Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/13/2008
Publication Date: 7/1/2008
Citation: France, K., Ganskopp, D.C., Boyd, C.S. 2008. Interspace/under-canopy foraging patterns of beef cattle in sagebrush. Rangeland Ecology and Management. 61(4):389-393 Interpretive Summary: With a potential Threatened and Endangered listing of sage grouse by the US Fish and Wildlife Service on the horizon, ranchers and land management agencies needed information on the patterns of forage selection and grazing behavior of cattle grazing on sagebrush / bunchgrass rangelands. Because sage grouse typically nest beneath sagebrush canopies, and adjacent vegetation provides nest screening cover, information was needed describing how cattle selected grasses out in the open and beneath sagebrush. We found cattle initially preferred to forage on grasses in inter-spaces between sagebrush. When 35 percent of the grass crop was removed, however, cattle begin looking beneath sagebrush to find and use ungrazed grasses. After cattle had removed 75 percent of the standing crop in pastures, ground level screening cover was reduced by only 5 percent, suggesting that sagebrush canopies furnished most of the nest screening cover. Cattle were also less likely to graze grasses beneath larger umbrella-shaped shrubs with branches near the ground. With the conservative stocking rates used on most public sagebrush dominated rangelands, managed cattle grazing should have little effect on potential nest site screening cover beneath shrubs. These findings will help both public and private land and livestock managers develop grazing programs that minimally affect birds nesting beneath sagebrush canopies.
Technical Abstract: Livestock grazing has been indirectly implicated in sage-grouse (Centrocercus urophasianus) declines in the western United States and southern Canada; however, there is little scientific research directly relating the two. Sage-grouse nest under sagebrush (Artemesia sp.) plants and near-nest herbaceous plants provide important screening cover for nesting birds . Our objectives were to investigate the grazing patterns of cattle with respect to under-canopy (shrub) and interspace grass tussocks, determine the influence of cattle grazing on nest-site screening cover, and relate shrub morphology to under-canopy grazing occurrence. We also determined the influence of stocking rate and geo-physical variables on grazing patterns at a larger pasture (800ha) scale. An 18-day, replicated, small pasture trial was conducted in the summers of 2003 and 2004 (trial 1). Grazing of under-canopy grass tussocks was negligible at light to moderate utilization levels (<35%). Grass tussocks under spreading, umbrella-shaped shrub canopies were less likely to be grazed than those under erect and narrow canopies. Screening cover at potential nest sites decreased with pasture utilization. Removal of 75% of the herbaceous standing crop affected a 5% decrease in ground level screening cover. Screening cover up to a 1-m height decreased at the same rate as lower strata (<30 cm) suggesting that shrubs may provide the majority of screening cover at our site. At the large pasture scale, livestock did not display a conclusive preference based on tussock position relative to sagebrush canopies as pasture utilization increased. Slope (P = 0.036), distance from water (P = 0.006), and stocking rate (P < 0.001) most affected the likelihood of forage selection across the pasture. This work suggests that factors affecting standing crop utilization levels and stock water manipulations can be used to manage potential herbaceous screening cover and distribution patterns of cattle on or near critical habitat.