ST. LOUIS -- The large ash trees that line the walkways and make up nearly half of the trees on the grounds of the Gateway Arch will be cut down, in part because of the inevitable arrival of a beetle that has already killed millions of trees in several states.
The National Park Service, which operates the Arch and its 91-acre grounds, said Thursday that it has completed an environmental assessment of how best to deal with the Emerald Ash Borer.
“The final determination was that eventually the trees are going to have to come out because the Emerald Ash Borer is impending, and because most of the (ash) trees have reached the end of their life cycle,” Arch historian Bob Moore said.
More than 900 of the approximate 2,000 trees on the Arch grounds are Rosehill ash trees, a species designed at a Kansas City, Mo., nursery around 1970 to be well-suited for an urban environment. The ash trees were planted in the early 1970s along the walkways of the grounds.
The Emerald Ash Borer, a small, metallic green beetle native to Asia, was first identified in the U.S. in Michigan in 2002. In has spread to 15 states and was identified near Lake Wappapello in southeast Missouri in 2008.
So far, it has not spread elsewhere in the state thanks in part to an effort to convince people not to move firewood, said Hank Stelzer, University of Missouri Extension forester and a member of the state’s Emerald Ash Borer task force.
Still, experts believe it is just a matter of time before the beetle spreads and kills ash trees across Missouri. Urban areas are particularly susceptible because ash trees—which cause little mess and provide good shade—are popular in the cities. In St. Louis, in addition to the Arch grounds, Forest Park is made up of thousands of ash trees.
Another factor in the decision to remove the Arch’s ash trees was their deterioration in a tough urban environment. Factors such as air pollution, less than ideal soil and stress from the hundreds of thousands of people who visit the Arch grounds each year have taken a toll on the trees, Moore said.
National Park Service officials have not determined the cost of removing the ash trees. There is no timetable, though they will be removed in phases coordinated with an effort under way to revitalize the Arch grounds and St. Louis riverfront by 2015, the 50th anniversary of the opening of the 630-foot-tall monument to westward expansion.
Moore said the ash trees will be replaced with one of eight species under consideration. Among them is the tulip poplar, which was the first choice of Dan Kiley, a landscape architect who worked closely with Arch designer Eero Saarinen.
Stelzer said the single-species replacement could invite further trouble in years to come if that species becomes susceptible to a disease or insect.
“What’s going to be the problem five years down the road?” he asked. “With our global economy and the bugs moving from all parts of the world, it’s inevitable there could be something else.
“What we’re advising folks is to diversify—no more than 20 percent for each species,” Stelzer said.
But Moore said the National Park Service is seeking to preserve the landscape as closely as possible to Kiley’s original plan, and that plan called for a single tree species along the walkways.