Restoration of semi-arid rangelands through alternative livestock treatments

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.