Fenn, ME; Allen, EB; Geiser, ALH
The Mediterranean California ecoregion (CEC 1997; Fig 2.2) encompasses the greater Central Valley, Sierra foothills, and central coast ranges of California south to Mexico and is bounded by the Pacific Ocean, Sierra Nevada Mountains and Mojave Desert. The ecoregion description is adapted from CEC (1997). It is distinguished by its warm, mild Mediterranean climate, chaparral vegetation, agriculturally productive valleys, and a large population (>30 million). Th e Coast Ranges crest at 600 to 1200 m. Th e broad, fl at, Central Valley is drained by the Sacramento and San Joaquin Rivers into the Sacramento Delta and San Francisco Bay. Rugged Transverse Ranges, peaking at 3506 m, border the Los Angeles basin. Soils are complex, mostly dry, and weakly developed with high calcium (Ca) concentrations. Summers are hot and dry (>18 o C), winters are mild (>0 o C) with precipitation from winter Pacifi c Ocean storms; coastal fog is common May through July. Annual precipitation (200 to 1000 mm) is highly variable and droughts are common. Vegetation is characterized by chaparral, patches of oak woodland, grassland, and some coniferous forest on upper mountain slopes. Th e chaparral has thickened, hardened foliage resistant to water loss and forms a cover of closely spaced, mostly evergreen shrubs 1 to 4 m tall. Common shrubs include chamise (Adenostoma fasciculatum), buckbrush (Ceanothus cuneatus), and manzanita (Arctostaphylos spp.). Coastal sagebrush (Artemisia californica) and summer-deciduous plants that tolerate more xeric conditions are found at lower elevations. A blue oak-California foothills pine (Quercus douglasiiPinus sabiniana) woodland community forms a ring around the Central Valley, which once had extensive grasslands and riparian forests. Th e southern oak woodland extends into the Transverse and Peninsular Ranges and includes Southern California walnut (Juglans californica) and Engelmann oak (Quercus englemannii). Mixed-conifer forests (Minnich 1999) occur at a higher elevation than chaparral and include a variety of species mixes depending on elevation and site conditions, but are typically characterized by dense mixed-aged stands composed of coniferous (pine [Pinus spp.] and often fi r [Abies spp.] and incense cedar [Calocedrus decurrrens]) and broadleaved species (commonly oaks).