More than two thousand bison now roam the Joseph H. Williams Tallgrass Prairie Preserve in Oklahoma.
North America’s largest remaining protected stretch of tallgrass prairie covers tens of thousands of acres within the Osage Reservation. The Nature Conservancy established the Joseph H. Williams Tallgrass Prairie Preserve in 1989 by purchasing the Barnard Ranch in Oklahoma. Four years later, Oklahoma oilman Kenneth Adams donated 300 bison to the protected landscape.
During winter, population counts sit between 2,100 animals, but the arrival of newborn calves each summer pushes that total up to about 2,700. Preserve staff round up the animals annually to administer vaccines and sell off a portion of the population to keep the herd ecologically sustainable.
Grazing Habits That Shape Oklahoma Plant Diversity
Bison do much more than populate a picturesque landscape. Their dietary preferences actively shape the ecosystem in ways that domestic cattle do not match.
Bison is what shaped this landscape. We have done a number of dietary studies and found 99 percent of a bison’s diet is grass.
Harvey Payne, the community relations coordinator for the Tallgrass Prairie Preserve
Unlike cattle, which graze indiscriminately across grasses and flowering plants alike, bison largely avoid forbs and wildflowers. This selective feeding leaves room for flowering plants to thrive, directly supporting a diverse mix of flora and fauna.
When you lose plant diversity, animal diversity typically follows.
Harvey Payne, the community relations coordinator for the Tallgrass Prairie Preserve
The preserve now supports more than 750 plant species and over 300 recorded bird species. Of those 750 plants, roughly 115 are grasses, while the remainder consist of broadleaf wildflowers that have been greatly reduced in number because of cattle grazing.
How Bison and Controlled Burns Manage Wildfire Risks
A single adult bison can consume up to 30 pounds of grass a day. Their voracious appetite extends to dry grasses, keeping accumulated biomass from turning into fuel for wildfires during unusually wet summers.
The animals also shape the physical terrain through wallowing. By rolling on the ground to groom themselves, they carve indentations that collect rainwater, creating small ponds that sustain local wildlife. They rub against small trees to shed winter fur, preventing woody brush from invading the prairie.
Preserve managers do not rely on grazers alone to control overgrowth. Staff execute prescribed burns on roughly a third of the preserve each year.
Burning is such an important part of land management — and it is a tool that America has forgotten.
Harvey Payne, the community relations coordinator for the Tallgrass Prairie Preserve
What Research Reveals About Bison-Driven Ecosystem Recovery
Scientific data from across the state line in Kansas underscores how effectively bison drive environmental recovery. Researchers at the Konza Prairie Biological Station of Kansas State University analyzed more than three decades of records, contrasting areas without large herbivores against pastures managed with cattle and those managed with bison.
Published in the Proceedings of the National Academy of Sciences, the study revealed that reintroducing bison roughly doubled plant biodiversity compared to ungrazed land, outperforming the biodiversity gains seen in cattle-grazed plots. When a severe drought struck the central Great Plains midway through the study period, the bison-grazed plots maintained their elevated plant diversity, proving the ecological benefits hold firm even under extreme climate stress.