2 Landscape Use

From the Civil War period to the early 20th century19th century 20th century 21st century more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901- 2000 in the sense of the Gre, the American Elm was the most widely planted ornamental tree in the United States and Canada. It was particularly popular for boulevard plantings in towns and cities, creating high tunneled effects that formerly characterized old towns in the U.S. Northeast. The American Elm has unique properties that made it ideal for such use: rapid growth, wide adaptation to a broad range of climates and soils, strong wood, resistant to wind damage, and vase-like growth habit requiring minimal pruning.

From ca 1850 to 1920 the most prized small specimen elm was the Camperdown ElmThe Camperdown Elm ('Weeping Elm') Ulmus glabra 'Camperdown' is a Cultivar, which cannot reproduce from seed. The grafted Camperdown Elm slowly develops a broad, flat head that will eventually build as high as 30 feet and a proportionately very wide, cont, a contorted weeping cultivarA cultivar is a cultivated variety of a plant species. Modern cultivars are often, but not necessarily, hybrids between species; they may equally well represent particularly desirable selections from populations of a single species. Cultivars generally ar of the Wych Elm Ulmus glabra 'Camperdown', grafted on a standard Wych Elm trunk to give a wide, spreading and weeping fountain shape in large garden spaces.

Large numbers of English Elms were planted in AustraliaAustralia is the sixth-largest country in the world (geographically), the only one to occupy an entire continent, and the largest in the region of Australasia. Australia includes the island of Tasmania, which is an Australian State. Its neighbouring count in the early 20th century19th century 20th century 21st century more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901- 2000 in the sense of the Gre. Because of its geographical isolation, Australia has so far been unaffected by Dutch Elm Disease (see below), and as such retains some of the world's best stands of elms; the long avenues of Royal Parade and St Kilda Road in Melbourne are perhaps the most beautiful examples.

3 Dutch Elm Disease

Dutch elm disease has been devastating to elms throughout the Northern Hemisphere. This is a fungal disease that is borne by a vector, the elm-bark beetle. It affects all species of elm native to North America and Europe to some degree, while at least some Asian elms are much more resistant, having evolved alongside the disease. Woodland trees in North America are not quite as susceptible to the disease because they usually lack the root-grafting of the urban elms and are somewhat more isolated from each other.

The disease was first introduced to North America in 1928 and has since become endemic.

4 Resistant Trees

Well-funded efforts to develop resistant trees have been underway since the 1960s. Research has followed two paths.

Hybridization of the American Elm with the Chinese Elm has produced trees with the greatest disease resistance. A number of named hybrids are commercially available. However, these trees have a smaller mature size and lack the vaselike form for which the American Elm was prized.

Separately, efforts have been made to develop resistant cultivars of Ulmus americana. The 'Liberty Elm', available commercially, represents the results of one such effort, and though marketed as a single product, consists of five cultivars chosen at random. These cultivars were the result of field selection of trees that survived in a region where the disease was endemic, followed by 2-3 generations of selection. Some of the cultivars are patented.

The 'Valley Forge' and 'New Harmony' elms are competing cultivars, produced using selection techniques similar to those used for the 'Liberty Elm'.

Since elm trees take decades to grow to maturity, and these introductions are recent, the performance of these trees in actual landscape conditions is not known with certainty.

A related effort is the commercial reintroduction of the 'Princeton Elm', which is a cultivar selected in 1920 for its landscape qualities. Large plantings have survived the disease, and testing in laboratory conditions revealed that this cultivar has considerable resistance.

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