Definitions

Metasequoia

Metasequoia

[met-uh-si-kwoi-uh]
Metasequoia: see sequoia.

Coniferous, nonevergreen tree (Metasequoia glyptostroboides), the only living species of the genus Metasequoia, of the family Taxodiaceae, native to remote valleys of central China. Both branchlets and leaves grow out in pairs from points along the stem. The bright green, feathery leaves turn reddish brown in autumn. Though Metasequoia fossils are abundant, the tree was thought to be extinct until living specimens were discovered in the 1940s. Only a few thousand are known to have survived, in central China. Since these stands were discovered, seeds and cuttings have been planted throughout the world.

Learn more about dawn redwood with a free trial on Britannica.com.

Metasequoia (Dawn Redwood) is a fast growing tree genus in the conifer family Cupressaceae of which Metasequoia glyptostroboides, native to the Sichuan-Hubei region of China, is the only living species. Metasequoia, along with Sequoia, Sequoiadendron and several other genera, were transferred from the Taxodiaceae family to Cupressaceae using DNA analysis. M. glyptostroboides is the only extant species in its genus, but three fossil species are known as well.

Appearance

While the bark and foliage are similar to another closely related redwood genus Sequoia, Metasequoia differs from the California redwood in that it is deciduous like Taxodium distichum (Bald Cypress), and like that species, older specimens form wide buttresses on the lower trunk. It is a fast-growing tree to 40-45 m tall and 2 m trunk diameter in cultivation so far (with the potential to grow to even greater heights). The leaves are opposite, 1-3 cm long, and bright fresh green, turning a foxy red-brown in fall. The cones are globose to ovoid, 1.5-2.5 cm in diameter with 16-28 scales, arranged in opposite pairs in four rows, each pair at right angles to the adjacent pair; they mature in about 8-9 months after pollination. The pollen cones are 5-6 mm long, produced on long spikes in early spring; they are only produced on trees growing in regions with hot summers.

Metasequoia was first described as a fossil from the Mesozoic Era by Shigeru Miki in 1941, but in 1944 a small stand of an unidentified tree was discovered in China in Modaoxi by Zhan Wang; due to World War II, these were not studied further until 1946 and only finally described as a new living species of Metasequoia in 1948 by Wan Chun Cheng and Hu Hsen Hsu. In 1948 the Arnold Arboretum of Harvard University sent an expedition to collect seeds and, soon after, seedling trees were distributed to various universities and arboreta worldwide for growth trials.

In the late 1980s, it was discovered that many of the second generation trees in cultivation suffered from inbreeding depression (extremely low genetic variability) which could lead to increased susceptibility to disease and reproductive failure. This was because most of the trees were grown from seeds and cuttings derived from as few as three trees that the Arnold Arboretum had used as its source. More widespread seed-collecting expeditions in China in the 1990s sought to resolve this problem and restore genetic diversity to cultivated Metasequoia.

Metasequoia has proved an easy tree to grow in temperate regions, and is now widely planted as an ornamental tree. Planted specimens have already reached 25-40 m in height and 1-1.3 m in diameter, despite being in cultivation for under 60 years. This rapid rate of growth has led to consideration for using the tree in forestry plantations.

It has been discovered that Metasequoia will thrive in standing water, much like the baldcypress, and if left branched to the ground in full sun, will develop the large, contorted boles that have made it famous. Limbing at an early age will prohibit this formation later on.

Paleontology

Metasequoia redwood fossils are known from many areas in the Northern Hemisphere; over 20 fossil species have been named (some were even identified as the genus Sequoia), but are considered as just three species, M. foxii, M. milleri, and M. occidentalis (Farjon 2005). During the Paleocene-Eocene Thermal Maximum, extensive forests of Metasequoia occurred as far north as Axel Heiberg Island (northern Canada) at around 80°N latitude. Large petrified trunks and stumps of the extinct Metasequoia occidentalis (sometimes identified as Sequoia occidentalis) also make up the major portion of Tertiary fossil plant material in the badlands of western North Dakota in the United States.

The trees are well known from late Cretaceous to Miocene strata, but no fossils are known after that. Before its discovery, the taxon was believed to have become extinct during the Miocene; when it was discovered , it was heralded as a "living fossil".

Conservation

There remains one Dawn Redwood forest, consisting of barely 5,000 trees. Since its discovery, the Dawn Redwood has become something of a national point of pride, and it is both protected under Chinese law and planted widely. As such, it's not likely to go extinct, but Dawn Redwood is critically endangered in the wild. Though cutting of trees or branches is illegal, the demand for seedlings drives cone collection to the point that natural reproduction is no longer occurring in the dawn redwood forest. Although the species will continue to live in yards, parks and on roadsides all over China, the Metasequoia forest ecosystem could disappear when its mature trees die.

See also

  • Sequoiadendron giganteum - Giant Sequoia or Sierra Redwood
  • Cryptomeria japonica - Sugi

References

  • Listed as Critically Endangered (CR A1c, C2a v2.3)
  • Farjon, A. (2005). Monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew. ISBN 1-84246-068-4.
  • Hanks, D.A. Crescent Ridge Dawn Redwoods Preserve (2005). http://www.dawnredwood.org
  • Jahren, A. H. & Sternberg, L. S. L. (2003). Humidity estimate for the middle Eocene Arctic rain forest. Geology May 2003 pdf file
  • Metasequoia stumps, Axel Heiberg Island (pdf file)
  • Williams C.J., LePage, B.A., Vann D.R., Tange, T., Ikeda, H., Ando, M., Kusakabe, T., Tsuzuki, T. and T. Sweda. (2003). Structure, allometry, and biomass of plantation Metasequoia glyptostroboides in Japan. Forest Ecology and Management, 180(103): 287-301.
  • Williams C.J., Johnson A.H., LePage, B.A., Vann D.R. and T. Sweda. 2003. Reconstruction of Tertiary Metasequoia Forests II. Structure, Biomass and Productivity of Eocene Floodplain Forests in the Canadian Arctic. Paleobiology, 29(2): 271-292.

Further reading

  • He, Zican, Jianqiang Li, Qing Cai, Xiaodong Li, and Hongwen Huang. 2004. "Cytogenetic Studies on Metasequoia Glyptostroboides, a Living Fossil Species". Genetica. 122, no. 3: 269-276.
  • International Metasequoia Symposium, Ben A. LePage, Christopher J. Williams, and Hong Yang. The Geobiology and Ecology of Metasequoia. Topics in geobiology, v. 22. Dordrecht: Springer, 2005. ISBN 1402027648
  • Proceedings of the Second International Symposium on Metasequoia and Associated Plants, August 6–10, 2006, Metasequoia: Back from the Brink? An Update. Edited by Hong Yang and Leo J. Hickey. Bulletin of the Peabody Museum of Natural History, Volume 48, Issue 2 31 October 2007, pp. 179–426.

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