View source for Quercus douglasii

{{Short description|Species of oak tree}}
{{Redirect|Blue Oak}}
{{Use mdy dates|date=April 2022}}
{{Speciesbox
| name = Blue oak
| image = Large Blue Oak.jpg
| image_caption = A large blue [[oak]] in a [[pasture]] in [[Mariposa County, California]]
| status = LC
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 12 November 2021">{{cite iucn |author=Beckman, E. |date=2016 |title=''Quercus douglasii'' |volume=2016 |page=e.T78914533A78914539 |doi=10.2305/IUCN.UK.2016-1.RLTS.T78914533A78914539.en |access-date=12 November 2021}}</ref>
| genus = Quercus
| display_parents = 2
| parent = Quercus sect. Quercus
| species = douglasii
| authority = [[William Jackson Hooker|Hook.]] & [[George Arnott Walker-Arnott|Arn.]]<ref name="IOS">{{cite web |url=https://internationaloaksociety.org/content/species-spotlight-quercus-douglasii-hook-arn |title=Species Spotlight: Quercus douglasii Hook. & Arn. |last=Wyly |first=Zarah |date=2019-02-08 |publisher=International Oak Society |access-date=2019-07-14}}</ref>
| range_map =  Quercus douglasii range map.jpg
| range_map_caption = Natural range
| synonyms_ref = <ref>{{ThePlantList |id=kew-172538 |taxon=Quercus douglasii}}</ref>
| synonyms =
* ''Quercus douglasii'' var. ''ransomii'' <small>(Kellogg) Beissn.</small>
* ''Quercus gambelii'' <small>Liebm.</small><ref group=note>Not to be confused with [[Quercus gambelii|''Quercus gambelii'' Nutt.]], a separate species.</ref> 
* ''Quercus oblongifolia'' var. ''brevilobata'' <small>Torr.</small>
* ''Quercus ransomii'' <small>Kellogg</small>
}}

'''''Quercus douglasii''''', known as '''blue oak''', is a species of [[oak]] [[endemic]] to [[California]], common in the [[California Coast Ranges|Coast Ranges]] and the [[foothills]] of the [[Sierra Nevada]].<ref name="hogan">{{cite web |last=Hogan |first=C. Michael |url=http://globaltwitcher.auderis.se/gt2/artspec_information.asp?thingid=85046 |title=Blue Oak ''Quercus douglasii'' |website=GlobalTwitcher |archive-url=https://web.archive.org/web/20130526020933/http://globaltwitcher.auderis.se/gt2/artspec_information.asp?thingid=85046 |archive-date=2013-05-26 |url-status=dead |access-date=2019-07-14 }}</ref> It is California's most drought-tolerant [[deciduous]] oak,<ref name="fs">{{FEIS |genus=Quercus |species=douglasii |type=tree |last=Fryer |first=Janet L. |date=2007}}</ref> and is a dominant species in the [[blue oak woodland]] ecosystem. It is occasionally known as '''mountain oak''' and '''iron oak'''.<ref name="usda">{{Silvics |volume=2 |genus=Quercus |species=douglasii |first=Philip M. |last=McDonald}}</ref><ref>{{Calflora|Quercus douglasii}}</ref>

==Description==
''Quercus douglasii'' is a medium-sized [[tree]] with sparse foliage, generally {{convert|6|-|20|m|ft|abbr=off|sp=us}} tall, with a trunk {{convert|36|-|60|cm|ft|0|sp=us}} in [[diameter at breast height]].<ref name="fs"/> Trunks are typically solitary, but some trees have multiple trunks.<ref name="fs"/><ref name="flora">{{eFloras|1|233501022|Quercus douglasii |first=Kevin C. |last=Nixon |volume=3}}</ref> The tallest recorded specimen was found in [[Alameda County, California|Alameda County]], at {{convert|28.7|m|ft|abbr=on}}.<ref name="usda"/><ref>{{Cite web |last=Ritter |first=Lyman V. |title=Blue Oak Woodland |url=https://erudita.pl/e/BOW.pdf |access-date=2022-04-12 |website=California Department of Fish and Game}}</ref> The trees grow slowly, about {{convert|12|in|cm|order=flip|abbr=on}} per year.<ref name="Cal Poly">{{cite web
 | url = https://selectree.calpoly.edu/tree-detail/quercus-douglasii
 | title = ''Quercus douglasii'' Tree Record
 | website = SelecTree
 | publisher = Cal Poly San Luis Obispo - Urban Forest Ecosystems Institute
 | access-date = 2019-07-14}}</ref> Individual trees over 500 years old have been recorded.<ref name="Stahle1">{{cite web |last=Stahle |first=David |title=Ancient Blue Oak Woodlands of California |publisher=University of Arkansas Tree-Ring Laboratory |url=http://www.uark.edu/blueoak/ |access-date=2019-07-14 |url-status =dead |archive-url=https://web.archive.org/web/20081204063001/http://www.uark.edu/blueoak/ |archive-date=2008-12-04}}</ref>

The [[Bark (botany)|bark]] is light gray with many medium-sized dark cracks. The blue-green [[leaves]] are tough and leathery,<ref name="hogan"/> deciduous, {{convert|4|-|10|cm|abbr=on|frac=4}} long, and [[Glossary of leaf morphology#entire|entire]] or shallowly lobed. The [[acorn]]s are {{convert|2|-|3|cm|in|1|abbr=on|frac=4}} long,<ref name="flora"/> with a moderately sweet [[nut (fruit)|kernel]], and mature in 6–7 months from [[pollination]].

''Q. douglasii'' is [[monoecious]] and wind-pollinated. Flower buds take a growing season to develop into [[catkin]]s.<ref name="fs"/> Blue oak pollen is severely allergenic.<ref>{{Cite web | url=http://www.pollenlibrary.com/Local/Specie/Quercus+douglasii/in/Santa%20clara%20County/CA/ |title = Blue Oak (Quercus douglasii) Species Details and Allergy Info, Santa Clara County, California |website=PollenLibrary.com}}</ref>

{{gallery|mode=packed
|Quercus douglasii-12.jpg|Leaves and acorn
|Quercus douglasii-17.jpg|Leaves in lobed form
}}

== Taxonomy ==
The species is one of over 80 named after Scottish botanist [[David Douglas (botanist)|David Douglas]]. The common name "blue oak" derives from the dark blue-green tint of its leaves.<ref name="IOS" />

Taxonomically it is placed in the [[white oak]] group<ref name="sudden">{{cite web |last1=Rizzo |first1=David M. |last2=Garbelotto |first2=Matteo |last3=Davidson |first3=Jennifer M. |last4=Slaughter |first4=Garey W. |last5=Koike |first5=Steven T. |date=2002 |title=''Phytophthora ramorum'' and Sudden Oak Death in California: I. Host Relationships |url=https://aroxmedia.pl/a/062_Rizzo.pdf |access-date=2019-07-14 |publisher=U.S. Forest Service}}</ref> (subgenus ''Quercus'', section ''Quercus'').

== Ecology ==
''Q. douglasii'' prefers dry to moist soil and plenty of sunlight.<ref name="Cal Poly" /> Its sparse foliage allows more light to reach the ground, and young trees may grow for decades below their parents' [[Canopy (biology)|canopies]].<ref name="fs" /> The species often co-habitates with [[gray pine]] (''Pinus sabiniana''),<ref name="fs" /><ref name="Peeters">{{cite book |last1=Peeters |first1=Hans J. |last2=Peeters |first2=Pam |date=2005 |title= Raptors of California |url=https://books.google.com/books?id=uTui3eJMri8C&q=blue%20oak&pg=PA147 |publisher=University of California Press |page=147 |isbn=9780520242005 }}</ref> and is also found with [[interior live oak]] (''Q.&nbsp;wislizeni''), [[coast live oak]] (''Q.&nbsp;agrifolia''), [[valley oak]] (''Q.&nbsp;lobata''), [[Oregon white oak]] (''Q.&nbsp;garryana''),<ref name="fs" /> and [[canyon live oak]] (''Q.&nbsp;chrysolepis'').<ref name="Canyon">{{FEIS |genus=Quercus |species=chrysolepis |type=tree |last=Tollefson |first=Jennifer E. |date=2008}}</ref> Natural hybrids between ''Q.&nbsp;douglasii'' and the related ''Q.&nbsp;lobata'', ''Q.&nbsp;garryana'',<ref name="fs" /> and [[shrub live oak]] (''Q.&nbsp;turbinella'') often occur where the species grow together in the same area. Sources consider ''[[Quercus × alvordiana]]'' to be a hybrid of ''Q.&nbsp;douglasii'' and either ''Q.&nbsp;turbinella''<ref name="Alvord">{{cite web |url=http://plants.usda.gov/plant-profile?symbol=QUAL2 |title=Plants Profile for Quercus alvordiana (Alvord oak) |author=<!--Not stated--> |website=Plants Database |publisher=USDA Natural Resources Conservation Service |access-date=2019-07-15}}</ref> or ''[[Quercus john-tuckeri|Q.&nbsp;john-tuckeri]]''.<ref name="fs" />

Old-growth [[blue oak woodland]] may be one of the most widespread [[old-growth forest]] ecosystems remaining in the state after European colonization.<ref name="Stahle2">{{cite journal |last1=Stahle |first1=D. W. |last2=Griffin |first2=R. D. |last3=Meko |first3=D. M. |last4=Therrell |first4=M. D. |last5=Edmondson |first5=J. R. |last6=Cleaveland |first6=M. K. |last7=Stahle |first7=L. N. |last8=Burnette |first8=D. J. |last9=Abatzoglou |first9=J. T. |last10=Redmond |first10=K. T. |last11=Dettinger |first11= M. D. |last12=Cayan |first12=D. R. |date=2013-05-22 |title=The Ancient Blue Oak Woodlands of California: Longevity and Hydroclimatic History |journal=Earth Interactions |volume=17 |issue=12 |pages=1–23 |doi=10.1175/2013EI000518.1 |bibcode=2013EaInt..17l...1S |s2cid=130820896 |doi-access=free }}</ref>

The acorns are eaten by wildlife and livestock.<ref>{{cite book |last=Little |first=Elbert L. |title=The Audubon Society Field Guide to North American Trees: Western Region |year=1994 |orig-year=1980 |publisher=Knopf |isbn=0394507614 |edition=Chanticleer Press|page=395}}</ref>

===Drought tolerance===
''Quercus douglasii'' is the most drought-tolerant of California's deciduous oaks. It has a smaller canopy than less drought-tolerant relatives, and invests proportionally more growth into roots rather than leaves throughout its life cycle.<ref name="fs"/> The leathery blue-green leaves contribute to its [[drought tolerance|drought resistance]];<ref name="hogan"/> during drought, the leaf color is more pronounced. Trees can also drop their leaves in summer rather than fall in dry years, but usually continue to develop their acorns through the fall. Drought may cause trees not to flower in spring.<ref name="fs"/>

[[File:Quercus douglasii-Galls.jpg|thumb|Galls on leaf]]

===Gall wasps===
Author Ron Russo writes that ''Q. douglasii'' hosts the "largest number of known species" of [[gall wasp]]s,<ref name="Russo">{{cite web |url=https://baynature.org/article/call-of-the-galls/ |title=Call of the Galls |last=Russo |first=Ron |date=2009-07-01 |website=Bay Nature Magazine |publisher=Bay Nature Institure |access-date=2019-07-15}}</ref> at more than 50.<ref name="Wirka">{{cite web |url=https://www.pressdemocrat.com/lifestyle/4489842-181/nature-sonoma-county-is-bursting |title=Nature: Sonoma County is bursting with galls |last=Wirka |first=Jeanne |date=2015-09-22 |website=The Press Democrat |access-date=2019-07-15}}</ref> The wasps trigger the formation of [[oak gall]]s in a wide variety of shapes, colors, and sizes.<ref name="Russo"/><ref name="Wirka"/>

===Sudden oak death resistance===
As of 2002, the disease known as [[sudden oak death]], caused by the [[oomycete]] ''Phytophthora ramorum'', had not been found in ''Quercus douglasii'' or any members of the white oak group. An experiment showed that ''Q.&nbsp;douglasii'' and ''Q.&nbsp;lobata'' (another white oak) appeared to be resistant to the pathogen.<ref name="sudden"/>

==Uses==

The acorns can be eaten but, if bitter, may need to have the [[tannin]]s leached.<ref>{{Cite book|last1=Elias|first1=Thomas S.|url=https://www.worldcat.org/oclc/244766414|title=Edible Wild Plants: A North American Field Guide to Over 200 Natural Foods|last2=Dykeman|first2=Peter A.|publisher=[[Sterling Publishing|Sterling]]|year=2009|isbn=978-1-4027-6715-9|location=New York|pages=228, 231|oclc=244766414|orig-year=1982}}</ref> [[Native Californians]] commonly gathered the acorns, which they considered good-tasting, and processed them into [[acorn flour]]. They made baskets out of blue oak seedlings, utensils such as bowls from the wood, and dye from the acorns.<ref name="fs"/><ref name="week">{{cite web |url=https://www.fs.fed.us/wildflowers/plant-of-the-week/quercus_douglasii.shtml |title=Plant of the Week: Blue Oak (''Quercus douglasii'' Hook. & Arn.) |last=Gauna |first=Forest |website=Celebrating Wildflowers |publisher=U.S. Forest Service |access-date=2019-07-15}}</ref> Commercially, the blue oak is mainly limited to use as firewood.<ref name="hogan"/>

==See also==
* ''[[Quercus × alvordiana]]''

==Notes==
{{Reflist|group=note}}

==References==
{{Reflist}}

==External links==
* {{Commons category inline|Quercus douglasii|''Quercus douglasii''}}

{{Taxonbar|from=Q666160}}

[[Category:Quercus|douglasii]]
[[Category:Endemic flora of California]]
[[Category:Natural history of the California Coast Ranges]]
[[Category:Natural history of the Central Valley (California)]]
[[Category:Plants described in 1840]]
[[Category:Trees of Mediterranean climate]]
[[Category:Garden plants of North America]]
[[Category:Ornamental trees]]
[[Category:Taxa named by George Arnott Walker Arnott]]
[[Category:Taxa named by Robert Wight]]