Quercus kelloggii, the California black oak, also known as simply black oak, or Kellogg oak, is an oak in the red oak section (Quercus sect. Lobatae), native to western North America. It is a close relative of the black oak (Quercus velutina) found in eastern and central North America.
California black oak is a deciduous tree growing in mixed evergreen forests, oak woodlands, and coniferous forests. California black oak is distributed along foothills and lower mountains of California and western Oregon.
It is found from Lane County, Oregon, south through the Cascade Range, the Sierra Nevada, and the Coast, Transverse, and Peninsular Ranges to San Diego County, California and into Baja California. The tree occurs in pure or mixed stands. Pure stands usually indicate sites unfavorable to conifer growth or recurring disturbance such as fire or logging activities. The tree can grow in many types of soils, but it is important that the soil be well-drained.
Q. kelloggii typically grows from 9–25 m (30–82 ft) in height and from 0.3–1.4 m (0.98–4.59 ft) in diameter. Large trees may exceed 36 m (118 ft) in height and 1.6 m (5.2 ft) diameter. The species also grows in shrubby scrub-oak form on poor sites. In open areas the crown is broad and rounded, with lower branches nearly touching the ground or forming a browse line. In closed stands, the crown is narrow and slender in young trees and irregularly broad in old trees. Trunks are usually free of branches on the lower 6–12 m (20–39 ft) in closed stands. Trunks are often forked, and usually decayed and hollow in older trees. The bark is thin and smooth in young trees, becoming thick, ridged, and plate-like with age. This oak grows from one to several vertical roots which penetrate to bedrock, with large, laterally spreading roots extending off from vertical ones. It also has a number of surface roots.
Acorns are relatively large in this species, from 2.5–3 cm (0.98–1.18 in) long and 1.5–1.8 cm (0.59–0.71 in) wide. The deeply lobed leaves are typically 10–20 cm (3.9–7.9 in) long. While individual trees generally have a lifespan between 100 and 200 years, California black oak can live up to 500 years of age.
The tree reproduces when its acorns sprout to form seedlings. It also reproduces vegetatively with new growth sprouting from the root crown after the tree is top-killed by wildfire, logging, frost, or other events.
The California black oak is a critical species for wildlife. Oaks (Quercus spp.) may be the single most important genus used by wildlife for food and cover in California forests and rangelands, and California black oak occupies more total area in California than any other hardwood species. Livestock also make heavy use of this species for food and cover.
Young California black oaks Cavities in the trees provide den or nest sites for owls, various woodpeckers, tree squirrels, and American black bears. Trees provide valuable shade for livestock and wildlife during the hot summer months. California black oak forest types are heavily used for spring, summer, and fall cover by black bear.
It is browsed by mule deer and livestock. Acorns are heavily utilized by livestock, mule deer, feral pigs, rodents, mountain quail, Steller's jay, and woodpeckers. Acorns constitute an average of 50% of the fall and winter diets of western gray squirrel and black-tailed deer during good mast years. Fawn survival rates increase or decrease with the size of the acorn crop.
It is a preferred foraging substrate for many birds. All of 68 bird species observed in oak woodlands of the Tehachapi Mountains of California used California black oak for part of their foraging activities. Acorn woodpecker, Bullock's oriole, and Nashville warbler show strong preference for California black oak. The parasitic plant Pacific mistletoe (Phoradendron villosum), which commonly grows on this oak, produces berries which attract birds as well.
Many animals cache the acorns, and acorns that have been stored in the ground or otherwise buried are more likely to sprout than those that remain on the surface.
The tree is adapted to wildfire. It is protected from smaller fires by its thick bark. If it is top-killed and burned away in a larger fire, it easily resprouts and has a good supply of nutrients and water stored in its root system.
Acorns sprout into seedlings after fire and sites that have been cleared of canopy and leaf litter in fires are ideal for seedling success.
This oak is vulnerable to sudden oak death.
California Native Americans preferred California black oak acorns over those of other species for making acorn meal. This acorn was a staple food for many Native American groups. Native Americans recognized the importance of fire to this oak, and purposely lit fires in oak woodlands to promote its health and ensure their food source. The wood is used for making furniture, pallets, and construction timber. It is used as an ornamental tree.