BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Lithocarpus densiflora | Tanoak 



GENERAL BOTANICAL CHARACTERISTICS : 
Tanoak is a slow-growing, shade-tolerant, native, sclerophyllous,
evergreen hardwood tree [31,33,42,53].  Tanoak ranges from 65 to 150
feet (20-45 m) in height [33], but mature trees usually do not exceed 82
feet (25 m) in height and 3.2 feet (1 m) in diameter.  Tanoak may live
to be 300 to 400 years old; average age on better sites in the Pacific
Northwest is approximately 180 years [42].  The reddish-tinged, pale
brown bark becomes thick and fissured as trees mature [22,34,37].  Large,
leathery, blunt-toothed leaves are retained for approximately 4 years
[49].  Male and female flowers are borne in the leaf axils of new
shoots.  The fruit is a large acorn approximately 1 to 2 inches (2.5-5
cm) long and 0.6 to 0.7 inch (1.5-1.8 cm) in diameter and usually borne
singly or in clusters of two to three [42].  At the soil surface, tanoak
possesses a woody, underground regenerative organ known as a lignotuber
[16,31,50].  The extensive root system consists of a deep taproot which
is associated with nitrogen-fixing bacteria [33].
       
Tanoak growth forms vary according to stand structure, stand
composition, and site quality.  When occurring as part of the conifer
canopy, tanoak develops a long, clear central bole and an excurrent
branching habit similar to that of conifers.  Where development beneath
conifers is delayed, understory tanoak may be multistemmed and/or
shrublike [42].  In more open hardwood stands, however, the main trunk
is usually short and thick and divides into several large, horizontal
limbs, forming a broad, rounded crown.  Shrub tanoak (var. echinoides)
is a stunted form typically associated with chaparral vegetation.
Heights range from 1 to 10 feet (up to 3 m); the branches are rigid with
small, thin leaves [34,42].


RAUNKIAER LIFE FORM : 
   var. densiflora
   Undisturbed State:  Phanerophyte (mesophanerophyte)
   Undisturbed State:  Cryptophyte (geophyte)
   Burned or Clipped State:  Cryptophyte (geophyte)
   var. echinoides
   Undisturbed State:  Phanerophyte (microphanerophyte)
   Undisturbed State:  Phanerophyte (nanophanerophyte)
   Burned or Clipped State:  Cryptophyte (geophyte)


REGENERATION PROCESSES : 
Tanoak regenerates sexually and vegetatively.  Seedling regeneration is
characterized by very slow recruitment rates.  Once established,
however, tanoak individuals are extremely persistent beneath conifer and
hardwood overstories, maintaining themselves through sporatic stem
mortality and sprout regeneration.  After being released from heavy
shade, suppressed tanoak "seedling banks" develop rapidly, often
dominating early successional stages.

Reproduction from seed:  Tanoak sprout clumps can produce acorns as
early as 5 years of age; consistent and abundant production of viable
acorns usually occurs when trees are 30 to 40 years old [31,42].  Acorn
production is frequent and prolific with large seed crops produced
almost every other year [30,42].  Tanoak produced bumper seed crops four
times over a 24-year-period on sites in California [27].  Complete seed
failures are rare and typically coincide with drought or frost [42].
Acorns are dispersed in the fall of their second year and are up to 79
percent sound.  Insect-infested acorns usually drop first.  Most fall
directly beneath the parent plant although long-distance disperal may
occur via mammal and bird vectors [30].  Despite abundant acorn
production, tanoak reproduces extremely slowly via seed.  Unless acorns
are rapidly covered by litter and leaves, the majority of acorns are
consumed by rodents, birds, or deer.

Germination rates vary from 19 to 80 percent; no dormancy-breaking
treatment is necessary [42].  On fall planted sites in southwestern
Oregon, tanoak germination and radical elongation began in late January
and early February; however, shoot emergence was delayed until mid July
[53].  Germination occurs much more rapidly in acorns positioned
point-up; alternate positions extend the germination period [27,31].  Some
germination also may occur during mild fall weather [42].  Whereas
optimal seedbeds consist of loose, moist mineral soil, tanoak also
establishes abundantly in deep litter [30,42,54].  Litter helps keep
acorns moist and provides insulation from temperature extremes.  A deep
covering of litter, however, tends to hinder germination [42].  Acorn
viability is usually short-lived [31].

Successful seedling establishment occurs most frequently in the duff and
litter beneath existing conifer and hardwood stands [50,54].  A firm,
woody hypocotyl greatly lessens first year mortality caused by
litterfall [50].  Seedling growth is best in partial shade.  Most early
growth is devoted to the formation of a lengthy taproot and shoot growth
is extremely slow by comparison.  Four-year-old seedlings typically
average less than 6 inches (15 cm) in height [30].  Seedling
establishment is quite rare on disturbed sites [31].  Inadequate moisture
and an unfavorable environment generally contribute to poor seedling
survival on shrub-free clearcuts in northern California [27].  Initial
establishment success also appears to be related to differences in seed
predation on clearcuts versus forested habitats.  Seed predation is
likely to be considerably higher on clearcut areas where small mammal
populations, particularly deer mice, are quite high [50].
Interestingly, survival and growth of emerged tanoak seedlings was
approximately equal over 4 years on clearcut and forested sites in
Oregon.

Vegetative regeneration:  Since regeneration occurs in dry, low light
environments, tanoak maintains itself through periodic diebacks.
Frequent stem mortality and resprouting apparently enhance its
persistence on a site by reducing respiratory losses from inefficient,
senescing stems [49].  If left undisturbed, tanoak seedlings consist of
single stem until the 5 to 12 years of age.  At this time the stem dies
back to the ground, a rudimentary underground burl develops at the stem
base, and from one to five resprouts are produced from perennating buds
located on the burl [31].  Burls enhance the sprouting potential of
tanoak by functioning as a source of numerous dormant buds [14,31] and
perhaps as storage for carbohydrates, nutrients, and water [16,31].  Burl
size increases with age.  Tanoak burls are usually well-developed by age
60, sometimes reaching up to 4.8 inches (12 cm) in diameter.  Burl
growth is related to site quality and is predictable on a given site
[31].  Bud numbers increase as burls enlarge; not only do preformed buds
divide, but adventitious buds also arise from callus tissues formed at
the base of dead stems.  Therefore, sprouting potential increases as
tanoak grows.  Some large tanoak stumps may have as many as 1,400 basal
buds (burl and stump surfaces) [42].

Young tanoak typically develop a multistemmed, shrublike growth form
beneath conifer and hardwood overstories.  Stem mortality and
resprouting commonly occur at least 3 to 5 times before the age of 60
[49].  Sprouts which develop from these diebacks, in addition to those
after the initial dieback, are generally referred to as "seedling
sprouts".  In young conifer-tanoak stands with high initial conifer
stocking, nearly half of the tanoak regeneration may loose all stems as
a result of conifer crown closure [49].  Stem mortality is most likely
in stems less than 6 inches (15 cm) in d.b.h.  From 60 to 90 percent of
the tanoak sprouts less than 6 inches (15 cm) in d.b.h. may die in
younger stands.  As a component of more mature conifer stands, however,
only 10 percent of the sprouts in this size class die.

Basal sprouting is a common characteristic of large, undisturbed tanoak
growing in older conifer stands [49].  Sprouts are frequently prostrate
and may occassionally layer.  Most large tanoak have more than one burl.
One of the largest tanoak within a mature conifer stand in Oregon had
five stems ranging from 25 to 63 feet (7.6-19.3 m) in height and from 39
to 94 years in age.  Twenty-two resprouts arose from the base.
Belowground, a rootlike structure connected four burls which ranged from
15.2 to 33.2 inches (38-83 cm) in diameter.

Tanoak also resprouts following fire or cutting [31,42].  Burning
younger, thin-barked tanoak generally kills aboveground portions of the
stem.  As a result, basal sprouting is the primary means of postburn
regeneration.  Following cutting, however, tanoak may also develop
"stool sprouts" near the top of higher stumps; stool sprouts originate
from either the vertical surface of the stump or from the cambium on the
horizontal cut [30,31].  Resprouting abilities develop exceptionally early
in tanoak.  Following a frost which killed the aerial shoots of
1-week-old seedlings, 75 percent resprouted; most had two to four
resprouts per plant [31].


SITE CHARACTERISTICS : 
Although adapted to a variety of sites [31], tanoak occurs most
abundantly along the lower slopes of coastal mountain ranges on sites
characterized by high levels of moisture and mild temperatures [1,34].
In southern Oregon and northern California where tanoak reaches its
maximum development, trees grow on east and north slopes at elevations
between 500 and 3,000 feet (152 and 915 m).  Toward the southern portion
of its distribution, tanoak occupies westerly aspects between 2,400 and
4,700 feet (732 and 1,434 m) [31].  Tanoak also competes well inland,
becoming locally abundant along the west slope of the Sierra at
elevations between 1,900 and 5,000 feet (580 and 1,525 m).  In warmer
environments of the central Sierra, tanoak typically occupies sites
having more favorable moisture regimes such as foothill riparian areas,
sheltered coves and ravines [42].  A ubiquitous species througout its
range, tanoak is commonly distributed as scattered individuals and in
clumps or groves within undisturbed conifer forests [31].  Extensive
stands often develop following logging or fire [31,42,36].

Climate:  Annual precipitation ranges between 40 and 100 inches (102 and
254 cm), 70 percent of which falls between November and February [42].
Monthly precipitation during the dry summer and early fall is often less
than 1 inch (2.5 cm).  Summer moisture is vital for tanoak survival [1].
Optimal sites are often associated with atmospheric moisture,
experiencing high humidities, summer fog, and low-lying clouds; such
conditions help to ameliorate temperature extremes.  Generally, tanoak
is restricted by moisture limitations on shallow soils, and by low
temperatures at higher elevations [1].

Soils:  Tanoak is most often associated with deep, fertile, well-drained
loamy, sandy or gravelly soils [31,42].  Its presence can be used as an
indicator of productive sites in southwestern Oregon [1].  Trees can
also grow well on stony or shallow soil sites located on north slopes.

Associates:  As a component of hardwood, mixed hardwood and conifer
forests, tanoak is associated with a wide variety of species.
Douglas-fir and Pacific madrone are by far the most common tree
associates.  Other common associates include [1,42]:  

conifers - redwood, white fir (Abies concolor), sugar pine (Pinus lambertiana),
Pacific yew (Taxus brevifolia), and ponderosa pine (Pinus ponderosa).

hardwoods - canyon live oak (Quercus chrysolepis), California black oak,
interior live oak, California laurel (Umbellularia californica), and
giant chinquapin (Castanopsis chrysophylla).

shrubs - California hazel (Corylus rostrata var. californica), poison
oak, salal, pinemat manzanita (Arctostaphylos nevadensis); and Cascade
holly grape.

forbs - Torrey peavine (Lathyrus torreyi), and mottleleaf ginger (Asarum
hartwegi).

ferns - sword fern (Polystichum munitum) and bracken (Pteridium
aquilinum).

grasses - bromes (Bromus spp.) and fescues (Festuca spp.).

Shrub tanoak (var. echinoides): The shrubby form of tanoak is commonly
associated with chaparral communities.  Plants occupy mountain tops and
exposed ridges at elevations between 2,000 and 8,000 feet (610 and 2,440
m).  Soils are dry and rocky [34,42,36].  Shrub tanoak is often the
dominant form on serpentine soils [42].


SUCCESSIONAL STATUS : 
Tanoak is a long-lived species capable of establishing beneath a full
canopy of hardwoods or conifers; establishment occurs under both
overstory and understory trees [42,54].  Substantial seedling
establishment is often delayed 25 to 30 years in conifer stands [49].
Once established, tanoak is extremely persistent on a site despite low
light levels.  Whereas tanoak may attain tree size where gaps develop in
the overstory, suppressed tanoak individuals are shrublike, maintaining
themselves through periodic diebacks [31,42].  Prolonged periods without
disturbance permits the slow, steady, annual accumulation of seedlings.

Tanoak is able to survive disturbances such as fire, logging, blow-down,
insect devastation, or mass soil movement [10,42,53].  Plants sprout
vigorously once released from dense shade and are extremely competitive
[1,30].  Even-aged sprout stands develop rapidly from banks of suppressed
individuals and may dominate early seral situations.

Although tanoak may form almost pure, climax stands within evergreen,
hardwood forests [1,10,42], it more often occurs as part of the climax
subcanopy on sites within mixed evergreen, redwood, Douglas-fir, and
mixed-conifer forests [1,10,47,54,55].  If left undisturbed, tanoak
eventually forms uneven-aged stands [31,54].  Fire exclusion has favored
the establishment of tanoak within redwood and mixed evergreen forests.
On many sites, fire-maintained Douglas-fir are now being replaced by
tanoak and other more shade-tolerant species [1,54].  With continued
fire exclusion, tanoak is the potential climax dominant throughout much
of the mixed evergreen zone [1,10].


SEASONAL DEVELOPMENT : 
Tanoak typically flowers from June through August, although blooming may
also occur during the spring or fall [34,42].  The foliage is often
concealed by the profuse, yellowish blooms.  Apparently a long dry
period is essential for setting of acorns.  Acorns ripen in the fall of
their second season and are generally dropped between September 20 and
November 15 [42].

Limited observations indicate the following elevational pattern of
vegetative bud burst in the Trinity River Valley near Salyer, California
[42]:

Elevation                                 Date
< 2,000 feet (610 m)                      mid-April
2,000 to 3,500 feet (610-1,067 m)         mid-May
3,500 to 4,400 feet (1,067-1,341 m)       late May
4,500 feet (1,372 m)                      early June

Related categories for Species: Lithocarpus densiflora | Tanoak