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Vallonea Oak
Quercus ithaburensis
California Black Oak
Quercus kelloggii

Quercus kerrii
  Owner:   C. Michael Hogan    

Black Oak, Sonoma County, California
California Black Oak
Quercus kelloggii

C. Michael Hogan PhD
August 29, 2008

The California Black Oak is associated with two chief woodland types. The Mediterranean California Lower Montane Black Oak-Conifer Forest occurs as far north as the Klamath Mountains of southwest Oregon and is found as far south as California's North Coast Ranges and lower western Sierra slopes.(Sawyer) Q. kelloggii may be the dominant tree in certain stands, and is often associated with White Oak and even conifers such as Douglas Fir or Ponderosa Pine, the latter two being sparse upper canopy elements dominated by lower closed canopy oaks. The forest understory is usually shrubby. Soil associations may be granitic, metamorphic or Franciscan formation.

The second type is North Pacific Oak Woodland, which is found as far north as the Puget Trough, extending through the Willamette Valley and to the Klamath Range of Northern California. (Sugihara) where many of the soils are well drained mesic.

More specific flora associations include: Q. garryana (western Oregon); P. Ponderosa (Willamette Valley); P. menziesii (Klamath-Siskiyou region); P. washoensis, (Modoc County); Q. agrifolia and Q. douglasii (California North Coast Ranges); P. coulteri (San Jacinto Mountains); and Q. wislizenii (Cuyamaca Rancho State Park near San Diego). California Black Oak also serves as an important forest/chaparral transition species, e.g. conifer forest to chaparral (Sequoia National Park)
Close-up of Black Oak foliage

Q. kelloggii typically attains a height of eight to 26 meters with circumference of one to six meters, depending on canopy density and soil types. Rarely, specimens may live over four centuries and achieve a circumference over eight metres. (Pavlick) This species commonly has a multifurcate trunk. In closed canopy situations, California Black Oak has a slender trunk with narrow crown, but older growth typically manifests an irregularly crown of considerable width; however, in a less common savanna setting a round crown is formed on a taller and straighter. In the less common case of arid or nutrient poor conditions, this species occurs as a scrub.

Bark is deep, platy and deeply fissured (up to three cm thick), but is normally smooth for recruits. The leaves of this deciduous species are typically nine to 21 cm long, and have somewhat deeply lobed shape with distinctive pointed lobe apexes. Flowers are unisexual. Acorns achieve a length of 2.3 to 3.1 cm, with a breadth of slightly more than 50 percent of their length.

In deep soils there is commonly one taproot, whereas thin or clayey soils promote multiple taproots. In either case there are pronounced lateral roots, often large and a proclivity to surface root forms. Roots of proximate Black Oaks may graft, forming a dense mass, which phenomenon may be linked to the frequency of apparent multifurcate specimens and which may also contribute to the fire resistance and drought tolerance of the species, by providing greater thermal protection and evaporative resistance for the root structures. Furthermore, new sprouts can generate from a root mass of Q. kelloggii that is totally burnt above ground. (Sudworth)

California Black Oak provide nest sites and cavities for numerous avian species such as Picoides albolarvatus (White-headed woodpecker), Contopus richardsonii (Western wood pewee); for a variety of owls; for amphibians and reptiles such as the California Slender Salamander, California Giant Salamander, Rough-skinned Newt and Ringneck Snake; for mammals such as the Gray Squirrel and American Black Bear. Arguably Q. kelloggii acorns provide the largest biomass of food material for wildlife in the western USA, in comparison to any other flora species. To illustrate the breadth of use by birds, all of the 68 bird species in the Tehachapi Mountains consume California Black Oak acorns. Q. kelloggi plays a key role in fire ecology by being able to resist flames and propagate after forest fires; in fact, the broad food consumption use plays a role via the dispersal of acorns by wildlife. In my California studies of the Western fence lizard, it has been evident that oak forests in general, and Black Oak stands in particular have a higher lizard density than grasslands, chaparral or conifer forests, presumably due to the great abundance and diversity of small arthropods in these Black Oak dominated ecosystems.

A key element of conservation biology in the western USA is re-vegetation of disturbed areas with oaks native to the locale.(Hogan) Oaks such as California Black Oak, Coast Live Oak and Valley Oak have been identified as particularly important in fashioning such programs aimed at wildlife conservation and restoration of areas disturbed by road construction, overgrazing, mining and other human intrusion. Common understory species in Black Oak dominated woodlands in include Western Poison-Oak, Toyon, Creambush and Coastal Wood Fern.

Prehistorically, Q. kelloggii has been a favored food source for Native American tribes within its range. Extensive extant California Black Oak forests in Yosemite Valley are due to preferential cultivation by Miwok tribes, who burnt understory in order to reduce the fraction of Ponderosa Pine.

* J.O.Sawyer and T. Keeler-Wolf (1995) A manual of California vegetation. California Native Plant Society, Sacramento. 471 pages
* Neil G. Sugihara, Jan W. Van Wagtendonk, Kevin E. Shaffer, JoAnn Fites-Kaufman, Andrea E. Thode (2006) Fire in Californias Ecosystems'', University of California Press ISBN 0520246055
* Bruce M.Pavlik, Pamela C.Muick, Sharon G.Johnson and Marjorie Pepper (1991) Oaks of California, Cachuma Press, 184 pages ISBN 0-9628505-2-7
* George Bishop Sudworth (1900) The Stanislaus and Lake Tahoe Forest Reserves and Adjacent Territory, U.S. Govt Printing.Office, 63 pages
* C.Michael Hogan, John Torrey, Brian McElroy et al.(1990) Environmental Impact Report for the City of Rohnert Park, California General Plan, published by Earth Metrics Inc and State of California Environmental Clearinghouse, Sacramento, Ca., Document 1990-10351.

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