Comments from the public on a proposal to contain or eliminate weeds on 35,000 acres of the Bitterroot National Forest (BNF) are mixed so far: Some want no herbicides applied on the forest, and others want more. The BNF recently completed an environmental impact statement on the 1.6 million-acre forest, and has come up with a proposal to aerial spray two chemicals—Tordon and Transline—on 5,000 burned acres considered at high risk for weed infestation.
Lori Clark, the BNF’s interim range manager, says that the weed problem gained public attention after the 2000 fire season when foresters realized that burned lands adjacent to already infested grasslands were at high risk for further infestation.
“Weeds alter the relative abundance of native plants for many reasons,” she says. Weeds, particularly knapweed, out-compete native species. They have an “alleopathic” quality in that they taste bitter to foraging wildlife, forcing grazing animals into other grazing areas, and even altering migration patterns altogether.
Knapweed produces an abundance of seeds and grows faster than native plants. Typically it’s the first plant in the spring to exploit nutrients and has no natural enemies in North America. And because it is a taprooted species, it does not hold soil together the way grasses can. During a hard rain, a knapweed-infested hillside can become a torrent of soil deposited into streams below.
Most of the aerial spraying would be done on big game summer and winter ranges in the Sula Ranger District. Herbicides would be applied by hand along 1,300 miles of forest roads, and “biological agents,” or insects brought from Europe, would be released on 14 sites, including big game winter ranges, burned areas, and would be released after herbicide treatment. Some mowing and hand-pulling of weeds would be done intermittently.
Clark says that biological controls have their critics as well. Some oppose the use of imported insects for fear they too will alter natural processes.
Ken Hotchkiss, the project team leader, says that Tordon, one of the selected herbicides, is the most persistent in the soil, with a measurable toxicity level lasting one year, and with a half life of anywhere from one month to three years. However, it is not 100 percent effective and more application would be needed.
The public comment period ends April 30, and so far it’s been a mixed bag, Hotchkiss says. Whatever is finally decided, weed management will receive greater attention in the future, but he warns, “We’re not going to do it all in one year. We don’t have the money or the people.”