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).

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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.