Some question choice of tree for Arch grounds

ST. LOUIS -- The ash trees on the grounds of the Gateway Arch are expected to die soon, and they're being removed. But the sapling picked as their replacement has its own problems.

The St. Louis Post-Dispatch reported the London plane tree also is threatened.

The emerald ash borer is a beetle first identified in Michigan in 2002. By 2010 it had been detected in 15 states, including southern Missouri. Experts say it is only a matter of time before the ash trees on the Arch grounds would succumb.

The National Park Service is replacing the ash trees with the plane tree. A black fungus has infected and killed tens of thousands of plane trees across Europe. It is known as canker stain disease.

Park service officials say no species is perfect. While tree experts mostly agree that the plane tree is a decent choice, arborists generally believe a better idea would have been to replace the ash trees with a variety of species.

"Anybody in my field would say don't do a monoculture, because you can lose them all at once," said Thomas C. Harrington, a professor of plant pathology at Iowa State University.

Harrington said he would recommend no more than 100 trees of one species. The Park service plans about 800 plane trees to line the walkways of the Arch grounds, technically the Jefferson National Expansion Memorial.

"I don't think they know what they're getting into," he said.

The park service recently consulted with about a dozen tree experts and all argued against the single-species planting, said Hank Stelzer, chair of University of Missouri forestry, whose department was involved in the process.

"History has a way of repeating itself," he said. "We lost the chestnut trees to the chestnut blight. Then we lost the American elm to the Dutch elm disease. And when all those left the urban environment, we said we'd put in green ash. It's resistant to drought, heat. It's pretty tough. Until this pest showed up."

The choice of the London plane tree for the Arch grounds was announced in May. The tree is known for broad leaves, peeling bark, height, hardiness and -- despite the recent canker stain disease -- resistance to disease.

Replacing the trees will cost about $1 million. It is part of an estimated $14 million in landscape improvements to the walkways leading to the Arch. The money is expected to come from private donations to CityArchRiver, the not-for-profit agency coordinating the concurrent $380 million tax-supported renovation of the Arch grounds.

News reports and scientific papers outline the damage to the plane tree in Europe: thousands cut down in Italy; 80,000 affected in southern France; 42,000 at risk lining the 200-year-old Canal du Midi. The disease even threatens plane trees along Paris' Champs-Elysees.

The park service never considered mixing multiple types of trees, said Bob Moore, a historian at the Arch grounds who worked on choosing the tree. The Arch, including its landscape, is a national historic landmark.

It's a fight between history and ecology, said Andrew Wyatt, vice president of horticulture at the Missouri Botanical Garden.

"It's whether you're willing to roll the dice and take the risk that a disease would wipe out the whole monoculture," Wyatt said.

"But I do have to say," he added, "the London plane tree is a reasonably good choice."

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Information from: St. Louis Post-Dispatch, http://www.stltoday.com