Theecology of California can be understood by dividing the state into a number ofecoregions, which contain distinctecologicalcommunities of plants and animals in a contiguous region. The ecoregions of California can be grouped into four major groups: desert ecoregions (such as theMojave Desert), Mediterranean ecoregions (such as theCentral Valley), forested mountains (such as theSierra Nevada), and coastal forests.[1]
Different authorities define the boundaries of ecoregions somewhat differently: this article follows the definitions of theWorld Wide Fund for Nature (WWF) and theUnited States Environmental Protection Agency (EPA)
California's high mountains block most moisture from reaching the eastern parts of the state, which are home to California'sdesert and xeric shrub ecoregions. The low desert of southeastern California is part of theSonoran Desert ecoregion, which extends intoArizona and parts of northernMexico.[2] California has two high deserts: theMojave Desert and theGreat Basin Desert. The Mojave Desert ecoregion is marked by the presence ofJoshua trees.[3] The dry cold Great Basin desert of California consists of theOwens Valley, and is classified intoGreat Basin shrub steppe by the WWF,[4] and into theCentral Basin and Range ecoregion by theEPA.[5]
The deserts in California receive between 2 and 10 inches (51 and 254 mm) of rain per year.[6] Plants in these deserts are brush and scrub, adapted to the low rainfall. Common plant species includecreosote bush,blackbrush,greasewood,saltbush,big sagebrush,low sagebrush, andshadscale.[6] Higher elevations have more precipitation, which allows drought-resistant trees to grow, such aswestern juniper andpinyon pine.[6]
The coast of California fromMonterey Bay south to the Mexican border, and inland fromSan Francisco Bay Area to the Sierra Nevada foothills contain California'sMediterranean ecoregions. This region is divided by the WWF into threeCalifornia chaparral and woodlands ecoregions, plus the Central Valley grasslands.[7] The EPA divides the region between the Central Valley (ecoregion 7), the Southern California chaparral (ecoregion 6), the Southern California mountains (ecoregion 8), and the Southern California coast (ecoregion 85).[5]
The WWF distinguishes between different chaparral ecoregions based on speciesendemism.[8] In the south, theCalifornia coastal sage and chaparral extends across the Mexican border into northwesternBaja California and Los Angeles.[8] The coastal sage ecoregion is notable for having the highest number of native bees in the United States, although much of the ecoregion is now urbanized.[8] TheCalifornia montane chaparral and woodlands include theTransverse Ranges north of Los Angeles as well as theSanta Lucia Range on theCentral Coast.[9] The montane chaparral consists of a mosaic of sage scrub, chaparral, and montane species, depending on altitude.[9] TheCalifornia interior chaparral and woodlands form a ring around theCentral Valley, covering the hills around the Bay Area as well as the foothills of the Sierra Nevada.[10] The interior woodland ecoregion contains several endemic species, due to unique soil types such asserpentine.[9]
These chaparral ecoregions contain numerous plant communities, including oak savanna,[10] oak woodland, conifer woodlands, chamise chaparral,coastal sage scrub, and coastal grassland.[8] These plant communities often occur as a mosaic,[9] caused by fire.[11]
California'sCentral Valley was once a largetemperate grassland containing nativebunchgrasses andvernal pools.[12]Grizzly bear,gray wolf,tule elk, andpronghorn antelope used to inhabit the grasslands.[13] The native grasslands and pools have now been largely replaced by livestock ranches and farms.[14] TheCarrizo Plain, where the native grass is preserved, is referred to as the "Serengeti of California".[15]
The cooler and wetter mountains of northern California are covered byforest ecoregions. Both the WWF and the EPA divide the mountains into three ecoregions: theSierra Nevada,[16] theKlamath Mountains,[17] and theEastern Cascades Slopes and Foothills (occurring on theModoc Plateau).[18]
The Sierra Nevada are home to half of thevascular plant species of California, with 400 species that areendemic to the region.[16] Like many mountain ranges, the plant communities of the Sierra group intobiotic zones by altitude, because of the increasingly harsh climate as elevation increases.[19] These biotic zones include montane forest dominated byconifers such asJeffrey pine andLodgepole pine,subalpine forest dominated bywhitebark pine, up toalpine tundra which cannot support trees.[20] The Sierra are also notable forgiant sequoia trees: the most massive on earth.[21]
The Klamath and Siskiyou Mountains are a notablebiodiversity hotspot, containing one of the four most biodiverse temperate forests in the world.[17] The diversity is caused by the ecoregion being adjacent to a number of other ecoregions, diverse soil, and havingrefugia caused by isolation in the lastice age.[17] Some endemic species in the Klamath mountains are limited to only one mountain or valley.[17]
The Eastern Cascades slopes of the Modoc Plateau are characterized by a mosaic of openponderosa pine forest, grasslands, and shrublands.[18] Although high, these slopes and mountains are in the rain shadow of theCascade Range, and hence are drier and more open.[20]
The coast of California north of San Francisco contains theNorthern California coastal forests (as defined by the WWF) and the southern section of theCoast Range ecoregion (as defined by the EPA). This ecoregion is dominated byredwood forest, containing the tallest and some of the oldest trees in the world.[22]
The redwood forests thrive in a thin belt up to 35 miles (56 km) wide next to the coast, where the trees are kept moist by winter rains and summer fog.[22] The redwood forests are also notable for having the highest forestproductivity in the world.[22]
