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Field Notes

Covering the natural wonders of the Pacific Northwest

June 23, 2011 at 4:03 PM

Mule deer vs. cows: Can livestock grazing benefit wildlife?

It has been one of the most controversial questions in southeast Washington: When livestock graze on public land does that ever actually help wildlife?

A host of science over the years has made clear that running cattle on sensitive landscapes can damage soils and streams and change the ecology of the land. But some research has suggested that livestock chomping away poor old grasses may in some cases improve the quality of food that remains for creatures like deer or elk.

Into this debate in 2005, stepped Gov. Chris Gregoire, the Washington Department of Fish and Wildlife and the Washington Cattlemen’s Association. With Gregoire eager to help ranchers, the state agreed to set up a “pilot grazing program” in the Blue Mountains in Asotin County. The program let ranchers graze on important wildlife lands in part to see if livestock could enhance the area’s “ecological integrity.”

The state spent hundreds of thousands of dollars and environmentalists sued, fearing damage to native plants and streams. A Superior Court judge ruled the state had not established a reason to think grazing would help wildlife; the state’s own biologists were sharply critical of the program.

Along the way, researchers at Washington State University were asked to look at a few key questions. One of those questions: Would grazing cattle in fragile shrub-steppe landscapes reduce old grasses and promote the growth of younger, more nutritious forage for mule deer?

The answer, released this week: It’s complicated.

Lisa Shipley, a wildlife ecologist at WSU and one of her graduate students, let cattle graze on several southeast Washington plots. Then they led tame mule deer to those plots to eat. The deer also browsed in plots where not cattle had grazed at all.

They learned that in areas where cows had grazed, deer actually ate diets marginally higher in protein. But they managed to consume less overall energy.

In other words, cattle had only a modest influence on the nutritional quality of vegetation eaten by deer. But the cows also reduced the area’s overall nutritional carrying capacity for wildlife.

“You might have expected it to be all really bad or all really good,” Shipley said in an interview. But “what our science says is it’s a tradeoff.”

Shipley was quick to point out there’s a limit to grand conclusions that can be drawn from this study. The results are specific to bluebunch wheatgrass landscapes like those found in Asotin County. It’s also not clear what the results would be over time.

But WSU, in its press release, described the study’s conclusions this way: “These results do not support the idea that spring cattle grazing will produce more nutritious forage for mule deer on these grasslands.”

Meanwhile, other larger questions still remain unanswered. WSU scientists also are studying cattle’s impact on soils and vegetation. Those results aren’t expected until 2012.



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