For many of you, the snake photo below will elicit a strong visceral response. The spider photo below might do the same. While it varies in intensity, humans seem to have an innate fear of both spiders and snakes. New research now provides further support for the idea that fear of spiders and snakes is something we’re born with, not something we learn. The European study showed that 6-month-old infants responded more strongly to images of spiders and snakes than of other creatures, even when those images were nearly identical in terms of color and brightness. It’s a fascinating study to read, and is available for free by following this link.
I handle both snakes and spiders fairly regularly, but I’ll still admit that my first reaction upon seeing one – especially when it’s a surprise – is to step backward. Then, my logical brain kicks in and I step forward and pick up the cute little critter to look at it more closely. I may be instinctively afraid of snakes and spiders, but it’s nice to know my brain has the ability to override that instinct – and I think most people have that same ability. Dating back to my time working at a nature center in college, I’ve probably helped thousands of people overcome that initial fright response and touch, or even pick up, their first spider or snake.
I think it’s important to help people understand that most snakes and spiders are harmless, and that even those few that could potentially pose a danger are not actively trying to attack them. First, it might help save the lives of snakes and spiders living in and around those people’s houses. That’s great, but probably won’t affect the fate of the world. More importantly, however, I hope making people more comfortable with snakes and spiders might also help them feel more comfortable wandering out into prairies and other natural areas.
I’m not sure how many people avoid exploring tall grassy places out of fear, but I’ve definitely met people who fall into that category. It’s hard enough to convince people that prairies are worth visiting without also having to convince them they won’t be ambushed by a vicious snake or spider. I take every opportunity to reassure people that our prairies are safe, and try to prove it by going out of my way to catch and admire the snakes and spiders we see while hiking around. Among my prairie conservation outreach strategies, demonstrating the harmlessness of snakes and spiders is surely not the most impactful, but I figure it doesn’t hurt. If nothing else, people tend to care more about places they’ve visited, so anything we can to do encourage more visits to prairies seems worthwhile.
There is an awful lot we still don’t understand about prairies (and the rest of the natural world, for that matter). First and foremost, we haven’t even come close to discovering all the species that live in prairies. We have probably identified all of the birds, and most of the other vertebrates, but there are still many prairie invertebrates no one has yet described. The world of microorganisms is beginning to open up to us, but that is still, by far, the biggest pool of unknown species. How can we manage a natural system when we don’t even know what’s there – especially when those inhabitants have a tremendous impact on ecosystem function?
We need to discover more species and understand the basics of their life histories, but there are some other really big prairie questions out there that need attention as well. I thought I’d share a few of the ones I think are most important. I’m hoping you’ll find them thought-provoking and join me in trying to chip away at them. We’re not going to answer any of them in the near future, but more people thinking about them and making careful observations will speed us more quickly along the path. Because each question takes some explaining, I’ll just deal with one here and cover the others in future posts.
Big Question #1: How big and connected does a prairie landscape need to be to support the majority of prairie species and essential natural processes?
This one has bothered me for a long time because not knowing the answer prevents us from setting reasonable goals for landscape-scale conservation efforts. As prairie landscapes get carved up by rowcrop agriculture (e.g., the Dakotas), how do we know how much fragmentation will be catastrophic to the ecosystem? On the flip side, in landscapes that were carved up long ago, what size prairie restoration projects should we aim for to truly restore sustainable prairie ecosystems?
We know that some prairie species require large patches of habitat. Based on quite a bit of research on birds, we can make reasonable guesses about the size of prairie landscape needed to maintain populations of most bird species. I’m not completely up to date on this research topic, but I think it’s fair to say that if you had a couple thousand acres of prairie and managed it for a diversity of habitat structure, you’d see most of the grassland bird species in your region show up to nest. To ensure that those populations were large enough to survive tough years, it’d be nice to have more like 5,000 or 10,000 acres. Depending upon where you live, that might sound like an impossibly big number or a very manageable one (Illinois doesn’t even have 10,000 acres of remnant prairie in the state, while 10,000 acres is pretty small for a ranch in the 12 million acre Nebraska Sandhills).
Assuming that 10,000 acres is a comfortably large prairie for grassland birds, you might think we could just use that as a benchmark for other species as well. Unfortunately, there are a number of problems with that assumption, many of which I laid out in an earlier post. One big problem is that bird habitat (quantified largely by factors like vegetation structure and insect abundance) is not necessarily quality habitat for pollinators, ants, or many other species that rely on high plant diversity. Each of those other species has particular needs, both for habitat size and habitat quality.
A few species (bison? prairie dogs? others?) might need considerably more than 10,000 acres to support a viable population. However, many other species probably need considerably fewer. In fact, 10,000 acres might seem like an entire universe to many invertebrate species – although the more we learn about insect migrations, the more complicated that picture becomes. Is 10,000 acres enough to provide for the vast majority of prairie species? Maybe. We really don’t know.
Regardless of whether or not it’s big enough to sustain populations, we know that restoring and/or preserving a single 10,000 acre block of prairie somewhere in the central United States would not be sufficient to conserve all prairie species. In order to preserve genetic health and allow populations to recover from catastrophic events, species need multiple habitats in multiple locations. They also need connectivity between those habitats so that individuals can move between populations. So, we will need multiple examples of large prairie blocks in every region of the country, with smaller prairies around and between them. (Questions about what constitutes connectivity and how much connectivity each species needs are also big important questions, but before we address those, we first need to know how large individual habitat blocks need to be.)
Why is this so important? I’ll give you two real world examples. First, think about a prairie landscape that has been relatively intact for thousands of years, but is now becoming fragmented by a rapid increase in new rowcrop agriculture. This is a situation all too familiar to conservationists in the Dakotas, where millions of acres of prairie have been converted to rowcrops over the last couple of decades. As those conservationists struggle to protect remaining prairie through conservation easements and other strategies, they are doing so with limited time and money. Knowing what size a prairie block needs to be to sustain species and ecosystem processes would be tremendously helpful.
Let’s say an organization obtains a conservation easement that prevents 5,000 acres from being farmed. Should they prioritize obtaining an additional easement next to it so that if everything else in the county gets farmed up, there will still be a 10,000 acre block of prairie remaining? What if they have to pay double the price to obtain that second easement? Is it worthwhile? Or should they spend the same amount of money on two more 5,000 acre easements in other locations? Not knowing the answer to what seems a pretty basic question makes it really difficult to know how to proceed.
My second example is at the other end of the spectrum. There are a number of large scale prairie restoration efforts going on around North America, where thousands of acres of cropland are being restored to high-diversity prairie communities. The best of those start with a number of unplowed prairie fragments and enlarge and reconnect those through restoration. The complexes of interconnected remnant and restored grassland they build are many thousands of acres in size. The Nature Conservancy’s Glacial Ridge project in Minnesota, Nachusa Grasslands in Illinois, and Kankakee Sands project in Indiana are all great examples of this, as is the US Forest Service’s Midewin Tallgrass Prairie in Illinois.
We have proven that we can rebuild prairie landscapes of 10,000 acres and larger. The sites look good, with beautiful plant communities and abundant wildlife, but are they big enough to sustain that biological diversity? Should those sites be spending $15,000 per acre to buy high-priced cropland around their borders and increase the size of their restoration projects? Or should they invest those funds in invasive species control and other management needs to protect the investment they’ve already made?
Unfortunately, the answers to these fairly simple questions are not going to be simple to obtain. We and others have taken a few baby steps by comparing the diversity and abundance of invertebrate species among prairie fragments of varying sizes and degrees of isolation, but we’re just getting started. I think a better approach would be a large collaborative project that focuses on some of our largest, most intact prairie landscapes such as the Sandhills of Nebraska and the Flint Hills of Kansas and Oklahoma. Studying how populations and ecosystem processes differ between core areas of those landscapes and the fragmented edges would be an excellent start. We could learn which species might be most vulnerable to the negative impacts of fragmentation, and then focus on those species through additional research looking at how they are doing in prairies of varying sizes across their ranges.
I’ve planted this idea with quite a few people, but nothing has really taken off yet. I’m not giving up. This is too important. Does anyone have a couple million dollars to spend answering one of the most pressing conservation questions of our time?
Here are a couple other examples of big research questions I think about. I’ll address them in more detail in future posts.
1. How effective is prairie restoration (converting cropfield to high-diversity prairie plant communities) at defragmenting prairie landscapes? Do populations of plants, insects, and wildlife in small prairie fragments grow larger and more interconnected when surrounding cropland is converted to prairie? What are the key ecosystem components that need to be restored in order for that to happen?
2. How do prairie species respond to fire and grazing management patches, and how should that affect the scale and frequency of those management treatments? What happens to a vole or other creature living in the unburned patch of a prairie when that patch burns? Can it travel to other suitable habitat? How does it know where to go? What kinds of habitat can it cross and how far can it travel?
3. How does plant diversity influence the productivity and sustainability of grasslands, especially in ways that directly influence agricultural production? Why should a rancher care about the plant diversity of his/her pasture? Are there demonstrable increases in soil health, pollination services, forage productivity, forage selection, etc., and are those strong enough that a rancher would trade slightly lower annual income for them?
Last week, I took some photos that powerfully demonstrate the importance of plant diversity.
Several years ago, we created some research plots to help us learn more about how plant diversity interacts with ecosystem function. As you can see above, the plots include a grid of squares (3/4 acre in size), each planted with one of three seed mixtures: monoculture (big bluestem), low diversity (grasses and a few forbs harvested in the fall), and high diversity (100 species). Working with academic partners, we have several research projects underway, including a couple that demonstrate the influence plant diversity has on the spread of invasive plant species.
Other researchers have found similar relationships between plant diversity and resistance to invasive species, but that is only one of many benefits from having a wide variety of plants in a prairie. Both herbivores and pollinators benefit from having a broad selection of food choices available to them. During extreme weather conditions (hot, dry, wet, cold), high diversity prairies always have plants that flourish under those conditions and help provide habitat and food conditions for animals. Most importantly, because of these and other reasons, prairies with high plant diversity also have high total biological diversity, including more species of microbes, insects, other invertebrates and vertebrates. That overall diversity is important for its own sake, but also because of the role each species plays in the functioning of the ecosystem.
The aerial photo I took from our small drone last week illustrates another benefit of plant diversity; prairies with high plant diversity have green vegetation for more of the growing season. Every plant species starts and ends their growth period at different times. Some start early, bloom, and are done before summer even starts. Others bide their time and don’t bloom until late in the fall. When you mix all those species together in one prairie, you end up with consistent, but ever-changing, availability of nutritious vegetation and flowers throughout the growing season.
Our monoculture research plots (big bluestem only) looked very different from our other plots last week because big bluestem was just starting to grow (on April 23). Even after we burned all the plots this spring, allowing the soil to warm earlier than it otherwise would have, the most advanced big bluestem plants only had leaves of a few inches in length. Our low diversity plots (mostly grasses) showed more green, but only due to the presence of one grass species, Canada wildrye (Elymus canadensis), a cool-season grass that begins its grown early in the year. By contrast, the high-diversity plots had many plant species growing, with some close to blooming.
Although the visual differences between plots on April 23 are striking, they are ecologically significant as well. Invertebrate and vertebrate herbivores (including cattle, if the plots were grazed) can find a variety of forage options in the high diversity plots right now – far more than in the low diversity or monoculture plots. Within a week or so, the high diversity plots will also have several different kinds of wildflowers in bloom, providing resources for early-season bees and other pollinators. The low diversity and monoculture plots will have far fewer resources for pollinators throughout the season. Furthermore, invasive plants species trying to establish themselves within the high diversity plots face stiff competition from plants using wide range of growth strategies. They will find a smaller amount of resistance in the other plots, where less diverse plant communities are not as efficient at taking up space and fully utilizing resources.
Plant diversity is incredibly important in natural systems for a variety of reasons, only a few of which are mentioned here. We still have a lot to learn about how plant communities function, and how plant diversity plays into that. However, we already know enough to recognize the value of having numerous players in the game. It was fun to see a visual demonstration of that value last week.
How important is plant diversity in restored prairies?
Are diverse prairies more resistant to drought and invasive species than less diverse prairies?
How does plant diversity influence invertebrate communities and their ecological functions?
These kinds of questions have been the focus of multiple research projects in our Platte River Prairies over the last decade or so. We have numerous restored (reseeded) and remnant (unplowed) prairies that provide excellent field sites, and have also established two sets of experimental research plots to help focus specifically on questions related to plant diversity. Those plots are 3/4 acre (1/3 ha) in size and represent varying levels of plant diversity, allowing us to investigate the functional differences between them. Researchers from the University of Nebraska, Kansas State University, the University of Illinois, and Simpson College have been involved in data collection efforts so far.
Craig Allen, Leader of the Nebraska Cooperative Fish & Wildlife Research Unit, and I are hoping to take the next step in these efforts by bringing on either a PhD or Post-Doctoral Research Associate. We have data to build upon, including some intriguing results regarding invasive species and insect herbivory rates at varying levels of plant diversity, but want to greatly expand upon those data. If you or someone you know is interested in these kinds of questions, please read below and contact Craig or me with questions.
Here is the official description of the position:
Ph.D. or Post-Doctoral Research Opportunity: Grassland diversity, restoration and resilience
Ph.D. graduate research assistantship or Post-Doctoral Research Associate. Available starting in May 2015, to investigate the relationship between grassland restorations and ecosystem services and resilience. The assistantship (or Post-Doc) is with the Nebraska Cooperative Fish and Wildlife Research Unit, in the School of Natural Resources at the University of Nebraska, working closely with the Nature Conservancy scientists and resource managers. The research project will include a synthesis of literature to identify prominent knowledge gaps related to the restoration of grasslands and resilience. In addition to synthesis, field work will occur on a suite of restorations in central Nebraska. Some questions of interest are listed below, but ultimately, successful candidates will be expected to develop a specific research project(s). The candidate could approach this project from a broadly ecological, or botanical, or entomological frame.
The successful applicants will be highly motivated, with a strong work ethic, strong and demonstrated writing skills, a passion for field work, and the ability to work in collaboration. Experience in restoration ecology is helpful, but not required. Ph.D. applicants should possess a M.S. in Wildlife, Biology, Zoology, Botany, or Entomology, or a related field and have a valid driver’s license. Post-doctoral applicants should possess a Ph.D.
Interested applicants should send a cover letter, names and emails of 3 references, GPA and GRE scores, and an updated CV as an electronic PDF or Word document to Craig Allen, email@example.com
Review of applications will begin March 15 and continue until a qualified candidate is identified. For more information on the Nebraska Coop. Unit and the University of Nebraska-Lincoln please visit us at:
Specific projects could include all or part of the following:
Relationship between restoration diversity and ecosystem services, such as invasion resistance and herbivory; interactive effects that might mediate some resilience properties; responses to multiple disturbances; how invasions might weaken the ability to cope with disturbance; microbial diversity and ecosystem function and services; response to pulse and press disturbances and mechanisms driving responses; functional trait diversity and redundancy and resilience.
S’mammal Spotlight: the Fearsome Northern Grasshopper Mouse
While I finish up the data entry for my independent project on small mammals, I thought it’d be fun to share some more information about some of the s’mammals out in our prairies. Some of them are really, especially awesome, and hopefully knowing a little more about them will elucidate why we think they’re worth studying!
I thought I’d kick off this series with one of my favorites, the northern grasshopper mouse (Onychomys leucogaster). There is no other way to describe this critter except beefy. This is a mouse made for fighting, for pouncing, for striking fear in the hearts of the other lil s’mammals (I haven’t obtained any critter statements about the last part, but if I was pocket mouse-sized, I’d be wary). They are a handful to work with – very aggressive, and surprisingly agile. They’re able to shrink out of pretty much any corner I try to limit them to, and their pointy carnivorous teeth ensure that I am very aware of the distance between my fingers and their mouth!
If you’re wondering if you’ve seen one, northern grasshopper mice have big eyes, big ears, and relatively short tails that are consistently about 42 mm long (Mike and I measured many grasshopper mouse tails). The majority of them are silky gray-brown on top and white below, though there are a few whose backs are more cinnamon-y than gray. Juveniles tend to be lighter colored. Most of the grasshopper mice I caught were approximately the size of my fist, maybe a little smaller, about 33-45g (for reference, pocket mice are generally 8-12 grams).
The impressive muscle mass of a northern grasshopper mouse is achieved by a largely carnivorous diet. True to their name, grasshopper mice consume a lot of grasshoppers, as well as other insects, and sometimes other mice, including others of their species. Allegedly, grasshopper mice stalk their prey and will emit a shrill cry before attacking. It is thought that they tend to have a longer period of maternal care than most mice (which isn’t saying much) so that young grasshopper mice can be taught to hunt. Ideally, I’d like to camp out by their burrows in the spring so that I can hear them sing and see their fearsome predatory skills in action.
If you’re looking for a northern grasshopper mouse, you are mostly likely to find them in sandy soils. They seem to prefer sandy areas that had sparser and often shorter vegetation. Apparently the sandhills portion of our Platte River Prairies are ideal habitat because they are loaded with northern grasshopper mice. It is exciting that we have such a robust population, especially because it gives us a chance to learn more about them.
Learning more about their habits will not only aid in our management of our prairie, but could potentially help fill some gaps in the broader scientific literature. While the life histories of some small mammals are pretty well understood, it seems to me that there is some updating to do in terms of the natural history descriptions of northern grasshopper mice. For example, most natural history sources will tell you that the northern grasshopper mouse is very territorial and will fight to the death any other grasshopper mouse that wander into its territory. However, Mike and I have been catching several northern grasshopper mice within 10-14 meters of each other. This seems like a much higher density than one would expect for a highly territorial species, especially one that is known to have a fairly large home range in relation to its size.
Greg Wright, a wildlife biologist at the Crane Trust says he’s seen reports that grasshopper mice might hunt as family units, which could explain the densities we were catching. [It will be intriguing to see if our data supports that idea]. It could also be that northern grasshopper mice are only especially territorial during the mating season? A small study in Colorado found that several individuals shared a burrow in the winter.
I think these critters have a compelling story, and I look forward to our future studies and new research questions so that we can expand our understanding of the awesome, fierce northern grasshopper mouse.
BEHIND THE SCENES
Editor’s Note: Ok, two things, gigglepants. First, have YOU ever tried to take a photo of a grasshopper mouse in the wild? Exactly. They don’t tend to sit still and pose, do they? Second, I have not hidden my photo techniques in the past, and on the rare occasion when I use something like a cardboard box to get a photo that would be otherwise impossible, I try to be transparent about it. Many readers will remember my very serious technical piece on how to use a wheelbarrow as a photo studio, for example. At least I don’t use something silly like a plastic bag… : )
Jasmine’s favorite s’mammal information sources:
University of Michigan’s Museum of Zoology Animal Diversity Web. This site has photos, skeletons/skulls, life history information, range, and usually some tidbits from recent studies. http://animaldiversity.ummz.umich.edu/
The Colorado paper I mentioned:
Size and Habitat Characteristics of Home Ranges of Northern Grasshopper Mice (Onychomys Leucogaster). Paul Stapp. The Southwestern Naturalist, Vol. 44, No. 1 (Mar., 1999), pp. 101-105
As you might expect, there is more to the story. It turns out that the frequent spring fire (with no grazing) regimes at Konza has other impacts. One example is that frequent fire favors grasses over forbs and decreases plant diversity over time. Prairies that are burned every year or ever two years develop a grass-dominated plant community in which many forb species are difficult to find. So, frequent fire is bad for plant communities… Right?
But in other tallgrass prairies, especially in more eastern prairies such as those in Illinois, researchers are seeing very different impacts of frequent fire. A paper by Marlin Bowles and Michael Jones, for example, found that frequent fire “stabilizes” plant communities in the Chicago, Illinois area, and that plant diversity was positively correlated with fire frequency. In fact, their results are almost the exact opposite of what was seen at Konza. In the Illinois study, frequent fire decreased the dominance of warm-season grasses and increased the diversity of summer wildflowers.
What the heck is going on??
If we could answer that question, we’d be miles ahead of where we are now in terms of understanding prairie ecology. I can come up with lots of potential reasons for the difference between frequent fire application in Illinois versus Kansas, but I can’t confirm or deny any of them – we simply don’t know. As I think about why prairie plant communities might become more dominated by grasses over time, I wonder about factors such as small scale plant diversity, soil productivity, and the soil microbe community – all of which may correlated with each other.
Eastern remnant (unplowed) prairies tend to have a higher density of plant species (e.g., plant species per square meter) than western prairies. High species density could potentially help suppress grass dominance because of the variety of competition strategies each of those plant species employs to take and defend territory. Those strategies include allelopathy (releasing chemicals that retard growth of nearby plants), rhizomes (underground stems that can connect even fairly distant stems of the same plant together), root density/depth, and many others. It seems logical that communities with that kind of well-established complex competitive environment would present a major challenge for any species (grasses or otherwise) trying to become dominant. Maintaining consistent growing conditions by burning or haying annually might facilitate stability within those plant communities because it essentially maintains a stalemate; no plant species is ever given a window of opportunity to gain advantage over its neighbors. Or this could all be balderdash – I’m just throwing out ideas here.
Does the rich soil organic matter content of eastern tallgrass prairies help suppress grass dominance? It’s probably the major reason for the higher plant species density in those prairies, so maybe. On the other hand, research at Konza and elsewhere in more western prairies shows that adding nitrogen to prairies (increasing productivity) increases grass dominance and lowers plant diversity. Hmm.
Soil microbial communities surely have a very important influence on plant diversity, but (as discussed in a previous post) we don’t know much about them yet. I’m optimistic that our understanding of soil microbes will grow tremendously during the next few decades, but the complexity of that world might mean that it will take many more decades before we start to get a grasp on it. In the meantime, we can use it as a convenient scapegoat. If something you don’t like is happening to your prairie, it’s probably a soil microbe problem…
Those of you who read this blog frequently may be surprised that I haven’t mentioned insects or other animals yet. Let’s talk about them now, shall we?
It’s very important to remember that even if frequent burning seems to maintain high plant diversity in (some) prairies, a prairie is much more than just plants. The use of frequent fire tends to create fairly homogenous habitat conditions across a prairie. Regrowth rates are similar across the whole burned area, so vegetation height and density is relatively uniform. Dead material, including both litter and standing dead vegetation, is scarce. Because habitat diversity is limited, so is the diversity of creatures that rely on that habitat. In taxonomic groups ranging from grasshoppers and spiders to mice and birds, research shows that habitat diversity is positively correlated with species diversity. Creating habitat heterogeneity – through grazing, patchy mowing, or other means can help facilitate a more diverse animal community. Burning in a less regimented way can help too, especially if that means splitting a prairie into multiple management units and burning only a subset of those each year.
In small isolated prairies, it’s also critically important not to burn (or mow) the entire prairie at the same time. With limited opportunities for species to recolonize from other prairies, a fire that kills all of the individuals of a particular species (e.g., an insect that overwinters in the stems of grasses or in the litter along the ground) can mean the end of that species’ existence in that prairie. Maintaining a floristically diverse prairie without a full complement of invertebrates doesn’t seem like success to me. On the other hand, I also appreciate the difficulties associated with managing small prairies.
To wrap this up, I think there are two really important points to make about fire frequency in prairie management. First, there are some big questions about why frequent fire seems to maintain high plant diversity in some prairies but encourages grass dominance in others. Figuring out the answers to those questions may be one of the more important keys to prairie conservation success. Second, even if frequent fire maintains high plant diversity and repels invasion by shrubs and trees, it still might not be the best choice for a prairie management strategy. There is much more to a prairie than its plants, and even if you don’t much care for invertebrates, birds, reptiles, or mammals (and how could you not?) those species – especially the invertebrates – are strongly tied to the long-term viability of the plant community, so it’s probably not good to ignore them. To be clear, I’m not saying people who use frequent fire are evil destroyers of animals. I’m just raising a flag of caution and pointing out some potential tradeoffs.
Those of us who work with prairies are used to the seemingly overwhelming complexity of grassland communities and the way those communities respond to management. In fact, for many of us, it’s a big reason we love prairies as much as we do. While we still have more questions than answers about effective prairie management, we have enough information to go forward with. Most importantly, prairies are pretty tough, so excepting drastic measures such as broadcast spraying with 2,4-D (and maybe burning an entire tiny prairie), we have the latitude to try out lots of ideas and see what works. We’ll learn as we go.
In the meantime, it’d be great if all you researchers out there would get cracking on the issue of disparate effects of frequent fire in eastern versus western prairies. It should only take a few decades to figure it out… Right?
A couple years ago, I wrote about some work from Kansas State University related to woody plant expansion in prairies. Many of us who work with prairies constantly wrestle with questions about trees in prairies. Why are they encroaching so quickly these days? What prevented them from doing that in the past? During our recent trip to Konza Prairie, we got to discuss this topic more in-depth with Jesse Nippert and other researchers at Kansas State.
Clearly, a combination of factors influences how quickly trees and shrubs enter and spread in grasslands. One big reason is the increase in “seed rain” in some of today’s prairies. Prairies in fragmented landscapes with numerous trees and shrubs in nearby woodlots, road ditches, shelterbelts, etc., are deluged with seeds from those woody plants. The vast majority of those seeds fail to establish, but the high number of seeds coming in means that some will find opportunities to grow.
Other factors may include the higher rates of carbon dioxide in today’s atmosphere and higher amounts of nitrogen deposition (from industry and agricultural facilities, for example), both of which tend to favor woody plant establishment. In addition, we are in a relatively wet climatic period if you look at the geologic record. While there have been droughts, including severe ones, in recent years, those droughts are nothing like the multi-decade severe droughts that can be seen in the relatively recent geologic records for the central United States. Long and/or frequent droughts favor herbaceous plants (such as grasses and wildflowers) over trees.
However, Jesse Nippert’s research into the way trees, shrubs, grasses, and forbs (wildflowers) compete for water belowground provides some additional insight into the march of woody plants into prairies. As we started talking about roots, Jesse confirmed something I’d heard from Dave Wedin at the University of Nebraska; even though grasses can have very deep roots, most of their water use is actually very shallow – within the top 25 cm of soil. Jesse says the reason those grasses persist during very dry periods is not because of their deep root systems, but because they can continue to grow and function when available soil moisture is very low. Forbs also pull a lot of their moisture from shallow roots, but utilize slightly deeper roots (50-75 cm deep) during droughts because they can’t compete well with the ultra-efficient fine-rooted grasses at the upper levels.
It turns out that understanding root competition might help us better understand woody plant encroachment as well. In many parts of Konza prairie, clonal shrubs such as rough-leaved dogwood and smooth sumac have expanded rapidly over the last several decades. As Jesse and his students have studied this phenomenon, they have concluded that an important factor behind this expansion is the strategy those shrub clones use to acquire water. While grasses and forbs are mostly using water from the top 1/2m of the soil, shrubs pull much of their water from deeper in the soil profile, allowing them critical access to water not being utilized by their competition – especially in years when the upper soil layers are dry.
The clonal form of dogwood and sumac gives them another advantage. As clones expand, the tillers (aboveground stems) on the outer edge of the clones have very small roots. However, by studying the isotopic signatures of the water in those shallow-rooted tillers, Jesse can tell that they are also accessing water from deep in the soil profile. He says this is almost surely because the older, deep-rooted plants in the center of the clone are sharing the water they acquire with the younger stems on the outside. Not a bad strategy.
Of course, as these clones of dogwood and sumac use their water acquisition and sharing strategy to advantage and spread into the prairie, they also shade out their competition – especially beneath the tall/dense tillers toward the centers of clones. Suppressing the growth of grassy undergrowth not only removes that competition for resources, it also helps make the clones fireproof. Since dried grasses are the primary fuel for prairie fires, the absence of grasses beneath shrub clones means that fires can’t burn through them. It’s not hard to see how the processes of deep water acquisition/sharing and fire-proofing can create a positive feedback loop that helps drive an inexorable expansion of shrubs into the surrounding prairie.
We didn’t talk about this in Kansas, but my experience is that fire-proof shrub clones are an important avenue for the establishment of trees as well. Many tree seeds are deposited into those shrub patches by birds that see those shrubs as convenient and prominent perching sites. If those seeds are able to germinate and establish within those clones – and they often can – the resulting trees can grow without fear of the fires that would otherwise threaten them. Hiding in the middle of big shrub clones also gives those trees a chance to grow in relative safety from marauding prairie land managers…
Because much of Konza prairie has been managed under a variety of long-term fire regimes (1,2,4,10, and 20 year frequencies), Kansas State Researchers have some pretty good data on how fire frequency affects shrub expansion as well. Essentially, prairies burned every year or every other year do not have encroachment by dogwood or sumac, but prairies burned less often are being gradually overtaken by shrubs. Interestingly, the fastest expansion appears to be in prairie watersheds managed with a fire frequency of every four years (which is also about what the estimated average fire frequency was for that landscape during pre-European settlement). While it might seem counterintuitive that a four year fire frequency allows for faster woody encroachment than a 10 or 20 year frequency, the explanation appears to lie in the way shrubs respond to fire. Fire seems to stimulate radial growth in dogwood and sumac, meaning that the plants put an emphasis in growing horizontally rather than just vertically after they are burned. Under very frequent fire, this is apparently immaterial, probably because the shrubs never get enough rest between fires to take advantage of that radial growth. However, when they are given 3 years to recover between fires, that radial growth response after each fire means that burning actually stimulates faster expansion of shrub clones. Under a 10 year fire frequency, that extra radial growth only occurs once every 10 years, so the overall expansion is actually slower than in under a four year fire regime.
Before you jump to the conclusion that burning every year or two seems the obvious best strategy for shrub control, remember that woody plant suppression is only one of many objectives for prairie management. I’ll address some of the other, less positive, effects of frequent fires at Konza in an upcoming post.
As I said earlier, there are multiple factors that affect the rate of tree and shrub encroachment on prairies. Seed rain might be as important as anything, and climatic conditions, increases in nitrogen and carbon dioxide levels, and fire suppression are all likely contributors as well. However, the way plants compete belowground, particularly the deep water use strategy of clonal shrubs such as dogwood and sumac, also seems to play an important role. Frequent fire application can be one way to prevent encroachment, though it comes with other baggage (see upcoming post…) and may not help remove shrub patches once they’re established. At Konza, they took some of the every-20-year-fire-freuency watersheds and started burning them annually to see if they could get rid of the shrubs and trees. Thirteen years later, those patches are still there, though the individual stems are much smaller. It seems that while frequent fire might help prevent woody plant establishment, frequent fire alone might not be able to reverse it – at least not on a very fast timeline.
Woody plant encroachment is one of the biggest challenges we face in prairie management today. A solid understanding of the mechanisms behind that encroachment should help us design more effective strategies to combat it. Shredding, burning and herbicide application are all useful tactics, but figuring out the timing, frequency, and intensity of those applications will be critical. We need to use the various competitive strategies of grasses, forbs, and shrubs to our advantage. As an example, some recent work by Dirac Twidwell (University of Nebraska-Lincoln) seems to indicate that burning under more extreme heat and drought conditions than we typically feel comfortable with might be one way to really tip the scales away from woody plants. The feasibility of that will be limited in some landscapes, but surely there are other innovative tactics that can help. If we work together and aren’t afraid to try some new ideas, we can figure this out.
Last week, several of us from the Platte River Prairies traveled south to visit the Konza Prairie Biological Station near Manhattan Kansas. Konza Prairie includes about 8,600 acres of prairie, jointly owned by Kansas State University and The Nature Conservancy. The prairie is managed and used as a biological station by Kansas State University’s Division of Biology, but hosts research projects from scientists around the world. The biological station has a three-fold mission: long-term ecological research, education, and prairie conservation.
Research results from Konza Prairie have been very influential for grassland managers across the world, but particularly in western tallgrass and mixed grass prairies of North America. Over the next couple of weeks, I’m going to report on several topics we discussed with researchers at Konza during our trip. Today, I’ll just give you an overview of the site and our visit.
We had two main reasons for our trip to Konza. First, our two Hubbard Fellows, Jasmine and Dillon, are designing research projects on small mammals and grasshoppers, respectively, and wanted to learn from Kansas State researchers on those topics. Second, researchers from Konza Prairie have produced some of the most important grassland science there is, and we wanted to learn as much as we could by touring the site with some of those researchers.
Thursday evening, we arrived just in time to take a short hike near the headquarters as the sun was going down. Then we went to bed early so we could get up before the sun Friday morning and accompany researcher Drew Ricketts as he checked his small mammal trap line. Drew is comparing the small mammal communities between patch-burn grazed prairie (with cattle), annually burned/grazed prairie, and ungrazed prairie burned every four years. Jasmine wanted to see his trapping and handling techniques and get some tips on identifying some of the species.
After we spent a couple hours with Drew, we met up with Kansas State professors Tony Joern, John Blair, and Jesse Nippert and started a four hour tour of the site that was so full of information and ideas my head is still spinning. We looked at the portion of the site grazed by a herd of 400 bison and talked about the impacts of bison vs. cattle grazing, the role of bison in keeping cedar trees out of prairie (they’re good at it), and several other related topics. Next, we drove through the ungrazed watersheds of Konza that have been burned on frequencies of 1, 2, 4, 10, and 20 years since as far back as 1978. The plant composition and habitat qualities of those areas have diverged in very interesting ways through time. We finished by looking at a (fairly) new restoration project and some small plots treated with various fire regimes and fertilizer treatments. Along the way, we talked about myriad other topics as well…
By the time Tony, John, and Jesse headed back to campus, we were ready to head home – not because it was hot (it was) or because we were hungry (we were), but because we didn’t feel like we could cram any more new information into our heads. As I said at the beginning of this post, I’ll try to synthesize some of that information for you over the next couple of weeks, but I’ll also try to put it into small manageable doses.
Over the last several years, we’ve begun to evaluate our prairie restoration work beyond just looking at plant communities. Our primary objective for restoration is to functionally enlarge and reconnect fragmented remnant (unplowed) prairies by restoring the land parcels around and between them. (See more on that topic here.) Because of that, it’s pretty important that we look at whether or not species – plant and animal – living in those remnant prairies are actually using and moving through our restored prairies. In 2012, we brought James Trager and Mike Arduser to our Platte River Prairies to help us start measuring our success in terms of ants and bees, respectively. We’re still early in that effort, but things look good for both so far. Most ant and bee species living in our prairie remnants are also showing up in nearby restored prairies.
Now we’re hoping to find similar patterns with small mammals. Mike Schrad, a Nebraska Master Naturalist, has volunteered to help us see whether the small mammal species in our remnant prairies are also in adjacent restored prairies. We’ve begun by looking at a single 200 acre prairie complex that consists of a remnant prairie surrounded by several restored prairies (former crop fields seeded with 150 or more plant species back in the mid-1990’s). Mike came out for three nighttime sampling periods in 2013 to see what he could catch in the remnant prairie and one of the adjacent restored prairies.
Mike and I have been looking over the data from this first year, and I’m pretty encouraged by what he’s found so far. He caught four species in the remnant prairie, and all four were also in the adjacent restored prairie. In addition, a fifth species, the short-tailed shrew, was caught only in the restored area – but only once. The five mammal species he caught were:
Prairie vole (Microtus ochrogaster)
Meadow vole (Microtus pennsylvanicus)
Harvest mouse (Reithrodontomys sp.)
Deer mouse (Peromyscus maniculatus)
Short-tailed shrew (Blarina hylophaga)
The relative abundance data for each species caught by site are interesting (see the table below), and reflect the fact that the sites had been largely rested from fire and grazing during the last couple of years. Voles are attracted to the kind of thatchy grassland habitat found in ungrazed/unburned prairie, and they were caught more often than any other species in our site. The higher numbers of voles in the remnant prairie might indicate a more dense vegetation structure there than in the restored prairie (or might have just been happenstance). It was also interesting to see more harvest mice caught in the restored prairie, though the total numbers were low enough that we aren’t drawing any strong conclusions from them. The total number of animals caught by species and site are below:
On the one hand, seeing the same species in both remnant and restored prairie might not seem very surprising. Our restored prairies have the same plant species in them as the remnant prairies, and are managed the same way. It seems likely that small mammals can find everything they need for food and shelter there. On the other hand, it’s dangerous to blindly assume that we’re providing for the needs of all species when we restore prairies. The mouse and vole species we saw this year have been pretty well studied, but we still don’t know everything about what they need to survive. What looks like two identical habitats to us might be very different to a 2 inch tall little critter. For those reasons, it’s nice to see some support for our assumptions – though we still need much more data.
Over the next month or two, Mike and I will be planning future sampling efforts. Ideally, we’ll repeat the same kind of trapping he did in 2013, but do so at other sites were we have adjacent remnant and restored prairies. If we continue to see the same pattern of use – the species in the remnant prairie also using adjacent restored prairie – I’ll start to feel even better about our ability to defragment prairies from a small mammals’ perspective.
However, even if we continue to see results similar to this year, there will be more to learn. First, there are several less common species of small mammals in our prairies (we think) that weren’t caught this year. Two of those are plains pocket mouse and plains harvest mouse, both of which could be in our upland areas and are priority conservation species in Nebraska. Another is Franklin’s ground squirrel, a species we see periodically in our lowlands, but which has disappeared from most tallgrass prairies in the eastern U.S. I’d like to know that we’re creating habitat for those less common species, as well as for the common ones we caught this year.
There is still a lot to learn about how well our restored prairies are working. However, with each step we take, I feel a little better about our ability to reduce the impacts of habitat fragmentation by restoring strategic parcels around and between prairie fragments. Knowing we can do it doesn’t make it economically or socially feasible, but those other factors are irrelevant if we can’t solve the technical issues first – and prove that we’ve done so.
Among some prairie enthusiasts, there seems to be a perception that plains bison are magical creatures that live in complete harmony with the prairie. They eat grasses but not wildflowers, they float just above the ground to avoid stepping on plants or compacting the soil, and they create tidy little wallows that fill with rainwater for tadpoles and wading birds. Cattle, on the other hand, are evil creatures that seek and destroy wildflowers, removing them from prairies forever. They also stomp all over prairies, trampling plants and birds to death and causing cascades of soil erosion and water pollution.
Let me be clear: I’m a big fan of bison. I feel very fortunate to spend time at The Nature Conservancy’s Niobrara Valley Preserve and other big prairies where I can observe and photograph bison up close. Bison are distinctive, attractive animals that evoke a sense of history and grandeur… but they are also big stompy animals that go wherever they want, poop all over the place, rub on trees, trample plants (and animals), and can cause erosion issues. None of that is good or bad; it just is.
I’m a fan of cattle too. They have big beautiful eyes, individual personalities, and can be more playful than their typically stoic faces might hint at. I enjoy spending time around cattle at our Platte River Prairies and in my own family prairie. In both places, they are a major part of our prairie management strategy, which is aimed at creating and maintaining diverse plant communities and high quality wildlife habitat. (And yes, cattle are also big stompy animals that go wherever they want, poop all over, rub on trees, trample plants and animals, and cause erosion issues.)
TREES AND PONDS
While both bison and cattle can be engaging creatures, there are a few real differences between the way bison and cattle utilize and impact prairies. However, those differences are less stark than you might think. Based on the best available research and expert knowledge, the biggest distinction between bison and cattle behavior in prairies essentially boils down to this: cattle hang around water and trees more than bison do.
That general pattern is reported in many studies comparing the two, but was most reliably demonstrated in a recent study at The Nature Conservancy’s Tallgrass Prairie Preserve in Oklahoma, where GPS collars tracked animal locations through time. That study looked at bison and cattle at similar stocking rates and under the same management regime (patch-burn grazing) – though the bison were grazing year-round in a 23,000 acre pasture while cattle were only present for 7 months/year in pastures of around 1000-2000 acres. The GPS collars showed that cattle were attracted to ponds and trees while bison tended to avoid areas near water and showed no attraction to trees. Importantly, the same study also showed strong similarities between bison and cattle behavior, namely that both were strongly attracted to the most recently burned areas of pastures and tended to avoid steep slopes.
The conclusion that cattle are attracted to water and shade fits with one of the big objections to cattle grazing by some prairie enthusiasts – that cattle tend to “wreck” areas near ponds and tree groves by repeatedly stomping around and defecating in those places. While that can be true, those impacts are highest under high stocking rates, and can be avoided by fencing out ponds and trees or greatly reduced by providing long rest periods between grazing bouts. Those impacts are also less severe in larger pastures, especially when multiple water and shade options are available and cattle are encouraged (or forced) to use each area intermittently. The attraction of cattle to wet and shaded areas can be a real challenge, but it’s not an insurmountable one.
The other beef prairie enthusiasts have with cattle (sorry) has to do with their diet. The perception of many is that bison subsist solely on grass, leaving wildflowers untouched, while cattle eat a high percentage of forbs (broad-leaved plants), often leading to the decline of those species over time. The purported result is that bison-grazed prairies maintain high plant diversity, including an abundance of rare plant species, while cattle-grazed prairies become degraded as numerous forb species are grazed out of existence. While that’s a big overgeneralization, it’s an understandable one because a number of research projects have reached that conclusion.
Unfortunately, those research projects have largely compared bison and cattle under very different circumstances. Diet comparisons are usually made between bison in a single huge pasture (often under patch-burn grazing management) and cattle in a rotational grazing system – often at a higher stocking rate. As a result, it’s not clear whether observed differences between bison and cattle diets are due to biological differences or grazing systems.
Imagine if you were given 30 days’ worth of groceries at the beginning of each month. You’d likely eat many of your favorite foods first and then make do with whatever’s left toward the end of the month. Comparing your diet to that of someone who was allowed to go grocery shopping every day would be completely unfair, wouldn’t it? Unfortunately, that’s essentially the comparison made by many research projects comparing the diets of cattle and bison. Cattle in a rotational grazing system can only choose from the available plants in their particular paddock, and don’t get a new set of choices until they are moved into a new paddock. In contrast, cattle or bison that spend their whole season in a large pasture, especially one in which a portion has been recently burned, can regulate their diet much more freely. They spend most of their time eating their favorite foods (mostly grasses) in the most recently burned patch, but they can also travel elsewhere if the supply in that patch runs low. In addition, by regrazing their favorite plants over and over, livestock can keep them in a state of high nutritional value for much of the season.
We did some research back in 2001 in which we evaluated the forage choices of cattle in a patch-burn grazing system under a moderate stocking rate (Helzer and Steuter 2005). Our data showed that those cattle were very selective toward grasses, and ate very few forbs under those conditions. That research, along with observations other scientists and cattle managers at patch-burn grazed sites, has led to an altered perception of the forage selection differences between cattle and bison – namely, that many of the differences are driven more by grazing system than by biology.
Prairie managers have to make difficult decisions about how to create and maintain diverse plant and animal communities at their sites. One big choice is whether to graze or not to graze a particular prairie. Regardless of whether it is grazed by bison or cattle, a grazed prairie is going to look and act very differently than an ungrazed prairie. Many plants will be stepped on and eaten. Some portions of the prairie will be more heavily visited than others and will get trampled down. Short-lived opportunistic plants will become more abundant, due to the weakening of dominant grasses through repeated grazing. Some managers will see those effects as positive, but others will not – depending upon the management needs of a particular prairie. Regardless, deciding whether or not to graze has far greater consequences than the subsequent decision about whether to graze with bison or cattle.
If the decision to graze has been made, it’s important to recognize the appropriate criteria for deciding between bison and cattle. Bison do act somewhat differently than cattle, especially around water and trees. However, those differences depend heavily on scale. Both cattle and bison create areas of bare soil around drinking water sources, and both create trails as they move from one favorite place to another. In small pastures, those impacts are multiplied because both bison and cattle are forced to visit the same places repeatedly, which can lead to repeated trampling of plants, soil compaction, and other issues. The differences between a small bison-grazed pasture and a small cattle-grazed pasture are pretty minimal.
In larger pastures (thousands of acres in size), grazing animals have room to spread out. At that scale, bison-grazed pastures tend to have fewer heavily grazed and trampled areas near trees and standing water than cattle pastures do. While that can certainly be a perk of using bison, it’s also important to remember that even in large cattle-grazed pastures, the proportion of the overall pasture that receives that kind of heavy impact is very small. In addition, there are management options that can be used to minimize the size and severity of those impacts by cattle. Those include fenced exclosures around sensitive areas and tactics that shift the locations where cattle spend most of their time (such as creating new burned patches, turning on/off drinking water facilities, and moving mineral feeders around). The upshot is that there can be some prairie conservation benefits of using bison. However, those benefits accrue most strongly in very large pastures, and even at that scale, there are cattle management strategies that can close that gap considerably. On the flip side, bison come with their own set of complications and costs.
I spend most of my time working at our Platte River Prairies, and I’m often asked why we don’t have bison at those sites. There are several good reasons for that, starting with management flexibility. The cattle that graze our Platte River Prairies belong to our neighbors, and our lease arrangements allow us to dictate how many, where, and for how long cattle graze each year. Between years, or even within years, we can pretty easily change those plans if we get unexpected weather patterns or just don’t like the way things look. That kind of adaptive management is much more difficult with bison, especially because if we had bison, we’d have to own the herd and keep them on our prairies year round.
A second reason we use cattle is financial. It takes a much lower investment in infrastructure and personnel to lease cattle than to own bison. We have to provide a good perimeter fence (usually a four-wire barbed wire fence) to hold cattle in our pasture, and provide water for them to drink. Beyond that, the owner of the cattle trucks them in when we ask for them, and then gathers and trucks them away again when we’re done. If we owned a bison herd, we would need a much stouter, and more expensive fence, and a very expensive corral system to use for an annual roundup, sorting, and inoculation process. In addition, we would be responsible for conducting that roundup, doctoring animals when if needed, and for dealing with buying/selling animals to maintain our desired herd size. All of that takes time and people, and that’s expensive. At our Niobrara Valley Preserve, the 22,000 acres of bison pasture can hold enough bison that income from selling excess animals covers many of those costs. That wouldn’t pencil out in our much smaller prairies down on the Platte River.
The last reason we run cattle instead of bison is that in our relatively small prairies (200-600 acres), the behavior of bison would not be very different than that of cattle. We might see less stomping around in standing water and under trees, but we can already manage those impacts by controlling whether/how often cattle have access to those areas. Most importantly, through our use of patch-burn grazing, electric fence enclosures and exclosures, and our ability to set and change grazing intensity, timing, and frequency, we are getting the prairie management impacts we want by using cattle. We can get cattle to graze very selectively in order to suppress grasses and give wildflowers a chance to flourish, and to create the kind of patchy habitat structure many wildlife and insect species need to thrive. In other cases, we can get them to graze much less selectively in order to create a particular habitat structure or other impact. As a result, we are maintaining resilient and diverse prairies – and that is our ultimate goal.
Plains bison nearly disappeared completely from the grasslands of North America as European settlement spread across the continent. The ongoing recovery of bison is an important indicator of prairie conservation success, and I hope that upward trend continues. At the same time, I worry about the tendency of some to heap accolades upon bison while dismissing cattle as inherently destructive. The differences between them simply don’t warrant that kind of broad categorization. If grassland conservation is our goal, we should be sure we’re open to using whatever strategies (or animals) can help achieve that. In very large prairies, bison may be the best fit – assuming the logistics and costs of owning bison make sense. In other situations, however, deciding whether bison or cattle are most appropriate is not a simple matter. It’s a decision that should be based on facts and management objectives – not on aesthetics or mythology.