New Research Supports Yellowstone’s Updated Bison Management Plan

The roughly 5,000 bison roaming Yellowstone National Park represent one of America’s greatest conservation success stories. The current herd descends from just two dozen individuals that found a haven in Yellowstone’s rugged interior while European settlers and the American military systematically exterminated millions of bison.

They play a vital ecological role across Yellowstone’s landscape—a role that may be bigger than we previously knew. A new study published in Science shows that Yellowstone’s free-roaming herds of bison not only shape the landscape, but make it healthier.

A large herd of bison grazing in Yellowstone National Park. Photo NPS/Jacob W. Frank

Researchers tracked the effects of migrating bison on Yellowstone’s grasslands between 2015 and 2022. They found that in areas where bison graze heavily, plants regrow with 150 percent more nutrients, making forage across the landscape more nutritious for all plant-eating wildlife. These benefits were strongest in wet, nutrient-rich valleys where bison repeatedly returned to graze along their 50-mile migration corridor, traveling nearly 1,000 miles each year.

Crucially, bison grazing didn’t damage the land. Instead, their movement patterns created diverse habitats and sped up nutrient cycling, leading to higher-quality forage and more stable plant growth and soil health. Importantly, Yellowstone’s grasslands stayed healthy and resilient even with far more bison than traditional livestock standards would recommend.

In short, Yellowstone’s ecosystem works best when bison are allowed to do what they’ve done for millennia—migrate freely across long distances, in large numbers. Managing bison like cattle actually diminishes positive ecological impacts.

This study underscores that it is past time to stop viewing Yellowstone bison management through a livestock lens. Wild ecosystems function differently than managed grazing lands. The valley bottoms are thriving ecosystems—defined by faster nutrient turnover, richer forage, and greater biodiversity. These visible differences are not signs of degradation; they are hallmarks of a healthy, functioning ecosystem.

The study offers a glimpse of how North American prairies functioned before bison were nearly lost and is directly relevant to how Yellowstone manages its bison herds today. This research underpinned Yellowstone’s updated Bison Management Plan, released in June 2024 after several years and more than 27,000 comments from the public that included Tribes, conservationists, businesses, and the state of Montana.

The new plan increased the outdated and politically driven population cap of 3,000 bison— reflecting population numbers over the last decade—and acknowledges the ecological and cultural value of larger, free-roaming herds. In response, the state of Montana filed a lawsuit against the Park in late December, demanding the population cap remain at or below 3,000. There is no credible or scientific basis for such a drastic reduction in the size of the Yellowstone bison population.

Bison migrating out of the Gardiner Basin. Photo NPS/Neal Herbert

Montana’s position ignores how much has changed in the 24 years since the old plan was adopted and these demands come despite the new plan setting a population range that has proven successful. Yellowstone has maintained separation between bison and cattle, there have been zero brucellosis transmissions from bison, and fewer conflicts today than 20 years ago.  

Conservation agreements and policy changes in the Gardiner and Hebgen basins have opened more critical winter habitat for bison outside the Park, and with tools like the Bison Conservation Transfer Program, healthy animals can be transferred to Tribes rather than slaughtered.

To achieve the state’s goal of killing more than 2,000 bison, the park would be forced to aggressively haze and kill animals migrating toward the park boundary as well as in Yellowstone’s interior. That would not only undermine the ecological benefits of migration but also put the herd’s genetic diversity and long-term viability at risk while threatening Tribal treaty rights and public hunting opportunities.

The science is clear: Yellowstone’s bison are not livestock to be contained or reduced to a politically convenient number—they are a keystone species whose presence reawakens and enriches the entire ecosystem.

Yellowstone is the last place on Earth with large, free-roaming herds of wild plains bison allowed to carry out their natural ecological processes. If we cede to Montana’s demands to eliminate thousands of these animals, we risk losing the ecological benefits of their migratory behavior forever. Now is the time to stand behind science-based conservation, honor our commitments to Tribes, and protect one of the last ecologically intact, temperate zone ecosystems on Earth.

— Shana Drimal, Wildlife Program Manager (Bozeman, MT)