Sequoiadendron giganteum

giant sequoia

Cupressaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Cupressaceae (cypress family). Genus - Sequoiadendron J. Buchholz (giant sequoia). P Species - Sequoiadendron giganteum (Lindl.) J. Buchholz (giant sequoia).

Ecology: Since its discovery in the mid-nineteenth century, giant sequoia, also called sequoia, bigtree, and Sierra redwood, has been noted for its enormous size and age, and its rugged, awe-inspiring beauty...One tree species has a greater diameter than giant sequoia, three grow taller, and one lives longer. In terms of volume, however, the giant sequoia is undisputedly the world's largest tree. The most massive specimen, the General Sherman tree, located in Sequoia National Park. The greatest known age of a giant sequoia is 3,200 years, determined from a stump count of rings.

The natural range of giant sequoia is restricted to about 75 groves scattered over a 420-km belt, nowhere more than about 24 km wide, extending along the west slope of the Sierra Nevada in central California. Giant sequoia groves lie wholly within the Sierra Nevada Mixed Conifer type-SAF (Society of American Foresters) forest cover type 243. A grove is distinguished from similar mesic habitats in this type only by the presence of giant sequoia itself: no other species is restricted to the groves. Nowhere does giant sequoia grow in a pure stand, although in a few small areas it approaches this condition.

Identification

The giant-sequoia is a massive evergreen tree, maturing to 250 ft. high with a girth of 80 ft. Bluish-green needles are crowded and spirally arranged on the twigs. The fluted trunk and red-brown bark are attractive landscape features, revealed as the tree loses its lower branches. The tree retains a narrow, pyramidal crown of foliage in the upper reaches at maturity. One of the world’s largest trees with fibrous, reddish-brown trunk much enlarged and buttressed at base, fluted into ridges, and conspicuously narrowed or tapered above; narrow, conical crown of short, stout, horizontal branches reaches nearly to base. Giant trees have tall, bare trunk and irregular, open crown.

This rare species ranks among the world’s oldest trees; felled trees show annual rings indicating up to 3200 years of age. Almost all Giant Sequoias are protected in Yosemite, Kings Canyon, and Sequoia national parks, in 4 national forests, and in state parks and forests. It is a popular, large ornamental tree in moist, cool temperate climates along the Pacific Coast and around the world. The lumber is no longer used, although many trees were cut and wasted in the early logging days. Seedlings and saplings are killed by forest fires, but the very thick bark of mature trees offers resistance. Douglas squirrels cut and store quantities of mature cones, and sparrows, finches, and chipmunks destroy many seedlings.

Threats

Fire effects: Fire is the most universal and probably most serious damaging agent of giant sequoia in its natural range. Seedlings and saplings of giant sequoia, like those of most other tree species, are highly susceptible to mortality or serious injury by fire. However, in those locations most favorable for successful establishment and early growth-that is, mineral soil seedbeds and well-lighted openings-fuels tend to be sparser and to accumulate more slowly than in adjacent forested areas. The more vigorous seedlings and saplings thus may be large enough to survive a light fire by the time one occurs.

Larger giant sequoias, because of their thick nonresinous bark and elevated crowns, are more resistant to fire damage than associated species. Nevertheless, repeated fires over the centuries sear through the bark of a tree's base, kill the cambium, and produce an ever-enlarging scar. Lightning strikes, besides starting ground fires, sometimes knock out large portions of crowns or ignite dead tops. Almost all of the larger trees have fire scars, many of which encompass a large percentage of the basal circumference. Few veterans have been killed by fire alone, but consequent reduction in supporting wood predisposes a tree to falling. Furthermore, fire scars provide entry for fungi responsible for root disease and heart rot. Decayed wood, in turn, is more easily consumed by subsequent fires.

Giant sequoia is shade intolerant throughout its life. Fires or other disturbances that bare mineral soil and open the canopy characteristically benefit intolerant species, including giant sequoia, and move plant communities to earlier successional stages. In contrast, successful regeneration of giant sequoia in shade and in the absence of disturbance is less likely than that of any associated conifer.

Old giant sequoias most commonly die by toppling. Weakening of the roots and lower bole by fire and decay is primarily responsible. The extreme weight of the trees, coupled with their shallow roots, increases the effects of this weakening, especially in leaning trees. Other causative factors include wind, water-softened soils, undercutting by streams, and heavy snow loads.

Insects do not seriously harm giant sequoias older than about 2 years. Carpenter ants (Campanotus laevigatus) do not directly harm the trees, although they do create pathways for fungi. Air-pollution creating acidic mists significantly reduce root growth of giant sequoia.

Reproduction

Flowering and Fruiting - Giant sequoia is monoecious; male and female cone buds form during late summer. Pollination takes place between the middle of April and the middle of May when the female conelets are only two or three times as large in diameter as the twigs bearing them.

Seed Production and Dissemination - Cones bearing fertile seeds have been observed on trees as young as 10 years of age, but the large cone crops associated with reproductive maturity usually do not appear before about 150 or 200 years. Unlike most other organisms, giant sequoia seems to continue its reproductive ability unabated into old age.

Giant sequoias have serotinous cones which, at maturity, may remain attached to the stems without opening to release seeds. For 20 years or more, cones may retain viable seeds and continue to photosynthesize and grow, their peduncles producing annual rings that can be used to determine cone age.

Browning or drying of cones, with subsequent shrinkage of scales and dispersal of seeds, is brought about largely by three agents, two of which are animals. The more effective of the two is Phymatodes nitidus, a long-horned wood-boring beetle. The larvae of the beetle mine the fleshy cone scales and cone shafts, damaging occasional seeds only incidentally. As vascular connections are severed, scales successively dry and shrink, allowing the seeds to fall...The second animal having a significant role in giant sequoia regeneration is the chickaree, or Douglas squirrel (Tamiasciurus douglasi). The fleshy green scales of younger sequoia cones are a major food source for the squirrel. The seeds, too small to have much food value, are dislodged as the scales are eaten..The third and perhaps most important agent of seed release is fire. Hot air produced by locally intense fire and convected high into the canopy can dry cones, resulting in release of enormous quantities of seed over small areas-for example, 20 million/ha.

Seedling Development - In contrast with most coniferous seeds, a large majority of seeds of giant sequoia die from desiccation and solar radiation soon after reaching the forest floor, especially during the summer...Height growth of giant sequoia seedlings in the groves is relatively slow during the first few years, presumably because of competition for light and moisture from the larger trees.

Vegetative Reproduction - Giant sequoias up to about 20 years of age may produce stump sprouts subsequent to injury. Unlike redwood (Sequoia sempervirens), older trees normally do not sprout from stumps or roots. A recent report, however, noted sprouts on two small stumps from suppressed trees about 85 years old. Giant sequoias of all ages may sprout from the bole when old branches are lost by fire or breakage.

Species Distribution

Citation

USDA Plant Database
USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov, 4 February 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Flora of North America
Flora of North America Editorial Committee, eds.  1993+.  Flora of North America North of Mexico.  19+ vols.  New York and Oxford.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers). USDA Forest Service Agricultural Handbook 654.

Intermountain Herbarium
Consortium of Intermountain Herbaria. 2016. http//:intermountainbiota.org/portal/index.php. Accessed on February 04.

Jepson Manual
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA. $131.95, hardcover; 1600 pages. ISBN-13: 978-0520253124.

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97.
Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.