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Blue Oak

The Quercus Douglasii is commonly known as Blue Oak, California Blue Oak, Iron Oak, Mountain Oak, as well as Mountain White Oak

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Growing Regions

Blue oak is endemic to California. It occurs in valleys and lower slopes of the Coast Ranges and in lower foothills of the Sierra Nevada. Its distribution almost completely encircles the Central Valley [30,53].

     

General Information

The currently accepted scientific name of blue oak is Quercus douglasii Hook. & Arn. [35,40,53,65]. There are no recognized subspecies, varieties, or forms. Blue oak hybridizes with the following species: x Q. turbinella Greene spp. californica Tucker (desert scrub oak): Q. Xalvordiana Eastwd. [40,65] x Q. dumosa Nutt. (California scrub oak) [65] x Q. garryana Dougl. ex Hook. (Oregon white oak): Q. Xeplingii C. H. Mull. [40,65] x Q. lobata Nee (valley oak): Q. Xjolonensis Sarg. [40,65]

Blue oak-dominated communities are highly variable in composition.  Blue
oak frequently associates with gray pine (Pinus sabiniana).  It also
occurs in monospecific stands or codominates with several other oak
species.  Oak codominants not listed in previous frames include interior
live (Q. wislizenii) and valley (Q. lobata) oaks.  The blue oak
community ranges in physiognomy from open savanna to farily dense
woodland with a shrubby understory.  It merges or forms a mosaic with
annual grassland at low elevation and with chaparral, other oak woodland
phases, or singleleaf pinyon-California juniper (Pinus
monophylla-Juniperus californica) woodland at higher elevation [26].

The following publications name blue oak as a dominant species:

Blue oak communities in California [3]
Association types in the North Coast Ranges of California [18]
Oak woodland [26]
Valley grassland [29]
Terrestrial natural communities of California [30]
The vascular plant communities of California [62]

Plant associations:  Overstory associates not previously listed include
Coulter pine (Pinus coulteri) and California buckeye (Aesculus
californica).  Shrub associates include leather oak (Q. durata),
California scrub oak (Q. dumosa), buckbrush (Ceanothus cuneatus),
California coffeeberry (Rhamnus californica), chamise (Adenostoma
fasciculatum), manzanita (Arctostaphylos spp.), poison-oak
(Toxicodendron diversilobum), and toyon (Heteromeles arbutifolia).  Some
common ground cover associates are annual bluegrass (Poa annua), annual
fescues (Vulpia spp.), annual ryegrass (Lolium multiflorum), medusahead
(Taeniatherum caput-medusae), ripgut brome (Bromus rubens), wild oat
(Avena fatua), bur clover (Medicago polymorpha), filaree (Erodium spp.),
star thistle (Centaurea spp.), and tarweed (Hemizonia, Holocarpha, and
Madia spp.) [5,6,16].

Much of the information presented here is attributed to:
Howard, Janet L. Quercus douglasii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available at USDA Forest Service.

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