Tag Archives: remnant prairie

What Is High-Quality Prairie Anyway?

Posted on by
7

Does this look like a high-quality prairie?

What about this one?

What if I told you the first one was 2 acres in size and the second was part of a 20,000 acre grassland block? 

Would it affect your opinion if you knew the first site was isolated from any other prairie habitat by miles of cropland and was directly adjacent to a busy highway?  What if I told you the second prairie hosts three different prairie dog towns and a herd of bison?

(None of this is true, by the way.  These are just hypothetical statements meant to be thought-provoking.)

The term “high-quality prairie” is often used in conservation circles, but people have very different definitions for it.  That’s not necessarily a bad thing.  In fact, it’s fascinating to see how the quality of a prairie is defined by people in different parts of North America, let alone in other parts of the world.  The cultural context is incredibly important to the way prairies are assessed and appreciated.

Here’s another example.

Does this look like a high-quality prairie?  Would it change your opinion if you knew it was planted on former row crop land?

Taking that further, does it matter if that restored prairie is about 10 acres in size and not connected to any other natural areas?  In contrast, what if it was 50 acres in size and connected two formerly-isolated remnant (unplowed) prairie parcels together?  Does that affect its quality or value?  Does it affect the quality or value of those remnant prairie parcels?

What are the criteria we should use for evaluating prairies?

A very common way to assess prairies is by looking at their plant species.  That makes good sense.  Prairie plants are beautiful.  In addition, of course, the plant community has a huge influence on the other components of the larger prairie community, including animals, fungi, and other soil microbes.  Maybe more importantly, you can always find plants.  They are literally rooted in place. 

When you visit a prairie, you might not see a pocket mouse, a katydid, or a badger, but if there’s a population of stiff sunflower, you can go to a particular spot and see it – it might even be in flower if you time it right.  Over time, it’s easy to see how that population is doing because you can check on it whenever you want.

There are multiple ways to evaluate a plant community.  The diversity of species is usually considered to be one important factor.  The presence of rare plant species, or species that have very specific habitat or management requirements, can be another.  The second can be particularly significant in landscapes where very little prairie is left.  Finding a prairie that still hosts rare plants is a big deal.

Prairie turnip (Pediomelum esculentum) is hard to find across much of its historic range. This one is part of a large population at the Niobrara Valley Preserve.

Looking at the diversity of plants and the presence and abundance of rare species is a very sensible way to begin evaluating a prairie.  I often do it myself.  You can visit a prairie at any time of year and make at least some assessment of the plant community – though it’s much easier during the growing season. 

In contrast, you have to time your visit carefully if you want to see what the bird community looks like (many species are only present for a few months each year).  Small mammals are tricky because they’re hard to see and you probably need some kind of trap system to even find any.  You can see a lot of invertebrates if you look closely, and of course you can pick up a sweep net and very quickly gather a bunch of them to inspect.  But invertebrates are notorious for having massive swings in population size from year to year, and many are only aboveground for short periods of time each season.  That means it can take a lot of time and a lot of effort to get any picture of what’s happening with invertebrate communities.

Insects like these bush cicadas can experience huge population booms and busts between years, making it hard to evaluate invertebrate communities.

However, notwithstanding the challenges of evaluating their populations, birds, small mammals, and invertebrates are all important components of prairies, right?  Any assessment of prairie quality should probably include them – not to mention reptiles, amphibians, large mammals, fungi and other soil microbes, and lots more. 

Looking at the plant community can provide hints about some of those other organisms.  Plant diversity is strongly correlated with invertebrate diversity, for example.  However, not all prairie animals have such strong ties to the diversity of a plant community, or to the presence or absence of particular plants.

Most grassland birds, for example, are really dependent upon the size of a grassland area and the habitat structure present. Some species nest in short grass, others in tall.  Still others need a variety of habitat patch types because they use different vegetation structure for nesting, brood rearing, wintering, and/or courtship displays.  In addition, a lot of grassland nesting birds are sensitive to the size of a prairie and/or won’t nest near wooded edges, roads, etc. (or suffer poor nest success when they do).

Upland sandpipers nest on the ground in large prairie patches with short, open habitat. They then take their young chicks into cover where the habitat is open enough the chicks can feed and move around easily, but there is overhead cover (especially broad-leaved plants) they can use to hide from predators and find shade.

Small mammals, reptiles, and invertebrates also respond strongly to the kind of habitat structure in a prairie.  Just as with birds, each species has its own preferences or requirements – some looking for short/sparse habitat, others for tall/dense cover, and some need something in the middle or a mix of all of those options.  Also, like birds, many of those animals and their populations will thrive best in larger prairies than in smaller ones. 

So, in addition to a “good” plant community, you could argue that a high-quality prairie should also be one that is large and managed in a way that provides a mixture of habitat structure.  Maybe, but this is where things get really interesting. 

In many places, large prairies just don’t exist anymore.  We’re left with small remnants of grassland, surrounded by row crops, urban areas, woodlands, or other land cover types.  Does that mean none of those prairies are high-quality?  Of course not.  But the context matters.  The quality of a site is measured against objectives (what do we want a prairie to be or to provide?) and objectives are informed by local culture. 

Small prairies can still provide excellent habitat for many species, including plants, invertebrates, and many small vertebrates, though stewardship gets really tricky.  It can be really challenging to manage those sites in a way that doesn’t eliminate any animal populations (by repeatedly burning the whole site, for example) while still staving off woody plants and invasive species.  However, when comparing a bunch of small prairies to each other, we can come up with criteria for determining which are higher or lower-quality.

On the flip side, there are parts of the world where we still have huge, unplowed grassland landscapes.  These prairies have the scale to support a lot of animals that can’t survive in isolated small prairies, and – if managed appropriately – the habitat structure those species need as well.  That might even include many large animals like bison and pronghorn, or other charismatic species like prairie dogs or prairie grouse. 

The Nebraska Sandhills is 12 million acres of contiguous native prairie.
Pronghorn – one of many large prairie animals supported by the Nebraska Sandhills.

However, in some of those landscapes, much of the prairie has lost plant diversity and/or populations of plant species that used to be there, and that has big implications.  Not only is the plant community an important component of “quality”, it also supports many of the other organisms that make up a strong, resilience grassland community.  Scale and habitat heterogeneity can make up for some of that, but species diversity is also a huge component of resilience.

Looking across a landscape like this, with lots of grassland but varying degrees of plant diversity and other components, we can pick out places that we think are of higher quality than others.  The criteria we use to make those decisions, though, will surely be different than the ones we use in a landscape where only small prairie patches remain.

Here’s why all this matters:

All of us who live around and work with prairies evaluate them through our own lenses.  Some of the criteria we use are shared, but others are heavily influenced by local conditions.  That’s ok, but we should recognize the biases we each have.  More importantly, we should make sure we’re talking to and learning from each other. 

About 15 years ago, I wrote a post about these different views on prairie quality.  In that post, I talked about how some of us focus a lot on the species composition (mainly plant composition) of prairies, while others look more at habitat structure and processes.  Those tendencies tend to be correlated with geography (east/west) and with the amount of grassland remaining in landscapes. 

In that post, I was hoping to stir people to expand their definition of prairie quality and to borrow perspectives from others.  There’s been some movement in that direction, but there are still some big differences in the way people assess prairie quality, and that strongly influences the way those prairies are managed.

As examples, I would love to see people working in fragmented prairie landscapes think more about how to vary habitat structure across even relatively small prairie parcels to benefit invertebrates and larger wildlife species.  At the same time, I wish people in landscapes with much larger prairies would pay more attention to plant composition.  While we have extensive prairies where the plant communities are in terrific shape, there are also lots of places where plant diversity is relatively low and many plant species are hard to find. 

My family prairie is is surrounded by cropland. I work really hard to provide a variety of habitat structure types each year to support wildlife, while constantly striving to improve the plant community. I’ve learned a lot about how to do this (and measure success) from colleagues and friends across the country.

There are lots of ways to create more heterogeneous habitat structure in prairies – even small ones.  We also have ways of managing for, and even rebuilding, plant diversity in places where it has diminished.  Good, creative land stewards working in today’s grasslands should be able to do all of that.  However, we aim our stewardship at the goals we set for ourselves, and those goals are tied to the way we evaluate prairie quality.

It doesn’t make a lot of sense to compare a 10-acre prairie fragment in northern Illinois to a 5,000-acre prairie pasture in central Kansas and argue about which is better.  It’s ok to say both are high-quality prairies (or not), based on local criteria.  What’s crucial is that we continue trying to learn from the way we each see and value our prairies.  All of us can benefit from expanding our perspectives, right?

When is a Prairie Restoration (Reconstruction) Project Successful?

Posted on by
15

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.