Category Archives: Prairie Restoration/Reconstruction

An Early Attempt to Evaluate Prairie Restoration Success by Looking at Insect Use.

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Back in February, I wrote a post that laid out some ideas about how to measure success when using prairie restoration (reconstruction) to stitch fragmented remnant prairies back together.  One of the main needs is to see whether species from the remnant are also using the restored prairie.  If I’m trying to make a small remnant prairie function as a larger prairie by adding restored prairie around it, the species in the remnant must be able to expand into and travel through the restored habitat.

I just got some data from a couple of volunteer amateur entomologists that apply to that kind of evaluation, so I thought I’d share what they found.  First, let me be clear that these are amateurs (“enthusiasts” may be a better term than “entomologists” – though they are much better at insect identification than I am!) and that these are not research data.  However, what they found was very interesting, and will make a good launching point for future work.

Four species of tiger beetles were among the insects found during the 2009 inventory work.

INTRODUCTION

In early 2009, I was approached by Chris Aubushon and Connie McCartney, who live in Grand Island, Nebraska – near our Platte River prairies.  Chris and Connie were initially just looking for new sites to hunt for insects, but as we talked, we developed a bigger idea.  They volunteered to come out once a month for during the 2009 growing season and collect as many insects as they could from 6 sites and to identify what they could.  The six sites were really three sites where I had a restored prairie next to a remnant prairie, and they collected insects from both the remnant and restored portions of those sites.

Chris Aubushon (left) and Connie McCartney (right) setting up plots for their insect inventory project in early spring 2009.

Again, this was not a research project, but Chris and Connie – and some helpers – did come out once a month for 5 months and collect a lot of insects.   They restricted their sampling to one 100 foot by 100 foot plot at each of the 6 sites, and used a combination of sweep netting and pitfall traps to catch the insects.

RESULTS

Chris and Connie were able to identify 136 species from those five months of collecting.  They also found (but didn’t identify to species) approximately 33 species of spiders.  When I got the list of species from Chris, I sent it to several friends of mine who are knowledgeable about insects to get their impressions.  The consensus among those entomologists was that the insects on the list were almost exclusively common species that are habitat generalists.  In other words, the list doesn’t include many rare species, or species tied to particularly “good” quality prairies.  Instead, Chris and Connie mostly caught insect species that can be found just about anywhere.   That doesn’t diminish their efforts, but it’s important to remember as you interpret the breakdown of results.

Of the 136 species caught, 28 were seen at only one site.  Interestingly, 8 of those 28 species were found only in remnant prairie, while 20 were found only in restored prairie.  (I don’t think it is necessarily important, but of the 20 species found only in restored habitat, half were beetles.)  Two species – a firefly and a burying beetle were found at two different sites that were not adjacent to each other.  In each case, they were found in one restored prairie plot and one remnant prairie plot.

The reference insect collection from Chris and Connie's work in 2009.

All of the remaining species (106 of them) were found in both halves of at least one remnant/restored prairie pair.  In other words, except for the two species mentioned above, every other species of insect found in more than one place was seen in both the restored and remnant portion of at least one prairie.  Remembering that these are all generalist species, I’m still surprised – and encouraged – by those results.  I had expected to see at least a few insect speces that were found in remnant prairies but that weren’t yet making the jump into the adjacent restored prairies.  In fact, I was kind of counting on seeing that so that I could design some follow-up data collection to figure out what the obstacles might be that were preventing them from using restored prairie.

CONCLUSIONS

So what have I learned?  First, the prairie restoration work we’ve been doing appears to provide adequate habitat for the most common and widespread insect species in our remnant prairies.  At least for those species, the restoration work we’re doing is successfully increasing the size and connectivity of fragmented remnant prairies.

Second, I’ve learned that I need to recruit a lot more entomologists to come collect insects from our prairies because every time I do, I learn something.  A little more than a decade ago, I worked with Kristine Nemec on her graduate school project to compare insects between remnant and restored prairies along the Platte River in Nebraska.  For her project, she inventoried insects in 3 restored and 3 remnant (degraded) prairies, but the restorations and remnants weren’t adjacent to each other.  Nevertheless, among grasshoppers, katydids, leafhoppers, planthoppers, and treehoppers, she found very few species that were found in remnant prairies but not restored prairies.  She also found very similar numbers of species between remnant and restored prairie for each of the insect groups she looked at.  You can see a brief summary of some of her thesis findings here. Nemec Results

Third, I’ve learned that the next steps in our efforts to evaluate insect use of our restored prairies will be harder.  We probably need to start by identifying species of insects in our remnant prairies that may not utilize nearby restored prairie – based on what we (meaning people besides me) know about their life history.  Then we need to do some targeted sampling to see whether they are or are not using those restored prairies.  It’d be even better if we could actually track individual insect movement to see if they cross the boundary between remnant and restored prairie.   (That should be easy, right?)  Broad sampling like we’ve done so far is useful, and a good first step, but now we need to hone in on a few target species and see what we can learn about them.  Species that rely on a particular plant species or that are tied to soil organic matter levels may be examples of those we need to study.

To sum up, there’s plenty of work to do.  To this point, we haven’t found any glaring problems with our restored prairies that are so severe that common insect species are restricted from using them.  That’s pretty nice to know, but it’s just the tip of the research iceberg.  Now we need to dive in and start working on the rest.

I’m extremely grateful to Chris Aubushon and Connie McCartney for all of their hard work collecting, sorting, and identifying insects for this project.  It was an amazing effort – and done for the simple love of exploration of the natural world.  Thank you.

I’m also grateful to James Trager, M.J. Hatfield, and Ted MacRae for helping me to interpret the results of the project.  Their comments and insight helped me tremendously as I worked to understand what conclusions I could and couldn’t pull from these data.

Using Defoliation of Dominant Grasses to Increase Prairie Plant Diversity

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 In many prairies, the primary suppressors of plant diversity are dominant grasses – both native and non-native.  These grasses, left unchecked, can monopolize light, moisture, and nutrients to the point that few other plant species can coexist with them.  I’m not sure why some prairies suffer from this more than others.  There is some evidence that hemi-parasitic and allelopathic plants such as pussy toes, false toadflax, and wood betony can play a role in suppressing grasses and facilitating forb diversity, but I don’t think that’s the whole answer because I’ve seen very diverse prairie plant communities without those species – or with only a few scattered populations of them.  Regardless of the reasons, we are left with many prairies that have lost – or are losing – plant diversity through domination by grasses, and we have to decide what to do with them.  Some of those prairies are restored (reconstructed) prairies that started out with high plant diversity but have since lost much of that diversity.  Others are remnant prairies that have been degraded by overgrazing and/or broadcast herbicide application.  Still others are relatively diverse remnant prairies that are slowly losing diversity as individual forbs die without reproducing.

Big bluestem. A good native grass, but sometimes so dominant that overall plant diversity suffers.

I think one of the best tools we have for combating grass domination in prairies is defoliation – the removal of above-ground portions of plants.  Defoliation has always been a major component of prairie ecosystems through fire and herbivory, and mowing and (non-lethal “burn back”) herbicide applications are additional options at our disposal today.  Plants respond to defoliation in various ways, depending upon the severity of defoliation, the frequency and/or duration of the defoliating event, the stage of the plant’s growth at the time of defoliation, and each species’ genetic programming.  The way each plant, and its neighbors, respond to a defoliation event determines which plants will gain or lose territory.  In other words, defoliation influences the competition between plants – and manipulating competition between plants is really what most prairie management is all about. 

Some of the earliest research I’m aware of on the effects of prairie plant defoliation can be found in range management research from the 1950’s and 1960’s.  The earliest paper that is often cited from that era is by F.J. Crider, who documented the effects of defoliation on the root growth of grasses.  He (and others since) found that a severe defoliation of a grass plant resulted in an immediate cessation of root growth as plants reallocated resources from root growth to regrow leaves and stems.  More importantly, those grass plants actually abandoned sections of living roots as well – shrinking the total root mass of the plant fairly dramatically.  This makes sense, since the plant has to support those roots through photosynthesis, and a severe defoliation takes away most of the plant’s ability to photosynthesize. 

A simplified look at how dominant grasses can affect plant diversity. In the top example (A) grasses have monopolized both aboveground (light) and belowground resources (moisture and nutrients). After defoliation (B), both the above and belowground parts of the grasses have shrunk, freeing up resources and allowing other plants to establish within that lost territory. As the grasses recover from the stress of defoliation, their vigor and size increase, but the new plants have a fighting chance - at least for a while - to hold the new ground they've taken.

Those early range science research data provide some useful context for today’s prairie management, but those researchers were primarily trying to figure out the intensity of grazing they could employ while still maintaining a dominant stand of grass.  As prairie managers, by contrast, we want to reduce the dominance of grass to increase the diversity of other plants.  We can still learn from what those range scientists discovered; we just want to employ it in a different way.  Since plants primarily compete for light, moisture, and nutrients, we want to find ways to make those three kinds of resources more available to plants other than dominant grasses.  Defoliation can reduce shading aboveground (removal of leaves and stems), while simultaneously freeing up the availability of moisture and nutrients belowground (reduction of root masses).

In prairies where dominant grass species are suppressing plant diversity, we want to defoliate those grasses in a way that forces them to cede territory to other species.  In order for that to work, the first important factor is that the defoliation has to happen during the growing season.  Defoliating a dormant plant (e.g. with an early spring burn) doesn’t have any impact on its root system, which is a critically-important part of its competitive ability.  In order to force a plant to reallocate resources away from its roots, defoliation needs to take place after the plant has already invested significant resources in above-ground growth.  This is why a late-spring burn can have a significant (if temporary) impact on cool-season exotic grasses such as smooth brome.  Burning, grazing, or mowing grasses when they are just starting to flower has the biggest impact on most species because they have invested the maximum amount in their above-ground growth by that point.  Alternatively, repetitive mowing or grazing of grasses can also have a strong – and perhaps longer lasting – impact on their root systems because every time the grasses start to regrow, they get nipped off again, forcing them to regroup and reallocate resources time after time.

The immediate result of that kind of severe and/or repeated defoliation of dominant grasses is a release of opportunistic plants that thrive under low levels of competition.  This includes many annual and biennial plants, but also perennial plants that are built to move quickly into open space.  The quick flush of these plants often turns people off of defoliation because of a widely-held misperception that those “weedy” plants are outcompeting “good” plants.  In truth, the weedy plants are only able to grow because the competition that normally holds them in check has been suppressed.  When the defoliation event is over, the dominant grasses and other perennial plants will slowly recover their vigor – at which point the weedy plants will retreat and wait for another opportunity.  Rather than indicating a problem, I use the presence of weedy plants to tell me that my defoliation treatment has succeeded in weakening dominant grasses and has opened up space for other plants to take advantage of. 

As common as the overly-dominant grass problem is in prairie conservation, there is a frustrating scarcity of research that addresses it.  However, a recently-published research project by Kat McCain and others at Kansas State University provides some very nice insight into what can happen when dominant grass species are suppressed in a restored (reconstructed) prairie.  Kat and her colleagues studied plots of seeded prairie that had become heavily dominated by big bluestem and switchgrass over time.  They found that removing half or all of the big bluestem tillers (stems) – by clipping and herbicide application – from a plot significantly increased plant diversity.  Interestingly, removing switchgrass tillers in the same way had much less impact.  Following the removal of big bluestem tillers, the researchers saw increases in the vegetative cover of some forb species, including roundheaded bushclover (Lespedeza capitata),  pitcher sage (Salvia azurea), and blue wild indigo (Baptisia australis) within those plots, as well as new establishment of forb species including whorled milkweed (Asclepias verticillata), green antelopehorn milkweed (Asclepias viridis), leadplant (Amorpha canescens), roundheaded bushclover, and heath aster (Symphyotrichum ericoides).  In other words, suppression of big bluestem competition led to increased vigor among existing forbs and also allowed new plants to establish in the territory previously held by the dominant grass.  The study bolsters the theory that grass competition is suppressing forb diversity in many prairies, but also provides information on how plant communities might respond if that grass competition is reduced.

Of course there is a difference between simple defoliation and the kind of clipping/herbicide combination used by McCain and her colleagues.  In addition, most defoliation treatments (especially prescribed fire and haying) in prairie management are non-selective, meaning that all plants are simultaneously defoliated – not just the ones we want to suppress.  Uniform defoliation likely decreases some of the benefits of suppressing grass vigor because the vigor of the plants we hope will respond is suppressed as well.  However, there will be still be plants that can take advantage of the newly available light and soil resources following a uniform defoliation treatment, and by altering the timing of defoliations from year to year, we can ensure that a variety of species get the opportunity to respond.

Haying is a good example of uniform defoliation. Every plant gets cut at the same height and at the same time.

 

Ideally, though, we would like the ability to defoliate only those species that are suppressing plant diversity.  One way to do that is by using a selective herbicide such as Poast, which affects only grasses (not forbs, sedges, or other plants).  Poast is labeled for control of annual grasses, but at light rates can also provide short-term burn-back (defoliation) of perennial grasses as well, and some prairie managers have seen plant diversity increase following treatments.  Because it can kill annual grasses, and calibrating the appropriate application rate with the desired result can be tricky, it’s probably best to use this treatment on restored prairie rather than on remnant prairies for now – and to test it on small patches first. 

Another way to get selective defoliation is by the use of grazing.  In an earlier post, I described our use of patch-burn grazing in our Platte River Prairies as a way to increase and maintain plant diversity.  Patch-burn grazing is essentially a technique that uses patches of burned prairie within a larger prairie to attract grazing animals, concentrating grazing activity in those burned areas while allowing other areas to recover.  Under a light stocking rate, we find that cattle – even in the burned patches – are very selective about the plants they choose to eat.  Their top choice of grasses in the spring is smooth brome, and their summer favorite is big bluestem.  These happen to be two of the top three grasses that appear to stifle plant diversity in our prairies (the third is Kentucky bluegrass, which cattle like less well).  In our application of patch-burn grazing, a burned patch of prairie is normally grazed intensively for an entire season before the next patch is burned and cattle shift their attention to that.  That length of intense defoliation has significant impacts on the plants that are grazed – and again, under light stocking rates, the primary plants that are defoliated are smooth brome and big bluestem.  Interestingly, switchgrass is much less attractive to cattle and is often left ungrazed – or lightly grazed – in our prairies.  I found it intriguing (and encouraging!) that McCain and her colleagues found that switchgrass appeared to have much less impact on plant diversity than big bluestem did.

The effects of selective grazing in a restored prairie. This photo shows the burned patch with a patch-burn grazing system where a light stocking rate allows cattle to be selective about their eating preferences. Big bluestem is cropped very short, while other grasses and forbs are ungrazed or lightly grazed. Species such as hoary vervain aren't typically grazed even under high stocking rates, but many species such as purple prairie clover (front left), illinois bundleflower (middle left) and stiff sunflower (blooming) are commonly considered to be favorites of cattle - but only at higher stocking rates.

It would stand to reason that selective grazing of big bluestem and smooth brome would favor the expansion of the ungrazed plant species growing with those grasses.  While I’ve not had the time or resources to conduct much full-scale research (help wanted!), I do have data that supports that idea.  Through annual data collection of plant species frequency, I’ve found that the density of species (the number of plant species per 1m2 plot) increases by 20 to 30 percent in the year following the burn/graze treatment in a patch of prairie – in both restored and remnant prairies. 

Data from two prairies under patch-burn grazing. In both cases, the graphs show the number of plant species per square meter over time from the year of fire and intense grazing through the two subsequent years. The East Dahms site is a degraded remnant prairie and the Dahms 95 site is a restored prairie that was seeded in 1995 with over 150 plant species. The error bars represent 95% confidence intervals.

Of course, the increase I see in species density following grazing includes many plants such as ragweed and other opportunistic species, but I also see species like purple prairie clover (Dalea purpurea), Illinois bundleflower (Desmanthus illinoiensis), and stiff sunflower (Helianthus laetiflorus) respond as well.   In addition to seeing this in my plot data, I can walk out into the prairies and see seedlings of these species around the adult ungrazed plants.  Not all of those young plants survive their first year or two, but some permanent plot data I’ve looked at shows that at least some of them do.  By the way, I see similar post-grazing increases in plant species density and establishment of species like prairie clover under patch-burn grazing with higher stocking rates (less selective grazing) as well. 

As I said in my previous post on grazing, I’m not advocating that all prairies need to be grazed.  I’m not even advocating grazing as the solution to all prairies that suffer from overly-dominant grasses.  However, as we search for answers to address grass suppression of plant diversity, grazing certainly appears to be one viable alternative that is worth more investigation.  I’m continuing to experiment with variations in the way we employ fire and grazing treatments, and will keep learning as I go.  I’m also combining seed additions with those grazing treatments to see if I can take advantage of the open space created by defoliation to help establish new plants from seed – something that appears to happen rarely without some kind of suppression of surrounding vegetation.  I’m seeing some positive results, but it’s too early to know how well it will work long-term, and I’m still tweaking seeding rates and other factors.

Whether it’s grazing, prescribed fire, haying, or herbicide application, defoliation may be the most powerful tool available to help us suppress dominant grasses and increase plant diversity in prairies – where that is an issue.  The biggest obstacle to its application is probably the fear of causing damage to prairie by burning, cutting, or grazing plants during the growing season, but I think that fear ignores the resilience of prairie communities.  We still have a lot to learn about the most effective ways to apply defoliation to achieve our objectives, but the only way we’ll learn is by experimentation.  I hope you’ll join me in testing these methods and tracking the results.  If you do, please share what you learn with the rest of us so we can all work to figure this out.