PAWHUSKA, Okla. — The late October morning is so bitterly cold that the vaccine a hardy Oklahoman cowboy is trying to administer to an impatient bison has frozen.

The rancher, Harvey Payne, tries to defrost the liquid against a small heater pumping out hot air in the office that faces the corral, but it’s not working.

“We’ll have to head back in for a couple of hours and wait for the sun to warm up,” Payne says as he squints at the sun rising above the tallgrass prairie. “Can’t vaccinate bison with frozen antibiotics.”

The group that’s gathered at the Joseph H. Williams Tallgrass Prairie Preserve trudges back to headquarters to wait until the temperature rises.

Oklahoma’s 39,650-acre preserve is the world’s biggest protected remnant of a massive grassland ecosystem that once stretched across 14 states, covering 170 million acres. But the grassland has been decimated, and only about 4 percent of the ecosystem remains, most of which is contained in the preserve in Osage County, home to the Native American Osage Nation.

A coalition of ranchers, environmentalists and Osage Nation landowners are working together to save the powerful weapon in the fight against climate change.

A bison waits as a rancher tries to defrost vaccines that have frozen due to the unexpectedly cold weather. Lucy Sherriff / NBC News

Acting as a powerful carbon storage container, or sink, the grasslands are a vital component in nature’s fight against climate change. Figures vary, but one study estimates that tallgrass can capture up to 1.7 metric tons of carbon per acre per year. In Oklahoma alone, protected grasslands mitigate nearly four metric tons of carbon dioxide per year — the equivalent of taking 4 million cars off the road.

Invasive plant species, urban sprawl and unsuitable grazing methods — where cattle are overgrazing or not grazing enough, which depletes productivity and species diversity — have conspired to diminish an ecosystem adept at capturing and storing carbon in the atmosphere. A lack of controlled burns that help the land regenerate and bad land management practices, such as tilling the soil and growing only one type of crop, have also contributed to the demise of grasslands.

Prairie grasslands are a more reliable tool for storing carbon than trees because they are less affected by droughts and wildfires. They sequester carbon underground, unlike forests that store carbon in wood biomass and leaves. When trees burn, carbon is released into the air. When grasslands burn, it remains in the roots and soil.

We love this land, and as ranchers not only do we love it, we make our living off it. We’re all in this together, for the long run."

The nonprofit organization The Nature Conservancy has been working with landowners in Oklahoma to preserve the U.S.’s remaining prairies, which were once home to as many as 60 million bison, an integral part of Native American culture. By 1884, their numbers had dwindled to around 325 because of European settlers' slaughter of the animals.

Bison are not only important to Native American identity, but they also play an instrumental role in the preservation of prairie grasslands.

“When we see a prairie horizon, we see that as creation’s morning light,” said Jo Conner, whose Osage name is Tse Daha, meaning buffalo hide. “I was born and raised on this prairie. The prairie for us is the essence of what made us Osage. The bison not only sustained us physically, but also spiritually.

The annual bison check-up starts at sunrise, when the animals, crucial to maintaining the health of prairie grasslands, are herded into corrals. Lucy Sherriff / NBC News

“A lot of people are frightened of the vista. They’ll say: ‘But where are the trees? Where are the people?’ But that’s not what the prairies are about. Our creation stories come from the horizon on the prairie. And it is so important to us to protect it.”

As part of The Nature Conservancy’s tallgrass preservation effort, bison were reintroduced to Oklahoma in 1993.

“To have the buffalo returned is a blessing for the tribe,” Conner recalled. “This is just a tiny piece of what our lands would have looked like hundreds of years ago.”

The herd of 300 has grown to 2,600, and they graze on the majority of the preserve, playing an important part in enhancing the prairies. Unlike cattle, which favor tall flowering plants, bison prefer to graze on grass.

Payne, who is the community relations coordinator for the Tallgrass Prairie Preserve, said: “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. Cattle eat 80-85 percent grass. The rest of what they eat is broadleaf plants.”

“Here, we’ve identified over 750 plant species, and about 115 of those are grasses. The rest are these broadleaf plants, which are the wildflowers. And these plants have been greatly reduced in number because of cattle grazing,” Payne said.

The wildflowers, in turn, produce seeds that sustain native insects and birds during the winter.

The flowers and broadleaf plants pull nitrogen from the air and deposit it into the ground, which fertilizes the soil.

Bison aren’t the only tool being used to manage prairies. The Nature Conservancy is working with ranchers to conduct controlled burns across the region that replicate how Native Americans historically managed the prairies. In 2019 alone, more than 15,000 acres of the preserve was burned, while the conservancy’s fire team worked with neighboring ranchers to burn nearly 35,000 acres.

Unusually wet summers have resulted in increased growth of vegetation, creating ideal conditions for uncontrolled wildfires, which have plagued the Southern Plains in recent years.

“Many of the cowboys here who are checking the bison will help us with the burns,” Payne said. “And we help them. Each year we’ll burn about a third of where the bison graze.

Ranchers discuss whether to postpone the bison health check-up until the sun has fully risen and it is warm enough to deliver vaccinations. Lucy Sherriff / NBC News

“Burning is such an important part of land management — and it is a tool that America has forgotten,” he said.

The Osage Nation and the cowboy community have been working together for decades, and now The Nature Conservancy is providing added support, giving the region’s residents hope that the prairies will grow and thrive for generations.

“We have the same common interests as the TNC and the Osage Nation,” said Ford Drummond, whose family has been ranching on the prairies for about a century. “We love this land, and as ranchers not only do we love it, we make our living off it. We’re all in this together, for the long run. We all want to leave the land better than we found it.”