Ulmus americana

Ulmus americana, generally known as the American Elm or, less commonly, as the White Elm or Water Elm, is a species native to eastern North America, occurring from Nova Scotia west as far as British Columbia, from northern Alberta at the top of its range, south to Florida and central Texas. It is an extremely hardy tree that can withstand winter temperatures as low as −42 °C (−44 °F). Trees in areas unaffected by Dutch elm disease can live for several hundred years. A prime example of the species was the Sauble Elm [http://www.flyingsquirrels.com/sauble_elm/], which grew in Ontario, Canada, to a height of 43 m (140 ft), with a d.b.h of 196 cm (6.43 ft) before succumbing to Dutch elm disease. Felled in 1968, a tree-ring count established that it had germinated in 1701.

Description

The American Elm is a deciduous tree, which, before the advent of Dutch elm disease, commonly grew to > 30 m (100 ft) tall with a trunk > 1.2 m (4 ft) d.b.h. The crown forms a high, spreading canopy with open air space beneath. The leaves are alternate, 7–20 cm long, with double-serrate margins and an oblique base. The tree is hermaphroditic, having perfect flowers, i.e. with both male and female parts, and is therefore capable of self-pollination. The flowers are small, purple-brown, and, being wind-pollinated, are apetalous; they emerge in early spring before the leaves. The fruit is a flat samara 2 cm long and 1.5 cm broad, with a circular wing surrounding the single 4–5 mm seed. As in the closely related European White Elm, U. laevis, the flowers and seeds are borne on 1–3 cm long stems. American Elm is wholly insensitive to daylight length (photoperiod), and will continue to grow well into autumn until injured by frost . The tree reaches sexual maturity at around 150 years of age and is unique within the genus in being tetraploid, i.e. having double the usual number of chromosomes. However, nowadays it is uncommon for the tree to reach over 100 years of age, such is its susceptibility to Dutch elm disease. The American Elm is the state tree of both Massachusetts and North Dakota

Cultivation and uses

In years past, the American Elm was used widely as a shade tree and as a street tree, because of its graceful, arching, vase-like growth form and its tolerance of most stress factors Furthermore, the cross-grained wood imbues the branches with great strength, and breakages were rare. The species has been planted beyond its natural range as far north as central Alberta, and south to Lake Worth, Florida. It also survives low desert heat at Phoenix, Arizona.

Introductions across the Atlantic rarely prospered, even before the outbreak of Dutch elm disease. Introduced to the UK in 1752, it was noted that the foliage of the American Elm was far more susceptible to insect damage than native elms . A few, mostly young, specimens survive in British arboreta. Introduced to Australasia, the tree was listed by nurseries in Australia in the early 20th century, and is known to have been planted along the Avenue of Honour at Ballarat and the Bacchus Marsh Avenue of Honour. It is only rarely found in New Zealand .

Ecology

The American Elm occurs naturally in an assortment of conditions, most notably on bottomlands and floodplains, although it also can thrive in well-drained soils. On more elevated terrain, as in the Appalachian Mountains, it often prefers to grow along streams. In the United States, it is a major member of four cover types: Black Ash-American Elm-Red Maple; Silver Maple-American Elm; Sugarberry-American Elm-Green Ash; and Sycamore-Sweetgum-American Elm. The first two of these types also occur in Canada.[http://www.na.fs.fed.us/spfo/pubs/silvics_manual/Volume_2/ulmus/americana.htm] Some hilltops near Témiscaming, Quebec, have a Sugar Maple-Ironwood-American Elm cover type The leaves of the American Elm serve as food for the larvae of various Lepidoptera. See List of Lepidoptera that feed on elms.

Pests and diseases

The American Elm is highly susceptible to Dutch elm disease (DED) and Elm Yellows; it is also moderately preferred for feeding and reproduction by the adult Elm Leaf Beetle Xanthogaleruca luteola [http://www.bioone.org/doi/full/10.1603/0022-0493%282001%29094%5B0162%3AROTCEU%5D2.0.CO%3B2], and highly preferred for feeding by the Japanese Beetle Popillia japonica [http://www.bioone.org/doi/full/10.1603/0022-0493%282001%29094%5B0445%3APOTCEU%5D2.0.CO%3B2] [http://www.sunshinenursery.com/survey.htm] in the USA. Trees grown in Europe have proven very susceptible to damage by leaf-feeding insects in general, far more so than native or Asiatic elms .

U. americana is also the most susceptible of all the elms to verticillium wilt , whose external symptoms closely mimic those of DED. However, the condition is far less serious, and the tree should recover the following year.

Dutch Elm Disease

DED is a fungal disease which has ravaged the American Elm, causing catastrophic die-offs in cities across the range. It has been estimated that only approximately 1 in 100,000 American elm trees is DED-tolerant, most known survivors simply having escaped exposure to the disease [http://www.ars.usda.gov/is/AR/archive/jul96/elms0796.htm]. However, in some areas still not populated by the Dutch Elm disease-carrying Elm bark beetle, the American Elm continues to thrive, notably in Florida, most of Alberta and British Columbia.

The American Elm is particularly susceptible to disease because the period of infection often coincides with the period, approximately 30 days, of rapid terminal growth when new springwood vessels are fully functional. Spores introduced outside of this period remain largely static within the xylem and are thus relatively ineffective .

A fair number of mostly small to medium-sized American Elms survive nowadays in woodlands, suburban areas, and occasionally cities, where most often the survivors had been relatively isolated from other elms and thus spared a severe exposure to the fungus. For example, in Central Park and Tompkins Square Park in New York City , stands of several large elms originally planted by Frederick Law Olmsted survive because of their isolation from neighboring areas in New York where there had been heavy mortality. In Akron Ohio there is a very old elm tree that has not been infected. In historical areas of Philadelphia, Pennsylvania, there are also a few mature American Elms still standing — notably in Independence Square and the Quadrangle at the University of Pennsylvania, and also at the nearby campuses of Haverford College, Swarthmore College, and The Pennsylvania State University, believed to be the largest remaining stand in the country. The large Massachusetts Champion Elm stands on Summer Street in the Berkshire County town of Lanesborough, Massachusetts, kept alive by antifungal treatments. Rutgers University has preserved 55 mature elms on and in the vicinity of Voorhees Mall on the College Avenue Campus in New Brunswick, New Jersey in addition to seven disease-resistant trees that have been planted in this area of the campus in recent years.

The American Elm's biology in some ways has helped to spare it from obliteration by the Dutch elm disease, in contrast to what happened to the American Chestnut with the chestnut blight. The elm's seeds are largely wind-dispersed, and the tree grows quickly and begins bearing seeds at a young age. It grows well along roads or railroad tracks, and in abandoned lots and other disturbed areas, where it is highly tolerant of most stress factors. Elms have been able to survive and to reproduce in areas where the disease had eliminated old trees, although most of these young elms eventually succumb to the disease at a relatively young age. There is some reason to hope that these elms will preserve the genetic diversity of the original population, and that they eventually will hybridize with DED-resistant varieties that are being developed or that occur naturally.

Two species of elm bark beetle, one of them native, are known to carry the disease in North America. Although the European elm bark beetle is known to have occurred across southern and central Alberta, it does not appear to be carrying the disease in these areas.

Some cities such as Kansas City, Missouri, had used mostly American elms in planting its city streets and had had some of the finest shaded residential streets in the nation, until the disease almost obliterated these plantings in the late 1960s and early 1970s. Many cities in the United States still have some surviving American elms, but generally this species requires frequent attention to check for elm bark beetles and DED infection. (The National Park Service often checks on the hundreds of elm trees under its care in the Washington, D.C., area for signs of illness.)

Fungicidal injections can be administered by a qualified arborist to valuable American elms, to prevent the trees' becoming infected. Such injections generally are effective as a preventive measure for up to three years when performed before any symptoms have appeared, but they may be ineffective as a treatment once the disease is not able to be seen.

Cultivars

See the list of Elm cultivars, hybrids and hybrid cultivars for more details.

Numerous cultivars have been raised, originally for their aesthetic merit but more recently for their resistance to Dutch elm disease The total number of named cultivars is circa 45, at least 18 of which have probably been lost to cultivation as a consequence of Dutch elm disease or other factors:

American Liberty, Ascendens, Augustine, Aurea, Beaverlodge, Beebe's Weeping, Brandon, Burgoyne, College, Columnaris, Deadfree, Delaware, Exhibition, Fiorei, Flick's Spreader, Folia Aurea Variegata, Hines, Incisa, Independence, Iowa State, Jackson, Jefferson, Kimley, Klehmii, Lake City, L'Assomption, Lewis & Clark (<tt>Prairie Expedition</tt>), Littleford, Maine, Markham, Minneapolis Park, Moline, Morden, New Harmony, Nigricans, Patmore, Pendula, Penn Treaty, Princeton, Pyramidata, Queen City, Sheyenne, Skinner Upright, Star, Valley Forge, Variegata, Vase, Washington

The National Elm Trial, begun in 2005, is currently evaluating 19 cultivars in scientific plantings across the United States to better assess the strengths and weaknesses of leading cultivars.

The few disease-resistant selections that have been made available to the public as yet include 'Valley Forge', 'New Harmony', 'Princeton', 'Jefferson', and a set of six different clones collectively known as 'American Liberty' . The United States National Arboretum released 'Valley Forge' and 'New Harmony' in late 1995, after screening tests performed in 1992–1993 showed both had unusually high levels of resistance to DED. 'Valley Forge' performed especially well in these tests. 'Princeton' has been in occasional cultivation since the 1920s, and gained renewed attention after its performance in the same screening tests showed it also to have a high degree of DED resistance. A later test performed in 2002–2003 confirmed the DED resistance of these same three varieties, and that of 'Jefferson'. 'Jefferson' was released to wholesale nurseries in 2004 and is becoming increasingly available for planting. Thus far, plantings of these four varieties generally appear to be successful.

In 2005, 90 'Princeton' elms were planted along Pennsylvania Avenue near the White House and to date are healthy and thriving. Introduced to the UK in 2001, 'Princeton' was selected by HRH The Prince of Wales to form the Anniversary Avenue from the Orchard Room reception centre to the Golden Bird statue at his Highgrove residence. In 2007, the [http://www.uoguelph.ca/arboretum/SpProjects/Elm_Recover1.htm Elm Recovery Project]from the University of Guelph in Ontario, Canada, reported that cuttings from healthy surviving old elms surveyed across Ontario had been grown to produce a bank of resistant trees, isolated for selective breeding of highly resistant cultivars [http://www.canada.com/ottawacitizen/news/story.html?id=33e91594-b329-453d-a4d5-62dba22f33b1&p=1] .

Hybrid cultivars

Thousands of attempts to cross the American with the Siberian Elm have failed [http://www.fs.fed.us/database/feis/plants/tree/ulmame/all.html]. Reports of successful artificial hybridization and verification of hybridizing American elm with other elms are rare, and are regarded with taxonomic suspicion. Two allegedly successful hybridizations were: 'Hamburg', and 'Kansas Hybrid', both with the Siberian Elm Ulmus pumila, but it has since been suggested that the American elm in question was more likely to have been the Red Elm Ulmus rubra.

Famous American Elms

An Ohio State Memorial commemorates the Logan Elm, an American Elm that stood at the site where, in 1774, Chief Logan of the Mingo tribe may have delivered a passionate speech - the most famous speech given by a Native American. Chief Logan's speech also may have been delivered by Simon Girty on his behalf at a peace treaty meeting under the Elm.

One of the largest elms in the U. S., the 65 foot tall tree had foliage that spread 180 feet in diameter with a trunk circumference of 24 feet. The Logan Elm died in 1964 from Dutch Elm disease combined with storm damage. To reach the park, where admission is free, travel 5 miles south of Circleville, Ohio, on U.S. route 23 and turn east one mile on State Route 361.

"I appeal to any white man to say, if ever he entered Logan’s cabin hungry and he gave him not meat; if ever he came cold and naked and he clothed him not. During the course of the last, long and bloody war, Logan remained idle in his cabin, an advocate for peace. Such was my love for the whites that my countrymen pointed as they passed and said, "Logan is the friend of white men." I had even thought to live with you but for the injuries of one man. Col. Cresap the last spring in cold blood and unprovoked murdered all the relatives of Logan; not sparing even his women and children. There runs not a drop of my blood in the veins of any living creature. This called on me for revenge. I have sought it. I have killed many. I have fully glutted my vengeance. For my country, I rejoice at the beams of peace. Yet do not harbor the thought that mine is the joy of fear. Logan never felt fear. He will not turn on his heel to save his life. Who is there to mourn for Logan? Not one."

The American Elm in literature

“There was not in the whole countryside another tree which could compare with him. He was matchless. Never a stranger passed the elm but stopped, and stared, and said or thought something about it. Even dull rustics looked, and had a momentary lapse from vacuity. The tree was compelling. He insisted upon recognition of his beauty and grace. Let one try to pass him unheeding and sunken in contemplation of his own little affairs, and lo! He would force himself out of the landscape, not only upon the eyes, but the very soul……” from Six Trees by Mary Eleanor Wilkins Freeman.

“At last, all at once, when I was not thinking of it--I declare it makes my flesh creep when I think of it now--all at once I saw a great green cloud swelling in the horizon, so vast, so symmetrical, of such Olympian majesty and imperial supremacy among the lesser forest growths, that my heart stopped short, then jumped at my ribs as a hunter springs at a five-barred gate, and I felt all through me, without need of uttering the words, 'This is it!' . . . What makes a first-class Elm? Why, size in the first place, and chiefly. Anything over twenty feet of clear girth, five feet above the ground, and with a spread of branches a hundred feet across, may claim, that title, according to my scale.” from The Autocrat of the Breakfast-Table by Oliver Wendell Holmes, Sr.

Accessions

North America
Arnold Arboretum, acc. nos. 250-53 (cult. material), 412-86 wild collected in the USA.
Bernheim Arboretum and Research Forest [http://www.bernheim.org/species_lists.htm], Clermont, Kentucky. No details available.
Denver Botanic Gardens, one specimen, no details.
Holden Arboretum, acc. nos. 2005-17, 65-632, 80-663, all of unrecorded provenance.
Longwood Gardens, acc. nos. 1997-0074, L-0352, sources unrecorded.
Missouri Botanical Garden, St. Louis, Missouri. acc. nos. 1969-6172, 1986-0206, 1986-0207, 1986-0208.
New York Botanical Garden, acc. nos. 877/97, 944/96, 1854/99, 2111/99, 06791, all unrecorded provenance.
Phipps Conservatory & Botanic Gardens, acc. nos. 00/1265, 99/0660.
Scott Arboretum, acc. no. S000339, no other details available.
U S National Arboretum [http://www.usna.usda.gov/index.htm], Washington, D.C., USA. Acc. nos. 64254, 64255, 64256, 66355, 66426, 68988, 69304, 66341.
Europe
Brighton & Hove City Council, NCCPG elm collection [http://www.brighton-hove.gov.uk/index.cfm?request=c1108042], 1 tree at Stanmer Park.
Dubrava Arboretum, Lithuania. No details available.
Hortus Botanicus Nationalis, Salaspils, Latvia acc. nos. 18087,88,89,90,91,92.
Royal Botanic Garden, Wakehurst Place, UK, acc. nos. 1994-67, 1994-68, 1991-1163. No provenance data.
Linnaean Gardens of Uppsala, Sweden, acc. nos. 1976-2713,0000-2170
Strona Arboretum [http://en.wikipedia.org/wiki/Ulmus_lamellosa], University of Life Sciences, Warsaw, Poland.
Tallinn Botanic Garden, Estonia [http://www.tba.ee/index.php?lang=eng], no accession details available.
Thenford House arboretum, Northamptonshire, UK, no details available.
University of Copenhagen, Botanic Garden, acc. no. P1971-5201, wild collected in the USA.
Australasia
Eastwoodhill Arboretum [http://www.eastwoodhill.org.nz/gardens--collection/collection.aspx?Type=&G=Ulmus], Gisborne, New Zealand, 11 trees, details not known.

Translation of "Ulmus americana"

German: Amerikanische Ulme, French: Orme d'Amérique.