Looking for Ecological Impacts? Urine Luck!

I came across a copy of one of my all-time favorite research articles the other day.  The paper tells a great story about the kinds of complex interactions that occur between the biotic and abiotic components of an ecosystem, including feedback loops and ecological hierarchies.  But more importantly, it’s a story about a guy who dumps bison urine on the prairie to see what happens.

The research paper, written by Ernie Steinauer and Scott Collins was actually a report from the second of two projects they conducted on bison urine impacts at the Konza Prairie Biological Station in Kansas.  Both projects were interesting, but I like the second one best because it focused on how bison urine can affect the prairie community at multiple scales.

Bison and cattle urine creates patches of high nitrogen concentration in the soil.  You can identify those patches in a pasture because they look like dinner plate-sized areas of extra dark green grass that, if left ungrazed, are taller than the surrounding vegetation.  Previous studies had shown that livestock urine increased the aboveground production of plants and altered plant species composition.  Other researchers had also found that herbivores preferentially graze urine-treated areas because of increased plant production and higher N concentration in leaves.  Steinauer and Collins fully expected to see the same patterns, but they also wanted to see whether or not those urine patches acted as initiation points for grazing lawns.

If you were to walk around a pasture being grazed at a moderate stocking rate, you’d see patches of uniformly short vegetation (often bathtub to bathroom-sized or so) surrounded by a matrix of somewhat taller vegetation.  Those short-cropped areas are called “grazing lawns”, and often consist of a single species of grass such as smooth brome (Bromus inermis) or big bluestem (Andropogon gerardii) that is particularly favored by grazers.  Grazing lawns are a result of livestock repeatedly feeding from the same plants all season long while ignoring others.  They do this because the regrowth from plants that have already been grazed tends to be more nutritious than more mature leaves of plants that haven’t. 

In their study, Steinauer and Collins wanted to see whether small deposits of bison urine would stimulate much larger grazing lawns around them.  If so, a small fertilization event by a bison would actually lead to a much larger disturbance to the prairie community.  In order to test their idea, they first needed some bison urine.  (How would you like to be handed that task?)  Fortunately, the great wealth of scientific literature includes a publication from 1978 that has a recipe for simulated bison urine.  Don’t you love science?  Steinauer and Collins helpfully reprinted the recipe in their research paper so the rest of us could join in the fun.

 (“…Excuse me, I’d like to buy a big batch of urea so I can mix me up some artificial bison urine.  Yes, I can wait a moment.  Oh, hello officer, where’d you come from?  You’d like me to step that way?  Sure.  Hey! Where are we going??”)

I’ve included links to both bison urine research papers by Steinauer and Collins at the bottom of this post, but in summary, they confirmed that bison preferentially grazed patches treated with urine (65% of urine-treated plots were grazed, compared to only 18% of untreated plots).  However, the bigger story is that those urine patches also acted as initiation points for larger grazing lawns.  In fact, many fewer untreated plots would have been grazed if they hadn’t been enveloped by grazing lawns that started in nearby treated plots.

What do we learn from this?  We learn that when a bison (or cow) decides to relieve itself in a particular place, it’s very likely starting a cascade of impacts…

  1. Urine fertilization increases the growth rate and nitrogen content of the plants in a small area.
  2. Those particularly nutritious plants attract a hungry bison, which after devouring the vegetation in that little spot, keeps its head down and eats a lot more of the same plants in the vicinity.
  3. The competitive balance between the plant species within the grazing lawn temporarily changes as grazed grasses lose root mass, opening up space for other plants that couldn’t otherwise compete with them.
  4. Grazing lawns improves habitat for a number of wildlife species, including insects and reptiles, that depend upon the availability of open sunny areas adjacent to taller shady vegetation.

A cow selflessly initiates a cascade of ecological processes in a prairie. This one happens to be within the burned patch of one of our patch-burn grazed prairies - thus, the uniformly short vegetation.

While Steinauer and Collins studied changes in plant composition within their urine patches, they only followed those plants for a single season, and found some conflicting results between their two studies.  Some of those may have come from the fact that their two studies took place on somewhat different soil types.  However, my own grazing research has shown that many of the effects of grazing are most evident in the year following the grazing event, after colonizing plants have had time to move into areas left open by weakened grasses.  It would have been very interesting to have followed the urine patches through several seasons to see how plant composition changed over that time period.

I’ve never met Ernie Steinauer but I bet I’d like him.  I say this because in addition to being crazy enough to mix up and dump bison urine on the prairie just to see what happened, Ernie also kept track of other interesting things that happened within his urine-treated patches.  One thing he noticed was that insect herbivory – especially on switchgrass (Panicum virgatum) – seemed to be influenced by urine treatments as well.  Now there’s the beginning to a great follow up project for someone!  After you try it, let me know what you find.

Here are the links to the two articles.

1995 article

2001 article

Why I Care About Prairies and You Should Too

Lately, I’ve been trying to figure out why I think prairie conservation is so important.  I’m not questioning my conviction – I feel very strongly that prairies are worth my time and effort to conserve – but if I can figure out exactly what it is that makes me care so much, maybe I can be more effective at convincing others to feel the same way.

I can list off all kinds of logical and aesthetic reasons that prairies are important.  Prairies build soil, capture carbon, trap sediment, grow livestock, and support pollinators.  Depending upon our individual preferences, prairies also provide us with flowers to enjoy, birds and butterflies to watch, and/or wildlife to hunt.

The buckeye is one of the more striking-looking butterflies that can be found in prairies.

Those are all very practical reasons to think prairies are important, but I don’t care deeply about prairies because they make soil and grow pretty flowers.  More importantly, those reasons are not enough to make someone stop and reconsider a decision to plow up a prairie to plant corn or broadcast spray 2,4-D just to reduce ragweed abundance.  If prairie conservation is going to succeed, you and I both need to understand and articulate the deeper reasons that we feel prairies are worth saving.

Which brings me to Dr. Seuss.

As I was mulling over why I cared so much about prairies, the story of “Horton Hears a Who” popped into my head.  In case you’re not familiar with the story, Horton the elephant accidentally discovers an entire community (Whoville) living on a speck of dust.  After he finds and starts talking with the Whos, Horton agrees to help protect them from harm.  The other characters in the book don’t believe Horton when he tries to tell them about the Whos, and actually go out of their way to steal and destroy the speck of dust he’s trying to protect.  Only when the Whos are finally successful at making enough noise to be heard do those other characters recognize the existence of the Whos and agree to help protect them.

Dr. Seuss’s intended moral to the story (repeated many times) is “A person’s a person, no matter how small.”  It’s a fine moral, but isn’t what drew me to the story as a metaphor of prairie conservation.  Instead, I was thinking about WHY the other characters in the story finally changed their minds.   The sour kangaroo and the Wickersham brothers didn’t give up their threats to boil the speck of dust in Beezelnut oil because Horton finally came up with the right logical argument to explain why the Whos were worth saving.  They changed their minds because when they finally heard the Whos making noise they recognized and identified with the Whos as fellow living creatures.

Can you see where I’m going with this?  I think the biggest thing that drives me to devote my career (and a fair amount of my free time) to prairie conservation is that I have developed a personal connection to the species that live in grasslands.  Not only do I know those species exist, I can also identify with them and what they’re doing to survive.  By becoming familiar with them, I became fond of them.

When I was in graduate school, I studied grassland nesting birds.  I got to know those bird species well, including where they lived, how they survived there, and what motivated and threatened them.  I saw prairies through their eyes, and that made me want to help make those prairies as hospitable to birds as I could.  Eventually, I began learning about prairie plants and insects as well.  I was fascinated to find that their stories were equally or more interesting than those of birds.  Each species had their own unique set of life strategies that allowed them to survive and interact with the world around them.  As a photographer, I usually learn about new species by taking a photograph of some interesting plant or insect, and then identifying it and researching its life later.  I’ve yet to come upon a prairie species that doesn’t have an amazing life story, which means the process of discovery continues to be fulfilling for me.

Pitcher sage (Salvia azurea) is one of my favorite flowers to photograph because of it's unique color and shape. It also seems to be a favorite haunt of many insect species, judging by the number that always seem to be crawling around on or near the flowers.

As the number of species I’ve gotten to know has increased, so has my commitment to prairie conservation.  Maintaining the resilience and vigor of prairie communities has grown from something that seemed like a good idea into a personal mission.  Now I’m working to protect things I love, not just species I’d read about or knew about only in the abstract.

Be honest, would you be more likely to send money to help people recovering from a natural disaster in a neighboring town or in a town on another continent?  With rare exceptions, we’d all choose the nearby town.  Why is that?  I think it’s because we can more easily identify with the people who live there.  We can imagine ourselves in their places.  We can see the disaster and their plight through their eyes.  It’s not that we don’t care about people on other continents, but they’re naturally a little less real to us.

By the way, forming sympathetic bonds with species can be dangerous when managing prairies.  The more I know about the species living in my prairies, the more I understand the ways in which those species are affected (positively and negatively) by management activities.  Any management treatment has negative impacts on some species, and impacts from activities such as prescribed fire can be quite dramatic.  Caring about individual species to the point where I’m unwilling to do anything to hurt them would paralyze me.  Management is all about tradeoffs, and while my management objectives are to sustain all the species I can, I have to be willing to knock populations of some species down periodically so that others can flourish.  I think the key is to become attached to the species, but not the individuals.  Tricky…     

Why does all this matter?  It matters because we need to recruit as many people to the cause of prairie conservation as we can.  Excluding a tiny minority of prairie enthusiasts, when the general public thinks about nature and conservation they look right past prairies to the mountains, lakes, and forests beyond – even when prairies are in their own backyard.  After all, what’s to care about in prairies?  It’s just grass.

If we’re going to fix that, we’ll need to do more than describe how prairies can help sequester carbon, filter water run-off, or support pollinator populations.   We’ll need to introduce people to the camouflaged looper inchworm that disguises itself with pieces of the flowers it eats – and to the regal fritillary caterpillar which, after hatching from its egg in the fall, sets out on a hike that will end by either finding a violet to feed on or starving to death.  They’ll need to become acquainted with sensitive briar, the sprawling thorny plant with pink koosh ball flowers whose leaves fold up when you touch them.  And who wouldn’t love to meet the bobolink – a little bird that looks like a blackbird after a lobotomy and flies in circles sounding like R2D2 from Star Wars?

The charming and vociferous bobolink.

Through this blog, as well as through numerous presentations, articles, and tours, I spend much of my time sharing what I’ve learned about prairie species with anyone who will listen – hoping that those stories will spur people to explore prairies on their own and start to form their own individual relationships with the species and communities they find.  My photographs and narratives aren’t themselves sufficient to convert people to the cause, but maybe they can at least get some of them to put on their hiking boots and go for a walk.

What about you?  Have you met the citizens of the prairie?  If not, let me help introduce you.  If you have met them, what stories can you tell?  How will you spread your passion about prairies to others?

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Here are some accounts I’ve written about prairie species I find fascinating.  If you find them interesting too, please share these links with others!

Camouflaged Looper – An inchworm that disguises itself with bits of the flowers it eats.

Yucca Moth – A terrific relationship between a plant and the single species of moth that has the capability to pollinate it.

Submarine Sora – Ever wonder why soras and other rails are so hard to find?

Sensitive Briar – A plant with a koosh ball flower, thorny stems, and leaves that fold up.

Pussytoes – One of the first spring-blooming flowers, and a surprisingly important resource for early season pollinators.

Of Mice and Clover – A great example of the complexity of interactions in prairies.

Crab Spiders – One of the great ambush predators of the world.

Flies – An unbelievably diverse group of insects with a wide range of ecological roles.

Grasshoppers – From their cute little faces to their complex communication strategies, it’s hard to beat grasshoppers.