Giant Sequoia
Sequoiadendron giganteum (Lindl.) Bucholz
Compiled by Jeneen Martin
Introduction
Other common names of this species include sequoia, mammoth-tree,
bigtree, giant redwood, and Sierra redwood. It has appeared in literature
under at least nine different scientific names including Sequoia giganteum
and Sequoia wellingtonia, however, the currently accepted classification
is Sequoiadendron giganteum.
Being in the Redwood family (Taxodiaceae), giant sequoia
is related to cypress (Taxodium spp.), dawn redwood (Metasequoia
glyptostroboides), and coast redwood (Sequoia sempervirens).
It most closely resembles coast redwood and was classified under the same
genus for some time. It was once even thought to be the same tree. Scientists
now agree that it should be in its own genus.
Giant sequoia was first discovered in the 1840s. Since
then it has been the focus of public fascination. A tree typically reaches
a diameter of 305 to 610 cm (120 to 240 in) above the butt swell and an
average height of around 76 m (250 ft). The General Grant tree in Kings
Canyon National Park has the greatest mean diameter at breast height (d.b.h.)
at 881 cm (347 in). This mean includes the abnormal buttress which, when
compensated for, puts the estimate at a more realistic maximum of 823 cm
(324 in) (Burns 1990). The reddish-brown outer bark is spongy and can be
12 to 24 or more inches thick with one report of the General Sherman tree
in Sequoia National Park having bark four feet thick. The General Sherman
tree also holds the record for the most volume. One estimate says it weighs
6200 tons and has 600,000 board feet of lumber (Schoonover 1951). Another
says this tree has a bole volume of 1486 cubic m (52,500 cubic ft) (Burns
1990).
Habitat
Native Range
"The natural range of giant sequoia (fig. 1) is
restricted to about 75 groves scattered over a 420-km (260-mi) belt, nowhere
more than about 24 km (15 mi) wide, extending along the west slope of the
Sierra Nevada in central California. The northern two-thirds of the range,
from the American River in Placer County southward to the Kings River,
takes in only eight widely disjunct groves. The remaining groves, including
all the large ones, are concentrated between the Kings River and the Deer
Creek Grove in southern Tulare County. Varying in size from less than 1
to 1619 ha (1 to 4000 acres), the groves occupy a total area of 14,410
ha (35,607 acres)…
"Elevations of the groves generally range from 1400 to 2000 m (4,950 to 6,560 ft) in the north, and 1700 to 2150 m (5,580 to 7,050 ft) in the south. The lowest natural occurrence of the species is 830 m (2,720 ft) and the highest is 2700 m (8,860 ft). The eight northern groves are all on slopes of a generally southern aspect. Between the Kings River and the southern boundary of Sequoia National Park, groves appear on north and south slopes with about equal frequency. Farther south, aspects are predominantly northerly."
-from Silvics of North America, Burns 1990
Climate
Giant sequoia is found naturally in a humid climate with
dry summers. Mean annual precipitation varies greatly year-to-year and
can be anywhere from 900 to 1400 mm (35 to 55 in). Between June 1 and September
30, less than 30 mm (1.2 in) usually falls. Most precipitation falls in
the winter in the form of snow (Burns 1990). The grove boundaries are apparently
limited by the availability of ground water in the summer (Rundel 1972).
Temperature extremes range from about -24 to 40 degrees
C (-12 to 104 degrees F). The average daily maximum July temperature is
usually 24 to 29 degrees C (75 to 84 degrees F). The mean daily minimum
in January ranges from 1 to -6 degrees C (34 to 21 degrees F). At the upper
elevational limits of its range and in areas that have severe winters where
it has been introduced, low temperatures seem to be a limiting factor (Burns
1990).
Soils
Most soils on which giant sequoias are found are granitic-based
residual and alluvial soils. Schistose, dioritic, and andestic rocks are
other common parent materials. Dome, Shaver, Holland, and Chaix are typical
soil series. The trees grow best in deep, well-drained sandy loams with
an average pH of 6.5, however, many soils will support the trees as long
as adequate soil moisture is available. Seedlings do not survive in wet
soils but must have enough soil moisture available to survive the dry summers
(Burns 1990).
Associated Forest Cover
Giant sequoia does not grow in naturally pure stands.
California white fir (Abies concolor var. lowiana) is typically
the dominant of giant sequoia stands. Other typical tree associates include
sugar pine (Pinus lambertiana), incense-cedar (Libocedrus decurrens),
California red fir (Abies magnifica), ponderosa pine (Pinus ponderosa),
and California black oak (Quercus kelloggii) (Burns 1990).
Reproduction and Growth
Flowering and Fruiting
Male and female flowers grow separately on the branches
of the same tree. Flowering and pollination usually occur in mid-April
to mid-May. Conelets are about half size in July and reach full size by
August when fertilization takes place. By late August of the year after
fertilization, the cones are morphologically mature.
Giant sequoias have serotinous cones. Cones may
remain attached and alive for 20 years or more producing annual peduncle
rings. Larger seed crops and more viable seed are produced in years
with ample soil moisture than in dry years. Two-thirds of the cone crop
is produced in the upper third of the crown (Young 1992). A mature tree
may have 10,000 to 30,000 cones at any one time, one third consisting of
dried, mostly seedless cones and the remainder green, closed cones (Burns
1990).
Seed Production and Dissemination
The seeds are well adapted to wind dispersal. They
are very light (there is an average of 200,000/kg or 91,000/lb) and they
have wings. Winds in late summer and winter in the Sierra Nevada can disperse
seeds up to 0.4 km (0.25 mi) from the crown of a mature tree (Burns 1990).
An average of 200 seeds are produced per cone (Young 1992).
Seeds are released from the cones in three ways. The cone
beetle (Phymatodes nitidus) larvae mine in the fleshy part of
the cone severing vascular connections. The cone then dries and the seeds
fall. Another animal, the chickaree or Douglas squirrel (Tamiasciurus
douglasi), eats the fleshy part of the cones and dislodge seed as they
eat. Damage and loss of the seeds by animals is negligible because of the
small size and low nutrient content. The most important cause of cone drying
is fire. Hot air created by fire is convected high into the canopy allowing
cones to dry and large quantities of seed to fall (Burns 1990).
Yield (MAI) and Rotation Length
Growth and yield information for giant sequoia is limited
partly because of its restricted natural range and relative unimportance
as a commercial species. Plantations have been established within and outside
of its natural range and the interest in giant sequoia as a timber species
is on the rise (Weatherspoon 1985).
Giant sequoia is an intolerant species. Studies have shown
that it competes well and does as well as or better than other species
in growth on a given site (Weatherspoon 1985). On one study, an 86 year
old stand of sequoia had a mean annual increment (MAI) of around 9 cubic
m/ha (126 cubic ft/acre). A look at an old-growth population showed an
average d.b.h. of 48 cm (18.9 in) at 100 years, 132 cm (52.0 in) in 400
years, and 219 cm (86/1 in) at 800 years. Studies in Yosemite National
Park Mariposa Grove show that in normal undisturbed old-growth, radial
growth is fairly constant at 0.04 inch per year. The General Sherman tree
grows at this rate and has been estimated by different methods to have
an average growth increment of 1.13 cubic m (40 cubic ft) per year and
1.44 cubic m (51 cubic ft) per year (Burns 1990).
Genetics
Giant sequoia has little genetic variation. Isolation
of the groves has existed long enough to create population differences.
Provenance tests in West Germany showed differences in cold hardiness and
early growth (Burns 1990). All studies have shown that the differences
are significant but to a much smaller degree than associated or related
conifers (Weatherspoon 1985).
There are fourteen known horticultural forms and only
two are common. There are no races of giant sequoia. There have been reports
of hybridization of giant sequoia with coast redwood in the Soviet Union
but none have been confirmed in western literature (Burns 1990).
Nursery Management
Propagation Methods
Giant sequoia may be propagated from seed or cuttings.
Cuttings from trees less than 30 years old are very successful whereas
limited success has been achieved with cuttings from older trees (Burns
1990). Seeds extracted from fresh, mature cones should be soaked overnight
in aerated distilled water and then cold treated for 60 days. This does
not increase germination but causes the seeds to germinate more as a group
(Fins 1981).
Pests
The main pest in nurseries for giant sequoia is grey mold
(Botrytis cinerea). This mold affects foliage and roots causing
death of tissue distally. It also causes a canker to form of the main stem
which could cause death. There is no cure for the mold but proper lighting
and air circulation will help prevent the mold from forming. Application
of benomyl, thiabendazole, chlorothalonil, or Difolatan will help control
its spread (Smith 1973).
Foliar blight and root rot caused by Phytophora citrophthora
is another cause of seedling death. This pest enters through the stoma
and affects foliage and roots. The infection is encouraged by overhead
irrigation (Sandlin 1993). Charcoal root disease caused by Macrophomina
phaseoli is another concern in nurseries.
Seedling Costs
Prices from the 1994 - 1995 Lawyer Nursery, Inc., Montana
catalog.
2 - 0 bare root seedlings SIZE #/BUNDLE COST($)/SEEDLING
6-9" 50 0.44
9-12" 50 0.54
12-15" 50 0.64
15-18" 25 0.80
Establishment Practices
Site Preparation
Giant sequoia seeds need bare soil to successfully germinate
and establish. The best way to bare the soil is with a prescribed burn.
A study showed that first-year giant sequoia seedlings established on treated
(bulldozed, burned, or both) areas were 30 to 150 times more numerous than
on undisturbed sites (Burns 1990).
Planting
Giant sequoia seedlings are planted by hand either from
bare root or containerized stock. Sprouts will grow from stumps of trees
around 20 years old or less. Older trees do not usually sprout form stumps
or roots (unlike the coast redwood) (Burns 1990).
Insects
Most giant sequoia seedling mortality is attributed to
dessication, not pests. There are a few known insects which graze on seedlings
especially those planted on sites burned only one year before planting.
These include the camel cricket and two geometrids. Cutworms have also
been reported to kill seedlings (Weatherspoon 1985).
There are several additional diseases that have been found
on giant sequoia but their importance is not known. A listing of some of
these pathogens can be found in the Index of Plant Diseases in the United
States (Agricultural Handbook #165).
Wood Properties and Uses
Logging companies who tried to harvest old-growth giant
sequoia not only had a difficult time handling the massive trees, but also
rarely made ends meet because up to 80% of the tree's volume was lost upon
impact. The wood is so brittle that it would shatter when it hit the ground.
Young-growth giant sequoia has as good, if not better, wood qualities
of young-growth coast redwood and other lumber species grown in the same
area (Weatherspoon 1985).
Specific Gravity (Weatherspoon 1985)
Giant sequoia Young-growth 0.35
Old-growth 0.30
MOR and MOE (Wood Handbook 1987)
MOR MOE
(Psi) (million psi)
Coast redwood Old-growth Green 7,500 1.18
Dry 10,000 1.34
Young-growth Green 5,900 0.96
Dry 7,900 1.10
Common Uses
Giant sequoia has many of the same uses as coast redwood.
It is used for shingles and anywhere a rot resistant wood of moderate strength
is needed, such as fence posts. The tree is planted extensively as an ornamental
in the U.S. and some other countries. It is used somewhat for Christmas
trees (Burns 1990).
References
Burns, R. M. 1990. Silvics of North America. Vol. 1. USDA
Forest Sevice. Washington DC: GPO.
Rundel, P. W. 1972. Habitat restriction in giant sequoia: the environmental control of grove boundaries. American Midland Naturalist, 87(1): 81-99.
Sandlin, C. M. and D. M. Ferrin. 1993. Foliar blight and root rot of container-grown giant redwood caused by Phytophthora citrophthora. Plant Disease 77: 591-594.
Schoonover, S. E. 1951. American Woods. Walting and Co.: Santa Monica, Calif.
Smith, R. S., Jr., A. H. McCain, and M. D. Srago. 1973. Control of Botrytis storage rot of giant sequoia seedlings. Plant Disease Reporter 57: 67-69.
USDA. 1987. Forest Service. Agricultural Handbook #72.
Weatherspoon, C. P., Y. R. Iwamoto, and D. D. Piirto. 1985. Workshop on management of giant sequoia (1985: Reedley , Calif.). USDA Forest Service: Berkley, Calif. 47p.
Young, J. A. and C. G. Young. 1992. Seeds of woody plants
in North America. Dioscordies Press: Portland, Oregon,
407 p.
Web Links
CSU Fullerton, Biological Science
http://www.nps.gov/seki/bigtrees.htm
http://weber.u.washington.edu/~uffda/python/songs/lumberjack.html
http://132.230.36.11/schule/earthquake/redwoods.html
http://www.nps.gov/redw/sequoias.htm
http://www.r5pswfs.gov/gsequoia/sequbrch.html
http://www.r5pswfs.gov/robriefings/briefingssept96/9609prescribedfire.html