Cause and effect on the prairie

April 21, 2006

UNION, Ore. – Oregon State University researchers will spend four years investigating the effect of cattle on soils, plants, invertebrates and ground-nesting birds in the Zumwalt Prairie, one of the largest and last native prairies in the Pacific Northwest.

Funded by a USDA National Research Initiative grant for $450,000, the OSU researchers will test different cattle stocking rates across about 1,600 acres of land in The Nature Conservancy's Zumwalt Prairie Preserve.

Using four fenced blocks, each divided into four 100-acre pastures, they will analyze high, medium, low and zero stocking rates. They will look at how cattle affect the availability of resources for other organisms, how habitat for wildlife communities change as stocking rates change and the effect grazing has on vulnerability and predation of ground-nesting birds in the area. The researchers will also evaluate at which stocking rates the cattle are most successful.

Due to population declines, the grassland birds that live among the Zumwalt's native bunch grass – the primary forage for cattle in the area – are of national conservation concern. These birds include horned larks, western meadowlarks and savannah sparrows.

"We may see a positive or neutral response in the ecosystem at low and moderate stocking rates," said Patricia Kennedy, an ecologist and avian specialist at OSU's Eastern Oregon Agricultural Research Center in Union. "At very low stocking rates, and in areas where there are no cattle, high grass densities may actually be prohibitive for feeding and nesting of native bird populations."

On the other hand, Kennedy added, high stocking rates may result in a lack of food resources and vegetation that is too open to provide adequate nest concealment for the birds.

Tim DelCurto, the superintendent of the Union research center and a specialist in range beef cattle nutrition and management; Sandy DeBano, an entomologist in the College of Agricultural Sciences; and Rob Taylor, an ecologist with The Nature Conservancy, are collaborating with Kennedy to take a deeper look into the question of grazing.

"This grant takes a food web approach," DeBano said. "For example, we want to know how various intensities of livestock grazing affect local invertebrate populations and how any changes in invertebrate abundance may, in turn, affect the birds that eat them."

"Looking at what happens to one link in the web without examining what's happening to the connecting links doesn't get you very far," DeBano added. "We're trying to look at the larger picture."

The roughly 220-square-mile Zumwalt Prairie is located in the northeast corner of Oregon between the Wallowa Mountains and Hell's Canyon. Its acreage is noted for a rich array of plants including several species of native bunchgrass, as well as Spalding's catchfly, a threatened wildflower. The area is home to one of the highest concentrations of nesting prairie hawks in North America, as well as Columbian sharp-tailed grouse, elk, mule deer, Snake River steelhead and red band trout.

"The question is whether grazing can co-exist in an area like the Zumwalt," said DelCurto. "Probably the biggest issue around grazing concerns sustainability, and that's really more of a question of management. Can we ensure that we can manage grazing in such a way that there will be an equal or greater amount of forage from year to year? Well, I expect we will see that grazing to a certain degree stimulates good forage rates, and the animal response will be best at the stocking rates that are also best for the system. We can have our cake and eat it too."

For generations, area ranchers have grazed their cattle on the prairie, rotating them to different sites in the winter when low temperatures and snow make the prairie uninhabitable for the livestock. Debates about grazing on the prairie, and elsewhere have gone on for years, said the researchers.

"In the course of this project we hope to really understand the effects of varied stocking rates on the ecosystem, and to help provide some scientific input into the debate," said Kennedy. "With more knowledge we can help formulate policies that then help producers make management decisions based on science."

Author: Aimee Lyn Brown
Source: Pat Kennedy, Tim DelCurto, Sandy DeBano