California's chaparral can been delineated as three types: 1) Chamise-Redshank Chaparral (4.1 million ha, 10.1 million acres), 2) Coastal Scrub (0.65 million ha, 1.6 million acres) and 3) Mixed Chaparral (1.3 million ha, 3.1 million acres), and Montane Chaparral (0.2 million ha, 0.5 million acres) for a total of about 6 million ha (15.3 million acres). Chamise-redshank chaparral occurs below 1200 m. (4000’) elevation, primarily in the Peninsular and Transverse Ranges, with extensive stands from the Tehachapi Mountains south to San Diego County. This cover type consists of greater than 50% chamise (Adenostema fasciculatum) or redshank (A. sparsifolium) or a mixture of both. Mixed chaparral occurs below 1500 m (5000’) elevation on steep dry slopes in the Coast Ranges and Sierra Nevada mountains and foothills, and extensively throughout the Transverse, Peninsular and Tehachapi Mountains. It is characterized by co-dominance of several shrubby species. Mountain Chaparral grows in close association with conifers from San Diego to Siskiyou County at elevations of 900 to 3000 m (3000 to 10,000’). Coast scrub occurs from sea level to 900 m (3000 ft.) in a discontinuous narrow band along the coast, usually within 32 km (20 mi) of the ocean. It runs nearly the full length of the state.
California’s chaparral shrub communities occur in a Mediterranean-type climate. Mediterranean climates can be found along the west side of continents in mid-latitudes from 30° to 50° N and 30° to 40° S, commonly in a belt of prevailing westerly winds. In Chile and Spain these Mediterranean shrub communities are called matorral, in France it is called maquis and in Italy, macchia. In South Africa it is known as fynbos and in southwest Australia kwongan. These Mediterranean shrublands are classified under Köeppen’s climate classification system as “Cs”. The “C” stands for warm temperature climates, where the average temperature of the coldest months is 64° F. The “s” stands for a dry season in the summer.
The winter Mediterranean climate is mild and moist. During the summer it is very hot and dry. The annual temperature range is between -1° and 38° C (30° and 100° F). Most of this biome only gets about 25-43 cm (10-17”) but in California rainfall amounts of 100 cm (40”) may occur at northern and high elevation locations. Most rain comes in the winter. Because of the long period of summer, only plants with hard leaves, such as scrub oaks and chamise shrubs, can survive.
Topography and Soils
Most chaparral vegetation occurs on steep hills and mountains below 1500 m (5000’) elevation. Only mountain chaparral occurs above this range. Chaparral soils range from deep, weakly developed soils to shallow, rocky soils. Generally chaparral is thought to occur upon thin, porous, and rocky soils that are relatively low in nitrogen, potassium and phosphorous. While chaparral and other Mediterranean-type vegetation changes over time (depending on fire and disturbance regimes), chaparral is likely to be the edaphic climax vegetation on well-drained rocky soils with or without the influence of fire. Due to their coarse grain size and their high content of weatherable minerals, these soils are susceptible to erosion, and on steeper slopes, to landslides.
Soils under chamise may exhibit hydrophobicity, repelling water on the soil surface. However, when water does penetrate the soil surface, it drains rapidly through the coarse soil textures, offering little water-holding capacity. Fire can cause some soils to become water repellent or hydrophobic. The mechanism of hydrophobic soil formation has been explained and identified as important to post-fire sediment yields.
Current Plant Communities
Chaparral is composed largely of evergreen, sclerophyllous shrub species that range from 1 to 4 m in height. Other growth forms including soft-leaved subshrubs, perennial herbs, geophytes (bulbs and corms), and annual herbs, are less abundant in mature chaparral but can be present in abundance in early and late successional stands of chaparral. Depending on the species composition and underlying topography and soil, the structure of chaparral can range from low, monotonous, smooth-textured vegetation to more heterogeneous stands approaching the vertical structure of woodlands.
Chaparral generally is thought to be a fire-dependent system, based on the many adaptations of its characteristic species, and its resilience in form and species composition to periodic burning. Most of the characteristic shrub species in chaparral can be organized into three adaptive strategies related to fire: (1) shrubs that have stems that regenerate following fire from below ground burls (resprouters); (2) shrubs that produce large amounts of dormant seed that persist for long periods of time and germinate by heat or chemical processes initiated by fire (obligate seeders); and (3) plants that apply both strategies.
The species composition of a particular chaparral stand is largely influenced by fire. Chaparral generally returns to pre-fire structure and composition within a normal fire regime; however, considerable research has documented various effects of fire regime on species mortality. Frequency of fire has been shown to affect chaparral species composition, where short fire intervals may eliminate obligate seeding species in favor of resprouters.
The most common and widespread species in “true” or “hard” chaparral is chamise (Adenostema fasciculatum). Other common shrub species include manzanita (Arctostaphylos spp.), ceanothus (Ceanothus spp.), oak (Quercus spp.), poison oak (Toxicodendron diversilobum), mountain mahogany (Cercocarpus betuloides), and toyon (Heteromeles arbutifolia).
In the coastal sage scrub or “soft” chaparral common species include coyote bush (Baccharis pilularis), Bush lupine (Lupinus spp.), California buckwheat (Eriogonum fasciculatum), sages (Salvia spp.), California sagebrush (Artemisia californica), deerweed (Lotus scoparius), and monkeyflower (Mimulus spp.).
Arthur W. Sampson, an early ecologist, separated the California chaparral association into five ecological regions on the basis of climatic variation and differences in floristic composition. The regions are 1) North Coastal Region, 2) Central Coastal Region, 3) South Coastal Region, 4) North Sierran Region and 5) South Sierran Region. Each of these regions has the same dominant growth forms in common but there are differences in topography and to some extent distinctive species.
The North Coastal Region extends from San Francisco Bay to Trinity and Shasta Counties.
The abundance and diversity of wildlife in California’s chaparral is not commonly recognized. The iconic, but now extinct, California grizzly bear (Ursus arctos californicus) and the majestic California condor (Gymnogyps californianus), which nearly became extinct and remains endangered, are the chaparral’s most famous animal residents. Chaparral habitat supports nearly 50 species of mammals, but none live exclusively in chaparral. Some are found primarily in mature chaparral and others in young chaparral and along ecotones between chaparral and other plant communities. Several prefer riparian areas in and near chaparral. Predators in California’s chaparral include mountain lions, bobcats and coyotes. These predators prey on blacktail deer, rabbits and ground squirrels (Quinn 1990).
Although many bird species travel over and through the chaparral, only a few reside year-round (California Chaparral Institute 2012). Common birds in chaparral ecosystems include the wrentit (Chamaea fasciata, observed mostly by call),Western Scrub Jay (Aphelocoma californica), California towhee, (Melozone crissalis), spotted towhee (Pipilo maculatus) and California thrasher (Toxostoma redivivum). Birds especially common in chaparral for several years after a fire include Costa’s hummingbird (Calypte costae, especially spring and summer), sage sparrow (Artemisiospiza belli, mostly winter), rufous-crowned sparrow (Aimophila ruficeps), lazuli bunting (Passerina amoena, April through September), Lawrence’s goldfinch (Carduelis lawrencei), and black-chinned sparrow (Spizella atrogularis, April through summer months).
Vegetation change in chaparral is largely the result of recurring fires. Compared to fire, Drought and grazing have limited influence on vegetation dynamics.
Chaparral has been described as “autosuccessional,” undergoing a rapid succession from largely herbaceous flora immediately after fire to relatively dense woody vegetation in a short time period, with minimal loss of species. Immediately after a fire the grasses and forbs initially dominate because of their sheer numbers and showy flowers. Within 2 – 5 years the seedlings of chaparral plants, and the shrubs resprouting from their crown or germinating in response to fire, take over. Their more aggressive root systems exploit deeper water reserves and they will eventually shade out the forbs and grasses and replace them. The shrub phase of succession starts from crown sprouts and seedlings the first year after a fire, and by the fifth year plants are tall enough to shade out the shorter herbs and approach a climax community.
Inhibition of seed germination between fires has been related to chemicals produced by some of the chaparral shrubs. This is termed allelopathy. For example, chamise leaves have a water-soluble compound that washes to the soil and stops germination of numerous herbs. This in part explains the bare soil appearance beneath mature chamise. Manzanita shrubs in all parts--leaves, stems, roots, and old leaf litter--contain chemicals which inhibit seed germination of itself and other plant species. Even upon removal of manzanita stems and leaves, the chemical compounds in the soil continue to inhibit seed germination for some years. Fire is important in burning the compound out of the soil so that seed germination can take place.
Yearly and Seasonal Variation
Biological activity in chaparral increases sharply with the first fall rains. At this time seeds of grasses and forbs germinate, grow through the mild winter, and flower by mid-spring. Next season’s seed matures by late spring or early summer when the dry season and high temperatures begin. The shrubs and trees do most of their annual growth at the start of the fall rains in October and November. Many are in flower as early as December and January. By flowering this early, there is adequate moisture available for seed maturation before the summer drought begins.
The dominant driving force in chaparral is fire. The majority of chaparral species are either adapted to occasional fire or are able to persist in fire prone ecological regimes. The distribution and species composition of chaparral, at the landscape-scale, is largely influenced by varying interactions between fire regime (frequency, seasonal timing, size, and intensity) and physical environment. The primary source of wildfires prior to human alteration of the “natural” fire regime was lightning. Although lightning-caused fires remain, fire regimes have changed due to increased human ignitions and fire suppression.
Volatilization of nitrogen and to a lesser degree potassium are important fire associated nutrient losses. Some nitrogen is recovered or replaced by nitrogen fixing legumes such as lupine (Lupinus spp.) and deerweed (Lotus spp.), and non-leguminous plants such as California lilac (Ceanothus spp.). The interrelationships among soil microorganisms, heating rates associated with wildfires or prescribed burns, soil moisture at the time of a fire, and various nitrogen-fixing plant species have been studied, but much remains to be learned about the dynamics of nutrients in chaparral systems. Soil erosion following fire results in large losses of all nutrients.
Chaparral vegetation is adapted to drought. Thus, drought is not really a disturbance in these ecosystems.
Grazing by domestic livestock is largly limited to early herbaceous stages of succession which last for only a few years. Grazing in coastal sage scrub may suppress succession back to a shrub-dominated community.
Fire is a normal part of chaparral communities and thus represents a major fire hazard that threatens public safety. Most management is directed at reducing fire hazard without adversely changing watershed function, water quality, biodiversity and habitat.
Following is a brief introduction to some chaparral issues and practices.
Prescribed burning is an issue because of the air pollution generated by fires and because most urban residents fear fire. California ranchers have been burning for range improvement under permit from the California Department of Forestry since 1945. Burning for human benefit has a much longer history in California, but records do not include how early fires were planned. While many recognize the potential value of fire for achieving resource objectives related to fire hazard reduction, range improvement, sediment and flood management, and wildlife habitat, liability issues are a big deterrent to prescribed burning.
Erosion on steep chaparral slopes is best described as an episodic process strongly influenced by complex internal thresholds. Because of experience on agricultural lands where topsoil is a valuable resource, all erosion is considered undesirable. But on steep, naturally unstable chaparral slopes, ecosystems have developed mechanisms for adequately replacing or foregoing lost nutrients. In the chaparral ecosystem, erosion is natural, and in the long term unpreventable. The real management issues created by erosion are flooding and sedimentation that occur in populated valleys below.
Within the Mediterranean-climate region of California and adjacent regions, invasive plants are largely concentrated in the lower elevation valleys and foothills. Fire has historically been an important part of the ecology of many of these ecosystems; however, anthropogenic disruptions of natural fire regimes have contributed to the widespread invasion of certain communities. Throughout the Coast Ranges and foothills of the Sierra Nevada and Cascades, high fire frequency has contributed to the type-conversion of shrublands and closed woodlands to annual grasslands dominated by alien grasses and forbs of Mediterranean Basin origin.
Most impacts on the physical characteristics of fire-impacted streams are evidenced by changes in sediment load. Increased sediment flows following a fire can impact both ecological health and drinking water operations. The large quantities of post-fire sediment can overwhelm the biological habitat available for aquatic organisms such as fish, as well as organisms that depend on water for some life stage, such as amphibians and insects.
Large post-fire sediment fluxes impact drinking water systems two ways. First and perhaps foremost is the danger that reservoirs, infiltration basins, and treatment works will be filled, damaged, or otherwise disrupted by sediment. Second, high sediment load is likely to increase pre-treatment processing needs (and costs) for suspended sediment removal. These impacts are highest in areas immediately adjacent to fires but may extend a 100 miles downstream.
The impacts of wildfire and prescribed burns on chemical composition of streams are not well-documented, but studies suggest that nutrient loads, particularly phosphorus and nitrogen, increase after fires, and that the effect may be greater from wildfires than from prescribed burns. Nitrogen is exported primarily as nitrate, and post-fire concentrations can exceed the federal drinking water standard of 10 milligrams per liter.
Urban development into chaparral ecosystems has resulted in frequent loss of life and property. The brushland fire-flood-erosion sequence is particularly well known in chaparral areas of southern California. Urban encroachment accelerates the cycle and adds the potential for tragedy. Unless adequate measures are taken in new developments, fire protection and flood control agencies are hard pressed to safeguard life and property. When hazardous conditions come about through improper land use or lack of planning, they are extremely difficult to correct by either private or public action.
According to studies by the Lawrence Berkeley Laboratory (U.S. Department of Energy), climate change may lead to dramatic increases in both the annual area burned by California wildfires and the number of potentially catastrophic fires — doubling these losses in some regions. These changes would occur despite deployment of fire suppression resources at the highest current levels, implying that climatic change could precipitate an increase in both fire suppression costs and economic losses due to wildfires.
Management Practices and Uses
A variety of methods including fire, mechanical and chemical controls have been used to manage chaparral and the fuel it represents. Reseeding has been used following brush control to convert brushlands to productive grazing land.
Prescribed burning has a long history of use in California. In some locations Native Americans set fires to remove brush and stimulate the growth of desired food and fiber plants. Starting in the 1800s ranchers set fires to reduce brush and increase grass. From the 1920s through the 1970s prescribed burning was used not only by ranchers but also by agencies to reduce fuel loads and increase forage. Starting in the 1960s suburban development in the state’s wildlands began to increase the liability of controlled burning. By the late 1900s the use of fire to control brush had declined due to liability issues, air pollution regulations and the public’s general fear of fire.
A variety of mechanical methods have been used to control shrubs in chaparral, including crushing and piling with bulldozers and blades, brush rakes, chains and ball, and chains. Brush can also be successfully chopped or shredded using brushland disks, roller choppers and brush shredders. Hand clearing has also been used successfully. All of these methods are expensive because of the equipment, fuel and/or labor involved.
From the 1950s to the 1970s 2,4-D and 2,4,5-T (also known as Agent Orange during the Vietnam War) were used to kill brush in chaparral and other woody plant communities. These highly toxic chemicals were frequently very effective but in 1970, the United States Department of Agriculture halted the use of 2,4,5-T. Replacement herbicides have been less successful and expensive. In California pesticides are strictly regulated and this has further reduced the use of chemicals to control brush.
Brush removal methods involving heavy machinery, chemicals or fire are expensive and require great care. Properly managed goat grazing can reduce the cost of brush control. Goats are particularly effective at controlling light stands or brush or brush that regrows following a fire. Goats should not be expected to control tall, mature brush, but they provide a promising alternative to herbicides for controlling brush regrowth. Goats pose specific problems in chaparral: the need for roads, fencing or herding, water, and supplemental feeding. They must also be protected from predators, disease, and poisonous plants. Because of some of these problems and their limited availability, goat grazing has not received widespread use.
Often fire, mechanical and chemical methods have been used to remove brush, followed by reseeding with grasses and legumes and follow-up control of brush regrowth. These methods have been very successful at increasing forage production on chaparral lands. They have also been used to create fire breaks to slow the progress of wildfires. Type conversions are expensive and have resulted in loss of ecosystem services. There have been instances where erosion increased and there have been losses of native biodiversity due to seeding with introduced species. Consequently type conversions are infrequent in the early 21st century.
California Chaparral Weblinks
- CALIFORNIA RANGELAND Research and Information Center Information about California rangelands (UC Davis)
- CALIFORNIA RANGELAND WATERSHED LABORATORY Research and outreach on the diverse managed ecosystems (UC Davis)
- CDFG – Biogeographic Data Provides GIS support for all DFG branches
- Ecology and Management of Grazing Online Course For-fee online course
- Manual of California Vegetation California Native Plant Society vegetation description system
- Mendocino/Lake Livestock and Range Topics
- Plant Information Information on California plants.
- Rangeland Forage Loss Estimating annual rangeland forage loss
- Rangeland Monitoring Monitoring publications
- Terrestrial Vegetation of California Book on California’s diverse and ever-changing vegetation published in 2007 (Michael Barbour and Todd Keeler-Wolf, eds.)
- Weed Research and Information Center Information on California weeds