Sequoia (tree)

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Introduction

Sequoia (tree), also known as redwoods, common name for a group of huge, majestic evergreen trees characterized by a columnar, reddish-brown trunk that can grow 30 m (100 ft) or more above a buttressed base. Sequoia species are conical in shape, with needlelike leaves and small, oval cones. The trees grow best in regions with relatively mild temperatures and moderate humidity year-round. The trees are named for the Cherokee leader Sequoyah.

Once widespread in the North Temperate Zone, most sequoias suffered extinction with the advancing glaciers of the last ice age more than 11,000 years ago. Only three species survived—the giant sequoia and coast redwood in California, and the dawn redwood in southwestern China. Fossil remains of sequoia trees have been found in geological strata as old as the Jurassic Period, from about 200 million to 145 million years ago—tannins in the wood protected it from decay. The Petrified Forest National Park in Arizona consists largely of extinct sequoia species.

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Giant Sequoia

The giant sequoia, or “big tree,” is found in a narrow strip about 300 km (about 200 mi) long on the western slopes of the Sierra Nevada range at elevations from about 900 to 2,400 m (about 3,000 to 8,000 ft). It is the most massive of all living forms. The largest specimen, the General Sherman Tree in Sequoia National Park, is 84 m (275 ft) tall, has a diameter of 11.1 m (36.4 ft) at the base, and was estimated in the early 1990s to weigh about 2,500 metric tons. Other trees range from 46 to 99 m (150 to 325 ft) in height, with diameters up to 9 m (30 ft). A count of annual rings on stumps has verified ages as great as 2,300 years. Some living trees, however, are believed to be close to 4,000 years old.

The leaves of the giant sequoia are scalelike and lie close to the branches. The bark of the trunk is fluted and is spongy in texture; in large trees it reaches a thickness of 60 cm (2 ft). The wood is light, coarse-grained, and highly resistant to insects and fire. Most of the giant sequoia groves are included within the National Park System or are otherwise under government protection—cutting of the big trees is prohibited.

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III

Coast Redwood

The coast redwood grows along the humid Pacific coast from southern Oregon to central California. Its height ranges from 30 to 112 m (100 to 367 ft), a size approached only by the eucalyptus of Australia, one specimen of which measures at least 97 m (at least 318 ft). The diameter of the trunk measures up to 7.5 m (25 ft). The life span of the coast redwood is believed to be 2,500 years. The leaves are bluer in tone than those of the giant sequoia and are more needlelike. The wood is similar but even-grained. Unlike most other conifers (cone-bearing trees), the stump of the coast redwood produces sprouts after cutting that can grow to considerable size in just 40 years. For this reason, and because the tree is more plentiful and its wood harder than the giant sequoia, it has been cut extensively. Some irreplaceable old-growth specimens are preserved in state and national parks, but survival of the redwood groves elsewhere is in question.

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Dawn Redwood

The dawn redwood was once the most common sequoia tree in North America. Scientists believed it to be extinct worldwide until 1941 when a forest of about 1,000 trees was discovered in Sichuan, China. This population has since dwindled and the IUCN Red List of Threatened Species has listed the tree as critically endangered in the wild. However, it is planted widely as an ornamental in China. In North America, seeds and seedlings collected in the late 1940s by the Arnold Arboretum in Massachusetts were widely distributed, and the tree eventually became cultivated in temperate regions worldwide.

The dawn redwood attains a height just under 30 m (100 ft) and averages 1.8 m (6 ft) in diameter. Its leaves are flat and grow in slender, opposite branches. Unlike the evergreen sequoias, the dawn redwood is a deciduous tree.

Scientific classification: Sequoias belong to the family Taxodiaceae. The giant sequoia is classified as Sequoiadendron giganteum, the coast redwood as Sequoia sempervirens, and the dawn redwood as Metasequoia glyptostroboides.

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