ZUMWALT PRAIRIE Medium-intensity grazing seems to cause little or no harm to most insects, plants, birds and other species found in Wallowa County's native grasslands, according to findings from a multi-year experiment The Nature Conservancy led here.
And though researchers are careful to avoid stating conclusions that absolutely support grazing, the recent findings are viewed as generally encouraging to local cattle producers.
Ranchers who graze their stock on any of the approximately 300,000 acres of prairie grassland within the county are the target audience for the Conservancy's and Oregon State University's July 21 field day highlighting research results, which may hold relevance for these stock growers.
Jeff Fields, director for the Conservancy's Zumwalt Project, thinks around 50 producers' operations fit the profile.
According to Fields, the Conservancy owns roughly 10 percent of the local area's grassland, which he said ought to remain a working landscape. Grazing, he adds, is one of the most compatible uses for this type of ground. So we have an interest in seeing grazing done well, he says, explaining the main motive underlying the experiment, which was conducted on 1,600 acres on the conservation organization's Zumwalt Prairie Preserve.
The study focused on four separate 400-acre blocks. Each block was in turn divided into four separate 100-acre pastures. Ecologist Rob Taylor, the Conservancy's principal researcher for the study, points out that 100 acres is a normal pasture size in real-world grazing.
After fencing off the blocks and pastures in 2005, researchers collected field data in 2006, before grazing commenced in 2007 and continued a second year in 2008. In both years, grazing occurred through two months, June and July. The post-project year of 2009 saw another round of intensive field data collection, setting up comparisons to the pre-grazing data.
Within each block, experimenters devoted pastures to different grazing intensities one pasture hosting no grazing, and the other three grazed at low, medium and high intensities, respectively. Low-intensity grazing included 12 cow/calf pairs and three heifers; medium had 16 cow/calf pairs and four heifers; and grazing at high intensity involved 20 cow/calf pairs and five heifers.
Making the Zumwalt study unique, researchers say, is the broad scope of potential effects it measured everything from soil compaction to prevalence or absence of plants, pollinating insects, and ground-nesting birds. In essence, it's looking at the entire food web, Taylor says.
The study also measured cattle performance and grazing efficiency.
While there seemed to be good news for ranchers in the paucity of negative effects associated with medium- or low-intensity grazing, a few such effects were observed. Perhaps most notable, spiders suffered at all grazing levels. Despite spiders' importance to birds, however, most songbird species nonetheless fared well in pastures with less-than-heavy grazing.
Generally, control, low and moderate stocking rates all seem to function well for songbirds, Taylor remarked.
Songbirds, as a group, were noticeably affected by heavy grazing. The impact was especially negative for savannah sparrows and grasshopper sparrows, Taylor said.
Among a number of other negative effects observed in high-stocked pastures:
A majority of bee species suffered, with bumble bees and mason bees taking the most remarkable hits. Taylor said ground digger bees coped a little better under heavy grazing.
Butterfly abundance fell 30 percent. Butterflies, like bees, are pollinators.
Soil compaction increased significantly. Too much compaction can inhibit water infiltration, a bad trend for a pasture.
Taylor said stock growers tend to be rather interested in soil conditions. It's the foundation of their business, he said.
Oregon State University, which cooperated in the study, will co-sponsor the July 21 field day. At one point during the day's program, local Extension agent John Williams will lead a discussion on producer ideas for future research.
The program will begin at 8 a.m. at Cloverleaf Hall, and later moves to the Zumwalt Prairie Preserve. Sponsors will provide transportation between Cloverleaf Hall and the Preserve.
Space is limited. To register, contact Fields at 541-426-3458 ext. 1.