Biological diversity in the California Floristic Province
As one of only five areas with a Mediterranean-type climate in the world – all of which are on the hotspot list – the California Floristic Province is characterized by hot, dry summers and cool, wet winters. The region contains a wide variety of ecosystems, including sagebrush steppe, prickly pear shrubland, coastal sage scrub, chaparral, juniper-pine woodland, upper montane-subalpine forest, alpine forest, riparian forest, cypress forests, mixed evergreen forests, Douglas fir forests, sequoia forests, redwood forests, coastal dunes, and salt marshes. Today, about 80,000 square kilometers (km2) or 24.7 percent of the original vegetation, remains in an almost pristine condition.
Floristically this province is within the Madrean Region of the Holarctic Kingdom. The California Floristic Province includes most of the State of California; a portion of extreme southwest Oregon; a very small piece of western Nevada around Lake Tahoe; and a portion of northern Baja California. The Province includes portions of the following mountain ranges: California Coast Ranges; Cascade Range; Klamath Mountains; Peninsular Ranges; Transverse Ranges; Sierra Nevada Mountains. The California Great Central Valley is an integral part of the California Floristic Province, although agricultural conversion has eliminated most of the natural environment of this valley.
Like other Mediterranean-type ecosystems, the California Floristic Province is distinguished more by the endemism of its plants than its animals. Of nearly 3500 species of vascular plants in the hotspot, more than 2,120 (61 percent) are found nowhere else in the world. Around 52 plant genera are also endemic.
|Diversity and Endemism|
|Taxonomic Group||Species||Endemic Species||Percent Endemism|
The high levels of plant species endemism in the California Floristic Province are due to its varied topography, climate zones, geology and soils. The number of vascular plant species found in the California Floristic Province is greater than the total number of species from the central and northeastern United States and adjacent parts of Canada, an area ten times larger than the California hotspot.
Four subregions within the hotspot are centers of exceptionally high plant diversity: the Sierra Nevada, the Transverse Ranges in southern California, the Klamath-Siskiyou region in the coastal mountain ranges of California and Oregon, and the Coast Ranges. The Transverse Ranges, represent a narrow strip that runs east to west in southern California, separating the Coast Ranges to the north from the Peninsular Ranges to the south. The Klamath-Siskiyou region bridges the coastal mountain ranges of California and Oregon, and is home to the most diverse temperate coniferous tree community in the world.
In addition, serpentine soil habitats occur along fault zones in the Central and North Coast and Cascade ranges, from sea level to an elevation of 2900 meters. Due to specific chemical and physical characteristics of the soils, these habitats are nutrient-poor, and this has led to the establishment of a highly specialized and diverse flora. It has been estimated that serpentine endemic plant species represent ten percent of the California Floristic Province's endemics.
The hotspot is also home to two spectacular endemic tree species, the giant sequoia (Sequoiadendron giganteum) and the coastal redwood (Sequoia sempervirens). The giant sequoia, which remains in 75 groves in the Sierra Nevada range, is the most massive species ever to live on Earth, reaching heights of 75 meters and circumferences of 30 meters in the oldest trees. The closely related redwood is often even taller (sometimes reaching 105 meters), although smaller in circumference.
Although there are fewer than 10 endemic bird species found in the California Floristic Province, out of a total of more than 340 recorded, more species of birds breed in this region than anywhere else in the United States. There are two Endemic Bird Areas (EBAs), as defined by BirdLife International, in the hotspot. One of these EBAs, Guadalupe Island, is the native range of the Guadalupe junco (Junco insularis, CR) and the now extinct Guadalupe caracara (Polyborus lutosus) and Guadalupe storm-petrel, the latter last recorded in 1912. The California condor (Gymnogyps californianus, CR), the largest North American bird, once ranged across most of the continent; its main stronghold is in this hotspot. Although there were only about 25-35 condors remaining in the 1970s, captive breeding programs have increased the population to more than 100.
Of the more than 150 native mammal species in the California Floristic Province, about 20 are endemic to the region. Several large mammal species once found in the hotspot have been extirpated from California since the arrival of European settlers. These include the grizzly bear (Ursus arctos), grey wolf (Canis lupus), jaguar (Panthera onca), and bison (Bison bison). Ironically, the grizzly bear appears on the state flag of California and has been the state symbol for more than 150 years. A hunter shot California's last grizzly in 1920. Although there are occasional jaguar sightings reported from southern Arizona, this cat has been driven from most of its U.S. range. The last jaguar in California was shot in Palm Springs in the year 1860.
Other flagship mammal species occurring in the California Floristic Province are the kit fox (Vulpes macrotis), the island fox (Urocyon littorialis, CR), the latter with six subspecies confined to the six largest of the eight Channel Islands, the widespread Roosevelt's elk (Cervus elaphus roosevelti), and the tule elk (Cervus elaphus nannodes), the largest and smallest of the North American subspecies, respectively. The tule elk was on the verge of extinction at the close of the 1800s. Today, habitat protection and breeding programs have helped establish a wild population of more than 1000 animals.
Four of the hotspot's nearly 70 reptiles are endemic, including two that are found only on Cedros Island, off the Baja California Peninsula: the Cedros Island diamond rattlesnake (Crotalus exsul) and Cedros Island horned lizard (Phrynosoma cerroense). A number of species have fragmented populations or low population numbers, including the coast-patched nose snake (Salvadora hexalepis virgultea), the venomous red-diamond rattlesnake (Crotalus ruber), and the western ringneck snake (Diadophis punctatus).
The highest levels of endemism in the California Floristic Province are found among amphibians, with over half of the nearly 50 species occurring found only in this hotspot. In general, the area is notable for its high endemism of salamander species. The most diverse genus of salamanders is Batrachoseps (nearly endemic to this hotspot), which includes the San Gabriel slender salamander (B. gabrieli), recently discovered in mountains in the Los Angeles metropolitan area. Two representatives of the salamander genus Hydromantes are endemic to this region. This genus is interesting in that it has an unusually disjunct distribution; its only other members are found within the Mediterranean region of southern Italy and France. Other noteworthy salamander species are the arboreal members of the Aneides genus, which ascend to the top of the tallest redwoods, and the endemic California tiger salamander (Ambystoma californiense, VU), which has emerged as a major point of contention between conservationists and developers in rapidly growing Sonoma and Santa Barbara counties. The rare arroyo southwestern toad (Bufo californicus, EN), a stocky upland toad found in the hotspot, is protected under the U.S. Endangered Species Act.
The California Floristic Province has a relatively small number of inland fishes (just over 70 species), because of its isolation from the large eastern North American fish fauna by the western mountains and deserts. One of the most interesting groups is a collection of lamprey species, including a cluster of localized landlocked species in the northern mountains.
The hotspot also has impressive invertebrate diversity. The state of California is home to an estimated 28,000 species of insects, about 9000 of which are endemic (32 percent). These species represent about 30 percent of all known insects in the United States and Canada.
The natural ecosystems of the California Floristic Province face serious threats from human activities and development. California's economy would rank it among the top seven countries in the world, and it is the most populated (estimated at 35 million people in 2002) and fastest growing state in the United States. California supplies one-half of all the agricultural products consumed in the United States each year. Direct pressures on ecosystems include urbanization, water pollution, habitat fragmentation; expansion of large-scale agriculture; strip mining and oil extraction; invasive alien species; road construction; intensive livestock grazing; deforestation; increasing use of off-road vehicles; and suppression of natural fires.
Human population pressures have rendered California one of the four most ecologically degraded states in the country, with all or part of the nation's eight most threatened ecosystems represented: beach and coastal strand, southern California coastal sage scrub, large streams and rivers, California riparian forests and wetlands, California native grasslands, old-growth ponderosa pine forests, cave and karst systems, and the ancient forests of the Pacific Northwest, which include the coastal redwoods.
Native grasslands and vernal pool habitats in the hotspot have been reduced to about one percent of their original extent by the conversion of natural lands to agricultural fields and livestock pasture, urban development, and the invasion of exotic grasses. The magnificent redwood forests, which once occupied 8,000 km2 along the California coast, have been reduced by intensive logging operations to 15 percent of their original standing area during the last 150 years (although many of these stands have regenerated).
Other seriously threatened ecosystems include wetlands, riparian woodlands and southern maritime sage scrub, which have all been reduced to 10 percent or less of their original area. Wetlands are destroyed by land filling and the diversion of water for agricultural, industrial, and residential development. The reduction in wetlands has been accompanied by a subsequent decline in shellfish, fish, and waterfowl populations that depend on these habitats. Riparian forests face threats from logging, grazing, and development (having been reduced by about 90 percent), while coastal sage scrublands are threatened by housing development, commercial development, and the increasing use of off-road vehicles.
Today, about 25 percent of the original vegetation of the hotspot remains in more or less pristine condition.
Conservation action and protected areas
A little under 110,000 km2, or 37 percent of the total land area of the California Floristic Province, is under official protection, although less than one-third of this is in IUCN categories I to IV. Among the mechanisms for protection in this region are several national parks (including two in northern Baja California); nearly 50 wilderness areas (managed by the U.S. Forest Service); 16 national wildlife refuges (managed by the U.S. Fish and Wildlife Service); 107 state parks; six U.S. military installations; and more than 50 areas managed by non-governmental organizations (NGOs). The creation of many of these protected areas was the result of the dedicated efforts of national conservation organizations, including the Sierra Club, The Nature Conservancy, and the Wilderness Society.
The hotspot includes two of the oldest national parks established in the United States: Yosemite National Park and Sequoia National Park (which provides protection to the biodiversity in the southern Sierra Nevada) were created within days of each other in 1890. Other important national parks in the region include Redwood National Park, officially establish in 1968 (and expanded in 1978) and the 1,010-km2 Channel Islands National Park, a series of islands off the coast of southern California that provide protection for nesting colonies of seabirds and breeding populations of seals and sea lions, as well as the island fox.
In the last several decades, California has spent more money on conservation and set aside more habitat for protection than any other state in the United States. Nonetheless, the situation in California, the wealthiest of the United States, serves as an important reminder that biodiversity loss and the lack of complete and adequate protection for unique and threatened ecosystems is not just a problem in developing countries.
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- The origin of this entry is based on contributions from William R. Konstant, Dean Taylor, David A. Wake, Scott Robins Loarie, Roxanne Bittman, and Barbara Ertter.
- For a complete list of all contributors to the Biodiversity Hotspot program, see Biodiversity Hotspot Site Credits.
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