Bison vs. Cattle: How the Disappearance of Bison and the Rise of Cattle Shaped Fire Risk in North Am

 By Debbie Hanson

The transformation of North America's grasslands following the near-extinction of bison and the introduction of cattle is a profound ecological narrative. Bison (Bison bison), once numbering in the tens of millions, were integral to the health and maintenance of prairie ecosystems. Their grazing patterns, migratory behaviors, and physical interactions with the land fostered a dynamic equilibrium that sustained diverse plant and animal communities. In contrast, the widespread replacement of bison with domesticated cattle (Bos taurus) brought significant changes to these landscapes, including increased fire risk and decreased ecosystem resilience.

Bison: Keystone Species of the Prairie

Bison were keystone species in North America's grasslands, meaning their presence had disproportionately large effects on the landscape. Their grazing was non-selective and wide-ranging, consuming various grasses and forbs. This helped prevent dominance by any single species, encouraged plant diversity, and created a patchwork of plant communities that supported biodiversity. Bison wallows also created temporary wetlands, enhancing microhabitats for other species. Their migratory movement redistributed nutrients, improved soil structure, and reduced continuous fuel buildup.

Collapse of Bison Populations and the Rise of Cattle

The 19th century saw a rapid and catastrophic decline in bison due to overhunting, habitat loss, and extermination campaigns. From an estimated 30–60 million, fewer than 1,000 remained by the late 1800s. As bison vanished, European settlers introduced cattle ranching to exploit the open grasslands. By 1900, approximately 30 million cattle had grazed where bison had once roamed (Great Bison Belt).

Cattle have fundamentally different effects on the land than bison. Their grazing is more selective and often overgraze the preferred plant species. Their sedentary behavior and heavier hooves cause soil compaction, reduce water infiltration, and degrade plant communities (USDA Forest Service).

Ecological Consequences of Cattle Grazing

Cattle often promote the spread of non-native and invasive plants, leading to a homogenized and fire-prone landscape. Their behavior increases fuel continuity and reduces natural firebreaks. Over time, this disrupts the ecological functions once maintained by bison, degrading soils, water cycles, and plant communities (Prairie Ecologist).

Fire Risk and Livestock Grazing

Cattle grazing has been used as a wildfire risk mitigation tool, especially in California, where they removed an estimated 3.5 billion kilograms of non-woody plant material in 2017 (Ecology and Society). However, these benefits are conditional—grazing intensity, poor timing, and mismanagement can lead to fuel buildup and soil degradation.

By contrast, bison create more diverse vegetation structures, reduce fuel continuity, and promote fire-resilient ecosystems through movement and grazing patterns.

The Case for Reintroducing Bison

Recent studies show that bison grazing significantly enhances ecosystem resilience. A 29-year field study found that bison increased native plant species richness by over 100% compared to areas grazed by cattle or left ungrazed. These landscapes also demonstrated greater resistance to extreme drought (PNAS, 2022).

Restoring bison to grasslands revitalizes plant and wildlife diversity and contributes to wildfire mitigation by breaking up fuel loads and maintaining healthy soil moisture levels. Bison-managed landscapes are less susceptible to catastrophic burns due to their more complex vegetation patterns.

Conclusion

The replacement of bison with cattle has increased wildfire risk, simplified ecosystems, and reduced the resilience of North American grasslands. Reintroducing bison and mimicking their ecological role presents a science-backed solution to support biodiversity, improve soil health, and lower wildfire vulnerability.

Sources:

• CAL FIRE (2024). Wildfire statistics and defensible space guidelines. https://www.fire.ca.gov/
• Brooks et al. (2004). Effects of invasive alien plants on fire regimes. BioScience. https://doi.org/10.1641/0006-3568(2004)054[0677:EOIAPO]2.0.CO;2
• USDA Forest Service. (2003). Impacts of grazing on soil and water. https://www.fs.usda.gov/rm/pubs_rm/rm_gtr285/rm_gtr285_013_019.pdf
• Coppedge, B. R., et al. (1998). Ecology of grazing impacts in tallgrass prairie. Restoration Ecology, 6(3), 251–255.
• Polley, H. W., et al. (2022). Long-term grazing by bison increases biodiversity and drought resilience in North American grasslands. PNAS. https://www.pnas.org/doi/10.1073/pnas.2210433119
• Ecology and Society. (2024). Livestock grazing as a wildfire risk reduction tool. https://www.ecologyandsociety.org/vol29/iss3/art10/
• Prairie Ecologist. (2010). Grazing in prairies. https://prairieecologist.com/2010/11/11/grazing-in-prairies-part-1/
• Wikipedia. Great Bison Belt. https://en.wikipedia.org/wiki/Great_bison_belt
• Phys.org (2022). Reintroducing bison improves grassland drought resilience. https://phys.org/news/2022-08-reintroducing-bison-grasslands-diversity-drought.html