In a woodland a half-mile north of Anoka High School lie the remains of one of the great buckthorn battles of recent years.

Nearly half of the 200-acre Anoka Nature Preserve along the Rum River has been cleared of snagging buckthorn and other invasive plants since February. Twenty-two semitrailer truckloads of vegetation have been shredded and hauled away already, and a nearly equal amount — a football field-sized pile, 15-feet high — will soon be obliterated by a 95,000-pound, 1,000-horsepower mulching machine.

The $179,000 project is part of a pilot program launched in 2008 by the Minnesota Department of Natural Resources, with the aim of restoring habitat and reaping a fuel source in the process. Hundreds of acres in the metro area have been ridded of invasive plants, and the mulch has been used as fuel at the District Energy plant in St. Paul, said Barb Spears, coordinator of the DNR's Woody Biomass Project, which ends this month.

For years, buckthorn has been removed largely with hand equipment and burned at the site. The DNR program "is an opportunity to get something good from buckthorn — bioenergy," Spears said.

At the Anoka Nature Preserve, the scenic change is dramatic. Hundreds of white and bur oaks, buried last fall by a thorny wall, are now visible. Hillocks once submerged in the thick, green buckthorn now add graceful contours to the returning oak savanna.

"Before, the buckthorn was so dense you couldn't see 30 feet ahead in the winter with all the gray stems. Now, you can see 250 feet and clearly see the big oak trees," said Chris Lord, project manager for the Anoka Conservation District, which has overseen the project.

Soon, the stack of invasives will be gone, after the grinding machine turns them into mulch. It will take about 20 semitrailer trucks, each carrying about 20 tons, to haul the remaining material to St. Paul.

There it will help fire a boiler in the District Energy plant that provides steam heat and cooling for downtown homes and buildings, including the State Capitol, said Jeff Guillemette, biomass fuel manager for Environmental Wood Supply. Twenty truckloads would feed the boiler furnace for less than half a day, he said.

The Anoka project is one of 24 that have received $886,000 in state grants over the past five years to remove invasive plants from 706 acres of parks, preserves and other areas, Spears said. The DNR started the project in 2008 with a $500,000 grant from the Legislature. The program got an extension in 2010 with $600,000 in State Lottery funds set aside to preserve and improve natural areas.

Ellen Anderson, a senior energy/environment adviser to Gov. Mark Dayton, is a former state senator who co-authored the bill that provided initial funding for the restoration-bioenergy project.

She said most project goals have been achieved: removing invasive species; creating a local, renewable fuel source; and improving wildlife habitat and landscapes in parks and natural areas. The missing piece was setting up a sustainable market for the woody materials removed, which compete against established fossil fuels.

"Eventually there will be a real strong market for more renewable materials, but the economics don't quite work yet," she said, noting that the invasive wood supply isn't stable enough.

Program ending; efforts won't

Although the DNR program ends June 30, state funds are still available through State Lottery and Legacy Amendment environmental grants to continue restoration and invasive plant-removal efforts, Spears said. "My emphasis through our projects has been to help people recognize and consider that when they plan a project, to call District Energy and see if they can use this material instead of piling and burning it on site."

The Anoka Preserve project started last October when Sentencing to Service inmates and others applied $30,000 worth of herbicide over three weeks to trunks of the buckthorn, prickly ash, small eastern cedars and other invasive plants, Lord said. After the herbicide had time to soak into plant roots, removal work began in February. About 800 tons of brush and trees were sheared at the base, hauled out and stacked for shredding.

A relentless plant

Buckthorn is a persistent competitor. Its roots give off a toxin that weakens or prevents nearby plant growth, Lord noted. Its berries contain a laxative that causes birds to excrete them, spreading seeds.

At the Anoka site, buckthorn seeds that have accumulated in the soil will emerge in a year and a controlled burn is planned to remove them, making way for raspberry, Juneberry, hazelnut and other native plants, Lord said.

The biggest project the DNR helped fund was the removal of invasive plants from 134 acres at the Belwin Conservancy in Afton in 2009-11. That oak restoration project sent 5,400 tons to the St. Paul bioenergy plant.

Wild turkeys now roam in newly opened areas and more redheaded woodpeckers seem to be nesting, said Tara Kelly, Belwin's director of ecological restoration. But the visual change is breathtaking. "You can see the forest for the trees now," she said.

Wild turkeys also are seen browsing in the pruned Anoka preserve and rodent hunting is a lot easier for hawks, owls and other raptors, Lord said. The biggest advantage, however, will be stronger oak growth because tree roots won't be affected by buckthorn toxins and the oaks will absorb precipitation previously shared with the invasive plants.

"There should be a much bigger crop of acorns," Lord said. That will provide lots of snacks for deer and turkeys.