The Bench Strength of Prairies in the Face of Climate Change

In case you hadn’t noticed, the climate is changing.  Things are getting weird, and they’re going to get weirder.  Here in central North America, we’re expecting more and more intense storm events and drought periods in the coming decades.  Scientists are scrambling to figure out how to predict and facilitate the inevitable changes those crazy weather events will bring to natural systems, including prairies.

Fortunately, prairies have been training for this for a very long time.  A few months ago, I wrote a post about the resilience of prairies, and how that resilience is built largely upon the diversity within their ecological communities and the size and connectivity of prairie habitats.  Prairies that are relatively big and still have the majority of their potential plant and animal species are going into this encounter with rapid climate change with what you might call solid bench strength.

Diversity of plants and animals is the keystone to ecological resilience. The Nature Conservancy’s Nachusa Grasslands, Illinois.

In sports, teams want to have lots of available players that represent a broad diversity of skills.  Each opponent they face will have its own individual mix of power, endurance, speed, and other attributes.  A successful team can build a roster for each game that counters their opponent’s strengths, no matter what they are.  The number and quality of their players is a team’s bench strength.

Healthy prairies have great bench strength too.  No matter what gets thrown at them, they can adapt by changing their roster of species.  The speed at which they can drastically change the makeup of their “team” is impressive.  Anyone who has spent many years watching the same prairie has seen this in action, but none of us have seen prairies go through what Professor John Weaver saw back in the 1930’s and 40’s.

Weaver, one of the best known prairie ecologists of all time, had been studying 30 “large typical prairies” across parts of Nebraska, Iowa, Kansas, and Colorado prior to the start of the Dust Bowl era.  His baseline data gave him an invaluable opportunity to document the dramatic changes to the plant communities of those prairies during and after the droughts of the 1930’s.  What he recorded, along with his former student F.W. Albertson, was an incredible testimony to the dynamism and resilience of those prairies.  Their 88 page 1944 publication, entitled “Nature and Degree of Recovery of Grassland from the Great Drought of 1933 to 1940”  encapsulates the bulk of their findings in one place, and is worth a read if you have the time.

In 2012, we got a small glimpse of what Weaver and Albertson saw in the 1930’s, but our drought – while severe – only lasted one year here in Nebraska.
In 2013, the response of the prairie to the 2012 drought included some explosions of wildflowers, including shell leaf penstemon (Penstemon grandiflorus).

One of the biggest plant community shifts Weaver and Albertson documented was the widespread and dramatic death of grasses such as big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), and Kentucky bluegrass (Poa pratensis), and the subsequent rise of other grasses such as prairie dropseed (Sporobolous heterolepis), sand dropseed (Sporobolous cryptandrous), porcupine grass (Stipa spartea), and most of all, western wheatgrass (Pascopyrum smithii).  Western wheatgrass populations exploded throughout the mid to late 1930’s, to the point where many prairies were completely dominated by it, to the near exclusion of other plant species. In fact, in a 1942 publication, Weaver said the following, “The large area of drought-damaged true prairie and native pasture now dominated by western wheat grass and the harmful effects of the successful competition for water of western wheat grass with species of greater forage value present a problem of much scientific interest and great economic importance.”

In other words, as they made massive substitutions within their lineups, prairies were changing so much they became almost unrecognizable, even to those who knew them best.  Weaver and Albertson watched waves of forb species they’d always considered to be of little value become stars on the field, and they and others didn’t quite know how to react.  Daisy fleabane (Erigeron strigosus), Missouri goldenrod (Solidago missouriensis), and heath aster (Aster ericoides) were all examples of wildflowers that suddenly rose to prominence in new and major ways.  The two dismayed scientists described how heath aster, a “nearly worthless native forb,” formed near monocultures across wide swaths of prairie, to the extent that it “ruined many of the prairies…for the production of hay, because of its brush-like growth.”  Others were out of their depths on this too, and Weaver and Albertson reported that “considerable native sod was broken because of the seriousness of this pest.”  In the following sentence, however, they begrudgingly added a short sentence, “Of course, it did protect the soil.”

While Weaver and Albertson considered heath aster to be “nearly worthless” it plays an important role in the prairie, and is an important food source for pollinators in the fall.

Exactly.  While the strategy was foreign and frightening to those who hadn’t seen prairies dealing with these kinds of conditions before, those prairies were just doing what they’ve done many times before – making whatever roster adjustments were necessary to keep functioning at a high level.  In addition to forb species they denigrated as weeds, Weaver and Albertson noted that many wildflowers with “large storage organs”, including bulbs and corms, also greatly expanded their population size during the dust bowl years.  This included species like Violet wood-sorrel (Oxalis violaceae), bracted spiderwort (Tradescantia bracteata), windflower (Anemone caroliniana), and wild garlic (Allium canadense).  Those species and others increased the size of the patches they’d occurred in previously, but also were found “in many new locations.”  Other native forbs that became superabundant in some prairies, especially early in the dust bowl years, included prairie ragwort (Senecio plattensis), white sage (Artemisia ludoviciana), and yarrow (Achillea millefolium).

Windflower (Anemone caroliniana) was one of the wildflowers with “large storage organs” that proliferated during the droughts of the 1930’s.

As rains started to return in the early 1940’s, Weaver and Albertson watched with amazement and renewed optimism as plant communities started “recovering”, which of course meant they were returning to a composition more familiar to the people observing them.  Grasses were often the first to rebound in prairies, including big bluestem, which initially formed large and lush monocultures in many places.  Wildflowers that hadn’t been seen for seven years or more, suddenly appeared everywhere, including blue-eyed grass (Sisyrinchium campestre), which grew “more thickly than if the stands of 7 normal years had been combined.”  Downy gentian (Gentiana puberula), which had been considered rare prior to the big droughts, became much more common in the early 1940’s than Weaver and Albertson had ever seen before, with abundances of “15 or more plants in a space of a few rods”.

Stiff sunflower (Helianthus pauciflorus) returned fairly quickly to “normal abundance” by 1943, as did many others, including silverleaf scurfpea (Pediomelum argophyllum), cream wild indigo (Baptisia bracteata), and buffalo pea (Astragalus crassicarpus).  Prairie violets (Viola pedatifida), pussy toes (Antennaria neglecta),  and others came back more slowly, but returned nevertheless.  Importantly, those returning species didn’t appear to be traveling from long distances.  Instead, they simply re-emerged, either from seeds or underground buds, from where they’d been sitting on the metaphorical bench, awaiting the call to step up to the plate again.

Buffalo pea (Astragalus crassicarpus) and many other wildflowers recovered from the long droughts at a speed that amazed Weaver and Albertson.

The prairies we know today have been through a lot.  In Nebraska and surrounding states, we have specific documentation of the kinds of extreme roster changes prairies can and have made to adjust to the world around them, thanks to the work of John Weaver and F.W. Albertson.  If you have a favorite local prairie, and I hope you do, it’s important to remember that the way it has looked for as long as you’ve known it is only a small sample of what it’s capable of.  Smart teams don’t reveal their secrets before they need to.

As we work to keep prairies healthy through this period of rapid climate change, it’s both useful and reassuring to remember what they’ve been through before.  Today’s prairies certainly have additional challenges to deal with today, compared to the dust bowl days (more invasive species, more landscape fragmentation, etc.), but many should still have sufficient bench strength to make the adjustments they’ll need to make in the coming years.  Our responsibility is to provide management that helps prairies sustain their plant and animal diversity, as well as to protect prairies from additional conversion to cropland or other land uses.  Where possible, restoring prairie habitat around and between prairie fragments can also help build resilience.  In short, we have to allow prairies to do what they do best – adapt and adjust.  Prairies are wily veterans and they’ve been in this game for a long time.  It’s a good bet they’ve still got a few tricks up their sleeve.

Prairie Word of the Day – Disturbance

It’s been too long since the initial installment of what was intended to be a regular feature of this blog – the Prairie Word of the Day.  Since one blog post does not make a series, I figured I’d better at least write one more.  I will try to add more to the series relatively soon. 

If you read this blog or any other source of information about prairie ecology or management, you’re likely to have seen the term “disturbance” used in some context (e.g., “ecological disturbance,” “disturbance regime,” “disturbance in the force”).  Ok, that last one is from a different context, but nevertheless.

Outside of prairie ecology or other ecological conversations, a disturbance is often something that requires contacting the police.  However, in almost every case, prairie managers would appreciate you not calling the police in response to disturbances in a prairie.  So what does the word “disturbance” mean in an ecological context?

Fire is one of the big three historical disturbances to which prairies are adapted to and rely on.
Fire is one of the big three historical disturbances to which prairies are adapted to and rely on.

It’s probably easiest to think about a disturbance in a prairie as something that disrupts the lives and processes of prairie organisms and creates a shift in the competitive balance among those species.  Historically, the big three disturbances in grasslands were fire, grazing, and drought.  Fire and grazing are still used as management strategies today, along with mowing/haying and, sometimes, herbicide treatments.  Drought (and other significant weather events such as a flood) is not something managers prescribe or apply to a prairie, but it certainly has significant impacts.

Both “natural” disturbances and those prescribed by prairie managers are critically important to the health of prairies, despite the fact that they have significant impacts on species.  In fact, many animals, plants, and other organisms often die as a result of disturbances.  Prairies, however, more than most other ecosystems, are not only well suited to survive disturbances, they are defined by and rely on those disturbances.  Without fire and drought, for example, prairies wouldn’t even exist – they would be woodlands instead (and who wants that??).

Every time a fire burns through a prairie, grazers chomp off much of the vegetation, or an extended drought turns a prairie brown in mid-summer, the competitive balance in a prairie is altered.  Depending upon the timing and intensity of a fire, for example, it’s likely to kill some trees and “top-kill” others, forcing them to restart from buds at or below the surface of the ground.  Fires can also kill or suppress the growth of other plant species, especially those most actively growing at the time of the fire.  At the same time, fires create opportunities for other plants – especially those in direct competition with the ones suppressed or killed.  Plants that thrive best in full sunlight and don’t do well under layers of thatch or beneath tall plants also respond very favorably after a fire.

These cedar trees died in a recent fire, but the vegetation around them is regrowing strongly. In fact, the cattle (in the distance to the top right) in this prairie will be attracted to that growth and graze this part of the prairie much harder than unburned parts.
These cedar trees died in a recent fire, but the vegetation around them is regrowing strongly. In fact, the cattle (in the distance to the top right) in this prairie will be attracted to that growth and graze this part of the prairie much harder than unburned parts – adding a second disturbance to the first.

Of course, fires can also kill or injure wildlife or insect species (not to mention microorganisms and other life forms) that are aboveground at the time of the fire and can’t evade the heat and/or smoke.  The season in which a fire burns plays a big role in which organisms are affected.  Dormant season fires can kill insects and other species that overwinter in vegetation or along the surface of the ground, but growing season fires cause even more fatalities because so many more species are active during that time of year.  Even animals that survive the fire itself may have to travel to unburned areas in order to find suitable habitat, and those trips can be hazardous as well.

Despite the immediate negative impacts of fire on individual insects, wildlife, and other species, however, periodic fire usually has longer-term benefits – even for those species that suffer fatalities.  Without fire – or some other disturbance that removes vegetation – prairies can become so overgrown that most species can’t survive there.  Suffocating layers of thatch, encroachment by trees and shrubs, and the potential for diseases and predator populations to build up over time are all conditions that can be found in prairies that go undisturbed for long periods of time.  In addition, if the same habitat and growing conditions prevail year after year in a particular patch of prairie, some species will thrive but others will not – leading to a loss of species diversity and overall prairie health.

Without going into details here, the impacts of drought and grazing on prairie species are similar to those of fire – each event will favor some species over others.  Prairie plants are well adapted to periodic burning, grazing, or drought.  Perennial plants have numerous buds at their base, from which they can grow new shoots after they’ve been burned or cropped off, and most can enter dormancy during a severe drought in order to conserve resources for better days.  Shorter-lived plants often rely on disturbances to create opportunities for them to grow with less competition from nearby perennials.  Those annual and biennial plants produce copious amounts of seed that fall to the ground and wait until the next time conditions favor their germination and growth.

Every vertebrate and invertebrate animal species relies on a particular set of habitat conditions.  Some thrive when vegetation is short and sparse, and others prefer tall dense vegetation.  The highest diversity of animals and insects is usually found where perennial plants have been recently weakened by fire, grazing, and/or drought, and short-lived plants are thriving while those perennials recover.  In any case, habitat conditions are tied to disturbances – some conditions are created during or in response to a disturbance, and others (tall dense vegetation) are created when a disturbance hasn’t occurred for a while.

Prescribed fire, along the grazing and mowing, are important ways for prairie managers to introduce disturbances into grasslands in order to maintain prairie health and biological diversity.
Prescribed fire, along the grazing and mowing, are important ways for prairie managers to introduce disturbances into grasslands in order to maintain prairie health and biological diversity.

As prairie managers, our job is to provide habitat and growing conditions for as many prairie species as possible.  We burn, graze, and mow prairies at prescribed intervals (and usually in patches, rather than across an entire prairie) in order to maintain a competitive environment in which all those prairie species can survive.  Whenever we burn a prairie or introduce large grazers to it, we know that some species will be harmed by that action, but that others will flourish because of it.  As long as we allow a patch of prairie to recover between disturbances and create a patchwork of habitats (some recently disturbed and others not), the prairie community will remain diverse and resilient.

Prairie management is complicated, and it can be difficult to make decisions and take actions that you know are going to negatively impact some species.  On the other hand, the other choice is to do nothing.

And that would be disturbing.

A Walk in What Used to be Woods

I drove up to the Niobrara Valley Preserve this week and arrived in time for a long hike before dark on Monday evening.  It was the kind of opportunity to wander and think that is critically important (but unfortunately rare) for land managers and ecologists.  I focused my time north of the river where steep ridges and “foothills” full of pines, bur oaks, prairie, and lots of eastern red cedar trees had experienced an intense summer wildfire during the severe drought of 2012.  Since the fire, our staff has been having lots of discussions about how we should be managing the site and its recovery.  It was great to have a few hours to just hike around, observe, and think.  I took some notes in my field notebook as I walked.  Here are a few of those notes (in italics), fleshed out with some of the further thoughts.

fallen ponderosa pine in 2012 wildfire area at TNC's Niobrara Valley Preserve, Nebraska.
A rare fallen ponderosa pine in 2012 wildfire area at TNC’s Niobrara Valley Preserve, Nebraska.  Most of the trees killed by the fire are still standing, and probably will be for many years to come.  This photo is looking southeast from the hills on the north side of the Niobrara River, where fire intensity was very high and killed nearly every pine and cedar tree.

No young cedar or pine trees anywhere.

As we started to assess the impacts of the wildfire, many of my biggest questions had to do with the future of this area north the river, where ponderosa pine and bur oak trees had been abundant, along with an extensive population of eastern red cedar.  I knew the Sandhills prairie would recover just fine (and it has), and I figured we wouldn’t see much pine re-establishment for a long time (none so far), but I was most concerned that cedars would re-infest the slopes north of the river faster than we could control them.  Because the pines and cedars had been so thick in many areas, I guessed it would be a while before grass colonized sufficiently to support a prescribed burn hot enough to kill cedar trees, and I worried that we’d end up right where we’d been within 10-15 years (except with all cedars and no pines).  As it happens, the grass is filling in pretty well in many places, but I haven’t seen a single young cedar tree yet.  Researchers from the University of Nebraska-Lincoln, who are helping us study the area, have apparently seen a couple, but they are exceedingly rare.  (One of those researchers, graduate student Amanda Hefner, is working to answer many of the questions we have about the recovery of these wooded areas.)

I’ve been talking to other people about their experiences with hot prescribed fires or summer wildfires that wiped out cedar trees in Nebraska grasslands.  Typically, without follow-up fire, a dense regrowth of cedars reaches head high or so within about 10 years.  Based on what I’m seeing so far, I don’t think we’re going to see that kind of rapid reestablishment.  So, why?  Did the fire scorch the seed bank?  Is the area far enough away from other fruiting cedar trees that it is temporarily safe from reinvasion?  I really need to spend some time walking near the edge of the big wildfire to see what the cedar re-invasion looks like there.

 

The wildfire didn’t appear to affect sumac, plum, or other deciduous shrubs – even in hottest areas.

A big topic in the prescribed fire circles here in Nebraska has been the proposal that we should consider conducting burns in hotter and drier conditions than we usually do.  University of Nebraska Range Ecologist, Dirac Twidwell, has been leading this push.  Research that Twidwell and others conducted in the southern Plains showed some dramatic positive results from summer burning under severe drought conditions – including mortality of some re-sprouting tree species that hadn’t previously been thought to be susceptible to fire.  I’ve been wondering about using hotter summer fires, perhaps during drought conditions, as a way to combat high populations of deciduous trees and shrubs in prairies.  Maybe burning under more stressful conditions (for the trees) would reduce their populations?  I’m still thinking about that idea, but what I saw at the Niobrara Valley Preserve makes me question how likely we are to see success.  Even in areas where cedars and pines experienced crown fires, and fire intensity was at its highest during the July 2012 wildfire (in hot weather, during a severe drought), I don’t see any evidence that sumac or wild plum were hurt at all.  I can see the outline of the shrub patches that burned during the fire, and today’s patches are even bigger – and maybe more dense – than they were before the wildfire.

Eastern red cedar skeleton in 2012 wildfire area at the Niobrara Valley Preserve, Nebraska.
There is a lot to see in this photo.  In the foreground, you see strong growth of grasses beneath what had been a big spreading cedar tree that had been shading the ground prior to the fire.  If you look closely, you can also see stems of smooth sumac beneath the tree and behind it to the left – a healthy spreading population.  In the background, you can see skeletons of pines, oaks, and cedars on grassy hills above the river.

 

Most bur oaks in steep draws were single trunks before the 2012 wildfire, but out in the open, many were multi-trunk trees.  They must have seen at least one big fire in the past?

People who spend more time than I do along the Niobrara may find this to be old news, but I was surprised at how many old bur oaks had multiple trunks prior to the 2012 wildfire – evidence that they’d likely been through a relatively severe fire that had caused them to respond by resprouting from their bases.  We should cut a few of those old trunks apart to date that fire.   Interestingly, however, those multi-trunk trees seemed to be mainly (exclusively?) outside of the steep draws.  Those draws were full of pines and cedars, along with oaks and a few other deciduous trees, and there wasn’t much herbaceous vegetation (grasses, sedges, and forbs) beneath those trees.  The combination of steep terrain, lack of herbaceous fuel for fires, and high soil moisture (shade from trees and steep terrain), probably kept previous fires from being intense enough in those areas to top-kill oak trees.  However, the 2012 wildfire was a completely different animal, and now nearly all the bur oaks north of the river are starting their growth over from the base.  It will be very interesting to see if they all turn into big trees with 4-5 trunks again.

Bur oak with resprouts in 2012 wildfire area at TNC's Niobrara Valley Preserve, Nebraska.
A bur oak at the top edge of a draw.  The tree had been growing with five big separate trunks prior to the 2012 wildfire, and is now has many resprouts from its base again.  Further down into the draw, all the oaks I found had only one single trunk.

 

The steepest slopes at the top of ridge are still dominated by annuals.  Perennial grasses are filling in well elsewhere, except steep slopes under (formerly) dense cedars and pines.

In general, I’ve been pleasantly surprised by the density of herbaceous vegetation in much of the 2012 wildfire area north of the river.  Even where pine and cedar density was fairly high, perennial grasses and sedges are filling in pretty quickly.  The thinnest vegetation is in places where topography is particularly steep and where big pines and cedars had been growing most thickly.  Where trees were thin or non-existent before the fire, the vegetation responded just as I’d expect prairie to do – there is great plant vigor and species diversity.  Where the vegetation had been thinner prior to the fire because shade from trees, today’s plant diversity seems lower, and many patches are dominated by one or two grass species.  Species such as sand lovegrass (Eragrostis trichodes) and Scribner’s panicum (Panicum oligosanthes), for example, have formed near monocultures in many places.  I think these will diversify over time, so I think it’s great (and interesting) to see them for now.

Grazed sedge in 2012 wildfire area at the Niobrara Valley Preserve, Nebraska.
On this steep east-facing slope of a draw, there is still a lot of bare ground, though perennial sedges and grasses occur here and there.  Whatever the particular sedge species in this photo is, it is apparently a favorite of deer because every plant I found had been cropped very short.

However, in those steeper areas, especially near the top of the ridge, perennial grasses and sedges are still very thin, and most vegetation is annuals.  This isn’t necessarily a problem, and the annuals seem to do a pretty good job of holding the soil, but it makes me wonder about the speed and eventual trajectory of the plant community recovery in these areas.  Mostly, I’m just curious to see what happens, but I’m also a little concerned that we might see some invasive species fill in before native perennials get a foothold.  As an example, smooth brome is common in the flats above the ridge, and it’d be a shame if it also gained dominance on the steep slopes below.  I’m hopeful that the soil conditions won’t favor brome, but we’ll have to just wait and see.

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Overall, these observations just add further complexity to discussions our staff has been having about how to manage this area in the future.  We still need to decide what we want the area to become so we can guide it in that direction.  It’s all fine and good to say we’ll just let it develop however it wants to, but if the site trends toward a cedar woodland with a smooth brome understory, for example, that’s not really going to be very positive for wildlife or biological diversity.

We’d really like to encourage the bur oak trees to survive and thrive but aren’t sure what kind of fire frequency or intensity might best facilitate that.  What about deciduous shrubs?  Are we ok with letting the current clones become so large and dense that they eliminate grasses beneath them?  They would essentially be fireproof at that point, and we’d have no easy way of thinning or otherwise managing them – especially in really steep areas.  More importantly, those shrub patches would likely provide safe haven for cedars and other trees to establish and grow within those fireproof shrub clones.  Is that what we want?  If not, what are our management options?  We have lots of ideas, but still have a lot of discussing, researching, and observing to do.

These kinds of questions and challenges are why land management is interesting and fun.  I’m really looking forward to watching this area (and all the others I get to help with) continue to develop over the next few decades.

Fenceline Timelapse

I got my hands on another batch of timelapse imagery for our Niobrara Valley Preserve last week.  I now have images from all nine of the Preserve’s cameras for the 2013 growing season (late April through the middle of October).  The photos from those cameras document the first year of recovery from the drought and major wildfire back in the summer of 2012.  As I work through the many thousands of images, I’ll be sharing some of the interesting stories I see.

I’ll start with a series of images from a camera set along a new fenceline.  As the staff at the Preserve set out to rebuild fences after the wildfire, they took advantage of the opportunity to shift the location of some fence lines.  In this case, they moved the south boundary fence of the east bison pasture and enlarged that pasture to more than 10,000 acres.  The fence was constructed through what had been a traditional cattle pasture (unplowed sandhills prairie that had been conservatively grazed by cattle for many years).  We chose to place a camera along that new fence for two reasons.  First, it was a good place to watch the recovery of the prairie plant community following the fire.  Second, it provided a good chance to look for differences between bison-grazed and cattle-grazed prairie.

Here is a slideshow of images from the 2013 season from May through mid-October.  If you hover your mouse over the images, you can click on the arrows and fast forward (or backward) through the photos to look at changes over time.  The left side of the fence is now bison pasture, while the right side is still cattle pasture.  Below the slideshow, I’ve written about some of what I see as I look through the photos.

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The first thing that’s obvious in the images is the rapid recovery of the prairie’s plant community from an intense drought and wildfire.  In the first image (May 2) it looks like there is nothing but bare ground.  Even the ash from the fire was washed/blown away, leaving almost nothing above ground.  However, as spring arrived, both annual and perennial plants seemed to jump out of the ground and fill the landscape with green vibrant vegetation.  It’s difficult to identify many of the plants, given the scale and resolution of the images, but there are two major flushes of blooms – the very pale pink flowers of wild roses (Rosa arkansana) in June and the yellow plains sunflower (Helianthus petiolaris) in August.  You might remember reading about the abundance of sunflowers across much of the sandhills from an earlier post.

One of the reasons I chose this particular location for the camera was to watch the yucca (aka soapweed or Yucca glauca) plants over time.  There is very little yucca in our bison pastures at the Niobrara Valley Preserve, but it is fairly common in cattle pastures.  That has less to do with bison grazing vs. cattle grazing than with the fact that the bison are in the pastures through the winter and the cattle are pulled out in the fall.  Both bison and cattle will graze on yucca during the winter because while the leaves are tough and spiny, they are green when almost nothing else is.  I think we’ll get to watch through time as the yucca on the left side of the fence gradually disappears through years of winter grazing by bison while the yucca on the right grows relatively unhindered.  We’ll see!  To see the yucca, it’s best to start on the last image of the slideshow (October 21) and look for the spiny green plants surrounded by brown vegetation.  Then you can watch those plants grow as you click from May through October.  Since I haven’t seen the images from this past winter yet, I don’t know if bison have been grazing the yucca, but I sure hope so (for the sake of the story…).

One difference that can already be seen between the bison side of the fence (left) and the cattle side is the formation of a trail along the cattle side of the fence.  I will provide more information on that in a post that will come out very soon, so I won’t talk much about it here except to say that while the formation of numerous trails are definitely a real difference between bison and cattle pastures, they are not necessarily a bad thing.  More on that topic, with a VERY interesting couple of timelapse photos, coming soon.

One last observation is that either the camera or fence moved quite a bit through the season, and since the fence clearly didn’t move, it had to be the camera.  I’m not sure how to explain that.  I don’t think it was being bumped when the memory cards were swapped out every month or two because the movements occurred in between those events as well.  I imagine the most likely scenario is simply that the massive wooden post we stuck in the ground (with concrete) shifted in the sandy soil.  We’ll see if that continues over time or if it settles into a location.  It’s not a problem, just something interesting.

Finally, one of the great things about timelapse imagery is the opportunity to capture beautiful images without having to be there to click the shutter on the camera.  Here are three photos from this camera that I thought were particularly pleasing.

Sunrise on August 19, 2013.
Sunrise on August 19, 2013.

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Moonlit prairie on the same day as the above photo - August 19, 2013
Moonlit prairie on the same day as the above photo – August 19, 2013

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Lightning during the night on June 21, 2013.  Wild rose flowers can be seen in the glow of the lightning.
Lightning during the night on June 21, 2013. Wild rose flowers can be barely seen in the glow of the lightning.

Many thanks to Mike Forsberg, Jeff Dale, David Weber, and everyone else at Moonshell Media that has been working on this timelapse photography project with us.  Special thanks also to the Nebraska Environmental Trust for funding the installation of the cameras as a way to help us better understand the effects of wildfire on Nebraska’s ecosystems.

Sunflowers!

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.

Photo of the Week – June 7, 2013

Prairies demonstrate their resilience regularly, but usually in a fairly subtle way.  They tend to adjust their plant composition after fire, grazing, or drought in ways you might not notice unless you were a botanist.  Once in while, however, prairies take it to the next level and really show off.

A profusion of penstemon in restored sandhill prairie at The Nature Conservancy's Platte River Prairies.
A profusion of penstemon in restored sandhill prairie at The Nature Conservancy’s Platte River Prairies.

Last year was the driest year on record for this area.  We had less than half of our average annual rainfall, and most of that came early.  By late August, very little green was left in most of our sites.  The prairie shown above had been burned in the spring and grazed most of the season.  Many people seeing it for the first time would have assumed it was dead and gone (see photo below).

This is the same portion of prairie shown in the first photo, but this images was taken August 24, 2012 after a year of fire, grazing, and severe drought.  Most of the green in the photo is western ragweed and a little goldenrod.
This is the same portion of prairie shown in the first photo, but this images was taken August 24, 2012 after a year of fire, grazing, and severe drought. Most of the green in the photo is western ragweed and a little goldenrod.

I’ve written about the ecological resilience of prairies before, and have presented long-term data showing how our prairies fluctuate in plant composition over time in response to drought, grazing, fire, and various combinations of those factors.  Many plant species rise and fall in abundance as conditions change (opportunistic species) and others tend to maintain a steady population size, though they may be more or less visible in particular years.  It’s one thing to see that in graphs and tables, but it’s also fun to see a spectacular green-up and explosion of wildflowers in person, especially after a long dry (brown) year.

In the sandhill prairie shown above, last year’s drought caused most of the perennial plant species to enter dormancy by July – effectively giving up on that season’s growth and reproduction potential and saving their remaining energy for the next year.  Before they went into dormancy, however, the perennial grasses had already been weakened by relatively intense grazing, reducing the size of their root masses and opening up space for opportunistic species to take advantage of.  One of those opportunistic species is the short-lived perennial shell-leaf penstemon (Penstemon grandiflorus) which is obviously thriving this season.  Shell-leaf penstemon has been generally increasing in abundance since this prairie was seeded in 2002, but it took a gigantic leap forward this year.  Based on what I’ve seen in other prairies, I expect it to decline in abundance over the next couple of years as the dominant grasses and other long-lived perennials recover from last year’s stress.  In the meantime, we’re happy to enjoy the prairie’s flamboyant demonstration of resilience.

Junegrass (Koeeria macrantha) is also having a great year, and provides a beautiful counterpoint to the penstemon in this photo.
Junegrass (Koeeria macrantha) is also having a great year, and provides a beautiful counterpoint to the penstemon in this photo.

If you’re in the area, now is a great time to come hike our trails.  Both the upland and lowland trails through the Platte River Prairies cut right through huge patches of penstemon.  If you’ve never been to our trails, you can find directions and more information here.

The mowed hiking trail through sandhills provides excellent exposure to the penstemon profusion this season.
The mowed hiking trail through the sandhills takes you right through penstemon profusion this season.

Should We Be Conducting Prescribed Fires During Drought?

As we enter a second year of drought in central Nebraska, I’m starting to hear discussions about whether or not it’s a good idea to conduct prescribed fires when conditions are so dry.  I have some ideas about this, but am curious to hear other perspectives as well.

Whether or not to burn in a drought year can be a tough decision to make.
Whether or not to burn in a drought year can be a tough decision to make.

Those of you who read this blog regularly will not be surprised that my answer starts with, “It depends upon your objectives.”

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Happy New (Dry) Year – 2013

Happy New Year!  It sure is nice to start 2013 with some moisture on the ground.  Let’s hope we get some more…

A welcome snowfall in late December will help replenish soil moisture, but it's still awfully dry.
A welcome snowfall in late December will help a little to replenish soil moisture, but it’s still awfully dry around here.  Helzer family prairie, near Stockham, Nebraska.

Ecologically speaking, the biggest local story in 2012 was the dry weather.  In fact, our nearest “large” city, Grand Island, Nebraska had its driest year on record.  The precipitation total came in just under 12 inches for 2012, breaking the previous record of 12.01 inches from 1940.  The average annual rainfall for Grand Island is about 26 inches, so 2012 precipitation was less than half of normal.  That’s pretty dry.

Back in 1940, the famous prairie ecologist, J. E. Weaver, was looking at the effects of about a decade’s worth of drought.  At the time, he and others assumed that many of the drastic changes they were seeing in prairie plant communities would be permanent.  In fact, quite a few prairies were plowed up in the early 1940’s because the owners figured that if the prairie grasses were dead, they might as well try to grow something else.

Fortunately, Weaver was wrong about the drought-stricken prairies in the 1940’s.  The plant communities he thought were irrevocably changed, and the plant species he thought would disappear rebounded nicely in subsequent years.  It’s hard to know whether 2012 was a dramatic, but short, dry spell or the beginning of another long drought for our part of the state.  Either way, it’s good to know that prairies and their inhabitants will survive, one way or the other.

Prairies look pretty dry this year.
The drought of 2012 left most of our prairies dry and crispy by mid-summer.  However, not all plants were affected equally, and some – like annual sunflowers – were able to flourish.  Other species entered dormancy early to conserve energy and moisture for the future.

As we enter 2013, the local long-range forecast is for average rainfall through the early growing season.  That would be great.  However, because we’ll start out with a significant deficit in soil moisture, our prairies will show the impacts of 2012 for quite a while yet.  And, of course, long-range forecasts are notoriously inaccurate, so we may not get the rains we’re hoping for anyway.

It’s easy to feel a little down during droughts – especially for those of us who rely on prairies for income as well as for enjoyment.  Trudging through crispy brown grass day after day can take a toll on the psyche.  However, since we can’t change the weather, the best strategy is to just sit back and watch prairies exhibit their most defining attribute…

…resilience.

I hope you have a tremendous and intriguing 2013.  As always – thanks for reading.

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2013 is off to a good start – with snow on the ground. Let’s hope that moisture keeps coming.

(Here’s a link to another interesting paper by Weaver, written in the mid-30’s before the worst of the drought had happened. Even at that time, he was already using terms such as “destruction” to talk about what was happening to prairie plant communities.)

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The Great Drought (Again)

A warm and dry winter, followed by a hot dry spring and summer…  Temperatures over 100 degrees Fahrenheit for weeks at a time…  Wildflowers blooming two to three weeks earlier than normal, and often for much shorter periods than typical…  Other plants withering and/or going dormant before they get a chance to bloom.

Sound familiar?  It’s a good description of the conditions across much of the central United States in 2012.  However, it’s also a description of eastern Nebraska back in 1934. The famous prairie biologist, J.E. Weaver and two colleagues published a 1935 paper detailing the response of prairie plants to the “great drought of 1934”, in which they describe the weather conditions and plant community responses in prairies near Lincoln.  The similarities between the drought of 1934 and 2012 are pretty strong.  The main difference  is that much of Nebraska actually had fairly wet conditions during the spring and summer of 2011, whereas in 1934 the extreme drought came on the heels of dry seasons in both 1931 and 1933.  Apart from that, a warm dry winter, very low rainfall, and extraordinarily long stretches of very hot temperatures characterized both 1934 and 2012. 

Most prairies look pretty dry this year.  In this burned and grazed prairie, only the most drought tolerant plants, including plains sunflower, western ragweed, and prairie sandreed, are still green.

The paper by Weaver, Stoddart, and Noll is interesting for a couple reasons.  First, it’s nice to see evidence that prairies have been through the kind of conditions we’re experiencing this year, and to know that those prairies rebounded.  We all know prairie communities are resilient, but with a high likelihood of more frequent and intense droughts in our future, it’s comforting to see some historical evidence that prairies have the capability to handle extreme weather (in fact, the drought of 1934 was followed by drought conditions for most of the rest of that decade).  Second, the authors describe the way individual plant species responded to the drought conditions of 1934, and it’s both fascinating and reassuring to see the same plant species responding in similar ways now.  Weaver and his colleagues describe the overall appearance of the prairie, season by season, and discuss the relationship between the ability of species to withstand drought conditions and their rooting depths and architecture.  Also of interest, Weaver published a follow-up paper in 1936, describing the way prairie plant communities looked in 1935 – one year after the big drought.

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Sunflower Party Time!

Plains sunflower (Helianthus petiolaris). This species is dismissed by many as a roadside or cropfield weed.

Sunflowers are seen by some people as big beautiful flowers, and by others as big ugly weeds.  Regardless of aesthetic opinions, however, sunflowers appear to be pulling their weight, and more, in the ecology of the Nebraska sandhills prairies this year.  After a long dry year, there’s not much green, let alone blooming, in the sandhills right now.  The biggest and most obvious exception is the plains sunflower (Helianthus petiolaris).

Plains sunflower, an annual, is one of the few flowers still blooming in the dry sandhill prairies this summer.  Most other plant species have already gone dormant.

While most other plants have given up on this year’s growth because of the very low soil moisture, these annual sunflowers are acting like it’s party time.  I imagine the long taproot helps the plant get deep moisture, but its root system isn’t any bigger or deeper than many other sand prairie plants, which sit brown and withered in the surrounding landscape.  Of course, being annual plants, plains sunflowers don’t really have the option that perennials do to just shut down for the remainder of the season during stressful years.  Once a plains sunflower seed germinates, it’s got exactly one growing season to flower and make seeds before it dies.  If it had a motto, it would be something like “Live like there’s no next year!”

A bee fly feeding on a plains sunflower.

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I’ll bet this fly is grateful for sunflowers.

There are a lot of insect and other species that should be awfully thankful for the ostentatious blooming of the sunflowers this year.  Sunflowers are probably the only thing keeping most pollinators alive at the moment, for example.  That’s great for those pollinator species, of course, but also for the predators and parasitoids that live of those insects. 

A cuckoo wasp rests on an annual sunflower.  These wasps lay their eggs in the nests of solitary bees, and the wasp larvae hatch and devour the young bee larvae and their provisioned food.  Thanks to Mike Arduser for the identification.

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This grasshopper is probably more glad about the green foliage than the flowers – although it may feed on the flowers as well.

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An ant on a sunflower petal. While it makes a good photo, I don’t think the ant was actually interested in what was on the front of the flower.

Ants have their own reasons for appreciating sunflowers – largely independent of the big showy flowers.  Sunflowers produce and excrete sweet sticky sap (known as extra-floral nectar) that attracts hungry ants.  It’s thought that attracting ants in this way might help repel herbivorous insects that might otherwise feed on the sunflower’s leaves and stems.  Ants are not predators to mess with if you’re a hungry caterpillar or other plant-eating insect… 

You can read more about prairie ants here

Ants collecting extrafloral nectar from the backside of a sunflower blossum.

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The density of ants on some sunflowers was pretty impressive. I’m not sure if this is out of the ordinary because other food sources are limited, or if I was just noticing more of them because there wasn’t much else to look at…

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This assassin bug (a predator) is also taking advantage of the attractiveness of sunflowers to other insects.

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Not only are the sunflowers stil blooming – there are more flowers yet to come! What an amazing plant.

While sunflowers are filling an important role this time of year, that importance might actually increase this fall and winter.  The seed crop for birds and other wildlife is going to be pretty paltry this year.  Sunflower seeds are always a favorite of migrating and wintering animals, but this year, they will be especially critical.  So – party like there’s no tomorrow, sunflowers.  And, on behalf of the inhabitants of the sandhills prairies… thank you!

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