When is a Prairie Restoration (Reconstruction) Project Successful?

This is a follow-up to last week’s post on using prairie restoration to enlarge and reconnect remnant prairies.  In this week’s post, I present a case study of a remnant sand prairie and an adjacent prairie restoration, and give thoughts about how to measure the effectiveness of that restoration project.  We’re (all of us) just getting started figuring out how to measure this kind of thing, so I’m hoping my thoughts will stimulate others to come up with their own ideas to improve upon – or contradict – mine.

Last week, I wrote about how we can improve our chances of conservation success in small isolated prairies by using prairie restoration (reconstruction) to enlarge and reconnect prairie fragments.  I even made a goofy analogy about catching falling popcorn.  At the end, I mentioned that when measuring the success of a prairie restoration – as a tool for enlarging or reconnecting remnants – we need to take a different approach than simply comparing the remnant and restored prairies to see how similar they are.  If the point of the restored prairie is to reduce the level of threat to species and natural communities inside the remnant prairie, that’s what we need to measure.

To explain what I mean, let me use a restored/remnant prairie complex along Nebraska’s Platte River as an example.  In 2000, The Nature Conservancy added several hundred acres to our Platte River Prairies through a land acquisition.  Most of the new land was cropland, but it also included 60 acres of remnant mixed-grass sand prairie with good plant diversity.  Two years later, using seed harvested from the remnant prairie and other nearby sites, we seeded 110 acres of cropland directly adjacent to the sand prairie.  The restored cropland has the same kind of hilly topography as the remnant, but also includes some low areas more appropriate for mesic tallgrass prairie.  Thus, the 162 species in our seed mixture included plant species from both mixed-grass sand prairie and mesic tallgrass prairie.

Remnant sand prairie at The Nature Conservancy's Platte River Prairies.

In June of 2010 I collected plant data from both the remnant and restored prairie (in its ninth growing season).  The data were collected by counting the plant species inside a 1m2 plot frame from 100 locations across each prairie.  Those data allowed me see the frequency of occurrence of each species (the % of plots in which each species was found).  To make the results easier for you to visualize, I’ve used a color-coding system to create what I call a plant composition signature for each prairie.  The complete comparison of the two prairies, with additional interpretation, can be seen here if you’re interested, but for this example, I’m just going to show some representative excerpts.

After the latin and common name for each species, you’ll see a column labeled “C”, which is the C-value (or coefficient of conservatism – defined by Swink and Wilhelm 1994).  If you’re not familiar with this categorization of species, a quick explanation is that lower C-value species are more opportunistic plants that can generally thrive in very disturbed environments and higher C-value species are more tied to intact native communities.  Another way to look at it is that higher C-value species are more vulnerable to habitat degradation.  All species are ranked on a scale from zero to ten (the values I’m using are specifically for Nebraska) and all exotic species get an automatic zero.

In general, the restored prairie has the same grass species as the remnant, although many are less abundant. Most of those less abundant species will spread over time as the restored prairie continues to mature. A few sedges, including sun sedge, do not establish well from seed, and we're attempting to bring them in as transplants and let them spread from there.

The main difference in "weedy" forbs between the remnant and restoration is the abundance of goldenrods in the restoration. Canada and late goldenrod were both from the seedbank, but stiff goldenrod was planted by us. At this point, I'm not concerned about the goldenrods (they don't appear to be as aggressive here as in some places) because they haven't been decreasing species diversity over time.

As with other species, I expect many of the more conservative forbs species will increase over time in the restoration.

Based on experience, I'm sure Kentucky bluegrass and smooth brome will increase over time in the restoration, but so far we've been able to manage those species to keep them from overwhelming the plant diversity in other older restorations. Apart from those two species there are no serious invaders that in the restoration that might threaten the remnant, which is good to see.

It’s easy to find differences between the remnant and restored plant communities in this example – some plant species are much more abundant in one than the other.  On the other hand, very few plant species from the remnant are missing completely from the restored prairie, and those that are less abundant are likely to increase over time.  As a prairie ecologist, I can see some obvious visual differences between the restored and remnant prairies, but most visitors to our site see the two as one large prairie.  But… Does any of this matter?  How do I decide?

First, remember that the objective of this restoration project was NOT to replicate the remnant sand prairie, but to increase the viability of the species and communities living in it.  Given that, the real questions I need to answer include the following:  Does the restored prairie increase the population size of species formerly constrained by the small remnant prairie?  Does the combination of the restored and remnant prairies provide suitable habitat for species that don’t occur in prairies the size of the remnant alone?  Does the restored prairie add to the overall resilience or ecological function of the remnant prairie?  Any questions about similarities or differences in the abundance of individual plant species need to be framed within the context of these kinds of broader questions – and tied to the specific objectives for the restoration project.  Comparisons outside of that context are relatively meaningless.

To begin evaluating the impact of the restored prairie, one first step could be to look at a few at-risk species in the remnant prairie to see if the restoration appears to benefit them.  If the remnant prairie has been harboring a small population of Franklin’s ground squirrels, for example, it’d be good to find squirrels (and their burrows) in the restored prairie as well.  If there was a rare penstemon species in the remnant (bumblebee pollinated) it’d be interesting to follow bumblebees from the plants in the remnant to see if they also visit penstemon plants in the restored prairie  – indicating that the restored prairie has facilitated growth of a genetically-interactive penstemon population.

Besides at-risk species, it would be worthwhile to search the restored prairie for the presence and/or abundance of species from other categories as well.  These categories might include:

-          Species that are representative of various types of relationships (e.g. predators and their prey, parasites/parasitoids and their hosts, insects and their larval host plants, etc.).

-          Species that have a cascading effect on other species and ecological processes (e.g. allelopathic or parasitic plants, burrowing insects/animals, etc.).

-          Species that are particularly important as food sources for a range of other species (e.g. springtails – aka Collembola, grasshoppers, “soft-bodied insects” like caterpillars and other similar larvae, etc.).

-          Area-sensitive species that may not have been able to survive in the small remnant alone but that might have a chance in the combined restored/remnant prairie (e.g. prairie chickens, badgers, and other vertebrates).

It’s also important to evaluate impacts of the restoration project on groups of species that influence ecological processes – such as pollinators and seed dispersers.  Pollinators are relatively easy to observe, and both the pollinators themselves and the resources they depend upon can be evaluated.  Ideally, of course, it’d be great to have several years of data on the species richness and abundance of pollinating insects in a small remnant prior to initiating a restoration project, followed by similar data collection after the restoration has established.    However, simply looking at whether or not purple prairie clover plants (for example) in the restored prairie are getting pollinated by the same species and numbers of pollinators as the prairie clover plants in the remnant could be very informative.  From the resource perspective, if the remnant prairie tends to lack an abundance of flowering plants at a particular time of year (late spring, for example, or early fall), measuring whether or not the restored prairie provides appropriate blooming plant species to fill that gap is very important.

Purple prairie clover being pollinated by a native bee.

There are numerous other things that could be measured, including taxonomic groups we really don’t know much about at this point.  For example, soil fauna, fungi, and obscure groups of invertebrates may very well have strong roles to play in ecological functioning of prairies, but we don’t know much about what those roles might be or how to evaluate them.  While it’s certainly important to learn more about those other taxonomic groups, our lack of knowledge shouldn’t stop us from measuring what we do know in the meantime.

The last thing to consider is whether or not a restored prairie could be actually be negatively impacting the adjacent remnant prairie or its species.  One example of this could be an invasive species that becomes established in the restored prairie – thus threatening the remnant.  A second possibility is that the restoration could function as an “ecological sink” for some species from the remnant, in which a species is drawn out of suitable habitat into attractive-looking but perilous habitat instead.  We’ve actually been testing for one possible example of this in our Platte River Prairies.  Regal fritillary larvae feed only on violets, but adults don’t lay their eggs directly on violet plants.  Our lowland remnant prairies have lots of violets, but our restored prairies have very few (so far) because we are unable to harvest large numbers of seeds.  We’re trying to make sure fritillaries aren’t laying eggs in the restorations where the larvae would be doomed to starve because of the near absence of violets.  (So far it looks like it’s not a big problem.)

As I mentioned at the beginning, we’re just starting think about how to measure the effectiveness of restored prairies as conservation tools.  Since the initial practical work of a prairie restoration project involves the establishment of a new plant community, it’s natural to assess the success of the various species we included in the seed mixture.  Unfortunately, it’s also easy to overemphasize the importance of floristic differences between a restored prairie plant community and nearby remnant prairies.  For many reasons, it’s not practical to recreate a historic prairie or replicate an existing remnant prairie.  However, it is possible to use prairie restoration to increase the viability of our remaining remnant prairies.  It is imperative to set clear objectives for this kind of restoration work, including the specific ways we want the restored prairie to help abate threats to species and communities.  Clear objectives will lead to easier decisions about how to measure success.

Many of the suggestions here are just first steps, and they and subsequent steps will require considerable resources, as well as collaboration with academic researchers.  Yes, there’s a lot to measure, but as we start to establish consistent patterns of success with some kinds of species or ecological processes, we can start focusing attention more narrowly on others.  We don’t have to test everything at once, and the most important measures at each site are those that evaluate whether or not specific objectives for that restoration project are being met.  However, it will be critical that we all share what we learn – successes and failures alike – to build up our cumulative knowledge as quickly as possible.

There are a number of examples of restoration projects where remnants have been enlarged or reconnected by restoring adjacent lands.  We should look closely at those existing sites to see if we can find evidence of success or failure (based on some of the suggested strategies above – and others).  That knowledge can guide us as we plan and implement new projects in the coming years.  It’s unlikely that we’ll be able to design restoration projects to benefit every prairie species and function, but we can certainly do a lot of good.  There’s a lot of work to be done, but I’m very optimistic about our ability to make a real difference.

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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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14 Responses to When is a Prairie Restoration (Reconstruction) Project Successful?

  1. Ernest Ochsner says:

    Chris, These two reports make me wonder about that prairie in a can I used for our back yard!

    Ernie

  2. Brandon Jones says:

    Chris,

    I couldn’t agree more with this post. Having worked in both SD and ND prairies and seeing the differences/challenges that restoration praires face, I have often wondered how to measure success. As you have mentioned in previous posts, we know quite a bit when it comes to birds in restored vs. remnant prairies, but we know very little about the other critters. For example, it has been well documented that ducks will nest in kentucky bluegrass just the same as needle & thread, so measuring success by targeting one species doesn’t seem logical to me either. I also agree that its not practical to try and restore prairie back to its orginal state. That being said, do you think remnant vs. restored prairie can serve as today’s mosaic pattern amongst continious blocks of prairie? Also from a management standpoint, how many times did you graze or burn or both over the 9 year span? What notable differences did you observe, if any, in plant response?

    • Chris Helzer says:

      Brandon – I’m not sure I understand your first question. Are you asking if restored prairie can serve the purpose of providing structural heterogeneity to the landscape as patches of habitat that are somewhat different from the matrix of native grasslands? (I would say yes, but that we could do the same thing for structure by shaking up the management within blocks of that grassland matrix)

      As to your second question, the restored prairie was burned and grazed a couple of times – within the last 3 years – under variations of the patch-burn grazing system. The remnant got the same kind of management. The two prairie types responded the same way in general (dominant grasses were temporarily weakened, opportunistic forbs took brief advantage, conservative forbs were relatively unaffected) but the plant species that responded were slightly different – because of the different plant composition between the two. For example, deer vetch (Lotus unifoliatus) really went to town after a summer fire/grazing treatment in the remnant, but in the restoration, there was less deer vetch and other species like yarrow, six-weeks fescue, and a biennial primrose filled that role. Same response, but not always from the same species. Very interesting – and I think very good. There were many other similar examples.

  3. Mel says:

    Chris,
    Reading these posts I have a simple question rattling around in my head. How do you define “prairie”? Given that, how do you know when you’ve got one? Your discussion is well reasoned for how to measure movement along a continuum from “not prairie” to “prairie” but without a clear definition of the expected result I’m unclear how you know whether you’ve moved in a positive or negative direction. Obviously there are lots of ways to slice the definition based on topography, biology, hydrology, etc. and use those slices for research. I’m just wondering what to look for when I point and say “look at that prairie”?

    Probably not a simply answer given all the variable you’ve mentioned just in this article but now you’ve peaked my interest.

    • Chris Helzer says:

      Mel – it’s a tricky question. When I wrote my book on prairie management, I stated up front that my definition for the purposes of the book was, “a grassland that has a diverse plant community dominated by native grasses and wildflowers.” That’s not too bad, I guess. I wanted to be clear that a restored prairie was just as much a prairie as a remnant prairie because I was writing a book on how to manage prairies and the same management challenges and strategies apply, whether the prairie in question is 10,000 yrs old or 10 years old.

      There are all kinds of other ways to define prairies, but I don’t know that it’s very valuable to get into them. In some ways, you could argue that a 1/2 acre prairie is no longer a prairie because it’s too small to provide for many characteristic prairie species. I think I would argue that it is a prairie – it’s just a different prairie than a 1000 acre version. Just like a restored prairie is a different prairie than a remnant – and a complex that includes both remnant and restored prairies together is different yet.

  4. Brandon Jones says:

    Chris,

    Thanks for clarifying my first question. That is exactly what i was inquiring about. Interesting stuff on the plant response. When we figure out a way to measure/define success naturally it will dictate how we manage for it.

  5. David says:

    Chris,

    Yet another very good blog post. You touched on all the measures that I can think of off-hand so I do not have anything to add. However, I thought I would share what we look at (or would like to).

    Invasive species – I hate to say it, but a remnant is generally easier to manage (weed wise) when it is surrounded by crop land. Measuring and controlling invasive weed populations in both the remnant and reconstruction is critical.

    At-risk species – We monitor populations in both the remnant and reconstruction.

    Key-stone species – To date we have only looked at plant communities. The main interest is on species that are believed to have strong influences on diversity and tend to be well represented in remnants. A few examples from our neck of the prairie include Wood Betony, Bastard Toadflax, and Northern Bedstraw.

    Soil composition – We have looked at some of the “easier” stuff such as nitrogen, phosphorus and hydrology between remnants and its neighboring reconstruction. It would be great if we had the knowledge to compare soil organisms between the two. I’d like to think (or envision) that soil organisms in the remnant slowly expand into the once tilled soil of the reconstruction. As you mentioned, it is relatively easy for an experienced person to locate the transitional boundary between the two by looking at the vegetation communities and structure. However, for really good reconstructions (measured by plant species richness and management), this transitional boundary does get blurred over time (ignoring physical differences such as plow lines). Conversely, the boundary will be visible, perhaps indefinitely, in typical reconstructions. It is often hypothesized that species such as Canada Goldenrod thrive in reconstructions because the soil composition/structure is so different than remnant soil. So perhaps it is useful to qualitatively assess whether the former boundaries of the remnant are expanding into the reconstruction?

    And finally, we do look at species richness between the two.

    Thanks for sharing your study and thought-provoking ideas.

    David

    • Chris Helzer says:

      David – thanks for sharing your thoughts on this. Sounds like you’re doing some great work!

      I agree with you about invasive species. It makes me cringe when people talk about buffering their remnants with restored prairie to protect the remnant from invasive species. There are a lot of great reasons to put restored prairies around remnants, but you’re absolutely right that if your highest priority is to protect the remnant from something like reed canarygrass it’s hard to beat cropland as a buffer.

      Chris

  6. James C. Trager says:

    Great post and comments!
    David, though I have observed the vigor and height reduction impact of Pedicularis and Comandra on some neighboring plants, I’m not familiar with northern bedstraw as a keystone species. Tell me more…

  7. David says:

    Hi James,

    I’m afraid I have no hard data on Gallium boreale (Northern Bedstraw) but only field observations. I have done some literature research but found no information on this species regarding hemiparasitic or allelopathic tendencies. However, I know of a couple of remnants where this species appears to greatly suppress grasses. It appears in that typical “fairy ring” pattern with grasses hardly visible inside the ring but very noticeable outside the ring. I have one experiment going where I planted plugs directly into smooth brome grass but it’s too early to draw any preliminary conclusions. The plugs are very slowly expanding in spite of the intense competition. If I can get my hands on some more plugs, I want to repeat this experiment in more mesic conditions as my remnant references are in more mesic conditions than my simple field experiment. I suspect that my remnant references are very old clones, perhaps decades old. There are other folks in my area who have seen similar behavior with this plant species. In general, I find myself very interested in plant species that have the ability to suppress grasses and increase diversity. We have so many prairie reconstructions, mainly from the CRP program, in our area that are dominated by the tall C4 grasses. I wish I had more time, resources and dedication to look into it more.

    David

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