Return of the American Elm

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Scientists create Dutch elm disease-resistant hybrids.

The American elm, long absent from cities and towns across the U.S. will soon line streets and parks with its majestic features once again, hope researchers at the U.S. National Arboretum who introduced two new varieties of Dutch elm disease-tolerant American elm trees in June.

The new trees, named Valley Forge and New Harmony elm, were developed by a team of scientists at the arboretum after more than 20 years of research.

At one time, "American elm trees were the main landscape tree in cities and towns," said Alden Townsend, the National Arboretum plant geneticist who worked on the project.

The American elm (Ulmus americana), which can grow more than 100 feet tall, is noted for its hardiness and tolerance to stresses in urban environments. It can withstand drought, air pollution, and deicing road salts, says Thomas Elias, director of the arboretum. The tree also supports many kinds of wildlife and has a spreading canopy that offers shade.

Since the 1930s, Dutch elm disease, caused by a deadly fungus (Ophiostoma ulmi), has destroyed more than 80 million American elm trees, wiping out 90 percent of the nation's supply, according to the Agricultural Research Service (ARS) of the U.S. Department of Agriculture.

The Hardwood Research Council notes that the Dutch were the first to recognize and document the fungus that causes the disease, but the disease did not originate in the Netherlands.

In the United States, trees infected with the disease were discovered in the Ohio River Valley in 1932 after a shipment of logs from France carried the fungus from Europe. Leaves on trees infected with the disease turn yellow, then brown, and show other signs of wilting, according to the ARS.

The Dutch elm disease fungus is carried from tree to tree by the bark elm beetle. The fungus quickly moves into the waterconducting vessels of the elm, clogging the flow of water and nutrients to the tree, according to the Elm Research Institute, a nonprofit institute based in Harrisville, New Hampshire.

The Valley Forge and New Harmony elms were chosen, through a screening process that began at the arboretum in the 1930s, as the trees that proved to best withstand repeated inoculations of the Dutch elm fungus. Although the trees are not completely immune to the disease, they have shown "unusually high levels of tolerance to the fungus that causes the disease," says Floyd Horn, administrator of the ARS.

According to the ARS, more than 100 rooted cuttings of the Valley Forge and New Harmony elms were distributed in the last two years to tree nurseries, experiment stations, and arboreta. Wholesale nurseries will propagate the trees for sale by late 1997 or 1998, while retail nurseries should have them in 1999.