One of my favorite aspects of my square meter photography project has been the chance to closely follow the lives of individual organisms over time. For example, I’ve closely followed the progress of the two butterfly milkweed (Asclepias tuberosa) plants within the boundaries of my square meter plot. The plants bloomed beautifully back in late June, which was great, though fewer pollinators visited the flowers than I had hoped. Perhaps correlated with that, only one seed pod was produced between those two plants. Since then, I have been watching that one pod very very closely…
This week, that pod finally opened up, giving me the long-awaited chance to photograph some milkweed seeds within my plot. As it turns out, it’s a good thing I was vigilant, because that pod opened up and emptied itself out out very quickly. Within only a few days, the pod went from tightly closed to completely devoid of seeds.
While many of the seeds were blown well out of my little plot, a handful got stuck on adjacent plants, giving me the chance to photograph them. Here are some photos of those seeds as they were coming out of the pod or after they got hung up within the borders of my plot.
This post was written by Olivia Schouten, one of our Hubbard Fellows this year. Olivia is an excellent scientist, with strong expertise in plants and plant communities, as you’ll be able to see from this post.
As a biologist with broad interests, I can usually find something to love in all living things, but I’ll admit that plants have a special place in my heart. This is probably a good thing, since I’ve spent the majority of my education and professional life cultivating my knowledge of plants. I’ve found that they are often underappreciated and often overlooked, which is a shame, because plants are some of the most amazing organisms out there (in my humble opinion).
Plants, in most places, not only form the basis of the food chain, but also provide the structure of habitat. A forest with towering trees is very different than an open grassland or a sparsely vegetated desert, and the animals that live there respond accordingly. Plants are eaten, trampled underfoot, exposed to the whims of the weather, and just generally beaten down by the world around them, all on top of competing with each other for resources and space. But while plants have it rough, they are also really good at persisting.
Trees are an excellent example of just how persistent plants can be. I was reminded of this earlier in the summer when I came across a grove of cottonwoods in one of our Platte Prairies while searching for musk thistles. At first glance I thought one of the cottonwoods had recently fallen and the leaves hadn’t died back yet. On closer inspection, however, I realized that the tree had probably fallen years ago, and instead of dying, the parts of the trunk that now contacted the earth had sprouted roots and continued on living. Branches had grown up from the trunk,and now looked essentially like three trees, all connected by the same fallen trunk.
Trees are clearly hard to kill, as anyone who’s tried to cut down a deciduous tree in your yard knows. Once the tree is cut you have to treat the stump with herbicide, otherwise the still-living roots will simply sprout again. Nearly every tree we cut here on the Platte to keep our prairies open needs to be treated with an herbicide. While it would be nice to not have to use chemicals in our stewardship work like this, that resilience of trees can also be a blessing. After the wildfire at our Niobrara Valley Preserve a few years ago, much of the forest along the river was killed. However, the oaks along the slopes are re-sprouting from their roots, as only the tops of the trees had been killed in the blaze. Because of this, these forests have a jump start on regenerating after the devastation of the fire.
Since I found that cottonwood looking for musk thistles, it’s probably worth talking about them and their own resilient strategies. As a biennial, these plants only have one chance to flower and produce seeds, so they produce thousands of them at a time. And they can fly. That’s not great for us, considering they are considered noxious weeds here in Nebraska, but as a strategy for this plant it certainly pays off.
But wait, there’s more! Even when uprooted or sprayed with herbicide, if the flowers on a musk thistle plant have been pollinated, they will still produce seeds! So when we control this plant, we not only cut off the root just under the ground and pull it out, we have to collect any flowers, or else nothing will actually have been controlled. This persistent ability of musk thistles makes things more difficult and time consuming for us to control, but you have to admit that it’s a cool adaptation, and in its native habitat, likely very useful.
So far these examples relate back to land management, and how the difficulty in killing plants affects our ability to effectively manage invasive plants in prairies. But we rely on these same tenacious qualities in our native prairies species as well. Chris talks a lot about the resilience of prairies on this blog, and a lot of that depends on the persistent nature of individual plants.
Consider big bluestem, a favorite of both cattle and bison. It can be cropped down again and again to within an inch of the ground over a growing season, but while such trauma might kill another plant, big bluestem holds on until the herd moves on and it gets a break, coming back taller and stronger the next year, until it’s back to full strength within a few years. In addition, even in those years that it’s hammered by grazing, big bluestem will find a way to flower, since all that short and weak vegetation around them makes for a good place to put out seeds.
Other plants may just find that conditions in a certain year aren’t for them. Maybe it’s too dry, or too cold, or the grasses around them are just too tall. Perennial prairie plants don’t let that stop them, as many will simply take a break, growing very little above ground for a year, relying more on stores of energy in their roots than anything else. To some, it may seem like those plants have died and disappeared from a field. But just wait, when conditions become favorable, most of those plants will show up again, just as strong, and benefiting from that strategy of waiting it out through the hard times.
Now, just because plants are tough doesn’t mean they’re invincible. If put under too much stress even the most stubborn plant will eventually die. Knowing how plants are able to persist can help us more effectively target those plants we don’t want, but also help ensure that our desirable plants always have a chance to let their persistent nature shine!
Last week, I
attended a science and stewardship conference of The Nature Conservancy in
Madison, Wisconsin. It was an inspiring
and thought-provoking week. There were a
lot of topics that will provide fodder for future blog posts, but I wanted to
start with an issue that came up in several sessions. The topic had to do with setting appropriate
objectives for conservation strategies, and for land management in
particular. In short, it’s really
important to make sure we’re not setting objectives that are focused on
strategies rather than outcomes.
illustration of what I mean. If I was
planning a vacation for next summer, I probably wouldn’t start with the
following question: “What mode of transportation should I take on my vacation
Clearly, it’s tough to answer that question without knowing more about the ultimate objectives of the vacation. Where do I want to go? What time of year am I going? How many people are going with me? If I’m planning to travel from Nebraska to Ireland, I probably won’t be able to do that by bus. I could conceivably travel by motorcycle (if I had one) to the Rocky Mountains, but probably not if I was going during the winter or planning to take little kids with me.
silly to start by thinking about how to get somewhere before deciding where to
go, but as land managers, it’s easy to fall into exactly that mindset. We sometimes set objectives about using fire
or grazing, for example, instead of first defining the outcome we want and then
thinking about what tools and strategies might get us there (which may or may
not include fire or grazing). In this
post, I’ve provided examples of how this trap can present itself, both to
managers of conservation land and private landowners, and some thoughts about
how to avoid the trap.
research has helped us understand the kinds of fire and grazing patterns under
which North American prairies developed.
For example, in many places, we have a pretty good idea how often a particular
site burned, on average, before European settlement. We also have reasonably good information on
the presence, abundance, and behavior of historic grazers. Based on that information, a land manager
could decide that the best management for their prairie would be to reinstate,
as closely as possible, the timing and intensity of historic fire and grazing
that site likely evolved under.
Patch-burn grazing is often described, for example, as “mimicking historic fire and grazing patterns.” Mob grazing advocates trumpet (though I’m skeptical) that their system replicates the way bison moved across a landscape. Some in the Upper Midwest region of North America point to research showing high populations of indigenous people and scarce evidence of abundant bison and argue that their prairies should be managed only with fire. We can argue about all three of those examples – and many more – but the bigger point is that none of those arguments should determine our management strategies. Again, we shouldn’t be setting objectives about the strategy we want to use without first identifying the outcome we want.
To make a
clunky return to my vacation travel analogy, it would be silly of me to choose
horseback as my preferred mode of transportation across the Great Plains to the
Rocky Mountains just because it’s what worked several hundred years ago. Today’s landscape is broken up into countless
fenced off private land parcels, which would make cross-country horse travel
difficult, to say the least. In
addition, there is a pretty nice set of modern opportunities (roads and vehicles)
I can take advantage of nowadays.
Likewise, our prairies exist within a different world today, with a new set of challenges and opportunities. Mimicking historic disturbance regimes won’t necessarily keep prairies in good shape in a world with habitat fragmentation, massive invasive species pressure, climate change, nitrogen deposition, and other factors. And speaking of good shape, our first and primary concern should really be to define what “good shape” is, right? Are we managing for plant diversity or a few rare plants? Are we trying to sustain diverse bird populations? Habitat heterogeneity? Is ecological resilience the goal? If so, what are the factors driving resilience, and how to we sustain those? There are countless reasonable goals for land managers to choose from, many dependent upon scale, but those goals should be based on the outcome we want.
I feel it’s important to say this here: I am a big proponent of both fire and grazing as management tools – you can find myriad examples of that by searching through my previous blog posts. However, while I think combining fire and grazing can create some fantastic results, those strategies/results don’t fit all objectives. More importantly, your particular site may or may not respond well to those kinds of fire and grazing combinations.
your primary objective is to provide habitat for as many species of grassland
birds as possible. First, you’ll need a
pretty big swath of land – many bird species have minimum habitat size
requirements. Assuming you’ve got
sufficient land, the major factor grassland nesting birds respond to is habitat
structure. Some birds prefer tall thatchy
structure, others like short/sparse vegetation, and others want something
in-between. A reasonable outcome-based
objective might be that you want to provide all three of those habitat types
across your prairie each year (and you’ll want to make sure the habitat are
being successfully used by a diverse bird community). Perfect.
Now, how will you create those habitat types?
spring fires can create short habitat structure that some birds really like to
nest in. However, some bird species
(e.g., grasshopper sparrows) usually like short habitat with a little more
thatch in the ground layer than is usually found in recently burned
prairies. Also, while burned areas are
short and unburned areas are tall, it’s difficult to create in-between
height/density habitats using only fire.
This is where other tools such as mowing and grazing might be
helpful. Mowing can reduce the height of
tall vegetation and create short or mid-height structure that grasshopper
sparrows, meadowlarks, and other species prefer. Grazing can do the same and can have the advantage
that cattle or bison are selective grazers, eating some plants and leaving
others. This can create structure with
both tall and short vegetation mixed together and can also help suppress
grasses and allow for greater expression of forbs (broadleaf plants) –
something birds such as dickcissels often prefer.
trying to create optimal bird habitat, then, fire, mowing and grazing might all
be useful tools to consider. It’s
important to understand how each tool can be used to affect habitat structure,
as well as the potential risks of using each (fire can sometimes kill
aboveground animals and stimulate invasive plants, grazers can sometimes target
vulnerable plants and create issues via trampling). With all of that information, you can start putting
together strategies that employ the right tools, and then test those strategies
against the OUTCOMES you desire. Notice
that the process I’ve just described is independent of the kinds of historic
fire returns for your area or whether or not you think grazing was a significant
factor in the evolution of regional plant communities. Define your objective by the outcomes you
want and test/adapt strategies based on that objective.
At my family prairie, we aren’t using prescribed fire because we’ve been able
to use grazing to meet our objectives of habitat heterogeneity and increasing
plant diversity, and we use loppers/herbicide to successfully control woody
invasion. In small prairies where
preserving particular plant species is the objective, a strategy using only
fire or mowing could be most appropriate.
If that small prairie has rare insects or reptiles that are especially
vulnerable to fire, maybe mowing is the best tool. Regardless, the right tools and strategies
depend upon the outcome-based objective.
and farmers who manage prairies, this same objective setting process should
apply, but of course those prairies also have to help provide sufficient income
to keep a family or business thriving.
Even in those cases, however, it’s still important to start with
outcome-based objectives. Those
objectives can include a certain amount of needed income but should also include
specific habitat or other ecological objectives. Once you’ve decided, for example, that you
really want to manage in a way that provides a certain amount of quail habitat
or provides consistent pollinator resources through the season, you can look
for ways to accomplish that while still providing the needed income. When a conflict between income and habitat
objectives arises, you can make the decisions that make sense to you, but at
least you’re making those decisions with all the information needed to fully
consider the options.
plenty of reasonable prairie management objectives to choose from, but they
should be based on outcomes rather than on tools and strategies. Employing more frequent prescribed fire is
not a good objective. However, using
more frequent prescribed fire might be a great strategy to reach a particular
outcome. (It could also be a terrible
strategy, depending upon your objective.)
Don’t fall into the trap of choosing your transportation method before
you know where you want to go.
P.S. I’m sure some of you are thinking it, so let me address what might appear to be a weakness of my vacation transportation analogy. Yes, it’s perfectly fine to start vacation planning by deciding that you want to take a cruise ship or motorcycle if the OUTCOME you really want is to ride on a ship or motorcycle. If you don’t care where you go, the destination isn’t the outcome, it’s just a by-product of your mode of travel. Fine. But I think you understand what I was trying to say, right? Sure, you could argue that conducting prescribed fires could be your objective if all you want is a legal way to light things on fire and watch them burn. If that’s your objective, though, you’re not managing prairies, you’re lighting things on fire – and there’s a big difference. Ok? Ok.
One of the most striking plants in our prairies this time of year is pitcher sage, also known as blue sage (Salvia azurea). It’s tall, of course, but more importantly, as the surrounding prairie is dominated by green-becoming-gold grasses and big yellow flowers, pitcher sage stands out simply because it is starkly and unabashedly blue.
A few weeks ago, I posted a photo of a bee that specializes on pitcher sage, but there are many more insects commonly seen on the plant. Last week, I spent about 45 minutes in our Platte River Prairies, photographing pitcher sage and as many visitors as I could.
I initially pulled my camera out because there were several monarch butterflies flitting around a patch of pitcher sage. While chasing them around (and, as always, being thankful no one was watching me), I came across quite a few other insects – some of which I managed to photograph.
In addition to being tall, striking, and beautiful, pitcher sage is also pretty good at withstanding drought. During late August of 2012 – a year of extreme drought, pitcher sage stood out against a background of brown dormant grass, blooming just like it does every year. Not only did it provide some welcome color when many other plants were wilting, it gave all the insects pictured above, and many others, something to eat when they needed it most.
During the last month or so, I’ve had several people tell me how aggressive marestail (horseweed, aka Conyza canadensis) is, and how this is a particularly bad year for it. One person suggested marestail should be added to Nebraska’s noxious weed list. This week, Olivia and I drove from our Platte River Prairies to the Niobrara Valley Preserve – right through the center of our state – and I tried to document what is certainly a summer of abundance for marestail.
Here are a few things you should know about marestail right off the bat. First, it is native to Nebraska and most of North America. It acts as an annual plant in states to the east of us, but acts as a biennial here, usually germinating in the fall and blooming the following summer. In its native habitats (including grasslands), marestail is a colonizer of bare ground, filling spaces between plants left open by disturbances like grazing, trampling, animal burrowing, drought, or fire. Because marestail loves open soil conditions, it isn’t surprising that it has become a weed in crop fields. It has garnered special attention lately because it has a strong ability to become resistant to herbicides, including glyphosate, which it started showing resistance to way back in 2006.
In other words, marestail is a tough native plant that has always scraped out a living when and where it can. However, it’s not a plant that can push other plants around. Instead, it sits in the soil (as a seed) and waits for a time when surrounding plants are weakened and abundant light is hitting the soil. Then it pops out of the ground and tries to grow, bloom, and produce as many seeds as it can during its short window of opportunity. In any particular year, marestail can be found here and there in most Nebraska prairies, especially those in the western 2/3 of the state. However, it also seems periodically to respond to certain weather patterns and exhibit a flush of abundance across a larger region – as it is doing this year. Many short-lived plants do the same thing, each with its own individual preferences for weather patterns. Many Nebraskans might remember the huge sunflower party across the Sandhills back in 2013, for example, following the big drought of 2012.
Whether it’s sunflowers or marestail, huge regional flushes in abundance don’t last long. By 2014, annual sunflower numbers in the Sandhills had returned to normal – patches of yellow flowers here and there, around livestock tanks and fence corners, and wherever else there was open soil to grow in. Marestail will do the same thing in 2019. That pattern of boom and bust is not evidence of an invasive plant. Instead it characterizes a plant that is too weak to compete most of the time and has to take ultimate advantage of the few windows of opportunity it gets. When it is abundant, marestail isn’t stealing resources from other plants, it is taking resources that weren’t being used. I don’t know for sure what weather patterns led to rampant marestail germination last fall, but I’m sure this year’s abundant rains have played a big role in the survival of a large percentage of those seedlings.
When short-lived plants like marestail and sunflower (along with ragweed, gumweed, and many more) are in the middle of a short-term explosion in your prairie, you could choose to fight them. You could, for example, mow them off, trying to prevent them from making seed. However, that’s a lot of work, and the plants will do everything they can to regrow and still produce seed – it’s what they do, and they only get one year to do it. Even if you do keep them from going to seed, there are many thousands of seed already in the soil, ready to spawn the next generation of plants whenever they get the chance. You could also spray short-lived opportunistic plants with herbicide, but I wouldn’t recommend it. First, you’ll likely kill the surrounding plants (the ones that normally out-compete marestail and sunflower) and just trigger another explosion of opportunistic plants the f0llowing year. Second, with most short-lived plants, by the time they’re big enough that you notice them (especially by the time they’re flowering) herbicide treatments just make them produce seed more quickly, so are counterproductive.
The smartest choice is to just sit back and marvel at these periodic phenemona, knowing you’re watching a short-term and harmless event. Marestail, of course, doesn’t have the wide aesthetic appeal of sunflowers (though not everyone likes sunflowers either), but it has its own distinctive charm. I think it adds an attractive texture to the landscape, but I’ll admit I’m a little odd. Regardless of whether you find it attractive or not, it’s here, and it’ll be here whether you like it or not.
Fighting back against these periodic flushes of marestail and other opportunists is expensive and futile, and usually results in weakening the plant community that normally keeps them in check. Most importantly, remember that, at least in grasslands, marestail doesn’t steal resources from the plants you like, it just takes what they can’t use. What’s to dislike about that?
Pardon the terrible poetry, but even outside of horticultural varieties, the flowers of both roses and violets can be many different colors. Less frequently, even sunflowers can display colors other than their typical yellow. For example, there is a clone of stiff sunflowers (Helianthus pauciflorus) blooming right now over at Lincoln Creek Prairie, here in Aurora, that includes beautiful red highlights.
The red color appears to be genetically linked because there is an entire clone (a patch of stems connected by underground stems called rhizomes) with the same feature. It reminds me of the way upright yellow coneflower (Ratibida columnifera), another yellow flower, can often include varying amounts of red. But that red variation is much more common in the coneflower – I almost never see it in sunflowers. In fact, I’m wondering if the other times I’ve seen it might have been in this same clone, but years ago…
Regardless, I took a few minutes to appreciate (and document) these unique blossoms last week. The bees feeding on them didn’t seem put off by the unusual color, which means maybe the genetic trait of that red color will be passed on and show up elsewhere. If I think of it, I might even go harvest some of that seed myself in a month or so… Here are a few more photos from that same flower patch.
I blame whomever named the plant. Giving a plant the name “ironweed”, apparently – according to Google – because of its tough stem, creates an unnecessarily negative connotation right from the start. It’s an unfair connotation for a plant that is both beautiful and important. It’s also a big favorite of butterflies; something I can attest to after spending a couple hours last weekend chasing monarchs and others around ironweed patches at our family prairie.
There are three species of ironweed (genus Vernonia) in Nebraska, and two that are common in the prairies I am most familiar with. Both of those – V. fasciculata and V. baldwinii – seem to act in similar ways, but the first likes a little wetter sites than the second. Both species can occur as scattered plants across a prairie, but are also often found in fairly dense patches where conditions favor them. That patchy local abundance is the first mark against them by people who don’t appreciate their value. The second mark is that cattle absolutely refuse to eat them. This both helps them stand out (especially when blooming) in heavily grazed pastures and helps them spread across those same sites since they gain a strong competitive edge when surrounding plants are all being grazed hard.
Like many other plant species I tend to admire and write about, however, ironweed is not an invasive plant – it’s an opportunist. It takes advantage of soil and management conditions that favor it, but doesn’t just spread aggressively across pastures. If you look online, it’s not hard to find websites that encourage its control in pastures. I dispute that. At least in my experience, ironweed has its favorite locations (often in draws or other low spots where moisture and nitrogen are high) and pulses in abundance within those locations as grazing treatments and weather vary from year to year. At our family prairie, ironweed is fairly abundant in some of the low draws where high nitrogen also strongly favors smooth brome, but while there are years when those patches are thicker than others, the overall patch sizes and stem densities of ironweed aren’t any higher today than they were 15 years ago. That matches what I see elsewhere in central and eastern Nebraska.
(I found a university website online that blamed ironweed for making cattle have to look harder to find grass, thus reducing grazing efficiency. Give me a break. That’s the same attitude that leads to people spraying pastures to remove everything that isn’t grass, and then wondering why they need to fertilize their grass and supplement their cattle’s diet. The same people blame others for the lack of wildlife and pollinators on their land. …Ok, I’m done ranting – let’s talk about butterflies.)
When I arrived at our family prairie last weekend, I immediately noticed monarch butterflies flying all over the place. I’d seen a surprising number of larvae back in July, so figured we might have a good August, but I was still impressed with how many adults I saw. I’m guessing there were 40-50 or more across our 100 acres of prairie. They kept moving, so it was hard to count them…
Almost every monarch I spotted was either flying or feeding on ironweed. A few other flowers got attention too, including wild bergamot (Monarda fistulosa), Flodman’s thistle (Cirsium flodmanii), and some early tall thistle blossoms (Cirsium altissimum), but ironweed clearly monopolized most of their attention. I started stalking monarchs with my camera and eventually found a couple that let me get close enough for to capture reasonable photographs. While I was doing that, I also spotted myriad bees, along with quite a few other butterfly and moth species.
Here are some photos of the butterflies and moths that were kind enough to let me get close. I didn’t ever get a good shot of a bee, though there were at least a dozen species feeding on the ironweed flowers, and I also never caught up to one of the many silver-spotted skipper butterflies that were all over the place.
Ironweed is too beautiful and important for its name. Maybe we need a campaign to rename it, and maybe that campaign would help convince people, including those at a certain unnamed university, to leave this plant alone to do its job. Either way, it might be fun to think about potential names. Any ideas?
Another month has passed, and I’ve managed to carve out some more time staring at the little square meter of prairie I’m photographing this year. In June, activity really picked up as lead plant (Amorpha canescens) and butterfly milkweed (Asclepias tuberosa) started blooming within the plot. However, there was plenty to photograph besides just those species and the many insects they attracted. I continue to be inspired by the diversity of life I’m finding in a very small plot of land. Hopefully, I can pass along some of that inspiration, both during these periodic updates and when I somehow assemble all of this at the end of the project. Here are just a few of the photos taken during June within one single square meter of Lincoln Creek Prairie in Aurora, Nebraska.
One of the biggest jobs of a prairie steward is to manage the competition between plants, ensuring that no species becomes too dominant and no species is pushed out of the community. In our prairies, much of our effort is directed toward some of the stronger grass species, including big bluestem, indiangrass, smooth brome, and Kentucky bluegrass. Left unchecked, those grasses (and a few others) can monopolize both light and soil resources and reduce plant diversity. Our management targets those grasses with fire and grazing, often using season-long defoliation by cattle or bison to weaken the competitive ability of those grasses, opening up space and resources for other plants to flourish. Our long-term plant data show that we’ve been able to maintain species richness and a full complement of plant species with this kind of management.
When those major grasses are weakened, one of the most obvious responses is a flush of “weedy” vegetation that quickly takes advantage of the soil and light resources that have become available. Research has shown that growing season defoliation temporarily causes grasses to abandon some of their roots (until defoliation stops and the grasses recover), opening up space for nearby plants to grow larger and more abundant. However, there are still many questions about the actual physical responses of grass roots to defoliation, and gaining a better understanding of that could be really important to prairie managers. Researchers at Kansas State University are actively working on those questions right now. Dr. Jesse Nippert, in particular, has done a lot of work on this subject, including some work on prairie shrubs that I wrote about a few years ago.
Last week, a couple of Jesse’s graduate students, Seton Bachle and Marissa Zaricor, were at our Platte River Prairies, collecting data on roots under grazed and ungrazed conditions. In addition, Seton brought along a nifty tool called an air spade, which uses compressed air to dig into prairie soil with enough force to expel soil particles, but not so much that it tears apart the roots of plants (with the exception of the tiny rootlets at the tips). Seton and I started talking about a year ago about the possibility of getting the air spade up here so we can look for visual evidence of grazing impacts to roots. Marissa and Seton are both doing very in-depth (ha!) measurements of plant root responses, but I also wanted to see what’s those roots really look like. The air spade seemed like a great way to do that.
For this initial trial, we chose a part of the prairie that was burned this spring and was being grazed intensively by cattle as part of our patch-burn grazing management. Abundant rain this year has meant that the cattle aren’t keeping the grasses as short as we’d really like, but we were still able to find some big bluestem plants that have been cropped pretty short. As a comparison, we went across the burn line to part of the prairie that hasn’t had much grazing pressure in recent years and, because it is unburned, hasn’t had much attention from cattle this year either. As a result, we were (ok, Seton was) able to excavate around the roots of big bluestem plants that had been grazed off to just a few inches of leaf height, as well as ungrazed plants with leaves around 12 inches high.
As Seton started blowing soil away from the roots (and I photographed the process with my camera and our drone), one of the first things that became obvious was the relatively shallow depth of the main root mass. The work of J.E. Weaver and others has shown that prairie plants, including grasses, have some very deep roots. However, more recent work, including that of Jesse Nippert of Kansas State, Dave Wedin at the University of Nebraska, and others, has shown that those grasses don’t appear to actually use those deep roots for much. In fact, grasses tend to concentrate the vast majority of their root masses in the top foot or so of the soil profile, effectively monopolizing most of the moisture and nutrients there. Forbs tend to pull most of their resources from below that, and shrubs work at even greater depths. I’ll write about this more in a future post, but for now, just trust me when I say that this is abundant evidence for this (and many more questions being pursued). Prairie grasses can have deep roots, but it’s the incredible root density at shallow depths that they most rely on, even during drought.
With the air spade, we could pretty easily see that most of the big bluestem roots were in that shallow depth, and only a few extended down below that. However, as Seton pulled out fully-excavated clumps of big bluestem shoots and roots, my initial reaction was one of disappointment. There didn’t seem to be any obvious difference in the density of roots or size of the overall root mass between the grazed and ungrazed plants.
My immediate thought was that because these plants had only been exposed to grazing for about a month, maybe there hadn’t been enough time to see changes in their root masses. In addition, it might be that some of the roots were no longer active, but were still connected to the root mass for now. We’ll be repeating this excavation process later in the season, and might see differences then that aren’t yet obvious. In addition, we’ll look at some roots of grasses that were heavily grazed all of last season and see what those look like. Still, I was a little disappointed not to see a bigger visual difference.
However, when Seton and Marissa looked at the roots, they pointed out something I hadn’t initially seen because I was so focused on root length and density. The diameter of most of the roots of the ungrazed bluestem appeared to be considerably larger than those of the grazed plants. We were working with a small sample size, but among all the plants we dug up, that size difference seemed to be pretty consistent.
Marissa explained that thicker roots have more carbohydrates stored in them. Plants that have been defoliated, and are trying to regrow shoots, have to pull carbohydrates from their reserves to do so – pulling them out of their roots and putting them into aboveground growth. Whether those roots kind of deflate as the carbohydrates are pulled from them or stressed plants just create skinnier roots is something Marissa and Seton are hoping to learn from their work. Regardless, carbohydrate storage plays into competitive ability. Grasses rely on their storage capacity to fuel growth and withstand further stress, so differences in root diameter could be part of the answer to why grazed grasses are less competitive. Seton and Marissa plan to examine some cross sections of the roots we dug up to see if they can see more under a microscope than we could by just looking at the roots with our naked eye.
Seton and Marissa’s actual scientific explorations will give us much better answers to questions about grazing impacts on grass roots than simply looking at a few samples, but it was fun to see the actual roots themselves. While the differences between grazed and ungrazed plants weren’t as stark as I’d expected, I’m still looking forward to our next effort later this summer – especially because all I have to do is photograph the results of the hard work Marissa and Seton are doing!
If you’re interested, here is a short 1 minute drone video showing the excavation process. You can also check out Seton’s science website here.
Special thank you to the Nebraska Environmental Trust for funding our drone purchase through a PIE (Public Information and Education) minigrant, administered through the Nebraska Academy of Sciences.