Water tumbles over Minnehaha Falls. Thousands of icicles line the rock ledges. Winter's first ice accumulates on the concave wall behind the falling water.

But all is not tranquil near one of the metro area's signature postcard scenes.

Hard-hatted workers tote chainsaws only a few hundred yards downstream, felling trees, hauling logs and bundling or burning brush along both sides of Minnehaha Creek. Fuel cans, plastic fencing and pickup trucks litter the frozen ground, making the area seem more like a construction zone than a park.

"This is an all-out attack," said Andy Lesch, project manager for the Minneapolis Park and Recreation Board.

He's talking about a five-year, $1 million effort to remove invasive buckthorn, honeysuckle and garlic mustard that are choking the narrow valley beneath the falls.

The cleanup promises to open sightlines and vistas of the creek that have been shrouded for decades by the overgrown brush, and to upgrade trails and add boardwalk to help hikers. Park officials call it the "lower glen," somewhat neglected until recently but known by others as a hidden treasure.

Many visit the 53-foot waterfall and take the stairway to view it from below. But most don't realize that the creek runs another 3/4 of a mile from the bottom of the falls to its confluence with the Mississippi River.

"We're hoping to eradicate the invasives here," said Lesch, walking along one of the trails that parallels the creek. "That's a lot to ask, but our goal is to get it under control so the native plants will come back."

All park areas remain open during the project, which began Nov. 18. Visitors are asked to steer clear of work spots.

It's going to take awhile. The lower glen includes 54 acres. There's enough work to keep 10 full-time workers busy removing buckthorn from now until the end of January, said Fred Rozumalski, a landscape ecologist for Barr Engineering, the project's consultant.

"It's going to be dramatic, and the creek will be a lot more visible," he said. "It'll feel a lot safer down here, too, when you get rid of all that dense vegetation."

Not a one-shot effort

Invasive plants are notorious for their ability to resprout and reseed. To prevent that, workers are painting stumps from cut trees with an herbicide. New growth next year will be stymied by more cutting, and by spraying seedlings with a plant hormone that does not let buds form. Clearing invasives in the park has occurred only on a small scale before, said Lesch, mainly by gardeners working around the falls overlook areas.

The native vegetation project is the latest phase of a $7 million effort. During the past two years, the Minnehaha Creek Watershed District restored shoreline and controlled erosion along parts of the creek near the falls. The U.S. Army Corps of Engineers constructed new concrete footings to save the limestone walls, which were built during the 1930s Works Progress Administration.

Now the Park Board is working with Barr Engineering on improving trails and restoring native plants and wildflowers. Rozumalski said taller canopy trees will remain, but the buckthorn trees and other invasives will be cleared by the contractor, Prairie Restorations Inc.

New boardwalk

Some replanting may be needed next spring, Lesch said, especially near the falls where terrain is steep, soil is dry, and pathways receive the most foot traffic.

"Other areas we'll do more nurturing of natural things that are here and try to bring them out," he said. That includes wild ginger, various ferns and sedges, zigzag goldenrod, trout lilies, anemones, jack-in-the-pulpit and marsh marigold. The changes will also improve habitat for warblers and other migrating and nesting birds, Lesch said.

The project will replace about 1,000 feet of boardwalk across muddy areas. The new steel decking is coated with plastic much like playground equipment, Lesch said.

Rozumalski said that unless the invasives are removed, much of the valley will become a bleak monoculture. Buckthorn impedes native trees and plants from sprouting because it blocks sunlight from hitting the forest floor, he said. Garlic mustard smothers wildflowers.

The lower glen deserves better, he said, and it's not too late to return it to a more natural state, which includes a small but rare black ash swamp. "It's really unique and really worth the investment in restoring," he said.

Tom Meersman • 612-673-7388