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Some trees face "extinction" threat

North America is at a crossroads when it comes to the future of its forests. Several new and devastating tree diseases are moving across the continent and, thanks to globalization, are also starting to crop up elsewhere around the world.

Forestry experts in Colorado this month warned that Thousand Cankers Disease (TCD) continues to spread in the state. The disease, which is transmitted by a beetle that carries a toxic fungus, seems to have originated in walnut trees in the southwestern U.S. and in northern Mexico. It threatens vulnerable black walnut trees in the Midwest and East.

Black walnut trees are native to the Midwestern and eastern U.S. They have been part of American history since colonial times. Along with the edible nuts, the tree's wood is highly prized for high-end furniture, gun stocks and as wood veneer.

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There's also growing concern that TCD, which is lethal to infested trees, could move further eastward and attack the economically important black walnut trees grown commercially in the American Midwest. In fact, according to Mike Eckhoff, a senior research scientist with the Colorado State Forest Service, there are national economic implications to TCD, with "$540 billion worth of [black walnut trees] at stake."

In Missouri, for example, black walnut tree farms are an important part of the state's industry, bringing in more than $850 million over a 20-year period.

Other infestations have previously ravaged America's forests like the mountain pine beetle that in recent years killed millions of acres of pine trees in the Rocky Mountain area and parts of Canada. But that pest is cyclical.

The difference with TCD is this that the disease has "jumped host -- it moved from one kind of walnut that it didn't hurt to black walnut, [which] it can hurt," said Whitney Cranshaw, professor of entomology at Colorado State University. "So it's a new disease."

Because there are for now no sprays or other treatments to control TCD, Cranshaw believes there needs to be a public campaign to make people aware of the disease, and to at least help slow its spread.

"There already is increased consciousness of this in regulatory posts," he said, "but I think what we really need is a call to arms in terms of wood workers, and other people who might be moving wood around. I mean, we're in a world of hurt if this gets into a place such as Missouri and it turns out to be even half as bad as it is [in Colorado]."

At the same time, another pest, the emerald ash borer, a beetle that originated in northern Asia and that was first discovered in the U.S. in 2002, is laying waste to North America's ash trees. The ash is another economically significant tree, with a reported market value of up to $60 billion (About half of all professional baseball bats are made out of white ash).

"This is an extinction event, functionally," Cranshaw said. "Ash, as a tree of the North American forest, will be gone in our generation."

As with other invasive species, globalized trade and faster travel have likely played a part in the spread of these tree diseases. Cranshaw said that Emerald Ash Borer likely was spread to North America through trade with China. He is planning to travel to France to consult with officials there about how to control the spread of TCD in Europe.

Editor's note: This article was updated at 11:30 a.m. ET to clarify some details about the spread of Thousand Cankers Disease (TCD) in the U.S.

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