American Elm (New York City EcoFlora Volunteer Guide)

American Elm

Ulmus americana

Summary ⁵

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, naturally occurring from Nova Scotia west to Saskatchewan 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 43 m (140 ft), with a d.b.h of 196 cm (6.43 ft) before succumbing to Dutch elm disease; when it was felled in 1968, a tree-ring count established that it had germinated in 1701.

At the Garden ⁶

American elms can be found in the Thain Family Forest.

Description ⁷

The American elm is a deciduous hermaphroditic tree which, before the introduction of Dutch elm disease, commonly grew to > 30 m (100 ft) tall with a trunk > 1.2 m (4 ft) d.b.h supporting a high, spreading umbrella-like canopy. The leaves are alternate, 7–20 cm long, 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. Ploidy (2n = 56, or more rarely, 2n = 28).

Central Park stand ⁷

New York City's Central Park is home to approximately 1,200 American elms, which constitute over half of all trees in the park. The oldest of these elms were planted during the 1860s by Frederick Law Olmsted, making them among the oldest stands of American elms in the world. The trees are particularly noteworthy along the Mall and Literary Walk, where four lines of American elms dramatically stretch over the walkway forming a cathedral-like covering. The elms are an important part of New York City's ecology by improving air and water quality, reducing erosion and flooding, and lowering the air temperature during the hottest days of the year.

While still vulnerable to the highly contagious Dutch elm disease, in the 1980s the Central Park Conservancy undertook aggressive counter-DED measures such as heavy pruning and removal of extensively diseased trees. These efforts have largely been successful in saving the majority of the trees, although several are still lost each year. Younger American elms which have been planted in Central Park since the outbreak are of the "Princeton" and "Valley Forge" variety of DED-resistant elms.

Sources and Credits

(c) tminatbe, some rights reserved (CC BY-NC), uploaded by tminatbe
(c) Charlie Hohn, some rights reserved (CC BY), uploaded by Charlie Hohn
François André Michaux (book author), Augustus Lucas Hillhouse (translator), Bessa (illustrator), Gabriel (engraver), no known copyright restrictions (public domain), http://commons.wikimedia.org/wiki/File:NAS-126_Ulmus_americana.png
(c) En el nido (Nest), some rights reserved (CC BY), http://commons.wikimedia.org/wiki/File:Ulmus_Rubra_or_Ulmus_Americana_-_panoramio.jpg
(c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Ulmus_americana
(c) bkmertz, some rights reserved (CC BY-SA)
Adapted by bkmertz from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Ulmus_americana

More Info

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American Elm

Summary 5

At the Garden 6

Description 7

Central Park stand 7