Identifying characteristics:
The American elm, a graceful, attractive tree, grows 75 to 100 feet tall.
The trunk of a mature tree usually branches at a height of 10 to 15 feet
and the vase-shaped crown is open-growing with drooping peripheral branchlets
that give the tree a weeping appearance. The elliptic leaves
are firm, dark green, smooth (sometimes rough) above and paler and usually
hairy below. They are simple, alternate and 3 to 6 inches long, with coarsely,
doulbly-serrate margins and conspicuously unequal leaf bases. The principal
veins, as is typical of elms, run straight to the teeth. Fall color is bright
yellow and color intensity varies from year to year. The small, greenish-red,
apetalous flowers are produced
on short, drooping stalks, in clusters of 3 or 4, in spring before the leaves
unfold. Trees usually do not flower until about 35 to 40 years of age. The
greenish-red fruit is a one-seeded,
oval samara with hairy margins, a deep notch at the top and a diameter of
0.5 inches. Fruits have a distinct seed cavity and mature in spring, from
May to June. The buds, which sit to one side above the leaf scars,
are covered with 6 to 10 red-brown scales with darker margins, arranged
in 2 vertical rows. A terminal bud is absent. Leaf scars are half
round with 3 distinct bundle scars, forming a "cat-face." The
grayish-brown bark is divided into
flat-topped ridges enclosing diamond-shaped furrows, but sometimes without
any distinct pattern. The outer bark in cross section shows alternating,
irregular white and red-brown layers.
Similar species:
- other elms (Ulmus sp.)
- ironwood (Ostrya virginiana)
Ecology:
Distribution: This is an eastern species, ranging from southern
Canada to central Florida, west to the foot of the Rocky Mountains. It is
native throughout Iowa.
Habitat: Hardy from zone 2 to 9, the American elm prefers rich, moist soils along river valleys and is absent in mountainous areas and on high land. It once dominated the flood plains of Iowa, and young trees (not yet attractive to bark beetles) may still be found there. It adapts to a variety of conditions and is moderately shade tolerant, moderately pH tolerant and soil salt will not adversely affect this species. Elm bark beetles are responsible for spreading Dutch elm disease. This disease, first seen in the Netherlands in 1919, was introduced to the US from Europe and causes wilting, yellowing, leaf curl and eventual death of infected trees. Dark flecks are visible in infected sapwood near the bark in cross sections of twigs. This disease has killed over 40 million landscape elms in the US since the 1920's. There is no cure, but early community-wide detection, sanitation and removal of affected trees can limit its spread. Cultivars resistant to the disease are available for purchase, but none equal the beauty of the true species. Bacterial wetwood, Verticillium wilt, cankers, elm case borer, elm leaf miner and elm borer may also be problematic.
Uses:
Wood: The wood is pale, and therefore this species is often
referred to as the "white elm." This was once the most important
timber elm in the US. The wood is strong, tough, hard, heavy and coarse-grained.
It was used for veneer, durable flooring, sporting goods, ship-building,
barrel staves and for the bent parts of furniture. The wood holds screws
well and was widely used for boxes and crates. Native Americans used the
bark to make ropes and the wood for canoes.
Wildlife: Elms are relatively unimportant to wildlife compared to oaks, maples and dogwoods. Songbirds, gamebirds and rodents feed on the seeds and buds. Deer and rabbits eat the twigs and buds and elms are often used as nesting sites by a variety of birds. This species was the favorite nesting tree of the Baltimore oriole.
Horticulture: With a tall, graceful outline and casting excellent shade, the American elm was once the most popular tree for street and yard planting in America. Cultivars resistant to Dutch elm disease, have replaced this tree in landscape use, although some so-called resistant cultivars have, with time, also succumbed to the disease. 'American Liberty' is reportedly a resistant form of U. americana; 'Urban Elm,' a cross between U. hollandica (from the Netherlands) and U. ameri (from Siberia) is a resistant form with an upright habit; and 'Delaware #2' is a highly resistant cultivar.
