email alerts

To receive email alerts for new posts of this blog, enter your address below.

Follow by Email

Tuesday, January 17, 2017

Bison Hypotheses

I was chided, rebuked, and otherwise treated to emotions by responses to two bison posts. I had celebrated the arrival of bison at Nachusa Grasslands – one of the great suspense-filled dramas and triumphs of contemporary conservation.  

Very quickly there emerged pro and con.

Many people quickly expressed a zeal for finding creative ways to get bison to their favorite Illinois prairies – as if a quality grassland couldn’t properly thrive without grazing. Opponents expressed passionate concern that “big stompy beasts” would destroy our last, precious prairie remnants.
Bison now graze part of Nachusa Grasslands. Will they wreck that part - or improve it? Or what?
So, to tackle the first question first:  

Do we need big grazers to have “real” and thriving prairies?

In my first bison post, I tried to convey the special and radical nature of the Nachusa experiment. Here’s a rehash of that footnote, upgraded now to main text:

Some people have criticized the restoration of plains bison (known scientifically as Bison bison) as “unnatural.” It is true that the eastern tallgrass prairie seems to have had Bison bison grazing it in large numbers only for only a couple of hundred years. Archeologists had wondered why they found few bison bones at Illinois Native American sites. Odder still, at the very oldest sites (10K+ years ago) they found many bones of two other species of extinct bison (Bison latifrons and Bison occidentalis) along with mammoth and mastodon bones.

As evidence mounted, a consensus developed that the eastern tallgrass prairie was so productive a habitat that the original Native American populations rapidly became too great for the coexistence with megafauna. Mammoths and Bison latifrons had evolved in prairies for millions of years – before the arrival of the crafty omnivorous humans. New to the continent at that time, human beings with the (stone) technology to hunt large mammals rapidly killed off the tallgrass megafauna. One smaller species of bison, the plains bison, survived in the sparsely inhabited western plains. Those bison that European explorers saw in Illinois had come east only after 1492 when European diseases began to reduce Native American populations drastically, some say by 90%.

Then after a couple hundred years of plains bison on the Illinois prairie, in the 1800s, the crafty omnivorous Euro-Americans drove Bison bison back to the plains once again. But almost all the plants and animals of the tallgrass prairie are much older than a few thousand years. They didn’t live here when this land was under glacial ice, but they perpetuated their kind on prairies that retreated south. Bison and a large proportion of other tallgrass plant and animal species evolved through the 2.6M years of the Pleistocene. One study suggested that most grassland bird species today are a few hundred thousand years old – evolving from earlier forms. 

Lurking in this history, as I perceive it, are two contrasting perspectives - both of which seem true to me. First, Illinois prairie remnants do not need bison to survive and thrive as healthily as they had for ten thousand years.  Second, bison are of great value at Nachusa if we hope to replicate how the  prairie species interacted for most of their millions of years of evolution. A consideration of these two contrasting but compatible perspectives also leads to questions about “the meaning of nature” – which we’ll get to a few paragraphs down (if your attention lasts that long).

For the last few thousand years our prairies may have evolved and flourished here with few large grazers. But evolutionarily, ten thousand years is a short time. Before the coming of people, the ancestors of prairie plants and animals flourished over much of North America, including what is now Illinois, with many large grazers playing a key role, as have world’s grasslands generally, for millions of years.  

Range Wars on Missouri Tallgrass

A lot of the “bison negative” comments originated from a long-running conflict in Missouri. Prairies on state conservation land there were said to be damaged by poorly managed cattle and bison. I tried to check out those reports.

Apparently the only "data" available were photographs. That seemed odd to me, since the critics were scientists, who you’d expect would have scientific sampling data. A photo, taken of a high-quality prairie in 1995, showed many coneflowers and coreopsis in bloom. A second photo, said to have been taken after over-grazing by cattle, at the same place and time of year in 2010, showed few flowers.

I had asked one knowledgeable scientist about those photos and was told that some people had panicked about some temporary impacts – but that after a few years the apparently overgrazed prairies were as healthy and diverse as ever. Perhaps I gave too much credence to that opinion?

Thus, I was disappointed to see the Nachusa experiment attacked on the basis of apparent misinformation. Yes, an experiment as bold as Nachusa's should welcome challenges and debate. But I kept hearing reference to out-and-out, proven calamities in Missouri. Was it needless panic or sure proof? Who was right?
In Nachusa's former corn fields, such quality plants as pale purple coneflower and white prairie clover
 now bloom in huge numbers over hundreds of acres. Too many cows can reduce or eliminate
 such conservative forbs. At Nachusa, bison seem to avoid them, so far. 
Ecosystem conservation is still in its “battlefield medicine” stage. As conscientiously as we pursue scientific decision-making, many questions are necessarily answered on the basis of “best available information and judgment.” Experts disagree, even on some of the fundamentals. Thus we experiment with and compare varying approaches, using the best data we can get.

There had long been conflict among Missouri conservationists about grazing prairies. Some good people argued that, if we are to retain large enough grasslands for rare prairie animal populations, our continent needs to retain the vast prairie acreages that survive only on private lands, owned by ranchers for grazing cattle. Conservation agencies and the government don’t have remotely enough land, so we conservationists need to be cooperative and friendly with the grazing industry.

No one disagreed with that goal, but biodiversity conservationists sometimes criticized some conservation agencies for taking “cooperation and friendliness” too far. It turns out that the Missouri Department of Conservation had decided to experimentally replicate bison grazing on high quality Niawathe Prairie with experimental patch-burn grazing by cattle.

Many government and private agencies have been developing techniques and expertise on patch-burn grazing (PBG). Some experiments showed PBG to be good for prairie birds and good for getting the most beef per acre. Some people had extrapolated those results to “PBG is best for cows, best for the soil, and best for biodiversity.” But there seems to be little data on that biodiversity question for high quality prairies in the eastern tallgrass region. Perhaps it will turn out that PBG is best for some rare species and not for others. The fundamental idea of biodiversity conservation is to save all the species, alleles, and ecosystem types, and it’s likely that a variety of approaches will work better than “one size fits all.”

 (The patch-burn grazing hypothesis is that over time the animals and plants will thrive, as grazed and un-grazed patches move around the landscape, because this was how this community evolved for millions of years.)

In response to the controversy, Doug Ladd, science director of the Missouri Nature Conservancy, wrote an eight page report discussing when and where grazing was compatible with biodiversity conservation. One of his summary statements was,
“Grazing … in … high quality prairies should be accompanied by disciplined, repeatable, dispassionate monitoring protocols … that document … the degree to which the most sensitive, least replaceable elements of the system are being sustained. These data should be available to provide adaptive management feedback on an ongoing basis.” 

Missouri DOC vs. Nachusa TNC

As I researched, I came across an impressive YouTube presentation by influential Missouri biologist Paul Nelson. He was alarmed by what he had seen cows do at Niawathe (and expressed concern about what bison might be doing at Regal Prairie). High-quality prairie species were being replaced by weedy, grazing-resistant ones, he said. He had once supported the concept of experimental grazing by cattle and bison, but he now believed that a worthwhile experiment had run amok.

In the YouTube video, Nelson was addressing a Missouri Academy of Sciences audience, including many prairie conservation advocates. He spoke to the politics of the situation. “What makes prairie management a challenge is that different managers and the public at large have different reasons or needs for management,” he said. Hunters, birdwatchers, cattle ranchers, and biodiversity conservationists all have desires to be satisfied on Missouri’s public lands. “There is diverse ownership with all these conflicting values.” 

Then he described a drama. After biologist Don Kurz disseminated a 45-page report critical of grazing by cows at Niawathe, conservationists raised their voices and got results. As Nelson put it:

“I am really proud and pleased to know that very quickly so many environmental interest groups and individuals rose up because of their concerns ... People are still sensitive to what we do and don’t do to manage some of the best high quality natural areas in the state.

Those who wrote letters included the Joplin Environmental Task Force, an Audubon society, a Nature Study Society, Missouri Native Plant Society, and, especially influential, an agency that had been one of the most ardent supporters of grazing, the Missouri Prairie Foundation.

When the Missouri Department of Conservation put PBG cows on Niawathe and bison on Regal Prairie, they did it as an experiment. They committed to take data and analyze the results. These may have been among the first times that patch-burn-grazing was employed on a high-quality tallgrass prairie. It was an important experiment. Surely by 2017 there would be well-analyzed data available to the scientific community and the interested public. Yet I could not find a published reference. I wrote to the agencies concerned and got no reply.

Nelson warned that on public lands, administrations change, and those new administrations might be dangerous to the ecosystem. He told his audience, “You have to have advocates – of scientists and organizations like you – to make sure that during those times of organizational change that managers are held accountable.”

Nelson’s 2010 talk assured the audience that an expert team was putting together an improved research plan. But now it’s seven years later. Is there no urgency to make better decisions on the basis of data and analysis?
How does the Missouri experience compare with Nachusa? The apparently troubled Missouri grazing experiments have had to deal with influential interest groups, politicians, and politics. The Nachusa decisions are being made entirely by conservationists, on the basis of science. (Of course the prairies too are quite different - on the richer Illinois soils compared to the ancient, unglaciated soils of southern Missouri.)

At Nachusa, many years of detailed study preceded the first nibble by the first bison. The accumulated data covers:
  • Plant communities: 22 fenced-off grazing exclosures with transects inside and outside each fence – plus over 100 additional permanent transects
  • Data on endangered plant populations including the prairie bushclover and prairie white-fringed orchid
  • Breeding bird transects and “point counts”
  • A number of long-term studies of invertebrate animals
  • Telemetry tracking of ornate box turtles and Blandings turtles
  • Snake monitoring transects

Nachusa manager Bill Kleiman is proud of the level of science under way at Nachusa, but he wants more. “We have about two dozen researchers out here, with science ramping up year after year.  Our Nachusa science budget is ten-fold what it was five years ago. But we still have more monitoring we would like to do.” It likely will take a couple more years at least before bison impacts, of whatever kinds, will show up in the data.

All the same, it would be great if Illinois could learn more from what happened in Missouri. It would be so helpful to see the best before-and-after data. How has the recovery gone, on the sites where the grazing has been reduced or eliminated? Were conservative plant or animal species lost or badly diminished? Were there other benefits or losses? What is being learned on the sites where the grazing continues?  
At Nachusa, some of the high, dry "grazed out" knobs have recovered to an impressive degree.
Will the buffalo herd reverse that recovery - or speed and improve it yet more?
Overall, the Nachusa experiment with bison is widely seen as ambitious and wise. But how about the small high-quality remnants within it? How are they being monitored, and how are decisions being made about them? Schafer Knob, perhaps the best quality remnant at Nachusa, had long been grazed down to the nubs, and what survived there should survive the worst the bison could do, at very least for a few years. Nachusa, of course, will not see the worst the bison could do. Good science and a large caring community of stewards will see to that. And then, most of Nachusa is not remnants; it is thousands of acres of former cornfields, sowed to prairie and now being grazed by bison. Indeed, that’s where these megafauna graze most.  
Twenty-two exclusion fences will help Nachusa monitors study the impacts of bison - pro, con, and otherwise. 
What will these experiments teach us about nature? This is the era on planet Earth that people are calling the Anthropocene. We the people, by necessity, make the decisions on which nature depends. We decide so much, on so many levels:
  • “How often and under what conditions will nature burn?”
  • “In the absence of wolves, should conservationists cull deer?”
  • “Will we bother to go to the hard work of restoring mega-fauna (like bison)?”
  • “Should a given preserve have 50 bison? Or 250? Or how many?”
  • “Should endangered species get extra care, or allowed to go belly up?”

In fact, these discussions remind us that as we learn, we continually need to grapple with yet more abstract questions: “What is a natural area?” “What is nature?” “What are our goals as conservationists?” We need answers because we have to make decisions.
The Midwestern natural areas programs in the 1970s launched something new on the planet. We hypothesized that certain little patches of rare plants represented “original nature.” The hypothesis expanded to a prediction that these areas would thrive if not disturbed in the future. We quickly learned that caring for little nature preserves would require a lot more work than we thought.
Over time, many conservationists became concerned that we were too exclusively focused on areas rich with rare plants, but too small for conservation of most animal communities, with which the plants were ultimately interdependent. Yes, our originally conserved “natural areas” are precious and crucial. They deserve respect and care (indeed, better care than they’re getting, in many cases). But so also do our larger areas deserve respect and care, where the goal is to restore as much of nature’s full dynamics as possible.
Stewards control invasive weeds on Dot's Knob. There may never have been a large grassland
with as much stewardship help as Nachusa. But every steward agrees, it deserves more. 
One great source of learning will be the large, well-managed, grazed and ungrazed grasslands at Nachusa (and comparable large and small efforts in so many places). Fun! Stay tuned! Or join in!
Flannery, Tim. The Eternal Frontier. 2001. Grove Press. Includes a good summary of the deep history of North American grasslands and their grazers.

Ladd, Doug. “Patch Burn Grazing and Missouri Tallgrass Prairies – The Nature Conservancy’s Perspective.”  January 2011
Paul Nelson. YouTube Video of a speech to the Missouri Academy of Sciences.
“Patch Burn Grazing: Is It Right for Missouri’s Remaining High Quality Prairies?”

“Nachusa: Fun People and Ornery Bison”  
“What Would Bison Do?” 


  1. I know you have intimate knowledge of Forest Preserves of Cook County lands that were over grazed before they were purchased. These parcels look very much like the after photos of heavy grazing at Niawathe Prairie shown in Paul Nelson’s presentation. My observation is that these heavily grazed areas are still in this degraded state even after decades of ownership by the FPCC. If these areas were on a trajectory of recovered then something should have improved by now. The division between these heavily grazed areas and adjacent high quality natural areas has not blurred much during these decades of conservation ownership.

    This is the reason your work is so important. If our natural areas just fixed themselves after being left alone then the many thousands of hours given by volunteers in our county each year would not be needed.

    Here is some further information from Minnesota that should be helpful. It is a list of grazing decreasers and grazing increasers for Wetland and Upland Prairie.

    "Orchids of the Western Great Lakes Region", by Fredrick W. Case, Jr., has a good subchapter titled “Disturbance by Animal Actions” on page 15 that is worth reviewing. The conclusion is basically that some orchids benefit from grazing, like Spiranthes lucida, whereas other orchids cannot tolerate grazing, like Platanthera hyperborea. Additionally, certain grazing situations can benefit other orchids like Cypripedium reginae even though the chapter starts with the following sentence.

    “The pasturing of wet meadows, if intensive, can be very destructive to cypripediums and certain platantheras.”

    Mr. Case writes that Platanthera leucophaea persisted in a pasture grazed by horse for 20 years. Mr. Case’s observations are in contrast to comments by the Minnesota Department of Natural Resources who write the following regarding Western Prairie Fringed Orchid sites. “None of the sites has a significant history of cattle grazing, although a few have a history of intermittent mowing for wild hay.”

    Ecology is a complicated subject. I agree that more information is needed and the studies being done at Nachusa will be important for conservation in our region.

  2. Stephen,

    I greatly appreciate the effort you spend to keep us informed about the Nachusa’s bison. It must take a good deal of time to put an informative post like this together.

    I know folks on both sides of the bison issue. Hopefully, Nachusa’s scientific approach in measuring the “before” bison versus “after” bison and the “bison areas” versus “no bison areas” will educate us all in the modern day use of bison in the eastern tallgrass prairie.

    Thanks, David

    1. I would like to second David's comment. It is good we have people like Stephen who are brave enough to continue difficult discussions on issues that create a lot of passionate responses from people.

  3. Bison management guided by sound science is the way to go. Bison grazing on a prairie are so evocative of an earlier time of what it "it used to be like", such that, even if not wholly accurate, can spur folks to care about a place. I worry about finding people willing to continue to protect and manage or remaining native/restored (semi)wild areas. If bison, through their evocative imagery, can motivate folks to invest in a place, perhaps it's worth it, even if the price is some small decline in biodiversity (which may or may not be true). My two cents.

  4. I offer this comment, not as scientific analysis, but more speculation based on observation. In our over 1,000 acres of rolling prairie, swale, ponds and newly created mud areas created out of regrading in a very wet mesic area, we found the value of the mud. Uncommon migratory birds never reported were here. The mud in the 170 acres will likely be short-lived as the restoration seeding takes hold, but we saw first hand the value of the mud. Although there are about a dozen ponds in the remaining areas, none have the mud to this extent.

    A second observation came recently as I saw a multi-decade study that correlated the tallness of prairie grasses to the populations of various grassland birds. Every grassland bird has a different preference. No wonder it's so hard for them to collectively find supportive habitat

    In both of these cases, it seems a reasonable rationale that the bison play a very important role in creating necessary disturbances that allow for constant fluctuation of the tallness of vegetation through grazing and keeping the vegetation down around ponds supporting mud flats. How can they not be an integral part of prairie dynamics that provide support for a vast array of of habitat structure? Since we don't have the natural predators that will scatter our beasts around, the challenge then is a bison management one that facilitates their movement to avoid prairie decline. It would seem.

    1. I have also observed interesting birds in local mud flat habitats. However, I don’t think bison impacts will ever get to the point of creating mud flats at Nachusa. Bison tend to avoid water. This is actually a big plus of having bison over cattle. The mud flat habitats I have observed are not a result of intense grazing, rather these habitats are a result of fluctuating water levels. This habitat type is commonly found in shallow flood water retention ponds locally.

      I have also contemplated the issue of utilizing grazing to create habitat for grassland birds. We are lucky to still have small areas that were fortunate enough to have escaped intensive grazing. This allows us to do a comparison. Many of these places are behind cemeteries, along railroad tracks, or just small scraps someone preserved because they liked the wildflowers. We should compare these small areas that appear to have escaped grazing with some of our states larger areas that were set aside after they had been intensively grazed. I have not visited enough of both these types of places to claim expertise. However, the handful of areas that I have visited which escaped intense grazing tend to have the tall prairie grasses, but they are a minor component. In contrast, the larger prairies I have observed that received intense grazing before they were protected are dominated by tall grasses. A good example of a large area that was intensively grazed before protection is Goose Lake Prairie. If someone has visited a larger number of both prairies that escaped significant grazing and prairies that historically had been intensively grazed I would be interested in their observations on the differences.

  5. very good observations and deductions, Pat. Most long-term restorations I see do not suffer from not enough grass; and if bison do show some detriment to a restoration, what is the worst that could happen? Learn, adapt, replant as needed.

    Check out the bison/prairie research at Konza Prairie, where they have been practicing LTER (long term ecological research) since the 80's, at the western edge of the 'eastern tall-grass prairie' biome.

  6. I enjoyed over read your blog post. Your blog have nice information,
    I got good ideas from this amazing blog
    gclub casino