Interest in grassland fire stems from its use as a management tool and unplanned events; however, there is increased interest in using fire to shift grazing animal distribution and to increase the structural heterogeneity of rangelands. However, experiments are lacking in the northern Great Plains that examine the effects of fire and grazing on grasshopper population dynamics. As part of a larger study examining patch burning effects on plant community dynamics, animal performance, grazing distribution and foraging efficiency at a northern mixed prairie site in eastern Montana, we examined how patch burning and livestock grazing affects grasshopper population dynamics from 2007 through 2010. Homogenous and heterogeneous management treatments were assigned to six pastures, with heterogeneity created by burning 25% of each treatment pasture in a given year. Total grasshopper density was estimated by counting the number of grasshoppers within a series of 60, 0.1m2 aluminum wire rings in each plot, with sweep net samples used to establish grasshopper community composition.
Results/Conclusions
Patch burning effects on grasshopper populations differed significantly between years, likely due to differences in fire timing and intensity. Weather effects on vegetation production led to differences in fire intensity across years. Grasshopper populations were strongly reduced in some years, including a one-third reduction following fire in 2009 which was associated with higher vegetation production. Burning during high vegetation production years has been shown to cause egg mortality of grasshopper species laying shallow egg pods, while direct mortality occurs when fire timing occurs when the dominant species are alive. Minimal impacts were observed following a spring burn, which occurred before the dominant grasshopper species hatched. No strong patch level impacts of post-fire livestock grazing on grasshoppers were detected. Although fire effects on grasshoppers have been well studies in more productive grassland systems, the results point to the need for additional research on how the timing and intensity of grassland fires affect grasshopper populations in less productive grasslands.