California interior chaparral and woodlands

Content Cover Image

Mt.St.Helena Palisades, Napa County, California. @ C.Michael Hogan

caption Cold Canyon, Vaca Range, California, USA. (Photograph by David Olson)

The California interior chaparral and woodlands ecoregion forms a nearly continuous ellipse of oak woodland and chaparral around the California Central Valley, ranging from 300 to 3000 feet in elevation. This California ecoregion continues across the coast ranges to the Pacific Ocean 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. This ecoregion is classified as an element of the Mediterranean Forests, Woodland and Scrub Biome. There is moderate faunal species richness,; for example, a total of 369 vertebrate taxa are recorded within the ecoregion.

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 marsh, 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.), Western Redbud (Cercis occidentalis), Chamise (Adenostoma fasciculatum), and Scrub Oak (Quercus dumosa). Coast Live Oak (Quercus agrifolia), Canyon Live Oak (Quercus chrysolepis), Leather Oak (Quercus durata), Valley Oak (Quercus lobata), Interior Live Oak (Quercus wislizeni), and maul oak are also part of the diverse oak flora of this ecoregion.

caption California interior chaparral and woodlands. Source: WWF 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 natural wildfires 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. Maritime chaparral around Monterey Bay is noted for a number of endemic species, including several genus Arctostaphylos species: Hooker Manzanita (Arctostaphylos hookeri), Monterey Manzanita (Arctostaphylos monteryensis), Pajaro Manzanita (Arctostaphylos pajaroensis), Sandmat Manzanita (Arctostaphylos pumila); other prominent shrubs here are: Monterey Ceanothus (Ceanothus rigidis), and Monterey Goldenbush (Ericameria fasiculata). Communities on serpentine are particularly rich in endemic plants and invertebrates, including Leather Oak (Quercus durata), Interior Silktassel (Garrya condonii), Milkwort Jewel-flower (Streptanthus polygaloides), and Muir’s Hairstreak (Mitoura 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 linearifolia).

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 to 25 years. Closed-cone pine communities historically burned about once every 25 to 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.


caption Mule Deer, Sonoma County. @ C.Michael Hogan Over seventy species of mammals occur in the ecoregion habitats, with five endemic and near-endemic species: the Giant Kangaroo Rat (Dipodomys ingens), Heermann's Kangaroo Rat (Dipodomys heermamni), Santa Cruz Kangaroo Rat (Dipodomys venustus), Sonoma Chipmunk (Eutamias sonomae), the ecoregion endemic Suisun Shrew (Sorex ornatus sinuosus), and the endemic Salt Marsh Harvest Mouse (Reithrodontomys raviventris), comprising the highest number of endemic mammal species for the USA and Canadian ecoregions. Another small mammal found here are the American Shrew Mole (Neurotrichus gibbsii). The most widespread cervid in the California interior chaparral and woodlands is the Mule Deer (Odocoileus hemionus), who is adaptable to browsing or grazing, depending on season and forage availability.


Plethodontid salamanders are diverse with five endemic species. A California (but not ecoregion) endemic is the Arboreal Salamander (Aneides lugubris). Also occurring in the ecoregion is the Pacific Giant Salamander  (Dicamptodon ensatus NT), a carnivorous California endemic, is one of the largest salamanders in North America. Another salamander found in the California interior chaparral and woodland is the California Slender Salamander (Batrachoseps attenuatus). One of the representative anuranAn amphibian that has limbs but no tail (includes all frogs and toads) taxa occurring in the ecoregion is the Northern Leopard Frog (Rana pipiens).

caption Coast Horned Lizard. Source: Robert Potts /CalPhotos/EoL Reptiles

A number of reptilian taxa are found in the California interior chaparral and woodlands ecoregion, including: the Coast Horned Lizard (Phrynosoma coronatum) and the the Yellow-backed Spiny Lizard (Sceloporus magister). Gilbert's Skink (Plestiodon gilberti) is a carnivorous species occurring within the California interior chaparral and woodlands ecoregion. Snakes occurring in the ecoregion include the California Mountain Kingsnake (Lampropeltis zonata) and the Two-striped Garter Snake (Thamnophis hammondii).


Among the roughly 100 species of birds that occur in this ecoregion, Scrub Jay (Aphelocoma coerulescens), Acorn Woodpecker (Melanerpes formicivorus), and Wren Tit (Chamaea fasciata), are some of the most characteristic avian species here. 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.

caption Bay Checkerspot (''Euphydryas editha bayensis''), California, United States. (Photograph by T. W. Davies, California Academy of Sciences & CalPhotos)


There is a profusion of butterfly species present in the ecoregion, with high endemism and diversity in serpentine soils loci; Ehrlich was one of the early researchers to study the relationship of butterfly diversity to ultramafic soils and plant hosts in the Palo Alto Hills within the California interior chaparral and woodlands ecoregion. Army ants (Neivamyrmex spp.) and primitive bristletails, and land snails are among the ecoregion’s large number of relict and unusual invertebrate species.

Conservation status

Habitat loss and degradation

caption Henry Coe State Park, California, United States. Source: John Morrison

Approximately thirty percent of this ecoregion can be described as intactThe condition of an ecological habitat being an undisturbed or natural environment, with such blocks concentrated in steeper foothill and montane areas. Virtually all native bunch-grass communities have been replaced by annual grassland understories in woodland areas, with introduction of alien species from Europe, exacerbated by overgrazing by livestock. Some woodland areas above 915 meters 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 overgrazing, alteration of fire regimes, harvesting of oaks, and the introduction of aggressive alien species. Only ten 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 intactThe condition of an ecological habitat being an undisturbed or natural environment 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 Bays. Military bases such as Vandenberg Air Force Base, Hunter-Leggett, and Naval Petroleum Reserve (near Maricopa) encompass extensive intactThe condition of an ecological habitat being an undisturbed or natural environment high quality habitat.

Degree of fragmentation

Habitat fragmentation is high given the extent of range modification, road-building, developments, and natural catchment basin topography. Many communities are naturally disjunct and fragmented, and man-caused fragmentation exacerbates their isolation.

Degree of protection

caption Annadel State Park, with Hood Mountain beyond. @ C.Michael Hogan Few good examples of this habitat type are adequately protected. The Nature Conservancy, Bureau of Land Management, California Department of Fish and Game, and U.S. Fish and Wildlife Service are working cooperatively to restore the vast Carrizo Plains. Additional reserves are Cold Canyon Nature Reserve managed by the University of California, Annadel State Park and Pinnacles National Monument near Monterey. Unfortunately, many of these reserves are too small for long-term viability, and most suffer from decades of fire suppression, invasion of alien 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 water pollution may ultimately degrade these habitats.

Ecological threat profile

Rural residential development and agricultural development are major threats to remaining low elevation oak woodlands. In the northern part of the ecoregion, e.g. Sonoma and Napa Counties, vineyard conversions are a chief threat; moreover, this wine production pressure is felt elsewhere in the ecoregion such as the Amador Valley and in the San Luis Obispo County foothills.

caption California Tiger Salamander (''Ambystoma californiense''), California, United States. Source: Gerald and Buff Corsi, California Academy of Sciences & CalPhotos

Overgrazing by domestic livestock, including sheep and cattle, as well as Mule Deer and rodents is a serious issue in the ecoregion. Blue oaks are not regenerating throughout their range because of high seedling mortality from overgrazing, 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. Riparian areas and surface water sources, formerly critical sites for maintaining wildlife and rare plant species during the arid summers, have been extensively degraded or destroyed by domestic animals and water diversions. 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. Introduced species are a serious and pervasive problem for native species. This ecoregion has 2105 different species of introduced plants, constituting 30 percent of the flora, the the highest for any ecoregion in the USA or Canada.

The U.S. 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.

Wetlands throughout the region continue to be threatened by development, draining, diversions, alteration of hydrologic conditions, and water 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. Control of expansion of Douglas Fir is needed, given the decades of aggressive fire suppression that has favored the Douglas Fir. 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. For example, thousands of acres have been taken over by the alien species, Star Thistle, which enhances and transforms natural wildfire cycles. Areas identified as supporting relatively intact natural communities are immediate targets for intensive fire management.
  • Overgrazing 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 parts of the ecoregion.
  • Protection and restoration of wetlands is urgently needed, wherever they occur. Restoration of hydrologic regimes is particularly important.

Conservation Partners

  • Audubon Society
  • U.S. Bureau of Land Management
  • California Department of Fish and Game
  • California Native Grass Association
  • California Native Plant Society
  • California Oak Foundation
  • U.S. Department of Defense
  • The Nature Conservancy of California
  • U.S. Fish and Wildlife Service

See also


  • Michael G. Barbour, Todd Keeler-Wolf, Allan A. Schoenherr. 2007. Terrestrial vegetation of California. University of California Press. 712 pages
  • Paul R. Ehrlich & Ilkka Hanski (eds.). 2004. On the Wings of Checkerspots: A Model System for Population Biology
  • Philip Alexander Munz, David D. Keck. 1973 . A California flora. University of California Press. 1905 pages
  • C. Michael Hogan. 2008. California Giant Salamander: Dicamptodon ensatus. Nicklas Stromberg (ed.)
  • Taylor H. Ricketts. 1999. Terrestrial ecoregions of North America: a conservation assessment. Island Press. 485 pages
  • Jake Ruygt. 2012. San Francisco Estuary Institute. Historical Atlas of Napa County.A Flora of Napa County
  • Mark R. Stromberg, Jeffrey D. Corbin, Carla Marie D'Antonio. California grasslands: ecology and management. 2007. University of California Press. 390 pages

Disclaimer: This article contains some information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.





Hogan, C., & Fund, W. (2014). California interior chaparral and woodlands. Retrieved from


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