Associated Forest Cover
provided by Silvics of North America
California black oak is a component of six forest cover types
(11). It is the prime constituent of California Black Oak
(Society of American Foresters Type 246) and a major component in
two others: Douglas-Fir-Tanoak-Pacific Madrone (Type 234) and
Pacific Ponderosa Pine-Douglas-Fir (Type 244). Black oak becomes
important in Sierra Nevada Mixed Conifer (Type 243) and Pacific
Ponderosa Pine (Type 245) after severe disturbance or fire. The
oak is a minor component in Canyon Live Oak (Type 249).
The successional status of California black oak is not clear. It
has been implied that the species was climax because the type in
which it was a part represented a degree of mesophytism between
that of the chaparral and the conifer forest (7). The species was
also thought to be more a persistent subclimax than climax.
California black oak, or its fossilized equivalent (Quercus
pseudolyrata), was much more widespread in past ages than
now. Fossil remains indicate that the species was abundant in
sedimentary deposits near Spokane and Ellensburg, WA, in the John
Day Valley and Blue Mountains of Oregon, and in northwestern
Nevada (6). These deposits date back to the Miocene epoch of 12
to 26 million years ago. Increasing aridity is the probable cause
for the smaller natural range of black oak today.
The most common botanical associate of black oak is ponderosa pine
(Pinus ponderosa var. ponderosa). The two species
intermingle over vast acreages, except that black oak is found at
lower elevations, on sites too poor to support pine, and in
certain areas within the redwood region of California where pine
does not grow. Another exception is that this oak is rarely found
in Interior Ponderosa Pine (Type 237) (11). In California and
Oregon, therefore, where the natural ranges of the two species
coincide, ponderosa pine sites generally are fertile ground for
black oak. And black oak sites are almost always fertile ground
for ponderosa pine.
At lower elevations, black oak often serves as a nurse tree to
conifers. Ponderosa pine, Douglas-fir (Pseudotsuga
menziesii), and incense-cedar (Libocedrus decurrens) seedlings
often become established beneath the sheltering crowns of large
black oaks while adjacent ground remains bare (2).
A rule-of-thumb is that black oak never grows through a stand of
ponderosa pine but can grow through brush (9). Without
disturbance, black oak is eventually crowded out of the best
sites and remains only as scattered remnants in mixed-conifer
forests. Here it often exists on "islands" of soil or
terrain not favorable for natural regeneration of conifers.
Black oak grows individually or in groves, some of which are quite
extensive. Usually each grove is of one age-class, the result of
sprouting after fire (34). Rarely does it exist as an understory,
especially beneath a closed canopy. The species is usually a
component of hardwood stands or of mixed hardwood and conifer
forests. Tanoak (Lithocarpus densiflorus) and Pacific
madrone (Arbutus menziesii) are the most common hardwood
associates of black oak. Other hardwood associates at lower
elevations are Oregon white oak (Quercus garryana), interior
live oak (Q. wislizenii), coast live oak (Q.
agrifolia), Engelmann oak (Q. engelmannii), and
blue oak (Q. douglasii). At higher elevations
Pacific dogwood (Cornus nuttallii), bigleaf maple (Acer
macrophyllum), California-laurel (Umbellularia
californica), and canyon live oak (Quercus chrysolepis)
intermix with California black oak.
Besides ponderosa pine, conifer associates at low elevations are
knobcone pine (Pinus attenuata), Monterey pine (P. radiata),
Digger pine (P. sabiniana), and redwood (Sequoia
sempervirens). At intermediate elevations within the natural
range of California black oak are California white fir (Abies
concolor var. lowiana), grand fir (A. grandis),
incense-cedar, Coulter pine (Pinus coulteri), sugar
pine (P. lambertiana), giant sequoia (Sequoiadendron
giganteum), Douglas-fir, California torreya (Torreya
californica), and bigcone Douglas-fir (Pseudotsuga
macrocarpa). At higher elevations black oak intermingles with
western juniper (Juniperus occidentalis) and Jeffrey pine
(Pinus jeffreyi).
Shrub associates include at least 30 species, some of the most
important of which are greenleaf manzanita (Arctostaphylos
patula), whiteleaf manzanita (A. viscida), deerbrush
(Ceanothus integerrimus), bear-clover (Chamaebatia
foliolosa), oceanspray (Holodiscus discolor), Brewer
oak (Quercus garryana var. breweri), Sierra
coffeeberry (Rhamnus rubra), Sierra gooseberry (Ribes
roezlii), and poison-oak (Toxicodendron diversilobum).
In parts of Shasta and Trinity Counties, and perhaps
elsewhere, black oak itself takes a shrub form. The stands so
formed usually are dense and tangled-ideal habitat for deer and
upland game.
Except on the fringe of black oak's natural range, especially at
the lowermost elevations, most shrubs generally are not
competitive, nor particularly abundant over most of the forest
land where black oak grows. After heavy cutting or fire, however,
some of the more aggressive shrubs often compete strongly with
black oak sprouts.
When compared with 15 of its most common shrub associates in the
Klamath Mountains of northern California, black oak ranked ninth
in need of soil moisture, third in demand on soil nutrients,
eighth in terms of tolerance, and first in rapidity of sprouting
(32). The species is able to withstand high moisture stress (37)
and to become established and grow well on harsh sites where few
other species are capable.
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Climate
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Hot dry summers and cool. moist winters characterize the climate
where California black oak grows. Within the species' natural
range, average annual precipitation varies widely. In the valleys
of southwestern Oregon, it exceeds 760 mm (30 in); in
northwestern California, it ranges from 760 to 2540 mm (30 to 100
in); and in northeastern California, only 300 to 380 mm (12 to 15
in) of rainfall annually. Throughout the range of black oak in
north-central and central California, annual precipitation
averages 1010 to 1780 mm (40 to 70 in) but may exceed 2920 mm
(115 in) locally. In these areas less than 4 percent of the
yearly precipitation falls from. June through September. In the
mountains of southern California, precipitation averages 910 mm
(36 in). Black oak achieves its best size and abundance in areas
where snowfall accounts for 10 to 50 percent of the year's
precipitation.
Average mean daily temperatures range from -1° to 8° C
(31° to 46° F) during January, and from 19° to 28°
C (66° to 82° F) in July. The last killing spring frost
is expected between March 15 and June 9, and the first killing
frost in the fall between August 30 and November 30. Periods free
of killing frosts range from 82 to 270 days. Throughout an
18-year period, the highest temperature recorded at 1125 m (3,700
ft) elevation in the center of black oak's zone of greatest size
and abundance was 39° C (103° F); the minimum
temperature was -15° C (5° F). The maximum number of
frost-free days was 215 and the minimum was 116 (35).
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Damaging Agents
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Fire is black oak's worst enemy. Crown
fires kill trees of all ages and ground fires are often fatal.
Only a little radiative heat kills the cambium and only a small
amount of flame along the trunk leaves long vertical wounds. Bark
thickness on mature trees varies from 2 to 5 cm (1 to 2 in), but
even the thickest bark provides little insulation to fire. Scars
from burning can become a point of entry for fungi. On larger
trees, repeated fires often enlarge old scars, sometimes toppling
the tree. Fluctuations in weather also cause injury. Heavy, wet
snow breaks branches and stems, particularly at forks, and sudden
high temperatures following cool wet weather severely injure
leaves (25).
California black oak is especially susceptible to fungi. Heart rot
of the bole and large limbs of living trees, caused mainly by two
pathogens, Inonotus dryophilus and Laetiporus
sulphureus, is the principal damage (24). These rots enter
the tree through broken branches or open wounds resulting from
fire or logging. Both fungi often reduce the bole and large limbs
of older, decadent trees to mere shells. The hedgehog fungus (Hydnum
erinaceus) also is found in the heartwood of living trees and
Polyporus adustus in the sapwood, though neither is
prevalent.
By the time a natural black oak stand is 85 years old, the
proportion of infected trees begins to increase rapidly. Almost
40 percent of trees 110 to 120 years old show incipient heart rot
(21). Rotation age of stands grown for wood products could be
influenced by this incidence-age relationship.
Another serious pathogen, Armillaria mellea, causes decay
of the roots and butt of older decadent black oak. Sometimes it
weakens the root system so much that the tree topples over on a
perfectly calm, still day (36). This pathogen is indigenous in
black oak, but younger vigorous trees do not seem to be affected
by it.
A comparatively recent damaging agent to black oak in the San
Bernardino Mountains of southern California is air pollution.
Although the oak appears less susceptible to air pollution damage
than associated conifers, radial growth has decreased in some
trees (12). Where high ambient oxidant air pollution levels are
chronic, damage to California black oak is expected to be
significant (26).
One virulent pathogen that black oak escapes, and indeed is
resistant to, is Heterobasidion annosum (14). For this
reason, California black oak is being planted in numerous
infection centers in southern California forests where conifers
are dead or dying.
California black oak is prone to several leaf diseases including
the oak leaf fungus (Septoria quercicola), oak
anthracnose (Gnomonia veneta), powdery mildews (Microsphaera
and Sphaerotheca spp.), a leaf blister fungus (Taphrina
caerulescens), a leaf rust (Cronartium spp.),
and true mistletoe (Phoradendron villosum subsp. villosum).
Damage from each of these pests has not been determined but
loss of growth increment probably is minor.
Animal damage to black oak is mostly from browsing. Foliage is
eaten during all seasons, but especially in spring when new
growth is tender and in winter when twigs are eaten. Deer eat
acorns, seedlings, sprouts, and foliage. Even in midsummer, newly
germinated seedlings with acorns attached often are consumed (8).
Occasionally, browsing is fatal. In Mendocino County, CA, for
example, a deer population of 1/2.4 ha (1/6 acres) almost
eliminated oak over large areas of the Coast Range. Cattle also
browse black oak, but in national forests, at least, their
numbers are declining.
Many insects derive sustenance from black oak. The damage is
usually secondary, reducing growth but seldom killing trees.
Among sucking insects, the pit scales (Asterolecanium minus
and A. quercicola) have the greatest potential for
damage (4). The most destructive insect, however, is probably the
carpenterworm (Prionoxystus robiniae), whose larvae mine
the wood of trunk and limbs and cause injuries that appear later
as defects in lumber (16).
Other insects are capable of heavy damage, especially when
infestations become epidemic. The Pacific oak twig girdler (Agrilus
angelicus) is the most damaging insect to oak in southern
California during drought years (4). In northern California, the
California oakworm (Phryganidia californica) is noted for
defoliating trees. So is the fruit-tree leafroller (Archips
argyrospila) which, in 1968, caused heavy damage throughout a
wide area in the Sacramento River drainage.
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Flowering and Fruiting
provided by Silvics of North America
California black oak flowers from
mid-March to mid-May depending on elevation, physiography, and
local climatic conditions. In general, trees near the coast and
at lower elevations bloom earliest.
Flowers on black oak are unisexual. The plant is monoecious.
Staminate flowers are long (3.5 to 7.5 cm or 1.4 to 3.0 in) hairy
aments that emerge from buds in the leaf axils of the previous
year's growth. The five to nine stamens in each ament have bright
red anthers and pale green filaments. The calyx is light green.
Pistillate flowers are borne singly or two to seven on a short
stalk that originates from leaf axils of the current year's
growth. The stigmas are dark red.
Acorns mature in the second year. Early in the second summer the
immature acorn resembles a small globe about 6 mm (0.2 in) in
diameter. At this stage, the acorn is completely encapsulated in
the cup. At maturity the light brown, thin-scaled cup encloses
from 0.5 to 0.75 of the acorn. Acorns form singly, or in clusters
of two to six, and vary widely in dimension. Sizes range from 1.9
to 4.4 cm (0.7 to 1.7 in) long and from 0.9 to 3.8 cm (0.4 to 1.5
in) in diameter.
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Genetics
provided by Silvics of North America
Two natural hybrids are recognized: Quercus x ganderi C. B.
Wolf (Q. agrifolia x Q. kelloggii) and Quercus x moreha
Kellogg (Q. kelloggii x wislizenii). Another hybrid,
Quercus x chasei (Q. agrifolia x kelloggii) has been
described in Monterey and Santa Clara Counties, CA.
Of the hybrids, Q. moreha is by far the most widespread,
ranging throughout California and even found, though rarely, in
south-central Oregon. The tree is distinguished readily in the
winter by its sparse evergreen foliage in contrast to the
completely deciduous black oak. New leaves in spring form a dense
mass of shiny green foliage on the hybrid.
Forma cibata, a form by which black oak has been
described, is a low shrub common to steep, rocky, talus slopes at
higher elevations. Although described as a true shrub form, this
status is questionable. No criteria are known for distinguishing
between it and scrubby black oak trees.
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Growth and Yield
provided by Silvics of North America
Because fire incidence throughout its
natural range is high, nearly all black oak trees originated from
sprouts. Consequently most California black oak stands are
even-aged.
Number of sprouts per stump influences growth, form and,
eventually, yield. The number per clump decreases rapidly with
age. By the time the sprouts are pole-size, competition within
individual clumps has reduced them to two or three, or
occasionally, four stems. By age 100, only one or two stems
remain. These data are based on 180 clumps at many California
sites (21).
The form of California black oak varies greatly. On the fringe of
its range and on marginal sites, black oak trees assume a scrubby
form. In closed stands on good sites, the oaks tend to be tall
and straight with clear boles and thin crowns. When open-grown,
black oaks generally fork repeatedly, becoming multistemmed and
broad-crowned.
The general age-height relationship of California black oak, based
on 393 dominant trees in northern and central California, is
curvilinear until age 140. Thereafter, tree height remains
constant regardless of age. Selected age-heights are 20 years, 8
m (26 ft); 40 years, 13 m (43 ft); 60 years, 17 m (56 ft); 100
years, 22 m (72 ft); and 140 years, 25 m (82 ft) (21).
Position on long continuous slopes also influences growth and
form. Trees at the toe of slopes or on gently sloping benches,
where deeper soils are likely, generally grow best and have good
form. Those at midslope are shorter and more scrubby. On upper
slopes, trees grow slowly and are even shorter. Aspect also
influences growth. Of the 393 trees noted earlier, 100-year-old
trees averaged about 26 m (85 ft) in height on east aspects; 22 m
(72 ft) on north aspects; 21 m (68 ft) on west; and 17 m (56 ft)
in height on south aspects.
Average site index at base age 50 years is about 15 m (50 ft);
better than average, about 18 m (60 ft); and poor, only 11 to 12
m (35 to 40 ft) (29).
Diameter growth is often slow during the first 25 years of a black
oak's life. Competition for position in the canopy tends to favor
height growth over diameter growth. At 25 years, the average tree
is nearly 11 m (35 ft) tall and about 10 cm (4 in) in d.b.h. and
is one of three sprouts in the clump. Black oak grows fastest in
diameter from age 25 to 65 (table 2). Its growth can reach one
ring per centimeter or three rings per inch. At age 65 the tree
is about 29 cm (11.5 in) in d.b.h. and has grown almost 0.5 cm/yr
(0.2 in/yr).
Table 2- Diameter growth in natural stands,
California black oak, 1968¹
Age
D.b.h.
Average
cumulative increment per decade
yr
cm
in
cm
in
20
9
3.4
4.32
1.7
30
14
5.4
4.57
1.8
40
18
7.2
4.57
1.8
50
23
9
4.57
1.8
60
27
10.8
4.57
1.8
70
31
12.2
4.42
1.74
80
34
13.4
4.27
1.68
90
37
14.6
4.11
1.62
100
40
15.6
3.96
1.56
110
42
16.6
3.84
1.51
120
44
17.5
3.71
1.46
¹ Basis: 405 dominant
trees in 45 even-aged stands, many California sites.
Black oak in an understocked stand averages 33 to 35 cm (13 to 14
in) in d.b.h. at 65 years; in an overstocked stand, it averages
between 18 and 23 cm (7 to 9 in). After age 65, diameter growth
slowly declines. By age 90 most trees are mature.
Diameter growth of California black oak can be increased greatly
by thinning. On a good site in the northern Sierra Nevada,
diameter growth rates of trees thinned when 60 years old were
twice that of unthinned trees of similar age 8 years after
thinning (23).
Black oak may live to be almost 500 years old, but age-diameter
relationships beyond 120 years are uncertain. Trees 51 cm (20 in)
in d.b.h. can range between 70 and 175 years. Trees 41 to 63 cm
(16 to 25 in) in d.b.h. were 175 to 275 years old, and those more
than 102 cm (40 in) were 175 to 325 years old.
Black oak seldom exceeds 1.5 m (5 ft) in d.b.h. or 40 m (130 ft)
in height. The largest living black oak known measures 274 cm
(108 in) in d.b.h. and 37.8 m (124 ft) in height. This tree grows
in the Siskiyou National Forest, OR (1).
Yield data are difficult to find. The "average" stand
contains 1,086 trees per hectare (440/acre), 8.9 cm (3.5 in) and
larger in d.b.h., and would yield slightly more than 409 m³/ha
(5,845 ft³ or 65 cords/acre). In 60-year-old mixed-hardwood
stands on good sites in the northern Sierra Nevada, black oak
produces 76 m³/ha (1,085 ft³ or 12.1 cords/acre).
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Reaction to Competition
provided by Silvics of North America
The tolerance of black oak to
shade varies with age. It most accurately can be classed as
intolerant because this condition exists throughout most of its
life (9). The oak is moderately tolerant in early life, growing
well in full sunlight but persisting in dense shade (31). As a
sapling and small pole, black oak is less tolerant and often
grows tall and thin until it reaches a position in the canopy
where it can receive light. The need for top light increases as
the tree ages. In dense stands, black oak often fills a "hole"
in the canopy, sometimes leaning 15 to 20 degrees to do so. If
overtopped, the oak either dies outright or dies back
successively each year. Short epicormic branches keep the tree
alive for a time, but with continued overtopping, death is
inevitable.
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Rooting Habit
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Various investigators have described the
rooting system of black oak as having no taproot but large
spreading roots (18); as deep and long lived; with a strong
taproot; and possessing strong laterals, more or less deep,
depending on depth to ground water (3).
Observations at road cuts indicate the general rooting pattern of
this oak. Usually, from one to several vertical roots extend
through the soil and penetrate to rock. Then they become lateral
and spread out directly above the rock. At fissures, "sinker"
roots penetrate the rock itself. A number of roots are found near
the surface, probably to exploit the nutrients there.
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Seed Production and Dissemination
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In natural stands,
black oak must be 30 years or older before it produces viable
seed. The oak produces some acorns sporadically between ages 30
and 75 but seldom large quantities before 80 to 100 years. A few
trees bear at least some acorns every year. Others of similar
diameter and crown characteristics rarely produce acorns. Trees
that are good seed producers continue abundant acorn production
at least to 200 years.
Age, diameter of bole, and crown width influence acorn yield (22).
A general relationship for a medium seed crop on a good forest
site is that acorn yield increases as bole and crown diameter
increase, at least through age 200:
Age
Bole
diameter
Crown
diameter
Acorn yield
yr
cm
in
m
ft
kg
lb
30
13
5
5
15
0
0
50
23
9
6
20
2
5
80
33
13
8
26
9
20
100
43
17
10
32
27
60
150
61
24
12
41
45
100
200
81
32
16
52
64
140
Estimates of acorn production by tree or size of seed crop are
scarce. One large, 150- to 200-year-old black oak in Butte
County, CA, produced about 6,500 acorns for a crop year rated as
fair. Acorns were large and heavy, numbering 115/kg (52/lb).
Black oak acorns usually are smaller, numbering between 115 and
324/kg (52 and 147/lb). Large acorns have been observed at both
low and high elevations and small acorns at medium elevations.
The factors influencing acorn size probably are many, but little
is known about their interaction. A single, large, well-developed
tree at a low elevation in Shasta County, CA, produced sound
acorns each year as follows:
1974
700
1975
1,000
1976
65
1977
0
1978
320
1979
231
1980
125
The magnitude and periodicity of seed crops appear to be quite
variable. One study reported that abundant seed crops for entire
stands were produced at 2- to 3-year intervals (31). At 760 m
(2,500 ft) elevation in Yuba County, CA, medium to bumper seed
crops were produced in 4 of 20 years. At 850 in (2,800 ft)
elevation in south-central Shasta County, medium to bumper crops
were borne on large black oaks in 4 of 8 years. At a lower
elevation in Shasta County (170 m or 560 ft), black oaks yielded
sound acorns in 6 of 7 years. Of these, two each rated as bumper,
medium, and light.
Insects destroy many acorns, primarily in the developmental stage.
Immature acorns are attacked by both lepidopterous and
coleopterous pests. The filbertworm (Melissopus
latiferreanus) and the filbert weevil (Curculio
uniformis) are particularly destructive, in some places
infesting up to 95 percent of the acorns and destroying most of a
crop (16). Fire may lessen these losses. On the Shasta-Trinity
National Forests in California, a prescribed burn in March 1978
resulted in a bumper crop of sound black oak acorns, while trees
on unburned ground nearby bore only unsound acorns. Apparently,
destructive insects in the duff and soil were reduced greatly by
the fire (33).
Fully developed acorns begin falling in mid-August at lower
elevations, and in mid-September at higher elevations. Almost all
acorns that fall first are hollow or infested with insects. Some
are still green or greenish yellow. Sound acorns begin dropping
from late September to early November and cease by November 15 at
lower elevations. At higher elevations almost all acorns have
fallen by early December.
Acorns generally drop just before or during leaf fall. Once on the
ground, temperature can be critical to continued viability, and
fallen leaves help keep acorn temperatures below lethal
thresholds. In one instance, fully mature acorns exposed to the
hot fall sun had withered cotyledons after 9 days. Acorns from
the same trees showed full-sized cotyledons after 21 days, if
protected by leaves and branches (21). Likewise, cotyledons of
acorns exposed to freezing temperatures turned gray and flaccid,
although cotyledons of acorns beneath tree crowns and covered
with leaves remained white, crisp, and firm.
A blue-gray mold also damages fallen seed. At one location, acorns
covered for about 2 months by wet leaves showed mold at the blunt
ends that had progressed well within the seeds. For other acorns
in this same environment, cutting tests showed that cotyledons
were unaffected. American Indians, however, gathered only freshly
fallen acorns to avoid the mold (15).
Because the acorns are large and heavy, most fall directly beneath
tree crowns. Few bounce or roll far on steep slopes covered by
duff, leaves, and litter. Animals play a vital role in
dissemination of acorns because they transport some of them away
from the parent tree. The western gray squirrel and the scrub jay
are the most important disseminators, for they bury the acorns,
sometimes spreading the species to areas nearby.
Black oak acorns are eaten by at least 14 species of song and game
birds, many species and subspecies of small mammals (mostly
rodents), and mule deer (20). Black bears in the San Bernardino
Mountains of southern California utilize the California black oak
type in spring, summer, and fall (28). For many of these
creatures, acorns are the primary foodstuff in the fall. Without
acorns, populations are affected. Fawn survival rates, for
example, increase and decrease with the size of the acorn crop.
Cattle, and, to a lesser extent, sheep, also consume many black
oak acorns each year.
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Seedling Development
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California black oak reproduces from
seed, but natural regeneration tends to be scanty, poorly
distributed, and uncertain. The most likely place to find black
oak seedlings is beneath large parent trees, where they number up
to 45/m² (4/ft²).
Before the seeds begin to germinate, a period of after-ripening to
overcome dormancy is required. Overwintering beneath the litter
on the forest floor normally breaks dormancy under natural
conditions. For artificial regeneration, acorns can be stratified
by cold storage in sealed polyethylene bags thick enough to
inhibit moisture loss, but porous enough to freely emit
respiration byproducts. Storage temperature should be just above
freezing and moisture content of acorns maintained at a level
where cotyledons are turgid or slightly flaccid, but not dried
out.
Natural seedbed requirements for germination are not exacting.
Either undisturbed leaflitter or, to a lesser extent, moist,
well-aerated mineral soil are good seedbeds. Establishment of
black oak is almost nonexistent on heavy clay soils or soils
compacted by logging machinery. These conditions reduce the
ability of the radicle to penetrate the soil far enough and fast
enough to avoid searing soil surface temperatures or the seasonal
drying of upper soil layers.
Acorns germinate in the spring when the weather warms. Germination
is hypogeal and highly variable, both in magnitude and timing.
The radicle is first to emerge and grows downward for some time,
often 10 to 20 days, before the epicotyl appears above ground.
This process benefits the seedling in getting to and staying in
available soil moisture, and in minimizing transpirational
losses. Sometimes a single acorn may put forth several epicotyls,
particularly if upward progress is hampered by a stony or crusty
soil.
Under optimum conditions, 15 to 25 days elapse between sowing of
stratified acorns and the beginning of germination. In nature,
the germination period may be several weeks or even months.
Germinative capacity varies considerably and changes with degree
of insect infestation, amount of mold, and depth of acorn in
soil, among other variables. Germination has been reported as
high as 95 percent and also as scanty (21 percent). Germinative
capacities in large-scale field tests in the northern Sierra
Nevada were 31 and 38 percent (22).
Black oak seedlings often reach heights of 10 to 15 cm (4 to 6 in)
and extend their taproots downward as deep as 76 cm (30 in) in
the first growing season. Development of a deep-thrusting
vertical root is necessary for seedlings to cope with the hot dry
summers characteristic of California black oak's range. For the
first few years, therefore, both lateral root development and
shoot growth are slow. Shoot growth probably does not begin to
accelerate until root capacity is extensive enough to obtain
adequate moisture. This may take 6 or 7 years or longer. Shoot
growth of some seedlings, particularly those stressed by
competing vegetation, never accelerates and these seedlings
eventually die.
Studies evaluating artificially regenerated California black oak
on the Plumas and Angeles National Forests in California indicate
that artificial regeneration of black oak is possible, providing
that competing vegetation and pocket gophers are controlled. Fall
planting of 1-year-old seedlings, without artificial watering,
resulted in good survival and growth on the San Bernardino
National Forest, California (30).
Fertilization appears to be one technique for enlarging root
capacity and stimulating height development of seedlings. In a
test in the northern Sierra Nevada, fertilized seedlings were
more than three times taller than unfertilized seedlings (0.2 as
against 0.8 m or 0.7 as against 2.5 ft) after five growing
seasons. Fertilizer in the proportion of 1620-0 for nitrogen,
phosphorus, and potassium was applied at about 0.1 kg (0.25 lb)
per seedling early in the spring of each year (22).
Young black oak seedlings are killed mostly by drought and pocket
gophers. Grasshoppers and other insects damage young seedlings,
and freezing by late spring frosts injures them. These injuries
usually are mitigated by sprouting from the root crown.
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Soils and Topography
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Probably the most important single soil variable that limits the
presence of California black oak is internal drainage. Black oak
is not found growing "with its feet wet." The species
is adapted to soils derived from diverse parent
materials-andesite, basalt, granite, pumice, quartz diorite,
sandstone, schist, shale, and volcanic tuffs and breccias.
California black oak only rarely is found on soils originating
from serpentine. Occasionally it grows on soils derived from
ultrabasic parent material, but mostly where above-average
amounts of calcium seem to offset the deleterious effects of
magnesium.
Soil textures favoring this oak range from medium-textured loams
and clay-loams to the more coarse-textured gravelly-clay-loams
and sandy-loams. Increasing clay content in the surface soil
usually means a decreasing incidence of black oak. In fact, this
species rarely is found on soils with clay topsoils, particularly
if the clay is heavy and sticky. Black oak usually grows on thin
soils and rocky slopes, but always at the cost of abundance or
form, or both. In general, black oak grows best on medium- to
coarse-textured, deep, and well-drained soils.
About 75 soil series in California have been identified by the
California Cooperative Soil-Vegetation Survey and the National
Cooperative Soil Survey as supporting California black oak.
Important soil series in the California Coast Range include
Boomer, Cohasset, Josephine, Sites, and Sheridan. In the Sierra
Nevada, Aiken, Chawanakee, Holland, Stump Springs, Corbett, and
Tish Tang support abundant black oak. Soils in the southern
Cascade and Klamath Mountains that often are clothed with black
oak include Aiken, Cohasset, McCarthy, Sites, Tournquist,
Behemotosh, Horseshoe, and Neuns. Fourteen soil series have been
identified in Oregon, mostly on series similar to those in
California. Most of the soils in both States are found at higher
elevations and support forest vegetation rather than oak woodland
or chaparral. Soil orders are mostly Alfisols and Inceptisols,
occasionally Mollisols.
The best black oak stands in the Coast Range and Klamath Mountains
are found on deep, slightly acid loams and gravelly-clay-loams
derived from sandstone and shale. In the southern Cascade Range
and northern Sierra Nevada, black oak grows best on deep loams
and clay-loams originating from metavolcanic rocks. In the
central and southern Sierra Nevada and in the Transverse and
Peninsular Ranges, this oak grows well on deep, acid to
moderately acid sandy-loam soils derived from granitic rock.
California black oak grows within a wide elevational range-from
the level gravelly floors of low valleys to alluvial slopes,
rocky ridges, and high plateaus. Most of the terrain is rugged,
steep, and dissected by major streams and ephemeral drainages.
In Oregon, the elevational range of black oak varies from 137 in
(450 ft) near Eugene, to more than 305 m (1,000 ft) on the low
rounded hills in the Umpqua River drainage (13). The oak also is
found within this elevational range on the eastern slopes of the
Coast Range and the western slopes of the Cascades. In south
central Oregon and the Klamath Mountains, black oak grows at
higher elevations of 610 to 915 m (2,000 to 3,000 ft).
In California's Coast Range, black oak is found from about 152 in
(500 ft) along the Mattole River in Humboldt County to 1830 in
(6,000 ft) in the Yolla Bolly Mountains. Black oak reaches its
lowest elevation (60 m or 200 ft) in the Napa and Santa Rosa
Valleys. Most black oak in the central portion of the Coast Range
grows between 305 to 1525 m (1,000 to 5,000 ft), gradually
increasing in elevation but narrowing in range to 1220 to 1982 m
(4,000 to 6,500 ft) in Santa Barbara and eastern Ventura
Counties. Farther south in the Transverse Range the species is
found at elevations of 1403 to 2135 m (4,600 to 7,000 ft) (39).
In the San Jacinto Mountains, black oak reaches 2440 in (8,000
ft) and, at its southernmost extension in the Peninsular Range of
San Diego County, it grows within the 1525- to 1830-m (5,000 to
6,000-ft) elevation.
The elevational range of black oak in California's Cascade Range
is from about 183 m (600 ft) in western Shasta County to 1906 in
(6,250 ft) in southcentral Shasta County. In the Sierra Nevada,
lower elevational limits for black oak range from 458 in (1,500
ft) in the north to 1220 in (4,000 ft) in the south. Upper limits
increase north to south from about 1982 to 2380 m (6,500 to 7,800
ft).
California black oak is most abundant and attains its largest size
in the Sierra Nevada. Extensive stands of excellent development
also are found in eastern Mendocino and Humboldt Counties of the
north Coast Range. Elevation and aspect often interact to govern
abundance and development. At elevations below 305 in (1,000 ft)
in north-central California, black oak is found primarily in
sheltered draws or on north slopes. With increasing elevation,
favorable aspects increase until at 762 to 915 m (2,500 to 3,000
ft) all aspects support California black oak, providing soil is
deep enough. Above 1067 in (3,500 ft), north- and east-facing
slopes often are devoid of black oak, although other vegetation
grows well. In the southernmost mountains, black oak is found on
west-facing slopes, but only where soils are deep, temperatures
are cool, and soil moisture is adequate.
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Special Uses
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Several attributes qualify the wood of California black oak for
commercial use: attractive grain and figure for paneling and
furniture, hardness and finishing qualities for flooring, and
strength properties for pallets, industrial flooring, and other
uses (19). The forks of open-grown black oaks were put to good
use in the 1870-80's in Mendocino County.
Those of specific dimensions were used as "naturally
assembled" ship keels and ribs. Wood products currently
produced are high grade lumber and pallets, industrial timbers,
sawdust for mulching, and bulk and prepackaged firewood. The wood
is prized for fuelwood and in some areas unrestricted cutting is
eliminating oak stands.
Although not presently utilized, black oak acorns, high in edible
oils, are a potential source for thousands of tons of human food
(38).
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Vegetative Reproduction
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California black oak sprouts
profusely after trees are cut or burned. Most sprouts develop
from latent buds, which lie under the bark at, or slightly above,
the root collar. Other sprouts originate from the top of the
stump or between the top and the ground. These are called stool
sprouts and are undesirable for two reasons. They are weakly
attached to the parent stump and frequently broken off by wind
and snow, and are prone to heart rot at an early age.
The size and vigor of the parent tree determine the number of
sprouts and their height and crown spread. In general, stumps
from larger trees produce a larger number of sprouts and more
vigorous ones. Only old, moribund trees fail to produce sprouts
after cutting.
Low stumps of nearly all diameters produce many more sprouts than
high stumps. High-stumping an older, larger tree yields
undesirable stool sprouts, and often no sprouts from below
ground.
Root crown sprouts grow vigorously, especially in full sunlight.
Forty-nine stumps were studied in stands on a good site in the
northern Sierra Nevada. Sprout density, height, and crown width
were evaluated in clearcuttings and in shelterwood stands where
50 percent of the basal area had been removed (22). Number of
sprouts, crown width, and especially height growth were
consistently greater in the clearcuttings (table 1).
Table- Development of California black oak
stump sprouts in a northern Sierra Nevada forest 10 years after
cutting
Year after cutting
Sprouts per
stump
Height
Crown width
Clearcut
Shelterwood
Clearcut
Shelterwood
Clearcut
Shelterwood
no.
m
0
55+
28
--
-- --
--
--
2
55+
23
1.2
0.9
1.2
0.7
4
35
17
2.4
1.2
1.8
1
6
23
15
3.7
1.5
2.3
1.2
8
18
13
4.9
1.8
2.6
1.6
10
15
12
6
2.1
2.9
2.2
no.
ft
0
55+
28
--
--
--
--
2
55+
23
4
3
4
2
4
35
17
8
4
6
3
6
23
15
12
5
8
4
8
18
13
16
6
9
5
10
15
12
20
7
10
7
The environment typical of shelterwood cuttings apparently is more
favorable to a cynipid gall wasp (Callirhytis perdens) than
that in clearcuttings. Damage to terminal shoots by this pest is
greater under shelterwood stands, accounting in part for the
poorer height growth of sprouts. Thinning sprouts to three or
four per stump at age 4 showed no gain in height but resulted in
undesirable damage to the bole from sunscald and increased
forking of stems (22).
Young black oak sprouts grow faster in height than other
vegetation, including coniferous associates. Consequently, they
remain dominant for many years. Although black oak seedlings
extend the species into new areas, sprouts keep the oak in the
same area and are responsible for regenerating many more stands
than seedlings. Only after the living crown has moved
considerably up the bole does black oak begin its role as a nurse
tree, aiding conifers to become established and grow to equal or
dominant positions in the stand.
Propagation by layering, rooting of cuttings, or grafting has not
been reported. But the wartime shortage of cork in the 1940's
stimulated grafting of cork oak (Quercus suber) to black
oak stocks. In a greenhouse trial, 70 percent of the grafts were
successful (27).
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Distribution
provided by Silvics of North America
The north-south range of California black oak is about 1255 kin
(780 mi). In Oregon, its natural range extends from just north of
Eugene, southward through the valleys west of the Cascade Range.
The species is especially frequent along lower slopes in fairly
dry sections of the Klamath and Cascade Mountains but never grows
near the Pacific Ocean. In California, black oak is found in the
northern Coast Range from the Oregon State line to Marin County
and then intermittently in the Santa Cruz and Santa Lucia
Mountains. This oak becomes more common on the San Bernardino,
San Jacinto, and Agua Tibia Mountains, extending to just south of
Mt. Laguna, and is now recognized as being in Baja California
(5). In California's Sierra Nevada, the species grows abundantly
along the west side, from near Lassen Peak to near. Kings Canyon.
California black oak becomes intermittent southward to the
Tehachapi Mountains, where it again increases in abundance.
California black oak is generally confined to the westside, but a
few stands have been found along the eastside of the Sierra
Nevada. The species approaches the Nevada State line northeast of
Beckwourth Pass but is not reported in Nevada.
-The native range of California black oak.
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Brief Summary
provided by Silvics of North America
Fagaceae -- Beech family
Philip M. McDonald
California black oak (Quercus kelloggii.) exceeds all
other California oaks in volume, distribution, and altitudinal
range. Yet this deciduous hardwood has had little sustained
commercial use and almost no management, even though its wood
closely resembles that of its valuable, managed, and heavily used
counterpart-northern red oak (Quercus rubra)-in the
Eastern United States.
First collected in 1846 near Sonoma, CA, the species was not named
until. 1857 when John Newberry called it kelloggii in
honor of Albert Kellogg, a pioneer California botanist and
physician (17). In later botanical works, the species was called
Q. californica and black oak or Kellogg's oak.
Acorns of California black oak were carried from San Francisco to
England in 1878. Thirty-two years later, trees from these acorns
were described as being 30 feet tall and making good growth (10).
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