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Sunday, July 17, 2016

What Would Bison Do?

Bison will change the way we understand the eastern tallgrass prairie. Scientists flock to Nachusa Grasslands to measure, prod, analyze, and test. But some of us can't wait to get a glimpse into this new world. This is a report of two days of hiking, listening, photographing, and no doubt barely understanding.

The Eastern Tallgrass Prairie is one of the planet’s richest grasslands – with ample rainfall and some of the world’s most fertile soils. Most of its five million years of evolution were without either scientists or human beings of any kind. Thousands of species and their genes are far older than the meager 10,000 years they’ve spent re-assembling in the The Prairie State since the last glaciation. During the most recent 200 years, we almost lost this ecosystem. Ongoing restoration of Nachusa Grasslands is the first opportunity since the dawn of ecological science to see how it all fits back together – original and restored eastern tallgrass prairie – and the bison – the large grazers that for millions of years were a fundamental part of it.

I started my adventure in a pick-up truck driven by Cody Considine, assistant preserve manager. Cody has the second greatest job on Earth. We intended to look at plants and study impacts, but by chance, there was the herd, right on our two-track. Cody wants to leave these wild animals alone as much as possible. So we stopped, and watched.

They seemed relaxed while we were in the truck, even letting a calf walk close to us, at least briefly, before they closed ranks around it. (They would behave very differently later, when I was on foot.)

After the herd moved on, our first stop was in a bison "grazing lawn" that Cody had noticed earlier. Bison eat grass and avoid most everything else. Bison, grass, and the prairie evolved together. This discrimination will have a big impact on the ecosystem over time. One of Nachusa's goals is to conserve many species of rare and endangered plants – and the animals that depend on those plants. Some plant species (and, thus, ultimately animal species as well) seem to be outcompeted on un-grazed prairies by too much tall grass. 

Here Cody is standing in the "tallgrass prairie" in midsummer. This is natural "tallgrass"? The bison have eaten the big bluestem down to lawn height – not just once, but repeatedly. The bison are always on the move around the preserve’s thousands of acres. But what they like most in summer (because it's most nutritious) is tall grasses that are growing fast – because they’ve been trimmed down. They come back to patches like this again and again. The result is a strikingly patchy prairie. 
Much of the preserve still looks like this – with no obvious bison impact. Some prairie lovers have worried that the bison-grazed prairie would look like an old pasture – depleted and bare. What the future holds is still a mystery, but for now the bison are focused on the small lawns they've made in the worst-quality restorations – the areas that are mostly tall grass. Bison will likely be grazing that grass back into a more natural balance with the forbs (“wildflowers”). The patches of Nachusa that are more diverse (and thus more ‘natural’?)  original and restored prairies  are passed through quickly as the herd travels among the best “grazing lawns” that they have created.    

Look closely above: This grazing lawn is typical. Patchily, the very grassiest areas are repeatedly eaten down, while the “forbiest” areas are mostly uneaten and untrampled. 

Here’s an example of a lawn edge. The pure grass is trimmed down nice and neat. But the prairie forbs aren’t even nibbled. (Forbs here include compass plant, wild quinine, pale purple coneflower, rattlesnake master and rosin-weed.)

Grass intermixed with forbs seems to be spared for now. Such selectivity may increase the diversity of niches in the recovering grassland. Here, the wildflower species that saved the grass include yellow coneflower, wild bergamot, purple prairie clover, and pasture thistle. On the other hand, what looks like re-sprouting red clover seems to be eaten with the grass. 

These diverse niches are surely important for many animals too. One obvious example is the lark sparrows, that seem to seek out the grazing lawns to find food.

One surprise to me was how the bison mouths discriminated among different grasses. The shaggy creatures love big bluestem and don’t seem to appreciate little bluestem, at least this time of year. The clump of little blue in the center of this photo was almost entirely avoided. With their big heads and big mouths, these big guys seem to have been able to graze right up to the base of this unfavored species without biting off even its lower blades. 

Cody also took me to visit some of the volunteer leaders who have the principal responsibility for restoration details. Here steward Bernie Buchholz shows us two sections of his area, the one on the right in its first year since he planted it. Mostly farm weeds. His planted grassland on the left has been growing for five or six years and is now mostly good-quality prairie. Many rare species are thriving; others are not. Stewards are experimenting with varied ways to plant, such that diverse species will out-compete the aggressives (like big bluestem) over time. All the stewards and staff have bated breath – waiting to see whether the bison will solve many of their problems, or create unexpected new ones, or what.

The next morning I set out on foot, alone, in the bison pasture, to see some areas that I especially wondered about. The wet prairies I visited showed little impact.

Rich remnant hilltops also showed only traces of bison activity.

But most of Nachusa is former cornfields, planted by various strategies, under various conditions, with varying results. As I studied them...

... I had little expectation on interacting with bison, but, suddenly, there was the herd, coming over a ridge and moving toward me. 

As the bison fence happened to be nearby, I found myself climbing to the other side. That gave me a great opportunity to save my skin  and see the bison close up. Notice the "people trail" on the left. I was not the first person to look at the bison along this stretch of fence.  

Staff and volunteers are allowed in with the bison  and use care and judgement. Casual visitors are not. The original plan was to let the public inside the bison fence, as at Yellowstone, with warnings about how to be safe. Apparently, some lawyers didn't think that was a good idea.

As I stood motionless and quiet, some members of the herd continued toward me, but staring suspiciously, very different from when Cody and I were in the truck. Now the females and babies kept well back, with mostly young males in between us. Were they curious? Aggressive? Both? 

After the bison passed, I climbed the fence back into the experiment and continued studying. I was reminded of trekking in Africa among rhinos, elephants, and zebra. (See:

I ran across some patches of Hill's thistle, one of the endangered species that may benefit from bison grazing. Will it be less endangered in years to come?

I ran across many "buffalo wallows." I'd expected a "wallow" to be muddy, but each one I saw was dry, and when I later saw bison rolling in them, they kicked up a lot of dust. 

Endangered regal fritillaries flew out of the way as I walked through a grazed remnant area, where grow their host plants, some rare violet species. Studies will tell us whether the regals and hundreds of other endangered or rare plants and animals will get a new lease of life thanks to the bison. 

Later in the day, Preserve Manager Bill Kleiman the person with the first best job in the world, took me out to study and think about Nachusa's rarest plant – the Federal-endangered prairie white-fringed orchid. Here we're looking at what was a corn field when The Nature Conservancy started this project three decades ago. With the orchid then missing from its whole region, Nachusa and the Fish&Wildlife Service brought in seed from where stewards were caring for a few plants, more than 100 miles away. Last year Nachusa counted about 425 blooming plants, more than any site on the planet. That's great, but they're almost all in one small, changing, rather newly-restored spot. 

This orchid grows in high-quality prairie, but seems to do best under conditions of disturbance. Will the bison work their magic with the white-fringed? Will they trample it into the mud some dry day? Bill Kleiman has the heavy responsibility and thrilling opportunity of worrying about such things and deciding what to do. 

The bison herd that roams Nachusa's hills and valleys now has about 60 animals (plus a few macho bulls that mostly keep to themselves). How many is the right number. As Bernie Buchholz put it to me, "The intended stocking rate is about 120 animals over 1,500 acres. One of Bill's big tools is to increase or decrease the number of animals as we start to understand how they are impacting the prairie. Ours is a conservation herd serving conservation goals. Ranchers would utilize far higher rates."

Nachusa Grasslands is one of the world's great experiments in conservation. Changes and surprises will be thrilling to watch for many decades to come. 

Postscript: After I wrote this post I learned that in other states there has been controversy about grazing high quality prairies. Some expert and dedicated conservationists have charged that grazing with cattle has irrevocably damaged irreplaceable remnants. I hope to research and write about these concerns regarding other sites elsewhere. Any input is appreciated.



  1. This is so cool!
    I have got to get up there this September to help Bill and Cody.

  2. thank you for the adventure.....

  3. This brings to mind the prairie research around the dust bowl era. They found that repeated hay mowing after a while reduced prairie grass vigor... And a few years of that also weakened their tenacious root systems. I imagine that during this "bison bullied" time the Forbes would be able to sneak down seedling roots into the sod. And after a few years the exhausted grass would be less tasty and the bison would adjust their browsing track to other "lawns". Natural rotation patch dynamics.

    1. Sounds right, and a great many newer papers would support your point. (Google: bison patch dynamics.) But those are all for the western prairies, where bison have had a bigger impact in recent millennia. The research at Nachusa should test those theories here.

  4. It is nice to see the bison are behaving as expected. It is well documented that over grazing by cattle has irreversibly damaged prairie ecosystems with species like prairie lily and prairie fringed orchids being some of the most sensitive.

    I must wonder if allowing the bison to repeatedly graze the same patches of grass over the season will be desirable in the future. It would be nice to see the difference between areas that were grazed just once in late spring compared with areas that are grazed repeatedly over the season to “lawn height.” I wonder if grazing the grasses just once in the spring would weaken them but not completely change the environment from partially shaded to baking summer sun thereby creating conditions more favorable to conservative plants. This type of grazing would likely better replicate grazing from bison which were free to migrate.

    I have to agree with the lawyers about not letting “casual visitors” enter the bison pasture. Most modern people have not been habituated to the dangers of interacting with bison. People often do not follow good advice posted on signs. Unlike some mistakes, using poor judgement around a bison might be their last mistake.

  5. I have one additional comment and one question. My comment is the decision to provide seed of eastern prairie fringed to historical habitats first is probably misguided considering the populations that have developed at Nachusa and the site you steward. My question is … have the bison helped by eating invasive species like the sweet clovers or reed canary grass?

    1. I agree that there's no need to limit seed to habitats that can be proven to have once had that species. There's so little info to go on. There's often regional info, which can be consulted. Some people compellingly argue that most prairie species were in most prairies - except for those that require a different soil type or hydrology.

    2. The thinking has been that if the prairie fringed orchid has disappeared from a habitat in the past few decades then seed from the few remaining populations should be sown in these historical habitats. The problem with this thinking is that there is likely a reason the orchid has disappeared, like the habitat is “changing” resulting in more strong competitors. Instead of focusing seed sharing efforts on historical sites and high quality prairies, maybe seed should be sown in sites that are in an earlier stage of succession (like at Nachusa and your site) where the orchid has a better opportunity to compete.

  6. Fascinating! Thank you:)

  7. I love this! Thank you so much for documenting what is going on here! I hope and pray for positive results for the health of the Nachusa Grasslands, and more people will see the value of this majestic landscape.

  8. Tremendous report and photos!