Restoring Bison to Yellowstone Has ‘Reawakened’ the Ecosystem as the Large Animals Migrate, Study Suggests

An analysis of plant diversity and soil health across the bison migration corridor suggests free-roaming bison lead to more nutrient-rich plants

Sara Hashemi | Daily Correspondent

September 3, 2025

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Bison—also known as buffalo—once ambled across North American prairies in enormous herds, with their full population reaching the tens of millions. Indigenous peoples across the continent relied on the animals for food, clothing and income. But by the late 1800s, the bison had been hunted to near-extinction, with long-lasting impacts on many Indigenous communities and the landscape.

Conservation efforts have since strived to restore bison populations, and about 5,000 of the animals currently call Yellowstone National Park home. Now, a new study underscores just how important these large mammals can be for maintaining a healthy and heterogeneous ecosystem.

Researchers looked at the impacts of large, migrating bison herds on Yellowstone’s landscape and found that the animals play a key role in the nitrogen cycle. As the herd travels about 1,000 miles each year, moving back and forth along a 50-mile migration route, the animals increase the amount of microbes in the soil. In turn, these microbes increase the amount of nitrogen for plants, improving their nutritious value by up to 150 percent. The findings were published in the journal Science on August 28.

“Humans have been applying dung as a fertilizer for millennia, so we know it’s an important fertilizer. Bison are a restoration story, and allowing their grazing in places like Yellowstone provides a ‘reawakening’ of the landscape,” study co-author Bill Hamilton, an ecologist at Washington and Lee University, tells Madison Dapcevich at Outside.

To conduct their research, Hamilton and his colleagues monitored plant growth and diversity, nutrient cycling and microbial abundance in soil across 16 sites between 2015 and 2022. They compared grazed and ungrazed areas and combined their findings with satellite imagery and GPS collar data to get an idea of bison movement and map the creatures’ impact across the landscape.

The merits of free-roaming bison have long been debated among researchers and conservationists. Some experts believe the animals should be constricted to certain areas because they can contribute to overgrazing and disease. “Yet, we found pretty much the opposite of that,” says Jerod Merkle, a biologist at the University of Wyoming and study co-author, in a statement. Their data revealed an increase in plant diversity along the migration corridor, and the soils were able to sustain nutrient storage.

But to deliver the benefits detailed in the study, the authors stress that bison need to be able to freely move at a large scale across the landscape—not be managed in small enclosures, as is the case in most places outside of Yellowstone. About 400,000 bison are currently living in North America, but some 95 percent of them are privately owned as livestock, per the paper. Most others are in relatively small conservation herds in constrained areas.

The findings also serve as a kind of time machine, allowing scientists to better understand what impact bison had before they were almost wiped out, and it hints at what the animals could offer if more of their populations were restored. “This kind of serves as an example of how, if large numbers could get large areas of land, what it might look like for restoring bison elsewhere,” Hamilton explains to Alexa Robles-Gil at the New York Times.

Overall, the study confirms what Indigenous peoples have long known about bison, as Tony Heinert, a member of the Rosebud Sioux tribe and chief of the branch of bison management for the Bureau of Indian Affairs, tells the New York Times.

“Buffalo helped shape this continent,” he adds. “And the more buffalo that are out there, the ecosystems are improved for all other animals as well.”

Sara Hashemi | Read More

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.