VALUE AND USE
SPECIES: Quercus douglasii | Blue Oak 



WOOD PRODUCTS VALUE : 
Blue oak wood is not used in manufacturing because of the tree's
frequently short stature and poor form.  Products are limited to
fenceposts and fuelwood [16].  Historically, the wood was used for shaft
supports in gold and silver mines [33].


IMPORTANCE TO LIVESTOCK AND WILDLIFE : 
Blue oak is an important species for livestock and wildlife.  Sixty-five
percent of California livestock forage is provided within blue oak-gray
pine woodland [14].  A 3-year study in the central Sierra Nevada
foothills showed that blue oak woodland is utilized by 92 species of
birds, 60 of which nest there [12].  Bird species of federal protected
status inhabiting the woodland are the bald and golden eagles.  It is
also inhabited by seven species of rodents, three species of lizards,
four species of snakes, and the state-endangered foothill yellow-legged
frog.

Blue oak is browsed by livestock, black-tailed deer, lagomorphs, and
rodents.  The acorns are eaten by at least a dozen species of songbirds,
several upland game birds, rodents, black-tailed deer, feral and
domestic pig, and all other classes of livestock [2,20,60].  The acorns
are a critical food source for black-tailed deer, who migrate from
high-elevation dry summer ranges to blue oak woodland for fall and
winter forage [16].  On the Tehema County winter range, blue oak acorns
account for about 15 percent of the total volume of food consumed by
black-tailed deer [60].


PALATABILITY : 
Blue oak acorns are highly palatable to livestock, black-tailed deer,
and other wildlife.  The sprouts are palatable to all classes of
browsing wildlife and livestock.  Sampson and Jesperson [60] gave mature
blue oak foliage the following browse rating:

     black-tailed deer:  excellent to good
     sheep:  fair to poor
     goats:  fair to poor
     cattle:  poor
     horses:  poor to useless


NUTRITIONAL VALUE : 
The crude protein content of young, partially expanded leaves of blue
oak on the San Joaquin Experimental Range averages 30 percent, while
that of fully developed leaves averages 11 percent.  The ratio of
calcium to phosphorus is nutritionally satisfactory in young leaves
(2.2:1.0), but disproportionate in mature leaves (15:1).  Acorns are low
in crude protein (4%) but high in crude fiber, fat, and oils [60].


COVER VALUE : 
Blue oak is the prefered nesting, foraging, and escape cover of the
Nuttall's woodpecker, plain titmouse, and white-breasted nuthatch [11].


VALUE FOR REHABILITATION OF DISTURBED SITES : 
Blue oak is planted for wildlife and riparian habitat and watershed
restoration.  Trees are established from acorn plantings or from
transplanting nursery stock.  Top-quality acorns are obtained by
harvested directly from branches in early to mid-fall.  They require
refrigeration at just above freezing for a few weeks to prevent
premature germination.  Acorns are planted in late fall or early winter
after soil is saturated from the first rains [48].  Dusting acorns with
captan fungicide prior to planting may improve emergence [2].  When
transplanting, 2-month-old nursery stock is recommended because it shows
better establishment and is cheaper to grow, transport, and plant than
older stock [1].  Protection against herbivory greatly enhances seedling
survival, and may include fencing or wire cages extending 36 inches (92
cm) aboveground and 18 inches (46 cm) belowground [56].  Fertilizer has
a negative effect on survival because it enhances growth of annual
grasses over that of blue oak; weed control improves blue oak seedling
survival.  Netting may be neccessary at some sites to reduce losses from
grasshopper herbivory [1].  Augering holes where seedlings or acorns are
to be planted will increase survival and growth rates.  Roots of
individuals planted in 3-foot-deep (0.9 m) auger holes are able to more
quickly access the deeper soil horizons where more moisture is available
[48].

Blue oak roots bind soil of steep watersheds, reducing the incidence of
mass soil movement downslope into permanent and ephemeral streams [16].
Blue oak was successfully used to revegetate upper streambanks in
Almaden Valley [25].

Blue oak scions can be grafted onto blue oak stumps following fuelwood
harvesting.  Grafting genetically superior scions onto rootstock allows
for more rapid reestablishment of depleted blue oak woodland [63].


OTHER USES AND VALUES : 
Blue oak is a valuable landscaping ornamental.  A study was conducted in
Mendocino and Sonoma Counties to assess the value of blue oak on lands
undergoing subdivision [61].  It showed that the aesthetic and amenity
values of trees at a density of 40 stems per acre (16 stems/ha)
resulted in a 21 to 27 percent increase in land value when compared
to acreage with no trees present.

California Indians made meal from blue oak acorns.  They used the acorn
leachate for dying baskets.  The wood was fashioned into bowls [64].


MANAGEMENT CONSIDERATIONS : 
Blue oak woodland covers 8 percent of California's total land area
[2,5].  Seventy-five percent of this resource is in private ownership,
14 percent is in the National Forest System, and 11 percent is in
various other public ownerships [13].  Management of this species is
controversial.  From the late 1950's through the early 1970's, several
studies showed that palatability and production of graze in the
understory of blue oak was low when compared to graze in open grassland
areas [8,34,36,37,54,55].  As a result of these studies, statewide
"rangeland improvement" was recommended, involving removal of blue oak
from grazing areas [8,67].  This recommendation resulted in the loss of
1 million acres (0.4 million ha) of blue oak woodland to cutting,
prescribed burning, and aerosol spraying [13,67].  In contrast, more
recent studies [20,31,32] found forage production to be from 15 to over
100 percent higher under blue oaks than in open grassland, and that
herbaceous plants beneath blue oak were nutritionally superior to plants
growing in open grassland.  Forage under blue oak started growing
earlier and remained green after surrounding graze had dried.
Additionally, Duncan and Clawson [20] reported that cattle prefer forage
beneath blue oak to that of open grassland, even in summer after graze
in both areas has dried.  Holland [31] found that death or removal of
blue oak resulted in a gradual decline in forage production.  Supporting
this, a separate study [37] showed an increase in tarweed (Madia
gracilis) following blue oak removal.  The discrepancy between early and
later studies on the effects of blue oak on forage production remains
unresolved.  One study [7] suggests that understory production increases
on dry sites but is lowered on wetter ones.  Another recent study [71]
indicates that blue oak with shallow, fine roots inhibits understory
production.  This may be partially attributable to allelopathic blue oak
root exudates as well as competition for water and nutrients.
Variations in root morphology may therefore explain differences in
understory production of blue oak.

Most current public rangeland managers regard blue oak as a desirable
species.  Continued clearing of blue oak for rangeland improvement
projects and poor natural regeneration were two major management
concerns identified by the Hardwood Task Force of the California Board
of Forestry [2].  Other factors contributing to species decline are road
construction, residential, and commercial development.  Limited data
suggests that development accounted for 46 percent of blue oak loss
between 1973 and 1985, surpassing the loss from rangeland clearing that
dominated before that time.  Water tables that have lowered from
historic levels may also be contributing to the decline of this species
[69].  In addition, use of blue oak for fuelwood has greatly increased in
recent years [16].

Damaging agents:  Blue oak is vulnerable to several species of fungi.
The most serious of these are Inonotus dryophilus, Laetiporus
sulphureus, and Armillaria mellea, which cause heart rot [16].

A large number of insects infest blue oak.  One study showed that 38
species of insects inhabit blue oak, attacking every part of the tree.
The most damaging of these pests in terms of regeneration are the acorn
feeders, which include various species of cynipid wasps, the filbert
weevil (Curculio uniformis), and the filbert worm (Melissopus
latiferreanus).  These insects can destroy large portions of a year's
mast [16].

Related categories for Species: Quercus douglasii | Blue Oak