“We’ve been working on research to restore oak savannas here since the 1960s, with mostly prescribed fire,” said Postdoctoral research associate Chad Zirbel.
“But, it’s become clear that prescribed burning alone is not giving us what we are hoping for in terms of management strategy,” said Caitlin Barale Potter, Cedar Creek’s education and community engagement coordinator.
Researchers at Cedar Creek have been rotating burn frequencies in study zones, but something is still missing. No matter how long in between fires, they haven’t found the right burn frequency to generate the growth of oak trees. No new trees are reaching maturity.
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“The reason we think that’s the case is because, the grasses – which are the dominant species out here and really important for savannas – they outcompete the oak trees for some of those resources the are needed for growth, like water and nitrogen,” said Zirbel.
The oak savanna can have different densities of oaks and other trees on the grasslands. Today this ecosystem is endangered and considered one of the rarest plant communities on earth.
“The oak savanna is a really special system,” said Potter. “It’s this quintessentially Midwestern ecosystem. It has a lot of specialist species including red-headed woodpeckers that people care about. As we start losing the ecosystem, we start losing some of these special species as well.”
To stop the loss, they are looking back to how things were hundreds of years ago, when the savanna was much more common in the area.
“Pre-settlement, there were dynamics that are now missing from the landscape,” said Potter.
“We know bison were important players in these savanna systems, but there’s been no research, or very little research on what happens when we put them back,” said Zirbel.
So, for the second summer in row, Cedar Creek has become home to small herd of bison, 17 to be exact. And they are using these bison in their research. They let the bison roam throughout 200 acres of their reserve, but certain parts of that are blocked off, so they can continue to study how their prescribed burns affect the land that haven’t been grazed by bison, while also seeing what happen when they do graze.
“Bison could be a really important tool for restoring prairies and savannas in Minnesota and across the Midwest,” said Zirbel.
Even though the project is young, they are beginning to see results.
“When we looked at survival rates of oak trees, anywhere that fires didn’t burn because the grazed, we saw 80 percent survival of those trees,” said Zirbel.
One reason for that, they think, is that the prescribe burns work through the savanna at a lower temperature once a lot of the grass is gone, giving the oaks a better chance of survival.
“They change the landscape so that fire behaves very differently, and we are starting to see some anecdotal impacts on bird communities as well shifting numbers of different species. It’s very early, too early to say anything definitively, but we are seeing an impact.”
Each Saturday through the summer, Cedar Creek opens a special bison viewing gazebo to the public. It is open from 10 a.m. to 2 p.m. through the end of August.
