What makes bison a keystone species?

Maia Welbel

A keystone species is..

An organism central to the health and stability of a natural ecosystem. The removal of a keystone species causes a cascade of effects that significantly alter and potentially damage the entire ecosystem.

Types of keystone species:


Keystone predators maintain stable populations within ecosystems by preventing any one species from becoming too dominant and overtaking a landscape with excess grazing or depletion of natural resources.


Keystone engineers transform surrounding ecosystems to create opportunities for plant life and other species to thrive.


Keystone mutualists engage in reciprocal behaviors that support all participating organisms, the loss of which would greatly impact the surrounding ecosystem.

What are bison?

The American bison is the largest land mammal in North America. As bovine, nomadic grazers, bison are herd animals, known for traveling in packs across the Great Plains.

Before European colonization, Native Americans on the Great Plains hunted bison for meat, used their hides for clothing and shelter, and built tools from their horns and bones. Herds were relatively stable with an estimated population of around 40 million animals in the late 18th and early 19th century. However by 1850, railroad construction, human population expansion, and a growing bison hide market, accelerated bison hunting dramatically. They also had to compete with horse and cattle herds for limited winter resources and were impacted by cattle-borne diseases. By 1890, fewer than 1,000 bison remained. With the development of commercial hunting and railway travel, the elimination of the bison became an efficient tool of western colonization. As herds were culled, Native tribes were pressured onto Indian reservations or to adopt non-indigenous hunting methods to survive.

With the efforts of government agencies and private restoration groups, bison have since slowly made a comeback on the Great Plains. There are currently just over 20,000 bison in the U.S. Still, habitat loss and other human impacts continue to threaten the species.

Bison as a keystone species

Historically, bison were the dominant grazer on the Great Plains. These herbivores shaped the landscape of the grasslands of North America, hence their designation as keystone engineers. Bison migration and foraging habits facilitate the health and stability of organisms throughout the entire ecosystem. Because bison evolved with these grasslands for millennia, their role in the landscape is invaluable.

While grazing, bison move liberally. As they trample, their hooves aerate the soil, allowing for a variety of plants to thrive and native seeds to disperse. Their thick fur often captures and redistributes additional seeds as they roam, breeding diverse plant life across the plains. Through urination and defecation, bison improve plant nutrition and increase nitrogen in the soil. Continuous grazing facilitates healthy plant species and food sources for other herbivores.

Bison also create wallows — packed holes of soil that fill with rainwater and provide breeding pools for amphibians and drinking water for other wildlife. As a herd migrates from place to place, it interacts with a variety of species. Like prairie dogs, whose habitats are improved by bison displacing soil and removing plant life, making it easier for the dogs to dig their burrows. These habitats also support key predator species like the black-footed ferret, and once abandoned, they offer shelter to burrowing owls and other small animals.

In the winter, bison clear pathways through the snow using their horns and sheer mass to search for food. These pathways uncover living vegetation, helping animals like pronghorn antelope and elk survive during colder months. Even when a bison dies, it provides food for scavenging animals and valuable nutrients for the soil. The ripple effects of a bison lifecycle maintain the vitality of grassland ecosystems, and the future of the Great Plains will depend on our efforts to support their survival.

The decline of the American Bison

Prior to the European-American settling of the west at the end of the 19th century, bison roamed  the plains in estimates of 50-60 million. A staggering number in comparison to the less than 1,000 bison that remained by the late 1880s. Persistent conversation efforts have increased numbers to over 500,000 today, with 5,000 of those animals roaming in the Greater Yellowstone area.

The dramatic decimation of the bison was spurred by habitat loss as ranching, farming, and railway development expanded across the interior plains. Non-indigenous hunting led by European settlers increased the demand for bison hides and meats, following a destructive policy set by governments to eradicate this vital food source of Native American populations. Bison hunting had been an integral spiritual practice and primary source of materials. As herds were culled, native tribes were pressured onto Indian reservations or to adopt non-indigenous hunting methods to survive. With the development of commercial hunting and railway travel, the elimination of the bison became an efficient tool of western colonization and the inevitable decline of the plains.

The importance of bison in restoring the Great Plains

The degradation of the Great Plains is a direct corollary of the decline of the Plains bison. Along with extensive deep plowing, the loss of the American bison spurred the 1930s Dust Bowl and still contributes to ecosystem failure today. As we look toward restorative practices for land restoration, the reintroduction of bison to the Great Plains is an important step in rebuilding biodiversity within these ecosystems. Bison facilitate deep-root grass systems that revitalize topsoil and support the growth of regenerative plants and microorganisms. Reestablishing bison populations will enable other herbivores and predators to return to degraded lands and create new habitats.

In 2020, after an absence of 140-years, bison once again inhabit the land of the Sicangu Lakota Oyate on the Rosebud Indian Reservation in South Dakota. The prairie is now the Wolakota Buffalo Range. The Lakota tribe, with support from World Wildlife Fund released 100 plains bison from the National Park Service. Less than a year later, the number of bison on the 27,680-acre parcel of tribal land rose to nearly 800 animals.

A 2022 study titled “The Potential of Bison Restoration as an Ecological Approach to Future Tribal Food Sovereignty on the Northern Great Plains,” discussed the potential contributions of bison to food sovereignty, sustainable economies, and conservation of a working landscape on the Plains. Researchers found that widespread bison restoration on Tribal lands could help mitigate the adverse impacts of industrial agriculture on the prairies, while improving food access for Native Nations.

Organizations to follow