Forest and Shade Trees of Iowa

Promising Trees for Iowa

374 n a t u r a l h i s t o r y a n d u s e s o f i o wa’s t r e e s Lindens are usually trouble-free, but the smooth, thin bark of younger trees is sometimes damaged by sunscald or cracking during winter. Borers and various leaf-feeding insects can also become a problem. Elms, Ulmus L. American Elm, U. americana L. Slippery Elm, U. rubra Muhl. Rock Elm, U. thomasii Sarg. Siberian Elm, U. pumila L. Chinese or Lacebark Elm, U. parvifolia Jacq. Oaks are known for their acorns, maples for their fall color, and elms, unfortunately , for a disease. Because of that disease, younger Iowans may never appreciate how common elms were, how beautiful they were, and how much they Littleleaf linden has an attractive symmetrical crown. f l o w e r i n g t r e e s 375 were favored as shade trees. Their demise ranks among the saddest chapters in America’s botanical history. The culprit is Dutch elm disease, originally from Asia but accidentally introduced to America from Europe. It is caused by a fungus, spread overland by elm bark beetles and in close quarters by root grafts between trees. Though most large elms are now gone, the disease is still here and always will be, killing trees as they grow large enough to attract the beetles. Since infected elms cannot be cured, prevention is the only option. Prompt removal of diseased and dead trees is essential, and where elms are growing close together, trenching to destroy root grafts between trees is recommended. Individual trees can be injected with a systemic fungicide. While greatly reduced in numbers, our native elms are still with us. They are prolific seeders and new trees continually appear in forest edges, waste places, and the woodland understory. Three species are native here. The best known is the American elm, once the most popular shade and street tree in America. Vigorous, adaptable, and easy to grow, it was beloved for its handsome foliage and graceful, vase-shaped crown. It was also common in nature, especially in floodplain forests. While a few large trees remain —possibly resistant to disease but more likely just lucky—streets lined with elms are a thing of the past. Slippery elm was not much planted as a shade tree, but large trees were common in the wild. Its rough leaves make it seem oddly named, but it is another part of the tree—its inner bark—that gave it its name. This has soothing properties and was once widely used as a wound dressing, poultice, and sore throat remedy. The species is also called red elm because its heartwood has a reddish cast. The third species is the rock elm, which was always less common than the others, even before European American settlement. Today it is rare, growing near streams and at the bases of moist wooded slopes or, less commonly, on rocky slopes and limestone bluffs. All three are valued for their hard, heavy, strong, and tough wood, which has interlocked grain and is thus difficult to split. Important uses include veneer , barrel staves, hockey sticks, and furniture, especially bent parts such as rockers and arms. Rock elm was once widely used for iceboxes, washing machines , and kitchen furniture because it is so strong and easily cleaned. It was also the preferred material for the hubs and spokes of automobiles during the early days of the industry. 376 n a t u r a l h i s t o r y a n d u s e s o f i o wa’s t r e e s If you encounter a large, healthy elm in Iowa today, chances are good that it is the introduced Siberian elm or a hybrid between it and the slippery elm. Though less attractive than the American elm, these are tough, adaptable trees that are resistant to Dutch elm disease. Unfortunately, Siberian elm does not age gracefully, and like most other fast-growing trees, it has weak, brittle wood that breaks easily in storms. It is also subject to leaf-eating insects, has no appreciable autumn color, and is very weedy. Siberian elm is often called Chinese elm, a name more properly applied to another species of tree. Its foliage resembles that of Siberian elm, but its flowers and fruits appear...