California interior chaparral and woodlands

Please note: These biome and ecoregion pages (and associated data) are no longer being updated and may now be out of date. These pages and data exist for historical reference only. For updated bioregion data, please visit One Earth.

This ecoregion forms a nearly continuous ellipse of oak woodland and chaparral around the California Central Valley, ranging from 300 to 3,000 ft in elevation (Barbour et al. 1993). The ecoregion continues across the coast ranges to the Pacific from Point Reyes to Santa Barbara, with breaks around the redwood belt south of San Francisco Bay and the montane communities of the Santa Lucia Range that parallel the coast south of Monterey Bay.

  • Scientific Code
  • Ecoregion Category
  • Size
    24,900 square miles
  • Status
  • Habitats

Biological Distinctiveness
Within the California Interior Chaparral and Woodland ecoregion, one finds a mosaic of grasslands, chaparral shrublands, open oak savannas, oak woodlands, serpentine communities, closed-cone pine forests, pockets of montane conifer forests, wetlands, salt marshes, and riparian forests. Oak savannas and chaparral are the most widespread and characteristic communities. Valley communities at lower elevation are characterized by foothill pine (Pinus sabiniana) and blue oak (Quercus douglasii), as well as a range of woodland and chaparral plants such as California buckeye (Aesculus californica), manzanita (Arctostaphylos spp.), redbud (Cercis occidentalis), chamise (Adenostoma fasciculatum), and scrub oak (Quercus dumosa). Coast live oak, canyon live oak, golden-cup oak, valley oak, interior live oak, and maul oak are also part of the diverse oak flora of this ecoregion. A number of endemic and relict pines and cypresses occur within the ecoregion, often restricted to single ranges or soil types such as serpentine (e.g., Sargent cypress, Cupressus sargentii, and McNab cypress, Cupressus macnabiana). Many of the closed-cone pines are dependent upon periodic fires to open their cones and prepare the understory for seedlings.

A diverse assemblage of shrubby and herbaceous plants occurs within the savannas and chaparral, with many local and habitat endemics. (Kartesz, pers. comm. 1996) estimates that the ecoregion harbors 2036 species of herbaceous plants, vines, and shrubs. Maritime chaparral around Monterey Bay is noted for a number of endemics, including Hooker manzanita (Arctostaphylos hookeri), Monterey manzanita (Arctostaphylos monteryensis), pajaro manzanita (Arctostaphylos pajorensis), sandmat manzanita (Arctostaphylos pumila), Monterey ceanothus (Ceanothus rigidis), and Monterey goldenbush (Ericameria fasiculata) (Schoenherr 1992). Communities on serpentine are particularly rich in endemic plants and invertebrates, including leather oak (Quercus durata), interior silktassel (Garrya condonii), milkwort streptanthus (Streptanthus polygaloides), and Muir’s hairstreak (Mitoura nelsoni muiri). Sandstone-derived soils near Coalinga support a number of disjunct populations of desert species, including Mojave sand verbena (Abronia pogonatha) and narrowleaf goldenbush (Ericameria linearifolius) (Schoenherr 1992).

Over seventy species of mammals occur in these habitats, with five endemic and near-endemic species– the giant kangaroo rat (Dipodomys ingens), Heermann kangaroo rat (Dipodomys heermani), Santa Cruz kangaroo rat (Dipodomys venustus), Sonoma chipmunk (Eutamias sonomae), Suisun shrew (Sorex sinuosus), and the salt marsh harvest mouse (Reithrodontomys raviventris), the highest number of endemic mammal species for U.S. and Canadian ecoregions. Plethodontid salamanders are diverse with five endemic species. Among the 100 species of birds that occur in this ecoregion, scrub jays (Aphelocoma coerulescens), acorn woodpeckers (Melanerpes formicivorus), and wrentits (Chamaea fasciata), are a few of the most characteristic species. The fresh and salt marshes of San Francisco Bay and other large estuaries along the coast once supported enormous populations of ducks, geese, shorebirds, and wading birds, particularly during the winter and migration seasons. Army ants (Neivamyrmex spp.) and primitive bristletails, and land snails are among the ecoregion’s large number of relict and unusual invertebrate species.

Many species and communities within the ecoregion are adapted to periodic fires, indeed many species depend upon fires for regeneration. An entire guild of annual herbaceous plants that occur in chamise chaparral have seeds that lie dormant for long periods until fires trigger their germination approximately every 20-25 years. Closed-cone pine communities historically burned about once every 25-50 years, and some species, such as the knobcone pine (Pinus attenuata), require fire to open their cones.

In summary, this ecoregion harbors a number of unique communities, with many species whose distributions clearly illustrate the ecological islands, specialization, relict nature, unique geologic history, and endemism of Californian biodiversity.

Conservation Status

Habitat Loss and Degradation
Approximately 30 percent of this ecoregion can be described as intact, concentrated in steeper foothill and montane areas. Virtually all native bunchgrass communities have been replaced by annual grassland understories in woodland areas. Some woodland areas above 915 m (3000 ft) in the Sierra Nevada belt still have larger blocks of relatively intact habitat. Valley oak savannas and woodlands, particularly those on valley bottoms and gentler slopes, have been largely eliminated. Valley oak savannas are presently much rarer than blue oak savannas. Habitat for a number of species has been lost through centuries of grazing, alteration of fire regimes, harvesting of oaks, and the introduction of aggressive alien species. Only 10 percent of all wetlands in the state of California remain, and much of what is left is highly threatened.

Remaining Blocks of Intact Habitat
The largest blocks of chaparral and sclerophyll-oak woodlands occur in the inner north and south coast ranges. Larger blocks of freshwater and salt marshes occur around Suisun and San Pablo Bay’s. Military bases such as Vandenburg, Hunter-Leggett, and Naval Petroleum Reserve (near Maricopa) encompass extensive high quality habitat.

Degree of Fragmentation
Habitat fragmentation is high given the extent of range modification, road building, developments, and natural watershed topography. Many communities are naturally disjunct and fragmented, and human fragmentation exacerbates their isolation.

Degree of Protection
Few good examples of this habitat type are adequately protected. The Nature Conservancy, BLM, California Department of Fish and Game, and USFWS are working cooperatively to restore the vast Carrizo Plains. Additional reserves are Cold Canyon Nature Reserve managed by the University of California, and Pinnacles National Monument near Monterrey. Unfortunately, many of these reserves are too small for long-term viability, and most suffer from decades of fire suppression, invasion of exotic species, and overgrazing by deer and rodent populations elevated through predator control. Much of the remaining salt marsh habitats in San Francisco Bay are protected to some degree, although external changes to hydrologic conditions and pollution may ultimately degrade these habitats.

Types and Severity of Threats
Rural residential development is a major threat to remaining low elevation oak woodlands.

Overgrazing by domestic livestock, including sheep and cattle, and wild deer and rodents is a serious problem. Blue oaks are not regenerating throughout their range because of high seedling mortality from grazing, seed predation, and, in some part, competition from introduced grasses. Cutting down trees for firewood and pasture is a persistent threat. The revival of wood-burning stoves has increased demand for oak wood in recent years. Clearing open woodlands for pasture also reduces forage quality (Barbour et al. 1993). Riparian areas and water sources, formerly critical sites for maintaining wildlife and rare plant species during the dry summers, have been extensively degraded or destroyed by domestic animals and water diversion. Expansion of agriculture, such as vineyards, and development projects, such as housing and golf courses, is swiftly converting many habitats in the Sierra foothills and areas near larger cities on the coast.

The continuing practice of type conversion of chaparral into grasslands through repeated burning and planting of annual grasses reduces habitat for species of herbaceous plants, invertebrates, birds, mammals, and reptiles that specialize on chaparral habitats. The loss of chaparral over the landscape is also thought to increase erosion and reduce water storage capacity of the habitat (Barbour et al. 1993). Introduced species are a serious and pervasive problem for native species. This ecoregion has 2,105 species of introduced plants, constituting 30 percent of the flora, the the highest for any ecoregion in the U.S. and Canada.

The Bureau of Land Management has been involved in a number of large conservation projects in the ecoregion, including the Carrizo Plains, Cosumnes River, Sacramento River, and Panoche Hills. However, the Bureau’s authorization of off-road vehicle use on the serpentine communities of the Clear Creek Recreation Area of the inner Coast Range threatens a globally unique habitat (Schoenherr 1992).

Wetlands throughout the region continue to be threatened by development, draining, diversions, alteration of hydrologic conditions, and pollution. Introduced rats, cats, opossums, foxes, and other predators also cause mortality in wetland specialists such as salt marsh harvest mice and clapper rails.

Suite of Priority Activities to Enhance Biodiversity Conservation

•Action to reduce the loss of oak woodlands is urgently needed. Management practices to promote regeneration of valley and blue oaks need to be widely implemented, including fencing of areas, planting of seedlings, and control of overabundant herbivores and alien plant species. Ranching techniques compatible with biodiversity conservation need to be devised and implemented.
•Restoration of fire cycles within their natural range of variation can be accomplished through controlled burns, fuel reduction, and control of alien plants. Areas identified as supporting relatively intact natural communities would be immediate targets for intensive fire management.
•Grazing of cattle and other livestock around riparian areas or in sensitive habitats (e.g., some edaphic communities and areas where locally endemic species persist) needs to be curtailed or carefully managed to mimic natural processes. Cessation of off-road vehicle activity is also needed for conservation in many areas.
•Protection and restoration of wetlands is urgently needed, wherever they occur. Restoration of hydrologic regimes is particularly important.
Conservation Partners

•Audubon Society
•Bureau of Land Management
•California Department of Fish and Game
•California Native Grass Association
•The California Native Plant Society
•California Oak Foundation
•Department of Defense
•The Nature Conservancy
•The Nature Conservancy of California
•Sierra Club
•U.S. Fish and Wildlife Service
•State Parks, County Parks, and local land trusts
Relationship to other classification schemes
The ecoregion boundaries used in this analysis closely match that of Omernik’s northern section of the Southern and Central California Plains and Hills (6). The interface between the Central Valley Grasslands and this ecoregion has been slightly modified by Bob Holland from Omernik’s original boundaries. When taken together, Bailey’s Northern California Interior Coast Ranges Section, Sierra Nevada Section, and Central California Coast Ranges Section roughly approximate this ecoregion. However, none of these sections continues to the coast, and the Santa Lucia Range and parts of the southern transverse ranges are incorporated into the latter section. Moreover, there is a break in the ring of sections at the northernmost area of the Central Valley. Küchler notes a variety of vegetation types within this ecoregion including California oakwoods, California steppe and prairie, yellow pine forest, and chaparral.

Prepared by: David Olson, reviewed by Robin Cox, The Nature Conservancy.