Quercus lobata 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Fagales Fagaceae

Scientific Name: Quercus lobata Née
Common Name(s):
English Valley Oak, California White Oak
Taxonomic Source(s): Trehane, P. 2007-2018. The Oak Names Checklist. Available at: (Accessed: 2 February 2016).

Assessment Information [top]

Red List Category & Criteria: Near Threatened ver 3.1
Year Published: 2017
Date Assessed: 2017-01-24
Assessor(s): Beckman, E. & Jerome, D.
Reviewer(s): Oldfield, S.
Contributor(s): Kaproth, M.
Although it has an extensive estimated extent of occurrence (EOO) of nearly 280,000 km2, Valley Oak (Quercus lobata) suffers from fragmentation and declining habitat due to agricultural and urban expansion, and only a few remnant groves remain in the Central Valley. The most extensive Valley Oak woodlands and savannas now exist in Coast Range valleys. Valley Oak is also likely to experience habitat shifting and contracting due to climate change leading to a decrease in both the quality and the extent of its habitat. Projections for this decline vary. Due to the high degree of nuclear genetic variation in Quercus lobata, the decline of the species will not be consistent across its range, therefore a conservative estimate of 27% decrease in suitable habitat by 2099 is being used. Using this projection Quercus lobata is Near Threatened under A3c.

Geographic Range [top]

Range Description:Valley Oak is endemic to California, with a distribution south from Shasta County to the Central Valley, including the foothills and valleys of the Sierra Nevada and Coast Ranges leading to Los Angeles. There is further presence on Santa Cruz and Santa Catalina Islands. Quercus lobata has an estimated EOO of nearly 280,000 km2, and can occur from sea level to 1,200 m Asl (USDA 2013).
Countries occurrence:
United States (California)
Additional data:
Continuing decline in extent of occurrence (EOO):Yes
Upper elevation limit (metres):1200
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:While there is no current data on the number of mature individuals for Quercus lobata, Natureserve reported well over 100 sites in a large area of California in 2005. Valley oak cover was once extensive, extending through lowlands and into foothills (Howard 1992). Declines in Valley oak's population due to climate change have been projected. A study by Potter and Hargrove (2013) that looked at a range of Quercus species under climate change conditions projected Quercus lobata to loose 18.9% of its suitable habitat range by 2050 due to climate change under a Hadley B1 GCM/emissions scenario combination. In another study by Kueppers et al. (2005), that looked specifically at Q. lobata, projected suitable habitat to decrease by at least 27–46% (average of 36.5) by 2099, using a global climate model (GCM) and a regional climate model respectively (RCM). For both of these models Valley Oak was projected to expand into northwestern California and the Sierra Nevada Mountains, with more expansion at the southern end of the species’ range under the GCM cases. Around 39% of the predicted future habitat is new under the RCM scenario and around 30% is new under GCM (Kueppers et al. 2005). This means that Quercus lobata's future population decline depends on its ability to disperse into these newly suitable habitats. Kueppers et al. (2005) also suggests that due to limited genetic exchange across the modern landscape Q. lobata's ability to migrate significant distances in response to climate change may be limited, leading to increased population declines under range shifts. Quercus lobata has a high degree of nuclear genetic variation across longitude, latitude, and elevation, which suggests that populations across the species’ range will not respond similarly to climate change; analysis would suggest that western regional populations may be more vulnerable to climate change than the eastern ones and that tolerance to climate change, in general, is going to be regionally dependent on the interaction between local genetic variation and climate conditions (Sork et al. 2010).
Current Population Trend:Decreasing
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:Quecus lobata is the dominant species in both Valley Oak Woodland and Valley Oak Riparian Forest. Often, the species is the only tree found within Valley Oak Woodland, where it lives widely spaced with grasses stretching between each individual. Within the riparian community, Valley Oak historically extended 1 to 8 km on each side of major rivers and is found among other trees such as Interior Live Oak, Blue Oak, Coast Live Oak, Black Walnut, Sycamore, and Gray Pine. These two dominant ecosystems have deep, rich soils that provide some of the best farmland in the world. Valley Oak is a deciduous tree that is both flood and drought tolerant, withstanding cool, wet winters and hot, dry summers (Pavlik et al. 1991). It is the largest North American oak, reaching 10 to 30 m with a rounded, spreading crown (USDA 2013).

Quercus lobata also comprises necessary habitat for multiple state-threatened species such as Swanson's Hawk, Sandhill Crane, and Yellow-billed Cuckoo, as well as the federally-threatened Elderberry Longhorn Beetle (Howard 1992). A variety of native species consume the tree's leaves and acorns as well. Valley oak is reported to be the largest and longest lived oak species in North America, reaching ages of 400 to 600 years (Tyler et al. 2006).
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):100-200

Use and Trade [top]

Use and Trade: Valley Oak lumber often cracks or warps while drying, and commonly acquires stains from fungus. However, these problems have been overcome through technology and a small commercial market is currently using Q. lobata for the manufacturing of cabinets, and occasionally for wine barrels. 
The species also supplies browse and acorns for various livestock. (USDA 2013)

Threats [top]

Major Threat(s): Over the last 150 years, Valley Oaks have been the victims of widespread agricultural and residential development in lowland areas. Where groundwater pumping has drastically lowered the water table, Valley Oaks have become slow growing and haggard. Field surveys of Valley Oak indicate that in many locations the numbers of seedling and sapling recruits are consistently very low. The factors most often cited as limiting oak recruitment are: acorn diseases, acorn predation, herbivory of established seedlings and saplings, competition between oak seedlings and non-native annual grasses for water, soil compaction by cattle, lack of fire, low rainfall in some years, and low tree population density (Tyler 2006).
Quercus lobata is projected to have a constricted habitat and a shift northward highly due to climate change; mostly likely owing to its sensitive at both seedling and adult stages to water stress (Kueppers et al. 2005).

Valley Oak Woodland, where Quercus lobata is a dominant species, is considered imperiled (G2) by Natureserve as of 2000. This woodland alliance was formerly extensive in the Sacramento and San Joaquin valleys, but high quality stands have been virtually eliminated by agriculture, fire-wood harvesting, and urbanization. Expanding urban areas have also destroyed many stands in the Coast Ranges. The remaining stands occur principally on private lands, and are still threatened by activities such as grazing, fuelwood cutting, clearing for pasture or cultivation, fire suppression, and non-native plant species. Hydrologic processes such as periodic, low intensity floods that help maintain this vegetation have been greatly altered (Natureserve).

Few examples of mature Valley Oak Woodland exist in the Central Valley, where up to 90% of Valley Oak woodland has been cleared for agriculture and urban development. While impacts have been less drastic elsewhere in the state, agricultural conversion and urban development continue to put pressure on Valley Oak throughout its range. In central California, the loss of large parcels of Valley Oaks to vineyard development has fueled heated debates between private landowners and public interest groups. While this issue also affects other oak species throughout California, loss of Valley Oaks is of particular concern because of their limited distribution and inadequate regeneration.  Currently, two main threats exist to the remaining populations of Valley Oaks: inadequate regeneration and removal of trees. To develop a comprehensive conservation plan for Valley Oaks, these two must be appropriately addressed (Standiford 2015).

Conservation Actions [top]

Conservation Actions: Quercus lobata can be found in 51 ex situ collections world wide according to BGCI (2016).
There is great interest among public and private managers to restore as much Valley Oak woodland and riparian forest as possible, and revegetation projects are numerous. Due to heavy acorn and seedling predation, however, mortality of newly-established populations often approaches 100% on project sites. Enclosing plants in a protective device such as wire caging is recommended until tree height exceeds the browse line (USDA 2013).Fragmentation and conversion of oak woodlands will continue in California as the human population expands and need for new agricultural lands increases. Public efforts to conserve Valley Oaks currently focus on saving individual trees or small patches of Valley Oaks. City and county ordinances often focus on heritage trees and set mitigation standards for removal of trees. Though these efforts are a step in the right direction, they may not result in the long-term survival of the species. Priorities for conservation and restoration of Valley Oak must be comprehensive, systematic, and have a strong scientific basis. While much research has been conducted over the past 20 years on Valley Oak, most has focused on aspects of regeneration. Ecosystem and landscape level research is limited. To develop a comprehensive conservation plan for Valley Oaks, certain critical information is needed. Knowledge of the species' current range and distribution, and current rates of land conversion are needed to assess loss of habitat. Information on stand structure, population dynamics, and minimum viable population size will help identify conservation priorities  (Standiford 2015).
The Integrated Hardwood Range Management Program has focused its efforts on educating landowners on multiple-use and sustainable-yield practices; researched economic incentives, wildlife relationships, tree reproduction and regeneration; and provided funding for many other research topics to form an understanding of oak woodland ecology. Other organizations and agencies have contributed substantially to this body of knowledge, but more information is needed (Standiford 2015).

Citation: Beckman, E. & Jerome, D. 2017. Quercus lobata. The IUCN Red List of Threatened Species 2017: e.T61983021A61983023. . Downloaded on 21 September 2018.
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