Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2010
Publication Date: October 6, 2010
Repository URL: http://hdl.handle.net/10113/44839
Citation: Branson, D.H., Sword, G.A. 2010. An experimental analysis of grasshopper community responses to fire and livestock grazing in a northern mixed-grass prairie. Environmental Entomology. 39(5): 1441-1446. Interpretive Summary: We recently argued in a review paper that burning and livestock grazing could be used as important habitat manipulation tools for use in ecologically-based grasshopper management strategies that seek to prevent or moderate the occurrence of damaging outbreaks. In contrast to chemical control, habitat manipulations have the potential to maintain or promote existing ecological feedbacks that keep grasshopper populations below economically-threatening levels. However, opportunities to conduct the long-term manipulative ecological experiments necessary to examine the effects of large-scale habitat manipulations on grasshopper populations are rare. In this study, we examined the effects of grazing and fire on grasshopper population density and community composition in a northern Great Plains mixed-grass prairie. We employed a large-scale experimental design across five years to examine the separate and interactive effects of three different grazing systems in burned and unburned habitats. Even during a period with low grasshopper densities, livestock grazing significant affected grasshopper community composition. However, additional long term studies during periods with increasing grasshopper densities are required to better assess if grazing or fire will act to reduce the probability of grasshopper outbreaks.
Technical Abstract: The outcomes of grasshopper responses to both vertebrate grazing and fire vary across grassland ecosystems, and are strongly influenced by local climactic factors. Thus, the possible application of grazing and fire as components of an ecologically-based grasshopper management strategy must necessarily be investigated in regional studies. In this study, we examined the effects of grazing and fire on grasshopper population density and community composition in a northern Great Plains mixed-grass prairie. We employed a large-scale, replicated, and fully-factorial manipulative experimental design across five years to examine the separate and interactive effects of three different grazing systems in burned and unburned habitats. Differences in grasshopper community composition were greatest between sites based on non-metric multidimensional scaling ordination. However, the results from a permutational MANOVA indicate that both fire and grazing significantly affected grasshopper community composition, with a significant fire*grazing interaction in season long grazing pastures. The finding of a significant grazing*fire interaction matches vegetation sampling data conducted as part of a larger study, as livestock removed more biomass from burned areas in season-long grazing pastures. Both Shannon diversity and numerical species richness were higher under rotational grazing than in either season-long grazing or grazing exclosures. Therefore, both fire and grazing affected grasshopper community composition but had minimal effects on overall grasshopper densities. As this study was conducted during a multi-year period with low grasshopper densities, additional long term studies conducted while grasshopper population densities are increasing will be required to assess how grazing and fire will impact the probability of grasshopper outbreaks.