Impacts of holistic planned grazing with bison compared to continuous grazing with cattle in South Dakota shortgrass prairie

Abstract

We assess holistic planned grazing outcomes in shortgrass prairie of the Northern Great Plains of North America. We compared key ecosystem functions on the ranch managed using adaptive multi-paddocks (AMP) grazing by bison with those on neighboring ranch paddocks managed using set stocked light continuous (LCG) and heavy continuous grazing (HCG) grazed by cattle. Sites on the neighboring ranches in each grazing category were paired for sampling by soil type and landscape position. In all paddocks, management practices had been constant for more than a decade. Positive results with AMP grazing include increased fine litter cover (P < 0.05), improved water infiltration (P < 0.06), two to three times the available forage biomass (P < 0.001), improved plant composition (P < 0.05), decrease in invasive plants (P < 0.05), and decrease in bare ground (P < 0.05). Higher infiltration occurred with AMP on soils having higher permeability but not on soils having a high clay content. Differences were greatest between AMP and HCG management with LCG being intermediate. Counterintuitively, herbaceous biomass in LCG was less than that of the more heavily stocked HCG (P < 0.05). This was due to decades of heavy continuous grazing resulting in HCG being dominated by invasive herbaceous plants of no forage value in contrast to LCG paddocks that had a greater proportion of palatable forages. The HCG paddocks were dominated by unpalatable invasive plants that were avoided by cattle. Soil carbon stocks increased under the AMP grazing but not on all soils. Total carbon stocks (TC), summing organic carbon and inorganic carbon, were not different between the AMP and LCG grazing strategies (P > 0.63) but both had higher TC values across all soils than HCG (P < 0.001). There were no differences in TC among grazing treatments on the different soils (P > 0.46) except on the Norrest silty clay loam soil that had the highest permeability. On this soil there were differences between AMP and HCG (P < 0.0001) and LCG and HCG (P < 0.0001). There were significantly lower TC levels at all soil depths with HCG than with AMP and LCG (P < 0.05). Using holistic planned grazing protocols with AMP grazing effectively limited overstocking and overgrazing by adjusting animal numbers to match available forage amounts and grazing for short periods followed by adequate recovery after grazing. This study indicated ecological improvements by AMP grazing on the 777 Bison Ranch compared to HCG pastures is contributing to improvements in this semi-arid short grass ecosystem.