Rewilding a Great Plains grassland by returning fire and bison: impacts on resilience and biodiversity

Keywords: Rewilding, megafauna, cultural burning, remote sensing
Abstract Type: Paper Abstract

Abstract

Two hundred years ago, the Great Plains was one of the most extensive grasslands on earth, but then underwent several rapid and widespread changes, including: 1) shifts in fire regimes after Europeans seized Native Americans, 2) the near extermination of the remaining native megafauna (e.g. bison, elk), and 3) the subsequent conversion of most grasslands to row-crop agriculture. This study reports from a large-scale, long-term experiment in a landscape of tallgrass prairie that escaped agricultural conversion. The experiment uses large-scale manipulations to explore the interactive effects of several different prescribed burning frequencies and grazing by reintroduced native megafauna (Plains bison, Bison bison) versus grazer exclusion or grazing by domestic cattle (Bos taurus). We found that: 1) bison increased plant diversity 85% to 106% compared to the removal of large grazers, which is twice the increase that grazing by non-native cattle caused, and 2) these gains were resilient to the most extreme drought and most extreme wet summer in 40 years. However, based on high resolution remote sensing, bison and cattle have facilitated woody plant encroachment in areas burned very frequently (1 to 2 years). This landcover change reduces freshwater recharge and forage production. Returning natural disturbances, such as fire and grazing, is critical to maintain diverse and resilient Great Plains grasslands. However, novel interventions may be needed to because climate change and the effect of elevated atmospheric CO2 make woody plant encroachment likely in many land-use situations.