Engineering Ecosystems: The Role of Bison in Montana’s Northern Great Plains

Abstract

The American bison (Bison bison, hereafter referred to as bison) was rapidly extirpated in North America during the 19th century. The ecological impact of removing and replacing bison, a large native herbivore, with non-native livestock remains uncertain across their historical range.The ecological impacts of bison rewilding have not been well studied in Northern Great Plains mixed grass prairies. Therefore, to assess the effects of bison behaviors on plants and soils, namely grazing and wallowing, I surveyed plant communities and collected soil samples during the 2023, 2024, and 2025 growing seasons in northeastern Montana prairies. I investigated the effects of bison grazing on plant community composition and aboveground biomass due to selective grazing pressures. I hypothesized that bison wallowing behaviors will alter plant biodiversity and species richness along a spatial and temporal disturbance gradient aligning with the Intermediate Disturbance Hypothesis (IDH). Additionally, I hypothesized that the effects of bison grazing on plant communities would increase plant diversity and species richness in areas with greater grazing activity. Physical and chemical soil properties were further expected to bealtered along a disturbance gradient due to trampling and urine/feces deposition at the wallow site. Results indicate that the intensity of bison use was a strong driver of plant community composition or aboveground biomass, but only in areas of recent (<1 year) reintroduction. Although bison wallowing effects were strongest at the wallow’s center, the effect decreased farther away from the wallow’s center. Time within the plant growing season was found to be a stronger driver of plant biodiversity and species richness than wallowing disturbance effects.Physical soil properties, such as bulk density, were dependent upon the location within the wallow, indicating a disturbance effect. Achieving restoration objectives through bison rewilding is dependent on ecosystem traits and local management practices. Policy decisions influence the implementation of rewilding bison in North America.