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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Sheep Grazing on Grasshopper Population Dynamics and Rangeland Vegetation

Authors
item Branson, David
item Haferkamp, Marshall

Submitted to: Research Update for Fort Keogh Livestock and Range Research Laboratory
Publication Type: Popular Publication
Publication Acceptance Date: October 15, 2003
Publication Date: January 15, 2003
Repository URL: http://www.larrl.ars.usda.gov/publications.htm
Citation: BRANSON, D.H., HAFERKAMP, M.R. EFFECTS OF SHEEP GRAZING ON GRASSHOPPER POPULATION DYNAMICS AND RANGELAND VEGETATION. RESEARCH UPDATE FOR FORT KEOGH LIVESTOCK AND RANGE RESEARCH LABORATORY. p. 19-20. 2003.

Interpretive Summary: Grasshopper outbreaks on rangeland result in competition with wildlife and livestock for limited resources. Little effort has focused on management strategies that may reduce the likelihood or intensity of grasshopper outbreaks. Recent research suggests that habitat manipulation in the form of grazing management can reduce grasshopper populations on rangeland in the Northern Great Plains, although the precise mechanisms are unknown. The timing and intensity of livestock grazing can impact grasshopper population dynamics by changing host plant quality and quality and habitat structure. An experiment was conducted in the summer of 2000 at Fort Keogh Livestock and Range Research Lab in Montana to determine how early summer, late summer, repeated, and no livestock grazing affects grasshopper population dynamics and vegetation characteristics: and, to determine if there are interactions between grazing treatments and grasshopper densities. 10m ² screen cages were stocked at 33% and 100% of field density, with ewes temporarily placed inside cages. Field grasshopper densities at stocking were 120 per m². Livestock grazing significantly reduced both vegetation biomass and grasshopper density, although the specific grazing treatments did not differ in their effects. There were no significant interactions. Grasshopper densities in 2001 were lower in treatments which has high grasshopper numbers in 2000. It appears grazing management may not have large effects when initiated during periods of high grasshopper densities. Similar experiments are needed with lower grasshopper densities and varying climate conditions to more fully examine the interactions between grazing and grasshopper population dynamics. Although there was no effect of sheep grazing on crude protein content of remaining grass in 2000, cages with sheep grazing had higher grass crude protein content in 2001. Cages with sheep grazing also had increased amounts of nitrate in the ion-exchange resin capsules, indicating more nitrogen was available for plants in 2001. Therefore, livestock grazing affected vegetation quality and nitrogen availability in the second year of the experiment. Although sheep grazing did not have large effects on grasshopper population dynamics during a severe grasshopper outbreak, the effects of livestock grazing on vegetation quality and nitrogen availability evident in the second year of the experiment are likely to indirectly affect grasshopper population dynamics.

Technical Abstract: Grasshopper outbreaks on rangeland result in competition with wildlife and livestock for limited resources. Little effort has focused on management strategies that may reduce the likelihood or intensity of grasshopper outbreaks. Recent research suggests that habitat manipulation in the form of grazing management can reduce grasshopper populations on rangeland in the Northern Great Plains, although the precise mechanisms are unknown. The timing and intensity of livestock grazing can impact grasshopper population dynamics by changing host plant quality and quality and habitat structure. An experiment was conducted in the summer of 2000 at Fort Keogh Livestock and Range Research Lab in Montana to determine how early summer, late summer, repeated, and no livestock grazing affects grasshopper population dynamics and vegetation characteristics: and, to determine if there are interactions between grazing treatments and grasshopper densities. 10m ² screen cages were stocked at 33% and 100% of field density, with ewes temporarily placed inside cages. Field grasshopper densities at stocking were 120 per m². Livestock grazing significantly reduced both vegetation biomass and grasshopper density, although the specific grazing treatments did not differ in their effects. There were no significant interactions. Grasshopper densities in 2001 were lower in treatments which has high grasshopper numbers in 2000. It appears grazing management may not have large effects when initiated during periods of high grasshopper densities. Similar experiments are needed with lower grasshopper densities and varying climate conditions to more fully examine the interactions between grazing and grasshopper population dynamics. Although there was no effect of sheep grazing on crude protein content of remaining grass in 2000, cages with sheep grazing had higher grass crude protein content in 2001. Cages with sheep grazing also had increased amounts of nitrate in the ion-exchange resin capsules, indicating more nitrogen was available for plants in 2001. Therefore, livestock grazing affected vegetation quality and nitrogen availability in the second year of the experiment. Although sheep grazing did not have large effects on grasshopper population dynamics during a severe grasshopper outbreak, the effects of livestock grazing on vegetation quality and nitrogen availability evident in the second year of the experiment are likely to indirectly affect grasshopper population dynamics.

Last Modified: 4/23/2014
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