Fast-growing Grass Restores Bitterroot's Burned Slopes

The burnt trees serve as a reminder of the wildfires that blazed along the Bitterroot Valley in the summer of 2000. A complex of 76 fires burned over 356,000 acres of public and private land, and, according to U.S. Forest Service reports, changed the local ecosystem more significantly than any other event in the last 100 years.

But the threat didn't disappear when the orange skies returned to blue and the last television news van pulled away. Several major rain events over the next year caused mud flows to block highways and secondary roads, obliterate stream channels and surround a number of houses and businesses. The sediment-laden flows diminished water quality and threatened the area's cutthroat trout fishery, important to local tourism.

"Most people worry about the spring snow melt after a fire but even more worrisome is the mid-summer thunderstorm that can gut everything," says Tim Wiersum, forester for the USDA Natural Resources Conservation Service (NRCS) in Missoula. "The Bitterroot fires burned hot and didn't leave anything to keep the soil in place on the steep slopes."

As part of the federal Emergency Watershed Program, several private landowners enlisted the assistance of the NRCS. Besides implementing erosion control efforts such as log and straw weirs, the NRCS Plant Materials Program used research from past fires to make plant recommendations for aerial seeding over 6,000 burned acres.

"We used 'Pryor' slender wheatgrass," says Larry Holzworth, NRCS plant materials specialist in Bozeman. "Our research on other rehabilitated wildfire sites in southwestern Montana has shown slender wheatgrass can establish fast and hold the soil in place."

'Pryor' slender wheatgrass is a native perennial grass selected and made available by the NRCS Plant Materials Center near Bridger, MT. The grass boasts a large seed size, allowing it to germinate faster. NRCS planted the 6,000 acres in November 2001, using over 64,000 pounds of 'Pryor' seed.

"The hillsides were just black toothpicks and now they're covered in a yellow-green carpet," Weirsum says. "This will slow the invasion of noxious weeds and protect the houses below."

Compared to unseeded burned sites, slender wheatgrass reduces erosion by more than 40 percent, says Hal Hunter, former NRCS state staff forester. He and Holzworth compared adjoining sites, seeded and unseeded, and found far less soil movement in the seeded areas and, also less spotted knapweed, the noxious weed particularly problematic in the Bitterroot valley.

"Spotted knapweed was taking over many of the unseeded areas we observed," Hunter says. "We found far less knapweed in the seeded areas. The rate these areas are going to recover is going to be significant compared to the others."

One of the primary challenges when reseeding fire-disturbed areas is encouraging regrowth of the native plant community, with its variety of bunchgrasses, wildflowers, shrubs and trees. Many ecologists worry the rapid establishment of newly seeded plants will leave little room for native species to recover. According to Holzworth, 30 years of monitoring burned sites has shown bunchgrasses like slender wheatgrass are not overly competitive.

"Slender wheatgrass starts the process of stabilizing soils, and building root mass and organic matter, making it more hospitable to other plants," he says. "Then, after two or three years, it dies back and allows the others to take root."

Holzworth and Hunter also found the seeded areas grow just as many tree seedlings as unseeded areas.

"When you look across, you see the grass," Hunter says. "But when you look down, you see the natives and already a tree or two popping up."

Besides offering erosion control and ensuring an opportunity for the native plant community to regrow, slender wheatgrass also provides a fast-growing and nutritious forage for wildlife and livestock. Several other grasses released by the NRCS Plant Materials Program show promise for fire rehabilitation including 'Sherman' big bluegrass and 'Critana' thickspike wheatgrass.

"Hopefully we don't have a repeat of the 2000 fire year," Holzworth says. "However, if we do, we're confident we now have the tools for rehabilitation if it happens."

By Jody Holzworth, Public Affairs Specialist, National Plant Materials Program
July 2003