Bison Bliss: Grazing Shapes Diverse Western Iowa Prairie

Sep 4, 2018

Bison are helping sustain a diverse native prairie in western Iowa through grazing.

More than 200 bison call The Nature Conservancy’s Broken Kettle Grasslands Preserve in the north end of the Loess Hills home. As Scott Moats, the Iowa conservancy's director of stewardship puts it, “We don’t have the prairie to maintain the bison. We have the bison to maintain the prairie.” 

In herds of at least a couple dozen, the bison roam freely around 1,900 acres of the roughly 3,000-acre preserve, munching on various grasses and sedges at any given time of day.

“I always equate it to a buffet,” Moats said. “If I go to Pizza Ranch for lunch, for instance, there’s a salad, there’s sprouts, there’s carrots, but there’s also fried chicken, there’s biscuits, there’s also dessert pizza…”

He continued, “Depending on what looks good to me and tastes good to me that day, I’m going to make those choices that day. That’s exactly what the bison…are doing as a grazing animal.” 

A herd of bison grazing at Broken Kettle Grasslands Preserve.
Credit Katie Peikes / IPR

As bison graze on their own buffet of grasses like big bluestem, little bluestem and indiangrass, their work opens up the area, providing sunlight and moisture for plants to grow and setting up habitat for other species. The conservancy's Western Iowa Land Steward James Baker said some birds that like to nest in the grasses prefer short grass; others prefer tall grass.

“Different animals like different things and by having the bison here, we provide hopefully as many species as possible what they like,” Baker said. 

Since the conservancy introduced a herd of 28 bison to the preserve in 2008, grazing has helped milkweeds thrive, attracting monarch butterflies to the area. The preserve has also attracted birds like killdeer, that nest in areas that have short grass. 

Baker said without the bison, vegetation would be uniform and would only be able to support some species.

The bison came from Wind Cave National Park in South Dakota and are unique in that their genes – as far as The Nature Conservancy can tell – do not have any cattle genes mixed in. Baker said interbreeding the two species was a common practice in the 1800s.

“The idea being that you’d get the toughness of a bison with the production value of a cattle,” Baker said. “What they ended up with was something that not a really good bison or a really good cow or cattle."

The conservancy has cattle on its preserve too, grazing on a separate pasture from the bison.

Scientists use them to graze areas of Broken Kettle Grasslands where there are prairie rattlesnakes. This helps keep habitat healthy for the endangered reptile so their population can stay functional here.

Baker said the cattle tend to eat more forbs than bison and also spend a lot of time around water sources. They’re also not as mobile as bison, whereas bison tend to travel all over the preserve each day.

The conservancy hopes to open up more of the 3,000 acre prairie to the bison in the future so they can graze on some untouched parts, allowing more land to reap the benefits of grazing. 

Approximately 364 days of the year, the bison are left to themselves, "just bison being bison," Baker said. Once a year, in October, scientists catch them to get them up to date on their vaccinations and treat them for parasites.