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Sometimes, a little homework has a lasting impact.

University of Montana biology professor Erick Greene noticed that when he recently took a walk through Greenough Park. Fifteen years ago, he'd asked a class of students to calculate how fast Norway maple trees might displace native plants and trees if left unchecked.

Their calculations showed the park along Rattlesnake Creek would become a monoculture of non-native maples within a couple decades if nothing was done. They presented their findings to the Missoula City Council and the Greenough Park Advisory Committee. Both bodies were impressed enough to order action.

"Walking down the trail, it hit me like a ton of bricks - the results were just phenomenal," Greene said. "I went to some of the same spots we used for those crystal-ball projections, and the management has been unbelievably successful. If this was knapweed on Mount Sentinel, people would be jumping for joy."

That hasn't been the case with Greenough, however. Many Missoulians have been irate about what appears to be brutal deforestation in big swaths of the park. Where the Norway maples have been cut down, virtually nothing but a few old black cottonwoods and ponderosa pine trees remain. The forest floor is bare.

Norway maples dominate the sidewalks and boulevards throughout Missoula's University neighborhood. The first ones were likely planted by Missoula founder Frank Worden, outside his family home on Pine Street. He probably brought them from his home state of Vermont, according to city conservation lands manager Morgan Valliant. They're one of the most commonly planted trees in the United States.

Unfortunately, they also dominate whatever place they're allowed to grow. The trees produce a huge canopy of leaves that block most sun from the ground. And their roots secrete chemicals that inhibit most other plants from growing.

The result is patches of Greenough entirely given over to Norway maples. On the ground, virtually nothing else grows. Greene refers to them as "the wall of death."

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The city stopped using Norway maples for boulevard trees in 1991. And after Greene's students made their presentation, park managers started attacking the infestation in Greenough in 1995.

The park was divided into 23 sections. As time, resources and priorities allowed, each section was cleared of Norway maples.

At first, the city could only clear a section every two or three years. In 2006, the Conservation Management Program put new emphasis on cutting the maples, and a section a year was logged. That's led to greater public outcry as well, especially when the maples put out their fall colors.

"I've had a bride call me to say I ruined her wedding," Valliant said, as he walked along the recently cleared section southwest of the picnic shelter. But the area, which was cleared this spring, already has chest-high cottonwoods growing back. A native Rocky Mountain maple shrub has spread to cover an oval 15 feet across.

Follow the trail heading northwest from the picnic shelter, and the difference becomes obvious. On the right, the 40- to 50-year-old maples form a thick green wall of leaves, with bare dirt around their roots. A few century-old cottonwoods and ponderosa pines tower above the maples, but no seedlings or shrubs can be found.

On the left, hawthorn, snowberry, ferns, elderberry and 45 other species of plants grow waist-high, and new cottonwood starts are 10 feet tall. The area was cleared of Norway maples eight years ago, and now looks like a normal Montana creekside. Pigmy nuthatches and cedar waxwings sing in the trees, compared to the relative silence of the maple grove.

"We just removed the maple here - no replanting," Valliant said. "The management is a one-time, intensive thing."

The cottonwoods in particular like the change. They grow best in disturbed areas, so a bit of maple logging triggers vigorous sprouting of new root suckers. In more visible sections, Valliant plants extra pine trees, elderberry bushes and other shrubs to speed along the restoration.

"When we clear and replant, in the first year new plants don't do well," Valliant said. "But in the second year, they take off. It takes time to clear the soil."

That's good, because Valliant's workload continues to grow. Norway maples have infested other parts of the Rattlesnake Creek drainage, Mount Jumbo, the Blackfoot River corridor, and Flathead Lake's Finley Point. Some eastern states have already declared it a noxious plant, he said.

The city allows anyone who calls in advance to take the cut maples for firewood, carving or other uses.

"The city and Greenough Advisory Committee have been really brave and really aggressive about taking out the Norway maples," Greene said. "There's been a lot of misinformation about the severity of the threat facing the park. But we've also had the speed of success."

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