American Bison (Bison bison): A Rangeland Wildlife Continuum

Abstract

American bison (Bison bison) are the largest extant land animal in North America and have an important history and contemporary role in modern conservation. Bison historically had the widest continental distribution of all native ungulates but now only function as wildlife under natural selection on < 1.2% of the original range. Bison as rangeland wildlife occur on an array of exclusive and overlapping governance jurisdictions (e.g., Federal, State, Provincial, County, and Tribes and First Nations), private not-for-profit conservation lands enterprises, zoo and education enterprises, and for-profit commodity production. The historical and prevailing relationships within and between these higher order sectors are very complex and often conflicting, yet each sector has invested tremendous effort and public and private resources to increase the total abundance of bison to present levels. Despite long-term public investment in wild bison conservation, the private sector has far out-stripped wild bison, resulting in a potentially divergent evolution trajectory towards species domestication. The primary ecosystem function of plains bison on rangelands is contributing to plant community heterogeneity through patchily distributed grazing events that create mosaics of grazing pressure. Additionally, bison exhibit a myriad of other roles in their environment through direct and indirect interactions. Perhaps more than with other rangeland wildlife species, genetics play an outsized role in current bison population management given historical bottlenecks and intentional cross breeding of bison and cattle. However, moving forward the interplay between population size, isolation, and genetic diversity is more important. Along the continuum of bison management there exist a wide variety of rangeland management techniques. However, as a wildlife species, the rangeland management practices associated with bison have generally focused on disturbance ecology with a more recent push to understand the impacts of bison grazing at scale. The question of scale is important given that every bison is behind a barrier, thus restricting their impacts on rangeland ecology and processes. Bison and cattle are considered by many to be potential competitors, due to large overlaps in diet and body size, and much research has focused on the ecological equivalence of the two species. While this is still not without controversy, bison and cattle are not incompatible when properly managed. Chronic infection of wild bison populations with diseases that can be transmitted to livestock and humans is an important factor affecting potential recovery of bison outside existing reserve boundaries. Climate change may represent the next major challenge to bison, as it is expected to directly affect bison through decreased forage and water availability and increased thermal stress. These threats, combined with the differences in bison management practices between sectors have led some to classify bison as moderately vulnerable to climate change, recommending the creation of a ‘bison coalition’ that could seek climate change adaptation solutions through shared stewardship. While much of the continental historical range is no longer available for bison restoration, there are exciting conservation opportunities that are finding voice through the vision of “Shared Stewardship” that embraces innovative collaboration to work together across jurisdictions and sectors to successfully address the scale, complexity, and ecological and cultural significance of wild bison.