The whir of brush saws echoes daily through Kelleher Park in Burnsville as workers cut down the invader: buckthorn. Cropping up in thickets of prickly shrubs and small trees, this pest has been slowly choking off the undergrowth of plants and wildlife in this rare bur oak savannah. So with the help of a state grant and volunteers, an unusual forest restoration project is under way to chop down and chip up the buckthorn and haul it to St. Paul, where a biomass plant will burn it to produce electricity.

It's one of 10 woody biomass experiments around the state funded with a half million dollars in grants from the Department of Natural Resources. Using a $78,000 grant, Burnsville's project is to be completed by Feb. 15, said Angela Hanson, the city's natural resources technician.

"We can't eradicate it," Hanson said of the buckthorn shrubs and trees, which can grow to 25 feet tall, while crowding out life in the understory. "We're just trying to stem the tide."

The 147-acre Kelleher Park just south of County Road 42 is home to a rare 26-mile expanse of bur oak savannah, one of the most critically endangered ecosystems in the world, Hanson said. Once common in parts of east-central and southern Minnesota, more than 99 percent of such savannahs have either disappeared or been converted to shady thickets dominated by buckthorn and other invasive plants, she said.

"That's partly why this project is so important -- it is an opportunity to restore unique and rare habitat types," agreed Barb Spears, the DNR woody biomass project coordinator.

The projects on public and private lands will help restore more than 7,000 acres of overgrown prairie, oak savannah and woodlands by removing undesirable growth, from buckthorn to prickly ash. Each project is within 75 miles of District Energy of St. Paul, the biomass plant that's the biggest hot water district-heating system in North America and a leader in renewable energy.

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Most of the labor on the buckthorn project at Kelleher Park in Burnsville is supplied by nonviolent offenders in Dakota County’s sentence-to-serve program. This crew was hauling and piling the buckthorn. It will be trucked to St. Paul, where a biomass plant will burn it to produce electricit

A major buckthorn removal operation was completed in December in Indian Mounds Park in St. Paul using some of the grant money approved by the Legislature in 2007. District Energy and an affiliate agreed to truck out the material that is chopped down at Kelleher in exchange for the right to burn it.

Jeff Guillemette, biomass fuel procurement supervisor for Environmental Wood Supply, which is getting the buckthorn to St. Paul, said it burns well for energy. He estimates that the firm will reap 20 trailers, each containing 100 cubic yards of the material, from Kelleher Park.

Buckthorn was imported to the United States as an ornamental shrub and shelterbelt in the 1800s. It spread fast, with seeds carried in the droppings of birds that ate the plant's black berries, which act as a laxative. It's now considered a noxious plant that cannot be transported.

It's become the bane of the suburbs and also agriculture, which dreads it because it provides a home for the destructive soybean aphid to overwinter.

In Kelleher, there's also much at stake, including a big population of kittentails (Busseya bullii). Rare in this region, they're the tiny, bell-shaped lavender flowers that are among the first to push up in the spring. It also is home to warblers, red-headed woodpeckers and the endangered Blanding's turtles.

To get the grant, Hanson developed a restoration plan. Applied Ecological Services, Inc. of St. Paul is leading the removal work at the park. Neighborhood volunteers are helping to tie pink ribbons around the small oaks and other valued trees that could otherwise be mistaken for buckthorn. More volunteers are needed.

Nonviolent offenders, which Hanson calls "the cheapest labor I could find," are piling the chopped-down buckthorn as they work off sentences through a Dakota County sentence-to-serve program.

"It's great," Hanson said. "There's a lot of manual labor involved in this project, hauling the cut brush, so they're very helpful. And it's a more interesting project to work on compared to what they're usually assigned."

On a sunny afternoon recently, Hanson and Spears crunched up and down snowy trails at the park, eyeing the progress. On one side of the trail, the brambly thickets and prickly shrubs had been removed, opening the view. On the other side of the trail, much work remained to remove the thickets, where Hanson's hair snagged on one of the branches of buckthorn -- just one of the many unpleasant traits of this species.

"Usually, we don't get enough money to do a project of this size," Hanson said. "This lets us get a good hold on the invasive plants, especially buckthorn. And we're happy to have it gone."

Joy Powell • 952-882-9017