be ineffective for the fires that burn during fierce winds, the very conditions that are most dangerous to life and property.

The management implication of Minnich's study is that suppression of all chaparral wildfires is self-defeating, because it ultimately results in very large and destructive conflagrations that cannot be controlled. The conclusion of Keeley and coworkers is that the very large chaparral wildfires that do the most damage have not increased in frequency. More fires are started and most are quickly extinguished, but the huge and unwieldy fires are natural and will continue to occur as long as chaparral is present.

Modern Fires

The ever growing danger of mixing chaparral with more and more human developments is evident from contemporary trends of wildfire size and destruction (pl. 33). The largest and most destructive fires in California are recent, and most of them were fueled by chaparral. Nine of the 10 largest wildfires in state history were in chaparral, and the other was in chaparral mixed with other vegetation. All but one of these huge fires occurred since 1970. They ranged in size from 117,000 to 280,000 acres, areas four to 10 times the size of the city of San Francisco. The Marble Cone fire of 1977 burned over most of the chaparral in the Los Padres National Forest of Monterey County. The Matilija fire of 1932 burned over much of the chaparral of Ventura County, traveling from the core of then remote mountains all the way to the sea.

In the fall of 2003 an arc of chaparral wildfires surrounded the vast metropolitan area of southern California. From the Mexico border to Ventura County, a complex of 10 fires blew against, around, and through the ring of spreading urbanization that has brought ever-larger numbers of people into a fire belt fueled by chaparral. In one week the flames consumed just under 700,000 acres, destroyed more than 3,700 homes, took 20 lives, and occupied over 14,000 firefighters. The combined property and other economic losses of those fires were estimated to be 3.5 billion dollars. The 281,000-acre Cedar fire burned across chaparral of San Diego County from the city of San Diego to the eastern backcountry, taking 14 lives and destroying over 2,200 homes, becoming the largest wildfire in the recorded history of California. Another very large chunk of San Diego County chaparral was burned by the 175,000-acre Laguna fire of 1970, which took 382 structures and 5 lives. Virtually all of the 2003 fires began in chaparral and were propelled by erratic Santa Ana winds. Some of these fires later spread into mountain forests. An estimated million tons of pollutants blanketed the region beneath a yellowish gray pall of smoke and rain of ash that kept children indoors and adults wearing face masks for a week, and eventually reduced visibility as far east as Texas. At the height of the fires a NASA satellite measured elevated levels of carbon monoxide a thousand miles out across the Pacific Ocean (pl. 12).

Exactly 10 years earlier a complex of 18 fires across southern California burned 189,000 acres, damaged or destroyed over 1,000 structures, caused 3 deaths and injured hundreds. A total of 30,000 people were forced to temporarily leave their homes. Damage from these regional catastrophes ran to billions of dollars—natural disasters on the same scale as those caused by severe earthquakes and hurricanes. These are examples of the worst of fire seasons. Over a 10-year period between 1985 and 1994 an average of 703 California homes were destroyed by wildfires each year. Not all of these were chaparral wildfires, but most were. Given present trends of new settlement adjacent to and within flammable vegetation, the annual losses from chaparral wildfires are likely to increase. Most of these losses are not inevitable. The many measures that can be taken by individuals and communities to protect themselves against chaparral wildfires are discussed in chapter 6.

Plate 33. Today most fires in the chaparral have a human rather than a natural cause.

Natural Responses of Plants and Animals to Chaparral Fires

Notwithstanding the effects of different fire regimes, plants and animals in the chaparral possess adaptations that enable them to survive wildfires. Below are some examples of plants and animals with special adaptations to fire.

Fire Annuals

The seeds of many species of chaparral shrubs and herbs require fire to break dormancy and allow germination. This is very different from the seeds of plants in most other places in the world, which require water, light, and reasonable temperatures but are otherwise free to germinate at any time.

The chaparral wildflowers that appear in luxuriant displays after fire are largely restricted to the first spring after fire (pl. 28). Of the more than 200 species of short-lived herbaceous plants that grow after fire, only a handful are found at any other time. This means that many of chaparral's most spectacular species will be seen infrequently and only after fire (see also chapter 4). The seeds of these plants may lie in the soil for a century or more, invisible to us, if there has been no fire. These particular plants are referred to as fire annuals, or pyrophyte endemics. These unique chaparral plants absolutely require the burning away of the mature shrubs before they will germinate.

Seeds of fire annuals have special systems to detect the passage of fire. Some species respond only to the chemicals produced when the wood of the shrubs is charred, or to the gases given off from combustion. For some species the cue is so specific that once in contact with the seeds, germination takes place within 24 hours. The seeds are not fooled by an exceptionally hot summer, manual clearing, or human manipulations. These seeds can survive for very long periods of time. This is due in part to their low moisture content, which is less than a dry paper towel. Similarly, the seeds of most species of shrubs also require fire in order to germinate. For some species it is the cracking or burning away of the hard seed coat that is needed, but for many others it is a special cue that comes only from fire. The seeds of most species of shrubs also rest in the soil for many years, lying dormant until the next fire. Shrub seedlings are consequently rare in the mature chaparral but become abundant as soon as those shrubs are burned away.

Fire Beetles

As with the plants of the chaparral, fire is crucial for some species of insects to survive and reproduce. Some are also named for their close association with fire and are the animal equivalent of the fire annuals of the plant community.

Fire beetles (Melanophila spp.) are so named because they depend on burned and indeed burning chaparral to reproduce. They are specially equipped to detect a fire in progress and will fly from 20 miles away to meet each other at burning chaparral shrubs. It is only on these smoldering ruins that they mate and lay eggs. Fire beetles begin courtship while the bushes are still burning. The mating ritual allows time for the shrubs to cool off to the preferred egg-laying temperature range of 100 to 115 degrees F. These really are red-hot lovers.

They are known to seek out areas as hot as 800 degrees F on the way to their mating sites.

These fire beetles are flat-headed wood borers that prefer to live in damaged trees or shrubs, especially those killed by fire. They have unique sensors in their antennae that detect atmospheric heat and smoke at considerable distances, and heat receptors along the underside of the body. These receptors are associated with glands that secrete a special wax. This wax aids the beetles by coating their undersides as they become warm, preventing water from evaporating from their bodies. Interestingly, these wax glands are found only on the females and are thought to be correlated with the need for her to sit for a period of time on hot branches while laying eggs. Female fire beetles have long ovipositors (egg-laying organs) that pierce the wood so that eggs are placed in cozy places within the burned stems and branches.

Fire beetles are attracted to burning chaparral shrubs in enormous numbers. Thousands of iridescent black beetles arriving almost simultaneously can form a glistening film on the trunks and stems within minutes of the fire's passage. Mating and egg laying take only a short time, and the adult beetles may disappear again within a few hours, leaving no visible trace. The larvae that develop from the eggs eat the dead and damaged wood of the shrubs and may live in these woody stems for several years. As predictable and fascinating an event as the appearance of fire beetles might be, very little is known about their total numbers or locations during non-fire periods. Fires are sporadic and geographically unpredictable and so too are the populations of their fire-dependent insects.

Fire beetles are attracted not only to burning chaparral shrubs, but also to oaks and pines and to some rather unlikely targets that might also be in a fire area. For example, fire beetles may cause problems for fire fighters because the beetles land on these people instead of on the burned trees and branches. In an effort to attach to a slippery, sweaty neck or shoulder the beetles will use their jaws as well as their legs to hang on to the surface, and their bite, while not serious, can be annoying. The sensitivity of these beetles to heat and smoke is so acute that they can also be drawn away from natural areas to human gatherings such as football games, barbecues, and roof tarrings. Football games at the University of California at Berkeley in the 1940s and 1950s, when cigarette smoking was highly fashionable, were regularly affected by a rain of fire beetles dropping from the sky in search of a suitable place to lay eggs! At one time they were so common near hot and smoky cement plant stacks in Riverside and Ontario in southern California that they were referred to as “stack beetles.” With improved air quality, these beetles are once again seen primarily when there are fires in chaparral and other natural vegetation.

Fire attracts other beetles as well, even though they do not have specific names that reflect this. For example, long-horned beetles (family Cerambycidae) are also attracted to burned and burning chaparral. Beetles of the genus Tragidion lay their eggs in the still-warm stems of burned chamise, scrub oak, and sugar bush (Rhus ovata). Their larvae can be seen for several years after fire in these shrubs. Xylotrechus, another genus of long-horned beetle, uses holes in the bark created by fire as entry points to search for water and sugar in the still-living but now exposed shrub stems. They do not attack healthy shrubs but may serve to finish off those greatly weakened by fire.