Rock Elm
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| Ulmus thomasii Sarg. |
Rock Elm Ulmus thomasii, also known as 'Cork Elm', is an elm native to eastern and central North America. The tree ranges from southern Ontario and Quebec, south to Tennessee, west to northeastern Kansas, and north to Minnesota. Its preferred habitat is moist but well-drained sandy loam, loam, or silt loam soil, mixed with other hardwoods. However, it also grows on dry uplands, especially on rocky ridges and limestone bluffs. The tree grows from 15-30 m tall and may live up to 300 years. It is moderately shade-tolerant. Like most North American elms, the Rock Elm is very susceptible to Dutch elm disease.
The leaves and are 5-10 cm long and 2-5 cm wide. They are asymmetrical with a round base and a tapering point, and have a hairy underside and incurved teeth. The leaf surface is shiny dark-green, turning bright yellow in autumn. The crown is cylindrical and upright with short branches, and is narrower most other elms. Rock Elm is also unusual among elms in that it usually has a monopodial growth habit. The bark is grey-brown and deeply furrowed into scaly, flattened ridges. Many older branches have 3-4 irregular thick corky wings. It is for this reason that the Rock Elm is sometimes called the Cork Elm. The petal-less, wind pollinated flowers are red-green and appear in racemes up to 40 mm long two weeks before the leaves from March to May, depending on the tree's location. The fruit is a broad egg-shaped key (samara) 13-25 mm long covered with fine hair. They are notched at the tip, maturing during May or June to form drooping clusters at the leaf bases.
The wood is the hardest and heaviest of all elms, and where forest grown remains comparatively free of knots and other defects. It is also very strong and takes a high polish, consequently it was once in great demand in America and Europe for a wide range of uses, notably shipbuilding, furniture, agricultural tools, and musical instruments. Much of the timber's strength is derived from the tight grain arising from the tree's very slow rate of growth, the trunk typically increasing in diameter by less than 2 mm a year. Over 250 annual growths were once counted in a log 24 cm square being sawn for gunwales in an English boatyard, while a tree planted at Kew Gardens, London, attained a height of only 12 m in 50 years.
Wholly unsuited to the more temperate, maritime climate of northern Europe, the Rock Elm is extremely rare in cultivation across the Atlantic. In the UK only one specimen is known to survive, in the NCCPG elm collection [1] held by Brighton & Hove City Council.
The tree was named in 1902 for David Thomas, an American civil engineer.
[edit] See also
[edit] References
- Bean, W. J. (1981). Trees and shrubs hardy in Great Britain, 7th edition. Murray, London.
- Elwes, H. J. & Henry, A. (1913). The Trees of Great Britain & Ireland. Vol. VII. pp 1848-1929. Private publication. [2]
- White, J & More, D. (2003). Trees of Britain & Northern Europe. Cassell's, London.
- Rock Elm, eNature.com
- Ulmus thomasii Sarg
- Rock Elm - domtar.com
- Rock Elm (Ulmus thomasii) - Wisconsin Department of Natural Resources
- Flora of North America: Ulmus thomasii RangeMap:
