BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Sequoia sempervirens | Redwood 



GENERAL BOTANICAL CHARACTERISTICS : 
Redwood is a native, evergreen, long-lived (greater than 2,200 years),
monoecious tree [38,40].  Redwoods are among the world's tallest trees;
trees over 200 feet (61 m) are common, and many are over 300 feet (91 m)
[40].  The largest tree thus far was measured at 364 feet (110.3 m) in
height and 20 feet (6.1 m) in d.b.h. [44].  The root system is composed
of deep, widespreading lateral roots with no taproot [40,44].  The bark
is up to 12 inches (30 cm) thick and quite fibrous [44].  Redwood
self-prunes well in dense stands [40]; the base of the bole is strongly
buttressed [38].


RAUNKIAER LIFE FORM : 
   Phanerophyte (megaphanerophyte)


REGENERATION PROCESSES : 
Redwood reproduces both sexually and asexually.  The male and female
strobili are borne separately on different branches.  Redwood begins
producing seeds at 5 to 15 years of age.  Large seed crops occur
frequently, but viability of the seed is low [8].  A dry period during
pollination allows better pollen dispersal and improves seed viability.
The seeds are small and light, averaging 120,000 seeds per pound
(265,000 seeds/kg).  The wings are not effective for wide dispersal
[19], and seeds are dispersed by wind an average of only 200 to 400 feet
(61-122 m) from the parent tree [40].

Redwood seeds do not require pretreatment to germinate.  Germination is
epigeal [40]; the best seedbed is moist mineral soil with some shade
[17,36].  Germination rates are generally low due to low viability
rather than to dormancy.  Germination rates with a mean of 10 percent
are the norm [8].

Seedlings require adequate moisture to survive.  The roots of redwood
seedlings do not have root hairs and are thus inefficient at extracting
soil moisture.  Once established seedlings can obtain remarkable growth
rates in the first season.  Growth of 18 inches (46 cm) is not uncommon.
Older saplings (4 to 10 years old) can grow 6.5 feet (2.0 m) in one
growing season [40].

Redwoods can reproduce asexually by layering or sprouting from the root
crown or stump.  Sprouts from the root crown are generally favored for
tree crops [10]; sprouts originating from the stump are generally not as
vigorous as root-crown sprouts, and are very susceptible to wind throw
[40].  Sprouts orginate from dormant or adventitious buds at or under
the surface of the bark [17,40].  The formation of these buds occurs at
a young age, as even seedlings have been observed to sprout after
top-kill [30].  The sprouting capacity of redwood decreases with size
and age [17].  Sprouting appears to be the greatest on the downhill side
of the tree [14].  Within a short period after sprouting each sprout
will develop its own root system, with the dominant sprouts forming a
ring of trees around the parent root crown [40].  The mean crop tree
sprouting potential per root crown is five, which adds many crop trees
to a given site [10].

Sprouts can achieve heights of 7 feet (2.1 m) in a single growing
season.  Shading does not decrease sprout height, but it does reduce the
number and weight of sprouts [14].  Density of sprouts also affects
sprout vigor; the higher the density, the less vigorous the sprouts
[40].


SITE CHARACTERISTICS : 
Redwood occurs in a maritime Mediterranean climate, where the winters
are cool and rainy, and the summers are dry.  The mean precipitation is
70 inches (180 cm), with 90 percent falling between October and May.
The dry summers are mitigated by a heavy fog belt [30].  The fog reduces
the drought stress of this hydrophilic plant by reducing
evapotranspiration and adding soil moisture.  Redwoods beyond the fog
belt appear to be limited to areas of high moisture.  Currently there is
considerable debate over the link between the fog belt and redwood
distribution [11].

Preferred sites for redwood stands are alluvial fans, coastal plains,
and benches along large streams [40].  The size of a redwood can be site
dependent:  a 400-year-old specimen on a hillside had a d.b.h. of 2 feet
(0.6 m), while a 600-year-old specimen on an alluvial fan had a d.b.h.
of 12 feet (3.6 m) [4].

Elevation:  Redwood occurs at elevations ranging from sea level to 3,000
feet (0-915 m), but most stands occur from 100 to 2,320 feet (100-703 m)
[11,40].  Redwoods are sensitive to salt spray [40], and are usually
separated from the coast by intervening grassland [22]

Soils:  Redwood has a strong affinity for deep, moist soils in the
Inceptisol and Ultisol soil orders [40].  The common parent materials
are graywacke sandstones, shales, and conglomerates [30].

Associates:  In addition to those previously listed under Distribution
and Occurrence, overstory associates include Sitka spruce (Picea
sitchensis), Pacific yew (Taxus brevifolia), California torreya (Torreya
californica), Gowen cypress (Cupressus goveniana), bishop pine (Pinus
muricata), Montery pine (P. radiata), bigleaf maple (Acer macrophyllum),
Oregon white oak (Quercus garryana), and Oregon ash (Fraxinus latifolia)
[40].

Understory associates include vine maple (Acer circenatum), chittam bark
(Rhamnus purshiana), evergreen huckleberry (Vaccinium ovatum), Pacific
rhododendron (Rhododendron macrophyllum), salmon berry (Rubus
spectabilis), and evergreen ceanothus (Ceanothus velutinus) [40].


SUCCESSIONAL STATUS : 
Faculative Seral Species
Obligate Climax Species

Redwood is classified as a shade-tolerant to very shade-tolerant species
due to its high photosynthetic capacity at low light levels [40].
Redwood releases well even at quite an old age.  One specimen after
1,000 years released from 30 to 6 rings per inch (12-2.4 rings/cm) [19].

There is some debate over the classification of redwood as a climax
species.  Some consider redwood a climax species, while others consider
it a fire-dependent seral species [15,41,54,55].  Osburn and Lowell [41]
reported that if fire is excluded from Redwood National Park over the
next 2,000 years redwood will disappear, and Sitka spruce, western
hemlock (Tsuga heterphylla), and western redcedar (Thuja plicata) will
dominate.  Viers [55] on the other hand reported that redwood is a
climax species in the vicinity of Redwood National Park because it
maintains uneven age distributions with or without fire.

After disturbance redwood dominates in early seres due to its ability to
sprout [27,58].

In the floodplain environment redwood deploys what has been called "the
endurer strategy."  After flooding and stem burial, redwood will develop
a new and higher lateral root system from buried buds on the bole of the
tree.  While the repeated flooding and deposition of soil (often to
depths of 30 inches [76 cm]) kills competing vegetation, redwood endures
[3,40,58].


SEASONAL DEVELOPMENT : 
Redwood female strobili become receptive and pollen is shed from late
November to early March.  Female strobili start ripening in September of
the first year.  Mature female strobili can be identified when their
color changes from green to greenish yellow.  Seed dispersal begins in
late October, with most of the seeds being dispersed from November to
February [8].

Related categories for Species: Sequoia sempervirens | Redwood