A Tough Plant, Not A Weed

I blame whomever named the plant.  Giving a plant the name “ironweed”, apparently – according to Google – because of its tough stem, creates an unnecessarily negative connotation right from the start.  It’s an unfair connotation for a plant that is both beautiful and important.  It’s also a big favorite of butterflies; something I can attest to after spending a couple hours last weekend chasing monarchs and others around ironweed patches at our family prairie.

Ironweed at our family prairie, growing abundantly in a smooth brome-filled draw.  The abundance of the plant goes up and down each year, but it never spreads beyond the draw or shades out the grass around and beneath it.

There are three species of ironweed (genus Vernonia) in Nebraska, and two that are common in the prairies I am most familiar with.  Both of those – V. fasciculata and V. baldwinii – seem to act in similar ways, but the first likes a little wetter sites than the second.  Both species can occur as scattered plants across a prairie, but are also often found in fairly dense patches where conditions favor them.  That patchy local abundance is the first mark against them by people who don’t appreciate their value.  The second mark is that cattle absolutely refuse to eat them.  This both helps them stand out (especially when blooming) in heavily grazed pastures and helps them spread across those same sites since they gain a strong competitive edge when surrounding plants are all being grazed hard.

Like many other plant species I tend to admire and write about, however, ironweed is not an invasive plant – it’s an opportunist.  It takes advantage of soil and management conditions that favor it, but doesn’t just spread aggressively across pastures.  If you look online, it’s not hard to find websites that encourage its control in pastures.  I dispute that.  At least in my experience, ironweed has its favorite locations (often in draws or other low spots where moisture and nitrogen are high) and pulses in abundance within those locations as grazing treatments and weather vary from year to year.  At our family prairie, ironweed is fairly abundant in some of the low draws where high nitrogen also strongly favors smooth brome, but while there are years when those patches are thicker than others, the overall patch sizes and stem densities of ironweed aren’t any higher today than they were 15 years ago.  That matches what I see elsewhere in central and eastern Nebraska.

(I found a university website online that blamed ironweed for making cattle have to look harder to find grass, thus reducing grazing efficiency.  Give me a break.  That’s the same attitude that leads to people spraying pastures to remove everything that isn’t grass, and then wondering why they need to fertilize their grass and supplement their cattle’s diet.  The same people blame others for the lack of wildlife and pollinators on their land.  …Ok, I’m done ranting – let’s talk about butterflies.)

When I arrived at our family prairie last weekend, I immediately noticed monarch butterflies flying all over the place.  I’d seen a surprising number of larvae back in July, so figured we might have a good August, but I was still impressed with how many adults I saw.  I’m guessing there were 40-50 or more across our 100 acres of prairie.  They kept moving, so it was hard to count them…

Almost every monarch I spotted was either flying or feeding on ironweed.  A few other flowers got attention too, including wild bergamot (Monarda fistulosa), Flodman’s thistle (Cirsium flodmanii), and some early tall thistle blossoms (Cirsium altissimum), but ironweed clearly monopolized most of their attention.  I started stalking monarchs with my camera and eventually found a couple that let me get close enough for to capture reasonable photographs.  While I was doing that, I also spotted myriad bees, along with quite a few other butterfly and moth species.

Here are some photos of the butterflies and moths that were kind enough to let me get close.  I didn’t ever get a good shot of a bee, though there were at least a dozen species feeding on the ironweed flowers, and I also never caught up to one of the many silver-spotted skipper butterflies that were all over the place.

This is one of many monarchs that were floating from plant to plant across ironweed patches last weekend.
I haven’t looked up this moth yet. Maybe one of you can save me the trouble? Thanks in advance.
I’ve been seeing a lot of adult swallowtails around lately, including this tiger swallowtail , which was pretty easy to spot, even from across a large draw.
Ok, this black swallowtail wasn’t on ironweed when I photographed it, but it went to ironweed after feeding on this native thistle.  I was taking bets (in my head) about whether or not the crab spider on that thistle would be able to take down the big butterfly. The butterfly eventually moved within striking distance, but the spider didn’t attack, so I’m guessing it decided to wait for something a little smaller.
Thanks to Neil Dankert, I can tell you that this gorgeous little brown skipper butterfly is a tawny-edged skipper.

Ironweed is too beautiful and important for its name.  Maybe we need a campaign to rename it, and maybe that campaign would help convince people, including those at a certain unnamed university, to leave this plant alone to do its job.  Either way, it might be fun to think about potential names.  Any ideas?

The Risks of Managing Prairies Exclusively for Plants

Prairies are often defined as plant communities dominated by grasses, sedges, and wildflowers.  However, prairies are also home to thousands of animal species, not to mention countless varieties of fungi, bacteria, and other microbes.  Animals are just as much part of the prairie as plants, and they can have immense impacts on the plant community and overall prairie function.

Mixed-grass prairie managed with periodic fire and intensive grazing. Gjerloff Prairie - Prairie Plains Resource Institute.
For most of us, prairies are characterized by the plants we see when we walk through them. Gjerloff Prairie – Prairie Plains Resource Institute. Nebraska mixed-grass prairie managed with periodic fire and intensive grazing.

Despite the importance of animals, many prairie managers and biologists focus largely on plants when evaluating the quality of a prairie or when making management decisions.  Interestingly, many ranchers do the same thing, though they tend to focus mostly on dominant grasses while biologists often look more at plant species diversity and/or rare plant species. Regardless, it is rare that the needs of harvest mice, leafhoppers, or smooth green snakes are incorporated into management plans or evaluations of prairie quality.  (A major caveat is that some prairies are managed primarily for bird habitat – either song birds or game birds – a practice that has its own set of ramifications.)

Deer mice and other small mammals are rarely considered during management planning. Small mammals and other animals have specific needs for habitat structure, however, and are also vulnerable
Deer mice and other small mammals are rarely considered during management planning. Small mammals and other animals have specific needs for habitat structure, however, and their populations can decline or disappear after several years of unfavorable habitat conditions.

To be fair, there are good reasons to give plants primary consideration in management planning.  Cattle ranchers correctly recognize that cattle feed mostly on grass, so maintaining robust stands of grasses is critical for a successful ranching operation.  For biologists and conservation land managers, plants are often good indicators of prairie health.  Plant communities are easier to assess than insect or small mammal communities, and they provide the foundation for many ecological processes.  Pollinators, for example, rely on plant diversity and abundance of flowering plants.  Many other insect species need particular plant species or groups of plant species for food and/or living quarters.  A diverse plant community also provides a consistent supply of vegetative growth and seed production for plant-eating animals.

Bees and other pollinators rely upon plant diversity to provide a consistent supply of flowers throughout the growing season. This bee (Svastra sp) is on a native tall thistle (Cirsium altissimum) in September.
Bees and other pollinators rely upon plant diversity to provide a consistent supply of flowers throughout the growing season. This bee (Svastra sp) is on a native tall thistle (Cirsium altissimum) in September.

Not only are plants helpful in assessing prairies, every plant species is also significant and worthy of conservation for its own sake. However, the same is also true for animal species.  A prairie without birds, ants, butterflies, or grasshoppers just wouldn’t be the same, and not just from an aesthetic standpoint.  The complex interactions between all the various organisms in prairies are difficult to study, but absolutely critical to ecological function.  Studies that have excluded or suppressed populations of small mammals or insects have documented tremendous changes to the plant community – usually resulting in lower plant diversity and dominance by a few species at the expense of others.

Animal communities are vital to prairie communities and ecological function, and conserving healthy animal communities relies on at least two broad factors: plant diversity and a variety of habitat structure. As mentioned earlier, most pollinators and herbivores rely upon a wide range of plant species in order to be able to find food at all times of the season, and many insects depend upon particular plant species for survival.  However, habitat structure is also critically important for animal communities, and because every animal has its own unique habitat requirements, prairies need to provide a wide variety of habitat conditions.

Habitat structure for animals is driven by factors such as the amount of plant litter covering the ground and the height and density of the vegetation.  Some animals depend upon short vegetation with lots of exposed bare ground, some need tall dense vegetation, and still others prefer something in-between – or combinations of several habitat types.  The size and distribution of habitat patches is also important.  For example, some animal species need fairly large areas of a particular habitat structure, while others thrive best in situations where small patches of short and tall vegetation are intermixed.

A variety of habitat structure types across a prairie helps ensure a diversity of animal species, including invertebrates, will thrive.
A variety of habitat structure types across a prairie helps ensure that a diversity of animal species, including invertebrates, will thrive.  This area of intensive grazing is adjacent to other patches of taller and thicker vegetation.  Restored prairie in The Nature Conservancy’s Platte River Prairies, Nebraska.
This is the same restored prairie as shown above, but in a diffrent yet
This is the same restored prairie as shown in the previous photo, but in a year when management provided different habitat structure.  Cattle have grazed much of the grass, but have left behind a diversity of blooming plants, including Canada milkvetch (Astragalus canadensis), compass plant (Silphium laciniatum), black-eyed Susans (Rudbeckia hirta), bergamot (Monarda fistulosa), and many others.  Platte River Prairies, Nebraska.

Prairie management regimes that don’t consider animals’ needs can lead to problems.  For example, prairies with relatively uniform vegetation structure provide limited options for animals, regardless of whether that structure is uniformly short, tall, or somewhere in the middle.  A subset of animal species will thrive in those prairies, but other species can experience significant population declines.  If those same conditions persist for too long, some animal species can disappear completely.  Whether or not those species return depends upon the mobility of the animals and the degree of habitat fragmentation around the prairie.

Some management tactics can also cause animal populations to disappear or decline dramatically.  While it is an important part of prairie management, prescribed burning can be particularly dangerous to animals, especially if an entire prairie is burned at once. Fire can directly kill animals, including insects overwintering or living inside plants, but animals can also suffer from the sudden loss of habitat.  These impacts are especially severe in fragmented landscapes where there is nowhere for animals with limited mobility to go for better habitat, and no way for recolonization by species wiped out by fire.  Uniform haying and intensive grazing can have some similar impacts to fire, although both tend to leave a little more habitat for at least some species.

Snakes like this red-sided garter can be vulnerable to fires that occur during the growing season. However, dormant season fires can also be very damaging for insects and other species that overwinter in grass litter or in aboveground stems of plants.
Snakes like this red-sided garter can be vulnerable to fires that occur during the growing season. However, dormant season fires can also be very damaging for insects and other species that overwinter in grass litter or in aboveground stems of plants.

Plant diversity and the survival of rare plant species are important objectives for prairie management.  However, the same can be said for animal diversity and rare animal species.  In some cases, well-planned management can largely account for the needs of both.  Providing a shifting mosaic of habitat patches across big prairies can usually facilitate plant and animal diversity, and accommodations can be made for rare species or species sensitive to particular management tactics such as fire or grazing.  Understanding the needs and evaluating responses of various groups of plants and animals, however, is crucial to successfully adapting management strategies over time.

Conserving all species is much more difficult in small and/or isolated prairies.  A single prescribed fire can potentially wipe out animal species, and repetitive use of any management tactic, including fire, grazing, haying or rest risks eliminating species as well.  Read more about the challenges of managing small prairies here.

In both large and small prairies, setting clear objectives for management is very important.  Ideally, those objectives will accommodate the needs of most or all animal and plant species and sustain ecological resilience.  In reality, it’s more likely that the needs of some species will have to be sacrificed or given less priority than others.  As an example, frequent burns might sustain high populations of many plants (including some rare species) and help suppress invasive trees or grasses, but are likely to eliminate some species of butterflies and other invertebrates, and potentially some snakes and other vertebrates as well.  Alternatively, applying periodic patchy grazing and rest treatments in the same prairie could increase habitat heterogeneity to the benefit of many animals, but could reduce the relative abundance of some sensitive plant species while stimulating higher populations of more grazing tolerant plants.

These kinds of management decisions can be extremely difficult, and there are no easy answers.  The disappearance of any species from a prairie is a big loss, particularly at isolated sites, and we don’t yet know how to predict the ripple effects of losing most species.  Even when management decisions don’t directly eliminate species, reducing population sizes can make species more vulnerable to diseases or other factors that could eventually wipe them out.

Regal fritillaries are
The regal fritillary butterfly is one of many prairie animals that has been shown to be vulnerable to disappearing from prairies because of incompatible management.  Even for fairly mobile species like butterflies, recolonization after local extinction is far from assured, especially in fragmented landscapes.

No matter what management decisions are made, it’s crucial that land managers consider the needs of as many species as possible – including both plants and animals.  It’s not necessarily wrong to manage a prairie primarily for plant diversity or to sustain populations of rare plants.  It’s also understandable that a cattle rancher would want to sustain consistent vigorous stands of grass.  However, in both cases, managers need to acknowledge and accept that optimizing conditions for a particular suite of plant species will lead to negative consequences for other species, including both animals and plants.

Hopefully, continuing research and experience will help us better understand the inescapable tradeoffs that come with these kinds of difficult decisions.  For now, the impacts of losing plant or animal species and the potential for those losses to affect ecological resilience are still very unpredictable.  The best we can do is to be clear and honest with ourselves and others about why we’re making decisions, and do our best to evaluate the results and learn as we go.

 

If you’re interested in learning more about how excluding or suppressing animal populations can lead to unexpected and complex reactions in grassland communities, here are a couple example research papers.

Herbivory and Plant Species Coexistence: Community Regulation by an Outbreaking Phyotophagous Insect.  Walter P. Carson and Richard B. Root.  2000.  Ecological Monographs 70(1):73-99.

 Secondary plant succession: how is it modified by insect herbivory?  V.K. Brown and A.C. Gange. 1992. Vegetatio 101:3-13

Massive and Distinctive Effects of Meadow Voles on Grassland Vegetation.  2006.  Henry F. Howe, Barbara Zorn-Arnold, Amy Sullivan and Joel S. Brown, Ecology 87(12):3007-3013

Effects of Coyote Removal on the Faunal Community in Western Texas.  1999.  Scott E. Henke and Fred C. Bryant.  Journal of Wildlife Management 63(4):1066-1081

Saving Pollinators One Thistle at a Time

Pollinator populations are in trouble for a lot of reasons.  Loss and degradation of habitat, pesticides, and diseases are all major contributors.  However, at least in the Central United States, much of the pollinator decline can be tied to spiny pink/purple-flowered plants and the way humans react to them.

Tall thistle, a native annual wildflower, is a big favorite among pollinator insects.
Tall thistle, a native annual wildflower, is a big favorite among pollinator insects.  However, it is seen by many people as a weed that needs to be eliminated from the earth.

On the face of it, thistles seem like they’d be pretty well-liked.  Thistle seeds are a major food source for birds and other wildlife, as well as for a variety of invertebrates. The abundant nectar and pollen found in thistle flowers make them one of the most popular plants among both pollinator and non-pollinator invertebrates.  As if that wasn’t enough, most thistles have large and/or abundant blossoms, which you’d think would make them very attractive to people.  Sure, they’ve got spines, but so do cacti, yucca, and many other plants gardeners love to landscape with.  So why do we hate thistles so much?

The cultural dislike of thistles is not at all a new phenomenon; references to the unpopularity of thistles can be found at least as far back as the Book of Genesis in the Bible.  There, thistles are mentioned when God curses Adam after he eats the forbidden fruit. Genesis 3:17-18 – “Cursed is the ground because of you… Both thorns and thistles it shall grow for you…”  Clearly, if God includes thistles as part of His curse on all humanity, they are not a crowd favorite.

Regardless of why thistles are so widely disliked, our contempt for them causes serious problems for pollinators.  This happens in two ways: 1) direct destruction of an important floral resource for pollinators, and 2) major side effects associated with #1.

Because thistles are so important to pollinators, our compulsion to destroy them is a major problem.  Sure, some thistle species are invasive and can cause enough ecological damage that their control is warranted.  Most thistle species, however, are targeted for destruction purely because they are thistles.  Many of those are native wildflower species and are not at all aggressive or problematic.  Regardless, there are few places where thistles are tolerated, let alone encouraged.  The result is the loss of a big source of food for many pollinators.

Musk thistles and regal fritillaries (before we chopped them because they are designated as noxious weeds and we are legally obligated to eradicate them.) The Nature Conservancy's Platte River Prairies, Nebraska.
Musk thistles and regal fritillaries.  Musk thistles are designated as noxious weeds and we are legally obligated to eradicate them.) The Nature Conservancy’s Platte River Prairies, Nebraska.

While the loss of thistles themselves is a big problem for pollinators, the methods we use to eliminate them can have much bigger impacts.  If we were content to dig thistles out of the ground one by one, things wouldn’t be so bad.  Of course, that’s not always feasible – some perennial species such as Canada thistle are rhizomatous and can’t be killed by digging.  Herbicide use is the other available option.  Spot spraying individual plants or clumps can be relatively innocuous, but only if the person spraying is judicious and selective about what they spray.

However, working thistles one by one takes a lot of time, and just because we hate thistles doesn’t mean we want to spend a lot of time getting rid of them.  Broadcast herbicide spraying, by airplane or boom sprayer, can kill lots of thistles in very short order.  It’s a great way to get rid of all those unsightly pink flowers in one fell swoop…at least for that season.  Unfortunately, broadcast spraying also kills a wide array of other wildflowers, and most of those never recover (the ones that do are the ones we tend to like least – like ragweeds).

The grand irony is that because broadcast spraying kills so many non-target plant species, the spaces left open by those dead wildflowers are usually colonized by thistles.  Thus, while broadcast spraying is quick, it tends to perpetuate thistle populations by destroying their competitors.  (Also, most large thistle populations are there because of chronic overgrazing or some other major disturbance that weakens perennial vegetation and creates space for thistles to grow.  Broadcast spraying doesn’t address those underlying issues.)  Oh, and by the way, killing off all the wildflowers in a pasture or roadside also wipes out the pollinators that depend upon them for food.

Our cultural dislike of thistles leads us to kill off as many as we can each year.  Since thistles are a major food source for pollinators, that’s grave news for pollinator conservation.  Our desire for more “efficient” ways to kill thistles has led to even worse news, however – the loss of plant diversity across millions of acres.  Since plant diversity sustains pollinators by providing varied and consistent food through the season, losing that diversity at a large scale is devastating.  We can rebuild some of what we’ve lost through restoration, and we can save what’s left, but only if we change the way we think about thistles.  We’d better hurry; pollinator declines are not slowing down.

I think we need a thistle fan club.  Who’s with me??  Let’s do this thing.  I’ve come up with a basic logo and tag line (below) to get us started.  Click here to get an easily printable version you can hang on your office door or tape to your car window.  It’ll be a great conversation starter!  In fact, let’s have fun with this.  If you feel like it, take a picture of how you displayed the logo and put it on your favorite social media with the hashtag #thistlehelp.  Not a social media person?  Feel free to email me a photo – maybe I’ll collect some of them and use them in a future post.  If you email me, please keep the file size below 1 mb…   Use this email address: chelzer(at)tnc.org.

The bees and butterflies of the world are depending on you.  This is going to sweep the nation, you’ll see!

ThistleFanClub

 

Lessons From a Project to Improve Prairie Quality – Part 1: Patch-Burn Grazing, Plant Diversity, and Butterflies

We recently completed a large multi-year restoration and management project at our Platte River Prairies.  Our specific objectives were to improve habitat quality for various at-risk prairie species and evaluate the impacts of our management on at-risk butterflies – particularly regal fritillaries.  The project was supported by the Nebraska Game and Parks Commission, who funded our work with two State Wildlife Grants (U.S. Fish and Wildlife Service money).  Over five years, we conducted fire/grazing management in our prairies and enhanced plant diversity through overseeding and seedling plugs.  We measured the results of that work by measuring changes in prairie plant communities and by looking at the use of our prairies by regal fritillaries and other butterflies.

Plant diversity and buttterfly habitat were the objectives of our 5-year project.
We’ve worked hard to get plant diversity in our restored prairies, including this one.  We wanted to know whether or not our management was maintaining that diversity, and also how it was affecting butterflies.  The prairie shown here was being grazed at the time of the photo – July 2009.  The Nature Conservancy’s Platte River Prairies, Nebraska.

The following is a brief summary of the major lessons we’ve gleaned from the fire/grazing component of the project, including implications for future management and restoration work.  I will summarize the overseeding/seedling work in a separate upcoming post.  If you want more details, you can see our entire final report to the funding agencies here.  As a warning, the report is 14 pages long, with an additional 21 pages of Appendices, full of tables and graphs.

What We Did
Between 2008 and 2012, we treated over 1,500 acres of prairie with varying applications of patch-burn grazing management.  During that time, we altered the timing of burning and the intensity of grazing from year to year, and included years of complete rest from grazing in some prairies.  For the purposes of this project, we evaluated the results of our work in two main ways:

–          We measured changes in plant diversity and mean floristic quality.

–          We conducted three years of butterfly surveys to evaluate how regal fritillaries and other butterfly species responded to our restoration and management work.

Continue reading

Revised Slideshows of Nebraska Nature

At the request of many of you, I’ve added captions to the slideshow photos I posted last November.  Those slideshows can always be found from the home page of this blog (under the Photography Page).  In addition, I’ve provided links to each at the end of this post.

A dragonfly in the early morning - Pawnee County, Nebraska

Now that I’ve got them labeled, I’d appreciate any help you can give me in identifying species correctly.  I’m pretty confident about the vertebrates and plants, but could sure use some assistance with the invertebrates.  If you see one that I’ve got wrong, or you can identify it more specifically, please let me know by adding a comment below the slideshow.

Thank you – I hope you enjoy the photos.

Slideshows:

Invertebrates

Plants

Vertebrates

Landscapes

Winter

Trying to Figure Out What We Did Right

When converting crop land to restored prairie, it’s always hard to predict what you’re going to get.  Numerous examples prove that even when you control as many variables as possible – including soil conditions and the rate, timing, and technique of planting – no two seedings turn out alike.  Sometimes, you can use hindsight to explain what happened (weather conditions, herbicide carryover, etc.) but most of the time it’s clear that we just don’t understand much of what’s happening out there.

I’ve been analyzing some data from one particular restored prairie lately, and trying to puzzle out what’s going on.  In this case, the results are good – which is nice.  It’d be nicer, of course, if I could explain WHY things worked so well and then replicate whatever happened…

The Dahms 2000 prairie restoration has turned into one of the most aesthetically pleasing prairies we manage along the Platte. It has tremendous diversity and abundance of wildflowers. Most importantly, its plant diversity is still increasing fairly rapidly after twelve field seasons.

The prairie in question was seeded with a mixture of about 200 plant species onto 69 acres of disked cropland that had been in corn the previous season.  The seed was planted sporadically between December 1999 and April 2000.  Wetlands were added to the site by excavating down close to groundwater and recreating the kind of swale/ridge topography that is typical of nearby Platte River meadows.  Those wetlands and sandy spoil piles (ridges) were seeded with appropriate seed as well. 

All of the seed was broadcast onto the site – some by fertilizer spreader and some by hand (I was experimenting) and no harrowing or packing of the soil was done.  Unfortunately, this was the last year BEFORE I started keeping good records of the amount of seed from each plant species I included in the mixture, so I only have a list of the species we harvested seed from that year.  What I know is that my seeding rate per acre was about 15 gallons of grass seed (mostly big warm-season natives) that was harvested by combine from nearby prairies, and about 1/2 gallon of hand-harvested forbs, grasses, and sedges.  That’s roughly 12 bulk pounds of grass seed and 1/2 pound of forb (wildflower) seed per acre.  I have no idea what germination rates were that year, but it was a pretty light seeding rate compared to what many others around the country use.  Today, our typical mix is a little lighter on grass and includes about twice the forbs.

To cut to the results, this prairie has turned into our most diverse and showy restoration we’ve ever done.  You’d never know we’d used such a light seeding rate of forbs by looking at the site now – its appearance is dominated by big showy wildflowers.  By every measure I use to look at the plant communities of our restored prairies, it comes out high.  I’ve found 178 plant species in the site so far, which is excellent.  The mean Floristic Quality (combination of species number and “conservatism values”) is high, and still climbing rapidly.  It averages twelve plant species per square meter, which is higher than most other restored or remnant prairies in the area.  (Yes, I know that seems like a very low number to you eastern tallgrass prairie folks, but it’s good for out here.  Don’t rain on my parade, ok?)  Twelve years after it was planted, tall warm-season grass species are still not very dominant.  The species found at the highest frequency is big bluestem, and it was only in about 80% of 1m2  plots stratified across the site last June.  In short, it’s a beautiful prairie.  And I don’t know why.

I know most of you are ITCHING to see the actual data tables and graphs, but because there are a few who aren’t, I’m including them as a PDF file, which you see by clicking here.  The PDF also includes a cumulative list of plant species found in the restored prairie.

Flower species such as black-eyed Susan (foreground) and bee balm (pink flowers in the background) are still dominating the plant community in this photo from 2009 (the 10th growing season of this seeding). The lasting abundance of those species is, I think, tied to the lack of dominance by major grass species.

It’s particularly impressive that this seeding turned out so well, because the odds seemed stacked against it early on.  It was seeded right at the beginning of a 7 year drought.  The first several years were dominated (as usual) by weedy species and a few colonizing native species such as Canada wild rye and common evening primrose, but in this prairie those species remained dominant for several more years than is typical.  Once other plant species started breaking through, there were few legumes present – and we don’t typically have problems establishing legumes in our prairies.  Those legumes are still more scarce than in other nearby sites, but they’re increasing over time.  Finally, in about its eighth season, the site stopped looking like a weed patch and matured into something that most people would recognize as a prairie.

As I’ve discussed in other blog posts, I’m still struggling to define success in our overall prairie restoration efforts, but at the scale of individual seedings, there are a couple things I look for.  First, I want to see a good diversity of plant species, and I want to see that diversity sustain itself over time.  Second, I don’t want to see invasive species increasing at the expense of that overall plant diversity, even as the prairie is exposed to disturbances such as drought, fire, and grazing.  So far, this restored prairie passes those tests with flying colors.  We’re moving toward implementing some measures of invertebrate use as well, but aren’t there yet.  Initial data and observations, however, show higher butterfly abundance and diversity in this site than in other nearby restored prairies – for whatever that’s worth.

The prairie has been managed with some periodic fire and grazing, which should be helping to suppress dominant grasses. However, this site has gotten much less of that kind of management than nearby restored prairies, and those other prairies have stronger populations of major grasses, so management can't explain the whole phenomenon. In this photo, cattle are grazing in the burned portion of this site - within a patch-burn grazing system. The grasses are primarily grazed short, helping to showcase the abundance of the forbs.

So why did this restoration turn out so well?  I really have no idea.  It caught a couple nice rains during its first spring, but the rest of the summer was awfully dry.  The overall seeding rate for forbs was considerably lower than we use now, but I don’t know how much seed we had of individual species.  I wish I understood why it has taken the big grasses so long to fill in, but I don’t.  I think the delayed grass dominance probably plays a role in encouraging the abundance and diversity of wildflowers at the site, but I don’t know how to replicate it.  The soils at the site are a little sandier than some of our other sites, but we’ve worked on sandier soils and had very quick grass establishment, so it seems unlikely that the sand is the key.

Besides its aesthetic appeal, the prairie is also a great seed harvest site because of its wildflower abundance. Nanette Whitten (left) and Mardell Jasnowski (right) are harvesting seeds in this photo.

The vast majority of our prairie restorations turn out pretty well, but this one is extraordinary, and I can’t explain it.  Was it something about our technique?  Something about the weather or soil conditions?  I know I should probably just be happy with the results, but I want to know WHY! 

Success is sure frustrating.

The Importance of Weedy Flowers for Butterflies

In our Platte River Prairies, regal fritillaries and other butterflies appear to depend heavily on a few weedy wildflower species as nectar plants.

I was in graduate school when I first started learning to identify butterflies.  I participated in several July 4th butterfly counts around Nebraska, and got to know some people who could help me with the tougher-to-identify species.  I was a good birder at the time, and quickly found many parallels between bird and butterfly identification.  One of those was that skippers were just like sparrows – lots of small drab-colored species that were really difficult to tell apart.  The difference, of course, was that I could catch skippers with my net to see them up close.

One species that wasn’t difficult to identify was the regal fritillary.  Once I figured out how to tell the difference between regals and monarchs I started seeing regals everywhere.  In fact, when I helped with July 4th counts, regal fritillaries were usually one of the most abundant species we saw.  I didn’t realize until later how rare regals are in eastern prairie states, and how fortunate I am to live in Nebraska where their populations are still strong.

Regal fritillary butterflies are still common in many western tallgrass prairies and mixed grass prairies, but have largely disappeared from most eastern prairies.

As I learned more about the species and its conservation status, I saw some inconsistencies between what regals were thought to need for survival in eastern prairies and what our Platte River Prairies were providing.  For example, many people I talked to from the east told me that regal fritillary larvae needed prairie violets for a food source.  However, our Platte River Prairies – which are full of regal fritillaries – only have the heart-shaped-leaf blue violet (Viola pratincola), and no prairie violets.  In addition, plant species like purple coneflowers (Echinacea spp) that are heavily used as nectar plants by regal fritillaries aren’t present in the floodplain of the Central Platte River.  In 2010, with the help of Dr. Ray Moranz of Iowa State University, we started a research project to learn more about how regal fritillaries survive and thrive in our prairies.

Through the project, we’re investigating multiple aspects of regal fritillary habitat use – including nectar plant use, the use of remnant vs. reconstructed prairies, and the way in which regals interact with a landscape managed with a combination of fire and grazing.  We’ve only completed one field season so far, and will need more time to answer those questions, but we have already seen some very striking results in terms of nectar plant use.

To collect our data, we regularly walked transects through our prairies and counted butterflies – noting nectaring behavior when we saw it, and recording the species of flowers the butterflies were nectaring on.  I’m only referring to the nectaring data in this post because we’ve got more work to do to analyze the other data we collected.  It’s also important to remember that these are just pilot-year data, although they match what I and others have observed for many years.

Though we saw many hundreds of regal fritillaries on our transects, relatively few were actually nectaring.  Early in the season when numbers were highest, we saw mainly males – patrolling for newly emerging females.  When those females finally arrived on the scene we started to see nectaring behavior from both males and females, but observations of nectaring were still relatively rare.  Multiple years of data collection will be important to confirm the patterns we saw this first year.

There were really only two kinds of wildflowers that attracted the vast majority of nectaring regal fritillaries through the 2010 season, and both are usually called weeds.  The first was hoary vervain (Verbena stricta) and the second was a small group of thistle species – primarily Flodman’s thistle (Cirsium flodmanii) and tall thistle (Cirsium altissimum).  Hoary vervain is a native wildflower that is largely considered to be a pasture weed by many people because it thrives in overgrazed situations.  Cattle don’t like to eat it and it can spread quickly when the surrounding grasses are weakened.  (However, it also decreases in abundance very quickly when the grasses regain their vigor.)  Flodman’s and tall thistle are two native thistles that are also considered to be weedy plants, and that do well in overgrazed pastures.  The third favorite plant was actually several species of milkweeds lumped together (primarily weedy species like Asclepias syriaca and A. speciosa).

During the early part of the summer, the majority of regal fritillaries nectaring on flowers chose hoary vervain.
In late summer and early fall, vervain largely stopped blooming and other species became more important for nectaring, particularly native thistle species.

Most of our data collection centered on regal fritillaries, but we also collected data on other butterfly species.  So far, there doesn’t appear to be much difference in the nectaring preferences of regals and the larger butterfly community.  During the early part of the season, hoary vervain was the primary choice for most butterflies and a variety of other species got only infrequent visits.  Later in the season when hoary vervain was largely done blooming, thistles and a few other species, including wild bergamot – aka monarda or Monarda fistulosa and rosinweed (Silphium integrifolium), shared the load.

Observations of early summer nectaring across all butterfly species showed that hoary vervain was the dominant selection for nectaring.
Later in the season, other flower species split the nectaring observations fairly evenly.

One of the most interesting aspects of doing this research on butterflies has been that I’ve been able to look at our prairies through the eyes of butterflies – and that’s given me some surprising insights.  Our remnant prairies are largely degraded by years of overgrazing and broadcast herbicide use, and we’ve been working to slowly bring them back to higher floristic quality.  I’ve assumed that increasing floristic quality would also be good for many other species, including butterflies.  In addition, we’ve worked very hard at getting the highest plant diversity we can into our restored (reconstructed) prairies.  While we’re not restoring those prairies for butterflies, specifically, I’ve always assumed that butterflies would benefit from high plant diversity.  From our very preliminary data on butterflies, it appears that while our restored prairies have many more flower species, including many showy species, they may not be providing any better nectaring opportunities than our remnants!  The flower species most used by regal fritillaries and other butterflies are hoary vervain and thistles, which are at least as common in our remnants as in our restorations.

Regal fritillaries, and other butterflies, seem to rely heavily on hoary vervain for nectar in our Platte River Prairies.

I’m confident that there many other benefits of the plant diversity in our restorations, of course, including the availability of a variety of larval host plants for butterflies.  But it’s a little humbling – and intriguing – to see butterflies relying on plant species that do well in beat-up pastures rather than flocking to our showy restored prairies!  It’s important, of course, not to extrapolate these results to other parts of the country.  I’m not saying that regal fritillaries can survive in beat-up pastures in eastern states.  If that was so, we’d have many places in the east with lots of regal fritillaries.  Nebraska and other western states with high numbers of regal fritillaries also have landscapes with relatively high amounts of native prairie – and that may be the most important factor for regal fritillary survival.

The other lesson from our early data seems to be that the value of “weedy” species shouldn’t be discounted just because they thrive in conditions many flower species can’t take.  Vervain and thistles could be the primary plant species supporting our butterfly populations along the Platte River right now.  That’s a pretty good argument for being valuable.  In addition, the violet species that the regals must be using as a larval food plant along the Platte is considered to be relatively weedy because it does well in degraded pastures.  I’m sure glad we have a lot of it – and so are regal fritillaries!  Other weedy plant species have value as well – apart from their obvious role in filling space when “good” plants are weakened by fire, grazing, or drought.  The seeds of native ragweed and annual sunflower species, for example, seem to be excellent food sources for many small mammals and birds (judging from the density of tracks around the plants when it snows).

I’m really looking forward to next season’s butterfly transects.  I enjoyed reacquainting myself with butterflies last summer, and it was good for me to look at our prairie work through a different lens.  I’m sure we’ll learn more as we collect and analyze more data.  In the meantime, we (and our butterflies) will continue to enjoy and appreciate our weeds.

A big thank you to Dr. Ray Moranz for his assistance setting up this project.  Also, Mardell Jasnowski directed most of the data collection in 2010, with help from Nanette Whitten, Nelson Winkel, and Natalie Goergen.