Mitch Stephenson, Range Management Specialist
Reduced rangeland health is often the result of poor livestock grazing distribution, or the uneven dispersion of grazing within a pasture. Livestock grazing patterns are influenced by a number of abiotic and biotic variables. Abiotic variables include topographic position on a landscape and the distance cattle must travel to water within a pasture. Biotic variables include spatial differences in plant species composition, forage biomass, and forage quality. Understanding the interaction between livestock grazing and spatial variability across a landscape is important for improving rangeland health and managing towards specific rangeland objectives.
Recent research collaborations with the USDA-Agricultural Research Service collected data from global positioning system (GPS)-collars on cattle at UNL ranches to quantify how cattle select areas of pastures under diverse management scenarios. Topographic positions within the pastures were classified as lowlands, flat plains, open slopes, and uplands (see Figure 1) and cattle selection preference was quantified based on the amount of time cattle grazed within these topographic positions (see Figure 2).
Cattle selected preferentially for lowlands and flat plains compared to uplands at both the Gudmundsen Sandhills Lab and Barta Brothers Ranch.
Figure 2. Selection ratio, or the predicted grazing use relative to the topographic position class area availability within a pasture, for cattle grazing at the UNL Gudmundsen Sandhills Lab and the UNL Barta Brothers Ranch. Values greater than 1 indicate preference, value less than 1 indicate avoidance or non-preference, and values near 1 indicate no preference or avoidance (i.e., neutral) of the topographic position class.
Spatial variability in topography is common in the Nebraska Sandhills. Dunes (slopes and uplands), lowlands, and flat plains influence the types of plant species present. For example, needlegrasses, little bluestem, and prairie sandreed are typically more common on the dunes compared to lowlands even at small spatial scales. Biomass is often higher at lowland positions because of increased early-season soil moisture and greater soil nutrient availability. Because of the higher grazing preference and selection, the lowland and flat plain areas between the dunes in the Sandhills are at a higher risk for being consistently overutilized. Greater grazing preference on these sites can reduce rangeland health and productivity, even if grazing pressure is only light on closely associated slopes and uplands.
Each grazing scenario is different and local abiotic and biotic variables on individual ranches provide challenges and opportunities for managing cattle grazing. Having areas within a pasture that typically receive heavy grazing and other areas that are underutilized may not be all negative. In fact, this gradient of use can be a desirable option for some wildlife and plant species because it creates a diversity of environments for different species to thrive. However, other areas that have a long history of heavy grazing pressure may benefit from management that reduces grazing pressure, improves grazing uniformity, and increases use of underutilized areas of a pasture. Having a clear understanding of your rangeland resources and how cattle graze them will aide decision making, improve rangeland health, and enhance ecosystem services provided by native rangelands.