Location and General Description
The California Coastal Sage and Chaparral encompasses coastal terraces, plains, and foothills along the Pacific coast of northwestern Mexico and southern California, United States. The Santa Rosa Mountains of the Peninsular Range are included, although the San Jacinto Mountains just to the northwest are considered under the adjacent ecoregion. The eight Channel Islands are also part of this ecoregion, as are Isla Guadalupe and Isla Cedros. The climate is mediterranean, with cold wet winters and dry hot summers. Precipitation levels range between 150-500 mm/year. The vegetation grows on soils made of volcanic rocks on the base of the San Pedro Martir Mountains and on soils of sedimentary origin closer to the coast.
The California Coastal Sage and Chaparral supports a diversity of habitats including montane conifer forests, Torrey pine woodland, cypress woodlands, southern walnut woodlands, oak woodlands, riparian woodlands, chamise chaparral, inland and coastal sage scrub, grasslands, vernal pools, and freshwater and salt marshes. Coastal sage scrub, chamise chaparral, and oak woodlands dominate much of the landscape. Coastal sage scrub is a diverse and globally rare habitat type occurring in coastal terraces and foothills below 1,000 m, interspersed with chamise chaparral, oak woodland, grasslands, and salt marsh. This habitat type is characterized by low, aromatic and drought-deciduous shrublands of black sage (Salvia mellifera), white sage (Salvia apiana), Munz’s sage (Salvia munzii), California sage (Artemisia californica), California buckwheat (Eriogonum fasciculatum), bush sunflower (Encelia californica), toyon (Heteromeles arbutifolia), lemonade-berry (Rhus integrifolia), and a diverse assemblage of other shrubs, herbaceous plants, cacti, and succulents. Opuntia, Yucca, and Dudleya are some of the most common succulent genera, with the latter represented by several locally endemic species.
In the drier southern portion of the ecoregion, Agave shawii, Opuntia prolifera and Bergerocactus emoryi appear as the most abundant plant elements. Like other chaparrals, coastal sage scrub is a fire-adapted community with many species that resprout quickly from root crowns or rapidly germinate after burns. A number of plants lie dormant in the seed bank for decades, only germinating and flowering after periodic fires. Fire frequencies in sage and chamise chaparral habitats are estimated to have ranged between 20 and 40 years. Unlike chamise chaparral, coastal sage is primarily active during the cool, wet winters and largely sheds leaves during the dry summers. Chamise chaparral generally occurs in higher elevations than Coastal sage scrub on the lower slopes of the ecoregion’s ranges, but can also be found near the coast in areas with deeper soils and increased moisture. Chamizo (Adenostoma fasciculatum), manzanito (Arctostaphylos spp.), and buckthorn (Ceanothus spp.) are some of the dominant chaparral plants (Pase & Brown 1982, cited in Challenger 1998).
Southern oak woodlands once covered much of the foothills and plains of the ecoregion. The Los Angeles basin and San Fernando Valley were noted for their extensive savannas of coast live oak (Quercus agrifolia) and valley oak (Quercus lobata). Canyon live oak (Quercus chrysolepis) is more common at higher elevations. California walnut (Juglans californica) woodlands once occurred in foothills around inland valleys in the northern portion of the ecoregion. A few vernal pools are scattered among the oak savannas and grasslands. Riparian woodlands once lined streams and supported several species of willow, cottonwoods, sycamore, coast live oak, ash, white alder, and a diverse flora of herbaceous plants, shrubs, and vines.
Many species of wildlife depend on riparian habitats for resources and habitat. Some of the higher inland areas support many of the same conifer communities found in the Transverse Range, including sugar pine (Pinus lambertiana), ponderosa pine (Pinus ponderosa), Jeffrey pine (Pinus jeffreyi), Coulter pine (Pinus coulteri), and incense cedar (Calocedrus decurrens). Black oak (Quercus velutina) canyon live oaks, and manzanitas (Arctostaphylos spp.) are common associates in these montane forests. Cuyamaca cypress (Cupressus arizonica arizonica) and Tecate cypress (Cupressus forbesii) occur only on a few isolated peaks. Much of the Channel Islands are covered in coastal sage and chamise chaparral, with some oak woodlands on the larger islands.
A large number of specialist and endemic species of plants and animals are found here, including the Quino checkerspot butterfly (Euphydryas editha quino), Hermes copper butterfly (Lycaena hermes), San Diego thorn mint (Acanthomintha ilicifolia), San Diego ambrosia (Ambrosia pumila), San Diego barrel cactus (Ferocactus viridescens), San Diego pocket mouse (Perognathus fallax), Merriam kangaroo rat (Dipodomys merriami), Stephens kangaroo rat (Dipodomys stephensi), red-diamond rattlesnake (Crotalus ruber), San Diego banded gecko (Coleonyx variegatus abbotti), San Diego horned lizard (Phrynosoma coronatum blainvillei), California gnatcatcher (Polioptila californica), and the coastal populations of the cactus wren (Campylorhyncus brunneicapillus).
The ecoregion supports between 150 and 200 species of butterflies, has the highest species richness of native bees in the United States, and has a number of relict species such as the Riverside fairy shrimp (Streptocephalus woottoni), found in vernal pools. The rosy boa (Lichanura trivirgata), California legless lizard (Aniella pulchra), and several relict salamanders are examples of the unusual and distinctive herpetofauna. The Mexican portion of the ecoregion constitutes the second largest area of scorpion diversity in Mexico, with 21species (Robles-Gil 1993), and is a prime zone of diversification for spiders, with 332 species of the 1000 known in Mexico.
The Channel Islands are noted for endemic and relict plant and animal species and subspecies, many being restricted to single islands. Buckwheats, locoweeds, oaks, and the succulent Dudleya’s are noted for several island endemics. The Catalina ironwood (Lyonothamnus floribundis) is a good example of a relict species once found throughout the mainland. The island night lizard (Xantusia riversiana), island fox (Urocyon littoralis), and Santa Catalina shrew (Sorex willetti) are other endemic animals. Near San Diego, the unique Torrey pine (Pinus torreyana) woodland occurs in Torrey Pine State Reserve. This tree occurs only here in a small population and on Santa Rosa Island. Nutall’s woodpecker (Picoides nuttallii) is endemic to this ecoregion, as are several endemic subspecies, which occur in the Channel Islands. Virtually all of the ecoregion is included in the California Endemic Bird Area (Stattersfield et al. 1998).
Much of the ecoregion has been lost to agricultural and urban expansion. Currently, only 15% of the region is intact (Castellanos & Mendoza 1991). Some scrub communities, such as Riversidian Alluvial Fan Scrub, are now confined to remnant patches along unaltered streams and washes. The vast majority of oak savannas and walnut woodlands have been destroyed. Most coastal habitats have been highly altered throughout the ecoregion. The Channel Islands have experienced widespread loss of original habitats and degradation from grazing and introduced species. In general, remaining coastal sage habitats are extremely fragmented and isolated in areas of intensive development, precluding effective dispersal of most species. Field studies suggest that isolated fragments of less than 1 km2 (10-100 ha) will lose their native vertebrate species within a few decades (Fleishmann and Murphy 1993). Isolated canyons in southern California lose at least half of their bird species within 20 to 40 years after isolation, although many have been observed in narrow corridors. Isolated blocks of relatively intact coastal sage scrub occur in Camp Pendleton Marine Corps base, Santa Monica Mountains parklands, San Joaquin Hills near Laguna Beach, and Irvine Ranch in Orange County. Patches elsewhere are quite small and highly fragmented. Chamise chaparral still occurs in relatively large blocks on some inland foothills. California walnut woodlands were formerly most abundant in the Puente Hills, but now the last remaining patches occur in the San Jose Hills south and east of Covina. Tonner Canyon and Soquel Canyon once had well-developed walnut forests, but these are being rapidly destroyed.
Torrey Pine State Reserve protects one of only two known populations of this rare conifer. The fragile coastal sage understory is often damaged by visitors. Native grasslands, vernal pools, and oak savannas with Engelmann oak (Quercus engelmanii) are conserved in the Santa Rosa Plateau Reserve near Elsinore, which is managed by Riverside Co., CDFG, and The Nature Conservancy. Existing laws offer only minimal protection; these include the Natural Communities Conservation Planning Program (NCCP) of 1991 that restricts destruction of some coastal sage scrub, and the Endangered Species Act listing of the California gnatcatcher, which created restrictions on destruction of habitat for extant birds. Native habitats on Santa Cruz Island are currently being restored by The Nature Conservancy, which manages the island as a reserve. In Mexico, several sites have been identified as Important Bird Areas, including Isla Guadalupe and Isla Cedros, and lower parts of Sierra Juarez and Sierra San Pedro Martir (Benitez et al. 1999). Furthermore, CONABIO identified Santa Maria-El Descanso as a terrestrial priority within this ecoregion (Arriaga et al. 2000).
Types and Severity of Threats
Native habitats continue to be cleared for housing, golf courses, orchards, and other forms of development. Much of the remaining habitat, particularly near the coast, occurs only in very small patches and is highly isolated, fragmented, and surrounded by development, which is generally hostile environment for most native species. Small habitat blocks face numerous threats, including invasion of alien species, predation by introduced animals and people, frequent fires from human activity, dumping, and pollution. Type conversion of chaparral and shrub communities to grassland is carried out through burning, grazing, and herbicide eradication of shrub species. Consequently, grasslands dominated by introduced species have greatly increased in the area. Decades of fire suppression in chaparral have allowed the accumulation of senescent vegetation, creating conditions for catastrophic hot fires that kill dormant seed beds and individual plants that are usually resistant to low-intensity fires.
Grazing by domestic livestock, particularly sheep, can have a serious impact on coastal sage scrub communities. Santa Cruz Island has been heavily damaged by 130 years of feral sheep grazing, with only 6 percent of the island still covered by degraded coastal sage scrub. Cattle, rabbits, deer, and pigs also contribute to similar situations throughout the Channel Islands. Plowing for agriculture or development destroys root crowns, thereby reducing any opportunities for regeneration. After fires and intense grazing, several invasive species can dominate, including foxtail fescue, red brome, and wild oats. Planting of ryegrass after fires as a short-term measure to prevent erosion can impede regeneration of native species. Controlled burns and brush removal are not necessary, because coastal sage scrub does not accumulate high fuel loads. Oxidants from smog have been implicated in damage and reduction in growth of coastal sage scrub. Numerous species of alien plants and animals compete for resources and kill native species. Introduced plant species make up 23 percent of the flora. Riparian woodlands are impacted by clearing, grazing, and the reduction of flow in streams, which alters successional patterns. The salt extraction industry is a threat in the Mexican portion of the ecoregion. An abundance of introduced and alien species of plants and animals compete for resources and directly kill native species.
Seventy-seven species in southern California are currently listed under the Endangered Species Act, and another 378 are under consideration. Some of the federally recognized threatened and endangered species include the California gnatcatcher (Polioptila californica), San Diego banded gecko (Coleonyx variegatus abbottii ), cactus wren (Campylorhyncus brunneicapillus), Merriam kangaroo rat (Dipodomys merriami), flannel-mouthed sucker (Catostomus latipinnis), western patch-nosed snake (Salvadora hexalepis), and cheese-weed moth lacewing (Chrysoperla spp.). Thirteen plant species of the coastal sage scrub are recognized as threatened or endangered. Unfortunately, many other species are threatened with extinction and extirpation, but the conservative listing practices of federal and state agencies preclude their formal recognition.
Justification of Ecoregion Delineation
In the United States portion this ecoregion matches Omernik’s (1995) Southern and Central California Plains and Hills (6). Bailey (1994) maps the coastal portion of this ecoregion as the Southern California Coast Section (261B) and the interior portion as the Southern California Mountains and Valley Section (M262B). The latter section extends further inland than Omernik’s boundaries, encompassing more montane and desert habitats. Küchler (1975) identifies several vegetation types within the ecoregion, including valley oak savanna, southern oak woodland, coastal sagebrush, chaparral, California prairie, southern Jeffrey pine forest, and coastal salt marsh. In Mexico our classification follows INEGI (1996) maps, from which we lumped "chaparral" and "subtropical matorral" and all enclosed agricultural vegetation types. This ecoregion is distinguished by species endemism (see description above) and unique species assemblages and processes. Linework was reviewed by experts during ecoregional priority setting workshops (CONABIO 1996 and 1997) in Mexico.
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Prepared by: David Olson, Alejandra Valero, Jan Schipper, and Tom Allnutt
Reviewed by: R. Cox and Eduardo Inigo-Elias