Cattle-wild ungulate effects on sagebrush plant communities

Background/Question/Methods

Livestock and wild ungulates co-exist on many of the world’s rangeland ecosystems, and alone or in combination can cause major changes to soils and plant communities. Distinguishing between the effects of domestic livestock and wild ungulates (e.g., deer and elk) which differ in diets and feeding habits is of both ecological significance and applied management importance.  Here we use a set of long-term exclosures to determine how livestock vs. wild ungulates affect sagebrush steppe plant communities which historically covered ~62 million ha in North America.  We used a series of long-term 90m x 90m exclosures to investigate the separate and combined effects of cattle (managed under a rotational grazing system) and wild ungulates in an area of sagebrush steppe in northern Utah.  We used semi-permeable fencing to create the following three exclosure treatments:  1) all large herbivores (i.e., cattle + wild ungulates) excluded, 2) livestock excluded, 3) no large herbivores excluded.  We sampled plant community composition and densities of key plant species  in 2013, twenty-two years after the initiation of the experiment.

Results/Conclusions

Plant community ordinations indicate that overall plant community composition varied far more among sites than among treatments. Effect size analyses of individual key plant species, however revealed over-riding effects of different types of herbivores. In particular, cattle appeared to drive an increase in abundance of sagebrush shrubs in the intermediate (most common) size class.  Densities of some perennial grass species, such as bluebunch wheatgrass (Pseudoroegneria spicata) were reduced by cattle but not wild ungulates, whereas other grass species such as squirreltail (Elymus elymoides) were reduced by cattle alone as well as the combination of both cattle and wildlife. These results suggest that although different herbivory regimes have not caused sagebrush plant communities to undergo major state changes, more subtle changes are occurring.