Imagine having a big, wide, tall, strong tree where you could swing, climb or build a tree house. Kids in the United States before 1940 played on millions of these trees, called American elms.
Elm trees were popular, and that's why you can find so many Elm Streets in cities and towns. Today, though, you'd have to look very hard to find any elm trees there. Over the last half-century, nearly all our American elm trees were "cut down"... by a creature so small you need a microscope to see it.
American elms were prized for city streets and parks and yards. They provided lots of shade. They could thrive in poor soil. They didn't seem to mind the smoggy air in a big city. Elms could also cope with bitter-cold winters and boiling-hot summers.
There was just this one tiny problem, and in the early 1940s the nightmare began. A disease called Dutch elm disease began spreading rapidly from one elm tree to another. The disease is caused by a fungus. A fungus can't walk or fly, but bugs known as Dutch elm beetles can. And they did, traveling throughout the land, carrying the fungus like an invisible hitchhiker.
The beetle was accidentally brought to our country on logs of elm trees imported from France for making furniture. Over the years, the bugs and their hitchhikers hopped off railroad cars on the way to furniture makers in Ohio.
Once infected with the fungus, leaves on elm trees turn yellow, then a dead brown. The fungus gradually creeps up the branches to the trunk. In a year, some branches die. Soon after that--often by the second year--the whole tree is dead.
"By the 1980s, Dutch elm disease had almost wiped out 77 million American elms," says Alden (Denny) M. Townsend. He's a plant geneticist for the U.S. National Arboretum that the Agricultural Research Service operates in Washington, D.C.
Here and there, some trees survived despite the fungus. Now, these survivors--and many years of work by Townsend and other scientists--just might end the nightmare on Elm Street.
Recently, Townsend and his co-workers released two new American elms, named Valley Forge and New Harmony. The story goes back more than 25 years, when the scientists started searching for and testing thousands of the survivors. Which ones, they wondered, had a natural ability to fight off Dutch elm disease? To start finding out, they cut fresh shoots from as near a tree's top as possible. Back in the greenhouse, they used a safe chemical that would make tiny roots sprout from the shoots. Then they put the fungus on these tiny plants, and waited to see what would happen.
Why bother with all that? Why not just get seeds from the survivors and plant them to grow new trees? After all, the survivors must have what it takes, right? Not so! "It is not uncommon," Townsend explains, "to find a single elm surviving by chance where others have died. Most of the thousands we tested turned out to be just lucky."
Through their tests, the scientists proved that only about one in 100,000 American elm trees are really disease-tolerant. The new elms, Valley Forge and New Harmony, are not completely immune. But they come very close!
Townsend says people should be able to buy the new super-trees by
1999. So, years from now, your own kids and grandkids can hang from tire swings
and build tree houses in a good old American elm.
--By Hank Becker, formerly with the Information Staff, Agricultural Research Service
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