Grasshopper abundance and offtake increase after prescribed fire in semi-arid grassland

Authors: HEIMBUCH, NICHOLAS - University Of Pittsburgh; McGranahan, Devan; Wonkka, Carissa; Vermeire, Lance; Branson, David - Dave

Submitted to: International Journal of Wildland Fire
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Especially during outbreaks, grasshoppers are a management concern in rangelands worldwide. While much research has gone into studying how fire affects grasshoppers directly, in terms of killing eggs and adults, less work has described how fire affects food resources for rangeland grasshoppers. This study compared grasshopper abundance and the amount of grass they ate across burned and unburned native mixed-grass prairie. We found that grasshopper numbers were much greater in recently-burned areas. Grasshoppers also consumed a lot more forage in burned areas, but essentially didn't consume any forage in unburned plots. Higher crude protein content in burned areas, on account of fresh regrowth and removal of old dead vegetation by fire, likely accounted for the greater attraction. Most of the grasshoppers observed were the migratory grasshopper, Melanoplus sanguinipes, a highly-mobile native species.

Technical Abstract: Grasshoppers are critical components of open ecosystems worldwide. While often seen as pest species competing with domestic livestock for forage resources and damaging crops, many species never reach abundances that result in economic damage and can provide essential ecosystem services. Grasshopper population and community dynamics are driven by dominant ecosystem processes; in open ecosystems, fire is one of the most ubiquitous. This study examined how indirect fire effects (improved forage quality) affect the density of and offtake by grasshoppers at two different times since fire and in unburned plots. Both offtake and density were significantly higher in burned plots compared to unburned plots. Burned plot grasshopper density increased over time, with greater rates of increase in recently burned plots, while density remained constant in unburned locations. These density and offtake patterns appear to be the result of higher crude protein content in burned plots, on account of them having a much higher proportion of recent growth after fire removed aboveground senesced material. These findings present a mechanism by which fire interacts with grasshopper abundance and distribution in open ecosystems. Long term assessments of fire and its interaction with grazing and weather patterns are necessary to determine if attraction to and consumption of post-fire vegetation will result in greater performance of pest grasshopper species or enhance community diversity, regulating pest species outbreaks.