Quercus lobata Woodland Alliance
Valley oak woodland and forest
Valley oak woodland and forest
USDA Ecological Section Map
Summary Information
- Primary Life FormTree
- Elevation0-775 m
- State RarityS3
- Global RarityG3
- DistributionUSA: CA (NatureServe) (FEIS)
- Endemic to CaliforniaYes
- Endemic to California Floristic Province and DesertsYes
- Date Added2025/02/27
Characteristic Species
Quercus lobata is dominant or co-dominant in the tree canopy with Aesculus californica, Quercus agrifolia, Quercus douglasii, Quercus kelloggii, Quercus wislizeni and/or Umbellularia californica. Shrubs are sparse and may include Toxicodendron diversilobum. Understory herbs include Bromus diandrus and/or Bromus hordeaceus.
Vegetation Layers
Trees < 30 m tall; canopy is open (greater than 10%) to continuous, or savanna-like (less than 10%, but evenly distributed). Shrub layer is sparse to open. Herbaceous layer may be grassy.
Membership Rules
- Quercus lobata > 50% relative cover in the tree canopy or > 30% relative cover when other tree species, such as Q. agrifolia or Quercus douglasii are present (Allen et al. 1989, Keeler-Wolf and Evens 2006).
- Quercus lobata > 50% relative cover in the tree canopy, or > 30% relative cover with Quercus agrifolia and/or Umbellularia californica in upland habitat (Buck-Diaz et al. 2021, Sikes et al. 2021).
- Quercus lobata > 50% relative cover in the tree canopy, or > 30% relative cover with Quercus agrifolia, Q. douglasii, Q. kelloggii, and/or Umbellularia californica in upland habitat (Sikes et al. 2023, Sikes et al. 2025).
Habitats
Valley bottoms; summit valleys; gentle to somewhat steep, lower to upper slopes and ridgetops. Soil textures are various, including loams and clays. Soils are alluvial or residual. The USACE Wetland Inventory (2018 national list) recognizes Quercus lobata as a FACU plant.
Other Habitat, Alliance and Community Groupings
| MCV (1995) | Valley oak series |
| NVCS (2009) | Quercus lobata woodland alliance |
| Calveg | Valley oak |
| Holland | Valley oak woodland |
| Munz | Northern oak woodland |
| WHR | Valley oak woodland |
| CDFW CA Code | 71.035.00 |
National Vegetation Classification Hierarchy
| Formation Class | Mesomorphic Tree Vegetation (Forest and Woodland) |
| Formation Subclass | Temperate Forest |
| Formation | Warm Temperate Forest |
| Division | Madrean Forest and Woodland |
| Macro Group | California Forest and Woodland |
| Group | Californian broadleaf forest and woodland |
Remarks
Quercus lobata is a large, deciduous oak that attains a height of 30 m and an age of 500 years. Recruitment from acorn seed is low in many areas as a result of both natural and human causes. Birds and small mammals disperse and cache the acorns. Germination can occur as soon as the acorns fall. Roots penetrate moist soil rapidly, and survival is high under the partial shade. Buried seeds have a greater chance of germination and successful establishment, as acorn predation and desiccation are usually high. Q. lobata is intermediate in shade tolerance, but has a high degree of tolerance to flood and drought (Howard 1992l).
Quercus lobata is endemic to California, and stands vary from open savannas to closed-canopy forests (Allen-Diaz et al. 2007). Both riparian and upland forests of Q. lobata occur in the deep, rich soil typical of floodplains and valley floors. However, this alliance includes only upland forests outside of riparian influence. These forests are only remnants of what once existed in the Central Valley, other valleys, and foothill locations in California (Allen-Diaz et al. 2007).
Upland and riparian expressions of Quercus lobata stands were previously combined in a single alliance in A Manual of California Vegetation, Second Edition (2009). Riparian and upland stands ofQ. lobata have now been split into the Q. lobata Riparian Alliance and this upland Q. lobata Alliance respectively. This alliance split follows the revised National Vegetation Classification's recognition of riparian groups separately from upland groups (NatureServe 2020).
Quercus lobata is endemic to California, and stands vary from open savannas to closed-canopy forests (Allen-Diaz et al. 2007). Both riparian and upland forests of Q. lobata occur in the deep, rich soil typical of floodplains and valley floors. However, this alliance includes only upland forests outside of riparian influence. These forests are only remnants of what once existed in the Central Valley, other valleys, and foothill locations in California (Allen-Diaz et al. 2007).
Upland and riparian expressions of Quercus lobata stands were previously combined in a single alliance in A Manual of California Vegetation, Second Edition (2009). Riparian and upland stands ofQ. lobata have now been split into the Q. lobata Riparian Alliance and this upland Q. lobata Alliance respectively. This alliance split follows the revised National Vegetation Classification's recognition of riparian groups separately from upland groups (NatureServe 2020).
Life History Traits of the Principal Species
| Quercus lobata | |
|---|---|
| Life forms | Tree; winter deciduous |
| Seed storage | Soil; transient |
| Seed longevity | Short |
| Mode of dispersal | Animal; gravity |
| Germination agents | None |
| Mode of sprouting | Buds on large branches or trunks; underground structures |
| Survivability after fire/disturbance | Fire-hardy; thick epidermis; high sprouter |
| Disturbance-stimulated flowering | No |
| Reproductive range | 10-500 years |
| Recruitment | Low |
| Regional variation | High |
Fire Characteristics
Literature describing post-fire natural regeneration and long-term fire recovery of Quercus lobata woodlands is minimal. Plants have the ability to survive fire, and stands probably burned frequently and hot, with dry grasses and oak litter carrying surface fires. Larger mature trees are usually resistant to moderate-severity fire because of their thick bark. While seedlings and saplings are top-killed by such fire, juveniles sprout from root crowns. However, older mature trees that are top-killed do not have this same ability. Animals such as scrub jays also facilitate regeneration of Q. lobata, because they prefer burned areas as acorn-caching sites, and buried acorns usually survive fire (Howard 1992l, Wills 2006). Hot surface fires may kill large trees that have extensive internal rot, and such fires usually kill small trees. Crown fires will kill a large number of valley oak of all size classes (Howard 1992l).
| Fire return interval | Short to medium (5-100+ years) |
| Seasonality | Summer-early fall |
| Size/extent | Medium to large; up to or beyond stand size |
| Complexity | Low to moderate |
| Intensity | Low to moderate |
| Severity | Low to moderate |
| Type | Surface-passive crown |
| Regional knowledge | Sierra Nevada and foothills, southwestern California |
Regional Status
- Central California Coast (261Aa, Ac-l). Stands exist in the Cone Peak Gradient and Wagon Caves RNAs (Keeler- Wolf 1990d in Cheng 2004) and generally in the section (Allen et al. 1989, 1991). Stands have been mapped at John Muir National Historic Site (O’Neil and Egan 2004). Stands occur in the East Bay, Santa Clara Valley, Santa Cruz Mountains, and San Francisco Peninsula (Sikes et al. 2021, 2023, 2025). Stands are mapped in Salinas Valley and Santa Maria subregions in CALVEG layer (USFS, Pacific SW Region 2018).
- Central California Coast Ranges (M262Aa-f, Ah, Aj). Stands occur on slopes in the Santa Lucia Mountains (Allen et al. 1989, 1991, Griffin 1977), in the San Benito Mountain area (Evens et al. 2006), Pinnacles National Monument (Kittel et al. 2012), and generally in the section (Allen et al. 1989, 1991). Stands in Fremont, Eastern Hills (Sikes et al. 2025), Paso Robles Hills, and Caliente Range subregions mapped in CALVEG layer (USFS, Pacific SW Region 2018).
- Great Valley (262Aa-j, Al-v, Ay-z). Stands in Delta, Delta Basins, San Joaquin Valley subregions mapped in CALVEG layer (USFS, Pacific SW Region 2018). Tulare Basin, South Valley Alluvium, and Elk Hills and Southern Valley Terraces are included due to stands occuring adjacent to their borders.
- Klamath Mountains (M261Ai, Am). Stands may occur in the Klamath Mountain Ecoregion but more sampling is needed to better understand its distribution here.
- Mojave Desert (322Ag). High Desert Plains and Hills included due to stands mapped in CALVEG layer along the southwestern border (USFS, Pacific SW Region 2018).
- Northern California Coast (263Ac, Ag, Aj, Al-m). Stands have been surveyed in Marin and Sonoma counties (Buck-Diaz et al. 2021; Klein et al. 2015) at mesic upland sites, typically on slopes and summit valleys, usually adjacent to other oak and grassland alliances, where Q. lobata can be dominant or co-dominant with Q. agrifolia, and often with grassy understories. Reports from Mount Tamalpais and (Evens and Kentner 2006) and generally in the section (Allen et al. 1989, 1991) describe the alliance.
- Northern California Coast Ranges (M261Ba-f). Stands occur in the mountains of Sonoma County (Klein et al 2015) and to the east of Lake Berryessa. Stands in Eastern Franciscan, Stony Creek Serpentine, Clear Lake Hills and Valleys, and Konocti Flows subregions mapped in CALVEG layer (USFS, Pacific SW 2018).
- Northern California Interior Coast Ranges (M261Ca-c). Stands are found in the foothills above the Great Valley.
- Sierra Nevada (M261Eg, Ep, Es). Stands occur to 1500 m elevation in the Tehachapi Mountains near Kernville and the town of Tehachapi, where stands contain Yucca brevifolia and other Mojave Desert plants. Stands may occur at the lower elevations in Upper Foothills and Lower Batholith subregions.
- Sierra Nevada Foothills (M261Fa-e). Mesic upland stands exist throughout the section (Allen et al. 1989, 1991, Klein et al. 2007) where Q. lobata can be dominant or co-dominant with Q. kelloggii, and often have a grassy understory and low shrub cover (Ratchford et al. 2024a). Stands are typically found on mid to upper slopes and ridgetops.
- Southern California Coast (261Ba-b, Bd-g). Upland stands occur in the Santa Monica Mountains (Thomas 1987, Keeler-Wolf and Evens 2006) and generally for the section (Allen et al. 1989, 1991). Stands in Santa Ynez - Sulphur Mountains, Oxnard Plain, and Los Angeles Plain subregions mapped in CALVEG layer (USFS, Pacific SW Region 2018).
- Southern California Mountains and Valleys (M262Ba-c). Stands occur near Gorman and in the Fraser Park area. Stands in San Rafael and Sierra Pelona subregions mapped in CALVEG layer (USFS, Pacific SW Region 2018).
Management Considerations
Anderson (2005) estimated that approximately 90% of Quercus lobata stands that existed prior to European contact have been destroyed by urbanization and intensive land conversion. Modified water patterns and nonnative plants have affected most remaining stands. Problems facing managers include lack of sapling recruitment, loss of mature trees because of lowered water tables, and saline irrigation runoff. Mature trees are sensitive to overwatering, pruning, grade changes, and asphalt covering their root systems. Feral pigs cause considerable damage (Howard 1992l). The California Oak Foundation (http://www.californiaoaks.org/), Oak Woodlands Conservation Program (http://www.wcb. Ca.gov/Pages/oak_woodlands_Act.asp) and others promote preservation and restoration (Griggs and Golet 2002). Restorationists have seen feasibility in establishing native oaks with the aid of weed control and irrigation (Alpert et al. 1999).
As a result of fire exclusion, valley oak woodlands frequently contain an understory of shrubs, evergreen oaks, and conifer saplings and trees, and a deep litter of oak leaves, needles, and downed woody debris. Prescribed burning in non-drought years could increase oak abundance. More regular fires could reduce or eliminate invasion by evergreen oaks and conifers and open up sites for valley oak seedling establishment or oak sprouting. However, the threat of severe fire in oak stands has increased greatly where valley oak woodlands border conifer forests. Also, deeply fire-scarred trees are susceptible to various heart-rot fungi and to wind throw (Howard 1992l).
Associations
Stands with a Mixed Tree Layer
- Quercus lobata - Quercus agrifolia / grass [1], [4], [5], [7], [8], [10], [11], [12], [13], [14], [16]
- Quercus lobata - Quercus douglasii [1], [3], [4], [16]
- Quercus lobata - Quercus kelloggii [1], [3]
Stands with a Simple Tree Layer
- Quercus lobata / Baccharis pilularis - Diplacus aurantiacus [4]
- Quercus lobata / grass [1], [2], [3], [4], [5], [11], [14], [15], [16]
References
- [1] Allen, B.H.;Evett, R.R. ;Holzman, B.A.;Martin, A.J. 1989
- [2] Evens, J.M.;Kentner, E. 2006
- [3] Ratchford, J.;Harbert, B;Boul, R.;Keeler-Wolf, T.;Evens, J. 2024a
- [4] Sikes, K.;Buck-Diaz, J.;Vu, S.;Evens, J. 2023
- [5] Keeler-Wolf, T.;Evens, J. 2006
- [7] Kittel, G.;Reyes, E.;Evens, J.;Buck, J.;Johnson, D. 2012
- [8] O’Neil, S.;Egan, S. 2004
- [10] Buck-Diaz, J.;Batiuk, S.;Evens, J.M. 2012
- [11] Klein, A.;Keeler-Wolf, T.;Evens, J. 2015
- [12] Buck, J.;Evens, J. 2010
- [13] Reyes, E.;Johnson, D.;Glass, A. 2019
- [14] Buck-Diaz, J.;Sikes, K.;Evens, J.M. 2021a
- [15] Sikes, K.;Buck-Diaz, J.;Evens, J. 2021
- [16] Sikes, K.;Buck-Diaz, J.;Vu, S.;Bibbo, M.;Evens, J. 2025
- Allen-Diaz, B.H.;Holtzman, B.A. 1991
- Allen-Diaz, B.H.;Standiford, R.;Jackson, R.D. 2007
- Alpert, P.;Griggs, F.T.;Peterson, D.R. 1999
- Anderson, M.K. 2005
- Barbour, M.G. 1988
- Berman, J.T.;Bledsoe, C.S. 1998
- Bernhardt, E.A.;Swiecki, T.J. 1997
- Callaway, R.M. 1992
- Cheng, S. 2004
- Danielsen, K.C.;Halvorson, W.L. 1991
- Evens, J.M.;Klein, A.;Taylor, J.;Hickson, D.;Keeler-Wolf, T. 2006
- Evens, J.M.;San, S.;Taylor, J. 2004
- Gaman, T.;Casey, K. 2002
- Griffin, J.R. 1971
- Griffin, J.R. 1973
- Griffin, J.R. 1976b
- Griffin, J.R. 1977
- Griggs, F.T. 1990
- Griggs, F.T.;Golet, G.H. 2002
- Howard, J.L. 1992l
- Klein, A.;Crawford, J.;Evens, J.;Keeler-Wolf, T.;Hickson, D. 2007
- Koenig, W.D.;Knops, J.M. 1997
- Koenig, W.D.;Knops, J.M.;Carmen, W.J. 2002
- McCreary, D.D.;George, M.R. 2005
- Menke, J.;Reyes, E.;Hepburn, A.;Johnson, D.;Reyes, J. 2013
- Meyer, V.C. 2002
- Pacific Southwest Region Remote Sensing Lab, USDA Forest Service (USFS), 2013+
- Pavlik, B.M.;Muick, P.C.;Johnson, S.G.;Popper, M. 1991
- Paysen, T.E.;Derby, J.A.;Black, H.;Bleich, V.C.;Mincks, J.W. 1980
- Sawyer, J.O. 2007
- Thomas, T.W. 1987
- Tyler, C.M.;Mahall, B.E.;Davis, F.W.;Hall, M. 2002
- VegCAMP (CDFW Vegetation Classification and Mapping Program);AIS, 2013
- White, K.L. 1966b
- Wills, R. 2006