Bison: A Keystone Species

Here are 10 ways the American bison functions as a keystone species in North American grasslands:

1. Shapes grassland structure through grazing – Bison graze selectively and move constantly, creating a shifting mosaic of short and tall grasses that increases habitat diversity.

2. Creates wallows that become microhabitats – Their dust-bathing wallows form shallow depressions that collect water and support unique plants, insects, amphibians, and birds.

3. Prevents woody plant encroachment – By heavily grazing grasses and trampling shrubs, bison help maintain open prairie and savanna ecosystems.

4. Enhances plant species diversity – Areas grazed by bison typically support more plant species than ungrazed or uniformly grazed grasslands.

5. Drives nutrient cycling – Bison redistribute nutrients across the prairie through dung and urine, fertilizing soils and stimulating plant growth.

6. Supports scavengers and predators – Carcasses provide food for wolves, bears, coyotes, vultures, eagles, beetles, and microbes, fueling entire food webs.

7. Improves habitat for grassland birds – Species such as prairie chickens, meadowlarks, and upland sandpipers benefit from the varied vegetation structure bison create.

8. Influences fire behavior – Bison-grazed areas often burn less intensely, while ungrazed patches carry fire more readily, creating a natural interaction between grazing and fire.

9. Disperses seeds over long distances – Seeds are transported in bison fur, hooves, and dung, helping maintain plant connectivity across vast landscapes.

10. Acts as an ecosystem engineer at large scales – Through grazing, trampling, wallowing, and movement, bison reshape prairie ecosystems in ways no other modern herbivore fully replicates.

Because bison alter grasslands physically, biologically, and spatially, their removal leads to cascading changes in vegetation, wildlife, fire, and soil processes—hallmarks of a true keystone species.