American prairies were once home to as many as 60 million bison. But when ranching and agriculture displaced elk and bison from the prairies, America’s grasslands all but disappeared. Now, the Nature Conservancy manages the largest remaining protected tract of tallgrass prairie in the entire world, the Joseph H. Williams Tallgrass Prairie Preserve in northeastern Oklahoma.
This 40,000-acre expanse is much more than grass. It is a biologically rich habitat that harbors a diverse collection of plant and animal species—more than 750 species of flora and 80 different mammals. This prairie is also a vital component in nature’s fight against climate change. The key to keeping the prairie healthy? Bison.
The Nature Conservancy reintroduced 300 bison to this prairie in 1993, and the herd has grown to more than 2,000 animals today. They graze on the majority of the preserve, playing an important part in enhancing the prairies. Combined with a method of land management known as patch burning—preserve managers torch about a third of the acreage every spring, summer, and fall, mimicking ancient seasons of fire—the tallgrass prairie is thriving.
[Joe Hanson] To you and me, these look like trucks, and well, technically, that’s true. But on this patch of Oklahoma prairie, they’re more like oversized sheepdogs, except the creatures they’re rounding up are a little bigger than sheep. They’re bison. Using 4x4s to chase bison might seem like a weird new sport, but what’s happening here could actually be the key to resurrecting a lost ecosystem. A long time ago, in the heart of the North American continent existed a vast sea of tall grasses and millions of bison. This tallgrass prairie stretched from Canada to Texas, an area encompassing 14 present-day states. But then, stop me if you’ve heard this story, Europeans came with their guns and plows, and both the bison and the prairie disappeared. As little as 5% of this original prairie exists today. The largest remaining protected area of Tall Grass Prairie in the entire world is here in Northeast Oklahoma. This 40,000-acre expanse is known as the Tall Grass Prairie Preserve. From horizon to horizon, it’s tall grass.
[Sam] These grasses are what we call perennial grasses. So they live year to year, and there’ve been reports of perennial grasses living as much as 50 years.
[Joe Hanson] Sam Fuhlendorf studies grassland ecology. He’s found these soil and plant communities are surprisingly complex. Some of these grasses’ roots reach 15 feet deep, making them a crucial piece of Earth’s carbon storage biosphere. And there’s more biological diversity here per square meter than in some tropical forests.
[Sam] We’ve tried to understand the way this system would have operated historically and restore it as closely as possible.
[Joe Hanson] Before it could be preserved, the prairie had to be restored. You see it; it didn’t always look like this. Not long ago, this was a cattle ranch. Ranches prioritize economics over ecology, which in practice means putting as many animals on the land as possible for as long as possible. That can lead to destructive overgrazing. So how did this turn into this? It started with this.
[Bob] These are grasslands evolved with grazing, principally by bison. And so, if you’re trying to put Humpty back together again, you start with some of the bigger pieces, more important pieces. Bison were the primary historical grazer. Boom! Let’s put those guys back.
[Joe Hanson] Bison were reintroduced to this preserve in 1993. Since that time, the original herd of 300 has grown to upwards of 2,000 animals.
These bison love eating grasses and forage for up to 11 hours a day.
[Bob] They are essentially a stomach with four legs.
[Joe Hanson] You’d think all that eating would destroy the prairie, but these grasses evolved to cope with the grazing of migratory bison. In fact, they’re actually healthier for it. Grazing bison keeps certain plant species under control and allows others to flourish.
[Bob] They’re kind of ecosystem engineers. And so that’s one of the principal reasons we bring them back and reintroduce them to these native prairies.
[Joe Hanson] This preserve is managed by the Nature Conservancy. Today, Bob Hamilton and his team are bringing in the herd for medical checkups. Dogs could get injured, so instead, they use trucks to lead the bison into the corral.
[Bob] You always have to be watching for the ones that are trying to cut
and turn and blow past. Hey! Hey!
[Perry Voiceover] You can have 300 of them going, and all of a sudden, one cow tries to dart out, and the rest of them try a follow. And you, you never know. It looks like you’re in control, but you’re not.
[Bob] At point sometimes, you and your vehicle are in the middle of this swirl. Yeah. It’s just chaos. Like a little bison, a bomb goes off. One of their really driving behaviors is this herd instinct. They want to be with other bison. So they have this very synchronized movement. And so it’s like, they’re moving a big organism. So as you’re moving them, it’s this real
synchronized turning. It’s like a school of fish.
[Joe Hanson] These 2,000-pound patients don’t care much for exams. Hey, bud. It’s okay. We all get nervous going to the doctor. So who’s my brave little guy?
[Bob] Well, looking for any kind of injuries. Are they still in good shape? Are they stable? If everything goes well, the animal is only confined for about 45 or 50 seconds, then they’re kicked out, and you’re onto the next one. They are kind of quintessential wild creatures. They’ve never been domesticated. And one of our policies is to respect as best we can the wildness of that species. As I see it, our responsibility to the bison is to maintain their health and kind of their proper impact on the prairie.
[Joe Hanson] And bison aren’t the only things these prairies need to survive. They also crave fire. Bob’s team burns as much as a third of the preserve each year. That may sound like a lot, but it mimics the ancient seasons of fire once common on these primaries.
[Bob] These native prairies have evolved with fire. If you remove fire from the prairie, it reasonably quickly converts to woodland.
[Sam] Many people think fire destroys stuff, but in some of the cases of landscapes like this, it eliminates the dormant vegetation, and it allows the new growth to do better than it would if the old growth had been there. So it kind of cleans the slate periodically and enables the prairie to truly express its growth and really be highly productive and very well suited to a bison.
[Joe Hanson] This prairie is thriving once again, proof that the recipe of wild bison plus seasonal fire actually works. But okay, let’s get real for a second. We can’t return all the Midwest to prairie or restore bison to their former glory. But the biggest benefit of this experiment could be a bit of newfound insight. By understanding how natural systems work, we can use that knowledge to restore them. Here on the prairie, it turns out that grazer species might not be as important as the way they graze.
[Bob] If you manage cattle in a more wild-type environment, you can get a lot of the same ecological impacts as you can with bison.
[Sam] Cattle will almost never manage that way. So it’s like bison are allowed to be bison, so that’s what makes them really different from cattle.
[Joe Hanson] So allowing cattle to be a little more like bison could be one key to restoring damaged grasslands around the world.
[Bob] We do control the world now. And so it’s ultimately our decision on whether and some of these ecosystems are going to persist or not. If we were to lose the prairie, we would lose an important part of our collective history. Open space is freedom; oh man, it’s freedom.