A Measure of Ecological Resilience in a Restored (Reconstructed) Prairie

Back in May of this year, I wrote about ecological resilience in prairies.  In Part 2 of that double post, I gave an example of a 1995 prairie seeding and talked about how it appears to be maintaining its plant community integrity – through wet and dry years, fire, and grazing.  Since that time, I’ve collected and analyzed more data from that same prairie seeding, and wanted to flesh out that earlier story.

With regard to prairie restoration, my objective is to use high-diversity seedings to expand and reconnect fragmented prairies and thus increase the viability of prairie species and communities.  Because of that, I don’t measure success by whether a prairie seeding looks like any particular remnant prairie.  Instead, I’m trying to establish as many native plant species as I can, let them sort themselves into communities that are adapted to today’s conditions, and use management techniques such as fire and grazing to maintain that plant diversity.  I’m assuming that by providing that plant diversity, I’m also providing the habitat needed by the animals in adjacent remnant prairies, and that those animals will move into – and through – prairie seedings, thus increasing animal population size and viability.  I’m beginning to test those assumptions, and will be ramping up that effort during the next several years.

In the meantime, I’ve been tracking the plant communities within our prairie seedings to look at how many plant species establish and maintain themselves.  More importantly, I’m tracking the long-term trajectory of those plant communities using plotwise floristic quality analysis (you can read more about that technique here).  If the prairie seedings are ecologically resilient, one measure of that resilience should be that populations of individual plant species, and overall species diversity, are stable over time – even through stress.   The 1995 seeding, for which I’m presenting data here, is located in our Platte River Prairies, south of Wood River, Nebraska, and it has certainly undergone stress.  Since it was hand-planted in 1995 by the Prairie Plains Resource Institute with approximately 120-150 plant species, it has seen both very wet years and a long severe drought (7 years), and has been managed with patch-burn grazing since 2002.  Over the years, I’ve accumulated a total plant species list of 164 species for the 45 acre seeding, which I’m very pleased with.  However, the real question is whether or not the seeding will be able to maintain its ecological integrity over time.  Below is a series of photos and graphs that tell that story – at least the story up to this point.

This is what the 1995 seeding looked like in its 5th growing season. Species such as prairie clovers, perennial sunflowers, and other "matrix prairie plants" were abundant. Management to this point in time consisted of a couple of prescribed fires.

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During the drought years between 1999 and 2006, there were times that the combination of intensive grazing and drought really stressed the plant community. This July photo shows warm-season grasses that have gone dormant, but also shows plant species such as rosinweed and prairie clover that were still green and growing - and largely ungrazed.

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Within our patch-burn grazing system, a new portion of the prairie is burned each year, and intensive grazing tracks those burned areas across the site. Once a new patch is burned, the previous burn patch begins to recover from intensive grazing. This photo shows a burned patch the year after it was burned. The combination of drought and grazing made it look like a young prairie seeding again because of the abundance of short-lived weedy plants that were able to take advantage of the weakened grasses.

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A burned patch in June, showing grazing impacts focused mainly on grasses, leaving many forbs ungrazed.

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Under a light to moderate stocking rate, cattle display their selectivity (choosing to graze grass over forbs) - resulting in a very patchy prairie with short grasses and tall wildflowers.

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In unburned patches, very little grazing occurs - providing rest for the plant community. This photo was actually taken this week, in a portion of the prairie seeding we fenced out this year to provide complete rest from grazing. We're beginning to include some periods of complete cattle exclusion into our patch-burn systems to ensure that no plant species is grazed every year. This growing season was very wet, so the rested prairie grew very tall - even though it had been grazed fairly hard in 2010.

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This graph shows the mean floristic quality of the prairie seeding between 2002 and 2011. These data are collected from approximately 100 1m plots each year. Floristic quality is calculated within each 1m plot and averaged across the site. Error bars indicate 95% confidence intervals. Mean floristic quality has remained stable during the entire sampling period.

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While the mean floristic quality of the prairie has remained stable, the frequency of some individual plant species (% of plots the species occurs in) has varied from year to year. This graph shows frequency (from top to bottom of the legend) of marestail, foxtails, annual brome, black medick, and curly dock - all opportunistic (weedy) species that would be expected to act in just this way.

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More variability in the frequency of plant species between years. This graph shows (from top to bottom) stiff goldenrod, Canada goldenrod, heath aster, western ragweed, daisy fleabane, and hoary vervain. Interestingly, the species don't seem to track with each other - indicating that each is driven by its own unique set of factors.

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In contrast to the two earlier graphs, these data show that perennial native grass species have relatively consistent frequencies between years - even though they were subjected to periodic years of severe drought/fire/grazing. From top to bottom, this graph shows data for big bluestem, Canada wildrye, indiangrass, little bluestem, prairie cordgrass, and switchgrass.

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Similar to the perennial native grasses, many long-lived prairie wildflowers are also maintaining stable frequencies between years. Species that were common in 2002 are still common now, and species that were uncommon remain the same. Though I'm only showing a subset of species in these graphs, I've not seen any plant species disappear from this prairie.

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Like others who restore prairies, I’m still experimenting with techniques for both establishing and maintaining diverse prairie plant communities.  However, data like these help me feel more comfortable that I’m being relatively successful to this point – and I see similar patterns in other seedings we’ve done.  I’m also more and more impressed with the toughness of prairies and prairie plants.  I tried to include photos that showed the kinds of variable stresses this prairie has endured during its 17 growing seasons.  Watching this and other prairies survive what they’ve survived helps keep me from worrying so much about whether the coming year will be dry or wet, or whether we’ve got the right number of cattle in the prairie each year. 

As I said earlier, there is still much to learn about how animals (vertebrates and invertebrates) are using our seedings, but that is a separate avenue of exploration.  Building resilient plant communities around and between those remnants is the first step to better prairie viability. 

So far, so good.

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About Chris Helzer

Chris Helzer is an ecologist and Eastern Nebraska Program Director for The Nature Conservancy. He supervises the management and restoration of approximately 4,000 acres of land in central and eastern Nebraska - primarily along the central Platte River. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press.
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15 Responses to A Measure of Ecological Resilience in a Restored (Reconstructed) Prairie

  1. Extremely interesting data. Your broad overview just might be useful for me. I manage a 6 year old recreated prairie of just 3 acres. I can tell mine was established with low diversity and excessive contribution of grasses. I didn’t burn a small portion in spring so that I can do it this fall. — I’ve heard that might give more benefit to forbs. That will also let me distribute increased variety of forb seeds this winter in that 1/4 acre area to check the outcome in the next few years. A neighbor has a few cows and it’s crossed my mind to see if I can “borrow” one of his cows for a few days to further further varify this little site’s occurrences and outcome.

  2. When one considers that a number of gorgeous and diverse Chicago-area prairie remnants in country cemeteries were mowed to lawn height for years before Bob Betz came to the rescue, that many in Wisconsin were grazed to brushy lawns scattered with coarse “weeds”, that some of the most botanically diverse public prairies in Missouri were hayed annually for decades before acquisition as public land, your finding seems the expected one.

  3. Bob Den Hartog says:

    Unlike a number of species covered in the “long lived” perennial species table, I notice there is an upward trend for the sunflower species. The perennial sunflowers are often referred to as “aggressive” species. I’ve ran across differing opinions on whether they can be a concern. At 30%+ occurrence and increasing, are you concerned? Any idea if the perennial sunflowers regress over a period of time in a reconstruction? Also, I believe there was a previous post on parasitic species (e.g. prairie dodder) that could potentially be used to hold aggressive species in check. Are there any parasitic species present on your reconstruction? And if so, is species diversity effected in the areas of the parasitic species in your observation?

    Another blog I follow (http://pvcblog.blogspot.com/) has referenced the potential of wood betony to reduce the dominance of grass species to open spaces for less dominant species and potentially greater species diversity. Is wood betony appropriate for Nebraska prairie reconstructions?

    • Chris Helzer says:

      Bob – good question. I’m not worried about the sunflowers – for a couple reasons. First, I think the trends are probably more of a reflection of sampling error than reality. If you look at the difference between the first and last years of the data, Max SF only changes from 39% to 52% and stiff sunflower only from about 22 to 32%. If you didn’t count this year’s data, Max sf would actually have decreased since 2002. I think with only 100 plots per year a difference of that much is not statistically significant (though I haven’t tested that by running the numbers). Second, I’ve not seen any evidence – or heard from others – that stiff sunflower is overly aggressive. I’ve seen it form some big almost monoculture clones in young restorations – especially in drought periods – but those always fill in later with many other plants. Maximillian sunflower does have a reputation for being aggressive in some circumstances, but I think that’s often a case of improved varieties being used in seedings. And, at least in my experience, much depends upon initial seeding rate. If you put a lot of Max sf in the seed mix, you get a lot out – and those plants can hold their ground for a long time. I don’t know for sure, but based on what I’ve seen in my own sites, that dominance decreases through time as other species gain ground – and management influences that pretty strongly. In the particular restoration these data came from, you’d certainly not look at it and think “sunflowers!”. In fact, this year it’s awfully grassy looking. The visually-dominant forb species tend to be prairie clovers and Illinois bundleflower. Sunflowers tend to be pretty subdued.

      We don’t have many parasitic plants in the Platte Valley other than dodder. We do, however, have pussytoes – a good allelopathic plant that affects vegetation around it. I wrote a post about that a while back. In my case, I rely on management to keep any particular species from becoming overly dominant by targeting them with fire, grazing, or other techniques. I’d love to have wood betony – I think it’s a neat species – but it just doesn’t occur here. But I’d like to have it more because I think its neat than because I feel like I need its parasitic abilities.

  4. David says:

    Hi Chris,

    Encouraging results. You mentioned that you will be ramping up your efforts over the next several years. Care to share what you have in mind? More plant species introductions, animal/insect surveys, bird nest monitoring, microhabitat creation, new management techniques, etc?

    Thanks, David

    • Chris Helzer says:

      David – more to come on this subject!! Essentially, I want to start better inventories of insects (and other animals) in my remnant prairies and then see how many of those are using the adjacent restored prairies. I’m planning a sort-of bio blitz next July to get that process started. As I work out more details, I’ll pass them along through the blog.

  5. Doug McEvers says:

    Chris, Fabulous information on prairie reconstruction, this is how we all learn, thank you for sharing it. The active pasture/reconstruction is of particualr interest because there is so much rangeland that has potential. Getting more from existing acres is the goal of every producer and species diversity will help greatly with soil fertility, reduced compaction and runoff.

  6. James McGee says:

    Chris,

    I would like to know if you or others are having success with the following species:

    Carex meadii (use neglected in restorations)
    Ceanothus americana (takes a long time to establish)
    Gentiana puberulenta ” ”
    Hypoxis hirsuta ” ”
    Lilium michaganensis (I’ve only observed success from transplanting. Lack of observed success likely due to long development period.)
    Lilium philadelphicum (no information on successful establishment)
    Lithospermum canescens (Sparse success observed. Long development likely limiting factor)
    Lithospermum incisum (Success observed seeding to bare gravel areas in local of parent population)
    Oxalis violacea (Not enough time to report results)
    Viola pedata (Success observed after planting, even with competition with tallgrasses)
    Viola pedatafida (No success observed after planting, attempting trial in area without tallgrass competition)

    These species are native to Nebraska. However, I do not know if they extend to your area. Therefore, some species may not apply to your efforts.

    Sincerely,

    James

    • Doug McEvers says:

      James,

      I have had Prairie lily show up in my restoration (I did not sow it), the seed from prairie lily has been found in prairie harvest seed mixtures in MN. Prairie lily is common in NW MN and our prairie remnants still have a good population, I suspect wind or animal dispersal is the reason the lily is spreading into our restored acres.

      • James McGee says:

        In my area, Lilium philadelphicum seems rather uncommon. I have never actually observed it. When I lived in New Hampshire I saw periodically brushed utility corridors full of this species. I think it does not like the limey soil in my area. However, I have seen a number of pictures
        people have taken of this species in preserve just outside of my typical range.

        I am currently growing Lilium philadelphicum. I planted some first year seedlings in a bed, but the tiny bulbs seemed to have gotten lost. Some frost heaved since I planted late in the year. Others were dug up by animals. They survived the winter completely out of the soil. However, I have since been unable to relocate them in the weeds. I have not seen any in a year. Some went dormant before I planted the plugs. The dormant individuals did did not get put in the ground. The ones that got left in the plug tray have continued to return each year. They apparently were able to thrive on on complete neglect. I’ve decided to leave these last one’s in the plug trays until they get bigger. Maybe then they will not get “lost in the weeds” after planting. I hope to track them and see how they progress.

        James

    • Chris Helzer says:

      James M – I can comment on only a few of those. The rest we just don’t have in the Platte Valley. We’ve had good luck with the Oxalis when we can get seed. I don’t have either of the violets you mentioned, just V. pratincola, but that comes in well from seed – it’s just that seed is hard to get in quantity, of course, and I’ve found that it needs to be dark colored upon harvesting or germ is very low (white seeds don’t seem to work). Hypoxis has only shown up a couple times from seed, even though we’ve worked diligently to collect it. No luck in the greenhouse either – we’ve tried seeding right after harvesting it and later, with our larger mix. No luck. We’ve started transplanting both that and the violet from abundant populations into restored prairies.

      We have very good luck with L. incisim, especially after we figured out that we have to pick the seeds earlier than we were. We were waiting until July because there were still seeds on the plants at that time, but it turns out most that hang on that long are empty. Good seed seems to turn into good plants for us. Don’t have L. canescens, but L. carolinense is very slow to show up. Have only seen a few come, and they were about 8 years post seeding.

      Two others you might talk to. Stephanie Frischie at TNC’s Kankakee Sands restoration in IN (email is first initial last name @tnc.org) and Bill Whitney at Prairie Plains Resource Institute (ppriAThamilton.net). They both have long experience with species I don’t deal with much.

  7. James McGee says:

    Chris, I’m surprised you do not have V. pedatifida or pedata. I thought these were the prefered food source for the Regal Fritillary. I grew Hypoxis hirsuta from seed this year. I alway tell people to forget the expensive grow lights and green houses. I just sow all my prairie plants into a tray of seed starting medium right after snow melt. I leave the trays outside exposed to the freeze thaw cycles. My germination rate was less than 4% for Hypoxis hirsuta. However, I did better than the Chicago Botanical Garden. A friend sent seed of Hypoxis hirsuta he laboriously collected to the Chicago Botanical Garden. Like you, they did not get any germination in their green houses. I am planning to leave the Hypoxis seedlings in the plug trays. I want to grow a bunch of them to make a seed source. They always disappear in the grass after blooming. I think it will be easier for me to collect seed from plants growing on my deck than to go to all the effort required to collect seed from the wild.

    A local restoration has a nice population of Hypoxis hirsuta from seed. Their success is likely because they have been restoring the site for over 20 years. My seedlings are really small. I expect they will take quite a few year to reach blooming size. I’m sure they would take even longer in the wild where lack of water further limits growth.

    I have been using seed nets made out of Chiffon fabric for years to collect seed. This allows me to only collect ripe seed. I also do not need to make more than two trips to a site for any given species. I cut the Chiffon into variously sized circles. I use different circles for different species. I melt the edges of the Chiffon fabric with a candle so they do not fray. I then weave embroidery thread along the outside of the circle. I tie a knot in the ends of the embroidery thread so it won’t pull through. I then pull the embroidery thread so the circle of Chiffon makes a little pouch. I have found there is a trick to cinching the seed nets on the seed head. Anything more than a half knot is difficult to untie. However, a half knot is not strong enough to keep the critters from stealing the seed nets. I solved this problem by making another half knot on the opposite side of the stem. The result is the stem of the seed head is in the middle of a square knot. This keeps the seed nets on the seed heads. It is also easier to untie two half knots than to untie any more secure knot.

    If people are interested, I can send them an example to use as a template.

    James
    james_andrew_mcgee@yahoo.com

  8. James McGee says:

    p.s. I use the seed nets on things like Viola pedata, Viola pedatifida, Phlox pilosa, Oxalis violacea, and Lithospermum canescens. Generally, only things that quickly disperse seeds after they have ripened. I collected seed from Hypoxis hirsuta differently. I tie small ribbons cut from surveyors tape around the base of the plant. I find the ribbon is necessary if I am going to relocate any quantity of the plants after they have flowered. Since the seed does not eject quickly, I return and collect it at the appropriate time.

  9. Pingback: Photo of the Week – June 7, 2013 | The Prairie Ecologist

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