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Bringing back the bison

Writer's picture: Hannah CorsiniHannah Corsini

Bison were hunted to near extinction by white settlers in North America. Nowadays, they are the focus of massive rewilding efforts. But what are the benefits - and potential costs - of rising bison populations?  


For thousands of years, the American bison (sometimes colloquially referred to as the “buffalo,” though confusingly not related to true buffalo) roamed the plains of the Americas in their millions. 


Everything changed after the American Civil War. The concept of Manifest Destiny - the goal for America to expand and for Americans - “God’s chosen people” to spread across the Western Hemisphere and then the globe. Part of this plan involved repressing Native American tribes, forcing them onto reservations and killing the bison which provided both  their livelihood - food, clothing and lodging - and spiritual meaning to them. This occurred even in spite of treaties with tribes where it was promised that the bison would be spared.  It is said that one colonel declared during a hunting trip: ‘Kill every buffalo you can! Every buffalo dead is an Indian gone!’


By the late 1880s, there were only 281 plains bison left. The settlers replaced the bison with cattle, which grazed the land and left it sparse with vegetation; they also planted the non-native crested wheatgrass which now forms a monoculture over large swathes of the plains. Research has also shown that this act severely hindered the economic development of bison-reliant Native American communities, leaving them far behind Native American communities which did not rely on bison, and even further behind white Americans. 


Bison have already been established by scientists as ecosystem engineers and keystone species. Their grazing, wallowing and soil disturbance shapes the world around them. ‘Wallowing’ is the term for when a bison rolls around on the ground, a habit they perform for a variety of reasons such as grooming, social interactions, sunlight exposure and insect repulsion. 


When bison wallow, they depress the soil, altering its characteristics. After a while of bison using a wallow, it will start to retain water more easily. This makes it less useful to the bison, who enjoy rolling on dusty, dry ground. They will then abandon this wallow and go make a new one somewhere else - leaving behind them a unique patch of soil which will be colonised by different plants to its surroundings. If the wallow fills with water, it can also serve as an amphibian breeding ground. These wallows can last for years, becoming essential parts of the landscape. 


But the primary focus of bison conservationists has been their grazing habits. Bison graze on a variety of plants, but they prefer graminoid (grass-like) species, which tend to dominate their ecosystems. An adult bison eats about 9kg of grass per day, and by eating the most common plants, bison make way for more plant biodiversity. Cows, meanwhile, like to browse by rivers - chewing up leaf litter and native shrubs, and thereby sapping up moisture from the soil and destabilising the riverbanks. 


The loss of native prairie has had ripple effects on ecosystems throughout the midwest. Vegetation is essential to the soil health of the Prairie, and well-vegetated creeks provide habitat corridors for large mammals such as mountain lions and black bears, allowing them to move from place to place. Grassland bird species are one of the fastest declining groups of vertebrates in the USA, but the increase in vegetation cover associated with bison presence has positive effects on bird biodiversity.


Although their numbers are higher than they were at the peak of overhunting, today they are still considered ‘near threatened’ and in fact, ‘ecologically extinct’ - meaning that they do not shape the ecosystems around them as they once did. The vast majority of bison existing in the US are managed for commercial reasons - kept as herds behind fences and not allowed to roam free on the land. 


Given the ample benefits they provide, it’s no surprise that rewilding programmes for bison have been taking place throughout the Great Plains of America. Yellowstone National Park has joined with the InterTribal Buffalo Council and the Fort Peck tribes to reintroduce American bison to tribal lands in Montana, whilst in South Dakota, an organisation called The Nature Conservancy owns 6600 bison spread across 12 preserves in 9 different midwestern states in an aim to restore them to the prairie landscape. They even have a special herd of 300 genetically rare bison based in Iowa, with traits dating back to the original bison. 


Another organisation, the American Prairie Foundation, has purchased over 1.7 million acres of land in Montana and reintroduced over 900 bison, with the aims of achieving 3.5 million acres and 5000 bison. Most of American Prairie Foundation’s land is private, but the Bureau of Land Management approved applications by the American Prairie Foundation to graze bison across 63,500 acres of federal land last year. Their environmental analysis found that this would improve the biodiversity of local wildlife, create jobs and improve water and air quality. 


However, there has been much opposition locally, and the Montana Stockgrowers Association, Montana Attorney General and the Governor’s office filed appeals seeking to stop the decision. Most opposition to bison rewilding projects typically comes from landowners, who oppose the potential damage to trees that bison may bring, and cite the possibility of a brucellosis outbreak, a bacterial disease which can cause abortions in bison, elk and cattle. 


In January 2025, Montana Governor Greg Gianforte opened up a lawsuit against the federal government over approved plans for Yellowstone National Park to increase the size of its bison herd and prioritise the transfer of live bison, meat and hides to Native American tribes rather than culling them. 


Yellowstone is the only place where wild bison have continuously lived since prehistoric times, but for many decades they were managed more like livestock than wild animals - including slaughter when the stock became too much to manage. Although Yellowstone is a vast park, it is still bounded, and limited in terms of resources. 


One of those resources is quaking aspen, one of the most abundant tree species in the US, but one which has been in heavy decline in recent years. Aspen supports wide biodiversity of vegetation in its understory, acting as efficient carbon sinks whilst providing a habitat to an array of wildlife. According to scientists, the presence of bison in Yellowstone park could be contributing to that decline. 


Bison begin rubbing against trees in the spring, as a method to shed their winter hair. As summer approaches, they continue this behaviour, but also start to scrape off the bark from the trees with their horns, likely as a means of easing irritation and ridding themselves of insects, but also possibly due to it being their breeding season - or ‘rut’. They also start to break the branches of young trees and saplings during this time - including aspen saplings. Both scraping off the bark and breaking the branches of the saplings will kill them. In this way, bison can stop the growth of new aspen. When fully grown aspen die - from disease or drought or otherwise - they are therefore not being replaced. 


In the west of the park, it was found that 34% of aspen saplings were being killed - either by branch breaking or bark stripping - by both elk and bison, but predominantly bison. One of the reasons for the severity of impact of bison on the local ecology is that they are not allowed to leave the park, and are confined to eating what is available within the park bounds.


The number of bison within the park currently stands at around 4000-5000, and in previous years was managed by annual culling, in attempts to mitigate their effect on the local vegetation. In the pre-settlement era, both bison and aspen were plentiful because the bison were allowed to migrate and their populations were kept in check by the indigenous people who hunted them. When Yellowstone park was established, armed soldiers were employed to prevent the displaced Lakota tribal members from ever returning. 


Recently, the park has aimed to make reparations for their history by engaging the Native American tribes it once persecuted. This includes allowing tribal hunting of bison once more, along with the transfer of bison to tribes in other states for conservation purposes. This could help to restore the balance between bison and vegetation in the Yellowstone area - if it isn’t blocked by Governor Gianforte in the meantime.


The US is not the only country implementing initiatives to rewild bison. Near Canterbury, in Kent, wild European bison were reintroduced in 2022, the first appearance of bison in England in thousands of years. They are the closest living relative of the last bison to roam the country: ancient steppe bison, who existed here over 12000 years ago. 


According to woodland ranger Donovan Wright, lack of proper woodland management is the main reason for biodiversity loss in the UK. He hopes that the $1.4 million project will revitalise the land, shaping the West Blean and Thornden woods. 


The idea is that the bison will kill trees by eating bark and open up trails by charging around and rolling around on the floor. This will allow more light to hit the forest floor, allowing plants to grow, and smaller organisms like insects and lizards to thrive. Even their dung can form a food source for insects, whilst their fur can be used by birds to line their nests. 


The successes of rewilding bison in the US make this a hopeful project, and one which an increasingly urbanised UK sorely needs. Changes have already been seen in the woods - from dung beetles and fungi inhabiting the bison dung, to the removal of some of the invasive plant rhododendron. In July 2024, the BBC reported the herd as “thriving.” Soon, visitors will be able to view the bison from the safety of aerial bridges constructed around the reserve. 


But, as shown, rewilding is ecologically and sociopolitically complex. The project will need extensive monitoring, and support from scientists and politicians if it is to thrive. If it does, it could pave the way for new rewilding projects across the country, helping to create a newer, wilder UK. 


Further reading


American Prairie Foundation (2023) ‘Bison restoration.’ American Prairie Foundation. Available at: https://americanprairie.org/bison-restoration/ [Accessed 23rd December 2023]


American Prairie Foundation (2023) ‘Bison restoration timeline.’ American Prairie Foundation. Available at: https://americanprairie.org/project/bison-reintroduction/ [Accessed 23rd December 2023]


Boyce, A., Shamon, H. & McShea, W. (2022) ‘Bison reintroduction to mixed-grass prairie is associated with increases in bird diversity and cervid occupancy in riparian areas.’ Frontiers in Ecology and Evolution. Volume 10.


Brown, M. (2021) ‘Governor drops bison plan, says he’s protecting ranchers.’ AP News. Available at: https://apnews.com/article/health-environment-and-nature-business-government-and-politics-bison-a4f491eb3c2f8abba0dbe41450e0344a [Accessed 23rd December 2023] 


Bureau of Land Management, US Department of the Interior. (2022) ‘Environmental Assessment. American Prairie Reserve Bison Change of Use.’ Eplanning BLM. Available at: https://eplanning.blm.gov/public_projects/103543/200243903/20056712/250062894/2022_03_24_APR_EA%20with%20Apps_508.pdf [Accessed 27th December 2023] 


Carrington, D & Davis, N. (2022) ‘Wild bison return to UK for first time in thousands of years.’ The Guardian. Available at: https://www.theguardian.com/environment/2022/jul/18/wild-bison-return-to-uk-for-first-time-in-thousands-of-years [Accessed 19th December 2024] 


Castle, V. (2024) ‘Bison: UK’s only free-roaming herd doubles in size in Kent woods.’ BBC. Available at: https://www.bbc.co.uk/news/articles/c6p250dw299o [Accessed 12th January 2025


Drimal, S. (2022) ‘Yellowstone National Park announces an important shift in bison population management.’ Greater Yellowstone Coalition. Available at: https://greateryellowstone.org/blog/2022/bison-yellowstone [Accessed 27th December 2024] 


Encyclopedia.com (2018) ‘Manifest Destiny.’ Available at: https://www.encyclopedia.com/history/united-states-and-canada/us-history/manifest-destiny#3401802517 [Accessed 20th December 2024] 


Feir, D., Gillezau, R. & Jones, M. (2022) ‘The slaughter of the bison and reversal of fortunes on the great plains.’ National Bureau of Economic Research. Working paper 30368. 


Ives, M. (2023) ‘Bison return to Native American lands, revitalising sacred rituals.’ The New York Times. Available at: https://www.nytimes.com/2023/07/04/us/native-american-tribes-bison.html [Accessed 21st December 2024] 


Jorgensen, D. (2023) ‘The bison are back thanks to Native Nations.’ PBS. Available at: https://www.pbs.org/wnet/nature/blog/american-buffalo-back/ [Accessed 21st December 2024] 


King, G. (2012) ‘Where the buffalo no longer roamed’ Smithsonian. Available at: https://www.smithsonianmag.com/history/where-the-buffalo-no-longer-roamed-3067904/ [Accessed 20th December 2024] 


Krupnick, M. (2022) ‘‘It’s a powerful feeling’ the Indigenous American tribe helping to bring back buffalo.’ The Guardian. Available at: https://www.theguardian.com/environment/2022/feb/20/its-a-powerful-feeling-the-indigenous-american-tribe-helping-to-bring-back-buffalo [Accessed 21st December 2024] 


Moran, M. (2019) ‘America’s recovering bison populations are restoring the US landscape.’ Inverse. Available at: https://www.inverse.com/article/52602-bison-are-back-and-that-benefits-many-other-species-on-the-great-plains [Accessed 23rd December 2024] 


National Farm Animal Care Council. (2017) ‘Code of practice for the care and handling of bison.’ Canadian Bison Association. ISBN 978-1-988793-04-7 (book) 


National Wildlife Federation (n.d) ‘Restoring bison to tribal lands.’ National Wildlife Federation Conservation. Available at: https://www.nwf.org/Our-Work/Wildlife-Conservation/Bison/Tribal-Lands [Accessed 20th December 2024] 


Nelson, M. (2022) ‘How Sitting Bull’s Fight for Indigenous Land Rights Shaped the Creation of Yellowstone National Park.’ Smithsonian Magazine. Available at: https://www.smithsonianmag.com/history/how-sitting-bulls-fight-for-indigenous-land-rights-shaped-the-creation-of-yellowstone-national-park-180979630/ [Accessed 27th December 2024]


Nickell, Z., Varriano, S., Plemmons, E. & Morant, M. (2018) ‘Ecosystem engineering by bison (Bison bison) wallowing increases arthropod community heterogeneity in space and time.’ Ecosphere. Volume 9. Issue 9. 


Nijhuis, M. (2008) ‘What’s killing the aspen?’ Smithsonian Magazine. Available at: https://www.smithsonianmag.com/science-nature/whats-killing-the-aspen-93130832/ [Accessed 26th December 2024] 


Painter, L., Beschta, R. & Ripple, W. (2023) ‘Bison alter the northern Yellowstone ecosystem by breaking aspen saplings.’ Ecology and Evolution. Volume 13. Issue 8. 


Phippen, J. (2016) ‘‘Kill every buffalo you can! Every buffalo dead is an Indian gone!’’ The Atlantic. Available at: https://www.theatlantic.com/national/archive/2016/05/the-buffalo-killers/482349/ [Accessed 20th December 2024]


Preston, C. (2023) ‘Why grazing bison could be good for the planet.’ BBC Future Planet. Available at: https://www.bbc.com/future/article/20231102-why-grazing-bisoncould-be-good-for-the-planet [Accessed 23rd December 2024] 


Puckett, K. (2015) ‘Prairie reserve still attracting fans, foes.’ The Great Falls Tribune. Available at: https://eu.greatfallstribune.com/story/news/local/2015/06/18/prairie-reserve-still-attracting-fans-foes/28944461/ [Accessed 23rd December 2024]


Regan, S. (2019) ‘Is American Prairie Reserve taking the West back to the future?’ Mountain Journal. Available at: https://mountainjournal.org/the-american-prairie-reserve-and-its-dustup-over-bison-and-property-rights [Accessed 23rd December 2024]


Saliman, A. & Petersen-Rockney, M. (2022) ‘Rancher experiences and perceptions of climate change in the Western United States.’ Rangeland Ecology & Management. Volume 84. Pages 75-85. 


Singer, A., Turnbull, R., Foster, M., Bettigole, C., Frey, B., Downey, M., Covey, K. & Ashton, M. (2019) ‘Sudden aspen decline: a review of pattern and process in a changing climate.’ Forests. Volume 10. Issue 8. Page 671. 


The Nature Conservancy (2018) ‘Putting bison back on the prairie in North and South Dakota.’ Nature.org. Available at: https://www.nature.org/en-us/about-us/where-we-work/united-states/north-dakota/stories-in-north-dakota/putting-bison-back-on-the-prairie/ [Accessed 23rd December 2024] 


The Nature Conservancy (2023) ‘American Buffalo return home to Tribal Lands.’ Nature.org. Available at: https://www.nature.org/en-us/about-us/who-we-are/how-we-work/community-led-conservation/american-buffalo/ [Accessed 23rd December 2024] 


Turrell, C. (2022) ‘Wild bison, taking over Europe and North America, will once again roam England.’ Mongabay. Available at: https://news.mongabay.com/2022/03/wild-bison-taking-over-europe-and-north-america-will-once-again-roam-england/ [Accessed 20th December 2024] 


Wildwood Trust. (2023) ‘Blean bison project.’ Available at: https://www.wildwoodtrust.org/conservation-and-rewilding/conservation-projects/blean-bison-project/ [Accessed 27th December 2024] 

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