Grasshopper responses to fire and postfire grazing in the northern Great Plains vary among species

Authors: Branson, David - Dave; Vermeire, Lance

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2015
Publication Date: 3/1/2016
Publication URL: http://handle.nal.usda.gov/10113/62127
Citation: Branson, D.H., Vermeire, L.T. 2016. Grasshopper responses to fire and postfire grazing in the northern Great Plains vary among species. Rangeland Ecology and Management. 169(2):144-149. doi:10.1016/j.rama.2015.10.005.

Interpretive Summary: Large grasshopper outbreaks typically lead to large scale chemical control efforts, but habitat management approaches to address grasshopper problems have received much less attention. As grasshoppers are highly responsive to factors such as altered habitat structure and food availability, rangeland management practices may affect grasshopper populations by impacting development, survival and reproduction. We examined the responses of grasshoppers to late summer fire and post-fire grazing intensity to aid in post-fire grasshopper management decisions. Fire reduced grasshopper densities by 36 to 53%, while post-fire grazing intensity had smaller effects. Late summer fire appears to be a useful management tool to reduce grasshopper populations in the northern Great Plains. Knowledge of grasshopper species composition, fire fuel levels, and the timing of fire are required to allow managers to accurately predict fire impacts. The results show that large reductions in grasshopper populations can be sustained for at least 2 years post-fire through a combination of adult and egg mortality, indicating that late summer fire can be a useful management tool that provides extended grasshopper control. To allow more accurate management recommendations, additional research is needed examining effects of the seasonal timing of fire on grasshopper populations in the northern Great Plains.

Technical Abstract: Rangeland management practices such as burning and grazing management may affect grasshopper populations by impacting development, survival and reproduction. Experiments are lacking in the northern Great Plains examining the effects of fire and grazing intensity on grasshoppers. As part of a larger study examining vegetation responses to late summer fire and post-fire grazing utilization in semiarid mixed prairie in eastern Montana, we examined the responses of grasshoppers to late summer fire and post-fire grazing intensity to aid in grasshopper management decisions. The experiment was repeated using adjacent blocks, with blocks receiving fire treatment in either 2003 or 2004 and grazing in the following year. Treatments were no fire and no grazing, and summer fire followed by grazing at 0, 17 or 50% forage utilization on a biomass basis. Grasshopper sampling was conducted before fire and for 2 years post-fire. Fire reduced grasshopper density 36 to 53% across experiments, periods and postfire grazing treatments. The two most abundant grasshopper species, Ageneotettix deorum (Scudder) and Opeia obscura (Thomas), were reduced 80 and 84% the first year after fire in Experiment 1, but only O. obscura was affected by fire in Experiment 2. The effects of fire were dependent on fire intensity and continuity, the timing of fire, and grasshopper species composition. Grasshopper populations were more strongly affect by fire than by post-fire grazing. Fire intensity will determine whether late summer fire would control populations of shallow egg laying species, while fire timing will determine the level of control for species laying deeper egg pods. As large reductions in grasshopper populations can be sustained for 2 years post-fire, late summer fire can be a useful grasshopper management tool.