California oak woodland is a plant community found throughout the California chaparral and woodlands ecoregion of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

and northwestern

Baja California Baja California (; 'Lower California'), officially the Free and Sovereign State of Baja California ( es, Estado Libre y Soberano de Baja California), is a state in Mexico. It is the northernmost and westernmost of the 32 federal entities of Mex ...

Mexico Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guate ...

. Oak woodland is widespread at lower elevations in coastal California; in interior valleys of the Coast Ranges, Transverse Ranges and

Peninsular Ranges The Peninsular Ranges (also called the Lower California province) are a group of mountain ranges that stretch from Southern California to the southern tip of the Baja California peninsula; they are part of the North American Coast Ranges, which ...

; and in a ring around the

California Central Valley grasslands The California Central Valley grasslands is a temperate grasslands, savannas, and shrublands ecoregion in California's Central Valley. It a diverse ecoregion containing areas of desert grassland (at the southern end), prairie, savanna, riparian ...

. The dominant trees are oaks, interspersed with other broadleaf and coniferous trees, with an understory of grasses, herbs, geophytes, and California native plants. Oak savannas occur where the oaks are more widely spaced due a combination of lack of available moisture, and low-intensity frequent fires. The oak woodlands of Southern California and coastal

Northern California Northern California (colloquially known as NorCal) is a geographic and cultural region that generally comprises the northern portion of the U.S. state of California. Spanning the state's northernmost 48 counties, its main population centers incl ...

are dominated by coast live oak ('' Quercus agrifolia''), but also include valley oak ( ''Q. lobata''), California black oak ( ''Q. kelloggii''), canyon live oak ( ''Q. chrysolepis''), and other California oaks. The foothill oak woodlands around the Central Valley are dominated by blue oak ( ''Q. douglasii'') and gray pine (''

Pinus sabiniana ''Pinus sabiniana'' (sometimes spelled ''P. sabineana''), with vernacular names including towani pine, foothill pine, gray pine, bull pine, and digger pine, is a pine endemic to California in the United States. Some sources discourage using the n ...

'').

California oak-woodland communities

* Oregon oak woodland is found in Northern California's Klamath-Siskiyou, Northern Coast Ranges, and southern Cascade Range. These woodlands are composed primarily of Oregon oak ( ''Q. garryana''), interior live oak ('' Q. wislizeni''), and coast live oak, together with California black oak, canyon live oak, blue oak, Pacific madrone ('' Arbutus menziesii''), California bay ('' Umbellularia californica''), incense cedar ('' Calocedrus decurrens''), coast Douglas fir ('' Pseudotsuga menziesii'' var.'' menziesii''), Coulter Pine and ponderosa Pine (''

Pinus ponderosa ''Pinus ponderosa'', commonly known as the ponderosa pine, bull pine, blackjack pine, western yellow-pine, or filipinus pine is a very large pine tree species of variable habitat native to mountainous regions of western North America. It is the ...

''). * Blue oak woodland is found in the inner coast ranges and the Sierra Nevada foothills, surrounding the Central Valley. It forms "one of the largest ecosystems in California". Primary species are blue oak ( ''Q. douglasii'') and interior live oak (or on west facing slopes facing the exterior ranges, particularly in Contra Costa and Alameda counties, coast live oak takes interior live oak's place), together with valley oak, canyon live oak, California scrub oak ('' Q. berberidifolia''), gray pine, California buckeye ('' Aesculus californica''), and western redbud ('' Cercis occidentalis''). * Coast live oak woodland is widespread in northern and southern California, and is dominated by coast live oak ( ''Q. agrifolia''), together with California buckeye, Pacific madrone, California bay, and California walnut ('' Juglans californica''). *Interior live oak woodland is found in north and south mountain ranges of California. It is dominant by interior live oaks(''Q. wislizeni),'' blue oaks, foothill pine and shrubs in common with blue oak woodland. * Valley oak woodland is found in the interior valleys of northern, central and southern California, and is dominated by valley oak ( ''Q. lobata'') and coast live oak, together with gray pine and Coulter pine ('' Pinus coulteri''). * Island oak woodland is found on the California Channel Islands, and is made up primarily of island oak ('' Q. tomentella'') and coast live oak, together with canyon live oak, MacDonald scrub oak (''Q. berberidifolia'') hybridized with valley or other oaks), Catalina ironwood ('' Lyonothamnus floribundus''), and bishop pine (''Pinus muricata''). * Engelmann oak woodland is found in a few locations in the northern

of Southern California, including the Santa Rosa Plateau and

San Gabriel Mountains The San Gabriel Mountains ( es, Sierra de San Gabriel) are a mountain range located in northern Los Angeles County, California, Los Angeles County and western San Bernardino County, California, United States. The mountain range is part of the Tr ...

foothills. It consists mostly of Engelmann oak ('' Q. engelmannii'') together with coast live oak.

Status and future of California oak woodlands

Blue oak woodlands cover about of the state, and of this area about 79%, or , shows no evidence of past cutting of trees. Recent research by the University of Arkansas Tree-Ring Laboratory has studied several unlogged stands of blue oak woodlands, and suggests that the state may harbor over of such old growth forests. This would make California's oak woodlands some of the most extensive old growth forests left in the state. However, most oaks of full tree size are more than one hundred years old, and few saplings are ever produced, because cattle often tear the plants to pieces. The Oaks 2040 survey estimates that of California oak woodlands are seriously threatened by 2040 as a burgeoning state population makes ever more use of the wildland. This comprehensive survey includes oak woodland maps and inventory data for the ten oak types found in California. By evaluating this new information against current State of California economic growth projections, the location and extent of oak woodlands most at risk of development are identified. Management practices, such as the grazing (or the lack thereof) can lower

soil fertility Soil fertility refers to the ability of soil to sustain agricultural plant growth, i.e. to provide plant habitat and result in sustained and consistent yields of high quality.

and nutrient level. A study performed by the University of California, Davis found that the prominent presence of oak trees in California oak woodlands creates areas of soil that are optimal for new growth. The Bureau of Land Management partnered with the California Biodiversity Council to carry out the Agreement on Biological Diversity, started in 1991, to protect and expand the following oakland wood areas: King Range National Conservation Area, Cache Creek Management Area, Yuba River Watershed in Inimim Forest, Consumes River Preserve, and Fort Ord. The methods used to ensure a healthy future for the California oak woodlands include maintenance and restoration of old-growth forests, watershed management and improvement, protection of

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through ...

, protection of wildlife species that have cultural and environmental value to the area, restoration of valley oaks, and the habitat maintenance of “special status botanical species” and select endangered species.

Examples of occurrence

The headwaters area of Yulupa Creek in Annadel State Park is cited as one of the best examples of California oak woodlands. Much of this woodland is a relatively pristine

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

with considerable

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity' ...

. An unusual characteristic of this Annadel forest is the high content of undisturbed

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use of ...

bunch grass

understory In forestry and ecology, understory (American English), or understorey (Commonwealth English The use of the English language in current and former member countries of the Commonwealth of Nations was largely inherited from British co ...

, testifying to the absence of historic grazing or other agriculture. The

Morro Bay Morro Bay (''Morro'', Spanish for "Hill") is a seaside city in San Luis Obispo County, California. Located on the Central Coast of California, the city population was 10,757 as of the 2020 census, up from 10,234 at the 2010 census. The town ...

watershed, located in Northern California, is an example of a coast live oak ecosystem. This sub-category of California oak woodland consists primarily of coast wild oak and are predominantly found in coastal regions, but can extend to foothill ecosystems.

Ecology of California oak woodlands

The composition and characteristics of California oak woodlands varies across the state, but are defined by three main oak species throughout coastal regions: coastal live oak, Englemann oak, and

Oregon white oak ''Quercus garryana'' is an oak tree species of the Pacific Northwest, with a range stretching from southern California to southwestern British Columbia. It is commonly known as the Oregon white oak or Oregon oak or, in Canada, the Garry oak. It ...

. The concentration of each of these oak species correlates with the location of the woodland throughout California. In southern and central areas, the predominant oak species is coastal live oak which grow on coastal valleys and foothills. In drier regions within this range, coastal wild oak is associated with

foothill pine ''Pinus sabiniana'' (sometimes spelled ''P. sabineana''), with vernacular names including towani pine, foothill pine, gray pine, bull pine, and digger pine, is a pine endemic to California in the United States. Some sources discourage using the n ...

valley oak ''Quercus lobata'', commonly called the valley oak or roble, grows into the largest of California oaks. It is endemic to California, growing in interior valleys and foothills from Siskiyou County to San Diego County. Mature specimens may att ...

and

blue oak ''Quercus douglasii'', known as blue oak, is a species of oak endemic to (and found only in) California, common in the Coast Ranges and the foothills of the Sierra Nevada. It is California's most drought-tolerant deciduous oak, and is a dominan ...

; whereas wetter areas are defined by

tanoak ''Notholithocarpus densiflorus'', commonly known as the tanoak or tanbark-oak, is a broadleaf tree in the family Fagaceae, and the type species of the genus ''Notholithocarpus''. It is native to the far western United States, particularly Oregon ...

canyon live oak ''Quercus chrysolepis'', commonly termed canyon live oak, canyon oak, golden cup oak or maul oak, is a North American species of evergreen oak that is found in Mexico and in the western United States, notably in the California Coast Ranges. This ...

and California bay. Coastal live oak woodland found in Southern California is associated with valley oak similar to drier northern sites, but also sees

interior live oak ''Quercus wislizeni'', known by the common name interior live oak, is an evergreen oak, highly variable and often shrubby, found in many areas of California in the United States continuing south into northern Baja California in Mexico. It general ...

Coulter pine The Coulter pine or big-cone pine, ''Pinus coulteri'', is a native of the coastal mountains of Southern California in the United States and northern Baja California in Mexico. Isolated groves are found as far north as Clearlake, California on th ...

and

California black walnut ''Juglans californica'', the California black walnut, also called the California walnut, or the Southern California black walnut, is a large shrub or small tree (about 20-49 feet tall) of the walnut family, Juglandaceae, endemic to Southern Calif ...

. Outside of the southern ranges of coastal wild oak are small areas of oak woodland characterized by Englemann oak. These sites can coincide with coastal live oak, however they can also occur as stands composed almost entirely of Englemann oak. Northern, wetter regions of California are populated with oak woodlands formed from Oregon white oak. These woodlands are associated interior live oak and canyon live oak similar to coastal live oak woodlands, but differ with

Pacific madrone ''Arbutus menziesii'' or Pacific madrone (commonly madrone or madrona in the United States and arbutus in Canada), is a species of broadleaf evergreen tree in the family Ericaceae, native to the western coastal areas of North America, from Bri ...

and

California black oak ''Quercus kelloggii'', the California black oak, also known as Kellogg oak, is an oak in the red oak section (genus ''Quercus'', section ''Lobatae'', series ''Agrifoliae''), native to western North America. Although genetically separated from t ...

. The variety of

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an ...

density which results from the diversity of tree species found in different woodland regions causes a wide range of understory grass and shrub density, and plant type. An example of this can be seen by the commonality of annual grasses in open woodlands, a phenomenon that is not seen in dense woodland areas. All three oak species which characterize California oak woodlands can be defined as "long-lived, slow-growing trees." The frequent fires seen within the region have resulted in species such as coastal live oak and Englemann oak (which grow in drier, more fire prone regions) to have developed a resistance to low-intensity fires. This resiliency has resulted in coastal live oak emerging as the predominant species in cleared regions, as the trees have higher fitness to survive compared to less resistant, deciduous oaks. The same cannot be said for Oregon white oak, which populate traditionally wetter, less fire-prone regions, resulting in the trees having little built-up fire resistance. Because of the lack of fires in these northern regions, white oaks can have the threat of being outgrown by

conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ex ...

growing in the understory. California oak woodland habitats contain some of the most wildlife in California. More than half of the species of terrestrial vertebrates in California are found in oak woodlands. This includes more than 120 species of mammals, 147 species of birds, and 60 species of amphibians or reptiles. The most diversity occurs when there is both multiple levels of vegetation heights and varied spacing between vegetation to create complex habitat structure both vertically and horizontally because there are more places for species that live in different layers of the vegetation. Among these species, the

California quail The California quail (''Callipepla californica''), also known as the California valley quail or Valley quail, is a small ground-dwelling bird in the New World quail family. These birds have a curving crest or '' plume'', made of six feathers, th ...

(''Callipepla californicus''), Beechey ground squirrels (''Spermophilus beecheyi''), Botta pocket gopher (''Thomomys bottae mewa''), Audubon cottontail (''Sylvilagus audubonii vallicola''), deer (''Odocoileus'' spp),

bobcat The bobcat (''Lynx rufus''), also known as the red lynx, is a medium-sized cat native to North America. It ranges from southern Canada through most of the contiguous United States to Oaxaca in Mexico. It is listed as Least Concern on the IU ...

(''Lynx rufus californicus''),

coyote The coyote (''Canis latrans'') is a species of canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecological ni ...

(''Canis latrans'') and the

Pacific rattlesnake ''Crotalus oreganus'', commonly known as the (northern) Pacific rattlesnake, Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates. (7th printing, 1985). 1105 pp. . is a venomous pit viper species found in western North ...

(''Crotalus viridis oreganus'') can commonly be found in California oak woodlands. Aspects of the California oak woodland that are important for wildlife of these habitats are habitat corridors, snags and downed wood.Natural vegetation create habitat corridors that connect the patches of habitat that host species. Habitat corridors provide protection and food for animals that migrate between patches such as deer, mountain lions, bobcats, or gray foxes. Snags are the standing wood that is left when trees die and are home to wood-eating insects that are food for animals such as birds. Snags provide temporary refuge for small birds, bats, swallows, salamanders, and lizards. Similarly, downed wood provide refuge for animals that require moist areas, such as amphibians, cover for nesting of multiple species of birds, and areas for dens for larger snags.

References

{{reflist

General bibliography

* Dallman, Peter R. (1998). ''Plant Life in the World's Mediterranean Climates.'' California Native Plant Society–University of California Press; Berkeley. * Gaman, Tom and Firman, Jeffrey (2006). ''Oaks 2040: The Status and Future of Oaks in California.'' Published by the California Oak Foundation, Oakland. * Pavlik, Bruce M., Pamela C. Muick, Sharon G. Johnson, and Marjorie Popper (1991). ''Oaks of California.'' Cachuma Press and the California Oak Foundation;

Los Olivos, California Los Olivos (; Spanish for "the olive trees") is an unincorporated community in the Santa Ynez Valley of Santa Barbara County, California, United States. Tourism is popular in this rural area which is an agricultural region with an emphasis on w ...

. * Schoenherr, Allan A. (1992). ''

A Natural History of California Allan A. Schoenherr (February 6, 1937 – May 31, 2021) was a Californian author, ecologist, and naturalist. He is the author of the widely used reference book, '' A Natural History of California''. He received his PhD in zoology at Arizona State ...

.'' University of California Press; Berkeley.

External links

Californiaoaks.org , Oaks 2040: The Status and Future of Oaks in CaliforniaUCanr.org , University of California Oak Woodland Management Program
California chaparral and woodlands Plant communities of California * *Oak *Oak *Oak C