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Giant Sequoia

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Giant Sequoia
Conservation status: Vulnerable

General Grant tree
in Kings Canyon National Park
Scientific classification
Kingdom:Plantae
Division:Pinophyta
Class:Pinopsida
Order:Pinales
Family:Cupressaceae
Genus:Sequoiadendron
Species:S. giganteum

Template:Taxobox section binomial botany

The Giant Sequoia or Sierra Redwood (Sequoiadendron giganteum) is one of a number of species of coniferous trees known as redwoods, classified in the family Cupressaceae in the subfamily Sequoioideae together with Coast Redwood and Dawn Redwood.

Giant Sequoia is the world's largest tree in terms of total volume. They grow to an average height of 70-85 m (230-280 ft) and 5-7 m (16-23 ft) in diameter. Record trees have been reported to be 93.6 m (307 ft) in height and 8.85 m (29 ft) in diameter. The oldest known Giant Sequoia based on ring count is 3,200 years old. Sequoia bark is fibrous, furrowed, and may be 60 cm (2 ft) thick at the base of the columnar trunk. It provides significant fire protection for the trees. The leaves are evergreen, awl-shaped, 3-6 mm long, and arranged spirally on the shoots. The seed cones are 4-7 cm long and mature in 18-20 months, though they typically remain green and closed for up to 20 years; each cone has 30-50 spirally arranged scales, with several seeds on each scale giving an average of 230 seeds per cone. The seed is dark brown, 4-5 mm long and 1 mm broad, with a 1 mm wide yellow-brown wing along each side. Some seed is shed when the cone scales shrink during hot weather in late summer, but most seeds are liberated when the cone dries out from fire heat and/or insect damage (see Ecology, below).

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Seqgigcones.jpg
Giant Sequoia cones. See also: Cone compared to Sugar Pine cone, Sugar Pine

Giant Sequoia regenerates primarily by seed, although occasionally it may reproduce naturally by vegetative methods; trees up to about 20 years old may produce stump sprouts subsequent to injury. Giant Sequoia of all ages may sprout from the bole when old branches are lost to fire or breakage, but (unlike Coast Redwood) mature trees do not sprout from cut stumps. Young trees start to bear cones at the age of 20 years.

At any given time, a large tree may be expected to have approximately 11,000 cones. The upper part of the crown of any mature Giant Sequoia invariably produces a greater abundance of cones than its lower portions. A mature Giant Sequoia has been estimated to disperse from 300,000-400,000 seeds per year. The winged seeds may be carried up to 180m (600 ft) from the parent tree.

Lower branches die fairly readily from shading, but trees less than 100 years old retain most of their dead branches. Trunks of mature trees in groves are generally free of branches to a height of 20-50 m, but solitary trees will retain low branches.

Contents

Distribution

Giant Sequoia is usually found in a humid climate characterized by dry summers and snowy winters. Most Giant Sequoia groves are on granitic-based residual and alluvial soils. The elevation of the Giant Sequoia groves generally ranges from 1,400-2,000m (4,600-6,600 ft) in the north, and 1,700-2,150 m (5,600-7,000 ft) to the south. Giant Sequoia generally appears on southern slopes in its northern distribution and on more northerly slopes in the south.

Giant Sequoia in the Mariposa Grove,
Enlarge
Giant Sequoia in the Mariposa Grove, Yosemite National Park

The natural distribution of Giant Sequoia is restricted to along a limited area of the western Sierra Nevada, California. It occurs in scattered groves, with a total of 65-76 groves (see list of sequoia groves for a full inventory), comprising a total area of only 14,416 ha (144.16 km² / 35,607 acres). Nowhere does it grow in pure stands, although in a few small areas stands do approach a pure condition. The northern two-thirds of its range, from the American River in Placer County southward to the Kings River, has only eight disjunct groves. The remaining southern groves are concentrated between the Kings River and the Deer Creek Grove in southern Tulare County. Groves range in size from 1,240ha (3,100 acres) with 20,000 mature trees, to small groves with only six living trees. Many are protected in Sequoia and Kings Canyon National Parks and Giant Sequoia National Monument.

High levels of reproduction are not necessary to maintain the present population levels. Few groves, however, have sufficient young trees to maintain the present density of mature Giant Sequoias for the future. The majority of Giant Sequoias are currently undergoing a gradual decline in density since the European settlement days.

Ecology

The Giant Sequoias are having difficulty reproducing in their original habitat (and very rarely reproduce in cultivation) due to the seeds only being able to grow successfully in mineral soils in full sunlight, free from competing vegetation. Although the seeds can germinate in moist needle humus in the spring, these seedlings will die as the duff dries in the summer. They therefore require periodic wildfire to clear competing vegetation and soil humus before successful regeneration can occur. Without fire, shade-loving species will crowd out young sequoia seedlings, and sequoia seeds will not germinate. When full grown, these trees typically require large amounts of water and are therefore often concentrated near streams.

Fires also bring hot air high into the canopy via convection, which in turn dries and opens the cones. The subsequent release of large quantities of seeds coincides with the optimal post-fire seedbed conditions. Loose ground ash may also act as a cover to protect the fallen seeds from ultraviolet radiation damage.

Due to fire suppression efforts and livestock grazing during the early and mid 20th century, low-intensity fires no longer occurred naturally in many groves, and still do not occur in some groves today. The suppression of fires also led to ground fuel build-up and the dense growth of fire-sensitive White Fir. This increased the risk of more intense fires that can use the firs as ladders to threaten mature Giant Sequoia crowns. Natural fires may also be important in keeping carpenter ants in check.

In 1970 the National Park Service began controlled burns of its groves to correct these problems. Current policies also allow natural fires to burn. One of these untamed burns severely damaged the second-largest tree in the world, the Washington tree, in September 2003, 45 days after the fire started. This damage made it unable to withstand the snowstorm of January 2005, leading to the collapse of over half the trunk.

In addition to fire, there are also two animal agents for Giant Sequoia seed release. The more significant of the two is a longhorn beetle (Phymatodes nitidus) that lays eggs on the cones, into which the larvae then bore holes. This cuts the vascular water supply to the cone scales, allowing the cones to dry and open for the seeds to fall. Cones damaged by the beetles during the summer will slowly open over the next several months. Some research indicates that many cones, particularly higher in the crowns, may need to be partially dried by beetle damage before fire can fully open them. The other agent is the Douglas Squirrel (Tamiasciurus douglasi) that gnaws open the cones to eat the seeds. The squirrels are active year round, and some seeds are dislodged and dropped as the cone is eaten.

Discovery and naming

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A Giant Sequoia with a car for scale

The Giant Sequoia was well known to Native American tribes living in its area. Native American names for the species include Wawona, Toos-pung-ish and Hea-mi-withic, the latter two in the language of the Tule River Tribe.

The first reference to the Giant Sequoia by Europeans is in 1833, in the diary of the explorer J. K. Leonard; the reference does not mention any locality, but his route would have taken him through the Calaveras Grove. This discovery was not publicised. The next European to see the species was John M. Wooster, who carved his initials in the bark of the 'Hercules' tree in the Calaveras Grove in 1850; again, this received no publicity. Much more publicity was given to the "discovery" by Augustus T. Dowd of the Calaveras Grove in 1852, and this is commonly, if incorrectly, cited as the species' discovery. The tree found by Dowd, christened the 'Discovery Tree', was felled in 1853.

The first scientific naming of the species was by John Lindley in 1853, who named it Wellingtonia gigantea, without realising this was an invalid name under the botanical code as the name Wellingtonia had already been used earlier for another unrelated plant (Wellingtonia arnottiana in the family Sabiaceae). The following year, Joseph Decaisne transferred it to the same genus as the Coast Redwood, naming it Sequoia gigantea, but again this name was invalid, having been applied earlier (in 1847, by Endlicher) to the Coast Redwood. The name Washingtonia californica was also applied to it by Winslow in 1854, though this too is invalid, belonging to the palm genus Washingtonia.

In 1907 it was placed by Carl Ernst Otto Kuntze in the otherwise fossil genus Steinhauera, but doubt as to whether the Giant Sequoia is related to the fossil originally so named makes this name invalid.

The nomenclatural oversights were finally corrected in 1939 by J. Buchholz, who also pointed out that the Giant Sequoia is distinct from the Coast Redwood at the genus level and coined the name Sequoiadendron giganteum for it.

Other English vernacular names include Sierra Redwood, Giant Redwood, or simply Big Tree.

List of the ten largest Giant Sequoias

As of February 2005, the ten largest trees by volume are:

Tree Name Location Height Circumference Volume
    (m) (ft) (m) (feet) (m³) (ft³)
General Sherman Giant Forest 83.79 274.9 31.27 102.6 1486.9 52,508
General Grant Grant Grove 81.72 268.1 32.77 107.5 1319.8 46,608
President Giant Forest 73.43 240.9 28.35 93.0 1278.4 45,148
Lincoln Giant Forest 77.97 255.8 29.96 98.3 1259.3 44,471
Stagg Alder Creek 74.07 243.0 33.22 109.0 1205.0 42,557
Boole Converse Basin 81.93 268.8 34.44 113.0 1202.7 42,472
Genesis Mountain Home 77.11 253.0 26.00 85.3 1186.4 41,897
Franklin Giant Forest 68.21 223.8 28.90 94.8 1168.9 41,280
King Arthur Garfield 82.39 270.3 31.76 104.2 1151.2 40,656
Monroe Giant Forest 75.53 247.8 27.82 91.3 1135.6 40,104

Source: United States National Park Service - [1] (http://www.nps.gov/seki/bigtrees.htm). Note that the volume figures have a low degree of accuracy, due to difficulties in measurement; stem diameter measurements are taken at a few set heights up the trunk, and assume that the trunk is circular in cross-section, and that taper between measurement points is even. The volume measurements also do not take cavities into account. The measurements are however trunk-only, and do not include the volume of wood in the branches or roots.

Uses

Wood from mature Giant Sequoias is highly resistant to decay, but is fibrous and brittle, making it generally unsuitable for construction. From the 1880s through the 1920s logging took place in may groves in spite of marginal commercial returns. Due to their weight and brittleness trees would often shatter when they hit the ground, wasting much of the wood. Loggers attempted to cushion the impact by digging trenches and filling them with branches. Still, it is estimated that as little as 50 percent of the timber made it from groves to the mill. The wood was used mainly for shingles and fence posts, or even for matchsticks.

Pictures of the once majestic trees broken and abandoned in formerly pristine groves, and the thought of the giants put to such modest use, spurred the public outcry that caused most of the groves to be preserved as protected land. The public can visit an example of 1880s clear-cutting at Big Stump Grove near Grant Grove. As late as the 1980s some immature trees were logged in Sequoia National Forest, publicity of which helped lead to the creation of Giant Sequoia National Monument.

The wood from immature trees is less brittle, with recent tests on young plantation-grown trees showing it similar to Coast Redwood wood in quality. This is resulting in some interest in cultivating Giant Sequoia as a very high-yielding timber crop tree, both in California and also in parts of western Europe, where it may grow more efficiently than Redwoods. In the northwest United States some entrepreneurs have also begun growing Giant Sequoias for Christmas trees. Besides these attempts at tree farming, the principle economic uses for Giant Sequoia today are tourism and horticulture (see Cultivation, below).

Giant Sequoia in cultivation

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Sequoi.westonbirt.600pix.jpg
Sequoiadendron giganteum at Westonbirt Arboretum, Gloucestershire, England. Another, at Kenilworth Castle (large image)

Giant Sequoia is a popular ornamental tree in many areas. It was first brought into cultivation in 1853 by Scotsman John D. Matthew, who collected a small quantity in the Calaveras Grove, arriving with it in Scotland in August 1853 (Mitchell 1996). A much larger shipment of seed collected (also in the Calaveras Grove) by William Lobb, acting for the Veitch Nursery, arrived in England in December 1853.

Growth in Britain is very fast, with the tallest tree, at Benmore in southwest Scotland, reaching 54 m at age 150 years (Tree Register of the British Isles (http://www.tree-register.org/)), and several others from 50-53 m tall; the stoutest is 3.55 m diameter, in Perthshire. Other areas where it is successfully grown include most of western and southern Europe, the Pacific Northwest of North America north to at least Vancouver, southeast Australia, New Zealand and central-southern Chile. Growth rates in some areas are remarkable; one young tree in Italy reached 22 m tall and 88 cm trunk diameter in 17 years.

In the northeastern USA there has been some limited success in growing the species, but growth is much slower there, and it is prone to Cercospora and Kabatina fungal diseases due to the humid summer climate there. The tallest reported in the east is one about 35 m tall, at Blithewold Gardens, in Bristol, Rhode Island. A recently selected cold tolerant cultivar 'Hazel Smith' is proving more successful in that area. This clone was the sole survivor of several hundred seedlings grown at a nursery in New Jersey.

References

  • Aune, P. S. (ed.) 1994. Proceedings of the Symposium on Giant Sequoias. US Dept. of Agriculture Forest Service (Pacific Southwest Research Station) General Technical Report PSW-GTR-151.
  • Mitchell, A. F. 1996. Alan Mitchell's Trees of Britain. HarperCollins ISBN 0-00-219972-6.
  • Thomas, H. H., Shellhammer, H. S., and Stecker, R. E. 1980. Giant sequoia ecology. U.S. Department of the Interior, National Park Service, Scientific Monograph Series 12. Washington, DC. 182 p.
  • Kilgore, B. 1970. Restoring Fire to the Sequoias. National Parks and Conservation Magazine 44 (277): 16-22.

External links

de:Riesenmammutbaum fr:Séquoia géant pl:Sekwoja

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