Exploring and Speculating in the Snow

Snow is a great boon to anyone trying to figure out what’s happening in the prairie during the winter. I’m just a casual observer, not a researcher of winter activity, but it’s definitely a topic of interest. A fresh snow fall provides a chance to look at tracks and try to interpret what’s happening.

Last week, I saw a couple interesting things in nearby snow-covered prairies. The first is something I’ve seen often before, which is evidence of the importance of western ragweed as a winter food. Ragweed plants sticking up above the snow are very commonly surrounded by bird tracks, and I saw lots of that at our family prairie last week.

Western ragweed (Ambrosia psilostachya) sticking out above the snow last week, showing the large nutritious seeds just sitting there ready to eat!
Bird tracks around western ragweed plants.

I know people tend to scoff at, or actively dislike ragweed, but it’s hard to dispute its value to wildlife. I understand those of you with severe allergies to ragweed pollen not being fans. Beyond that, though, it tends to get an undeserved bad rap from farmers/ranchers who mistakenly think it is aggressive and outcompetes grasses. The reverse is true – its populations expand when the grasses are weakened and shrink when grasses are strong.

Others dismiss it because it is a ‘weed’ and/or doesn’t have showy flowers to attract pollinators. Sure, it’s very common, and perpetual high abundance can be a sign of poor prairie management, but it’s also a native plant that plays an important role in grasslands. In addition to its ability to fill and temporarily hold space when the surrounding plant community is stressed, it’s impossible to dismiss the attractiveness of its seeds to wildlife. If you have any doubt, look for ragweed plants the next time you’re in a snowy prairie. Most likely, you’ll be able to follow tracks right to them!

Here, you can see both bird tracks and a few dropped seeds below the plants, where birds were pulling other seeds off to eat.

The second interesting thing I saw last week connects to another observation earlier this year. Back in April, I was walking through a recently burned area at Prairie Plains Resource Institute’s Gjerloff Prairie and found a pile of seeds I’m pretty sure were from marbleseed, aka false gromwell (Onosmodium molle). They might also have been from fringed puccoon (Lithospermum incisum) – the seeds of those two species are awfully similar.

Seeds at Gjerloff Prairie after a spring prescribed fire. I think these are from marbleseed, based on their size, though they might have been puccoon seeds too.

The way the seeds were gathered together made me think it was a seed cache, created by some kind of mouse the previous year. The fact that it was still there after the winter made me wonder if the mouse didn’t survive (or just didn’t find its cache). Either way, it was neat to see and fun to speculate about.

Last week, at our family’s prairie, after perusing the bird tracks around ragweed plants, I came across a mouse trail that led to a small area where it looked like the mouse had dug down to the ground. The tracks led pretty directly to the excavation site, making me think the mouse probably knew where it was going (as opposed to just wandering/foraging randomly).

Mouse tracks and an excavation.

Looking closely in the hole, I saw some seeds that looked just like the ones I discovered at Gjerloff Prairie back in April. Aha! More evidence. I know mice create seed caches, but I don’t know much about what kinds of seeds they might store, where they store them, or how good they are at finding them later. If anyone can enlighten me on this subject, I’d love to hear from you.

Here’s another photo from a little closer to the hole. I used Photoshop to open up the shadows and show the details inside the hole, and you can just barely see a few remaining seeds at the bottom. (Click on the image to see a closer view).

Just based on observation and speculation, it looks to me like some small mammal harvested and piled some marbleseed/puccoon seeds up – presumably in the early to mid summer when those seeds were ripe. (Based on a lot of years of seed harvesting, those seeds disappear from plants pretty quickly after they’re ripe – probably because of mice!) Then, on a sunny day after a snow, that same mammal (?) appears to have trekked across the snow and dug up the cache. Did it know exactly where it was? Based on the tracks, it sure looked that way to me – either that or it somehow smelled the seeds beneath the snow. One way or the other, I’m impressed.

As I said at the beginning of this post, I’m no expert on winter survival, especially by birds and small mammals. I do, though, enjoy trying to figure out what I can learn through observation, and snow is really helpful in that venture. Last week’s snow is melting fast now, but I’m hoping for a few more chances to explore later this winter. If anyone can help me interpret what I saw in these photos, I’d sure appreciate it!

Plants On The Move!

Recently, I’ve posted a lot about our timelapse photography project documenting the recovery of the Niobrara Valley Preserve from a 2012 wildfire.  Repeatedly photographing the same scenes over three full field seasons has been a great way to show ourselves and others the resilience and beauty of the natural communities in the Niobrara River Valley.

We tried something a little different with one of the nine cameras we deployed – we set it up on a boom and pointed it straight down at the ground in bison-grazed prairie.  My hope was to document the recovery of individual plants by watching from above.  I also hoped to use the long-term nature of the timelapse process to showcase how much those plants move around from year to year.  With the help of Jeff Dale of Moonshell Media, we got the camera installed in April of 2013 and have been watching from above ever since.

One of our nine timelapse cameras; this one aimed straight down at one patch of prairie. The Nature Conservancy's Niobrara Valley Preserve, Nebraska.

One of our nine timelapse cameras; this one aimed straight down at one patch of prairie (and armored to protect it from being rubbed on by bison). The Nature Conservancy’s Niobrara Valley Preserve, Nebraska.

Most people think of plants as pretty immobile (“rooted in place”, you might say) but that is definitely not the case for many species.  Plant communities are battlefields in which various forces are always looking for new territory to conquer.  Plants use features such as seeds and rhizomes (underground stems) to travel around and establish themselves in new places.  Some plants move short distances but hold their territory tightly, while others range more widely but have less staying power.  When you stand in a prairie, you stand on top of a dynamic and complicated power struggle among plants that are anything but immobile.  Because that struggle happens in relatively slow motion (over months or years rather than minutes), timelapse photography can provide a unique opportunity to watch battles play out.

Photos taken from above may not have quite the same scenic value as those from cameras that include lots of sky, river, and other facets of the landscape, but when you stare at them long enough (trust me…) they reveal some truly fantastic stories.  To look at one of those stories, the movement of plants between years, I pulled photos from mid-June of each of the three field seasons covered by the camera.  Unfortunately, the camera shifted somewhat between 2013 and 2014 and I couldn’t quite line up the photos enough to be comfortable that I was watching the same exact area, so I cut out the 2013 photo and just used the two from June 2014 and 2015.  To save myself from having to track too many plants, I cropped the images in about half by cutting out the outer portions of each.  The resulting images were (I’m guessing here) about 5 x 8 feet in size (1.6 x 2.6m).

If you’re reading this via an email subscription, the slideshows may not display correctly.  If they don’t, try clicking on the title of this post at the top of your email to view the post through a web browser.

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In the above slideshow, you can see the two cropped photographs I used to watch plants between 2014 and 2015.  By using the arrows in the slideshow, you can toggle back and forth between them.  The big silvery-gray leadplant (Amorpha canescens) in the top right quadrant acts as a landmark between the two photos.  I focused on tracking plant species that were easy to identify (when I zoomed into the images).  Those species included stiff sunflower (Helianthus pauciflorus), cudweed sagewort (Artemesia ludoviciana), prairie wild rose (Rosa arkansana), and western ragweed (Ambrosia psilostachya).

The 2012 fire certainly affected the plant community at this site, but probably not as much as did that year’s drought.  2012 was an extremely dry year, and by the time the wildfire swept through in late July, many of the perennial plants had already gone dormant because of the heat and dry conditions.  Those dormant plants probably felt little impact from the fire because they weren’t actively growing at the time, but their vigor was likely much reduced by the combination of drought and bison grazing during the season leading up to the fire.  That impact was probably felt most by some of the dominant grasses because they were grazed most intensively by bison.  Those grasses not only suffered through dry soil conditions, but did so with shorter and shorter leaves (and thus roots) as bison continued to graze them until they finally gave up and went dormant.  When they re-emerged in 2013, their shrunken root systems couldn’t support the same number of aboveground stems as they could before the drought.  This opened up temporary aboveground and belowground space for annuals and other opportunistic plants.

As I went through the images looking for these plants, I put a dot at the base of each plant, using red dots for plants found in the 2014 image and yellow for those in 2015.  Then I put those dots on a blue background and toggled back and forth between them to look for differences.  You can do the same by using the arrow keys below each pair of images, or you can just wait and they should toggle automatically every few seconds.

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Stiff sunflower is obviously a very abundant plant in the Nebraska Sandhills, and was one of the more common within these photos as well.  It is a kind of pseudo-annual plant.  It acts as a perennial in that it sends out rhizomes (underground stems) each year, and new stems emerge from buds on those rhizomes the next year.  However, the “parent stem”, from which those rhizomes initiate, dies after only one year – like an annual plant.  Because of this quirky lifestyle, I knew I’d see a lot of shifting in the location of the sunflower plants between years, and I certainly did.  Conditions also seemed to favor survival and reproduction for stiff sunflower during 2014 because the 127 plants in 2014 apparently produced 168 plants in 2015 (within this viewframe, anyway).

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Growing season moisture was good in 2013-2015, so dominant grasses and many other perennial plants have been increasing in abundance, retaking territory from the opportunistic species that thrived in the immediate aftermath of the drought and fire.  In addition to stiff sunflower, another rhizomatous plant that seemed to expand its territory during this recovery period was cudweed sagewort.  In the images above, the number of sagewort “plants” (technically, they are ramets, or stems, of a few plants – all connected to each other by rhizomes) increased from 14 in 2014 to 30 in 2015.

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Prairie wild rose, a woody rhizomatous plant, didn’t seem to change in abundance much between 2014 (10 plants) and 2015 (9 plants – that I could see).  Wild rose can certainly move, and often forms large colonies, but at least during this short time period, it seemed to stay in about the same location.

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In what might be the most interesting result from this little photo examination exercise, western ragweed abundance dropped dramatically between 2014 (218 plants) and 2015 (98 plants).  While this is a perennial rhizomatous plant, it is not a strong competitor compared to dominant grasses and many perennial forbs.  Western ragweed is deplored by many ranchers because it can become quickly abundant following intensive grazing, and if that grazing continues yearly, ragweed maintains high populations.  Ranchers often make the mistake of thinking the visual dominance of ragweed means it is suppressing the growth of grasses, but the opposite is actually true.  The two images above show how quickly this species can be suppressed when other perennial plants are allowed to recover.

Hopefully, we’ll keep this camera running for quite a few more years, and I’ll be able to watch these and other species through multiple drought, fire, and grazing events to see how they respond.  While it’s only a single location, not a robust scientific study with replicated samples across a site, being able to watch the actions of plants so directly is a unique and valuable opportunity.