Photo: Bison in Yellowstone National Park. Copyright 2020 Delena Norris-Tull
Cattle versus bison grazing: Effects on reduction of noxious weeds
Summaries of the research and commentary, prepared by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, 2020, updated. November 2024.
Towne, Hartnett, & Cochran, 2005, point out that bison “played a keystone role” in the development of tallgrass prairies. For the past 150 years, cattle have been the primary herbivores in Kansas grasslands. Towne, et al., 2005, wanted to study the similarities and differences between the grazing effects of these two large herbivores.
In a 10-year study, Towne, Hartnett, & Cochran, 2005, “compared vegetation changes in Kansas… tallgrass prairie that was burned and grazed season-long at a moderate stocking rate by either bison or cattle.” The control was ungrazed prairie that was also burned annually. They “held management practices constant between the herbivores and equalized grazing pressure by matching animals so that the total body mass in all pastures was similar each year.” They constructed 8 pastures. Four were grazed by bison and four were grazed by cattle. The pastures were grazed from May to October.
Towne, et al., 2005, found that, “Temporal trends in the cover of perennial warm-season grasses increased in the absence of grazing but did not significantly change through time in either bison or cattle pastures.” But there were differences between cattle and bison grazing in the growth responses of individual plant species. “Big bluestem cover increased… in cattle pastures and in ungrazed prairie, but did not significantly change through time in bison pastures… Little bluestem cover declined… in bison pastures, but remained stable in pastures grazed by cattle and in ungrazed prairie… Switchgrass… cover increased in the absence of grazing, declined in pastures grazed by cattle, and remained unchanged through time in bison pastures.” Tall dropseed declined in ungrazed prairie. Side-oats grama increased in pastures grazed by both bison and cattle. Indiangrass cover remained stable in all treatments. [These are all native perennial grasses important to American prairies.]
Within cool-season graminoids, Scribner’s panicum and prairie Junegrass both increased in bison and cattle pastures, but decreased in ungrazed prairie. These are both native perennial grasses. Kentucky bluegrass cover “did not change significantly through time in either grazed or ungrazed prairie.” Sedges also increased in both bison and cattle pastures, “and declined through time in ungrazed prairie.” [Kentucky bluegrass is not native to North America, but is commonly used in lawns, and can become weedy in disturbed areas.]
“Perennial [native] forb cover increased… in response to grazing, but the temporal changes were greater in bison pastures.”
Annual forbs “increased at a greater rate in pastures grazed by bison than in pastures grazed by cattle, and did not change through time in ungrazed prairie… Average cover of annual grasses (primarily Japanese brome [an invasive]… and six-weeks fescue [a native grass]) was higher… in bison pastures than in pastures grazed by cattle, but their cover never exceeded 0.5% in any year. Annual grasses were absent in ungrazed prairie.” Shrub cover did not differ among treatments, with the exception of leadplant cover, which “increased… in response to cattle grazing, but did not did not change through time in either bison pastures or ungrazed prairie.”
Towne, et al., 2005, found that, “Grazing by either herbivore increased the canopy cover of annual forbs, perennial forbs, and cool-season graminoids, but both annual and perennial forb cover increased at a greater rate in bison pastures than in cattle pastures.” They found that, “Although bison and cattle differentially altered some vegetation components, the plant communities in bison and cattle pastures were 85% similar after 10 years of grazing.” And after 10 years, there was only 62% similarity between bison grazing and ungrazed priaire; and 67% similarity between cattle grazing and ungrazed prairie).
Towne, et al., 2005, concluded that, “Species richness… increased… in response to grazing,” but the richness was greater with bison grazing. “After 10 years of grazing, species richness was 37% higher in bison pastures and 29% higher in cattle pastures than in ungrazed prairie… Exotic species averaged 3.6% of the floristic richness in bison pastures, 3.4% in cattle pastures, and 2.0% in ungrazed prairie.” “Moderate stocking with either bison or cattle increased spatial heterogeneity and promoted biodiversity of tallgrass prairie.”
Delena’s thoughts: This one-of-a-kind, long-term study demonstrates the complex nature of using grazing either for increasing species diversity in tallgrass prairie or for controlling encroachment by invasive species. The ungrazed prairie had slightly less encroachment by invasives, but far less species diversity over time. Unfortunately, it is rare for biological researchers to obtain grant funding that allows such a long-term study to be carried out. And it may be that we have to accept a certain level of encroachment in order to preserve native prairies.
Reference:
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Cattle versus bison grazing: Effects on reduction of noxious weeds
Summaries of the research and commentary, prepared by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, 2020, updated. November 2024.
Towne, Hartnett, & Cochran, 2005, point out that bison “played a keystone role” in the development of tallgrass prairies. For the past 150 years, cattle have been the primary herbivores in Kansas grasslands. Towne, et al., 2005, wanted to study the similarities and differences between the grazing effects of these two large herbivores.
In a 10-year study, Towne, Hartnett, & Cochran, 2005, “compared vegetation changes in Kansas… tallgrass prairie that was burned and grazed season-long at a moderate stocking rate by either bison or cattle.” The control was ungrazed prairie that was also burned annually. They “held management practices constant between the herbivores and equalized grazing pressure by matching animals so that the total body mass in all pastures was similar each year.” They constructed 8 pastures. Four were grazed by bison and four were grazed by cattle. The pastures were grazed from May to October.
Towne, et al., 2005, found that, “Temporal trends in the cover of perennial warm-season grasses increased in the absence of grazing but did not significantly change through time in either bison or cattle pastures.” But there were differences between cattle and bison grazing in the growth responses of individual plant species. “Big bluestem cover increased… in cattle pastures and in ungrazed prairie, but did not significantly change through time in bison pastures… Little bluestem cover declined… in bison pastures, but remained stable in pastures grazed by cattle and in ungrazed prairie… Switchgrass… cover increased in the absence of grazing, declined in pastures grazed by cattle, and remained unchanged through time in bison pastures.” Tall dropseed declined in ungrazed prairie. Side-oats grama increased in pastures grazed by both bison and cattle. Indiangrass cover remained stable in all treatments. [These are all native perennial grasses important to American prairies.]
Within cool-season graminoids, Scribner’s panicum and prairie Junegrass both increased in bison and cattle pastures, but decreased in ungrazed prairie. These are both native perennial grasses. Kentucky bluegrass cover “did not change significantly through time in either grazed or ungrazed prairie.” Sedges also increased in both bison and cattle pastures, “and declined through time in ungrazed prairie.” [Kentucky bluegrass is not native to North America, but is commonly used in lawns, and can become weedy in disturbed areas.]
“Perennial [native] forb cover increased… in response to grazing, but the temporal changes were greater in bison pastures.”
Annual forbs “increased at a greater rate in pastures grazed by bison than in pastures grazed by cattle, and did not change through time in ungrazed prairie… Average cover of annual grasses (primarily Japanese brome [an invasive]… and six-weeks fescue [a native grass]) was higher… in bison pastures than in pastures grazed by cattle, but their cover never exceeded 0.5% in any year. Annual grasses were absent in ungrazed prairie.” Shrub cover did not differ among treatments, with the exception of leadplant cover, which “increased… in response to cattle grazing, but did not did not change through time in either bison pastures or ungrazed prairie.”
Towne, et al., 2005, found that, “Grazing by either herbivore increased the canopy cover of annual forbs, perennial forbs, and cool-season graminoids, but both annual and perennial forb cover increased at a greater rate in bison pastures than in cattle pastures.” They found that, “Although bison and cattle differentially altered some vegetation components, the plant communities in bison and cattle pastures were 85% similar after 10 years of grazing.” And after 10 years, there was only 62% similarity between bison grazing and ungrazed priaire; and 67% similarity between cattle grazing and ungrazed prairie).
Towne, et al., 2005, concluded that, “Species richness… increased… in response to grazing,” but the richness was greater with bison grazing. “After 10 years of grazing, species richness was 37% higher in bison pastures and 29% higher in cattle pastures than in ungrazed prairie… Exotic species averaged 3.6% of the floristic richness in bison pastures, 3.4% in cattle pastures, and 2.0% in ungrazed prairie.” “Moderate stocking with either bison or cattle increased spatial heterogeneity and promoted biodiversity of tallgrass prairie.”
Delena’s thoughts: This one-of-a-kind, long-term study demonstrates the complex nature of using grazing either for increasing species diversity in tallgrass prairie or for controlling encroachment by invasive species. The ungrazed prairie had slightly less encroachment by invasives, but far less species diversity over time. Unfortunately, it is rare for biological researchers to obtain grant funding that allows such a long-term study to be carried out. And it may be that we have to accept a certain level of encroachment in order to preserve native prairies.
Reference:
- Towne, E.G., Hartnett, D.C., & Cochran, R.C. (Oct. 1, 2005). Vegetation trends in tallgrass prairie from bison and cattle grazing. Ecological Applications, 15: 1550-1559.
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