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

Abstract

Background Fire modulates herbivore dynamics in open ecosystems. While extensive work demonstrates the interaction between fire and vertebrate grazers, less research describes how grasshopper herbivory dynamics respond to fire. Aim We examined how fire increased grass crude protein content and increased the density of and offtake by grasshoppers relative to unburned mixed-grass prairie. Methods We deployed grasshopper exclusion cages to determine grasshopper offtake of aboveground plant biomass, counted grasshopper abundance throughout the study period, and measured crude protein content of aboveground grass biomass. Key results Offtake and density were higher in burned versus 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. Conclusions We present a potential mechanism by which fire interacts with grasshoppers in open ecosystems. It is likely that greater grasshopper offtake and density in recently-burned plots is at least partially attributable to higher crude protein content, as grass in these plots has a much higher proportion of recent growth after fire removed senesced material. Implications Grasshopper herbivory likely acts as a multiplier of livestock herbivory in burned rangeland. Restoring fire regimes can balance direct negative effects of heating against nutritional benefits.