american elm (ulmus americana)
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Ulmus americana, generally known as the American elm or, less commonly, as the white elm or water elm, is a species native to eastern North America, occurring from Nova Scotia west to Alberta and Montana, and south to Florida and central Texas. The American elm is an extremely hardy tree that can withstand winter temperatures as low as −42 °C (−44 °F). Trees in areas unaffected by Dutch elm disease can live for several hundred years. A prime example of the species was the Sauble Elm, which grew beside the banks of the Sauble River in Ontario, Canada, to a height of 140 feet, with a DBH of 6.43 feet before succumbing to Dutch elm disease; when it was felled in 1968, a tree-ring count established that it had germinated in 1701.
Classification
Ulmus americana was first described and named by Carl Linnaeus in his Species Plantarum, published in 1753. No subspecies or varieties are currently recognized within the species.
Description
The American elm is a deciduous hermaphroditic tree which, before the introduction of Dutch elm disease, commonly grew to > 100 feet tall with a trunk > 4 feet, with the trunk supporting a high, spreading umbrella-like canopy. The leaves are alternate, with double-serrate margins and an oblique base. The perfect flowers are small, purple-brown and, being wind-pollinated, apetalous. The flowers are also protogynous, the female parts maturing before the male, thus reducing, but not eliminating, self-fertilization, and emerge in early spring before the leaves. The fruit is a flat samara 2 cm long by 1.5 cm broad, with a circular papery wing surrounding the single 4–5 mm seed. As in the closely related European White Elm Ulmus laevis, the flowers and seeds are borne on 1–3 cm long stems. American Elm is wholly insensitive to daylight length (photoperiod), and will continue to grow well into autumn until injured by frost. U. americana is unique within the genus in being tetraploid, i.e. having double the usual number of chromosomes (2n = 56).
Ecology
The American elm occurs naturally in an assortment of habitats, most notably rich bottomlands, floodplains, stream banks, and swampy ground, although it also often thrives on hillsides, uplands and other well-drained soils. On more elevated terrain, as in the Appalachian Mountains, it is most often found along rivers. The species' wind-dispersed seeds enable it to spread rapidly as suitable areas of habitat become available. American elm produces its seed crop in late spring (which can be as early as February and as late as June depending on the climate) and the seeds usually germinate right away with no cold stratification needed (occasionally some might remain dormant until the following year). The species attains its greatest growth potential in the northeastern US, while elms in the Deep South and Texas grow much smaller and have shorter lifespans, although conversely their survival rate in the latter regions is higher due to the climate being unfavorable for the spread of DED.In the United States, the American elm is a major member of four major forest cover types: black ash-American elm-red maple; silver maple-American elm; sugarberry-American elm-green ash; and sycamore-sweetgum-American elm, with the first two of these types also occurring in Canada. A sugar maple-ironwood-American elm cover type occurs on some hilltops near Temiscaming, Quebec.
Classification
Ulmus americana was first described and named by Carl Linnaeus in his Species Plantarum, published in 1753. No subspecies or varieties are currently recognized within the species.
Description
The American elm is a deciduous hermaphroditic tree which, before the introduction of Dutch elm disease, commonly grew to > 100 feet tall with a trunk > 4 feet, with the trunk supporting a high, spreading umbrella-like canopy. The leaves are alternate, with double-serrate margins and an oblique base. The perfect flowers are small, purple-brown and, being wind-pollinated, apetalous. The flowers are also protogynous, the female parts maturing before the male, thus reducing, but not eliminating, self-fertilization, and emerge in early spring before the leaves. The fruit is a flat samara 2 cm long by 1.5 cm broad, with a circular papery wing surrounding the single 4–5 mm seed. As in the closely related European White Elm Ulmus laevis, the flowers and seeds are borne on 1–3 cm long stems. American Elm is wholly insensitive to daylight length (photoperiod), and will continue to grow well into autumn until injured by frost. U. americana is unique within the genus in being tetraploid, i.e. having double the usual number of chromosomes (2n = 56).
Ecology
The American elm occurs naturally in an assortment of habitats, most notably rich bottomlands, floodplains, stream banks, and swampy ground, although it also often thrives on hillsides, uplands and other well-drained soils. On more elevated terrain, as in the Appalachian Mountains, it is most often found along rivers. The species' wind-dispersed seeds enable it to spread rapidly as suitable areas of habitat become available. American elm produces its seed crop in late spring (which can be as early as February and as late as June depending on the climate) and the seeds usually germinate right away with no cold stratification needed (occasionally some might remain dormant until the following year). The species attains its greatest growth potential in the northeastern US, while elms in the Deep South and Texas grow much smaller and have shorter lifespans, although conversely their survival rate in the latter regions is higher due to the climate being unfavorable for the spread of DED.In the United States, the American elm is a major member of four major forest cover types: black ash-American elm-red maple; silver maple-American elm; sugarberry-American elm-green ash; and sycamore-sweetgum-American elm, with the first two of these types also occurring in Canada. A sugar maple-ironwood-American elm cover type occurs on some hilltops near Temiscaming, Quebec.
American elm. (2007, July 6). In Wikipedia, The Free Encyclopedia. Retrieved 00:30, October 17, 2014, from http://en.wikipedia.org/w/index.php?title=American_elm&oldid=142939879