PS 19-54 - Impacts of different large herbivores on ecosystem function: Cattle increase mean productivity, and wild herbivores reduce variability around the mean

Wednesday, August 10, 2016
ESA Exhibit Hall, Ft Lauderdale Convention Center
Grace K. Charles, Department of Plant Sciences, University of California, Davis, Lauren M. Porensky, Rangeland Resources Research Unit, USDA-ARS, Fort Collins, CO, Corinna Riginos, Department of Zoology and Physiology, University of Wyoming, Laramie, WY, Kari E. Veblen, Dept. of Wildland Resources & Ecology Center, Utah State University, Logan, UT and Truman P. Young, Dept. of Plant Sciences, University of California, Davis, Davis, CA
Background/Question/Methods

Wild herbivores and livestock share the majority of rangelands worldwide, yet few controlled experiments have addressed their individual, additive, and interactive impacts on ecosystem function. While ungulate herbivores generally reduce standing biomass, their effects on aboveground net primary production (ANPP) can vary by herbivore identity and species richness, intensity of herbivory, and spatial and temporal context. Some evidence indicates that moderate levels of herbivory can stimulate aboveground productivity, but few studies have explicitly tested the relationships among herbivore identity, grazing intensity, and ANPP. Here, we used a long-term exclosure experiment to examine the effects of three groups of wild and domestic ungulate herbivores (megaherbivores, meso-herbivore wildlife, and cattle) on productivity in an African savanna. Using both field measurements (productivity cages) and satellite imagery, we measured the effects of different herbivore guilds – separately and in different combinations – on productivity across both space and time. 

Results/Conclusions

Results from both productivity cage measurements and satellite NDVI demonstrated a positive relationship between mean productivity and total ungulate herbivore pressure, driven in particular by the presence of cattle. In contrast, we found that variation in productivity across space and time was driven by herbivore type; wild herbivores (primarily meso-herbivore wildlife) significantly reduced heterogeneity in ANPP across both space and time. Our results indicate that replacing wildlife with cattle (at moderate densities) could lead to similarly productive, but more heterogeneous herbaceous rangelands.