Tag Archives: restored prairie

What Is High-Quality Prairie Anyway?

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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?

Down A Deer Vetch Rabbit Hole

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A single observation recently led me down a pleasant rabbit hole of data, plant species trends, and unanswered questions about interactions between climate, grazing, fire, soils, and other factors.  Read on if you want to follow me down that hole…

The journey started because I noticed an abundance of deer vetch (Lotus unifoliolatus) in one of our restored prairies this year.  Deer vetch (also known as American bird’s-foot trefoil, though not the bird’s-foot trefoil you’ve probably heard of) is a native annual legume that likes sandy soils.  It’s a neat little plant and we target it during seed harvesting efforts to ensure that it shows up well in our restored prairies.  I first noticed a lot of deer vetch in the portion of prairie that was burned and intensively grazed all of last year, so I figured it was responding to that grazing.  But then I found even bigger patches of it in the other half of the same prairie where there had been no fire and only very light grazing.  Interesting…

Deer vetch, aka American bird’s-foot trefoil (Lotus unifoliolatus – formerly Lotus purshianus)

This prairie was established on former cropland in 2000, using a seed mix of about 180 different prairie and wetland species.  It is one of our showiest sites, in terms of flower abundance and color.  Below are a couple photos of from the portion of the prairie that was burned in the spring and intensively grazed all summer (as part of a patch-burn grazing system).  You can see from the images that most of the grass was grazed pretty short all season.  Many of the wildflowers in the burned patch were also grazed, but some still managed to bloom and set seed.  I apparently didn’t get any photos from the unburned/ungrazed side of the prairie last year, so you’ll just have to squint at these and imagine them with taller grass and more blooming flowers…

In 2016, the west half of this restored prairie was burned and then grazed intensively all season. This August 2016 photo shows that most of the grass was very short, though at least some wildflowers were ungrazed.

Here’s another August 2016 photo of the intensively grazed portion of the prairie. Note the grazed Canada milkvetch (Astragalus canadensis) plant near the lower left corner of the image. That species and rosinweed (Silphium integrifolium) are two of the favorites of cattle at our sites.

As it happens, I collect data from this particular site every other year as part of a project looking at how plant communities respond to management within our prairies.  To collect the data, I walk back and forth across the prairie and lay down a plot frame at regular intervals.  I list all the plant species that occur within that one square meter plot frame each time I set it down.  The data allow me to look at trends in individual species populations and at how species diversity/richness changes over time.  Here is the data for deer vetch, which confirms my observation that it is having a particularly good year.  In 2017, it showed up in about 35% of my sampling plots.

The relatively steady increase of deer vetch over time made me wonder if other short-lived plants were acting the same way.  I pulled out some of the more common annual and biennial species at that prairie and graphed them out.

In order, the species on this graph are: small peppergrass, six-weeks fescue, annual sunflower, yellow woodsorrel, black medic, and deer vetch.

Clearly, not all the short-lived plants were following the same trend as deer vetch, but it was striking to see how many had a peak in abundance in 2013, the year after our severe 2012 drought.  That makes sense since the drought was pretty hard on perennial grasses and other strong competitors in the prairie.  It created space for opportunistic plants to exploit.  However, not all of the short-lived plants followed the same pattern of response to the 2013 drought.

The plants listed on this graph are marestail, downy brome, and white sweet clover, though I lump downy/Japanese brome and white/yellow sweet clover together in my data.

None of the three species in the above graph show any noticeable response to the drought.  Instead, they each seem to be on their own path.  Marestail has declined significantly since the early days of the prairie’s existence, but had a resurgence (for some reason?) in 2015.  Sweet clover has been persisting at relatively low levels during the entire life of the restoration, and annual brome has been on a steady increase, much like deer vetch.  We’re far enough east that our average annual rainfall (25 inches/year) keeps annual brome from being problematic, so I’m not concerned about that increase, but I was curious whether or not deer vetch and annual brome were filling a gap left by the decline of other species.

Next stop on the rabbit hole journey coming up…

The species in this graph’s legend are Canada wildrye, big bluestem, Indiangrass, short-beaked sedge, and Kentucky bluegrass.

Thinking maybe declining grass dominance might explain the rise of deer vetch and annual brome, I looked at how the populations of perennial grasses are doing at the site.  In most cases, they are on an upward trend.  The above graph shows some of the more abundant perennial grasses and sedges in the prairie and the graph below shows some of the less abundant species.  (There are many more grass species not shown because they don’t appear often enough in my sampling plots to see patterns.)  A glaring exception to the overall pattern is Canada wildrye (Elymus canadensis) which seems to be following the same pattern as it does in most of our restored prairies – it is very abundant when the prairie is young and then gradually declines to about 30% occurrence after 10-15 years.

These less abundant (but still common) grasses are: Scribner’s panicum, switchgrass, little bluestem, tall dropseed, and smooth brome.

By this point, I’d kind of forgotten why I’d started my journey, but after looking at annual plants and perennial grasses, it seemed logical to look next at perennial wildflowers.  Some of those species have also been pretty steadily increasing over time, and may or may not be leveling off in recent years.

Plants listed in the legend are western ragweed, wild bergamot, woolly yarrow, and stiff sunflower.

Other perennial wildflowers have had much less predictable paths, with big jumps between sampling periods, during which they (at least) doubled their level of occurrence in my sampling plots.  Interestingly, those jumps happened in different years for each species.  Having data only from every other year makes it tricky to interpret these patterns, but it seems clear that each of these species is responding a little differently to factors such as climate, fire, grazing, and/or competition from other plants.

These species are Illinois bundleflower, hoary vervain, stiff goldenrod, and heath aster.

Many of the wildflowers shown in the above two graphs are species that I’d expect to thrive under patch-burn grazing.  With the exception of stiff sunflower (Helianthus pauciflorus), Illinois bundleflower (Desmanthus illinoensis) and heath aster (Aster ericoides), they are plants that cattle don’t particularly care to eat.  The plant species I watch most carefully under this kind of management are those that are favorites of cattle.  The graph below shows those species maintaining very steady population numbers.  None of them are super abundant, but they’re holding their places very well.

Species here are white prairie clover (purple prairie clover shows a similar pattern but is slightly less abundant), Canada milkvetch, and rosinweed.

Prairie clovers (Dalea sp) are certainly enjoyed by cattle, but rosinweed (Silphium integrifolium) and Canada milkvetch (Astragalus canadensis) must taste like brownies to our cattle – they are grazed down to the ground wherever they grow, regardless of whether they’re in the burned or unburned portion of the prairie.  Because of the affinity cattle have for species like this, we periodically exclude cattle from our prairies for an entire growing season, giving those plants a chance to bloom and produce seeds, buds, and rhizomes.  This is actually one of those years in which we’ve excluded cattle, and it’s nice to see abundant flowers from both the rosinweed and milkvetch.

Canada milkvetch is blooming prolifically this year in the absence of cattle – it is shown here in the same area that was grazed intensively all last year and grass vigor is still suppressed.

Here’s Canada milkvetch in the area not grazed hard last year – the grasses are much taller here…

Of course, looking at how individual species are doing made me wonder how all those trends add up at the community level.  Here is a graph showing how the average species richness (number of species) at the square meter level has changed over time.

This graph shows the average number of plant species found in square meter plots each year. In our part of Nebraska, 10-12 plant species per meter is a very respectable number.  It appears we may have reached a saturation point for species density in this site, though there is still variation from year to year.

Looking through all of these data, I see two main themes.  First, I see a restored prairie that is still finding its identity, even after 17 years.  Some plant species are still increasing in their abundance (including many not shown here). I expect many of those trends to level off within the next several years as those species find and colonize all the little patches of prairie where they are well adapted to growing.  That would fit with what seems to be a plateau in terms of species richness per square meter.  I don’t see any plant species (including those not shown here) that have disappeared from the site, and only a few short-lived species that have declined precipitously over time – and even those still appear to remain embedded within the community, able to proliferate whenever the right conditions appear.

Second, I see positive signs of ecological resilience in the way many of these plant species have quickly increased and decreased their population sizes over time.  Sometimes I can tell what conditions (fire, grazing, drought) might have led to those population changes, but other times I can’t.  Regardless, the ability of a community to flex and adapt as conditions change is a key component of ecological resilience, and it’s really great to see that within a restored prairie.

 

……..What was I talking about again?

Oh yeah, deer vetch.  Yep, deer vetch is doing really well this year.  Thanks for asking.

One last photo of the area burned and intensively grazed in 2016. Rosinweed (yellow flower in the foreground) can be seen blooming throughout the site, along with many more opportunistic plants such as the pink-flowered wild bergamot.