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