Researchers in Idaho have found a way to use sheep to rid vast swathes of public grazing sagebrush lands of invasive weeds.
The weeds, spotted knapweed (Centaurea maculosa) and leafy spurge (Euphorbia esula), are native to Europe. They were introduced to the United States in the 1800s and now infest much of the northern U.S.
"Those plants come from where the sheep come from, if you want to think about it that way," said Steven Seefeldt, a researcher with the U.S. Department of Agriculture's Agricultural Research Service in Fairbanks, Alaska.
Seefeldt recently conducted research at the service's Sheep Experiment Station in Dubois, Idaho. Most cattle, the dominant livestock grazed on public lands, prefer not to eat spotted knapweed or leafy spurge, the rangeland scientist said.
Research at the experiment station shows that some sheep, however, love the stuff. If they are put in a pasture at the appropriate time—when the weeds are growing and native grasses are still dormant, for example—the sheep can impede the alien invasion.
"At the sheep station our goal has been, OK we have this bio-control agent we know eats these plants. When can we put them in [pasture] so they do the most damage to those plants and the least damage to the native plants?" Seefeldt said.
Endangered Sagebrush
Native grasses support cattle grazing and provide forage and shelter for native wild animals, such as elk, bighorn sheep, and sage grouse.
But invasive weeds outcompete these grasses, thanks in part to their fire resistance. Spotted knapweed is not killed by fire, but sagebrush is.
After a fire, Seefeldt explained, the surviving knapweed taps into moisture deep in the soil. With much of the sagebrush having been killed by fire, the exotic species is free to absorb the available water.
"It takes off like gangbusters and makes it harder for sagebrush to re-establish," Seefeldt said. "And that's a real concern."
Environmental groups have long cited livestock grazing and related development, such as roads, fences, and waterways, as major contributors to the degradation of sagebrush ecosystems.
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