What Does Long-Term Bison-Grazed Prairie Look Like?

Bison-grazed pastures tend to have higher forb cover and vascular plant diversity in prairie (bison have been there now for 35 years), but what does this look like. I have some pictures from quadrats from field work at in Konza’s N2B watershed (Bison + Fire every other year) taken nine years ago. It’s worth noting that spring burning at Konza is usually conducted between late March to early May, which is mostly/usually well into the growing season there (I used to volunteer, and Baptisa australis was often flowering at burn time), and that large swathes of bison watersheds lack enough fuel to burn when fire is applied (every other year is the frequency of fire application, not actual burning).

The below photos were taken in August. I’m not going to say here whether I like what I see or not. It should be pretty obvious. These are from a reference area of “intact” prairie used for a woody removal study that is in preparation. Another grad-student colleague and I helped by collecting baseline vegetation data. The woody removal did not work in the long-term, because TNC didn’t want cut woody vegetation treated near the stream. It was simply cut and left to resprout. …and woody vegetation removed included a few open-grown chinkapin and bur oaks about 150 years old (I counted rings on the stumps), which had green dragon and wild coffee under their canopies. That’s a tangent, but sometimes the big picture in science misses some of the nuance of what is being studied.

This area is indeed forbier and more diverse than frequently burned Konza watersheds that aren’t grazed, which are over-dominated by the big warm-season grasses, because burning is late (within the growing season) and probably also due to legacies of past broad-leaf herbicide application that would have occurred for warm-season pasture management. Here, the most prominent forbs are western ragweed (Ambrosia psylostachya), Canada goldendrod (Solidago canadensis; or tall goldenrod, Solidago altissima. The former is on the Konza list and I didn’t know the difference in the early 2010s when I did this work), Baldwin’s ironweed (Vernonia baldwinii), stiff goldenrod (Solidago rigida), and hoary vervain (Verbena stricta). These were easy quadrats to do!

Konza is just one site (even if subdivided into pseudo-replicates, which are reasonable at that scale), and results, I’m sure, will vary with duration, seasonality, stocking rates, and geography.

I distinctly remember getting out of the truck in a bison watershed on my first tour of Konza before my graduate program began and being struck that this was more or less the vegetation, and I haven’t seen a case yet that struck me differently. This could be Minneopa State Park in Minnesota, for instance. Bison are appropriate at Konza and elsewhere in the western tallgrass and on the Great Plains where they were an important historical presence, but the devil is in the details of fencing them in.

This links to Konza’s bison fact sheet.

Looking into the bison enclosure at Minneopa State Park near Mankato, MN. This is also has a lot of forbs–Erigeron and Artemisia.

A few decades ago there was a debate between Konza researchers and those working on more eastern prairies about what the context of and results from Konza mean for prairie management–and simply what maintains prairie. See the Bioscience article and response. It’s worth a look.

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Botanists are NOT Ruining Prairies

Wait, what?!

More than a decade ago Prairie Ecologist asked, “Are botanists ruining prairies?” I’d met the author, worked with him to set up a portion of my dissertation research. I’d come west from Iowa in 2008 with an open mind, drawn by the larger landscape prairies in Kansas, Nebraska, and Oklahoma. If anything, Prairie Ecologist was a role model, someone who had my attention, and whose career I would have been happy to mirror.

But with all the time I spent walking prairies, between the western margins of the tallgrass and its heart in Iowa, an uneasiness crept in. Then Prairie Ecologist posed the question, and I didn’t actually find the post for a while, but after I read a few paragraphs and had to step away. I put it out of my mind.

Recently the post showed up in my Google search results, so I read the whole thing. I’m thankful to my past self for sparing me the exasperation. The post is framed as lighthearted, a prod, but it’s a hot fallacious mess that reveals a lot of underlying biases and assumptions and both caricatures and minimizes the work and dedication of the people we have to thank for the prairies we still have today.

Prairie Ecologist claims that the prevailing dogma is that high quality prairies have a lot of “conservative plants,” and that these plants are defined as being rare in most prairies and…perhaps even “fragile.” FRAGILE. What follows is a free-wheeling essay on why it might not be the best thing that the botanists are so adamant about protecting small patches for Fabergé plants.

For starters, conservative plants are defined quite differently. If you are standing in the field looking at a very conservative plant, indeed, you are probably not standing on an old slag heap or in a recently fallowed field—but much more likely a remnant natural community that Europeans haven’t screwed up with novel disturbance or exclusion of essential indigenous disturbance. Are conservative species fragile if they lose ground or disappear in response to being fenced in with livestock, turned under by the plow, bulldozed? Are we really going to call any organism fragile and ignore the course of its entire evolutionary history and biogeography up to the present? Fragile? It’d be silly. Had we succeeded in eliminating the bison, would it be fragile? If ever there was a strawman put up, setting up conservative plants as fragile is one.

Four acres of fragility.

The post goes on to say “A compass plant is usually considered to be a conservative wildflower in prairies,” and “so, a prairie filled with lots of fragile plants is considered to be a high quality prairie.” A compass plant is fragile? The same compass plants that have pushed back up along county roads after multiple rounds of grading, withstood severe droughts, fires, and deep frost to live lord knows how long? Fragile, just because they’d have died if they stood on the same side of the fence as the cattle? On initial reading I was still hoping that the author wasn’t serious. …waiting for the punchline.

The post goes on to say “a prairie filled with prairie plant species that are tough and scrappy is considered to be degraded.” In another post he derides prairies packed with conservative species as “calendar prairies.” All this while every one of those calendar prairies species still has its suite of “scrappy” species—it’s black-eyed Susans, biennial evening primroses, wedgegrass, rough dropseed, and prairie thistles in addition to those “fragile,” conservative ones. Those scrappy species are not considered conservative, because they also grow in fallow fields, along roadsides…on slagheaps. It’s wonderful that they do! But crossing paths with them doesn’t tell you that you’re standing in an in an old growth prairie. It also doesn’t tell you that you’re not standing in one. …but that would be a more difficult concept to parlay into the question of whether botanists are ruining prairies. That said, I won’t dispute that the scrappies in an old-growth prairie are pushed to the margins by the “fragile” species whose resource use efficiency and complex and mutual interactions force them to the week spots in the sod—the gopher mounds and abandoned ant hills.

Leiberg’s panic grass, a conservative species sensitive to grazing and excessive litter accumulation.

Prairie Ecologist said “we tend to think about human society in much the same way…society consists of fragile people with clean fingernails and uncalloused hands who have to hire low-society people to cook, clean, garden, and take care of their fancy cars,” and “low-society people work hard to feed themselves and their families, wear functional clothes (without designer labels)….” What fresh projection is this? So the species that don’t stand and cheer after the cattle move on to the next pasture are the rich takers? Do-nothings? A Silphium stem borer or a phlox moth might beg to differ. Look at your hands. I hope they’re calloused (mine are). Phew.

Prairie ecologist further caricatures champions of “fragile” plants, “It’s certainly understandable that people who dedicate their lives to plants would be concerned about preserving those plant species that are the most difficult to preserve.” Is there a point? Perhaps unintentional, this feels like a minimization of the work of dedicated botanists, and also stewards and ecologists that see things differently. I’m often called a botanist, though my undergraduate and graduate training gave me no formal training as such. My training was a broad biological, ecological, and statistical one. But I learned long ago that the flora is a powerful lens through which to view the world, so I’ve become a passably good field botanist that can say a lot about a place based on the plants I see. There are other lenses, sure. My first biological loves were reptiles, amphibians, and fish. It’s easier to dismiss a point of view if you can claim the competing perspective is a narrower one than yours. If the botanists were out there irrationally dedicating their lives to plants, why would it even cross their minds to assign them scores that indicate affinity to old-growth natural communities?

Prairie’s gotta earn a living. “Most grasslands in today’s landscapes have to earn their keep, and are managed in ways that tend to favor species that are tough and scrappy, rather than those that are fragile.” Well, the first third is true. We continue to force the land into our Old World ways of doing things. We value hard workers. After all, they feed the world, right?

Pieris rapae? Strong as an ox. Papaipema beeriana? Soft bean counter. Prairie Ecologist would never say that. It’s preposterous. I wouldn’t either.

I will concede that in the world we live in, the only way to get more surrogate grassland on the landscape is if it somehow generates wealth. I would argue, however, that for conservation’s sake we can hold some some apart from servitude.

“The question of whether conservative plants were distributed in similar ways historically or were more widespread is a topic of much debate in prairie conservation circles.” We (Europeans who basically stepped in it upon arriving on the scene) eliminated them by the plow and with our confined pasturage of livestock. It’s true that the extent of this is hard to fathom. But it’s really quite the opposite. This is a question I’ve only heard posed from people trying to justify grazing in the context of conservation as though painting over rust fixes things. The reliability of our ability to track “fragile” species down based on how far they are from the barn, what side of the fence cattle weren’t on, and other modes of separation from livestock and the plow makes no sense if these species were not once generally the typical ones. Their persistence at all, given their life histories, wouldn’t make sense otherwise.

“Two groups of Illinois entomologists have each developed their own index of prairie quality based on “conservative” insect species,” and “both of them have found that there is often little correlation between the number of conservative insect species and the number of conservative plant species in a prairie.” Why should there be? Anyone that dabbles in floristics knows that the pitfalls are misuse and misinterpretation are rampant. It’s the worst with richness and evenness. It’s still pretty bad with FQI. Mean coefficients of conservatism are better, and weighted coefficients perhaps better, but where prairie is degraded by a long history of mid-spring burning or broadleaf herbicide application and grasses with moderate coefficients are over-dominant, it can buffer against discernment of the real story (another chapter there). …but number of conservative species? Hmph. So let’s square the potential misinterpretation!

Prairie Ecologist writes at length about there still being a lot of Regal Fritillaries, Gorgone Checkerspots, and grassland birds on Kansas and Nebraska prairies as though that proves something. Regal fritillaries need their host violets. Their host violets avoid grazing by virtue of their low stature. Those violets remain on eastern prairies infested with “fragile” plants, and so do Regals in the rare cases that there is enough landscape. I sincerely doubt regals would fair any better on prairie fragments with “scrappy,” “hard-working” plants in Nebraska if 99.9% of the land was turned under by the plow, taken over by thicket, and developed. But the problem is that darn, regal-killing, “fragile” plant management! We don’t have big prairies, but the small ones we still have support rich, conservative flora…so at least we maintain the possibility of expanding those prairies in all their fragile richness from the species and genes that remain. How to do this is the frontier of ecological restoration in the Upper Midwest.

Maybe easy street is still having landscapes to work with, which are part of a prevailing agricultural economy rather than the opposite.

Prairie landscapes like this still support relatively high numbers of grassland birds, including greater prairie chickens, but that’s not because they are used for pasture, it’s because they are large, open landscapes.

Let’s pause for a moment to pose two questions.

1) Does one native species have more fundamental right to exist or importance than another? If so, where does the logic extend? Once you put a price on a species, wealth can always pay to remove it. This is true even when we put the value on something with no clear economic relevance. Ecosystem services are the biggest conservation own-goal of all time…in my opinion.

2) How many of the “fragile” species that are often abundant on less abused eastern prairies find their range edges eastern Nebraska and Kansas or farther east? The answer is many. Wood betony. Compass plant. Prairie dock. Leiberg’s panic grass. Senega snakeroot. Rattlesnake master. Prairie blazingstar. Prairie coreopsis. Sky blue aster. MANY more. …and many different, more western species come onto the scene. Historical importance of bison as consumers ramps up east to west. …so maybe it’s all a big misunderstanding?

A prairie ecologist said, “High quality prairies – using the botanists’ definition – tend to be small.” What?! Attribution please! Oh yeah, we’re under cover of thought experiment. I’ve never met someone that didn’t desperately want to buffer and expand a small, high quality prairie remnant by reconstructing prairie or at least promoting maintenance of grassland around it. We (and by we I mean botanists, ecologists, stewards) dream about big prairies! We look out over the corn and see a lost landscape! Exhibit A would be the Mounds View Grassland. Those darn Midwest-easterners are just full of surprises.

Talking about prairies full of “fragile” species, Prairie Ecologist says “it’s also clear that those prairies can’t be the sole focus of conservation if we’re going to preserve the entirety of prairie species diversity.” Well clearly, but are we preserving it by minimizing elements of prairie diversity with dire conservation needs, old growth grasslands that don’t recover from disturbance on human time-scales? We can’t preserve prairie species diversity without those small, remaining prairies, and what is the entirety of prairie diversity? Prairie chicken reintroductions? Wolves? Cougars? Repatriation of land to American Indian people? These things tend not enter discussions of working prairies, but ungulates sure do!

The crescendo, “If some of those prairies were managed for more heterogeneous vegetation structure they might become more valuable to many insect and wildlife species.” Is this just a case of all eastern tallgrass looking the same to someone coming from the western margin? Heterogeneity abounds. Wood betony creeps across the prairie like an amoeba, lowering the vegetation height. Gradients abound in soils and drainage with even subtle topographic undulations, but you can see them in the plants and their structure. And the prairies are calendar displays, different in every month, not just in bloom, but also form. Species relative abundances and flowering ebb and flow across years in response to fire and weather. The heterogeneity is there in space in time. It looks different. Maybe it’s just all the green out here. But Prairie Ecologist continues, “It seems to me that some of those larger prairies could accommodate some experimentation with summer fire, fire-driven grazing, and/or other less traditional management strategies by testing those strategies on a portion of each prairie.”  Why would we sacrifice something that is rare and just about as close to irreplaceable as you can get to manage for “scrappy” species in the name of heterogeneity? These are scrappy species. They are easy to establish. We could just put in prairie plantings to poke and prod at will. Why would we burn in summer or fence in large ungulates when those weren’t the driving factors behind the assembly of tallgrass prairies, and it’s not clear that anything is broken that needs fixing beyond our greed for exploiting land (other topics, but the most numerous large herbivore out this way historically was a familiar one, deer). Sometimes experimentation is held up as science, when it’s really implementation. And this is happening. Take the patch-burn graze debacle at Taberville Prairie in Missouri as an example. And it’s a threat, because having big ungulates on grass is truthy. People like it. Sounds right. Alan Savory gave a Ted Talk. Never mind it was a load of bull (not that we’re talking about that graft here). To many laypeople, it’s all the same. Calves romping in the grass in front of the sunset on humid summer evening? It’s happy nature. It’s a win-win as far as dinner is concerned. It sells. Green is green, so never mind that we’ve lost some grasses and wildflowers.

Prairie Ecologist rightly says, “Regardless of answers to the above questions, there is one thing I feel very strongly about:  Good prairie managers consider more than just their favorite plant species as they think about how to manage their prairies.” I have never met one whose goal is prairie conservation that doesn’t. This extends beyond plants though, and plenty of mediocre managers consider a lot. Good land management more than anything comes from listening to what the land has to say.

The post ends rather magnanimously. I’m used to people talking and writing this way, having grown up in Iowa. In saying things that might offend, here making a long list of assertions and painting with a broad brush, claiming it’s in good fun and appealing for open minds are tactics to disarm and deflect those that would disagree head on. This is innate rather than intentional. I’ll consciously end more abruptly. It’s not the botanists that threaten any of the prairies I know. That prize goes to neglect, and the silver goes to the bulldozer. Save Bell Bowl Prairie! Even if it’s small collection of fragile organisms.

Posted in biodiversity, Conservation, Conservation own-goals, native plants, restoration, Stewardship | Tagged , | 3 Comments

Thoughts on Fire Frequency and Refugia

Eastern prairies and oak savannas lose prairie-dependent plant species without frequent or even annual burning (see Bowles and Jones, 2013; Alstad et al., 2016; Alstad and Damschen, 2016; Ladwig et al., 2018), and with those plant species, they lose all the specialists consumers that depend on them. Clonal woody species increase more rapidly with infrequent burning (less often than every third year) than they do very frequent burning (Ratajczak et al., 2016). Moreover, effects of prescribed fire frequency are dominant over those of precipitation change in determining woody encroachment in tallgrass prairie (Brunsell et al., 2017); this is not surprising, given the the historical occurrence of savannas and even areas of open grasslands in much of the wet eastern US prior to significant European presence, even in the Shenendoah Valley of Virginia (Omer Stewart, Forgotten Fires). Fire can override changes in precipitation. The use of frequent fire is necessary to maintain prairies and should serve as valuable tool in helping prairies and associated communities remain resistant to and resilient from climate change.

None of this should surprise people that visit remnant prairies and associated communities in the eastern tallgrass prairie region. Prairies with long histories of frequent burning are in far better shape than those not frequently burned or those with on again, off again management. Especially where there is much woody vegetation on the surrounding landscape, prairies burned less often than every 2-3 years are being rapidly degraded or lost. Places like Chiwaukee Prairie in far southeast Wisconsin are deteriorating and the hard work cutting and treating brush is wasted more and more as burns remain too infrequent to hold the line as the brush as pushed back. Frequently burned sites like Black Earth Rettenmund Prairie thrive, despite their small size and the abundance of woody vegetation on the surrounding landscape, which was all formerly prairie, oak savanna, and oak woodland.

Spring in a burned portion of Black Earth Rettenmund Prairie State Natural Area, which is burned frequently. Two thirds of the site had been burned during the preceding dormant season when this photo was taken in 2021. Note the small unburned area lower right. That spot would have burned completely had their been a few consecutive years of litter accumulation.
The unburned portion of Black Earth Rettenmund Prairie in the distance, which lacks expression of the early floral resources that are in in great abundance on the two burned thirds of the site. This remnant management strikes a good balance, especially that too infrequent of fire contributed to degradation of this site in the past. It’s recovery with frequent fire AND brush work is amazing.

This brings me to topic refugia that are left unburned for the roughly 40% of prairie insect taxa that experience at least brief population reductions with prescribed fire (Panzer 2002) [I will set aside that most of those recover within one growing season and the question of whether population reductions are universally bad, as we know native plant species get out of balance on poorly managed prairies, so it would be surprising if insects didn’t. We have floristic quality assessment to account for this, but not invertebrate quality assessment]. Refugia are often necessary where rare, fire-sensitive insects remain, because most remnant prairies are small, so insects that likely depended on recolonization from refugia naturally present at larger scales prior to the loss the prairie landscape need assistance to lower the risk of extirpation resulting from the very necessary use of frequent fire.

These refugia need to move. Without moving them, the prairie within them will degrade as described above and host plants will be lost within refugia, and if that happens, it stands to reason that insects will favor areas outside of refugia where their food plants grow with greater vigor and abundance, and where they are more vulnerable to fire. This seems to be what happened with a Powashiek skipperling site near me. Restoration involving frequent fire restored health, the rare butterfly was detected, burning stopped, the site accumulated excess litter and became brushier, and to my knowledge it’s been several years now since Powashieks were detected. Let us take regal fritillary as another example. It requires any of several species of violets that occur on prairies. Refugia for that species should be sited where good populations of violets are present. However, infrequent or no fire leads to the loss of violets, because violets are low-growing and smothered by accumulated litter (Henderson et al. 2018), so permanent, unburned refugia would probably be counter-productive for regal fritillary, host violets, and prairie conservation. This will be true for many, if not most prairie plant species that serve as host plants for rare, prairie-dependent insects, if those particular insects are among the minority sensitive to fire. For this reason, I believe the most prudent approach is to place refugia where high quality, prairie-dependent plant species occur, which are the most likely to host rare, prairie-dependent insects, and move footprints to adjacent portions of the area of high quality vegetation from year to year. The healthier and more abundant the vegetation and host plant populations become, the more options for refugia there will be. Habitat quality is of critical importance here. The problem of rarity is not caused by fire. It is caused by lack of good prairie habitat, and good, diverse prairie habitat cannot be maintained in the long-term without frequet fire.

I’ll add as an aside, that many dry-mesic to dry prairies, sand prairies, and many savannas and oak woodlands have lower, sparser vegetation with intervening areas between vegetation covered by cryptobiotic crusts of mosses, lichens, and cyanobacteria. However, litter does accumulate over time such that fires burn more intensely in areas left unburned for several years (so long as they aren’t overtaken by buckthorn or honeysuckle) than where fire is frequent or annual (patches of crust are often left unsinged); fire intensity (Byram’s equation) is the product of fuel heat of combustion, rate of fire spread, and quantity of fuel consumed in the flame front. Unburned or infrequently burned sites, unless they are hyper-xeric and very sparse, actually lose the crusts, which need light, and frequently burned sites tend to have them. This is just a personal observation, but it should be a consideration, because it surely affects the environment invertebrates face. We often consider the effects of single fire events versus the long term effects of how a particular fire frequency structures (sensu lato) the community. The short-term effect of a fire where none has occurred for four years may be very different (more severe) from that where fire occurred the year before. Studies of insect responses to fire must consider host plant responses and view short term responses in light of the long-term consequences of fire frequency for the community as a whole. It’s not killing insects that’s of concern; it’s their population maintenance and the health of the community that supports them, and that can be more sensitive to loss of habitat quality and host plants than direct mortality caused by fire.

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