Curious about patch-burn grazing? Want to get together with other grassland enthusiasts, ranchers, researchers, and wildlife managers and talk about a variety of ways to manage for diverse wildlife habitats and plant communities? The annual Patch-Burn Grazing Meeting might just be for you.
This is an annual, and informal, gathering held at a different location each year. This year, we get to host it here at the Platte River Prairies, so we’ll be sharing some of what we’ve learned (successes and failures) about managing prairies with various combinations of fire, grazing, haying, and other tools. Discussion topics will also include potential differences between how patch-burn grazing works in southern vs. northern grasslands, whether/how it might work on Nebraska sandhills ranches, alternate methods for creating habitat diversity besides “traditional” patch-burn grazing, and some practical issues such as figuring stocking rate and dealing with livestock health issues.
The meeting will be held August 13 and 14 in Grand Island, Nebraska, with a tour on the 14th of our Platte River Prairies just to the west. There is no registration fee, but food and lodging will be at your own expense. If you’re interested in attending, you can see the agenda for the meeting here and the registration form here. Registration is due July 20.
It’s been a difficult year for conducting prescribed fires so far – the wind seems to be blowing even harder and more consistently than in recent memory. And that’s saying something, living in the Great Plains.
A couple of weeks ago, we were able to pull off one prairie management burn here in the Platte River Prairies. The fire went well, and this week I took a quick walk through the burned area to see how the regrowth of vegetation was coming along. It’s been a cold and dry spring, following a dry fall and winter, so plant growth has been slow, but things are finally starting to kick in. Within the burned area, many plant species are a little behind their compatriots growing outside the burned area, but others are ahead. Those that are behind are the species that were already starting to grow when the fire came through – those species had to start again, so are behind schedule. The species that are further ahead in the burned area are those that are taking advantage of the warmer soil and have either germinated or emerged faster than those in the cooler soil of unburned areas.
Regardless, plants are growing well in the burned area. That’s good, because cattle will arrive within the next week or so, and we want the burned area to be particularly attractive to those grazers. One of the major objectives of our fire was to concentrate grazing in one portion (the burned patch) of the prairie this season, leaving the remainder of the pasture with much less intensive grazing. Hopefully, the result will support our efforts to create a variety of habitat patches across our prairies, and to shift the location of those patches from place to place each year.
The patch we burned this spring has had no fire and very little grazing over the last couple of years. Last year, it had tall vegetation and abundant thatch – conditions that favor a certain set of plants and animals, but not others. This year, it will have very little thatch and the vegetation will be short in stature because of season-long intensive grazing. Next year, it will begin a multiple season recovery period from that fire and grazing until it is burned again sometime down the road. (You can read more about patch-burn grazing here.)
Burning a different patch of prairie each year helps ensure that a mixture of habitat types is always available and most or all wildlife and invertebrate species can find the habitat they need. Our prairies usually have a patch of very short habitat, several patches in some stage of recovery from intensive grazing, and some areas that are tall and very lightly grazed – or ungrazed. Some animals will follow those habitat patches across the landscape. Others will go through boom and bust periods within one portion of a prairie, depending upon what conditions they thrive best under.
Because we’re always changing the location of habitat patches, plant species also experience changing conditions from year to year. This means that some species flourish one year, but may have to wait a few years before those favored conditions return. In the meantime, other plant species will find success. Constantly changing conditions help ensure that no group of species becomes too dominant, but that all species can survive and maintain a place in the plant community. Our long-term data has shown the our plant communities have stable to increasing plant diversity under this kind of management, and we’re not seeing any plant species disappear.
Another benefit of burning only a portion of our prairies each year is that it helps us avoid catastrophic impacts on plant and animal species that are negatively impacted by fire. Invertebrates that overwinter above ground, for example, can be destroyed by an early season fire. Growing season fires can kill animals (invertebrates and vertebrates) that are unable to escape by leaving the area or retreating underground. These kinds of impacts are somewhat unavoidable, regardless of the season of fire, but by burning only a portion of our prairies, we can try to restrict impacts to a relatively small proportion of the population of each species, allowing the majority of individuals to survive and recolonize the burned patch over time. Burning an entire prairie, especially in highly fragmented landscapes in which recolonization is unlikely, can result in completely and permanently obliterating vulnerable species from a site.
Hopefully, the wind will pause a few times during the remainder of the spring, and we’ll create a few more burned patches in our prairies. If not, we’ll try to create patches of short habitat by haying or by temporarily fencing cattle into an area to knock vegetation height down. We’ve found that all three methods (burning, haying, temporary enclosures) can create a patch that attracts livestock grazing afterward – and therefore pulls that grazing off of other portions of prairie. There are lots of ways to create patchy habitats, and none are necessarily best. As long as there is always a mixture of habitat types across our sites, we feel pretty good about our management.
Hopefully, the species living in our prairies feel pretty good about that management too.
First impressions: Patch-burn Grazing in Short Grass Steppe vs. Mixed Grass Prairie
Our Platte River Prairies here in south central Nebraska are lovely, flowery pastures, but I needed to travel to get a more complete concept of how patch-burn grazing works across different landscapes and precipitation regimes. It was this drive that brought me to the Central Plains Experimental Range (CPER) in the short grass steppe of Pawnee National Grassland in eastern Colorado.
My two guides, David Augustine and Justin Derner, were kind enough to spend a morning showing me around their site. First impressions- the obvious: CPER is much drier. They average 13 inches of rain annually to our 25. We don’t have much in the way of species overlap between our sites. Blue grama with small patches of buffalo grass, wheatgrass, and prickly pear seemed to be the dominant community at the CPER pastures we visited. In comparison, we see big blue stem/switch grass/dozens of forbs/etc etc as the major species in our mixed grass system.
A major management impact of this different precipitation regime is that their sites cannot carry fire year round. There simply isn’t enough fuel. Their estimated fire return interval (the average ‘natural’ length of time between burns on a site) is much longer than ours. The estimate they gave me was 10-40 years. By comparison, much of the tallgrass ecosystem is believed to have a return interval of approximately 3 years. Luckily for them, the harsher conditions are keeping woody encroachment at bay, so they don’t need to burn frequently.
I spent much of my visit puzzling out the major value of fire to the short grass steppe. The benefits in the mixed grass prairie are dramatic. However, most of the positive impacts of fire that we see here in Nebraska (preventing woody encroachment, changing the balance of power within a plant community to favor forbs) just aren’t evident in eastern Colorado. As mentioned previously, trees are not a problem in their drier climate, and forbs were largely absent even on burned areas.
Justin and David explained that burns are critical for habitat heterogeneity, particularly for clearing ground to produce ideal habitat for birds like the mountain plover. They also see a decrease in the amount of prickly pear at a burned site. Burns remove the spines, and pronghorn come in to forage on them over the winter. Forage quality of the native grasses also improves after a burn, similar to at our sites, but this is a smaller and more transient effect as distribution of precipitation over time and the landscape takes over as the most important ecological factor.
I left Colorado with the impression that the mixed grass prairie ‘leans east’, if you will. It is more similar to the tallgrass prairie than the shortgrass steppe. It’s as if some precipitation threshold is crossed once you move west of the mixed grass system, and an entirely new set of challenges replaces what we have east of that line. Here in the mixed grass, periodic, varied disturbance seems to be the key to biodiversity. In the west, perhaps the periodic, varied change in conditions is embedded within the precipitation regime itself. As I travel, I will continue to explore the question of how grassland management for biodiversity changes in different regions.
We recently completed a large multi-year restoration and management project at our Platte River Prairies. Our specific objectives were to improve habitat quality for various at-risk prairie species and evaluate the impacts of our management on at-risk butterflies – particularly regal fritillaries. The project was supported by the Nebraska Game and Parks Commission, who funded our work with two State Wildlife Grants (U.S. Fish and Wildlife Service money). Over five years, we conducted fire/grazing management in our prairies and enhanced plant diversity through overseeding and seedling plugs. We measured the results of that work by measuring changes in prairie plant communities and by looking at the use of our prairies by regal fritillaries and other butterflies.
The following is a brief summary of the major lessons we’ve gleaned from the fire/grazing component of the project, including implications for future management and restoration work. I will summarize the overseeding/seedling work in a separate upcoming post. If you want more details, you can see our entire final report to the funding agencies here. As a warning, the report is 14 pages long, with an additional 21 pages of Appendices, full of tables and graphs.
What We Did Between 2008 and 2012, we treated over 1,500 acres of prairie with varying applications of patch-burn grazing management. During that time, we altered the timing of burning and the intensity of grazing from year to year, and included years of complete rest from grazing in some prairies. For the purposes of this project, we evaluated the results of our work in two main ways:
We’ve been conducting field surveys of regal fritillary butterflies for the last three years. During that time, we’ve learned a lot about how those butterflies are responding our prairie management and restoration work. So far, there are two overwhelming lessons we’ve learned from our work.
1. The number of regal fritillaries produced in our Platte River Prairies is primarily tied to two factors: violets and thatch. During the spring, when adults are first emerging from their chrysalises, butterfly abundance is highest in degraded remnant (unplowed) prairies that have few showy native wildflower species, but lots of common blue violets (Viola sororia). While they don’t have much to excite a prairie botanist, these prairies sure produce a lot of regal fritillaries. We don’t find many regals in recently burned portions of these prairies – only in portions that have built up some thatch.
2. After regals emerge and mate in those thatchy violet-rich prairies, they spread out into more flowery sites to feed. In our Platte River Prairies, those feeding sites tend to be restored (reconstructed) prairies located around and between those degraded remnants. Those restored prairies have significantly fewer violets than remnant prairies, but lots of the favorite nectar flowers for regals, including hoary vervain (Verbena stricta), milkweeds (Asclepias spp.), wild bergamot (Monarda fistulosa), and thistles (Cirsium and Carduus spp.). Interestingly, while we don’t see regals emerging from recently burned prairie, some of the most-used summer nectaring sites are our most recently burned sites.
It’s awfully frustrating when I fail to solve a puzzle – especially when all the information I need is right in front of me. As an ecologist, I’m supposed to be good at this sort of thing. Ecologists, after all, study the interactions between plants, animals, and their environments. Why it’s taken me so long to figure out why annual sunflowers are so abundant in some places/years and not in others is beyond me.
What’s more impressive in a prairie than a bull bison? Standing over 6 feet tall at the shoulder, and weighing up to 2000 lbs or more, they can inspire awe, fear, and hope all at once. While truly massive, bison are also surprisingly nimble and fast – they can run at speeds up to 40 miles per hour.
These three bulls were grazing in a recently-burned portion of sandhills prairie when I came upon them while hiking last May. I kept my distance and tried to get a few photographs of them as they slowly sauntered away – not exactly running away, but not hanging around either. The bulls had been feeding in a recently burned portion of the prairie, and while they moved out of it to get away from me, I’m sure they returned to that lush new growth after I left them alone.
If you read this blog frequently, you know I manage many of our prairies with combinations of prescribed fire and grazing. I like the heterogeneous habitat structure I get from patch-burn grazing, and have documented benefits to plant diversity in our prairies. (I’ve summarized the experiences I’ve had with multiple variations of patch-burn grazing here.)
Patch-burn grazing with cattle is still viewed with skepticism by many people – especially some in eastern tallgrass prairies. I can understand why people would be concerned about the potential impacts of cattle grazing on some plant species and prairie communities, and I certainly don’t advocate cattle grazing for all prairies. However, I also think that many common concerns stem from limited experience with cattle grazing. If the only cattle grazing I’d ever seen was the kind that annually beat grasslands down to the ground and resulted in soil erosion and a gradual loss of native plant diversity I’d be skeptical too – to say the least!
However, chronic overgrazing is one extreme in a broad spectrum of grazing regimes, and cattle can also be used in ways that produce very positive results for plant diversity and wildlife habitat. The first time I saw a prairie being stomped and chomped by lots of cattle it was pretty unsettling. However, watching that prairie recover the next year after cattle had been removed gave me a much greater respect for prairies than I’d had before. Over the last 20 years, I’ve seen that process over and over in many tallgrass and mixed-grass prairies, and the resilience of prairie plants never ceases to amaze me. Of course, I’ve also seen instances where repeated overgrazing has degraded prairie communities, but that degradation has usually come from not giving plants sufficient opportunity to rest and recover from grazing bouts – not from grazing per se. (And often because of a history of broadcast herbicide use as well.)
Most of my personal experience with grazing (and patch-burn grazing in particular) has come from mixed-grass and lowland tallgrass prairies in east-central Nebraska. I’ve also seen a lot of grazing on western tallgrass prairies in Kansas and Oklahoma. However, my experience with cattle grazing in eastern tallgrass prairies is much more limited – mostly because it is such a rarity. This summer has given me two chances to observe the impacts of patch-burn grazing on eastern prairies in Indiana and Missouri. I wrote briefly about the Indiana experience in a previous post, but I want to spend more time on what I saw in Missouri last week.
The Missouri Department of Conservation (MDC) began a research project on the use of patch-burn grazing on public lands prairies back in 2005. One of their hopes was to increase the habitat quality of those grasslands for prairie chickens and many other grassland species without hurting the diversity or quality of the plant communities. Many of the prairies they grazed during the project were considered to be some of the higher-quality prairies in Missouri (botanically speaking) so protecting the diversity of those plant communities – and the rare and conservative plant species in them – was extremely important. Several people, including me, with prior experience using patch-burn grazing provided input to MDC as they designed the project. During the summer of 2007, I finally got the chance to see some of the grazed prairies during the third year of the research project. One of those prairies was Taberville Prairie, north of Eldorado Springs.
I remember being a little shocked as I walked around Taberville Prairie back in September 2007, because the cattle had grazed it much harder than I’d expected to see. The most recently burned patches of the prairie were nearly universally cropped close to the ground, with only a few plant species remaining lightly grazed or ungrazed. That was pretty different from my own sites, where our relatively light stocking rates lead cattle to graze pretty selectively in burned areas, leaving many forb species ungrazed – even many that are typically considered to be favorites of cattle. At Taberville, even unburned portions of the prairie showed evidence of moderate grazing, and it was difficult to find conservative plant species such as compass plant, purple coneflower, blazing star, and leadplant. What I was seeing at Taberville made me wonder whether MDC had pushed the prairie a little further than was prudent. Of course, the plan was to rest the prairie for several years following the three years of patch-burn grazing, so logic and experience told me this was something the prairie could easily recover from – but even so, I’ll admit it was a little disturbing to see.
Since my 2007 trip there has been considerable discussion (to put it mildly) among prairie enthusiasts and biologists in Missouri about the impacts of cattle grazing in those prairies where patch-burn grazing was tested, especially on conservative plant species. I can easily understand why people were concerned – especially after my own experience at Taberville. I was anxious to see for myself how the prairies had recovered, so I was glad to accept an invitation from MDC to participate in a grassland ecology workshop last week. The day before the workshop started, I got a tour from Len Gilmore and Matt Hill of MDC, and made my return to Taberville prairie.
We started the tour in a portion of Taberville than had not been included in the grazing back in 2005-2007, but that was currently in year three of a patch-burn grazing rotation. Len, who manages Taberville Prairie, showed me the kinds of habitat structure they’re trying to create with patch-burn grazing, including nesting habitat for prairie chickens. We also discussed other aspects of patch-burn grazing MDC is concerned about (and testing) – including potential impacts to headwater streams, most of which are currently fenced out. The overall look of the prairies under patch-burn grazing this year was similar to those I saw in 2007. This time, however, I looked harder for conservative plants, and was able to find them in the patches that weren’t the most recently burned. Most weren’t blooming, but they were certainly alive and well.
What I really wanted to see, however, were the portions of the prairie I’d seen in 2007 that had been rested (with one burn) since I’d last seen them. When we arrived, I think I let out an audible sigh of relief. The prairie looked great. Even in what was a very dry summer, the prairie looked like my visual image of Missouri tallgrass prairie. Lots of showy blazing star flowers and abundant conservative plants, including leadplant, compass plant, purple coneflower, rattlesnake master, and others. Len took me to several locations where they had built grazing exclosures during the original patch-burn grazing research project. The exclosures had allowed MDC researchers to compare the ungrazed plant community inside the exclosures to adjacent plots that were exposed to cattle grazing. Even without seeing the data, being able to walk through and compare those areas that had never been grazed with those that had been exposed to three years of patch-burn grazing (the exclosures had been removed but their locations were still marked) was a powerful testament to prairie resilience. I looked hard for differences, but the truth is, if Len hadn’t told me which areas had been the grazed areas and which had been the exclosures, I never would have known.
During the next several days at the grassland workshop, I listened to MDC biologists from wildlife and fisheries divisions talk about what they like and don’t like about their experiences so far with patch-burn grazing. One of the interesting issues they (and I) are wrestling with has to do with the appropriate length of grazing and rest periods. Figuring out how to mix grazing and rest periods in a way that allows all plant and animal species to “win” periodically is a major challenge. There was also considerable discussion about how to better evaluate potential impacts to plant communities and streams – as well as exploration of ideas about how to modify current management to better address needs of pollinators, amphibians, and other species. I think those who are worried about patch-burn grazing in Missouri would have been comforted to hear the thoughtful discussion and see the obvious dedication of MDC staff to the prairies in their charge.
There are still plenty of important questions about whether, where, and how cattle grazing should be used to manage eastern tallgrass prairies, but the Missouri Department of Conservation is leading the effort to answer some of those. Early results show improvements in habitat structure for many species of insects and animals, including greater prairie chickens – where they occur. MDC has asked faculty from two universities to help evaluate impacts on streams, and is fencing out the majority of headwater streams until that evaluation is complete. The responses of plant species and communities to various fire, grazing, and rest treatments is still being evaluated, and probably will be for some time. In the meantime, it was good to see confirmation of the ability of plants to bounce back from periodic grazing, even in prairies that are pretty different from the ones I know best. I think the knowledge that plants (even conservative species) don’t immediately die from being grazed for a season or two gives us a little cushion as we forge ahead with our attempts to find appropriate tools and strategies for maintain the broad array of biological diversity in what remains of tallgrass prairie. If you live and/or work in the tallgrass prairie region, I hope you’ll be a productive part of that effort. We need all the help we can get.
It’s a great time to hike the trails at The Nature Conservancy’s Platte River Prairies! Regal fritillaries are out in force, along with a number of other butterfly and insect species, and big wildflower season has begun, with many of the more showy species just starting to bloom. Find out more about the public trails and download directions and trail guides here. We’re only two hours west of Omaha, and just south of the Wood River I-80 exit (#300). If you’re passing through our area on the interstate and need a place to stop and stretch your legs, stop by!
This season has been an intriguing one so far, ecologically speaking. Each time I walk the prairies I’m learning something new and surprising. The abundance of rain and the high groundwater level has meant lush growth and wet wetlands. The cool weather has meant delayed blooming for many plant species, leading to an interesting mix of flowers right now (a combination of species normally done by now and others that are blooming on time).
We weren’t able to get all the prescribed burning done that we wanted to this spring, so have been using alternative strategies to get the kind of disturbance impact we want on those sites. On the prairies where we did burn successfully, the patch-burn grazing impacts look really really nice. Much of my time in the field so far has been trying to interpret what I’m seeing in terms of the response of plants and insects to those management strategies.
My most recent attempt at ecological interpretation deals with our patch-burn grazing and milkweeds. Over the last 10 years, I’ve spent a lot of time collecting formal and informal data on the impacts of grazing on prairie plants. Up till now I’ve spent a little time thinking about milkweeds, but since I’m trying to see my prairies through butterfly eyes this year (a good idea, by the way – looking at your site through the eyes of various species) milkweeds have become a higher priority. I’ve known that milkweed flowers can be a target for cattle grazing, but now I’m looking more directly at how many flowers are grazed or ungrazed within our patch-burn grazing systems.
This week, I looked at one of our prairies under patch-burn grazing, and counted milkweeds (grazed and ungrazed) within both burned and unburned portions. It was still an informal data collection attempt, but instructive. I looked at about 150 common and showy milkweed plants (Asclepias syriaca and A. speciosa), and found that 83% of the flowers had been nipped off in the burned portions of the prairie, and about 57% in the unburned. Those are pretty high percentages in a system that is set up to encourage grazing in burned areas but not unburned areas, and contrasts with the selective preferences of grasses over wildflowers that we typically see. It’ll be interesting to watch what happens during the rest of the season.
There are various layers of interpretation here. First, the fact that the cows are eating blooms in the first place is intriguing because while that’s common in many grazing systems, it’s not common in our lightly-stocked patch-burn grazing system. The attractiveness of those flowers ito cattle is apparently very high. Second, the grazing of flowers in the unburned portions of the prairie is REALLY interesting because there is almost no other grazing taking place there. In fact, I wondered if the flowers were being grazed by cattle or deer, and had to check the exclosure we have on the site to confirm that there are no flowers grazed off there (there aren’t). It still could be deer, but I doubt it.
On the positive side of things, there are still milkweed flowers available throughout the site, even in the burned/grazed portions. There could be more, but from a pollinators standpoint, there are still milkweeds there. (And the grazed milkweeds are still alive and growing – they just don’t have flowers) Also, the grazing is not having a severe immediate negative impact on the plants – in fact several that were grazed earlier in the season have re-bloomed now. If those plants are prevented from flowering successfully for many years in a row, it could hurt the population, but periodic grazing shouldn’t be a big deal to these perennial plants.
As I try to find management strategies that optimize biological diversity in prairies, one of the biggest objectives is to prevent any species, plant or animal, from being negatively impacted by our management year after year. I’ll continue to watch milkweed grazing as the season progresses, but it might be that these species are more vulnerable to grazing than most, and that they could be a good indicator that can help me tweak our management over time. The current plan under which this particular prairie is being managed calls for patch-burn grazing for two years, followed by one year of complete rest. Under that system, I’m not concerned about the long-term vigor of the milkweed plant populations because they’ll have at LEAST one year out of three to bloom and reproduce successfully (through both seed and rhizome). I’m also not worried about insects that use those milkweeds because in addition to those in the prairie, there are numerous milkweeds in exclosures, outside fencelines, and other locations in the very nearby neighborhood. Plenty of milkweed to go around.
So – this upshot is that it’s been valuable to look at the prairie from a perspective that forces me to consider species I hadn’t paid as much attention to in the past. I’m not seeing anything that makes me think we’re heading in the wrong direction, but milkweed flower grazing seems to be a good thing to add to the aspects of this and other prairies that are part of my annual evaluation efforts.
As an aside, the patch-burn grazing system we’re trying on the prairie mentioned above includes a fairly high stocking rate early in the season, followed by a lighter stocking rate in the summer/fall. In May, I saw fairly regular grazing of forbs such as compass plant, Canada milkvetch, Illinois bundleflower, and rosinweed. Now that the stocking rate is reduced, I see very little grazing on those plants, and rosinweed and compassplant are just getting ready to bloom. The milkvetch and bundleflower plants are growing strong, and should also bloom. Also, most of the milkweed plants that are being grazed are only getting the tops nipped off, so the vigor of the plant is not really being reduced much. It’s all very interesting to watch.
This is Part 2 of a two part series on ecological resilience in prairies. In Part 1, I interviewed Dr. Craig Allen about the basic definition of ecological resilience and then wrote about the relevance and application or resilience to prairie ecosystems. In Part 2, I explore how ecological resilience can influence the way we restore and manage prairies, and about how much we still have to learn about how to do that.
Influencing Resilience through Restoration and Management
Understanding ecological resilience should help us better design restoration and management strategies that build and maintain resilience in prairies. Using the components of resilience discussed in Part 1, it seems apparent that when restoring (reconstructing) prairies, it’s important to maximize species diversity in seed mixtures. More importantly, prairie restoration that adds to the size and connectivity of existing prairie remnants should make the entire complex of restored/remnant prairie more resilient (see earlier post on this subject). Finally, selecting and altering restoration sites, when possible, to include topographic and other habitat type variation – and multiple examples of each type – can also help ensure the resilience of the resulting restored prairie.
Designing management strategies for prairies that sustains ecological resilience is trickier because we still have much to learn. We’re far from fully understanding the various stable states prairies may exist in, or flip to, let alone where the thresholds are between those states. In addition, the level of plasticity, or range of adaptive capacity, of prairies is a subject of great debate right now among prairie ecologists – although the discussion is not usually framed in those terms. The real question is – How much can prairies change their plant and animal species composition and still remain “in the bowl”?
As an example, I manage a sand prairie that was hayed annually in the mid-summer for about 20 years before The Nature Conservancy purchased it in 2000. Over that 20 year period, the plant community in that prairie adjusted to that annual haying regime. Species such as stiff sunflower, leadplant, and sand cherry became restricted to a few steep slopes where hay equipment couldn’t go. Early summer grass and forb species became very abundant, but later season flowering plants were less so because they were mowed off around their flowering time each year. The prairie was a nice quality mixed-grass prairie, with good plant diversity, but definitely had the “look” of an annually-hayed prairie.
When we took over the management in 2000, we let the site rest for about 5 years and burned portions of it each year during that time. Then, we began introducing some combined fire and grazing treatments at different intensities and at varying times of the season. As a result, the prairie looks fairly different now. Stiff sunflower and leadplant have spread considerably through the site, re-taking lower slopes where hay equipment had earlier eliminated them. Cool-season grasses (native and non-native) change in abundance from year to year, but warm-season native grasses are certainly more dominant than they previously were. Overall forb diversity is about the same as it was, but the relative abundance of many forbs has changed, and those abundances now vary from year to year, rather than remaining fairly stable.
In the context of plasticity, or adaptive capacity, this prairie has demonstrated that the 20 years of haying was not enough to move the plant community into a new stable state from which recovery, if that’s the right word, was not possible. The community was altered by that haying regime, but upon alteration of that regime, the community composition morphed to match changing conditions – without losing plant diversity. In other words, assuming that the prairie hasn’t lost anything critical during the 11 years of our management, both the haying regime and our current management have kept the prairie “in the bowl”, though it changed appearance fairly dramatically. Its adaptive capacity is broad enough to include the “hayed” look and the “crazy Nature Conservancy management” look. The real test of this, of course, would be to reintroduce haying for another 20 years and see if the plant community reverted back to something very similar to the condition it was in when we purchased it.
Here’s another example from my own experience. We have a 45 acre restored prairie (prairie reconstruction) that was seeded in 1995 by Prairie Plains Resource Institute adjacent to a degraded remnant prairie. The seed mixture included approximately 150 species of mesic prairie plants, most of which established successfully. We managed the prairie with periodic spring fire for its first seven years, and then incorporated it into our experimental patch-burn grazing system (light stocking rate). During nine years of patch-burn grazing management, (6 of which were during a severe drought) the plant species composition in any one place has bounced around quite a bit due to the fire/intense grazing/rest cycles imposed by the patch-burn grazing management system. Overall, however, the prairie has maintained its mean floristic quality within 95% statistical confidence intervals (I collect annual data which entails calculating floristic quality within 100 1m2 plots and averaging the values across those plots). Read more about our patch-burn grazing work and results at this restored prairie and others here.
That’s not to say the prairie hasn’t changed – it has. Some plant species have increased in frequency among my annual data collection plots, some vary in frequency from year to year, and others stay fairly stable. However, no species has dramatically declined over the time period. (I wish I had data on other species, particularly insects, but I don’t.) Perhaps the most interesting, and somewhat concerning, phenomenon has been an increase in the frequency of Kentucky bluegrass in my plot data. The increase has been fairly steady over the nine years of patch-burn grazing and data collection, and bluegrass is now in about 75% of my 100 1m2 plots, though it rarely looks dominant where it occurs. To this point, that increasing frequency doesn’t seem to be impacting the overall diversity or floristic quality of the plant community, but that doesn’t mean it won’t at some point. Two possibilities are: 1) Our management is allowing bluegrass to enter the plant community but remain a minor component, or 2) Kentucky bluegrass is on a steady march of increasing dominance and will eventually turn my restored prairie into the same kind of low-diversity degraded prairie that exists in the adjacent remnant prairie. I won’t be completely shocked by either scenario, but I have hope that #2 won’t happen because of the way bluegrass is acting in the community to this point. It’s way too early to know for sure.
Interestingly, I have some large exclosures within this restored prairie that have never had grazing, only prescribed fire at a similar frequency to the grazed portion. Those exclosures have very little Kentucky bluegrass in them – probably because of both the differing management and the fact that the exclosures are on the far side of the restoration from the neighboring bluegrass-dominated remnant prairie. However, the exclosures also have much lower plant diversity and mean floristic quality than the grazed portion of the restored prairie. Visually, they are dominated by warm-season grasses and a few large forbs (e.g., perennial sunflowers). At this point, I prefer the grazed portion of the prairie because it seems to line up better with my management objectives of maintaining diverse and resilient plant communities (assuming it’s not slowly becoming a bluegrass wasteland).
To relate this example back to adaptive capacity, it appears likely that the grazed portion of the restored prairie has the adaptive capacity to retain its integrity as a prairie community through fairly wild fluctuations in species composition as a result of stresses from fire, grazing, and drought. This is, again, remembering that I’m only evaluating the plant community and that the experiment is far from over. On the other hand, it appears the exclosed portions of the prairie have lost plant diversity over time. Whether the communities in those exclosures are still “in the bowl” or in a new stable state of lower diversity is a big question. To address it, I’m going to open one of them to fire/grazing this coming year and exclude a portion of the currently-grazed prairie and see what happens. If the two plant communities trade identities to match their new management regimes, I’ll know that both were still “in the bowl” and understand more about the adaptive capacity of our prairies. If they don’t, that will be equally instructive!
Building and sustaining ecological resilience in prairies may be the most important component of prairie conservation in the coming decades. Threats from invasive species, habitat fragmentation and detrimental land management practices, compounded by climate change, will make conservation extremely difficult. Armoring prairies with ecological resilience gives us the best chance of success.
In order to build that resilience, we first have to understand it better. It is certainly more complex than the few simple examples I’ve provided. There are numerous belowground processes and systems we still know relatively little about. Even aboveground, there are many more questions than answers regarding the way species interact with each other and their environment – and what is required to maintain those interactions. To gain a better understanding of these natural systems, we have to rely on experimentation and observation. I think there are essentially two broad questions:
What is the adaptive capacity of prairies, and where are the thresholds between the desired state and other, less desired, stable states? This will certainly vary between tallgrass and mixed-grass prairies, and between sand prairies and black soil prairies, etc., but there will almost surely be some consistent themes.
How important is it to keep the ball moving within the bowl? In other words, are prairies really like our human bodies, in that the more we stress and rest them, the better prepared they are for future stresses? (Does the bowl shrink if we don’t keep pushing at the edges?) Or do we just have to keep prairies from being stressed too far in any particular direction?
We can work toward answering these questions with direct experimentation on prairies we manage (similar to my simple experiment with grazing and exclosures in the restored prairie example presented earlier). In addition, though, we can learn much from prairies that “flip” to less desirable stable states (hopefully not the ones we’re managing!) by documenting as much as we can about what happens to them and why.
Most importantly, I hope that thinking about ecological resilience with regard to prairies will make you look at the prairies you’re familiar with in a new way. Seeing prairies as balls rolling around in a bowl makes watching and managing prairies a much different experience than seeing them as a stable “climax community.” When we expect change, it’s easier for us to perceive change, and the more observant we are, the more we’ll learn. And goodness knows we have plenty to learn.
If you’re interested in learning more about ecological resilience, here are some relevant references that Craig Allen recommends (I’m pretty sure it’s just a coincidence that he’s a co-author on all of them). The Gunderson et al. book reprints a lot of the classic / foundational papers on the subject.
Sundstrom, S., C. R. Allen and C. Barichievy. Biodiversity, resilience, and tipping points in ecosystems. Conservation Biology: in review.
Gunderson, L., C. R. Allen, and C. S. Holling. 2010. Foundations of Ecological Resilience. Island Press, New York, NY. 466pp.
Allen, C. R., L. Gunderson, and A. R. Johnson. 2005. The use of discontinuities and functional groups to assess relative resilience in complex systems. Ecosystems 8:958-966.
Forys, E. A., and C. R. Allen. 2002. Functional group change within and across scales following invasions and extinctions in the Everglades ecosystem. Ecosystems 5:339-347.
Peterson, G., C. R. Allen, and C. S. Holling. 1998. Ecological resilience, biodiversity and scale. Ecosystems 1:6-18.