Fall 2018
Image courtesy of Forest Isbell

Bringing back the bison


“They’re not going to charge, but they’re curious.”

Those aren’t necessarily words you want to hear after driving into a 210-acre enclosure that’s home to 32 male bison, then leaving the safety of the vehicle to look more closely at a fenced-in area of grasses, shrubs, and oak seedlings. Both the bison and the protected plot are part of a study on how grazing affects oak savanna at Cedar Creek Ecosystem Science Reserve, part of the U of M’s College of Biological Sciences.

Back in the truck, Forest Isbell, associate director at Cedar Creek and lead researcher for the study, explains that bison were part of the oak savanna ecosystem that once covered 10 percent of Minnesota but is now confined to a few protected reserves. Cedar Creek, located north of the Twin Cities in East Bethel, is one of the rare places where you can still see the beauty of this landscape: an open field of grasses and wildflowers, dotted with burr oak and Northern pin oak, that’s home to hundreds of species of insects and dozens of species of birds. 

And, as of June 2018, bison.


Oak savanna is one of the most difficult landscapes to restore once it’s been destroyed, Isbell says. Since 1964, Cedar Creek researchers have used controlled burns to replicate the fires that were once part of the natural ecosystem. Some areas are burned once every three years, some are burned two out of every three years, and some are left alone. The question scientists hope to answer is which fire frequency does the best job maintaining the savanna.


The Cedar Creek Ecosystem Science Reserve might be one of the U’s best-kept secrets. The 2,200-hectare site encompasses diverse habitats such as forest, prairie, oak savanna, ash and cedar swamps, acid bogs, marshes, and sedge meadows. 

Since the 1980s, it’s been home to long-term ecological research that was started by David Tilman, Cedar Creek director and Regents Professor in the College of Biological Sciences. That work is now being led by professors Sarah Hobbie and Eric Seabloom. 

But it’s not just scientists who explore Cedar Creek’s natural riches. Each year, more than 10,000 schoolchildren, teachers, and other guests visit the site—in some cases with travel expenses covered by gifts from donors. To better serve school groups and the general public, the reserve is raising funds for a new Minnesota Ecology Walk that will provide hands-on learning for visitors of all ages.

“Unfortunately, the answer is none of the above,” says Isbell, pointing out that the reserve has numerous mature oaks but very few oak seedlings or young oak trees. That’s because older trees can withstand the effects of fire, but younger trees are less likely to survive.

Part of the problem is that native prairie grasses crowd out oak seedlings, preventing them from growing large enough to survive a prescribed burn. In addition, these grasses provide plentiful fuel, making the fire hotter and more uniform in its path. 

That’s where the bison come in.

“In many grasslands, bison are recognized as a management tool and as an important natural part of the ecosystem, but there isn’t any research that’s trying to understand the role of bison in savannas,” Isbell says. The study at Cedar Creek is the first to do so.

He says researchers hypothesized that the bison would graze on the  prairie grasses and leave the oak seedlings alone. To test this, they planted burr oak and Northern pin oak seedlings alongside existing prairie grasses, both inside and outside fenced-off enclosures that are protected from hungry bison. 

Isbell says you already can see the effects just by looking at the landscape. The bison are not eating or trampling the oaks, he says, but they’ve grazed heavily on the grasses. 

He hopes that without as much competition from grasses, the oak seedlings will grow tall enough to survive the controlled burns planned for this coming spring—and because the grasses are less plentiful, the fires will skip over some areas rather than burn uniformly.


The bison, which Cedar Creek leased from Wisconsin-based NorthStar  Bison, were rounded up in September and transported back to the company’s winter enclosure. Cedar Creek’s bison research has funding for two more years from the state’s Environment and Natural Resources Trust Fund, which covers expenses for a post-doctoral researcher and the fencing for the bison enclosure. 

Isbell says additional funding would allow him to purchase radio collars to make the bison easier to track. This summer, two researchers spent an hour and a half each day driving and walking around the enclosure, making sure none of the animals were hurt or sick.

Another group eagerly watching the bison is the public. Each Saturday in July and August, trained naturalists talked to visitors about the oak savanna research and answered questions about the animals. Isbell says 50 to 100 people showed up each week. “Everybody likes the bison,” he says.

Amy Sitze is a contributor to Legacy magazine.

Watch the herd being released at Cedar Creek.
College of Biological Sciences