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.
This cottonwood, in true tree fashion, just refused to die. Photo by Olivia Schouten
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.
It’s probably a good thing musk thistles are so showy, otherwise it would be much more difficult to find them. Photo by Olivia Schouten
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.
We collected about three tubfuls of musk thistle flowers by the end of the control season. We let the flowers rot to make sure any seeds were destroyed before throwing them out. Photo by Olivia Schouten
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.
This patch of big bluestem has been hit pretty hard by cows this year, but that didn’t stop it from blooming. Photo by Olivia Schouten
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.
This mixed-grass prairie is managed with both prescribed fire and grazing. However, neither fire nor grazing is the objective, they are tools that are strategically employed to create desired outcomes. Gjerloff Prairie – Prairie Plains Resource Institute
Here’s an
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
next year?”
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.
It seems
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.
Significant
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.
Historically, prairies in this region probably burned on an average of every 4-5 years. However, within that average range, there would have been wide variation. More importantly, this prairie sits within a very different landscape today, with challenges not faced by those historic prairies.
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.
This annually-hayed prairie maintains high plant diversity but provides only one type of habitat structure for nesting birds and other wildlife species. Depending upon the objectives for the site, that could be fine, but it very much depends upon what the manager wants to accomplish.
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.
Let’s say
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?
Grasshopper sparrows tend to nest in prairies with relatively short structure, but with some thatch (which they use to build nests) along the ground. Some of the highest abundances of grasshopper sparrows around here are found in relatively heavily-grazed prairie.
Fall or
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.
Upland sandpipers prefer to nest where vegetation structure is short, but often move to sites with strong forb cover and a little patchier structure when their chicks become active.
If we’re
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.
Other examples:
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.
This photo was taken in the burned patch of a patch-burn grazed prairie at Konza prairie, near Manhattan, Kansas. The grazing created varied habitat structure because of the selective grazing by cattle. Leadplant and other ungrazed forbs contrast with surrounding short grasses.
For ranchers
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.
Prescribed fire can be a great tool for accomplishing some objectives, but it can also be difficult to implement for some managers. While it is an important ecological process in prairies, employing prescribed fire should still be seen as a tool/strategy, rather than as an objective in and of itself.
There are
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.
The Prairie Ecologist 