Tuesday, August 7, 2007 - 2:30 PMCOS 57-4: Restoration of semi-arid rangelands through alternative livestock treatments
Matthew R. R. Loeser, Yakima Valley Community College, Thomas D. Sisk, Northern Arizona University, and Timothy E. Crews, Prescott College.
The restoration of degraded rangelands in the American Southwest is a common goal of livestock ranchers, land managers, and those who advocate for cattle-free rangelands. Surprisingly divergent viewpoints have been advocated for the shared goal of increasing diversity and productivity of a plant community. These views range from complete cessation of livestock grazing to dramatic increases in cattle density. In a northern Arizona grassland, we evaluated responses of native and non-native plant species to a gradient of grazing treatments (cattle removal, moderate grazing, and high-impact grazing) during an eight year experiment. We found strong evidence that 1) grazing effects on the plant community were contingent upon climate; 2) cattle removal consistently showed decreased native plant species richness relative to moderate grazing; 3) neither cattle removal nor high-impact grazing reduced non-native plant species richness; and 4) high-impact grazing led to an eight-fold increase in the annual non-native, Bromus tectorum (cheatgrass). Our results suggest that some intermediate level of cattle grazing may maintain greater levels of native plant diversity than the alternatives of cattle removal or high-impact grazing. Furthermore, episodic drought interacts with cattle grazing, leading to infrequent, but biologically important shifts in plant communities. In semi-arid rangelands, alternatives to current livestock practices may typically require decadal time scales to achieve broad restoration goals for plant communities.