Sequoiadendron giganteum - Definition and Overview

Giant Sequoia Conservation status: Vulnerable
General Grant tree in Sequoia National Park
Scientific classification
Kingdom: Plantae Division: Pinophyta Class: Pinopsida Order: Pinales Family: Cupressaceae Genus: Sequoiadendron Species: giganteum
Binomial name
Sequoiadendron giganteum (Lindl.) J. Buchholz

The Giant Sequoia (Sequoiadendron giganteum) is one of a number of species of coniferous trees known as redwoods, classified in the family Cupressaceae in a part of this family formerly segregated as the Taxodiaceae.

Description

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 may remain green up to 20 years.

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 the related Coast Redwood) mature trees do not sprout from cut stumps. Young trees start to bear cones at the age of 20 years. Cones may remain attached to the tree for 8-20 years and much of the seed will be retained. During the late summer, however, some seed is shed when the cone scales shrink. Most seeds are liberated when the cone dries out and becomes detached. Each cone yields an average of 230 seeds.

A Giant Sequoia with a car for scale

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 generally are free of branches to a height of 30-40 m (100-150 ft), when standing in a grove. Solitary trees keep all of their branches.

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, Yosemite

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 National Park 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.

Reproduction

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

Even though these trees are the largest in the world, their cones and seeds are small (see photo). These seeds can only germinate in mineral soils and possibly only soils derived from metamorphic rock. Periodic fire to clear competing vegetation, large amounts of water, and the climatic conditions that exist at 1,500-2,400 m altitude in the Sierra Nevada are important for regeneration. 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.

The Giant Sequoias are having difficulty reproducing in their original habitat. They are trees that historically depend on periodic fires for regeneration. Sequoia seeds germinate and grow best in open mineral soils with minimal forest litter. Such soils are produced by low-intensity ground fires. Furthermore, Giant Sequoia are more likely to release seeds due to hot air caused by a fire. Due to fire suppression efforts and livestock grazing during the 20th Century, low-intensity fires no longer occur naturally.

Other names

Until 1939, the Giant Sequoia was classified in the same genus as the Coast Redwood, as Sequoia gigantea, though this name was invalid under the botanical code, having been applied first (in 1847) to the Coast Redwood and only later (in 1854) to the Giant Sequoia. The nomenclatural oversight was corrected by botanist 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 for it. The names Wellingtonia or Washingtonia have also been applied to it, though these names are also invalid, correctly belonging respectively to the tropical southeast Asian broadleaf tree Wellingtonia arnottiana in the family Sabiaceae, and the palm genus Washingtonia. Other vernacular names include Sierra Redwood, Giant Redwood, or simply Big Tree.

List of the ten largest Giant Sequoias

As of December 2002, the ten largest trees by volume are:

Source: US 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, e.g., the 35 m deep, 3 m diameter cavity recently discovered in the Washington tree, accessible only by a hole situated 58 m above the ground. The measurements are however trunk-only, and do not include the volume of wood in the branches or roots.

Giant Sequoia in cultivation

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, when a large shipment of seed arrived in Britain, collected in the Calaveras Groves (now in Calaveras Big Trees State Park). Growth in Britain is very fast, with the tallest tree, at Benmore in southwest Scotland, reaching 54m at age 150 years (Tree Register of the British Isles (http://www.tree-register.org/)), and several others from 50-53m tall; the stoutest is 3.55m 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 22m 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 just over 30m tall, at Manistee in Michigan. A recently selected disease-resistant and cold tolerant cultivar 'Hazel Smith' is proving more successful in that area. This clone was the sole survivor of several thousand seedlings grown at a nursery in New Jersey.

Reference

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.

External links

• Gymnosperm Database - Sequoiadendron giganteum (http://www.botanik.uni-bonn.de/conifers/cu/se2/index.htm)
• Arboretum de Villardebelle - photos of cones & shoots with phenology notes (http://www.pinetum.org/cones/Sequoiadendron.htm)
• Forest Service database entry on Sequoiadendron giganteum (http://www.fs.fed.us/database/feis/plants/tree/seqgig/)
• Giant Sequoia Fire History in Mariposa Grove, Yosemite National Park (.pdf file!) (http://www.nps.gov/seki/fire/pdf/ts_yc90.pdf)