Prof: Grazing a mixed bag

There's a lasting and fiery debate between some conservation-minded people and beef ranchers and eaters: Do cows harm the land? The parties in this argument have become polarized, to the point of dueling research stating vegetation absolutely can or absolutely cannot thrive without cattle, said Tom Sisk, a professor and conservation biologist at Northern Arizona University. So Sisk and colleagues set out a little more than a decade ago to shed some light on the question, and what they found was a little surprising to them. Starting in 1997, Sisk and researchers Matthew Loeser and Timothy Crews began sectioning off small parts of the 90,000-acre Flying M Ranch on Anderson Mesa east of Flagstaff. Some parts got intensely heavy grazing, chewing down most of whatever was there. Some got none. And most of the land received moderate grazing, with about 850 head of cattle currently. All of them were removed temporarily when the ranch ran out of water in 2002. The experimental areas heavily grazed produced more biomass (some plants began growing more quickly), but they were also much more vulnerable to an invasive plant, cheatgrass, that can take over a landscape and burn wildly. The non-grazed areas didn't grow more plant material faster. Most surprising of all: The areas grazed at a moderate level produced food well and had the most diverse plant life of any area, the most biodiversity. "It's really not about the cows," Sisk said. "It's about how long the cows are out there, how intensively the cows are out there, and more than anything, it's climate."...AzDailySun