BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Quercus lobata | Valley Oak 



GENERAL BOTANICAL CHARACTERISTICS : 
Valley oak is a long-lived, flood- and drought-tolerant, monoecious,
deciduous tree [28.56,53].  It is the largest North American oak
[34,53,61] Trees are typically 30 to 75 feet (10-25 m) tall and from 1.8
to 2.4 feet (0.5-0.7 m) in d.b.h. but may become much larger [13,53].  A
record tree in Gridley measures 9.3 feet (2.8 m) in d.b.h.  [13], and
Griffin [30] reported a 138-foot (30 m) valley oak at the Hastings
Natural History Reservation of Carmel Valley.  Large oaks are usually
hollow or rotten in the center, making exact age determinations
impossible.  Age estimates of very large trees range from 400 to 500+
years [8.30].  Mature stands are typically from 100 to 200 years old
[8].

The crowns of open-grown trees are very broad [30].  Valley oaks have a
highly branched growth habit.  The oaks are sensitive to chloride
aerosol, and trees growing less than 4 miles (7 km) inland tend to be
scrubby and flagged [55].  Valley oak typically has several vertical
roots that tap groundwater and extensive horizontal root branches
[28,31].  Vertical root depth has been measured as deep as 80 feet (262
m) in some individuals [45].  Acorns are long (1.2 to 2.0 inches [3-5
cm]) and slender (0.5 to 0.8 inch [1.2-2.0 cm]).  The bark is thick and
deeply furrowed [53].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual:  Valley oak is wind pollinated.  Catkins are frost sensitive and
are sometimes killed by freezing temperatures [29].  The age of sexual
maturity and maximum acorn production are not recorded in the literature.
Trees growing in full sun produce the greatest number of acorns [43].
Seeds mature in 1 year [15].  Acorns collected at the Bobelain Audubon
Sanctuary were 58 percent viable; loss of viability was attributed to
insect predation [43].  There is no dormancy requirement.  Some acorns
germinate before falling off the parent tree, and many others germinate
soon afterward [27,65].  Seed-caching animals which bury acorns, such as
scrub jay and California ground squirrel, are important to species
survival.  Acorns burried by these animals have a greater chance of
germination and successful establishment, as predation of acorns is
usually high [15].  At the Hastings Natural History Reservation, Griffin
[32] reported 100 percent consumption of acorns on the ground.  Some
acorns, however, remained until spring when black-tailed deer and cattle
were excluded from the area.

Germination is hypogeal.  Seedling emergence is best in seedlings buried
2 to 4 inches (5-10 cm).  Shallowly-buried acorns usually desiccate or
are dug up by seed predators [70].  Seedlings grow best in partial shade
or on northern aspects; seedling survival is low on southern aspects
[32].  Valley oak is less browse-resistant than competing live oaks, and
current levels of herbivory are too high to permit significant seedling
recruitment on most sites [6,30].  Random plot samples taken throughout
valley oak's range showed sapling-to-mature tree ratios of 1:10 or worse
[52].  Exceptions are in localized ecotonal and riparian areas [43].
Loss of seedlings due to pocket gopher root herbivory is high [34].
Pocket gopher populations in the Central Valley, once controlled by
drownings during seasonal innundations, have greatly increased following
the building of flood-control dams.  Aboveground herbivory by pocket
gopher and other animals causes much mortality as well.  Recruitment at
one unproductive site in the Santa Monica National Recreation Area began
once cattle were excluded and weeds removed from around germinants [71].
Seedlings are sensitive to competition from grasses and forbs,
particularly annual grasses.  Where soil moisture is limiting, annual
grasses outcompete valley oak seedlings for water [21].  Once saplings
grow above the browse line, mortality is low [30].

Vegetative:  Valley oak seedlings and saplings sprout from the root
crown following damage to aboveground portions of the plant [30].
Mature trees do not have this ability, but often grow epicormic sprouts
following damage to branches [32].


SITE CHARACTERISTICS : 
Valley oak grows in the deep, rich soil typical of floodplains and
valley floors [34,43].  Slope rarely exceeds 35 percent [2].  Soil
textures include silty loam, clayey loam, and sandy clay loam.  Valley
oaks near undammed waterways receive annual inputs of silty alluvium
[39].  The oaks depend on water-table access [14].  Best growth is
attained when water tables are about 33 feet (10 m) below the surface
[5].  They will tolerate poorly drained soil and wet seeps [11,41].
Valley oaks in riparian forests receive subsurface irrigation.
Historically, these forests were innundated about every 5 years [26].
Where distribution overlaps with other oaks, valley oaks are found on
the more mesic sites with deeper soils [48].

The oaks grow in a Mediterranean climate, characterized by wet, mild
winters and hot, dry summers.  Coastal valley oaks receive from 20 to 80
inches (51-203 cm) of annual precipitation; inland populations receive
from 6 to 30 inches (14-76 cm) [7].  Fog is common along the coast in
summer and inland during winter [29].  Elevation ranges from sea level
to a maximum of 5,100 feet (1,700 m) in the Tehachapi Mountains [30].

Plant associations:  Overstory associates not listed as SAF COVER TYPES
include Fremont cottonwood, white alder (Alnus rhombifolia), arroyo
willow (Salix lasiolepsis), valley willow (S. goodingii), Oregon ash
(Fraxinus latifolia), Hind's walnut (Juglans hindsii), California black
walnut (J. californica), California buckeye (Aesculus californica), box
elder (Acer negundo), Coulter pine (Pinus coulteri), interior live oak,
Engelmann oak (Quercus engelmannii), and pin oak (Q. plaustris).  Common
exotics are eucalyptus (Eucalyptus spp.), tree-of-heaven (Ailanthus
altissima), and fig (Ficus caria) [5,12,30,36,40].

Shrub associates include poison-oak (Toxicodendron diversilobium),
coffeeberry (Rhamnus californica), redberry (R. crocea), Mexican tea
(Chenopodium ambrosiodes), California blackberry (Rubus vitifolius),
coyotebush (Baccaris pilularis var. consanguinea), California rose (Rosa
californica), buckbrush (Ceanothus cuneatus), birchleaf
mountain-mahogany (Cercocarpus betuloides), squawbush (Rhus trilobata),
and Mexican elderberry (Sambucus mexicana) [1,9,12,53].

Herbaceous associates include bermuda grass (Cynodon dactylon), purple
needlegrass (Stipa pulchra), Harding grass (Phalaris tuberosa var.
stenoptera), wild oat (Avena fatua), pine bluegrass (Poa scabrella),
soft chess (Bromus mollis), yellow star thistle (Centaurea
solstitialis), annual agoseris (Agoseris heterophylla), golden brodiaea
(Brodiaea lutea), and California melicgrass (Melica californica).  The
state-endangered California hibiscus (Hibiscus californicus) occurs
within the valley oak riparian forest habitat type [9,11,21,35,64].

Other:  Creeping woody plants using valley oak for vertical support
include wild grape (Vitis californica); poison-oak often assumes this
growth form as well [39].  Mistletoe (Phoradendron villosum) is a common
valley oak parasite [60].  Physconia detersa is frequently the dominant
lichen on valley oak bark [68].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Valley oak is intermediate in shade tolerance [49].  It is a climax
species in floodplain riparian forests; it is also a secondary colonizer
there [69].  On swales denuded by gold dredging on the Merced River,
valley oak seedlings established under the shade of young willows.
Since no parent trees were nearby, it is believed that the oak seedlings
grew from animal-buried acorns [78].

Most authorities classify valley oak woodlands as fire climax, and seral
to mixed hardwood or coniferous forests in the absence of fire
[12,18,30,31,39].


SEASONAL DEVELOPMENT : 
Valley oak seasonal development is as follows:

        catkins emerge:  March to April [53]
        leaves emerge:   March [14]
        acorns ripe:     October to November [15]
        leaves fall:     November [14]

Related categories for Species: Quercus lobata | Valley Oak