Chaparral
Chaparral
Chaparral is an evergreen shrub vegetation that dominates the rocky slopes of southern and central California. It forms a nearly continuous cover of closely spaced shrubs 6 to 12 feet (2 to 4 meters) tall, with intertwining branches that make the vegetation nearly impenetrable to humans. Herbaceous vegetation (grasses and wildflowers) is generally lacking, except after fires, which are frequent throughout the range. Because of complex patterns of topographic , soil, and climatic variations, chaparral may form a mosaic pattern in which patches of oak woodland, grassland, or coniferous forest appear in sharp juxtaposition . Fire frequency and soil are major factors that determine these patterns. Chaparral is replaced by grassland on frequently burned sites, especially along the more arid borders at low elevations (where shrub recovery is more precarious due to drought) and on deeper clay soils and alluvial plains , and by oak woodland on more moist slopes (where fires are less frequent and often less intense).
California chaparral is distributed in a region of Mediterranean climate, which has cool (40°F), wet winters and hot (95°F), dry summers. Rainfall is 10 to 20 inches (25 to 100 centimeters) annually, two-thirds of which falls November to April in storms of several days duration.
Plants of the Chapparal
The most widely distributed chaparral shrub is chamise (Adenostoma fasciculatum ), an adapted shrub with short needlelike leaves, which is distributed from Baja California in the south to Oregon in the north. Buckbrush (Ceanothusspp.) and manzanitas (Arctostaphylos ) are large genera (about seventy species each) and often form pure stands commonly referred to as manzanita chaparral or ceanothus chaparral. Some species are highly restricted in distribution, whereas others are nearly as widespread as chamise. Most species in these two genera are endemic to the California chaparral and have suites of characters reflecting a long association with fire. For example, many species of Ceanothus and Arctostaphylos have woody tubers at their base that sprout new stems after fire. All species in these two genera produce deeply dormant seeds that accumulate in the soil and require fire for germination.
At the lowest elevations throughout much of its range, chaparral is commonly replaced by a smaller and highly aromatic vegetation known as soft chaparral or coastal sage. This vegetation differs from chaparral by being summer-deciduous; this loss of leaves during drought confers a greater ability to tolerate the drier conditions at low elevations. The dominant shrubs are only 3 to 6 feet (1 to 2 meters) tall and include California sagebrush (Artemisia californica ), black sage (Salvia mellifera ), California buckwheat (Eriogonum fasciculatum ), deerweed (Lotus scoparius ), and monkeyflower (Mimulus aurantiacus ). These smaller shrubs grow rapidly and have well-developed wind dispersal of seeds so they often colonize disturbed sites.
The Californian Mediterranean climate is conducive to massive wild-fires. Mild, wet winters contribute to a prolonged growing season, which, coupled with moderately fertile soils, result in dense stands of contiguous fuels. Long summer droughts produce highly flammable fuels that are readily ignited by lightning from occasional thunderstorms but more commonly as the result of human carelessness. On average fire frequency for any one area is about every two to three decades, but this may be more frequent than in the past. Throughout much of its range, chaparral forms a continuous cover over great distances, and as a result, huge wildfires that cover tens of thousands of acres are common, particularly during Santa Ana wind conditions. These dry winds from the east occur every autumn and often exceed sixty miles per hour. Some scientists have suggested that massive wildfires are an artifact due to modern-day fire suppression, which causes an unnaturally heavy accumulation of plant fuel. Others dispute this conclusion, pointing to evidence that shows this vegetation has always experienced large, high-intensity fires.
The Role of Fire
Although shrubs dominate chaparral, the community comprises a rich diversity of growth forms, many of which are conspicuous only after fire. In addition to evergreen shrubs and trees, there are semi-deciduous subshrubs, slightly ligneous (hardened) suffrutescents , woody and herbaceous vines, and a rich variety of herbaceous perennials and annuals. A large number of these species arise from dormant seeds deposited into the soil decades earlier, following an earlier fire. Dormancy is broken in some seeds by heat but in many other species smoke from the fire triggers germination. In the first spring following fire, there is an abundant growth of herbaceous plants, which are relatively short-lived and are replaced by shrubs within the first five years. The postfire herbaceous flora often is dominated by annual species that live for less than one year, and species diversity is typically greatest in this first year after fire. Recovery of shrub biomass is from basal resprouts and seedling recruitment from a dormant soil-stored seed bank.
The striking contrast between the diminished herb growth under mature chaparral and the flush of herbs after fire is thought to be caused by allelopathic (chemical) suppression of germination by the overstory shrubs. Many of the smaller shrubs, such as sage (Salvia spp.) or sagebrush (Artemisia spp.), release volatile, aromatic compounds , and it has been suggested that these compounds inhibit the growth of competing grasses and wildflowers. This theory holds that fire destroys these toxins , and that this occurs throughout the shrub land and in a zone at the border between shrub lands and grasslands, forming a meter-wide strip known as the bare zone. However, experiments in which animals have been excluded from the bare zone demonstrate that the lack of herbaceous plants in and around mature shrub lands is as much due to animal predation as it is to chemical inhibition. In addition, it appears that the vast majority of species that germinate after fire do so more because their dormant seeds are stimulated to germinate by fire.
Resource agencies often respond to wildfires with emergency revegetation programs, which drop grass seed on newly burned sites with the expectation that this will reduce soil erosion and eliminate the threat of mud-slides and flooding. The rationale for this management is that burned sites have greatly increased surface flow of rainwater and thus high soil erosion. Emergency seeding is considered essential on sites following exceptionally intense fires because of the anticipated negative effects. Throughout the state of California the seed of choice has been the nonnative annual rye-grass (Lolium multiflorum ). However, there is abundant evidence that this practice fails to substantially reduce threats of mudslides and flooding and competitively displaces the native flora.
Some scientists have suggested that chaparral shrub lands become senescent if they are free of fire for more than a few decades. Detailed studies, however, find that these shrub land ecosystems can retain productive vegetation for a century or more, and in fact some shrubs require long periods without fire for successful seedling recruitment.
see also Allelopathy; Biome; Ecology, Fire.
Jon E. Keeley
Bibliography
Callaway, F. M., and F. W. Davis. "Vegetation Dynamics, Fire, and the Physical Environment in Coastal Central California." Ecology 74 (1993): 1567-678.
Davis, F. W., M. I. Borchert, and D. C. Odion. "Establishment of Microscale Vegetation Pattern in Maritime Chaparral After Fire." Vegetation 84 (1989): 53-67.
Davis, F. W., D. E. Hickson, and D. C. Odion. "Composition of Maritime Chaparral Related to Fire History and Soil, Burton Mesa, Santa Barbara County, California." Madroño 35 (1988): 169-95.
Davis, F. W., P. A. Stine, and D. M. Stoms. "Distribution and Conservation Status of Coastal Sage Scrub in Southwestern California." Journal of Vegetation Science 5 (1994): 743-56.
Davis, S. D., and H. A. Mooney. "Water Use Patterns of Four Co-occurring Chaparral Shrubs." Oecologia 70 (1986): 172-77.
Haidinger, T. L., and J. E. Keeley. "Role of High Fire Frequency in Destruction of Mixed Chaparral." Madroño 40 (1993): 141-47.
Keeley, J. E. "Chaparral." In North American Terrestrial Vegetation, 2nd ed. M. G. Barbour and W. D. Billings, eds. Cambridge: Cambridge University Press, 2000.
——. "Demographic Structure of California Chaparral in the Long-Term Absence of Fire." Journal of Vegetation Science 3 (1992): 79-90.
Tyler, C. M. "Factors Contributing to Postfire Seedling Establishment in Chaparral: Direct and Indirect Effects of Fire." Journal of Ecology 83 (1985): 1009-20.
Zedler, P. H. "Fire Frequency in Southern California Shrublands: Biological Effects and Management Options." In Wildfires in California Brushlands: Ecology and Resource Management, J. E. Keeley, and T. Scott. Fairfield, eds. Spokane, WA: International Association of Wildland Fire, Fairfield, 1995.
Chaparral
Chaparral
A chaparral is a geographical region characterized by mild, cool winters and hot, dry summers. Chaparral is sometimes called "scrubland" because the periods of drought and regular fires allow only a certain type of thorny scrub or thicket to thrive there.
A chaparral has what is called a Mediterranean climate because of its mild, moist winters and very dry summers. Besides the Mediterranean however, there are other parts of the world that have a similar climate, such as southwestern Australia, central Chile, the Cape region of South Africa, and southwestern California and northern Baja California, Mexico. The lands in these different areas usually have their own particular names ("mallee" in Australia, "mattoral" in Chile, and "fynbos" in South Africa), and the name chaparral most often refers only to a certain part of California and Mexico. The word chaparral comes from the Spanish word chapparo which originally described a thicket of evergreen shrubs.
PLANT LIFE IN A CHAPARRAL
It is the vegetation that grows in this particular climate that most characterizes a chaparral. Typically, a chaparral is composed mainly of woody evergreen shrubs that have adapted to summer drought and fire. There are few tall trees. The leaves of most of these shrubs are small and usually have a waxy, or leathery, covering. Their small size minimizes moisture loss, as does the waxy outer covering. Since the shrubs are evergreen and are not deciduous (they do not lose their leaves all at once), they are ready to absorb rainwater whenever it falls.
Dormancy (in which a plant slows down all its processes) is another way that these plants conserve water loss during a drought. Most chaparral plants have two sets of roots that make them ready to take in any available
water. One of these is a very long taproot that can obtain water deep underground. Another is a lateral root system that grows barely under the surface and can absorb water before it soaks down deeper into the soil.
Fire is another constant in a chaparral, and all of the shrubs that grow there have adapted in some way to surviving fire and sometimes even using fire to their benefit. Chaparral fires happen naturally every ten to forty years, and they are beneficial in the long run. They remove dead plants that built up over the years and release their ash and minerals into the soil to be reused. They also open up the ground, letting more light in and allowing new plants to grow. Most chaparral plants can sprout from their burned base following a fire, and some even need a fire to open their seed coats.
ANIMALS IN A CHAPARRAL
Just like the plants that live in a chaparral, the animals that make their home there have adapted to its extremes. Common chaparral animals in the United States are the mule deer and coyotes. Rodents, reptiles, and rabbits use shrubs to hide from the red-tailed hawk and barn owl. Rattlesnakes and deer mice are also usually abundant. Many of these animals have adapted to their environment since they are able to go without water for long periods, and most avoid activity in the intense midday heat.
Humans are a different story and they are now threatening the natural balance of chaparral. As the chaparral in California becomes an increasingly popular place to build a home, people are having a major effect. Fires that once were natural and needed in a chaparral are suppressed since they would threaten homes. Thus the chaparral becomes thicker and denser, so that when a fire does break out and cannot be contained immediately, the fire that results is ferociously hot and fast-moving, destroying not only homes but even plants that had been fire-adapted. These super-hot fires destroy both shrubs and seeds entirely. Since the seeds or shrubs cannot resprout as before, mud slides often result since there is no vegetation to hold the soil. As a result, these mudslides may cause harm to people, animals, and plants and result in further damage to the chaparral itself.
[See alsoBiome ]
Chaparral
Chaparral
Chaparral is an ecological community consisting of drought-resistant evergreen shrubs and small trees that are adapted to long, hot, dry summers and mild, rainy winters. The chaparral is found in five places on earth where there is a warm land mass and a cool ocean: southern California, the Cape Town area of South Africa, the western tip of Australia , the west coast of South America, and the coastal areas of the Mediterranean in southern Europe. Total annual precipitation ranges between 15 and 40 inches per year, while annual temperatures range from 50–64.4 °F (10–18 °C). Droughts and fires, which are often set by lightning during the summer/autumn dry season, are common in the chaparral. In fact, because the release of minerals occurs as a result of fire, many chaparral plants grow best after a fire.
The chaparral may have many types of terrain, including flat plains, rocky hills, and mountain slopes. The word chaparral comes from the Spanish word chaparro, meaning a dry thicket of oak shrubs.
The plants and animals that live in the chaparral are adapted to the characteristic hot and dry climatic conditions. Most of the plants are less than 10 ft tall and have leathery leaves with thick cuticles that hold moisture. Many of the shrub flora are aromatic, contain flammable oils, and are adapted to periodic burns. Examples of chaparral plants include poison oak, scrub oak, pine, manzanita, chamise, yucca, and cacti. The animals are mainly grassland and desert types, including coyotes, jack rabbits, mule deer, rattlesnakes, mountain lions, kangaroo rats, foxes, bobcats, lizards, horned toads, praying mantis, honey bees, and ladybugs.
[Judith L. Sims ]
RESOURCES
BOOKS
Collins, Barbara. Key to Coastal and Chaparral Flowering Plants of Southern California. Third Edition. Dubuque, IA: Kendall/Hunt Publishing Company, 2000.
Ricciuti, Edward. R. Chaparral (Biomes of the World. Tarrytown, NY: Benchmark Books, 1996.
OTHER
Collins, Barbara J. Wildflowers of Southern California: Photographs of the Chaparral. California Lutheran University, February 23, 2002. [cited May 27, 2002]. <http://ww1.clunet.edu/wf/>