Giant sequoia

Appearance

Giant sequoias are the world's largest single trees and largest living thing by volume. Giant sequoias grow to an average height of 50–85 m (164–279 ft) and 6–8 m (20–26 ft) in diameter. Record trees have been measured to be 94.8 m (311 ft) in height. Claims of 17 m (56 ft) diameter have been touted by taking an author's writing out of context, but the widest known at chest height is closer to 8.2 m (27 ft). Between 2014 and 2016, specimens of coast redwood were found to have larger trunk diameters than all known giant sequoias.

The oldest known giant sequoia based on ring count is 3,500 years old
Sequoia bark is fibrous, furrowed, and may be 90 centimeters 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 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 from fire heat or is damaged by insects .


Giant sequoia regenerates by seed. 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 mature trees do not sprout from cut stumps. Young trees start to bear cones at the age of 12 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 180 m 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.

Naming

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 publicized. 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 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 December 1853, who named it ''Wellingtonia gigantea'', without realizing this was an invalid name under the botanical code as the name ''Wellingtonia'' had already been used earlier for another unrelated plant . The name "Wellingtonia" has persisted in England as a common name, though is deprecated as cultural imperialism . 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 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.

John Muir wrote of the species in about 1870:
Do behold the King Sequoia! Behold! Behold! seems all I can say. Some time ago I left all for Sequoia and have been and am at his feet, fasting and praying for light, for is he not the greatest light in the woods, in the world? Where are such columns of sunshine, tangible, accessible, terrestrialized?

Distribution

The natural distribution of giant sequoia is restricted to a limited area of the western Sierra Nevada, California. It occurs in scattered groves, with a total of 68 groves , comprising a total area of only 144.16 square kilometres . 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 12.4 square kilometres 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.

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 1,400–2,000 metres in the north, and 1,700–2,150 metres to the south. Giant sequoia generally occurs on the south facing side of northern mountains, and on the northern face of more southern slopes.

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.

Habitat

The giant sequoias are having difficulty reproducing in their original habitat 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 fully 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 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 that gnaws on the fleshy green scales of younger cones. The squirrels are active year round, and some seeds are dislodged and dropped as the cone is eaten.

Uses

Wood from mature giant sequoias is highly resistant to decay, but due to being fibrous and brittle, it is generally unsuitable for construction. From the 1880s through the 1920s logging took place in many 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 General 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 coast redwoods. In the northwest United States some entrepreneurs have also begun growing giant sequoias for Christmas trees. Besides these attempts at tree farming, the principal economic uses for giant sequoia today are tourism and horticulture .