Ulmus americana L. American Elm Ulmaceae Elm family Calvin F. Bey American elm (Ulmus americana), also known as varies from none in Florida to about 200 cm (80 in> white elm, water elm, soft elm, or Florida elm, is in the Northeast. A few areas, mainly around the most notable for its susceptibility to the wilt fungus, Great Lakes, get 254 to 380 cm (100 to 150 in) of Ceratocystis ulmi. Commonly called Dutch elm dis- snow per year. ease, this wilt has had a tragic impact on American The average frost-free period is about 80 to 160 elms. Scores of dead elms in the forests, shelterbelts, days for the northern tier of States and Canada to and urban areas are testimony to the seriousness of about 200 to 320 days for the gulf coast and the disease. Because of it, American elms now com- Southeastern States. prise a smaller percentage of the large diameter trees in mixed forest stands than formerly Neverthe- Soils and Topography less, the previously developed silvical concepts remain basically sound. American elm is most common on flats and bottom lands throughout its range but is not restricted to Habitat these sites. On the southern bottom-land region, it is found widely in first bottoms and terraces, especially Native Range on first bottom flats, but not in deep swamps. At higher elevations in the Appalachians, it is often American elm (figs. 1,2> is found throughout East- limited to the vicinity of large streams and rarely ern North America. Its range is from Cape Breton appears at elevations above 610 m (2,000 ft). In West Island, Nova Scotia, west to central Ontario, Virginia, however, it does appear in high coves at southern Manitoba, and southeastern Saskatchewan; elevations of 760 m (2,500 ft). In the Lake and south to extreme eastern Montana, northeastern Central States, it is found on plains and morainal Wyoming, western Nebraska, Kansas, and Oklahoma hills as well as on bottom lands and swamp margins. into central Texas; east to central Florida; and north Along the northwestern edge of the range, it is usual- along the entire east coast. ly restricted to valley bottoms along watercourses. Although American elm is common on bottom-land Climate soils, it is found on many of the great soil groups within its range. The soils include well-drained Within the natural range of American elm, the sands, organic bogs, undifferentiated silts, poorly climate varies from warm and humid in the drained clays, prairie loams, and many intermediate southeast to cold and dry in the northwest. Average combinations. temperatures are as follows: January, from -18” C American elm grows best on rich, well-drained (O” F) and below in Canada and 16” C (60” F) in loams. Soil moisture greatly influences its growth. central Florida; July, from 16” C (60” F) in Manitoba Growth is poor in droughty sands and in soils where to 27” C (SO’ F) in the Southern States; annual max- the summer water table is high. In Michigan, on imum, 32” C (90” F) to 35” C (95” F) in the Northeast loam and clay soils, growth is good when the summer and 38” C (100’ F) to 41” C (105” F) in the South and water table drops 2.4 to 3.0 m (8 to 10 ft) below the West; annual minimum, from -40” C (40” F) to -18” surface, medium with summer water table at 1.2 to C (0’ F) in the North and -18” C (0” F) to -1” C (30” 2.4 m (4 to 8 ft), and poor when topsoil is wet F) in the South. throughout the year. On sandy soils underlain with Average annual precipitation varies from a scarce clay, growth is medium to good where the summer 380 mm (15 in) in the Northwest to a plentiful 1520 water table is 0.6 m (2 ft) or more below the soil mm (60 in) on the gulf coast. Over the central part surface. Organic soils are usually poor sites, but of the species range there are about 760 to 1270 mm those with a summer water table at least 0.6 m (2 (30 to 50 in) per year. Throughout the range most of ft) below the surface are classed as medium sites for the precipitation comes during the warm (April-Sep- American elm. tember) season. Average annual snowfall generally In the South, American elm is common on clay and silty-clay loams on first bottoms and terraces; growth is medium on wetter sites and good on well-drained The author is Staff Assistant, Of&e of Deputy Chief for Research, flats in first bottoms (8). In the arid western end of USDA Forest Service, Washington, DC. the range, it is usually confined to the silt or clay 801 Ulmus americana Figure l-The native range ofAmerican elm. loams in river bottoms and terraces. In shelterbelt Soil acidity under stands of American elm varies plantings on the uplands, however, survival is from acid on some of the swamp margin sites in the generally best on sandy soils where the moisture is Lake States to mildly alkaline on the prairie soils. A more evenly distributed to greater depths than in soil reaction considered suitable for this species ran- fine-textured soils. American elm most commonly ges from pH 5.5 to 8.0. grows on soils of the orders Alfisols, Inceptisols, Mol- Leaf litter of American elm decomposes more lisols, and Ultisols. rapidly than that of sugar maple (Acer saccharum), 802 Ulmus americana cover types: Black Ash-American Elm-Red Maple (Society of American Foresters Type 39), Silver Maple-American Elm (Type 621, Sugarberry- American Elm-Green Ash (Type 93), and Sycamore- Sweetgum-American Elm (Type 94). It is a minor component in 20 other forest types. Black Ash-American Elm-Red Maple (Type 39) ap- pears throughout the Northern Forest and into the Boreal Forest in Canada, and throughout the Lake States and into the northern edge of the Central Forest. In this type the most common associates, other than the type species, are as follows: In the Lake States and Canada, balsam poplar (Populus balsamifera), balsam fir (Abies balsamea), and yellow birch (Betula alleghaniensis); in Ohio and Indiana, silver maple (Acer saccharinurn), swamp white oak (Quercus bicolor), sycamore (Platanus occidentalis), pin oak (Quercus palustris), black tupelo (Nyssa syl- vatica), and eastern cottonwood (Populus deltoides); in New England and eastern Canada, sweet birch (Betula lenta), paper birch (B. papyrifera), gray birch (B. populifolia), silver maple, and black spruce (Picea mariana); and in New York, white ash (Fraxinus americana), slippery and rock elms (Ulmus rubra and U. thomasii), yellow birch, black tupelo, sycamore, eastern hemlock (T’suga canadensis), bur oak (Quercus macrocarpa), swamp white oak, and silver maple. Silver Maple-American Elm (Type 62) is common throughout the Central Forest and extends into Canada. Major associates in this type are sweetgum (Liquidambar styraciflua), pin oak, swamp white oak, eastern cottonwood, sycamore, green ash (Fraxinus pennsylvanica), and other moist site hardwoods. Sugarberry-American Elm-Green Ash (Type 93) is found throughout the Southern Forest within the flood plains of the major rivers. Hackberry (Celtis occidentalis) replaces sugarberry 02. Zaeuigata) in the northern part of the range. Major associates are water hickory (Carya aquatica), Nuttall (Quercus nuttallii), Figure 2-Forest-grown American elm. willow (Q. phellos), water (Q. nigra), and overcup (Q. shagbark hickory (Carya ouata), white oak (Quercus lyrata) oak, sweetgum, and boxelder (Acer negundo). alba), and northern red oak (Q. rubra). Under Mis- Sycamore-Sweetgum-American Elm (Type 94) ap- souri conditions, the leaves crumble readily after 18 pears as scattered stands throughout the Southern months on the ground. They have a relatively high Forest region and lower Ohio River Valley. Common content of potassium and also of calcium (1 to 2 associates include green ash, sugarberry, hackberry, percent). Because its litter decomposes rapidly and boxelder, silver maple, cottonwood, black willow (Salix contains many desirable nutrients, American elm is nigra), water oak, and pecan (Carya illinoensis). considered a “soil-improving” species. Life History Associated Forest Cover Reproduction and Early Growth Throughout its range, American elm seldom grows in pure stands and is usually found in mixture with Flowering and Fruiting-The process of flower- other species. It is a major component of four forest ing, seed ripening and seed fall in American elm 803 takes place in the spring throughout the range. The temperatures of 30” C (86” F). However, germination glabrous flower buds swell early in February in the is almost as good when daily temperatures range South and as late as May in Canada. The flowers between 10” C (50” F) and 21” C (70” FL Seeds can appear 2 to 3 weeks before leaf flush. Soon after wind germinate in darkness, but germination increases in pollination occurs, the fruit ripens, and seed fall is light. Seeds also can lie on flooded ground for as long usually complete by mid-March in the South and as 1 month with little adverse effect on germination, mid-June in the North. except possibly where siltation occurs in flooded bot- American elm flowers are typically perfect and toms. occur on long, slender, drooping pedicels, about 2.5 American elm seedlings can become established on cm (1 in) long, in 3- or 4-flowered short-stalked fas- moist litter, moss, and decayed logs and stumps, but cicles. The anthers are bright red, the ovary and do best on mineral soil. Although they do grow in full styles are light green, and the calyx is green tinged sunlight, seedlings perform best with about one-third with red above the middle.