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.

Prairie Restoration (Reconstruction) as a Landscape-Scale Prairie Conservation Tool

As promised, here is a summary of the presentation I gave last weekend to the Winter Meeting of the Iowa Prairie Network.  I advocated using prairie restoration to increase the size and connectivity of fragmented remnant prairies and improve our chances of conservation success.

INTRODUCTION

Of all the threats to prairie conservation, habitat fragmentation is by far the most serious.  Encroachment by invasive species and woody plants, chronic overgrazing, and broadcast herbicide/pesticide spraying are big threats to prairie species and communities too, but the fragmentation of grasslands into small isolated pieces makes all of those other threats even more dangerous and difficult to counteract.

When a large contiguous prairie landscape (left) is broken up into small isolated fragments of prairie surrounded by cropland, roads, and other human developments, prairie conservation becomes very difficult.

For example, pressure from both predation and invasive weeds and trees is usually most severe near the boundaries of a prairie.  Because of their size, small prairies have very little area that is not exposed to these “edge effects”, so resident prairie species have no refuge from high predation rates and invasive species.  In addition, the intensity of invasive species pressure in prairies with a lot of edge exposure increases the need for control efforts and makes excessive responses like broadcast application of herbicides more likely.  Small prairies can also be more likely to be overgrazed because they’re not large enough to make up a significant part of an agricultural landowner’s income – and thus don’t get the careful management that larger grasslands would.

Most importantly, small prairies simply aren’t large enough to provide the physical space and population sizes needed to sustain many species of plants, insects, and animals.  Small populations, whether of birds, butterflies, or wildflowers, are much more vulnerable to local extinction because a disease, weather event, management treatment, or other stressor can easily affect the entire population.  If one of those small populations is wiped out by a particular event (or series of events), the only chance of that species reappearing is through recolonization from nearby prairies – but in a small AND isolated prairie, that’s unlikely to occur.

The fragile nature of small populations in tiny isolated prairies makes those prairies extremely difficult to manage for biological diversity.  Every management decision is going to favor some species at the expense of others.  Because small populations aren’t very resilient, it’s easy for them to be much more strongly affected by individual management decisions than they would be in a larger prairie where populations are larger and management treatments are less likely to spread across the entire site (leaving refuges for species to recolonize from, if necessary).

Here’s a goofy but perhaps useful analogy.  Imagine that prairie conservation is like trying to catch hundreds of pieces of popcorn falling from the sky.  In order to save a species (a piece of popcorn), you have to catch it as it falls.  Managing small prairies is like trying to catch all of that falling popcorn in a coffee cup.  Because the cup is small, the task is impossible.  If you move one way to catch some popcorn pieces, you’ll miss others.  And even if you’re really agile, your cup isn’t big enough to hold all the popcorn anyway – so you’re doomed to failure before you start.

Conserving prairie species in tiny prairies is like trying to catch falling popcorn in a coffee cup. (sort of)

The difficulty of maintaining a prairie ecosystem in small isolated fragments leads to feelings of frustration and helplessness among prairie managers.  It also leads to conflicts between managers and advocates of various prairie species/groups.  For example, some rare prairie butterfly experts advocate managing prairies without the use of prescribed fire because fires can destroy larvae, and a fire that burns an entire small prairie can completely wipe out the whole population of some rare butterfly species.  Avoiding the use of fire may make sense for those few butterfly species, but what about all the other species that would suffer from a lack of fire?  Do we manage some prairies exclusively for butterflies – and whatever other species can survive with that management?  I don’t think we have enough prairies left to start managing each of them for individual species or groups of species.  And yet, the threat of losing butterfly species is real – and important.   Unfortunately, the underlying issue is not whether or not fire should be used to manage small prairies, the issue is that rare butterfly populations are small because the prairies they rely on are small and isolated.

Ok, so small isolated prairies create all kinds of problems for conservation, but they’re all we have in many places, particularly in North America’s tallgrass prairie region.  What do we do about it?  One choice is to continue trying to catch popcorn in our coffee cups, knowing that we will eventually fail to save many species.  The second choice is to make more prairie – and enlarge and reconnect some of the existing remnant (pre-existing and unplowed) prairies to give ourselves a better chance of conservation success.  In other words, we can turn our prairies into something more like a wading pool – instead of a coffee cup – so that it becomes easier to catch the falling popcorn.

It's much easier to catch falling popcorn (conserve prairie species) with a wading pool (large prairie) than with a coffee cup (small prairie).

Our ability to restore (reconstruct) prairies by harvesting seeds and converting cropland to diverse plant communities has come a long way since its early days.  Numerous local pioneers have worked out successful methods of seed harvest, site preparation, planting, and weed control, and know how to establish hundreds of acres of restored high-diversity prairie each year.  Those prairies can contain hundreds of plant species, and can support many of the insects and animals found in remnant prairies.  However, there’s still much to learn about the extent to which restoring prairie around and between remnants increases population viability for those species, and we still need to identify those species that can’t make the jump between remnants and restorations – and find out why.  That said, we know enough to start using restoration to make prairies larger and more connected (and we don’t really have a lot of other options.)

It's not feasible to restore entire landscapes to prairie, but if we can strategically restore parcels of land around and between remnant prairie fragments (right), we can greatly increase our chances of conserving prairie species.

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GETTING IT DONE

If we’re going to use prairie restoration to make a real difference in conservation, the first step is to get better at strategically targeting our restoration efforts around and between existing small and isolated prairies.  This is being done at a few sites, but the vast majority of prairie restoration work is scattered piecemeal across the landscape.  Because restored prairie doesn’t compete economically with rowcrop agriculture, prairie restoration on privately-owned land generally happens when an individual landowner makes it a high priority and/or when Farm Bill programs like the Conservation Reserve Program (CRP) or other similar cost-share programs can help close the financial gap.  The agencies that administer those cost-share programs typically have little capacity to go out in the field and sell the programs to strategically-located landowners.  Instead, they usually sign up the people who come to them (and there are usually enough of those to use up the available money).  As a result, the location of prairie restoration depends more upon which landowners express an interest than where their property is located.

Another issue we need to address is the way in which these cost-share program funded restorations are designed.  For the most part, agency guidelines allow only enough funding per project to pay for a low-diversity seed mixture.  This is largely because the continued funding of these programs by Congress depends heavily on the total number of acres enrolled each year – making it necessary to spread the available money broadly instead of focusing it on a few high-quality projects.  While low-diversity seed mixtures can help species like grassland birds, many other species (including pollinators) rely on a high diversity of plant species, and the overall ecological function of a high-diversity prairie is much higher than that with only a few plant species.

Improving the strategic location and quality of prairie restoration will mean taking several approaches.  In some cases, conservation groups can simply attempt to purchase tracts of land around and between remnant prairies and restore them.  While effective, this can be difficult and expensive.  However, if fundraising efforts are targeted toward our highest priority remnant prairies and situations in which the potential for success is high, even small parcels of conservation ownership can be helpful.

In order to bolster the viability of more than a few high priority prairies, however, private lands are going to have to be a large part of the strategy as well.  Because agencies like NRCS (Natural Resources Conservation Service) don’t usually have the ability to direct market their programs to landowners, other conservation groups can help by approaching owners of key land parcels and discussing the potential for conservation program enrollment with them.  Finding a few interested landowners and helping them enroll can pay big dividends because one successful project often leads to other enrollments by neighbors who see the aesthetic and conservation benefits from across the fence.

Influencing the design of restoration projects funded by NRCS and other agencies is often possible as well.  For example, the biggest obstacle to using higher-diversity seed mixes is the cost.  If conservation groups can help find additional funds to increase the number of plant species in seed mixes – and if the landowner helps push for it – restoration quality can improve dramatically.  In addition, those conservation groups can help by building and maintaining long-term relationships with enrolled landowners.  Helping landowners understand the benefits of their restored land, and how it fits into a larger conservation strategy, will improve the chances that the restored prairie will be carefully managed (and even retained as prairie) as the years go by.

Prairie conservation is difficult.  In highly fragmented landscapes it can sometimes seem nearly impossible.  However, we have the ability to greatly improve our chances of success by converting isolated prairies from coffee cups to wading pools, so to speak.  Success will depend upon a concerted and collaborative effort between conservation groups, government agencies, and private landowners, but it is possible.  Surely we can agree that prairies are worth the effort?

Epilogue: How do we measure the success of prairie restoration?

I’ll deal with this more extensively in an upcoming post, but a brief mention is important here.  When using restoration as a strategy to expand and re-connect remnant prairies, the objective is not to copy the existing remnants (or some historical version of them) but to complement them with restored plant communities that allow the plants, insects and animals within the remnants to have larger and more interconnected populations.  Because of this, evaluating differences between remnant and restored communities should not be the primary measure of success.

There are a number of research papers that have shown differences between the relative abundance of individual plant species, levels of soil organic matter, composition of the insect and soil fauna communities, etc., between remnant and restored prairies.  These papers often interpret those differences as indicators that we’ve not yet restored “real” prairie.  I think that kind of research is interesting, but largely misses the point.  If our objective is to replicate existing or historic prairie we will surely fail – but why would we expect otherwise?  Trying to recreate exact copies of ecological communities that formed over thousands of years – and doing so on degraded soils, in different climatic conditions, and under pressure from vastly different invasive species and other threats – is not a recipe for success.

However, when we look at restoration as a tool for improving the viability of existing remnants, the most important measures are those that evaluate whether or not prairie populations and communities are larger, more interconnected, and more resilient.  Those are difficult things to evaluate, unfortunately, and we need develop better measures than we currently use.  That means we’ll need to shift our current research focus from identifying differences between remnants and restorations to investigating how well they interact with each other.