Hu and W.C.Cheng, 1948
Metasequoia glyptostroboides, the dawn redwood, is a fast-growing, endangered deciduous conifer, the sole living species of the genus Metasequoia, one of three species in the subfamily Sequoioideae. It is native to Lichuan county in the Hubei province of China. Although shortest of the redwoods, it can grow to at least 165 ft (50 m) in height.
In 1941, the genus Metasequoia was originally reported by palaeobotanist Shigeru Miki as a widely distributed extinct genus based on fossils, before attracting considerable attention a few years later when small populations were found in central China. It is a particularly well-known example of a living fossil species. The tree faces considerable risks of extinction in its wild range due to deforestation, and so has been planted extensively in arboreta worldwide, where it has proved a popular and fast-growing ornamental plant.
Though once common across the northern hemisphere, the dawn redwood was originally considered extinct. The genus Metasequoia was first described in 1941 as a fossil of the Mesozoic Era, and none of the fossils discovered were less than 150 million years old. Dr. Shigeru Miki (1901-1974), a paleobotanist from Kyoto University, identified a divergent leaf form while studying fossil samples of the family Cupressaceae and realized he was looking at a new genus, which he named Metasequoia, meaning "like a sequoia".
In the same year a forester named T. Kan came across an enormous living specimen while performing a survey in Sichuan and Hubei provinces. Though unaware of Miki's new genus, he recognized the unique traits of the tree. It formed part of a local shrine, where villagers called it Shui-shan or "water fir".
In 1943, Zhan Wang (1911-2000), a Chinese forestry official, collected samples from an unidentified tree in Modaoxi, China (presently, Moudao, Lichuan County, Hubei)--now believed to be the same tree Kan discovered. The samples were determined to belong to a tree yet unknown to science, but World War II postponed further study.
Professors Wan Chun Cheng and Hu Xiansu made the pivotal connection between Miki's genus and the living samples in 1946, and provided the specific epithet "glyptostroboides", after its resemblance to the Chinese swamp cypress (Glyptostrobus).
In 1948 the Arnold Arboretum of Harvard University funded an expedition to collect seeds from Kan's original tree and, soon after, distributed seeds and seedlings to various universities and arboreta worldwide for growth trials. Of these, two were distributed to the H. H. Hunnewell estate in Wellesley, MA, where they are still alive as of 2016.
Together with Sequoia sempervirens (coast redwood) and Sequoiadendron giganteum (giant sequoia) of California, M. glyptostroboides is classified in the subfamily Sequoioideae of the family Cupressaceae. Although it is the only living species in its genus, three fossil species are known as well. The other Sequoioideae and several other genera have been transferred from the Taxodiaceae to the Cupressaceae based on DNA analysis.
While the bark and foliage are similar to another closely related genus of redwoods, Sequoia, M. glyptostroboides differs from the coast redwood in that it is deciduous, like Taxodium distichum (bald cypress). Similar to T. distichum, older trees may form wide buttresses on the lower trunk. M. glyptostroboides is a fast-growing tree, exceeding 35 m (115 ft) in height and 1 m (3.3 ft) in trunk diameter by the age of 50, in cultivation (with the potential to grow to even greater dimensions). The trunk forms a distinctive "armpit" under each branch. The bark is vertically fissured and tends to exfoliate in ribbon-like strips.
The largest dawn redwood recorded was an isolated specimen in China about 50 meters (165 feet) tall and 2.2 meters (7.2 feet) wide. This tree was killed by a lightning strike in 1951. Several dawn redwoods of this height still live in the eastern part of Shuishaba Valley, AKA Metasequoia Valley, where the tree was discovered. The tree's true potential size is much larger, as logs up to 8 meters (26 feet) wide at the base have been discovered in rice paddies.
The thickest and tallest dawn redwoods listed by Momumental Trees are both in the Longwood Gardens of Kennett Square in Pennsylvania, United States. The widest has a girth at breast height of 5.79 m (19 ft, average diameter 1.84 m, 6 ft), and is 30.18 m (99 ft) tall. The tallest is 41.15 m (135 ft) tall, and has a girth at breast height of 3.35 m (11 ft, average diameter 1.07 m, 3.5 ft). Both trees were planted in 1948 and measured in 2018.
The leaves are opposite, 1-3 cm (0.39-1.18 in) long, and bright fresh green, turning a foxy reddish brown in fall. The pollen cones are 5-6 mm (0.20-0.24 in) long, produced on long spikes in early spring; they are produced only on trees growing in regions with hot summers. The cones are globose to ovoid, 1.5-2.5 cm (0.59-0.98 in) 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.
In Lichuan, Hubei, there is a dawn redwood forest consisting of barely 5,000 trees (by another count, around 5,400 trees.), and some smaller groups (typically, under 30 trees each). The floodplain of Metasequoia Valley in Hubei had already been turned to rice paddies by the time of the tree's discovery, but was once probably a more extensive dawn redwood forest. Such a forest would have been similar to bald cypress forests in the United States, with many similar species growing in association. Nearly 3,000 trunks were found in the floor of the valley, ranging from 2 meters (6.5 feet) to 8 meters (26 feet) wide at the base. Additionally, houses made of Metasequoia wood 200-300 years old still exist and probably date back to the original settlement of the valley. Since its discovery, the dawn redwood has become something of a national point of pride, and it is protected under Chinese law and also planted widely. However, it is still listed as endangered in the wild. Cutting of trees or branches is illegal, but the demand for seedlings drives cone collection to the point that natural reproduction is no longer occurring in the dawn redwood forest. In addition, the landscape has been highly modified by human use, and a 1980 expedition found that the habitat has significantly degraded since the tree's discovery. Most of the other vegetation has been cut, and most of the area is no longer suitable ground for seedlings. Between 1950 and 1980 several hundred were logged in Metasequoia Valley, some over 2 meters (6.5 feet) wide. A survey in the 2000's counted and measured all wild dawn redwoods. The remaining healthy trees range from 25 cm (10 in) to 1.65 m (5.4 ft) wide at breast height, 12-51 m (39.5-167.5 ft) in height, and estimated 41-265 years in age. The average size was 27 m (88.5 ft) tall and 0.45-0.9 m (1.5-3 ft) wide at breast height, with an estimated age of about 95 years. (The type tree, 2.48 m (8 ft) at breast height, was in poor health and therefore excluded from the study) No seedlings were found, and if they ever do appear it is legal to remove and transplant them. The species will continue to live in yards, parks and on roadsides all over China, but the M. glyptostroboides forest ecosystem could disappear when its mature trees die.
Since the tree's rediscovery in 1943, the dawn redwood has become a popular ornamental tree in parks and gardens worldwide.
Dawn redwood has proved an easy tree to grow in temperate regions, and is now widely planted as an ornamental tree. Planted trees have already reached at least up to 1.84 meters (6 feet) in diameter at breast height and 41.15 meters (135 feet) tall, despite being in cultivation for only 70 years. This rapid rate of growth has led to consideration for using the tree in forestry plantations. It has been discovered that M. glyptostroboides will thrive in standing water, much like Bald Cypress, and if left branched to the ground in full sun, will develop the large, contorted boles that have made it famous. Limbing or pruning at an early age will prohibit this formation later on.
In cultivation, M. glyptostroboides is hardy to USDA Zone 5, making it hardy down to lows of -25 °F (-32 °C). It is tolerant of soggy, waterlogged soils; in the wild it is adapted to growing on flood plains. Until it is established in a specific site, it is prone to drought and inadequate water availability. The dawn redwood is recommended for urban areas in the Midwest, Southeast, and East Coast of North America, as its fast growth rate and tolerance for air pollution make it widely adaptable and able to thrive where other species might suffer. This species tends to struggle without irrigation in arid climates such as the American West unless planted directly on or adjacent to a body of water such as a pond or stream. This species is also highly susceptible to damage from contact with heavy amounts of winter de-icing salt.
In the 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. Many sources claim that the original 1947 seedlots came from as few as one tree, however this has proven to be false. The original seeds did have a wide range of source trees, and the inbreeding depression is more likely to come from self-pollination by isolated trees. However, the total cultivated population still had less genetic variation than the wild ones, and more widespread seed-collecting expeditions in China in the 1990s sought to resolve this problem and restore genetic diversity to cultivated M. glyptostroboides.
The dawn redwood is frequently encountered across the UK. Growth has been fastest in the south-east, but it is believed the tree may have a longer future in the more humid western regions. The TROBI Champions are at Woking Park, Surrey: 22 m height by 144 cm d.b.h, Clare College, Cambridge: 21 m × 129 cm (planted 1949), and Wayford Woods, Somerset: 32 m × 99 cm.
Dawn redwoods thrive over a large, crescent-shaped region that encompasses the eastern and southern United States. Many institutions, such as the Arnold Arboretum of Harvard University have fine specimens, but the Crescent Ridge Dawn Redwoods Preserve in North Carolina remains the only endeavor for the re-introduction of the species into a natural setting in the US.
There is a small grove of dawn redwoods at Bailey Arboretum in Locust Valley, NY, including one tree which is claimed to be the world's largest by diameter. The New York City Department of Parks and Recreation has begun planting dawn redwoods on sidewalks throughout Manhattan and Brooklyn.
Displaying autumn foliage in Victoria, British Columbia, Canada