Giant Sequoia

Sequoiadendron giganteum is a conifer of the family Cupressaceae in the subfamily Sequoioideae, and it is also called giant redwood, Sierra redwood or Wellingtonia. The Forest Service review states that there are no recognised subspecies and that the giant sequoia is the only living species in its genus. Giant sequoia specimens are the largest trees on Earth; they are native to groves on the western slopes of the Sierra Nevada in California but have been planted widely around the world.

The range of the giant sequoia is limited to the western slope of the Sierra Nevada mountains in California, while the coast redwood keeps to the central and northern coast. The Forest Service's fire-effects review places the species only on the western slope of the Sierra Nevada, in 65 to 75 disjunct groves within montane mixed-conifer forest. The species is a paleoendemic found in scattered groves: a total of 81 groves covering only 144.16 square kilometres, or about 35,620 acres, on the western Sierra Nevada. The tree grows only in the mixed conifer zone on the west slope of the Sierra Nevada, in groves scattered over a strip 260 miles long and less than 15 miles wide. A 1990 review reported groves ranging from under 1 hectare to 1,619 hectares and totalling about 14,410 hectares along the western slope of the Sierra Nevada.

Giant sequoias grow at middle elevations on the west slope of the Sierra Nevada; they are not the world's oldest trees but are known to reach ages of up to 3,400 years. The species' range today is a narrow mid-elevation band in the Sierra Nevada, historically the elevation zone where half of the precipitation falls as snow. Coast redwoods are the tallest trees on Earth, soaring to 380 feet in one known instance, while giant sequoias hold the record for volume rather than height.

Giant sequoias and coast redwoods both belong to the cypress family, an extraordinary family with species living on every continent except Antarctica. That family includes the world's thickest tree, the Montezuma cypress, the world's tallest tree, the coast redwood, and the world's largest tree overall, the giant sequoia. Giant sequoias have pointy tapering needles that clasp tightly around twigs to minimise water loss in the dry Sierra Nevada air, unlike the fern-like coast redwood foliage. Giant sequoias are a pioneer species, among the first trees to take root after a disturbance opens the canopy and exposes mineral soil.

The General Sherman Tree is the largest in the world at 52,508 cubic feet; the General Grant Tree is second at 46,608 cubic feet of trunk volume. The General Sherman Tree grows in the Giant Forest, which alone contains five of the ten largest trees in the world by trunk volume. When branch volume is counted along with trunk volume, the President Tree becomes the second largest sequoia and the General Grant Tree the third largest. A growing giant sequoia produces about 40 cubic feet of wood each year, roughly equal to the volume of a tree 50 feet tall and one foot in diameter.

The giant sequoia first gained wide attention in 1852 when the grizzly hunter Augustus T. Dowd came upon the Discovery Tree in Calaveras Grove, the species' first publicised discovery by non-natives. In 1939 John Theodore Buchholz corrected decades of invalid names and coined Sequoiadendron giganteum, recognising the giant sequoia as a genus distinct from the coast redwood. An avenue of 218 giant sequoias was planted in 1865 near Camberley in Surrey, England, and the trees have since been surrounded by modern real estate development. In 1956 President Eisenhower declared the General Grant Tree a National Shrine, and it remains the only example of a living national shrine anywhere in the United States.

Over 85 percent of all giant sequoia grove acreage across the Sierra Nevada burned in wildfires between the 2015 season and the 2021 season, against a quarter in the preceding century.

The giant sequoia reaches an average height of 50 to 85 m (164 to 279 ft) with a trunk 6 to 8 m across, and record trees have been measured at 94.8 m tall. Unlike the coast redwood, whose trunk tapers at lower heights, the giant sequoia grows a more columnar trunk that keeps larger diameters up to greater heights. The largest sequoias stand as tall as an average 26-storey building, and their diameters at the base exceed the width of many city streets. The bark is fibrous and furrowed, reaching up to 90 cm (3 ft) thick at the base, and the sap carries tannic acid that provides significant protection from fire damage.

Trunk volume is the measure by which the largest sequoias are ranked. The General Sherman Tree is estimated at 52,500 cubic feet of wood, which in lumberman's terms is about 630,000 board feet from a single tree. The General Grant trunk holds 46,608 cubic feet (1,320 cubic meters). The trunk of General Sherman alone weighs nearly 1,400 tons, roughly the weight of 15 adult blue whales or 25 military battle tanks.

Growth continues at a remarkable rate even in maturity. In just one year an average mature giant sequoia adds enough wood to make a sixty-foot tall, three-foot diameter oak tree. Measured as volume, the annual wood increment of a mature tree is about 40 cubic feet (one cubic meter). A single mature tree also produces 300,000-400,000 seeds in a year.

The oldest known giant sequoias have been dated by dendrochronology to between 3,200 and 3,266 years of age. The National Park Service cites maximum ages of up to 3,400 years for the species. In the verified record of tree lifespan the giant sequoia ranks fourth, behind the Great Basin bristlecone pine and the alerce. Its longevity is matched by sustained vigor: growth remains rapid well into old age, which is why individual trees can reach both great age and great height.

Such ages are not merely a matter of survival but of circumstance. Giant sequoias were rare during a warm period about 10,000 to 6,000 years ago, and their present abundance dates back only about 4,500 years. The groves in which the oldest trees stand occupy a narrow elevational band, running from about 1,400 to 2,000 metres in the north and from 1,700 to 2,150 metres in the southern part of the range. Within these settings the species receives mean annual precipitation of about 900 to 1,400 mm.

Fire has shaped the lifespan of the species over the long term. Tree-ring records show that frequent surface fires were the typical pattern of fire occurrence over the past two thousand years, until the pattern changed in the 1860s. In the Giant Forest grove widespread fires burned at intervals ranging from about 6 to 35 years depending on the period. That decline in regional fire was probably caused by intensive sheep grazing, a decrease in fires set by Native Americans and then fire suppression by government agencies. To reconstruct these histories scientists extracted pencil-width cores from 659 giant sequoias in Giant Forest, Atwell and Mariposa groves and counted tree rings to date each tree's establishment.

Recent drought tested the species against other conifers and revealed a marked resilience. California's 2012 to 2016 hotter drought was the most extreme in the instrumental record and perhaps in the last several centuries, and it left visible foliage dieback in sequoias. Non-sequoia conifers suffered extensive mortality in that drought while sequoias mostly did not, although 33 sequoias died standing, linked to native bark beetles and basal fire damage. Sequoias showed leaf and canopy responses that kept water available inside the tree for the vast majority of individuals, and very few died compared with other conifers. USGS scientists and park managers documented 33 giant sequoias that died standing during and after the 2012 to 2016 hotter drought, killed by native Phloeosinus bark beetles.

The fires of 2020 and 2021 imposed losses on a different scale. A study of those fires estimated 7,974 sequoia deaths, 30.2 percent mortality, and showed that prescribed burns within ten years cut mortality odds by 77 percent. Between 13 and 19 percent of the world's large sequoias are estimated to have died in the Castle, KNP Complex and Windy fires combined, some 8,431 to 11,897 trees. For the KNP Complex alone an estimated 1,330 to 2,380 sequoias over four feet in diameter had been killed or would die within three to five years. Treated trees were roughly four times more likely to survive than untreated ones.

The naming history of the giant sequoia is a record of enthusiasm outrunning botanical precision. When William Lobb's sequoia material reached Britain, John Lindley marvelled at what he called a tree of portentous aspect and almost fabulous antiquity. Lindley described the species in December 1853 as Wellingtonia gigantea, apparently without knowing that the name was already occupied by an unrelated plant in the family Sabiaceae. The result was a period of competing and invalid designations that persisted for decades.

Stability came only in 1939, when John Theodore Buchholz corrected the accumulated invalid names and coined Sequoiadendron giganteum. In doing so he recognised the giant sequoia as belonging to a genus distinct from the coast redwood, separating the two great Californian trees at the generic level. The full author citation for the accepted name is Sequoiadendron giganteum (Lindl.) J.Buchh., 1939, which credits Lindley as the original describer and Buchholz as the author of the current combination.

The giant sequoia is confined to the western slope of the Sierra Nevada, where its natural range is restricted to about 75 groves scattered over a 420-kilometre belt nowhere more than about 24 kilometres wide. Counts of the groves differ by source: one tally gives 81 groves covering 144.16 km2 (about 35,620 acres), while a US Forest Service review of 1990 records about 75 groves over a 420-km belt with a total of about 14,410 ha. Satellite estimates suggest fewer than 80,000 naturally occurring giant sequoias remain in the Sierra Nevada, a small remnant of a once far wider range.

Mean annual precipitation in the groves varies from about 900 to 1,400 millimetres, with high year-to-year variation and most of it falling as snow between October and April. Mean annual snowfall in the groves ranges from 366 to 500 centimetres, and snow depths of 2 metres or more are common in midwinter. This snowpack supplies the mountain water sequoias depend on.

Most groves sit on granitic-based residual and alluvial soils, and three are on glacial outwash from granite, though schistose and dioritic rocks are also common parent materials.

Massive ancient giant sequoias live in three groves in Yosemite National Park, with Mariposa Grove near the South Entrance the most easily accessible of them and holding over 500 mature giant sequoias. Sequoia National Park was established on 25 September 1890 and today protects 404,064 acres of forested mountainous terrain in the southern Sierra Nevada.

Fire has reshaped the groves over the past decade: 82 percent of giant sequoia grove area burned in wildfire over the decade to 2024, against 24 percent over the century before it, and more than a sixth of large sequoias have died since 1984. Treatment and wildfire together have left 26 percent of grove area at high resistance to severe fire, 38 percent at moderate resistance, 2 percent at low and 16 percent with none.

Giant sequoia seeds are borne in serotinous cones that may stay attached to their stems without opening for up to 20 years, an aerial seed bank waiting for fire or beetles. Locally intense fire convects hot air high into the canopy and can dry cones to release enormous quantities of seed, on the order of 20 million per hectare. Beetles and squirrels release about 1 million seeds per hectare a year, keeping the seed rain roughly constant even when new cone crops vary.

Sequoia seeds are winged and light, about 200,000 to the kilogram, and late-summer and winter storms can carry them more than 0.4 kilometres from the parent crown. Their wind adaptation is measurable: winged and light, they fall in still air at only 1.2 to 1.8 metres per second. Even the mightiest sequoia starts from a tiny seedling, and it is at this seedling stage that giant sequoias are the most vulnerable to drought and heat.

Tree-ring records show frequent surface fire over the past two thousand years until the pattern changed in the 1860s, probably through intensive sheep grazing, reduced Native American burning and then government fire suppression. In Giant Forest widespread fires burned at intervals of about 6-35 years. Fire was most frequent at four of five studied groves during the warm, drought-prone period from 800 to 1300 AD. Scientists cored 659 trees in Giant Forest, Atwell and Mariposa groves to date establishment.

The species is a pioneer, among the first to root after disturbance opens the canopy and exposes mineral soil. Its population was stable or increasing to the 1800s but the 1900s brought a massive failure of reproduction as fire was excluded. Fire adaptations include the aerial seed bank, thick resin-free bark, resprouting from latent buds, rapid growth, tall height and self-pruned lower branches.

The National Park Service began controlled burns of sequoia groves in 1970. Prescribed fire is a planned ignition under optimal conditions by qualified staff.

Its estimated natural population numbers fewer than 80,000 trees. The species once spread far beyond California, but its range contracted drastically after the last ice age. It was rare roughly 10,000 to 6,000 years ago, and its present abundance dates back only about 4,500 years.

California's 2012 to 2016 hotter drought was the most extreme in the instrumental record and perhaps in the last several centuries, and it left visible foliage dieback in sequoias. Non-sequoia conifers suffered extensive mortality in that drought while sequoias mostly did not. Even so, 33 sequoias died standing, linked to native bark beetles and basal fire damage.

The Castle Fire of 2020 is estimated to have wiped out 10 to 14 percent of the giant sequoia population, about 7,500 to 10,600 mature trees, including the King Arthur Tree.

The giant sequoia genome was published in 2020. It comprises 8.125 billion base pairs assembled into eleven chromosome-scale scaffolds. At that date it stood as the largest genome assembled for any organism.

Massive ancient giant sequoias live in three groves in Yosemite National Park. Mariposa Grove near the South Entrance is the most easily accessible of them. It is also the largest grove in Yosemite and holds over 500 mature giant sequoias. The Tuolumne and Merced groves are far smaller by comparison, holding roughly two dozen each.

The Tuolumne Grove holds about two dozen mature giant sequoias. Reaching it requires a one-mile hike with 500 feet of elevation loss.