American Elm (Ulmus americana)

A deciduous tree from the Elm Family (Ulmacea)

American Elm, once a stately and magnificent tree that lined America's city streets, has partly followed in the footsteps of the American Chestnut, with many large American Elms succumbing to Dutch Elm disease. This pathogen (transmitted by the elm bark beetle) plugs the vascular system of the tree, preventing the flow of water and nutrients and slowly killing it. However, young trees are immune to the disease, and many reach reproductive age before falling victim to this foreign fungus.

Also known as White Elm (probably in reference to the creamy white wood), this large, vase-shaped tree is native to the entire eastern and central portions of the United States, extending into southern Canada. It is found throughout all of Ohio, primarily in moist sites such as bottomlands and ravines, but commonly seen in open fields, fencerows, and open woodlots, where the ground is dry in summer. Its arching canopy is majestic at maturity, but most trees now die by the time they reach 40 feet tall. Individual specimens, isolated from other Elms, may reach 80 feet tall by 60 feet wide. As a member of the Elm Family, it is related to Hackberry, Zelkova, and the numerous other Elms.

Planting Requirements- American Elm prefers moist, deep, rich soils of variable pH, but can tolerate soils that are dry and of average composition. Its winged seeds readily disperse over a wide area in spring, and the root structure of seedlings is initially taprooted, but quickly develops into a fibrous system that transitions to shallow roots with age (as is typical of species that like moist soils). It thrives in full sun to partial sun, and is found in zones 3 to 9.

Potential Problems- American Elm has been devastated by infection with Dutch elm disease, and fully mature specimens are getting harder to find. Isolation of trees (to reduce the spread of the fungus from infected trees, transmitted by both flying beetles and by roots that can graft between adjoining trees) is the best first line of defense, followed by annual spraying programs.

American Elm is also subject to elm phloem necrosis, which has symptoms similar to Dutch elm disease. In addition, the Elms in general are subject to numerous pests and pathogens which adversely impact their foliage, bark, wood, and roots, with the effects ranging from seasonal cosmetic blemishes, to serious threats to tree health.

Leaf Identification Features

Like almost all Elms, the alternate leaves of American Elm have asymmetrical bases, doubly serrated margins, and prominent veins that run straight out to the edge of the leaf. American Elm has leaves that vary tremendously in size from one tree to another, but all are elliptical to ovate, and have leaves that are usually smooth (but occasionally slightly rough) on their upper surfaces.

Fall color is usually green and chartreuse, with occasional golden or yellow leaves interspersed in the canopy.

Other Identification Features

American Elm is one of the first trees to come into flower, with floral bud swelling often beginning to occur in the few warm days of January into early February, with fully opened flowers usually occurring by mid-March and continuing into April. The perfect, creamy-brown to greenish red flowers do not have petals, but are noticeable because they sway on long pedicels in the winds of March, when most other trees are devoid of any type of growth.

The perfect flowers soon develop into small, oval, flat fruits (samaras), each of which has a distinctive notch and tiny hairs at the edge of the papery fruit. Fruits abscisce soon after maturation in mid-spring.

Twigs of American Elm have two types of buds, easily distinguished in late winter. The floral buds (already beginning to swell) occur at the base of the previous season's twig growth, while the vegetative buds remain dormant for a longer period of time, and are at the top of the twig. Twigs are generally smooth or only slightly pubescent.

The bark of American Elm develops flattened ridges with intervening furrows, having a gray-brown coloration. Ridges may be straight on younger bark, but may interlace on mature bark. American Elm is characterized by its stereotypical vase shape; a straight trunk that quickly divides into several massive branches, which then spread to form an overall vase shape, with some of the outer branchlets arching almost back to the ground, for a very graceful mature growth habit. Some forms of American Elm have different shapes, however, including a spreading form and an upright form.