Variation in grasshopper (Acrididae) densities in response to fire frequency and bison in tallgrass prairie
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Authors: A. Joern
Date: 2004
Journal: Environmental Entomology
Volume: 33
Number: 6
Pages: 1617-1625
Summary of Methods: The effects of bison grazing (graze or ungrazed) and long-term application of four fire intervals (1, 2, 4 and 20 years) on grasshopper densities were studied at the Konza Prairie in Kansas for one summer. Grasshopper densities estimations were made over two weeks in August. Canopy height, plant species richness and biomass of grasses and forbs were measured at the same time.
Article Summary / Main Points: Bison grazing and fire frequency increase grasshopper densities at varied levels, though the interaction of grazing and fire had no effect on the number of grasshoppers. Overall, grasshopper densities were higher on grazed sites. Fire frequency did not affect grasshopper densities, although numbers tended to be lower on sites burned every 20 years. As grass biomass and canopy height increased grasshopper densities decreased; as the spatial variability of canopy structure increased so did grasshopper densities.
Vegetation Types: Tallgrass Prairie
MLRA Ecoregions: 106 Nebraska and Kansas Loess-Drift Hills
Agrovoc Control Words: Grasshoppers Grazing Postfire ecology
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: bison grazing, konza prairie, orthoptera, population dynamics, prescribed burning
Annotation: The specific findings from this one year replicated study are only applicable to tallgrass prairies, though the general principles effecting community structure and habitat selection are applicable to all rangeland communities. As is true for all grazing research, the results are most directly applicable to areas with similar landscapes, type of ungulates, weather conditions and season of use. Further research into climatic factors, such as long term effects of drought or wet years on grasshopper populations is needed. As this was only a one-year study, the long-term effects of grazing management still need to be addressed. Grazing studies on grasshopper densities suggest that the impact of livestock grazing on grasshoppers depends upon the season, the species, and the plant community. Therefore, some grasshopper species benefit from grazing while others are negatively impacted depending on climate and intensity of grazing. Jepson-Innes and Bock (1989, Oecologia 78:430-431) showed that cattle grazing can have a positive or negative impact on grasshoppers, depending on the species and the type of forage relevant to that species. Joern (2005, Ecology 86:861-873) studied the effect bison grazing and fire frequency has on grasshopper species richness, also available on the RSIS website; with both Joern papers highlighting apositive correlation grazing has on grasshopper densities and species richness.
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