The emotional response you have to this photo will say a lot about your background, experience, and cultural influences.

A profusion of sunflowers in sandhill prairie at The Nature Conservancy's Niobrara Valley Preserve in north central Nebraska.

A profusion of annual sunflowers (Helianthus petiolaris) in sandhill prairie at The Nature Conservancy’s Niobrara Valley Preserve in north central Nebraska.

The sandhills of Nebraska consist of nearly 20,000 square miles of prairie.  The scale can be hard to comprehend until you have driven through it for hour after hour, gaping at the beauty spreading out all around you.  When I drove through a good portion of the eastern sandhills this week, a lot of it looked like this photo – covered with blooming yellow sunflowers.

Many readers of this post will be thinking, “Wow!  What a beautiful year in the sandhills!”  But I know others of you are thinking, “Ugh, what do we have to do to get rid of these invasive weeds?”

I’m going to get to that discrepancy, but let’s first back up and look at why the sunflowers are so abundant this year.  First, the sunflower species we’re talking about here is an annual called plains sunflower (Helianthus petiolaris).  It germinates from seed in the spring, flowers in the summer, and dies at the end of the same year.

During the drought of 2012, annual sunflowers were among the few plant species able to continue growing and flowering during the hot dry summer.  Because of that, sunflowers were able to produce copious amounts of seed, many of which ended up on the ground at the end of the year.  Few other grassland plants produced anything comparable to the seed crop of those sunflowers.

The spring of 2013 brought abundant rain to the dry sandhills.  In addition, the plant litter from last year’s dry growing season was thin and sparse, allowing a lot of light to hit the soil. That combination of abundant light and moisture was exactly what all those plains sunflower seeds needed, and they germinated.

Of course, germination doesn’t ensure survival, and many annual plants germinate each year, only to be quickly overshadowed and outcompeted by strong perennial plants.  Perennials have the advantage of a pre-existing root system that can monopolize moisture and nutrients from the soil while annuals are still struggling to get started.  In years when perennial grasses and wildflowers are strong, there is very little space for annuals to grow, except in places where the soil and plant community were disturbed by digging animals or intensive grazing/trampling.

However, in the spring of 2013, not only were conditions perfect for plains sunflower germination, competing perennial plants were also weak from drought and grazing in 2012, leaving lots of open space belowground for sunflower roots to take advantage of.  In short, you couldn’t have designed a better situation for the sunflower.  It was one of the few plant species to produce seed in 2012, and then it got light, moisture, and weak competition in 2013.  It’s no wonder the hills are yellow!

Some people will look at this photo and see an amazing abundance of pretty wildflowers.  Others will see weeds running amuck.

Some people will look at this photo and see an amazing abundance of pretty wildflowers. Others will see weeds running amuck.  At the Niobrara Valley Preserve, last year’s wildfire increased the favorable conditions for plains sunflower by creating massive amounts of bare ground for germination.  While it looks like a monoculture from a distance, hidden among the sunflowers are lots of grasses and other plants that are slowly regaining their vigor.  By next season, this will be a very different looking prairie.

Ok, back to the perception issue.  Sunflowers are one of the most popular and well-known flowers in the world.  They are big, attractive, and easy to recognize.  On the other hand, many farmers and ranchers have grown up learning that sunflowers (of any kind) are weeds.  The presence of sunflowers in a field or pasture – especially an abundance of them – can be seen as a badge of shame for the landowner who is clearly not managing his/her weed problems adequately.

The important thing to remember if you’re a rancher, however, is that the sunflowers are not outcompeting perennial grasses.  Instead, the sunflowers are opportunists, taking advantage of the fact that grasses are weak.  As perennial grasses recover from last year’s drought and/or grazing, they will reclaim the root space they lost in 2012 and sunflowers will have much less room to grow next year.  Plains sunflower is a native prairie plant, and it’s role is to fill the space left when other plants are weakened (similar to ragweeds and other opportunistic species).  If sunflower wasn’t filling that space, another “weedy” species would, and the alternative could be much worse.

Some ranchers will be tempted to spray their pastures to kill off the “invading” sunflowers, but that’s actually a counterproductive strategy.  First, the annual sunflowers are going to die at the end of the season anyway, so if you want fewer sunflowers next year, the best strategy is to focus on limiting the germination and growth of next year’s crop by allowing perennial grasses and wildflowers to regain their dominance.  Second, herbicide spraying will kill a number of other plant species that are both valuable as forage and competitors with sunflowers and other annuals.  Why spend money to weaken the long-term viability of your grassland?

It’s also important to remember that cattle do eat sunflowers – they particularly like them early in the season when the leaves and stems are tender, but will also seek out the nutritious buds and flowers later in the season.  The evidence of that can be seen right now; pastures grazed at certain times this year have many fewer blooming sunflowers than those that haven’t yet been grazed this season.  In addition, of course, sunflowers are among the most valuable grassland plants in a prairie for wildlife and pollinators.  They produce large nutritious seeds for birds and other wildlife, and have abundant and accessible supplies of nectar and pollen that attract numerous pollinator species.  In short, sunflowers may not be everyone’s favorite plant, but they’re far from a useless weed or invasive threat.

For those of you who started out reading this post as fans of sunflowers, good for you!  If you get the chance, you should take a drive through Nebraska’s sandhills this summer and enjoy the scenery – it’s not likely that we’ll see another year like this for a while.  For those who are appalled by the abundance of sunflowers this year, maybe you can take some comfort from the fact that it’s a temporary phenomenon, and one tied to a particular combination of weather factors more than anything you or others did as land managers.  Things will be different next year.

Regardless of whether or not you like sunflowers, I guess there’s one thing we can all agree on.  The year 2013 will be one to remember!

Note:  Nebraska has nine species of native sunflowers, seven of which are perennials.  All of them are valuable for wildlife and pollinators, and important components of a healthy grassland community.

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