Of bark and bite

City Sage

| November 27, 2013

We've all seen those photos — Colorado Springs, 1871. Half a dozen shabbily dressed men stand before a couple of ramshackle wooden buildings. No streets, no trees, no other sign of human habitation. But for Pikes Peak looming in the background, we might as well be in Kansas, or anywhere in what was then called "The Great American Desert."

The city's founders wanted trees for shade, comfort and shelter from fierce prairie winds. They sought to create an oasis in the desert, transplanting the verdant landscapes of New England and the Midwest to the arid prairie.

Gen. William Palmer's men transplanted young cottonwoods from the banks of Monument Creek to line Cascade Avenue. Thanks to irrigation, the cottonwoods thrived, as did elms, maples, oaks and other non-native species.

The oasis grew, and the urban forest thrived. Colorado Springs has been designated a "Tree City" by the National Arbor Day Foundation for 36 years, longest of any Colorado city. Our urban forest includes 200,000 street trees with an appraised value of $828 million, according to the city's website. (Amazingly, one of Palmer's cottonwoods still stands in the 500 block of North Cascade.) More than a million trees are located on private property, making the urban forest's aggregate value about $5 billion.

The most common urban tree is the ash. Several of the 20 or so U.S. species or variants of ash are designated as acceptable street trees by the city forester; they're attractive to private owners as well. Ash trees are adaptable, fast-growing and drought-resistant. While no specific numbers are available, various ash species likely make up 20 to 25 percent of the urban forest.

And thanks to a tiny green beetle, every ash in Colorado Springs may be dead within a decade.

An Asian migrant, the emerald ash borer was first identified in Michigan during 2002. The insect's larvae feed on the inner bark of ash trees, disrupting the tree's ability to transport water and nutrients. The beetle has no natural enemies, and infected trees are hard to identify. There is no cost-effective way to treat or prevent infection.

Since 2002, the borer has spread to 21 states and two Canadian provinces. It has killed tens of millions of ash trees in southeastern Michigan alone, and tens of millions more in states from North Carolina to Minnesota.

In September, infected trees were found in Boulder, and the state issued an emergency quarantine rule. Tree nurseries can't move stock out of the quarantine area, nor can firewood or slash be transported away.

"We have hundreds of thousands of ash trees," said Springs city forester Paul Smith. "In some of the suburbs built in the '70s and '80s like Old Farm and Village Seven, probably more than 50 percent of the trees are ash."

In St. Paul, Minn., the ash borer was identified four years ago. That city, according to a recent story in the Denver Post, is now spending $1 million annually to remove and replace street ash trees. St. Paul has more than 40,000 ash trees on public property, and none are expected to survive.

"Understand: Ash trees will be extinct," St. Paul City Council President Kathy Langtry told the Post. "They will not exist in the city of St. Paul."

"There's about a five-year window," says Colorado urban forestry coordinator Keith Wood. "If you haven't identified and begun to control the bug by then, it may be too late."

Identification is difficult. The external indicators of infection are identical to drought-related stress, while the tiny metallic green beetles are barely noticeable. And, Smith pointed out, every ash in the city has been drought-stressed during the past 10 years. The borer may already be here.

"It can be two or three years before you realize you have them," said Smith, "and by that time they can build up a substantial population. And now that they've reached the Front Range, it's not a question of if, but when."

It remains to be seen whether the urbanized Front Range is as hospitable to the borer as the dense, deciduous forests of the Midwest. If so, the prognosis isn't encouraging.

"Do you remember back in the 1970s when we lost all of our elms to Dutch elm disease?" asks Smith. "We replaced them with ash trees. And now this has the potential to be the same kind of epidemic."

hazlehurst@csindy.com

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There is a natural enemy.
http://emeraldashborer.info/treatment.cfm#…

report   
Posted by JENSENBIZ on 11/29/2013 at 4:08 PM
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