BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Quercus chrysolepis | Canyon Live Oak 



GENERAL BOTANICAL CHARACTERISTICS : 
Canyon live oak is a rounded, spreading, sclerophyllous evergreen which
grows as a large shrub or small-to-large tree [63,83,97].  Height
commonly ranges from 15 to 70 feet (4.6-21.4 m), with an average maximum
d.b.h. of 2.5 to 5.0 feet (0.8- 1.5 m) [72].  On exceptional sites,
broad-crowned canyon live oaks can reach 100 feet (30.5 m) in height
[45].  The tallest canyon live oak is measured at 106 feet (32 m) at
58.3 inches (148 cm) d.b.h., whereas the record trunk size is 128.5
inches (326 cm) d.b.h. at 72 feet (22 m) [8].  Shrublike growth forms
often have multiple trunks but single-stemmed individuals are also
common [59].  In relatively open stands, the dense canopy may reach
nearly to the ground.  However, in closed stands, crowns tend to be of
smaller diameter and take up only the top one-third to one-half of the
tree [72].  Canyon live oak is typically long-lived, and many plants are
believed to grow to at least 250 or 300 years of age [72,97].

Undisturbed bark is smooth, scaly, and pale gray in color [63,72].
Furrows develop in stems greater than 3 inches (7.6 cm) in diameter, and
the outer bark of older trunks develop variable strips [72].  The root
system is typically deep [35], with roots frequently extending to at
least 24 feet (7.3 m) beneath the soil surface [32].

The leathery, variable, oblong leaves of canyon live oak are green and
glossy above, but golden-yellow below [45,72,83].  Leaf margins are
usually smooth or entire but may be spiny-toothed, particularly when
young.  Leaves generally persist for at least 3 years [72].

Canyon live oak first flowers between 15 and 20 years of age.  Male
flowers are tawny catkins whereas female flowers are sparsely-flowered
spikes.  Both male and female flowers are borne on the same tree [91].
The oblong to ovoid acorns are covered with fuzzy golden scales [61,81].
Acorn size is variable, ranging from 1.0 to 3.0 inches (2.5-7.6 cm) in
length [72].

The variety nana is primarily distinguished by its compact shrubby
growth form.  Leaves of this variety range from 0.8 to 1.6 inches (2-4
cm) in length [63].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Both seed production and vegetative sprouting are important modes of
regeneration in canyon live oak.

Seed:  Variable, ovate-to-ovoid acorns 1.0 to 3.0 inches (2.5-7.6 cm) in
length are borne singly or in clusters [63,72].  Acorns of canyon live
oak are relatively large [73] and can weigh up to 0.7 ounces (19 g) [3].
Cleaned acorns average approximately 150 per pound (330/kg) [66].  Seeds
mature after two growing seasons and drop from the trees during the late
summer or fall [13,41].  Prolific seed crops are produced at somewhat
irregular intervals [71].  However, canyon live oak was found to have
the highest mean annual production of five California oaks sampled.
Approximately 19 percent of the individual canyon live oaks produced no
acorns during the course of this study, whereas 43 percent produced
acorns in 4 or more years.  Good crops were consistently produced by
this species during the 7-year period [13].  Some trees apparently
produce acorns every year [91].

Acorn production by weight is often high, and yields of from 1,960 to
6,000 pounds per acre (2,195-5,200 kg/ha) have been reported [3,98].
Trees in dense stands or clumps generally produce fewer acorns than
large, single trees.  A single open-grown tree can produce up to 400
pounds (182 kg) of acorns annually [91].

Seed dispersal:  Acorns are readily dispersed by gravity, and by many
small birds and mammals.  Squirrels cache acorns and are effective
dispersal agents even though they consume many seeds [5].  The acorn
woodpecker caches seed in trees, whereas the scrub jay hides acorns in
the ground for later use [13].  Although most of these acorns are eaten,
a few subsequently germinate.

Germination:  Germination of canyon live oak tends to be slow.  Matsuda
and McBride [52] observed 50 germination within a 35 day period under
favorable laboratory conditons.  Development may be particularly delayed
at higher elevations.  In California, acorns germinate from November
through January at lower elevations, but germination may not occur at
higher elevations until January or February [51,52].  Evidence suggests
that cold stratification can enhance germination of canyon live oak
[16], although exposure to cold is not necessary for good germination
[51].  Germination appears to be inhibited by darkness [41].  Viable
acorns can be harvested 1 1/2 to 2 months prior to normal ripening, but
germinate only if the tip of the pericarp is removed before planting
[16].  Results of germination tests are as follows [66]:

     germination test       temperature F        duration       germination
     (cold strat. days)     day      night       (days)         capacity (%)

          0 to 60           86       68          56 to 60       56 to 75

Seedling establishment:  Acorns are vulnerable to bird, mammal, and
insect predators.  Animals may consume large numbers of acorns, with
utilization approaching 100 percent where deer, pigs, or bear occur [5].
High acorn mortality has also been attributed to mold or rot.  Acorn
mortality has ranged from 3 to 77 percent under carefully controlled
laboratory experiments [51], suggesting that high mortality does occur
under natural conditions.  In some areas, competition from grasses can
completely eliminate seedling establishment except in particularly moist
years.  Seedling establishment is typically best beneath a forest
canopy.  Where good establishment occurs, seedlings may be dense and
evenly distributed.  Large numbers of canyon live oak seedlings
accumulate in some stands [91].  Growth of seedlings is typically slow
[55].

Vegetative regeneration:  Canyon live oak typically sprouts vigorously
from the stump or rootcrown after fire or mechanical disturbance
[49,72,89,97].  The subsurface rootcrown often sprouts prolifically when
the canopy is only "marginally defoliated" [59,72], and even seedlings
are capable of sprouting after disturbance [49].  Young, vigorous plants
generally sprout readily, although older, weakened trees may fail to
sprout, or may produce only a few stool sprouts.  Sprout growth can be
rapid.  Sprouts may reach 1 to 3 feet (0.5 to 1 m) during the first year
of growth [91].  Four year old sprouts 3 to 6 feet (1-2 m) in height
have been observed [60].  The number of sprouts per clump is reduced as
resources are concentrated on the most vigorous individuals [91].


SITE CHARACTERISTICS : 
Canyon live oak occurs across a wide range of climatic and topoedaphic
conditions [28,49].  It grows on steep, rocky, often exposed slopes or
ridges, in narrow canyon bottoms, sheltered coves, rock crevices, dry
washes, and arroyos [19,28,71,73,93].  Canyon live oak often occurs in
pure stands on steep slopes or bouldery canyon bottoms [49], and in
continuous bands above chaparral [60].  It occasionally forms dense
thickets approximately 10 to 16 feet (3-5 m) in height [17].  Canyon
live oak is particularly common on slopes of 55 percent or more [8].

Soils:  California oaks grow well on a variety of well-drained soils
including fine-grained, cobbly, or gravelly sandy loams, or poorly
developed skeletal soils.  Soil pH commonly ranges from 5.6 to 7.5
with depths of 20 to 40 inches (50-100 cm) [73].  Canyon live oak occurs
on fine, gravelly, rocky, or gravelly-loamy soil, and sand [83,93], but
best growth occurs on rich, moist soils of canyon bottoms [72].  Parent
materials vary but include diorite and gabbro in the Siskiyou Mountains
[100] and serpentine in parts of the Santa Ana Mountains of California
[99].  In northwestern California, canyon live oak grows on soils
derived from serpentine, peridotite, and sedimentary, meta-sedimentary,
and granitic rock types [91].  It generally grows well on poorly
developed soils derived from granitic, metamorphic, or sedimentary
parent materials [49].

Climate:  Canyon live oak grows in coastal areas that receive more than
110 inches (2,780 mm) of annual precipitation, as well as in interior
mountains that receive less than 6 inches (150 mm) of precipitation
annually.  Mean summer temperatures range from 68 to 74 degrees F (20-23
deg C) in the north, to 70 to 77 degrees F (21-25 deg C) in the south.
Winter temperatures average 37 to 41 degrees F (3-5 deg C) in the north,
and 41 to 45 degrees F (5-7 deg C) in the south.  Average growing season
length ranges from 160 to 230 days [91].

Elevation:  Canyon live oak grows from near sea level to 9,000 feet
(2,740 m) [49].  Generalized elevational ranges are as follows
[10,61,72,93,91]:

          from 5,300 to 8,500 feet (1,615-2,591 m) in AZ
               1,000 to 5,000 feet (300-1,500 m) in northern Sierra, CA
               2,500 to 9,000 feet (750-2,740 m) in southern Sierra, CA
               4,100 to 6,300 feet (1,250-1,920 m) in eastern Mohave, CA
               3,280 to 6,888 feet (1,000-2,100 m) in n. Baja CA, Mexico
               1,600 to 5,000 feet (500-1,500 m) in southwestern OR


SUCCESSIONAL STATUS : 
Canyon live oak is an important component of many early seral
communities, primarily because of rapid, prolific sprouting.  In the
northern portion of its range, canyon live oak is prominent in early
seral community on good sites, but it is eventually outcompeted and
disappears from climax stands [91].  In many areas, canyon live oak is a
primary colonizer on rocky crevices and talus piles [17,81].  Once
established on these harsh sites, it generally persists for long periods
of time [17].  

This oak often dominates brushfields created by burning or logging, and
although these brushfields develop soon after disturbance, they may
persist for decades.  Relatively long-lived brushfields made up of
vigorous, shade-tolerant sprouters such as canyon live oak can slow the
rate of forest succession by interfering with conifer regeneration [22].

Canyon live oak is long-lived, and shade-tolerant when young [72,97].
These attributes enhance its importance in a variety of later seral or
climax communities.  It commonly persists as a subordinate species in
climax stands on dry, open forested sites.  Canyon live oak occurs as a
climax dominant on steep, rock-walled canyons [91].

In bigcone Douglas-fir-canyon live oak forests of southern California,
disturbances such as fire can cause some internal shifts in species
composition, but the community itself changes little [49].  Canyon live
oak, although present in seral stages, appears to persist in climax or
even postclimax stands.  Bigcone Douglas-fir forests may be replaced by
canyon live oak woodlands or live oak chaparral under a regime of
frequent fires.  A period of at least 40 to 70 years may be required for
bigcone Douglas-fir to grow beyond 16 to 30 foot (5-9 m) tall stands of
canyon live oak.  It may take "many centuries" for bigcone Douglas-fir
to again assume dominance after a relatively intense fire.  In the
absence of fire, bigcone Douglas-fir slowly grows above canyon live oak
and eventually replaces it [55].

Canyon live oak is generally regarded as an important species in many
fire-maintained disclimax chaparral communities of southern California
[17].  Actual postfire stand turnover is often minimal because of the
prolific sprouting ability of this plant.  Oak typically grows from 3 to
10 feet (1-3 m) within 15 to 30 years after fire or other disturbance,
and dense closed canopy stands 15 to 30 feet (5-10 m) in height develop
within approximately 30 years [59].  Open canyon live oak woodlands are
converted into live oak chaparral if burned at frequent intervals
[37,49].  Although the growth form becomes much more shrublike, the
species itself persists, and the community reverts to an oak woodland if
it is subsequently protected from fire [49].  Tree-sized canyon live
oaks are generally present only in areas which have not burned within 50
years [58].


SEASONAL DEVELOPMENT : 
Canyon live oak flowers from April to June [64,93].  Acorns mature after
two seasons, with ripening time largely dependent on elevation and
growing conditions [71,72].  Acorns generally ripen after mid-August,
although some annual variation has been observed [71].  Immature acorns
which have been damaged by wind, hail, rain, or insects begin to fall
from the tree as early as May [56].  Ripe, undamaged acorns of canyon
live oak are dispersed during the fall [41].  Individual leaves of this
evergreen frequently remain on the tree for at least 3 years [72], with
leaf fall generally occurring in early summer [59].

Related categories for Species: Quercus chrysolepis | Canyon Live Oak