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Ulmus americana (L.) Carr. American elm

Leaf showing the strong parallel secondary veins that end in a large forward-pointing tooth that has secondary toothing along its outer edge

Also known as: white elm.

Habitat

White elm occurs on lowlands and bottomlands, often where spring flooding occurs. It occurs in river valleys and on moist soils along streams, but grows best where soils are rich and reasonably well drained.

Mature tree

Form

White elm has a distinctive, vase-shaped form, in that the stout stem often divides into several large upwardly and outwardly arching branches that form a wide- spreading rounded, umbrella-like crown. The trees may grow to heights of over 30 m and stem diameters may be up to 120 cm. Larger stems are usually buttressed at the base.

Morphology

Twigs showing lateral and pseudo-
termnal buds

The leaves are deciduous, simple and arranged alternately along the shoots. Each is 6–5 cm long, elliptic-oblong to obovate, often inequilateral, especially near the base, and drawn in to a short point at the tip. The margins are coarsely doubly to triply toothed, with each large tooth, reached by a nearly straight secondary vein, hooked forward. The upper leaf surface may be rough to the touch, because of short, stiff, forwardly pointed bristles, and the lower surface may be somewhat hairy.

The greyish-brown twigs are slightly hairy and often zigzagged. The end bud, a pseudoterminal bud, is usually angled over the tip of the twig, and lateral buds tend to be appressed to the twig. The reddish-brown buds are ovoid and round tipped with overlapping scales that have hairy and darker margins. The buds are often somewhat offset from the small, oval V-shaped leaf scars which each have three vein scars.

Fruits ripen and start to fall as leaves expand

In spring, before the leaves expand, the crowns of older trees thicken with clusters of pale yellowish flowers. From these, fruits develop quickly, ripen, and fall by the time that the leaves have nearly expanded to full size. Each fruit has a flat, nearly circular wing with a hairy fringe, attached around the lower central seed pocket that contains one seed.

Fruits rapidly developing as shoot buds near the bursting stage

 The bark is smooth and grey when young, but quite quickly becomes greyish brown with obliquely intersecting flat ridges. In old age, the broad ridge tops become ashy grey and scaly. Broken surfaces of outer bark frequently show alternating dark brown and orange- brown bands.

Fruits showing their fringed edges and splits in the wings at their ends

Notes

The yellowish-brown, ring-porous, hard wood of white elm has an attractive grain, making it suitable for panelling, furniture, and veneer. It is also used for caskets and in boat building.

White elm was formerly a common tree in lowland areas and in towns and cities where it was often planted as a shade tree.

Bark of stem, 28 cm in diameter

Dutch elm disease, an introduced fungal disease that is spread by elm bark beetles, arrived in New Brunswick at Woodstock in 1957. In the years that followed, the disease spread rapidly and intensified along the St. John River Valley. It was common for tree losses to exceed 90% in only 8 years.

Sanitation, the practice of removing any dead or decadent trees and careful pruning of the healthy trees, eliminated the breeding material for the elm bark beetles and controlled the spread of Dutch elm disease. This has been demonstrated in the City of Fredericton, with its large population of century-old elms, which has had a consistent sanitation program since before the disease arrived in 1961. The City has retained over one half of its elms even though Dutch elm disease has been present for nearly 40 years.

Elm is still regenerating along streams and rivers in New Brunswick. Unfortunately, as soon as an elm reaches the sapling stage, elm bark beetles move in carrying Dutch elm disease, and the young tree is infected and dies.