Are bison the key to bringing back Minnesota prairies?

Minnesota's last wild bison was seen nearly 150 years ago, and the grasslands that held herds in the thousands have since dwindled to small slivers and protected patches across the state.

Now it's becoming clear to scientists and park managers that they cannot restore those crucial prairies to hold anything close to their historical resiliency or diversity of life without their biggest ingredient: the American buffalo.

Bison need prairies. And, it turns out, healthy prairies absolutely need bison, said Tom Lewanski, natural resource manager for Dakota County.

"They're one of those species that has a much larger impact on the community than you'd expect for the number of animals they have," Lewanski said. "They're a keystone."

Lewanski and Dakota County are planning a living experiment of sorts, to reintroduce a small bison herd to about 150 acres of prairie they've been trying to restore at Spring Lake Park Reserve in Hastings. If they're successful, and the bison are brought back, they'll be able to study in real time exactly how the giants influence the land around them.

Every community — human or animal — relies on a complex network to keep it alive, Lewanksi said.

As bee and pollinator populations have collapsed, and a number of species of songbirds and plants have fallen to the brink, restoring and saving what is left of the prairies has become a priority for state and local agencies.

Certain pieces of a prairie's community are important enough that when they're lost, it hurts just about every other part.

Lewanski likened it to a town with a major factory, and all the schools, stores and restaurants that grow up around it. When the factory closes, it's not just those jobs that are lost, but all the businesses and schools that close, too. In the world of a Minnesota prairie, bison were that major factory, Lewanski said.

The bison's most important contribution in shaping the environment may be how much grass they eat, said Ed Quinn, natural resource supervisor for the Department of Natural Resources (DNR).

The DNR and the Minnesota Zoo have been carefully growing a herd of genetically pure Plains bison, which has been in the state since the 1960s, over the last eight years or so. They now have about 150 of the animals spread out over three locations: Blue Mounds State Park in Luverne, Minneopa State Park in Mankato and at the zoo.

They'll forage around these parks for up to 11 hours a day, eating "so much of the grass that they change what the structure of the vegetation looks like," Quinn said.

The bison walk as they eat, on the move together in a herd, mowing down some of the denser clusters and leaving more space and sunlight for flowers and other plants. Everything they eat takes fuel away from future wildfires, helping to manage the intensity of the flames.

Sometimes they wallow, throwing their 2,000-pound bodies into the earth and tearing up anything that might be growing, which exposes fresh soil to seeds and sun.

"That's really how these pioneer species of grass grow," Quinn said. "Certain grassland birds need these sparser areas, where others prefer the denser areas. This wallowing is how you get both on a landscape."

Bison can pack down the earth, too, when they wallow and turn what had been vegetation into small watering holes that become crucial breeding grounds for insects, frogs and other amphibians. Seeds even get stuck on their fur, which is also used for birds' nests, and carried throughout the prairie.

But with limited space, too many bison will degrade a prairie, stripping it bare, Quinn said.

The magic number seems to be around one bison for every 8 to 10 acres, meaning Dakota County's park near Hastings could expect to hold somewhere around 15 animals within an area that would be fenced off.

It takes about 500 bison to have enough genetic diversity to keep a sustainable herd that won't collapse on itself due to inbreeding, Quinn said. With populations maxed out at the zoo and the state parks, the only way to get Minnesota's herd to that number will be to create a network of scattered parks, adding places like Dakota County into the mix, he said.

Dakota County's plan cleared a major hurdle last month when the commission that helps decide how to spend the state's Environment and Natural Resources Trust Fund dollars every year recommended granting $560,000 for the project. If lawmakers OK the financing in the spring, the bison could be in the park by fall of next year, Lewanski said.

If the project moves forward, the county will need to be ready for an influx of visitors.

Since Minneopa introduced the bison in 2015, annual attendance at the state park has jumped by about 70%. The park has a road that winds through the center of the bison area, and visitors can drive to within a few feet of the animals, depending on where the herd decides to walk that day.

Dakota may not have enough room to make its own bison road, but there are enough trails and parking space that viewing the animals shouldn't be a problem, Lewanski said.

He said his hope is that bison will start a positive cycle both in the ecosystem of the prairie and with the people who come to see them, who may stay to learn more about the restoration and efforts to bring back other rare but less loved animals, such as bull snakes.

"People think 'prairie restoration' and they think plants," Lewanski said. "But it's not only the plants. It's bringing back as many of these animals as possible."