American Elm
|
|
| American Elm | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Missing image Img_ulmus_americana_2209.jpg Ulmus americana (American Elm) | ||||||||||||||
| Scientific classification | ||||||||||||||
|
The American Elm Ulmus americana is a species of elm native to eastern North America, occurring from Nova Scotia west to southeast Saskatchewan, and south to Florida and central Texas. It is also sometimes known as White Elm or American White Elm.
It is a deciduous tree, reaching 20-35 m tall with a trunk up to 1-2 m diameter. The crown forms a high, spreading canopy with open air space beneath. The leaves are alternate, 7-15 cm long, with double-serrate margins and an oblique base. The flowers are small, purple-brown with no petals, and produced in early spring before the leaves. The fruit is a flat samara 2 cm long and 1.5 cm broad, with a circular wing surrounding the single 4-5 mm seed; like the closely related European White Elm U. laevis, the flowers and seeds are borne on 1-3 cm long stems.
American Elm has been seriously affected by an introduced fungal disease, Dutch elm disease, with heavy mortality in most of the range.
Cultivation and uses
In years past, it was used widely as a shade tree and street tree because of its graceful, arching, vase-like growth form and its tolerance of stress from the hustle and bustle below. Furthermore, the cross-grained wood gives a level of strength to the branches that resists easy breaking.
Dutch elm disease devastated the American Elm, causing catastrophic die-offs in cities across the range. Once this disease infected one tree on a street, all the other trees close to it would die quickly because the fungus would infect them via the roots through root grafts that the trees had formed. There still are many American elms in the woods, but in cities, the ones that survived were generally ones that were isolated from other elms. An excellent example of this is Central Park in New York City: there is a beautiful large stand of several elms near the center of the park originally planted by Frederick Law Olmstead, but these elms are a rarity indeed as neighboring areas in New York had large die-offs. (To this day these are not impervious to disease.)
Such cities as Kansas City, Missouri, had used mostly American elms in planting its city streets, and had some of the best-shaded residential streets in the nation until the disease almost obliterated these plantings in the late 1960s and early 1970s.
Attempts have been made over the last few decades to breed disease-resistant elms. The Liberty elm is one example. "Valley Forge" and "Princeton" are two other examples of cultivars, and to date have been used in plantings in Washington, D.C.
Trees commonly used as substitutes for American elms are Zelkova and Chinese Elm.