Dear GlobalTwitcher user,

A few weeks back, I “gave notice” that I was no longer able to economically keep online. The donator scheme that I introduced in 2010 still far from supports the external costs necessary to keep the site online. The interest in the site has however increased quite a lot over the past few years and now on average has some 25,000 hits per month (close to 1,000 per day). However, of the 750+ active users that regularly use the site to register and update their sightings and upload photo, only 15% have made donations as contributing members.

Today, I am happy to inform you that the immediate threat to the closure of the site has been removed. I have been able to get support from a sponsor who has injected some much needed equity funding and also has agreed to devote time to primarily support the administrative and commercial aspects of driving the activities around the site. Together with Bengt-Eric Sjölinder, an active member and a global twitcher himself, I have established a partnership that now owns and a private shareholding company has been duly registered in Sweden and will be operating as from now. We have a clear objective and vision to develop the site into the premier site for registering, keeping and sharing records of animals and plants on a global scale.

Even though this partnership addresses the immediate financial problems and adds the management capacity that allows me to focus on building the site functions, I would like to emphasize that increased funding from members is necessary to keep the site online long-term. We therefore invite all active users who have not already done so to please, sign up as contributing member. The details are posted under Membership on the site and we will also reach out to those users in a separate communication. In parallel, we will be looking at other avenues to generate funds and increase the numbers of members. We therefore see no need, nor have any plans to increase the membership fees in the future over and above the current levels already indicated on the site.

The site also requires a lot of voluntary input from an international team of administrators. I would like to take this opportunity to thank the administrator team for their dedication and support to the site - their efforts are required to keep the site and the database information up-to-date and broaden it into all aspects of the animal and plant kingdom. Much of my own input is to take the site to another level in a new version of GlobalTwitcher - the plan is to roll out this 2nd version from the end of the 1st quarter 2012. Based on user demands communicated to me over the past few months, quite a few additional features are also in the pipeline to be rolled out in due course.

Finally, I would like to thank you as a user of GlobalTwitcher which in itself is a great support since without all of your data the site is of little value – it also proves the need for a site of this type and it encourages me to continue to develop it for the long-term.

Kind Regards,
Nicklas Strömberg

[Back to the species page]      [HISTORY] Owner:   C. Michael Hogan    

Blue Oak, Annadel State Park, California
Blue Oak
Quercus douglasii

C. Michael Hogan PhD
September 24, 2008

Blue Oak, a California endemic, is a dominant tree of the Coast Ranges and western Sierra Nevada foothills, occurring over approximately two million hectares of mixed oak forest and savanna. This species is associated with considerable ecological biodiversity within the California Floristic Province, and within its range it is viable in arid, hot climate zones.


Q. douglasii is common within its range, and dominant in almost fifty percent of the California oak woodlands. The species is found in valleys and on lower slopes of the Coast Ranges and in lower elevations of the Sierra Nevada, with the distribution forming an almost complete two-dimensional ovate torus with almost null distribution in the core of the Central Valley. Blue Oak occurs in 39 of the California counties ranging from Riverside County north to Del Norte County. Isolated populations are found in the Central Valley, mainly in the form of savannas. Disjunctive stands are found within the Trinity, Siskiyou and Klamath Mountains, east of the Cascade Range. Disjunctive populations occur on Santa Cruz and Santa Catalina islands as limited stands, and are likely the result of prehistoric transport by Chumash and other coastal Native American peoples using plank canoes crossing the narrower ocean channel that existed in the early Holocene.

Q. X alvordiana is the most common hybrid of the Blue Oak, occurring in the Inner Coast Ranges from the Tehachapi Mountains to Carmel Valley; this semi-deciduous hybrid may be dominant within that range.
Close-up of Blue Oak fall foliage


Most often occurring as a single trunked form, Blue Oak does not uncommonly exhibit a multi-furcate version. In any case the crown presents a generally rounded somewhat open canopy with crooked branches and sparsely distributed leaves. Bark is a light ashy gray in thin, scaly, checkered form. This tree has little commercial value beyond firewood, and it has rich brown heartwood, whereas sap wood is light brown. (Pavlik). The bluish green leaves are tough and leathery; serving as a drought protection mechanism; moreover, they manifest smooth wavy margins and extend two to seven cm in length. While normally deciduous, the tree may exhibit a semi-deciduous form in moister habitats.

Q. douglasii may attain a height of seven to 22 meters, with depth of roots commensurate. In shallow soils, this tree may take on a more shallow rooted laterally spreading form, whereas in deeper soils or fractured-rock soil roots will attain their full depth equal to above-ground height. Acorns are light brown at maturity and have dimpled shallow caps, rarely covering the acorn length by more than nine mm. The total acorn length is two to four cm, with a shape of a tapering elongated oval. Mass of acorns is typically three to ten grams.


Acorn of the Blue Oak
Blue oaks typically reach reproductive capability at a height of five meters, but often such growth takes a considerable number of years (approximately 20 to 35); however, trees can also regenerate from stumps following fire, even though this is not a robust method of growth. Acorns typically germinate within 30 days of falling, and this germination is facilitated by a forest floor of moderate leaf litter. Very low early winter temperatures impede germination and seedling survival. The wind pollinated flowers are unisexual, and little biotic energy is allocated to reproduction until after pollination (Koenig) Flowering occurs from March to May, with earlier blooming transpiring in more southerly or warmer regimes. Almost three fourths of the first year seedling growth is invested in root, rather than aboveground growth, as measured by dry-weight. In many cases sapling development is very slow.


Blue Oaks are adapted to considerable aridity and summer heat, with the ability to tolerate weeks of daily maxium temperature of 35 degrees. In years of extreme summer heat, Q. douglasii aestivates and slips into true dormancy, after which the tree continues to produce acorns using its food stores. Following such aestivation, no growth will occur until the ensuing spring Within the core range, typical average annual precipitation spans the range of 50 to 100 cm, although a small part of the southern range is less than half that minimum, and the far northern range sees up to 150 cm per annum.

The typical density of Blue Oak is 10 to 50 trees per hectare, with higher densities on moderate slopes of well drained soils. Q. douglasii will not thrive in heavy clay and hardpan soils (Whitney); moreover, Blue Oak is out-competed by Q. kelloggii (Coast Ranges) and Q. wislizeni (Sierra foothills) in deep rich soils. A shade intolerant species, Blue Oak is rarely an understory plant, (McDonald) but is found in more open canopy environments, including savanna, oak woodlands with a paucity of taller species and rocky arid hillsides of thin soils. A common associate on higher and drier regimes is the Digger Pine (e.g. Inner Coast Ranges and Sierra foothills), which is tall but exhibits a more open canopy, that does not deter Blue Oak sapling growth.

In the North Coast Ranges Blue Oak occurs frequently in association with California Black Oak. (Hogan) Q. douglasii also occurs with Pinus ponderosa and P. Attenuata in the Sierra foothills; and Heterondes arbutifolia and Aesculus californica in the North Coast Ranges. Common understory forbs in sunny patches of the forest floor include Calochortus luteus, Mimulus aurantiacus and Wyethia helenioides. Frequently Blue Oak is associated with a tall grass understory, prehistorically perennial bunch grasses such as Nassella pulchra or other species within the genus Stipa, but since European contact increasingly with introduced grasses such as Avena fatua.


Blue oaks evolved from angiosperms that emerged in the Early Cretaceous period. Q. douglasii apparently developed in response to drier, warmer climates during the previous ten million years The Paleobotanic record illustrates that Q. douglasii comes from a Miocene progenitor taxon, the Quercus douglasoides which had a very broad distribution (McDonald). Subsequent to formation of the Sierra Nevada mountains, Blue Oaks became isolated and thus evolved into a differentiated species.


* Muick Pavlik, Pamela C. Johnson, Sharon G. and Popper Marjorie (1991) Oaks of California.
Cachuma Press, Los Olivos, California, 184 pages
* W. Koenig, R. Mumme,. W.Carmen, and M. Stanback (1994). Acorn production by oaks in Central Coastal California: variation within and among years Ecology. 75: 99-109.
* Stephen Whitney (1994) Western Forests. National Audubon Society, Knopf, New York, N.Y.
* C. Michael Hogan (2008) California Black Oak: Quercus kelloggii, Globaltwitcher, ed. N. Stromberg

(The foregoing was prepared for use by GlobalTwitcher by C.Michael Hogan, who retains copyright to this work. Facts derived from the above may be used by full citation.)
Kingdom Plantae
Phylum Magnoliophyta
Flowering plants
Class Rosopsida
True Dicotyledons (Eudicots)
Order Fagales
Family Fagaceae
Beech family
Genus Quercus
Species douglasii
Blue Oak
Hook. & Arn.
This page was last updated 2011-11-14 23:15:27
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