When settlers arrived on North America’s Great Plains, they encountered tens of millions of bison (often called buffalo). By the end of the nineteenth century, less than 1,000 remained. The bison has since been saved, but it no longer is a keystone species shaping America’s grasslands.
The Nature Conservancy is putting bison back on the prairie, restoring its ecological role on select preserves. Most bison today are managed as commercial livestock; the Conservancy’s bison are allowed to roam as conservation herds that replicate their former role on the Great Plains.
Almost three decades ago, the Conservancy established its first herd of bison at the Samuel H. Ordway, Jr. Memorial Preserve, a 7,800-acre expanse of prairie that is the Conservancy’s largest preserve in South Dakota. There are now 250 bison at Ordway and the plan is to grow the herd to 300 animals.
Healthy grasslands are grazed periodically by cattle or bison. The Conservancy uses both.
Mary Miller, Ordway’s manager, says bison are good for prairie. “They graze all year, even in winter, and focus on grasses, allowing wildflowers to thrive. The result is a varied grassland that is good for more kinds of butterflies, pollinating insects and grassland-nesting birds. Biodiversity is enhanced.”
Because bison move constantly they graze specific areas intensely but for short periods. Prescribed burns that stimulate new native grass and plants can be used to direct their movements. This technique is called patch-burn grazing and it can be used to rotate cattle, which are also beneficial to maintaining healthy grasslands.
But bison aren’t cattle. They are difficult to handle. “The more you try to force them to do something they don’t want to do, the more they push back,” says Miller. The Ordway bison are handled minimally: once a year, the animals are brought in to be checked and those that will be sold are removed from the herd.
Eric Rosenquist, manager at the Conservancy’s Cross Ranch in North Dakota, agrees with Miller that bison are good for the prairie. Bison have been at Cross Ranch for more than 25 years; they are the Conservancy’s second herd.
“Prairies need disturbance, like the disturbance created by fires and by bison,” says Rosenquist. “Both prevent the build-up of a litter layer beneath the grass that can shelter invasive, non-native species. Bison graze the grasses that contribute to the litter, and also create open areas in their wallows or by trampling the ground that become good locations for the seeds of new prairie plants to germinate.”
Rosenquist is also impressed by how well-adapted bison are to their environment. “They are resilient. They can withstand both the heat of summer and the freezing cold of winter. They even seem comfortable in the two feet of snow and 40-below temperatures of the ranch in January.”
“There are just four things bison need: food, water, other bison and room to roam,” said Rosenquist, who has been helping the Conservancy bring bison back to other grassland landscapes.
Bison herds established by the Conservancy in recent years can be traced back to Wind Cave National Park in South Dakota. The Wind Cave herd is a genetically valuable “gene bank.” Because bison were nearly exterminated (all bison today are descendants from relatively few animals), the species has passed through a genetic bottleneck. But the animals at Wind Cave have lost less of that genetic diversity than most herds. They also have few, if any, cattle genes.
The bison at the Conservancy’s Lame Johnny Creek Ranch in South Dakota came from Wind Cave and some of those animals are being sent to establish a new bison herd at the Conservancy’s Dunn Ranch preserve in northwestern Missouri. Other bison from the Wind Cave population have been placed at the the Conservancy’s Broken Kettle Grassland Preserve in Iowa and at the Rancho El Uno Ecological Reserve in Mexico, which is near the southern limits of bison’s historic range.
Bob Paulson, the Conservancy’s Western Dakotas Program Director, envisions working with landowners and partners to create large herds of 1,000 or more bison that would graze and shape the prairie across North America.
“We have all the pieces of the American Serengeti but not to scale,” Paulson said. By bringing bison back to the prairie, the Conservancy is helping complete the picture of the once vast Great Plains.
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