Sequoiadendron giganteum
Sequoiadendron giganteum ''' is a species of coniferous tree, classified in the family Cupressaceae in the subfamily Sequoioideae. Giant sequoia specimens are the largest trees on Earth. They are native to the groves on the western slopes of the Sierra Nevada mountain range of California but have been introduced, planted, and grown around the world.
The giant sequoia is listed as an endangered species by the IUCN with fewer than 80,000 remaining in its native California.
The giant sequoia grow to an average height of with trunk diameters ranging from. Record trees have been measured at tall. The specimen known to have the greatest diameter at breast height is the General Grant tree at. Giant sequoias are among the oldest living organisms on Earth. The oldest known giant sequoia is 3,200–3,266 years old.
Wood from mature giant sequoias is fibrous and brittle; trees would often shatter after they were felled. The wood is unsuitable for construction and instead is used for fence posts or match sticks. The giant sequoia is a very popular ornamental tree in many parts of the world.
Etymology
The etymology of the genus name was long presumed, initially in The Yosemite Book by Josiah Whitney in 1868, to be in honor of Sequoyah, who was the inventor of the Cherokee syllabary. An etymological study published in 2012 debunked that "American myth", concluding that Austrian Stephen L. Endlicher derived the name from the Latin word sequi, because the number of seeds per cone in the newly classified genus aligned in mathematical sequence with the other four genera in the suborder.Description
Giant sequoia specimens are the most massive individual trees in the world. They grow to an average height of with trunk diameters ranging from. Record trees have been measured at tall. Trunk diameters of have been claimed via research figures taken out of context. The specimen known to have the greatest diameter at breast height is the General Grant Tree at. Between 2014 and 2016, it is claimed that specimens of coast redwood were found to have greater trunk diameters than all known giant sequoias – though this has not been independently verified or affirmed in any academic literature. The trunks of coast redwoods taper at lower heights than those of giant sequoias which have more columnar trunks that maintain larger diameters to greater heights.The oldest known giant sequoia is 3,200–3,266 years old based on dendrochronology. That tree has been verified to have the fourth-largest lifespan of any tree, after individuals of Great Basin bristlecone pine and alerce. Giant sequoia bark is fibrous, furrowed, and may be thick at the base of the columnar trunk. The sap contains tannic acid, which provides significant protection from fire damage. The leaves are evergreen, awl-shaped, long, and arranged spirally on the shoots.
The wood is famously resistant to decay. A "nearly complete" S. giganteum log has been discovered south of the Nelder Grove which gave a radiocarbon-14 date of 10,000 years. Due to the longevity, fast growth, and large growth of this species, it also has high carbon storage potential for carbon sequestration.
The giant sequoia regenerates by seed. The seed cones are long and mature in 18–20 months, though they typically remain green and closed for as long as 20 years. Each cone has 30–50 spirally arranged scales, with several seeds on each scale, giving an average of 230 seeds per cone. Seeds are dark brown, long, and broad, with a wide, yellow-brown wing along each side. Some seeds shed when the cone scales shrink during hot weather in late summer, but most are liberated by insect damage or when the cone dries from the heat of fire. The trees do not begin to bear cones until they are 12 years old.
Trees may produce sprouts from their stumps subsequent to injury, until about 20 years old; however, shoots do not form on the stumps of more mature trees as they do on coast redwoods. Giant sequoias of all ages may sprout from their boles when branches are lost to fire or breakage.
A large tree may have as many as 11,000 cones. Cone production is greatest in the upper portion of the canopy. A mature giant sequoia disperses an estimated 300,000–400,000 seeds annually. The winged seeds may fly as far as from the parent tree.
Lower branches die readily from being shaded, but trees younger than 100 years retain most of their dead branches. Trunks of mature trees in groves are generally free of branches to a height of, but solitary trees retain lower branches.
Distribution
The natural distribution of giant sequoias is restricted to a limited area of the western Sierra Nevada, California. As a paleoendemic species, they occur in scattered groves, with a total of 81 groves, comprising a total area of only. 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 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.The 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 in the north, to to the south. Giant sequoias generally occur on the south-facing sides of northern mountains, and on the northern faces of more southerly 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 sequoia groves are currently undergoing a gradual decline in density since European settlement.
Pre-historic range
While the present day distribution of this species is limited to a small area of California, it was once much more widely distributed in prehistoric times, and was a reasonably common species in North American and Eurasian coniferous forests until its range was greatly reduced by the last ice age. Older fossil specimens reliably identified as giant sequoia have been found in Cretaceous era sediments from a number of sites in North America and Europe, and even as far afield as New Zealand and Australia.Artificial groves
In 1974, a group of giant sequoias was planted by the United States Forest Service in the San Jacinto Mountains of Southern California in the immediate aftermath of a wildfire that left the landscape barren. The giant sequoias were rediscovered in 2008 by botanist Rudolf Schmidt and his daughter Mena Schmidt while hiking on Black Mountain Trail through Hall Canyon. Black Mountain Grove is home to over 150 giant sequoias, some of which stand over tall. This grove is not to be confused with the Black Mountain Grove in the southern Sierra. Nearby Lake Fulmor Grove is home to seven giant sequoias, the largest of which is tall. The two groves are located approximately southeast of the southernmost naturally occurring giant sequoia grove, Deer Creek Grove.It was later discovered that the United States Forest Service had planted giant sequoias across Southern California. However, the giant sequoias of Black Mountain Grove and nearby Lake Fulmor Grove are the only ones known to be reproducing and propagating free of human intervention. The conditions of the San Jacinto Mountains mimic those of the Sierra Nevada, allowing the trees to naturally propagate throughout the canyon.
Ecology
Giant sequoias are in many ways adapted to forest fires. Their bark is unusually fire resistant, and their cones will normally open immediately after a fire. Giant sequoias are a pioneer species, and are having difficulty reproducing in their original habitat due to the seeds only being able to grow successfully in full sun and in mineral-rich soils, 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. These trees require large amounts of water and are often concentrated near streams. Their growth is dependent on soil moisture. Squirrels, chipmunks, finches and sparrows consume the freshly sprouted seedlings, preventing their growth.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 postfire 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 leads to ground fuel build-up and the dense growth of fire-sensitive white fir, which increases 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, two animal agents also assist 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. Reduction of the vascular water supply to the cone scales allows 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 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.
More than 30 identified species of bird have been observed living in giant sequoia groves.