MINNEAPOLIS — University of Minnesota officials hope a herd of bison will help restore a threatened ecosystem in a nature reserve.

More than 30 bulls immediately began to graze on grass when they were released into the 200-acre (80-hectare) Cedar Creek Ecosystem Science Reserve in East Bethel on June 13.

“To see animals be released like that and behave naturally is amazing,” said Caitlin Potter, the education and outreach coordinator at Cedar Creek.

There are no wild bison in the area. The herd of two-year-old bulls is from a ranch in Wisconsin.

The bison program is part of a larger initiative to restore the oak savanna ecosystem, said David Tilman, the director of Cedar Creek. Bison have largely been absent in the state for nearly the past 190 years, he said.

“The biggest danger to nature is humanity,” Tilman said.

Bison feed on grass, which creates room for oak trees to grow, according to Chad Zirbel, a post-doctoral ecology researcher.

Researchers have planted 660 oak seedlings in the enclosure, along with other seedlings in locations closed off from the bison in order to compare growth in both areas. Researchers plan to monitor the plants’ growth as the bison graze.

The herd will return to the Wisconsin ranch in the fall for breeding season.

The Environment and Natural Resources Trust Fund awarded researchers a $388,000 grant for the project last year.