South Dakota Grassland Coalition

by Jake Comer and Lora Perkins

Sept 2019

In the northern Great Plains

Land surface disturbances, such as grazing and fire, are responsible for creating one of the largest grasslands on earth. Historically, bison would graze large expanses in response to wildfires that occurred ever 5 to7 years. This natural rotation, of grazing and fire, resulted in highly diverse ecosystems. However, wildfire was largely eliminated and bison were hunted to near extinction during the time of European settlement. This dramatically decreased diversity as plant communities most beneficial and palatable to livestock were favored. This decline in diversity reduced ecosystem services, which is defined as the benefits people obtain from the ecosystem.

As plant and livestock people, we might not think about soil microbes and soil hydrology so much. However, both are key players for ecosystem services; but we do not know how land surface disturbances (such as fire and grazing) impact soil microbes and soil hydrology. Soil microbes help promote plant growth and species diversity. The soil microbial community also drives nutrient and carbon cycling. Soil hydrological processes (such as runoff and soil loss) are also obviously important for maintaining ecosystem services. Therefore, we con-ducted research at Cottonwood Research Station to investigate how high-intensity winter grazing and a wild-fire impacted the soil microbial community and soil hydrology.

Our intense winter grazing (IWG) included 120 heifers that were grazed on approximately 150 acres until the vegetation reached a height of about 3 inches, which occurred in roughly one month. This was compared to two adjacent treatment areas, a wildfire (WF) and conventional grazing (CG) that involved grazing 20 yearling steers on approximately 150 acres during the summer growing season (May-Aug). In each of these areas, soil tests were performed to determine total soil microbial biomass and diversity. Computer modeling paired with field data was used to determine the severity of runoff and soil loss that occurred in each treatment area.

The results from this study suggest that the soil microbial community diversity and microbial biomass is resistant to grazing and wildfire. However, aboveground vegetation greatly influenced the soil microbial community. Areas that had higher amounts of tall-grass species had much higher total soil microbial biomass than areas with a higher percentage of shortgrass species following the wildfire. Therefore, specific site characteristics may influence the soil microbial community more than grazing or wildfire.

Conversely, grazing and fire greatly influenced the amount of runoff and soil loss that occurred. Intense winter grazing did not increase the amount of soil loss that occurred when compared to the conventional grazing strategy. However, following wildfire the amount of soil loss increased 444% – 3,094% when compared to conventional grazing. This supports that winter-grazing at high intensities can be used without causing adverse effects to the amount of runoff that occurs.


To compare the impacts of high-intensity winter grazing, wildfire, and summer-long conventional grazing on soil microbial communities and hydrological processes. We found that winter grazing does not cause adverse effects on the soil microbial community or soil loss. Wildfire also did not result in adverse effects to the soil microbial community but did increase soil loss. With a better understanding of the impacts of high-intensity winter grazing, decisions can be made about the suitability of this alternative grazing strategy used in the Northern Great Plains.

Source: SDGC Newsletter

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