It’s a good ol’ fashioned blizzard here today. As I’m sitting snugly in my warm house, I’m feeling a little badly for some of wildlife out there in the snow and wind. The boys went outside to play in the snow for a little while, and both of them spent most of their time building shelters from the weather. Many wildlife species, of course, migrate to warmer places or find/build themselves underground burrows to overwinter in, but there are some animals out there in the prairie right now, and this has to be a bad day for them.
Sitting here on my comfortable couch, I’ve been thinking about the prairies I manage or help with, trying to remember what kind of cover is out there. Overall, I feel pretty good about the situation. Our shifting habitat mosaic approach involves providing a wide range of vegetation structure types in each of our prairies, including everything from short sparse vegetation to the kind of thick dense cover wildlife are probably seeking out today. Nelson (our Platte River Prairies land manager) and I have periodic conversations in which we try to envision ourselves as creatures that prefer various habitat types. How far would we have to travel to find cover? If we burn one patch of dense cover, where is the next closest patch of similar cover, and what would animals have to travel through to get to it? We have a lot of factors to consider and balance as we discuss management plans each year, so it’s always helpful to see the world through the eyes of the various species that will have to live with (literally) the decisions we make.
To be completely honest, I probably don’t think enough about winter cover as I’m trying to consider the perspective of various creatures. I’m more often thinking about nesting habitat for birds, breeding cover for small mammals, or sunning areas for invertebrates and reptiles that need to thermoregulate during the growing season. Days like today are a great reminder that while all those considerations are important, at least some species will probably live or die based on what kind of shelter they can find during winter storms like the one roaring outside right now.
I’m thinking today about meadowlarks, for example. As I’ve walked our prairies during the last month or two, I’ve seen a lot of meadowlarks flying around in small groups. My understanding is that meadowlarks that breed around here head south to Kansas or Oklahoma, and the ones we see during the winter come from up in the Dakotas. In other words, meadowlarks don’t migrate en masse to one general destination. Instead, each bird just goes a little southward from where they spent the summer. I wonder if they each wait until they start seeing birds from the north show up and then head south to get away from the crowd…
Regardless, birds like western meadowlarks need some kind of shelter out in the prairie on days like this. We know a lot less about the winter habitats used by grassland birds than we do about summer habitat use, and as far as I know, no intrepid biologist has yet gone out to see where meadowlarks or other birds are hanging out during blizzards. (If you’re an intrepid biologist who HAS done this, please let me know!) I think it’s fair to assume that most birds (and any other wildlife who aren’t underground) try to get out of the wind during this kind of storm. It’d be interesting to know whether they stay in open grassland and look for tall dense vegetation or venture into brushy or wooded areas where they might not normally go.
Not knowing much about individual wildlife species and how they each choose to shelter from winter storms, I guess the best strategy is to provide as many habitat types as possible so they can all find what they need. That way, meadowlarks can forage in short or “weedy” areas during pleasant sunny days, but move to a nearby patch of dense grass (or whatever other cover they like) when they need to nestle in thatchy vegetation and get out of the wind.
Here in our comfy house, we’ve been talking about trying to fix the drafty corner of our kitchen, where one of our walls needs a little better insulation. Our poor little feet get cold when we’re making toast on windy winter mornings! It’d be really nice to get that fixed. On the other hand, it’s just the kind of hardship that helps me understand what meadowlarks are going through on days like this. I bet their feet were cold at breakfast time too…
At our Niobrara Valley Preserve (NVP), we’re experimenting with prairie management techniques to see if we can create a wider range of habitat conditions than is found throughout much of the Nebraska Sandhills. On many Sandhills ranches, pastures look fairly similar to each other in terms of vegetation structure. That’s because Sandhills ranchers tend to be careful in their grazing management to avoid wind erosion that can cause “blowouts” of bare sand. As a result, pastures are rarely grazed intensively enough to create wide expanses of bare ground. If intensive grazing does happen, it’s usually on a small scale and/or for short periods of time, which allows for quick recovery of grasses.
Overall, the ecology of the Nebraska Sandhills seems very healthy. It’s a huge and mostly intact grassland landscape, and because of the dry sandy soils, topography and diversity of vegetation, there is quite a bit of habitat heterogeneity that is independent of management. As you walk across most Sandhills pastures, you will move through both short/sparse vegetation and taller/dense vegetation, and occasionally come across other structural components like yucca plants or plum thickets. Wildlife and insect species can often find the habitat structure they need somewhere in that pasture, though it might be in a small patch surrounded by other habitat types. That seems to be true even for many bird species, which have relatively large breeding territories. As an example, in pastures with fairly tall vegetation, we often see and hear horned larks that are (apparently) nesting in a few small and scattered patches of the short vegetation structure they prefer. Those patches of short habitat often occur in gravelly flat areas or in favorite feeding areas for cattle, where grass growth is weak because of frequent grazing.
We’re trying to figure out more about how management with patch-burn grazing or other similar grazing systems affects Sandhills ecology. Patch-burn grazing has part of the management of our bison pastures at NVP since the early 1990’s. Because of that, we know Sandhills vegetation can recover from fires that are followed immediately by season-long intensive grazing. However, we still don’t know much about how many animal species might respond – positively or negatively – to the kind of large patch heterogeneity created by this kind of management. Instead of pastures with interspersed small areas of tall and short vegetation, we’re trying to create large patches (500-1000 acre patches within 10,000-12,000 acre pastures) of each habitat type and then shift the location of those patches between years.
Creating large patches of various habitat types could bring both advantages and disadvantages to different species. As an example, large patches could create an abundance of resources that support larger and more viable populations of some animal species. On the other hand, a vole who likes thatchy habitat could wake up in the middle of a 1000 acre burn, and it would have to make a long dangerous trip to find a more suitable place to live. Trying to evaluate those potential costs and benefits is a big challenge for us.
One possible advantage of the kind of shifting mosaic of habitat approach we’re trying is that it helps avoid risks that come from having the same habitat conditions in the same place year after year. Just as crop rotation can help avoid buildups of pests and pathogens, shifting habitat types from place to place could have important benefits. For example varying the location of habitat types from year to year could limit disease outbreaks and help prevent predators or herbivores from building up large and potentially destabilizing populations.
The most intriguing part of our experimentation for me, though, is the idea that we could create large ‘recovery patches’ where grasses have been weakened by a full season of intensive grazing and the plant community is temporarily dominated by opportunistic, mostly short-lived plant species. That combination of short grasses and tall ‘weedy’ wildflowers can provide excellent brood-rearing habitat for some birds and important structure for reptiles and invertebrates that need to regulate their body temperature by moving quickly from sun to shade as needed. Studies in other landscapes have shown that this kind of recovery patch habitat creates pulses of high insect biomass, which could have numerous impacts – including the provision of an awful lot of food for wildlife. In addition, if an abundance of opportunistic plants include species beneficial to pollinators, that could provide quite a bonanza of resources for bees, butterflies, and other insects.
In most of the Sandhills, patches of ‘weedy’ habitat tend to be in small, static and widely scattered locations such as around windmills or other places where cattle or bison frequently congregate. We’re wondering what might happen if we created big patches of the same habitat type and shifted their location from year to year. In our Platte River Prairies, patch-burn grazing (and similar strategies) has sustained prairie plant diversity over many years, but we haven’t looked closely for similar responses in the Sandhills. In addition, we know a little about how birds respond to patch-burn grazing in the Sandhills, but not much about impacts on other species like lizards, pollinators, small mammals, or invertebrates. Now we’re trying to collect data on the responses from all those different organisms.
I’ve really enjoyed digging into all the questions we have about our attempts to create more habitat heterogeneity in the Sandhills. We haven’t had time to answer many questions yet, but we feel like we’re at least creating something different than what exists throughout most of the Sandhills landscape. A few years from now, we might conclude that the heterogeneity we created didn’t really result in any significant positive or negative impacts compared to what exists elsewhere. If that’s the conclusion, we’ll move forward with that in mind. On the other hand, we might find that there are some important positive (and/or negative) impacts of the shifting mosaic approach we’re testing. In the meantime, it’s exciting to have the opportunity to try something different and watch what happens. Stay tuned…
For example, can a prairie be the size of a kitchen table? Let’s say someone converted a landscape full of prairie to an immense gravel parking lot, leaving only a round kitchen table-sized parcel of vegetation in the middle. Is that tiny isolated parcel a prairie?
The question might seem silly, but the question became a useful little thought experiment for me.
That little parcel certainly wouldn’t be big enough to meet the needs of most prairie animals. Birds, small mammals, snakes, and even smaller creatures like grasshoppers and bees would be unable to find enough food to survive within that small area. The loss of those animals would affect many of the ecological services and functions that make prairies work. Those services include pollination, nutrient cycling, herbivory and more.
Some tiny herbivorous invertebrates might be able to survive in that little parcel of vegetation, but probably not enough of them to support most predators that feed on them. The lack of predation would allow those invertebrate populations to grow much larger than they otherwise would, leading to significant damage, or even mortality, to the plants they feed on. Once their food is gone, the invertebrates would starve and die as well.
Plants that manage to survive invertebrate attacks and an absence of pollinators in our little parcel would still face major challenges. In the long-term, they would probably suffer from a huge genetic bottleneck because they don’t have other individuals of their species to cross breed with. In the meantime, it would take a lot of intensive and thoughtful management to keep them alive.
Invasive species management would be a huge problem because it wouldn’t take long for an aggressive invader to quickly dominate that small area. Quick action would be needed to remove invasive plants as they arrive. Fire or mowing would also be needed to prevent a smothering thatch from accumulating as plants grow and die back each year. Unfortunately, every fire would kill most invertebrates aboveground at the time and destroy their food sources. We could try to burn only a portion of the parcel and save some of the insects, but with such small populations, we’d still probably lose most species eventually. Mowing and raking might be an alternative, but we’d still end up removing either the invertebrates or their food sources.
Ok, so we’d just have to live without most prairie animals, but we’d still have plants. Or at least a few of them. Some of those plants would be more competitive than others, especially in an animal-less environment, so it would take a lot of effort to keep them from pushing the less competitive plants out. And, of course, we’re assuming the mysterious belowground processes that allow plants to survive would still function in our tiny parcel – microbial relationships that allow plants to access and process water and nutrients, for example. If those are sufficiently intact, we’d have some plants.
Would that be a prairie?
I’m pretty sure no one would argue that a kitchen table-sized area containing few plants is a prairie. Even in the first moments after the parking lot was created, I would argue the remaining patch of vegetation had ceased to be a prairie, even though it still contained a reasonable diversity of plants and animals. It wasn’t really a prairie anymore, just a doomed fragment of its former self.
If we can agree that a kitchen tabled-size patch of land is too small, how big would we have to make that patch before we’d be willing to call it a prairie? What species and/or ecological processes should we use as criteria?
Can we agree a prairie needs to be big enough to support a healthy pollinator community? Does it need to be able to sustain viable populations of small mammals, snakes, leafhoppers, spiders, and other little creatures? Is it a prairie if it doesn’t have a full complement of grassland bird species? Does that requisite bird community include larger birds such prairie chickens or other grouse species? What about at least moderately-sized predators such as badgers and coyotes (or even bigger ones) or large ruminants like bison or elk? Which of those components are we willing to live without, and more importantly, which can a prairie live without and still sustain itself as an ecological system? A prairie without badgers, coyotes or bison is functionally different than one with those animals, but is it a non-prairie or just a different kind of prairie?
Even if we reach consensus on the key components of a prairie, we’re still hamstrung by our lack of information about how big a prairie needs to be to support each of them. We have decent data on the prairie size requirements for many grassland bird species, but beyond birds, we’re mostly just guessing. If we want the full complement of species, including bison and other large ruminants, we’re going to need thousands of acres, but how many thousands?
More importantly, what does this mean for the many remaining patches of prairie vegetation too small to support whatever we decide are the key components of a prairie? It certainly doesn’t make them worthless, but it might be important to make sure we’re viewing them realistically. What are the likely ramifications of the missing components? The absence of prairie chickens or upland sandpipers might be disappointing, but might not have the ripple effect that the absence of pollinators or coyotes might have. Can we identify and compensate for the absence of key prairie components by managing differently or more intensively? If not, how do we adjust our vision of the future for that prairie parcel, and how does that adjusted vision affect how much management effort we invest? (You can read more about the challenges of managing small prairies here.)
For many of today’s small prairie patches, the only chance of preserving their species and ecological functions is to make those small patches larger and/or more connected to others. Restoring adjacent land back to high-diversity prairie vegetation allows formerly landlocked populations to expand and interact with others, and creates enough habitat for larger animals to survive. Identifying potential restoration opportunities might be the highest priority conservation strategy for those of us working with small prairies.
Our family prairie is a little over 100 acres in size, is managed with large ruminants (cattle), and has regal fritillary butterflies, coyotes, badgers, upland sandpipers, and even an occasional prairie chicken. However, I’m certainly not comfortable that our 100 acre island within a sea of cropland will to sustain a prairie ecosystem indefinitely. This thought experiment has forced me to think more seriously about prospects for increasing the size of our prairie and building connectivity to other grasslands. I hope it’s useful to others as well.
Last week, I attended a conference aimed at creating a statewide conservation plan for monarch butterflies. The meeting was really informative and thought-provoking. I learned a great deal about the ecology and conservation needs of monarchs from Chip Taylor of Monarch Watch and others, and was part of some good discussions about potential strategies to help the species recover. I thought I’d share some of what I learned from those discussions because they helped me better understand the issues surrounding monarch conservation. Any errors in the following are a result of my misunderstanding what smart and knowledgeable people told me, and I apologize in advance.
The monarch butterfly is a migratory species, but it takes multiple generations to make the migration from parts of North America to Mexico and back. Here in Nebraska, we’re part of the Eastern Population of monarchs, which extends from roughly the east edge of the Rocky Mountains to the east coast. The butterflies in this population leave their Mexico wintering grounds in late February each year and head north. They lay eggs in the southern United States and the monarchs produced by those eggs then head north into the northern half of the U.S. and the southern edge of Canada during May and early June.
During the summer, there are a couple generations of monarchs that mature and lay eggs without migrating. However, in mid-August and September, monarch adults get the urge to migrate and start heading south. Those that survive the trip usually reach the Sierra Madre Mountains of Mexico by early November.
Threats to Monarchs
There are two categories of threats to Monarchs: 1) Factors we can control, and 2) Factors we can’t. The big factor we can’t control is weather and the way it interacts with migration timing and butterfly survival. Weather can have a tremendous impact on butterflies, and many millions of butterflies are killed by hot weather, storms, or other events. However, since we can’t control the weather, we have to focus on what we can control.
There is a long list of human-induced factors that affect monarch populations. Those include the conversion of grasslands, roadsides, and field edges to row crops (largely facilitated by government policies) as well as farming practices that have nearly eliminated milkweed from farm fields. Pesticide use is another factor, including pesticides used for farming and pesticides used for other purposes, including mosquito control. Logging of forests in the wintering grounds of Mexico is another important issue.
I’d heard that the loss of milkweed from crop fields was a big deal for monarch butterflies, but hadn’t really understood why. At the conference, we heard that research has shown that about four times as many eggs/plant are laid on milkweed plants in crop fields as on milkweed plants in other habitats. (I’m not sure anyone understands why.) In addition, while the eastern population is spread across a huge area of North America, about 50% of the butterflies that reach Mexico are born in the cornbelt of the U.S. – the intensively farmed Midwestern states. Prior to the widespread use of glyphosate-resistant crops, milkweed was a pretty common inhabitant in crop fields throughout this prime breeding area for monarchs. Now that farmers are so much more efficient at weed control, we’ve lost the most productive egg-laying habitat in the country’s most important breeding area for monarchs.
Because monarchs can only be raised on milkweed, getting more milkweed plants in the landscape, especially within the cornbelt states, is a key part of increasing the monarch population. It’s likely that more than a billion additional milkweed plants will be required to stabilize the monarch population. Increasing milkweed populations to that extent will require a wide range of strategies. In addition, protecting and restoring the wildflower-rich grasslands and other natural areas that provide food for adult monarchs, as well as for thousands of bee and other pollinator species, is also vitally important.
One clear strategy is to plant more of monarchs’ favorite milkweed species in gardens, parks, roadsides, nature centers, and many other sites. In the north-central U.S., milkweed species such as common (Asclepias syriaca), showy (A. speciosa), and swamp milkweed (A. incarnata), are known to be favorites, while green antelope horn (A. asperula) is important in more southern states. You can find sources of seeds and plants at Monarch Watch or from the Xerces Society’s Project Milkweed website. Sites like monarchgard.com can help with garden and landscape design ideas.
More milkweed in gardens and landscaping can make a big difference, but an even bigger part of monarch recovery needs to come from a change in the way milkweeds – and the weedy, edge habitats they thrive in – are perceived by the public. Elimination of milkweed from roadsides, field edges, and odd corners and margins of our landscapes happens because we are uncomfortable with the “messiness” of those areas if they aren’t frequently mowed and/or sprayed with herbicides to make them look uniform in height and composition. Allowing milkweed and other wildflowers to thrive in those odds-and-ends habitat areas can have a huge impact on monarchs and other pollinators, along with pheasants, song birds, and many other wildlife species. Reducing mowing frequency and spot-spraying truly invasive plants – instead of broadcast spraying to kill anything that’s not grass – in these habitats saves both money and time as well.
The Role of Prairies?
Last week’s meeting also encouraged me to focus even harder on an additional aspect conservation I’ve already been working on – improving the contributions of native prairies and rangeland to pollinators. The experts at our meeting, along with other sources of information on monarchs, seem to be focused largely on milkweed and the kinds of farm fields, edge habitats and landscaping mentioned above. While all those are very important, I can’t help but think about the value of native prairies – especially in places like Nebraska where we still have millions of acres of grassland.
A healthy prairie with a diverse wildflower community is invaluable to bees and other pollinators, and also provides nectar resources needed by monarch butterfly adults. If that prairie contains vibrant populations of milkweed species that provide egg-laying habitat to monarchs, that’s even better. Many prairies don’t currently have strong milkweed populations. Some milkweed species are not strong competitors in a tight-knit plant community, and certain grazing and other management practices tend to further discourage milkweeds. Over the next several years, I am hoping to learn more about how to make prairies support stronger milkweed/monarch populations. Hopefully, we and others can help make North American prairies even better contributors to the survival of monarch butterflies.
Do you know what time it is? It’s time for another PRAIRIE WORD OF THE DAY!
Today’s Prairie Word of the Day (fine, it’s actually two words) is:
Heterogeneity is really just a longer word for Diversity, which is another way of saying “lots of different things”. So why use the word “heterogeneity” instead of just saying “lots of different things”? Well, for one thing, using big words makes a person sound smart, and when you’re a prairie ecologist and no one really understands what it is you do for a living, it’s good to at least sound smart.
More importantly, there’s a nice alliterative (another big word!) feel to the phrase Habitat Heterogeneity, which happens to be one of the most important phrases in prairie ecology. In fact, I would argue that the foremost objective of any prairie manager should be to create habitat heterogeneity within the prairie(s) they manage.
Habitat heterogeneity simply means diversity or variety in habitat types. Habitat homogeneity is the opposite – a lot of habitat that is all the same.
Every organism in a prairie has its own unique habitat requirements, so the number of different habitat types in a particular prairie is correlated with number of species that can live there. Let’s use prairie birds as an example. Birds such as upland sandpipers like to nest in large patches of relatively short-stature grassland. Around here, a big hay meadow is great habitat for them, especially if it was cut fairly late in the previous year and is still short in stature when the subsequent breeding season starts. On the other hand, Henslow’s sparrows want to nest in prairie habitats with relatively tall and dense vegetation. It would be highly unusual to find Henslow’s sparrows and upland sandpipers nesting in the same patch of prairie because their habitat preferences are very different. So, if you want both species in your prairie, you have to provide both short and tall/dense habitat. Other birds have their own unique habitat requirements, including nearly bare ground (e.g., horned lark), relatively short, but with abundant thatch (grasshopper sparrow), tall with lots of tall/weedy wildflowers (dickcissels), tall and nearly impenetrably dense vegetation (sedge wrens), and many others. Only if your prairie provides all those different habitat conditions will you attract all those different bird species.
The same diversity of habitat preferences exists in other groups of prairie species as well. Among small mammals, for example, voles tend to prefer habitats with abundant thatch, while pocket mice are more often found where bare ground is abundant – and there are many others. Insects and other invertebrates have the same kind of diversity in habitat preferences
Scale is important. While a bird, mammal, or insect might have a broad preference for a certain kind of habitat structure, it is likely to need some heterogeneity within that habitat too. A mouse, for example, might prefer patches of prairie with fairly sparse vegetation, but it is likely to need a few clumps of vegetation dense enough to hide in when predators are near. Insects and reptiles are ectothermic (cold blooded) and need to regulate temperature, so while a snake might like to hide in tall dense so it can bite your ankle as you walk by (I’M KIDDING!), it also needs some places to bask in the sun. All of this means that habitat heterogeneity is important any many different scales. Heterogeneity at a fairly large scale (acres) helps provide places for many different animals to live in a prairie, but heterogeneity within the home range or territory of each animal (square meters, or even centimeters) can be important too.
Some habitat heterogeneity occurs simply because soil texture, nutrients, and moisture, along with topography all vary across a landscape. A prairie is likely to have areas of more productive soils where vegetation grows tall and thick, and less productive soils where vegetation is more sparse, for example. In addition, water will pool in some areas of a prairie more than others because of topography, altering the habitat for both plants and animals. However, despite this “naturally occurring” heterogeneity, it’s still important for prairie managers to look for ways to provide more.
Prescribed fire and haying/mowing do a great job of altering habitat structure at a fairly large scale (acres). By applying those treatments in different parts of a large prairie each year (and varying the timing of each from year to year), a manager can create a shifting mosaic of habitat patches that supports a wide diversity of animals. However, both fire and mowing are pretty non-selective – most or all of the vegetation within a burned or mowed area gets the same treatment. Leaving unmowed patches of grass here and there and varying the height of the mower as it moves across the site can help leave more heterogeneity behind. Designing prescribed fires so that not all vegetation burns (e.g., mowing around some patches ahead of time, burning on days with lower temperatures or higher humidity, etc.) can also help with habitat heterogeneity – though those kinds of fire might also be less effective at killing trees or accomplishing other objectives.
In prairies where livestock grazing (cattle or bison, for example) is feasible, it is much easier to create small scale heterogeneity because grazers pick and choose which plants, and how much of each plant, to eat at any one time. By controlling grazing intensity, and varying it across both time and space, managers can create prairie patches that are ungrazed, almost completely grazed, and in various stages of partial grazing – with a mixture of tall vegetation and nearly bare ground. The uneven application of “fertilizer” from the rear ends of grazers contributes even more to habitat heterogeneity by temporarily altering soil productivity in lots of little spots across the prairie.
Whether it’s fire, mowing, grazing, herbicides or various combinations of those, creating habitat heterogeneity may the most important job of a prairie manager. We still have a lot to learn about how the scale and configuration of habitat patches affect wildlife and insect populations. What we do know, however, is that the prairies thrive when they have a lot of different types of habitat. …When they have habitat heterogeneity.
Who could be mad at these big beautiful brown eyes?
As it turns out, lots of people can.
The differential grasshopper is one of a long list of native North American species, headlined by white-tailed deer and raccoons, that have adapted very well to today’s agricultural landscapes. Whether you call these species adaptable generalists or pests probably depends upon whether or not they’re eating your sweet corn. Regardless, you have to admire (or at least recognize) the traits that allowed them to thrive under changing habitat conditions that have pushed many other native species to the brink of extinction.
Before Europeans took over the continent, differential grasshoppers lived mainly in low grasslands, feeding on a wide variety of grasses and wildflowers – but, purportedly, with a particular affinity for giant ragweed. When the landscape began changing to one dominated by rowcrops, alfalfa, and short-grazed grasslands, it basically created heaven on earth for differential grasshoppers. Today, they are abundant enough that they can be found almost anywhere across the landscape (at least in Nebraska). Apparently, they can move as much as 10 miles a day to find food.
One of 108 grasshopper species recognized as native to Nebraska, the differential grasshopper is one of only a small handful that actually cause any economic damage to crops. All of those grasshopper species – pests or not – are important food sources for birds and many other wildlife species. In years when differential grasshopper populations are particularly high, they can cause more problems for farmers and gardeners, but also provide even more food for wildlife.
It’s ironic that many traits we admire in people (resilient, adaptable, successful) become indicators of pest-ness when we’re talking about wildlife. Really, we should give differential grasshoppers some kind of award for their ability to take lemons and make lemonade (that’s just a metaphor, kids). Hooray for differential grasshoppers!
Unless, of course, they’re eating your sweet corn.
While driving through central Nebraska last week, I couldn’t help notice all the fuzzy creatures crossing the highway in front of me. They weren’t raccoons, deer, or even voles. They were tiny little caterpillars, and they were moving FAST.
I’m not entirely sure why the caterpillars are on the move, or where they are going. Some internet searching turned up some university extension and similar pages that infer that the caterpillars are simply searching for a good place to spend the winter. That could be true, but if so, they sure don’t seem to be doing it in any organized fashion! There were just as many caterpillars crossing the road from left to right as there were from right to left. It made me wonder if they just kept going back and forth… (tiny little brains.)
As I drove, my scientist mind was spinning, despite my best intentions. I kept track of the land cover types on both sides of the road, trying to figure out what kind of habitats the caterpillars might be leaving or heading for. If there was a pattern, I didn’t see it. The caterpillars crossed the road in places where there were soybean fields on both sides as well as places where there were miles of sandhills prairie on both sides. They didn’t seem to be heading from high ground to low or from tall vegetation to short – or vice versa.
My photographer brain was also in full gear, which meant I had to keep stopping to take photos of the little buggers. Fortunately, the roads I was traveling were not very well populated with other vehicles, but I still had to be discreet to avoid uncomfortable conversations. Whenever I heard a vehicle coming I just pretended I was stopped to make a phone call or just to admire the view. Otherwise, I would have ended up having conversations something like this:
“Me? Yeah, I’m fine.”
“Oh. I just wondered why you were lying in the middle of the highway.”
“Um, yeah. I was actually taking a photograph of a caterpillar.”
“In the middle of the highway?”
“Well, yeah. I wanted to know why it was crossing the road.”
“Is that a joke?”
“No, but now that you mention it, it might not be a bad start to one…”
“So you don’t need any help?”
“No, I’m good, but thanks for asking. I’m just trying to get some pictures.”
“In the middle of the highway. On your belly.”
“Well, yeah. You see, I’m a prairie ecologist.”
“Oh! Why didn’t you say so? Carry on then…”
Anyway, I did manage to get some photographs of the commuting caterpillars. I’m glad I did because seeing them up close made me realize there were several different species of them making the crossings. I also (I can’t believe I’m admitting this) timed them to see how fast they were going. What? I was just curious…
I wish the caterpillars well on their journeys. There were surprisingly few smooshed caterpillars on the road, so I’m assuming the majority made it across the road. I hope that means they found a nice place to spend the winter, or whatever they were looking for.
I also hope no one saw me photographing them.
You probably don’t care, but in case you’re wondering, the caterpillars were making the 32 foot trip across the highway in about 80 seconds. If my math is correct, that means they were traveling about 4.8 inches per second. That’s moving right along for a tiny critter with stubby little legs!
I got the chance to spend a couple days in Iowa last week, talking about conservation grazing with staff of the Iowa Department of Natural Resources. They invited me to join a two day workshop discussing various ways to use grazing for conservation objectives. My main role was to kick off the meeting by providing various examples of objectives that can be addressed through grazing. Beyond that, I was asked to participate in the remainder of the workshop and contribute thoughts and ideas as appropriate. I am grateful to have had the opportunity to participate, and came away with a better appreciation for the challenges faced by Iowa prairie managers.
I thought I’d share some of what I covered in my presentation. Essentially, I focused on two broad categories of prairie management objectives that can be addressed through cattle grazing. Those are:
Reducing grass dominance to increase plant diversity
Increasing heterogeneity of habitat
Reducing Grass Dominance
Dominant grass species can sometimes suppress prairie plant diversity by monopolizing soil and light resources. Two categories of prairies seem particularly vulnerable to this: 1) prairies that have been degraded by chronic overgrazing or broadcast herbicide use, and 2) restored (reconstructed) prairies. In Nebraska and Iowa, dominant grasses can include non-native invasive species such as smooth brome (Bromus inermis), Kentucky bluegrass (Poapratensis), tall fescue (Schedonorusarundinaceus), and reed canarygrass (Phalarisarundinacea), as well as native species such as big bluestem (Andropogon gerardii).
When attempting to reduce the dominance of these grasses, it’s important to be clear about what you’re trying to accomplish. If the ultimate goal is to increase plant diversity, it’s not enough to just suppress the vigor of grasses. In order to be successful, a variety of other plant species have to colonize territory abandoned by that weakened grass. A late-spring prescribed fire can temporarily suppress the growth and vigor of smooth brome or Kentucky bluegrass, but often results in robust growth of big bluestem later that season. Trading a dominant invasive grass for an aggressive native grass may not be success if wildflower diversity remains low.
Grazing can play an important role in increasing plant diversity by repeatedly defoliating major grass species that limit plant diversity. The timing, stocking rate, and frequency of grazing can all be adjusted based on the grass species and objectives at a particular site. As an example, we sometimes combine an early spring prescribed fire with intensive grazing (through about June 1) to suppress cool-season invasive grasses such as smooth brome and Kentucky bluegrass. If big bluestem is abundant in the same place, we’ll leave cattle in for much of the summer as well, but at a lower stocking rate. The strategy is to suppress both the invasive cool-season grasses and the native warm-season big bluestem while allowing other plants to thrive and expand their footprint.
At low stocking rates, cattle tend to keep big bluestem closely cropped, but don’t target most wildflower species. We usually see an abundance of new plants growing in and amongst the weakened brome, bluegrass, and bluestem during the year of grazing and the following year. Those new plants include both short-lived “opportunistic” plants and longer-lived perennial plants. The result is a bump in plant diversity. If we repeat the same kind of treatment every few years, we can often maintain a richer plant community than we can with other management options such as fire or mowing alone.
There are countless ways to employ cattle grazing to weaken dominant plants and stimulate higher plant diversity. I’ve written about other examples previously. You can find a couple of those here and here.
Increasing Habitat Heterogeneity
Cattle grazing can create habitat structure that other management options such as fire and mowing can’t. As they work to meet their nutritional needs, cattle graze some plant species (mostly their favorite grasses) preferentially. Stocking rate, or the intensity of grazing, correlates with grazing selectivity. At low stocking rates, cattle are free to eat only what they really want, resulting in closely cropped patches of grass interspersed with taller clumps of less palatable grasses and wildflowers. When stocking rates are higher, cattle are forced to eat a wider range of plant species, creating a more uniformly short vegetation structure. Both the “lower-stocking-rate-patchy-habitat” and “higher-stocking-rate-uniformly-short-habitat” can be valuable to wildlife and invertebrate species.
The ideal situation is to provide the widest possible range of habitat types within a prairie, or within a series of adjacent or connected prairies. That way, regardless of their habitat needs, most wildlife and invertebrate species will be able to find a place to live. Changing the location of each of those various habitat types from year to year helps keep any species (plant or animal) from becoming so abundant that it impacts other species to the point of reducing diversity.
Because of the unique vegetation structure created by grazing, a wider range of habitat types can be created with grazing than with either fire or mowing. However, it’s also very important to ensure that grazing doesn’t have a detrimental impact on plant diversity in the name of creating wildlife habitat. Significant periods of rest from grazing and careful monitoring of grazing impacts and populations of sensitive plant species are important. If conservation is the primary goal, grazing should be used only when there are specific objectives to meet, not as a default strategy.
I’ve written much more on the topic of creating heterogeneous habitat with grazing in previous posts as well, and you can find a couple examples here and here.
Setting Useful Objectives – And Then Using Them
Regardless of the management tool(s) being employed, the biggest challenge for a prairie manager is to set clear objectives and then follow up on them. Start by defining the outcome you want (different habitat structure, more plant diversity, etc.) and then describe precisely what success looks like. Monitoring doesn’t have to mean spending hours on your knees with a plot frame, it just means measuring the outcome you desired.
For example, if you want more habitat diversity, you could start by listing the types of habitat structure you want (tall/dense, short sparse, patchy forbs with short grass, etc.) and how much of the prairie you’d like to be in each category. Then, you could make a rough map of how the site looks before the treatment and estimate percentages of each habitat type. After your grazing, fire, or mowing treatment, make another map and see if you reached your objective.
If plant diversity is important, decide how you will measure that. This is where a plot frame and repeated sampling across a prairie can be helpful, but there are simpler ways as well. You could pick out 3-5 small areas (less than 10 square meters) that you can find each year and then annually list the plant species you find in each area to see if that number changes over time. You don’t have to identify all the species, just list how many there are. If you are using grazing, it’s also important to figure out which plant species are favorites of the cattle and use that information to ensure that your management allows those plants enough rest from grazing that they can bloom and make seed every few years.
Most importantly, your objectives should drive the adjustments you make to management from day to day and season to season. If you can define what you want, you can see if your management is moving you in the right direction. It’s fine to change objectives as you learn, or as conditions change. In fact, in our Platte River Prairies, while we have some broad objectives (plant and habitat diversity), we set new specific objectives and management strategies each year to respond to what we’re seeing on the ground.
Cattle grazing is just another tool that can be used for the conservation of prairies. It’s not appropriate for all prairies or situations, but can help meet some objectives in ways that other tools (fire, mowing, herbicides) can’t. Conservation grazing differs from ranching in that income doesn’t have to be a major part of the decision-making process each year. On land where conservation is the primary objective, managers can decide when and how to employ grazing (or not) based purely on the conservation challenges they face.
Thanks again to the Iowa Department of Natural Resources for inviting me to their conservation grazing discussion last week. I was impressed by the thoughtfulness and creativity of the staff I met, and I look forward to hearing more about their prairie management and restoration work down the road.
This week, I present four photographs from one of the timelapse cameras along a restored wetland in our Platte River Prairies. All four photographs were taken automatically by the camera, and none are particularly striking images, artistically speaking.
Nice sales job, eh?
Despite their quality as images, or lack thereof, they are very meaningful photographs to me. In fact, the two photos of least photographic quality are actually the two I like best because they tell a story I’ve been hoping for since we first started the wetland restoration project more than 10 years ago.
When we first started talking about converting a long sand pit lake (left over after sand and gravel mining operations from early last century) into something different, we had several objectives. Those included:
– removing the trees around the edge of the site to improve habitat for open-grassland and wetland wildlife species.
– providing shallow stream and wetland habitat for fish, amphibians, reptiles, invertebrates (including mussels), and other species.
– restoring diverse plant communities including emergent wetland, wet meadow, wet-mesic, and upland sand prairie communities.
– providing habitat for migratory whooping and sandhill cranes and many other waterbird species with similar habitat requirements.
The first three objectives were pretty easy, and we’ve seen abundant evidence of success. In terms of bird habitat, we’ve always had great utilization of the site by ducks, geese, herons, snipe and other birds during both migration and breeding season. But no cranes.
Until this spring.
The chance that one of (approximately) 260 whooping cranes will ever land in this particular wetland is very remote, but I have been expecting to see sandhill cranes using the site; if not for overnight roosting habitat, at least as a place to feed and loaf during the day. After all, there are hundreds of thousands of sandhill cranes here each spring – surely some of them should see this as an attractive place to hang out now and then. And if we see sandhill cranes using the site, we can reasonably assume that it’s suitable for whooping cranes too (though that’s not universally true).
However, during the 10 years since we started the restoration work, I’ve been looking in vain for a crane of any sort, or even tracks that would indicate they’d been there. Nothing. Last year, we had timelapse cameras up during the spring crane migration season but they malfunctioned and didn’t give me any evidence one way or the other. But this year, I finally got what I wanted.
I downloaded images from the cameras in mid-March and immediately scanned through them in the truck, hoping to see some evidence of crane use and – there they were! Three sandhill cranes showed up in multiple photos over the period of a couple weeks. Most of the photos were daytime photos, but it also appears they roosted overnight at least a few times, standing in the shallow water. Three cranes is certainly not evidence that we’ve added significantly to bird conservation, but it is evidence that our wetland isn’t completely abhorrent to cranes – and that’s a good start.
Then, as I kept looking through the images, I got an even better surprise. Late in the evening on March 11, there was a whole flock of cranes standing in the shallow wetland, apparently preparing to roost. Even better, the camera picked them up again early the next morning – pretty solid evidence that they roosted overnight. It only happened once (through mid-March) but I’ll take it!
The pictures aren’t of terrific quality. They were taken by a camera set to fire every hour on the hour (during daylight hours) and low light and wind combined to the images a little blurry. Nevertheless, I think they’re pretty great photos.
Of course, now that I’ve gotten my evidence of crane use, my scientist brain is kicking in and asking questions. Why did the cranes only roost one night? Why that particular night? Why did they pick that particular part of the wetland?
And, there’s one more question my brain is asking, which I’m trying to ignore because I don’t think it’ll ever happen.
…Will we ever see a big white crane in one of those photos?
It took me a long time to decide to write a book on prairie management. One of my worries was that I was learning a tremendous amount each year, and a book captures a moment in time. One of the reasons I like writing this blog is that it allows me to share lessons as I learn them, modify my ideas over time, and – best of all – get instant feedback from readers. I learn a lot from watching prairies, but I learn even more from discussions with other people who watch prairies.
My prairie book came out in 2010, but I actually did most of the writing in 2008 – five years ago. By the time the final manuscript passed through reviews and layout and made it to the publishing stage, there were already a few sections I would have liked to modify. Now that five years have passed, there are even more changes I wish I could make.
Don’t get me wrong, I’m still very proud of the book, and satisfied with its contents. But reading through it recently, I picked out some portions that I would handle differently if I was writing the book today. Here are a few of those:
Page 12 – “Mycorrhizal fungi help plants fix nitrogen”. Ok, I really flubbed this one. As Inger Lamb kindly pointed out to me after the book came out, mycorrizhae help plants pull in food and water more effectively. Bacteria are what help plants fix nitrogen. I should have just skipped the whole topic in the book, given my very rudimentary knowledge of what happens belowground. In my defense, the book went through several technical reviews, and none of the reviewers caught the error either.
…On the plus side, I did manage to spell “mycorrhizal” correctly.
Insects. The insect section in the book was originally three times longer. I was urged (coerced?) by the publisher and reviewers to chop it back drastically because it was so much longer than similar sections on mammals, birds, etc. I wish I’d fought harder to keep it long. As I’ve discussed numerous times on this blog, insects and other invertebrates are WAY more diverse and important to the way prairies functions than any other group of above-ground creatures. The existing insect section in the book is a good primer on some of the insect communities of prairies and their impacts, but doesn’t go nearly far enough. Maybe I’ll write a whole book on prairie invertebrates someday. (But probably not – can you imagine how quickly THAT book would become out of date? We still have a massive amount to learn about invertebrates.)
Page 79 – “Managing prairies really means managing the competition between plants.” This is a nice statement, but it’s too narrow. If I was writing that now I would replace “plants” with “species”. In general, my biggest beef with my 2008 self is that I was too focused on plants, and not enough on habitat for other species.
In the prairies I know best, maintaining plant diversity appears to be dependent upon periodically suppressing dominant grasses and giving other plants a chance to thrive. Our management strategies create a dynamic disturbance regime that helps keep any single group of plants from bullying others out of the prairie. However, not all prairies work like the ones I manage. Especially in some eastern tallgrass prairies, which have abundant rainfall and deep organic soils, many prairie plant communities seem to be pretty stable without any management that suppresses grasses. For example, very frequent spring fires seem to do a fine job of maintaining populations of most plant species in some of those sites – maybe because there is less intense competition between plants when soil moisture is abundant?
While frequent fire is able to sustain diverse plant communities in some prairies, I still think the shifting mosaic of disturbances I advocated for in my book is very important. Burning an entire prairie every year creates a single habitat structure across that prairie. That’s great for the species that like that habitat structure. However, a prairie with patches of short, tall, and mixed-height structure is going to provide for more animal species than one with uniform structure. I’m convinced that creating heterogeneous habitat can be done without hurting the plant community, and I think it’s a critical component of good prairie management. So – I think my management advice in the book is still sound, I just wish I’d explained the value of it differently.
Small Prairies. I spent a little time in the book talking about the challenges of managing small prairies, but I’ve spent more time thinking about this subject during the last few years. I wrote a post that summarized much of that thinking back in March, 2012. Many prairies are small enough that providing the kind of habitat patchiness I just discussed might not be feasible or even appropriate. In the eastern tallgrass prairie, many grasslands are only a few acres in size, and much of what I talked about in the management portion of the book would be difficult to apply. I wish I could go back and put in a whole chapter that fleshes out what I discussed in my blog post.
Too bad, so sad. Those are a few of the things I’d change if I could alter my book today. Unfortunately, because of layout challenges and other issues, I can’t just add a few paragraphs or re-write a chapter and then just reprint the book. Even if I could, there’d still be a couple thousand books in people’s houses and offices preserving my out-of-date ideas forever.
I may write another book someday. I might even go back and revise the one I’ve already written, though I dread that process. In the meantime, I’m going to enjoy the opportunity to write in this blog format, which allows me to constantly adapt my ideas as I learn from prairies and from you. Thank you for helping me with that process.