Hubbard Fellowship Blog – Olivia Marvels at the Persistence of Plants

This post was written by Olivia Schouten, one of our Hubbard Fellows this year.  Olivia is an excellent scientist, with strong expertise in plants and plant communities, as you’ll be able to see from this post.  

As a biologist with broad interests, I can usually find something to love in all living things, but I’ll admit that plants have a special place in my heart. This is probably a good thing, since I’ve spent the majority of my education and professional life cultivating my knowledge of plants. I’ve found that they are often underappreciated and often overlooked, which is a shame, because plants are some of the most amazing organisms out there (in my humble opinion).

Plants, in most places, not only form the basis of the food chain, but also provide the structure of habitat. A forest with towering trees is very different than an open grassland or a sparsely vegetated desert, and the animals that live there respond accordingly. Plants are eaten, trampled underfoot, exposed to the whims of the weather, and just generally beaten down by the world around them, all on top of competing with each other for resources and space. But while plants have it rough, they are also really good at persisting.

Trees are an excellent example of just how persistent plants can be. I was reminded of this earlier in the summer when I came across a grove of cottonwoods in one of our Platte Prairies while searching for musk thistles. At first glance I thought one of the cottonwoods had recently fallen and the leaves hadn’t died back yet. On closer inspection, however, I realized that the tree had probably fallen years ago, and instead of dying, the parts of the trunk that now contacted the earth had sprouted roots and continued on living. Branches had grown up from the trunk,and now looked essentially like three trees, all connected by the same fallen trunk.

This cottonwood, in true tree fashion, just refused to die. Photo by Olivia Schouten

Trees are clearly hard to kill, as anyone who’s tried to cut down a deciduous tree in your yard knows. Once the tree is cut you have to treat the stump with herbicide, otherwise the still-living roots will simply sprout again. Nearly every tree we cut here on the Platte to keep our prairies open needs to be treated with an herbicide. While it would be nice to not have to use chemicals in our stewardship work like this, that resilience of trees can also be a blessing. After the wildfire at our Niobrara Valley Preserve a few years ago, much of the forest along the river was killed. However, the oaks along the slopes are re-sprouting from their roots, as only the tops of the trees had been killed in the blaze. Because of this, these forests have a jump start on regenerating after the devastation of the fire.

It’s probably a good thing musk thistles are so showy, otherwise it would be much more difficult to find them.  Photo by Olivia Schouten

Since I found that cottonwood looking for musk thistles, it’s probably worth talking about them and their own resilient strategies. As a biennial, these plants only have one chance to flower and produce seeds, so they produce thousands of them at a time. And they can fly. That’s not great for us, considering they are considered noxious weeds here in Nebraska, but as a strategy for this plant it certainly pays off.

But wait, there’s more! Even when uprooted or sprayed with herbicide, if the flowers on a musk thistle plant have been pollinated, they will still produce seeds! So when we control this plant, we not only cut off the root just under the ground and pull it out, we have to collect any flowers, or else nothing will actually have been controlled. This persistent ability of musk thistles makes things more difficult and time consuming for us to control, but you have to admit that it’s a cool adaptation, and in its native habitat, likely very useful.

We collected about three tubfuls of musk thistle flowers by the end of the control season. We let the flowers rot to make sure any seeds were destroyed before throwing them out.  Photo by Olivia Schouten

So far these examples relate back to land management, and how the difficulty in killing plants affects our ability to effectively manage invasive plants in prairies. But we rely on these same tenacious qualities in our native prairies species as well. Chris talks a lot about the resilience of prairies on this blog, and a lot of that depends on the persistent nature of individual plants.

Consider big bluestem, a favorite of both cattle and bison. It can be cropped down again and again to within an inch of the ground over a growing season, but while such trauma might kill another plant, big bluestem holds on until the herd moves on and it gets a break, coming back taller and stronger the next year, until it’s back to full strength within a few years. In addition, even in those years that it’s hammered by grazing, big bluestem will find a way to flower, since all that short and weak vegetation around them makes for a good place to put out seeds.

This patch of big bluestem has been hit pretty hard by cows this year, but that didn’t stop it from blooming.  Photo by Olivia Schouten

Other plants may just find that conditions in a certain year aren’t for them. Maybe it’s too dry, or too cold, or the grasses around them are just too tall. Perennial prairie plants don’t let that stop them, as many will simply take a break, growing very little above ground for a year, relying more on stores of energy in their roots than anything else. To some, it may seem like those plants have died and disappeared from a field. But just wait, when conditions become favorable, most of those plants will show up again, just as strong, and benefiting from that strategy of waiting it out through the hard times.

Now, just because plants are tough doesn’t mean they’re invincible. If put under too much stress even the most stubborn plant will eventually die. Knowing how plants are able to persist can help us more effectively target those plants we don’t want, but also help ensure that our desirable plants always have a chance to let their persistent nature shine!

Diversity, Redundancy, and Resilience

Grasslands face a long list of challenges.  In many regions, habitat loss and fragmentation top that list, leaving prairies to struggle for survival as tiny isolated patches of habitat.  In addition, invasive plants and animals keep finding new footholds within both fragmented and unfragmented prairies.  Many of those invaders are aided by nutrient pollution – increasing levels of nitrogen, for example, which help species like reed canarygrass and smooth brome monopolize formerly diverse plant communities.  Most of all, the climate continues to flail crazily about, ratcheting up the temperature and tossing out more and more extreme weather events.

How can grasslands possibly survive all of that?

I’m actually pretty optimistic about the future of prairies.  Prairies are inherently resilient, and if we do our jobs as land managers and supporters of conservation, we can help ensure their continued resilience and survival.  Resilience in prairies and other ecosystems is the capacity to absorb and adapt to whatever challenges are thrown at them, while sustaining their essential functions and processes.  That resilience is built largely upon two pillars: biological diversity and the size/connectivity of the habitats that biological diversity depends upon.

Plant diversity is a key component of ecological resilience, along with the other biological diversity associated with it.  Taberville Prairie, Missouri.

We’ve severely compromised the “habitat size/connectivity” pillar in many regions of North America, but even in little prairie fragments, there is an incredible diversity of organisms, providing the countless services needed to sustain life and productivity.  In a healthy and diverse prairie, not only are all the bases covered, there is considerable redundancy built in to the system because of the number of different species present.  If one plant, animal, or microbe is unable to do its job because of drought, fire, predation or disease, another can step up and fill the role. Diversity provides redundancy, and redundancy helps ensure that prairie systems stay healthy and productive, regardless of circumstances.

It’s not hard to find examples of this kind of built-in redundancy in prairies.  In fact, you can find it within some very recognizable groups of species.  Let’s start with sunflowers.

While most people know what a sunflower looks like, you might not realize how many different kinds there are.  Here in Nebraska, we have at least nine different sunflower species, plus a lot of other flower species that look and act much like sunflowers.  Two of our official sunflowers are annuals, often classified as weeds because of their ability to quickly colonize areas of bare or disturbed soil.  The other seven species are long-lived perennials, each with its own set of preferred habitat conditions.

Plains sunflower, an annual, is a rapid colonizer of exposed in sandy prairies around Nebraska. The Nature Conservancy’s Niobrara Valley Preserve.

All sunflowers are tremendously important providers of food and shelter to wildlife and invertebrates.  There’s a reason sunflower seeds are so prevalent in bird feeders – they pack an enormous amount of nutrition into a little package.  Because of that, a wide array of both vertebrate and invertebrate animals feed eagerly on sunflower seeds when they can find them.  Sunflowers also produce an abundance of pollen and nectar, and make it very accessible to pollinators and many other creatures by laying it out on a big open platter.  It’s rare to find a sunflower in full bloom that doesn’t have at least one little creature feeding on its nectar, pollen, or both.  Grazing animals can get a lot from sunflowers as well; the forage quality of sunflowers is very high, especially before they bloom.

During or after droughts, intensive grazing bouts, fires or other events that leave bare soil exposed, annual sunflowers thrive, and they can provide abundant resources at a time when many other plant species can’t.  We see this often in the Nebraska Sandhills, where plains sunflower (Helianthus petiolaris) turns the hills yellow during the summer after a spring fire or the year after a big drought.  Plains sunflower isn’t the only plant that flourishes under those conditions, but its presence in plant communities is a great example of the kind of built in redundancy that helps ensure there are plants for animals to eat, even when many normally-abundant prairie plants are scarce or weakened.

Nebraska’s perennial sunflowers span a wide range of habitats, from wet to dry and sunny to shady.  You can find a sunflower in just about any habitat type in Nebraska.  That’s another great example of built-in redundancy, and a reason for optimism about the future.  As climate change alters the growing conditions across much of Nebraska, it seems unlikely that any habitat will change so dramatically that it will become devoid of sunflowers.  Instead we’ll probably see changes in the relative abundance of each species from place to place.  In addition, remember that what we call a sunflower is a fairly arbitrary categorization; there are lots of other wildflowers that provide very similar resources/services, including plants like rosinweed (Silphium integrifolium), false sunflower (Heliopsis helianthoides), sneezeweed (Helenium autumnale), and many more.  Those sunflowerish plants also span a wide range of habitat preferences and growth strategies, making it likely that some of them will be blooming abundantly every year, no matter what drought, fire, or grazing conditions are thrown at them.

An illustration of the general habitat preferences of several perennial sunflowers found in Nebraska.  The variety among habitats used by these species makes it likely that some kind of perennial sunflower will persist in most locations, regardless of how climate and disturbance patterns change over time.

Milkweeds are another group of organisms that demonstrate the diversity and redundancy in prairie ecosystems.  There are 17 milkweed species here in Nebraska, along with several other related species (like dogbane) that produce the same kind of sticky white latex.  While that latex is toxic to most creatures, a number of invertebrates have figured out how to feed on milkweed plants without suffering harmful effects.  Many have actually turned the toxin into an advantage by ingesting the substance and making themselves toxic to potential predators.  The most famous of these critters, of course, is the monarch butterfly, which uses milkweeds as larval hosts.

A selection of milkweed species found in Nebraska, demonstrating the variety in flower colors and shapes among the group.

When you picture a monarch caterpillar on a milkweed plant, you probably envision a tall plant with a big pink flower.  In reality, monarchs can use many (maybe all?) milkweed species as larval hosts.  Because each species of milkweed has its own unique set of preferred habitat and growing conditions, the diversity of milkweed species in Nebraska should help monarchs find a place to lay eggs regardless of weather, disease outbreaks, or other events.

The spring of 2017 provided a compelling example of this.  In most years, monarchs overwintering in Mexico fly into the southern United States and lay eggs on milkweed plants there.  The subsequent generation than flies northward into Nebraska and other  nearby states.  For some reason, many monarchs broke from that pattern in 2017, and arrived in Nebraska much earlier than normal.  This caused a great deal of concern because the milkweed most commonly used for egg laying – common milkweed (Asclepias syriaca) wasn’t up yet, and just as it started emerging, a freeze knocked it back down.  Fortunately, common milkweed wasn’t the only option available to monarchs.  Whorled milkweed (Asclepias verticillata) is also fairly common, starts growing earlier in the year than common milkweed, and is more resistant to cold weather.  Monarchs seemed happy to lay their eggs on the skinny leaves of whorled milkweed, and those of us worried about monarchs breathed a sigh of relief.  Once again, diversity created redundancy, and monarchs found habitat for their babies, even though they arrived well ahead of schedule.

A monarch egg and caterpillar on whorled milkweed earlier this spring (April 27, 2017) in Nebraska.

A broader example of redundancy and resilience in prairies includes the interdependence between bees and plants.  If you’ve followed this blog for long, you’re surely aware that there are thousands of bee species in North America, and potentially 80-100 or more species in a single prairie.  Most of those bees can feed on the pollen and nectar from many kinds of wildflowers, though some are restricted by their size or tongue length from accessing certain species. Because most plants only bloom for a few weeks, and most bees need considerably longer than that to successfully raise a family, bees require more than one kind of wildflower near their nest.  In fact, in order to support a broad diversity of bee species, a prairie needs an equally diverse set of wildflower species.  That way, a bee can find sufficient food throughout the growing season, even if drought, grazing, or other events keep some plant species from blooming in a particular year.

On the flip side, most wildflowers rely on the diversity of bees and other pollinators to ensure successful pollination.  While some insect-pollinated plants are very selective about who they let in, most rely on the availability of many potential pollinators.  If some species of bees are suffering from a disease, or have a weather-related population crash, it’s awfully nice to know that there are other bees (along with butterflies, moths, wasps, and other insects) that will still be able to transfer pollen from one flower to another.  A diverse pollinator community relies on a diverse wildflower community, and vice versa.  Diversity, redundancy, and resilience.  No matter what happens, flowers make fruits and seeds – which, by the way, is pretty important all the various creatures that rely on those fruits and seeds for food.

Bees rely on plant diversity to ensure a consistent supply of pollen and nectar across the growing season. In this case, tall thistle, an important native wildflower, is supplying food to a bee in return for pollination services.

All of us have our favorite prairie species, whether we’re fans of flowers, butterflies, birds, or some other group of organisms.  It’s easy to focus our attention on those favorite species, and worry about whether they will survive all the challenges that face prairies today.  If we really care about prairies, however, we should probably focus more on (and celebrate) the richness of species that keep prairies humming along, no matter what gets thrown at them.  The variety of yellow-flowered sunflowerish plants, the broad array of latex-producing milkweed-like plants, the complexity of the plant-pollinator relationship, and countless other examples of diversity and redundancy help ensure the survival of prairies well into the future.  That resilience is why I remain optimistic about the future of prairies.

A Hopeful Metaphor for Prairie Managers

Recently, I listened to a conference presentation by Doug Ladd, the Director of Conservation for The Nature Conservancy in Missouri, and one of the smartest people I know.  Doug talked about the importance of conserving biodiversity, habitat diversity, essential ecological processes, and irreplaceable habitats and species, and stressed the need to better connect people with nature.  It was an excellent talk, and I could spin many of his points into entire blog posts.  For now, however, I want to focus on one short phrase he uttered, which relates to something I often think about.  The phrase was “There is no endgame in conservation.”

The importance of that phrase might not strike you immediately, but for those of us who dedicate much of our lives to prairie conservation, it’s an idea we need desperately to come to terms with.  No matter how much time and effort we put into restoring or managing prairies, we won’t ever reach a place where we can stop and just let nature handle the rest.  Many people harbor the romantic notion that if we could make prairies big enough and provide them with their full complement of species – including everything from soil microbes to bison, we could step away and the system would run itself without human intervention.  Unfortunately, that’s just not the way it works.  Nature relies on people just as much as we rely on nature, and it’s really not even fair to mention nature and people as if they are two distinct entities.

Even in places like the Nebraska Sandhills, with roughly 12 million mostly contiguous acres of prairie, the role of humans is still critically important and necessary.

Because there is no endgame in prairie conservation, we need to develop an appropriate mindset. Most importantly, we have to be able to look at the future without despair.  As an example, it’s easy to look at many grasslands and wonder how we can possibly deal with all the invasive species threatening the site today, let alone all the new ones that will inevitably join them.  It can feel like trying to hold back a river with a garden hoe.  Issues like habitat loss and fragmentation, nitrogen deposition, and climate change just make the picture even more bleak.  Knowing that our prairies won’t ever be able to stand on their own might seem the same as knowing that we can never win.  All we can do is stave off loss for as long as possible.  That’s seriously depressing.

Since this is the life I’ve chosen for myself, I’ve thought a lot about the idea that there is no endgame in conservation, and I’ve come up with a metaphor that makes me feel a lot better about it.  I don’t see myself as a hopeless defender of prairies, trying to stave off inevitable destruction.  Instead, I see myself as part of a long series of mechanics.  I inherited the prairies I work with from prior mechanics, and someday I’ll hand those prairies off to future mechanics.  As such, my job isn’t to save the prairie, it’s to keep it running until the next mechanic takes over.  The metaphor applies to an individual manager and a single prairie, but it also applies to each generation of conservationists and the earth we’re all working to maintain.  Success is being able to hand off a functioning prairie, biome, or earth to the next generation of mechanics.

To understand my metaphor, you have to move away from the idea that most mechanics are only able to keep a particular car, for example, running for a certain period of time before it inevitably dies and goes to the scrap heap. While that is the way it usually works, it doesn’t necessarily have to be.  Imagine starting out in 1908 with a brand new Ford Model T automobile and giving a series of mechanics the charge to keep the vehicle functional forever.  For a while, keeping the car running just means replacing fluids and parts that break or wear out.  Eventually, however, there will be needed updates to parts, and even changes to the overall design of the car, so it can be adapted to keep up with a changing world.  Over time, because of changes in road design, safety and fuel efficiency rules, and needs of drivers, the car will have to be made to drive faster, brake more efficiently, use different fuel, and evolve in numerous other ways.  As each generation of mechanic finds innovative ways to keep the vehicle on the road and running well, the vehicle will be continually and repeatedly transformed.  Today’s version of the vehicle would be nearly unrecognizable to the mechanic who first worked on the Model T.  Very few original parts would remain, but today’s version of the vehicle would still perform the same essential function of transporting people and/or goods from place to place.

Prairies and other ecosystems are both easier and harder than cars to maintain over time.  On the one hand, prairies are infinitely more complex than cars, and come with many more challenges (though auto mechanics might argue that last point).  On the other hand, prairies consist of networks of living organisms, which can adapt as individuals and as communities to evolving challenges.  That inherent adaptability means that the prairie manager’s job is really to help the prairie maintain its resilience – its ability to retain its essential functions – as the world changes around it.

Just as the vehicle in my mechanic metaphor is constantly transforming, prairies and other ecosystems have to do the same, and land stewards have difficult choices to make as those changes occur.  As an example, many of today’s prairies have numerous and abundant species that weren’t even on the continent a few hundred years ago.  A profusion of introduced plants have entered the scene, some of which are apparently innocuous, and others that have dramatically changed the balance of power within plant communities.  In addition, white-tailed deer have become superabundant across most prairie regions, pollinator populations are crashing, and many other changes to animal communities have severe impacts on ecological processes.  Belowground, non-native earthworms and pill bugs are just two examples of species that have fundamentally altered the soil fauna in ways we don’t really understand.  Habitat fragmentation, high levels of nitrogen deposition, and a rapidly changing climate all combine to further drive important transformations in prairie species composition.

Yellow bedstraw (Galium verum) is a yellow flowered plant that seems to be invading low meadows in portions of the Nebraska Sandhills.  Making decisions about whether and how to address invaders like this can cause a lot of anxiety for land managers.

Fortunately, our job as land stewards is not to prevent our prairies from changing; our job is to help prairies preserve their character and function as they change, and then hand those prairies off to the next generation of stewards.  How do we do that?  We can manage for plant diversity and habitat heterogeneity to maintain ecological resilience.  We can prevent or suppress invasive species that have serious negative impacts on that resilience and diversity.  We can enhance the viability of small isolated prairies by restoring adjacent habitats and making those prairies larger and more connected.  As time goes by and conditions change, prairies will transform in ways that might make them nearly unrecognizable to land stewards of previous generations.  Rather than a sign of failure, those transformations are a sign of success, as long as they preserve the components and processes that are characteristic* of prairies.  After all, a 2017 Tesla Model 3 is a far cry from the 1908 Ford Model T, but which would you rather drive through today’s world?

*Defining the essential characteristics of prairies is something we don’t discuss nearly enough.  It seems like a simple enough exercise to outline what makes a prairie a prairie, but if you believe that, give it a shot…

Prairies like this are surely very different today than they were in the past or than they will be in the future. Change is good and healthy, as long as we can preserve the essential components and processes that define and sustain prairies and prairie communities.

Why Does Plant Diversity Matter? Help Us Figure It Out!

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.

2013 photos from
2013 photos from our experimental research plots.  The plots from left to right were planted to a monoculture (big bluestem), a low diversity mixture (mostly grasses and a few late season wildflowers) and a high diversity mixture (100 plant species).  We are investigating functional differences between these kinds of plant communities.

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, allencr@unl.edu

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:

http://snr.unl.edu/necoopunit/default.asp

Applicants should also review:

https://prairieecologist.com/

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.

Contrasting Approaches to Prairie Management: Leopold, Land Health and Cabbages.

“A Land Ethic” is the concluding essay in Aldo Leopold’s 1949 book, A Sand County Almanac, and is the most powerful and relevant piece of conservation writing I’ve ever read.   Leopold’s essay spells out the changes we need to make in the way we view our relationship with the land, and it is both impressive and frustrating that nearly everything in that essay still reads true today.  If anyone reading this blog post has never read A Sand County Almanac, please stop reading this, go pick up a copy of the book, and read it.

I’ll wait…

Instilling a land ethic in my kids is one of my highest priorities as a parent.
Instilling a land ethic in my kids is one of my highest priorities as a parent.

One of my favorite parts of “A Land Ethic” is the section titled “Land Health and the A-B Cleavage”.  I’m always blown away by how neatly Leopold synthesizes the field of conservation into the first three sentences of that section:

A land ethic, then, reflects the existence of an ecological conscience, and this in turn reflects a conviction of individual responsibility for the health of the land. Health is the capacity of the land for self-renewal. Conservation is our effort to understand and preserve this capacity.

The very next paragraph introduces an issue I’ve been wrestling with for a long time.

Conservationists are notorious for their dissensions. Superficially these seem to add up to mere confusion, but a more careful scrutiny reveals a single plane of cleavage common to many specialized fields. In each field one group (A) regards the land as soil, and its function as commodity-production; another group (B) regards the land as a biota, and its function as something broader.

Leopold goes on to describe how some in his field of forestry are “quite content to grow trees like cabbages” while others have a less agronomic and more ecological approach.  He also points out that the fields of wildlife management and agriculture each have their own parallel examples of this dichotomy.  These contrasting views of the world still exist in various forms, from the way farmers think about their fields to the way people in cities value natural resources.

I see Leopold’s A-B cleavage very clearly in prairie management.  One example can be found in the way prairies are used for livestock production.  Many livestock producers see prairies primarily as grass farms, and the worth of a plant is determined by its palatability and nutritional value to livestock.  Broadcast herbicide application is commonly used in an attempt to remove “weeds” and leave only the grasses cattle or other livestock most like to eat.  Optimization of grass production also manifests itself in grazing strategies; particularly systems that move cattle through multiple paddocks with the primary goal of increasing the production and dominance of grass.  Grass farmers are exasperated by the perennial reoccurrence of “weeds”, despite their best efforts to prevent them. They don’t see that those weeds fill ecological roles grasses can’t, including roles that improve the overall health and productivity of the land.

A grass farmer's nightmare, these ragweed plants and other "weeds" play important ecological roles and fill in open spaces created by intensive grazing or drought.
A grass farmer’s nightmare, these ragweed plants and other “weeds” play important ecological roles, including filling open spaces created by intensive grazing or drought.  Removing them with herbicide application only results in more “weeds”, which fill the same spaces again.  Perennial grasses easily outcompete these opportunistic plants under light or no grazing pressure.  In fact, a year after this photo was taken, this site was dominated by big bluestem.

Other ranchers, however, see prairies as much more than grass farms.  Instead, they recognize that their livelihood relies on an extraordinarily diverse community of organisms above and below ground.  To these ranchers, the only weeds are those that reduce the diversity of the prairie community and make the land less healthy by Leopold’s definition of health: the capacity of the land for self-renewal.  Livestock producers on this side of the cleavage understand that they and their livestock depend upon soil, plants, pollinators, predators, pathogens, and the interactions between them.  A plant’s importance is not judged only by whether or not a cow will eat it, but also by the roles it fills in the larger community.  Those contributions include the communities of microbes living in the plant’s root system, pollen and nectar for pollinators, and food for herbivores, which in turn support predators that regulate populations of their prey.  Ranchers with an ecological perspective gain as much appreciation from watching bees buzzing from plant to plant as they do from watching the weight gains of their cattle, even though the latter is what allows them to pay their taxes and keep their land.

Just as there is a broad range of perspectives among livestock producers, there are wide contrasts among those who manage prairies for recreation and conservation purposes as well.  Some prairie managers have a single species or narrow set of species as their primary management target.  Those targets are include game species such as ring-necked pheasants, white-tailed deer or ducks, but may also be butterflies or a particular class of plants or grassland birds.  Narrowly-focused managers tend to manage their prairies in much the same way each year so as to provide a consistent set of conditions that best suit their preferred species.  Over time, prairie species not favored by that kind of repetitive management regime diminish in number or disappear, decreasing the overall diversity of the prairie community.  Since ecological resilience (today’s term for Leopold’s “land health”) relies heavily on species diversity, the loss of species from the community weakens its ability to support others, including the managers’ favorites.  Ironically, as the community weakens, managers tend to become even more agronomic in their approach by adding food plots, controlling predators, or increasing herbicide use to suppress plants taking advantage of a less diverse community.

Prairie managers with a broader ecological perspective start with the premise that a diverse prairie community is of utmost importance.  They manage in ways that prevent any particular species or group from becoming too dominant at the expense of others.  These managers don’t judge success by the abundance of one species or another, they focus on processes such as pollination, predator/prey interactions, and other indicators of community diversity and ecological resilience.  Variation in the species composition of a prairie between years is a cause for celebration rather than trepidation.  Year-to-year variation means that many different species (especially insects and animals) experience success over time, rather than just the few who thrive under more stagnant conditions.  Managing for diversity is not a simple process, and requires a careful eye and flexible approach, but the result usually produces strong and stable populations of all species – including those desired by more narrowly-focused managers.

Prairies managed for overall diversity have strong ecological processes that support all species - including game animals, songbirds, insects, plants and livestock. Prairies managed for overall diversity have strong ecological processes that support all species - including game animals, songbirds, insects, plants and livestock.
Prairies managed for overall diversity have strong ecological processes that support all species – including game animals, songbirds, insects, plants and livestock.

Whether we are managing for livestock, game species, butterflies, or flowers, the approach we take is critically important.  There is a strong temptation to continually maximize what we think are the enabling conditions for the species we’re most interested in, but that approach ignores the broader complex system those species depend upon.  The grass that cattle eat relies on productive soil, and that soil’s productivity is supported by a diversity of plants, microbes, pollinators and other prairie community members.  Similarly, the fate of butterflies, pheasants, and deer all depend upon the roles played by their fellow citizens of the prairie.

Trying to deal with all of that complexity may seem daunting, but take another look at Leopold’s definition of land health and conservation: Health is the capacity of the land for self-renewal. Conservation is our effort to understand and preserve this capacity.  Note that Leopold doesn’t say conservation entails fully grasping and perfectly managing the complexities of the land.  Instead, he defines conservation as the effort to do so.   I like that.  We don’t have to know everything to be successful.  Instead, conservation is an adaptive process of learning, incorporating new knowledge into our actions, and then trying again.  That means that conservation is accessible to anyone who appreciates the broad complexity of natural systems and attempts to work within them, rather than against them.

…And isn’t that more fun than just growing cabbages?

Disclaimer:  The author of this post intends no disrespect to those who grow cabbages.  Instead he was simply referring to a quote from earlier in the post to reinforce a point and attempt to end a long and heavy essay with something a little lighter.  Cabbage growing is a perfectly legitimate and important activity, especially when done with appropriate consideration for the broader ecological context of soil and other ecosystem processes required to sustain long-term production…  …Ok, I’ll just stop now.

Previous related posts you might be interested in:

Calendar Prairies

Are Botanists Ruining Prairies?

Photo of the Week – June 7, 2013

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

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

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

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

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

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

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

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

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

The Right Metaphor for Prairie Restoration

Prairie restoration can be a powerful tool for grassland conservation, but we’re not taking advantage of its full potential.  Too often, we think and talk about prairie restoration (aka prairie reconstruction) in the wrong way.  Instead of trying to restore an ecosystem, we try to reproduce history.

Nelson Winkel, land manager for The Nature Conservancy’s Platte River Prairies, harvests grass seed using a pull-behind seed stripper.

I was in Washington D.C. a couple weeks ago and visited Ford’s theater, where President Lincoln was assassinated in 1865.  After the death of the president, the building went through drastic changes, including being completely gutted after a partial collapse of the interior.  By the time the decision was made to restore the building for use as a historic site, the National Park Service basically had to start from scratch.  Regardless, through painstaking research and a lot of hard work, the theater was rebuilt to closely resemble Ford’s theater of 1865.

The rebuilding of Ford’s theater is a decent metaphor for much of the early prairie restoration (or reconstruction) work dating back to the 1930’s in North America – as well for some of the restoration work that continues today.   In the case of prairie restoration, someone identifies a tract of land that used to be prairie but has been converted into something completely different (usually cropland), and tries their best to restore what was there before it was converted.  Just as in the restoration of Ford’s theater, the prairie restoration process requires lot of research and hard work to identify, find, and reassemble what had been there before.

Unfortunately, the Ford’s theater approach has turned out to be a poor fit for prairie restoration.  Prairies aren’t buildings that have specific architectural plans and well-defined pieces that can be collected and assembled to create a pre-defined end product.  Prairies are dynamic ecosystems that are constantly changing and evolving, and their components include organisms that interact with each other in complex ways.  Trying to recreate a prairie that looks and functions just as it used to – especially on a small isolated tract of land – is nearly impossible.

Reseeded prairie at The Nature Conservancy’s Kankakee Sands Restoration Project in Indiana. If the plant community today looks different than it did before it was farmed, is that really a failure of the restoration project?

That doesn’t mean small scale prairie restoration is a bad idea.  I think reestablishing vegetation that is similar to what was at a site many years ago can have tremendous historic and educational value, and can also provide important habitat for many grassland species.  Where this kind of prairie restoration falls flat is when we expect too much from it.  It’s really easy to find glaring differences between the restored prairie and what we know or think used to be there – soil characteristics are different, insect and wildlife species are missing, plant species are too common or too rare, etc.  These “failures” have led some people in conservation and academia to become disillusioned with the whole concept of prairie restoration.

In reality, prairie restoration has proven to be very successful, and is a tremendous tool for grassland conservation.  We just need to find and apply a better metaphor.

A Better Metaphor for Ecological Restoration

Unlike efforts to restore old buildings, prairie restoration projects should not be aimed at recreating something exactly as it existed long ago.  Instead, effective prairie restoration should be like rebuilding a city after large portions of it are destroyed in a major disaster.  When reconstructing a metropolitan area, replicating individual structures is much less important than restoring the processes the inhabitants of the city rely on.  The people living and working in a city depend upon the restoration of power, transportation, communication, and other similar functions.  Those people don’t care whether roads, power lines, or communication towers are put back exactly as they were before – they just want to be able to get the supplies and information they need, and to travel around so they can to do their jobs and survive.  Restoration success is not measured by how much the rebuilt areas resemble the preexisting areas, but by whether or not the city and its citizens can survive and thrive again.

Similarly, restoration of fragmented prairie landscapes should not be an attempt to recreate history.  It should be an attempt to rebuild the viability of the species – and, more importantly, the processes – that make the prairie ecosystem function and thrive.  Success shouldn’t be measured at the scale of individual restoration projects, but at the scale of the resultant complex of remnant and restored prairies.  Are habitat patches sufficiently large that area-sensitive birds can nest successfully?  Are insects and animals able to travel through that prairie complex to forage, mate, and disperse?  Are ecological processes like seed dispersal and pollination occurring between the various patches of habitat?  When a species’ population is wiped out in one part of the prairie because of a fire, disease, or other factor, is it able to recolonize from nearby areas?

Pollination is an example of an important process that drives prairie function. Increasing the size and/or connectivity of prairies by restoring areas around and between prairie fragments can enhance the viability of pollination and other processes.

At first glance, choosing the appropriate metaphor for prairie restoration may seem insignificant compared to other challenges we face in grassland conservation.  However, if we’re going to successfully restore the viability of fragmented prairies, we can’t afford to waste time and effort worrying about whether or not we’ve matched pre-European settlement condition, or any other historical benchmark.  Instead, we need to focus on patching the essential systems back together.

After all, we’re not building for the past, we’re building for the future.

.

Read more on this subject…

– An earlier blog post about using prairie restoration as a landscape scale conservation tool.

– A prairie restoration project case study, with ideas about how to measure its success.

– Some recent early attempts we’ve made to measure restoration success by looking at the responses of bees and ants.

– A post about the importance and definition of ecological resilience in prairies.

The Great Drought (Again)

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

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

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

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

Continue reading

Why Grassland Birds are Poor Indicators of Prairie Quality

I presented this argument to a Nebraska symposium on grassland birds in 2008 and managed to escape relatively unscathed.  Now I’m testing my luck with a wider audience.  At least no one can throw things at me through the computer…

Let me start by saying that I’m a big fan of birds.  I really enjoyed working on my graduate research, which focused on grassland birds and their vulnerability to prairie fragmentation.  I also think birds are generally pretty and interesting. However, the truth is that prairie birds make up only a tiny percentage of the species in prairies (most of which are invertebrates, followed by plants).

Grassland birds make up a tiny percentage of the species living in a prairie - the vast majority of which are invertebrates and plants.

However, grassland birds are often held up as indicators of whether or not a prairie – or a prairie landscape – is “healthy” or “high quality.”  A common refrain in prairie conservation goes something like this; “If we have our full complement of grassland birds in this prairie and/or landscape, it’s a good bet that all the other species are also doing well.”  Unfortunately, while prairie birds are relatively easy to study and monitor, they may not do a good job of reflecting how the rest of the prairie is doing.  Let’s look at some of the most important attributes of prairies and some of their major threats – and consider how well birds correlate with them.

Species Needs – Survival, Reproduction, and Dispersal.

First and foremost, species have to survive and reproduce in order to persist in a prairie.  This applies to every species, from large vertebrates to tiny invertebrates and the entire suite of plants.  It’s important for us to know that grassland birds are surviving and reproducing, but can they tell us whether other species are doing the same?  You could argue that because they eat insects, grassland birds could have an impact on the survival of some insect species.  That’s true to a point, but grassland birds are generalist feeders – they tend to eat whatever insects are easiest to catch at any particular time – so while the abundance of grassland birds might impact the overall abundance of insects, you can’t really tie the presence of a particular grassland bird species to the survival of a particular insect species (or vice versa).  In other words, the plight of a rare leaf hopper or butterfly species is unlikely to be correlated with grassland birds.  Nor are grassland birds good predictors of plant species survival – the presence of meadowlarks or Henslow’s sparrows tell us nothing about whether or not compass plant or leadplant is thriving.  Grassland birds require certain habitat structure types (short vegetation, tall/dense vegetation, etc.) but they don’t much care whether that vegetation consists of smooth brome and sweet clover or a large diversity of native plants.

Henslow's sparrows are a bird of conservation concern and their presence in a prairie can be seen as a conservation success. However, although they tend to require fairly large prairies, and can indicate the presence of certain vegetation structure types, they don't indicate whether or not a prairie has a diverse plant or insect community.

In addition to basic survival, animal and plant species need to be able to move around the landscape in order to recolonize places where they have disappeared, and to maintain genetic interaction between populations (important for genetic diversity).  In landscapes where prairies exist as isolated remnants, moving between prairies becomes very difficult.  Corridors of prairie vegetation between prairies become important in those landscapes, and prairies near each other provide better opportunities for interaction within species than do more isolated prairies.  Because most grassland birds fly south at the end of each season and return the next year, (and the ones that don’t can still fly long distances between prairies) they don’t rely on those physical connections between prairies like most other animals and plants do.  Since grassland birds are pretty unique in terms of long-distance flying ability, they are a poor indicator of conditions that affect less mobile species.

Ecological Services and Ecological Function – Pollination, Seed Dispersal, etc.

Apart from the needs of individual species, prairies rely on certain processes to keep everything humming along.  Pollination and seed dispersal are two good examples.  Both affect the viability of prairie plant species, and neither has much to do with grassland birds.  Pollination primarily relies on plant diversity and bees – the most important pollinator group in prairies – and both plant diversity and bees are pretty disconnected from grassland birds.  We don’t know much about the role of prairie birds as seed dispersers, but it’s a good bet that they do very little seed dispersal during the summer when they’re primarily eating insects.  The role of migrating grassland birds as seed dispersers would be an interesting thing to study – but our use of grassland birds as indicators of prairie quality is always based on their presence during the breeding season.  If you were going to measure whether or not pollination and seed dispersal were functioning adequately, you’d likely evaluate the diversity of plants, the abundance of bees, and some of the potential obstacles to seed dispersal (tree lines, isolation of prairies, etc.), but I don’t think measuring grassland birds would tell you much.

Resilience – Redundancy and the Ability to Withstand Stresses and Invasive Species.

One way to think about the resilience of a prairie is as a measure of how well the prairie can bounce back from stresses.  For example, species diversity adds resilience to a prairie because when many species are present – especially when they overlap in the roles they play – the loss of an individual species can be a relatively minor blow.  If there are dozens of bee species pollinating flowers in a prairie, a disease that wipes out one or two species will probably not have a huge impact on seed production.  A diversity of plant species can also help to dampen the impacts of an event such as a severe drought or intensive grazing that temporarily weakens the vigor and growth of dominant plant species.  When there are lots of plant species present, the weakening of some leads to increased growth and abundance of others.  This helps maintain a stable supply of food for herbivores, and also helps prevent encroachment by invasive species that might otherwise take advantage of the weakened plant community.

Grassland birds may help bolster the resilience of a prairie in some ways.  They might, for example, help suppress an outbreak of grasshoppers by focusing their feeding on that easy-to-find prey species, and thus limit its abundance.  However, as discussed earlier, they don’t have much to do with pollination, nor would they help provide food for herbivores during a drought.

If you want pollination you need bees, not birds.

Threats to Prairies – Habitat Fragmentation, Invasive Species, Broadcast Herbicide Use, and Chronic Overgrazing.

One of the best arguments for grassland birds as an indicator of prairie health is that they are vulnerable to the loss and fragmentation of grassland habitat.  This is true.  A diverse and successfully reproducing community of grassland birds requires relatively large and unfragmented grassland.  In addition, because some grassland breeding birds need short vegetation and others need tall/dense vegetation, a diversity of birds can indicate a diversity of available habitat structure  – and that’s important to many other wildlife species as well.  Greater Prairie Chickens are often promoted as particularly good indicators because they are a single species that needs both large grasslands and a diversity of habitat structure.

However, there are a couple of other things to consider.  First, while some grassland bird species need large prairies, we don’t really know whether the minimum area required by grassland bird species is larger or smaller than that required by plant or insect species.  We know that many prairie plant species have survived for a very long time in tiny isolated prairies.  But because individual plants of many species can live almost indefinitely, due to their ability to generate new plants through rhizomes and other asexual means, the populations of plants in those tiny prairies could be in a death spiral due to the lack of genetic interaction with other populations.  You could make the argument that plants need much larger prairies than birds (thousands of acres, perhaps?) in order to maintain genetic fitness.  We simply don’t know.  And we know even less about the prairie size needs of insects.

Second, while grassland birds do require fairly large grasslands, most don’t actually require PRAIRIES.  Prairie chickens and many other grassland bird species have benefitted greatly from Conservation Reserve Program (CRP) fields that have added large numbers of acres of switchgrass, brome, and low-diversity grasslands to agricultural landscapes.  However, those same CRP fields have done very little for native wildflower populations or pollinator insects (or other insects that rely on diverse communities of native plants) so the increase in grassland birds in landscapes with CRP doesn’t really tell us much about the health of most other prairie species.

This smooth brome-dominated grassland is of very little to most prairie species, but would provide relatively good habitat for some grassland bird species (except for the trees in the background).

Because grassland birds can live comfortably in grasslands made up of a few native grasses, or even non-native grasses, they are poor indicators of the impacts of most invasive species – a major threat to prairies.  Similarly, broadcast herbicide use that greatly reduces the number of plant species in a prairie has little impact on the grassland birds nesting there.  Finally, a prairie that is being overgrazed would certainly have different bird species than one that is not being grazed at all, but a prairie that was chronically overgrazed for decades – and then managed well again – would have a pretty low number of prairie wildflower species but a very nice-looking grassland bird community.

One threat that grassland birds can be an excellent indicator for is tree encroachment on prairies.  Most grassland birds avoid nesting anywhere near even a solitary tree, let alone a grove of them, so a prairie with few birds could indicate a tree problem.  On the other hand, it’s pretty hard to miss a bunch of trees growing in a prairie…

Summary

Here’s the real point.  Grassland birds are an important component of prairies.  A prairie without all of its appropriate prairie bird species, or in which those species are not successfully raising broods, is missing something valuable.  Improving grassland bird success in prairie landscapes is an important and worthwhile objective.  At the same time, however, a prairie that has a full complement of successful grassland bird species doesn’t necessarily have diverse plant and insect communities, functioning ecological processes, or a low risk of invasive species or other threats.  In other words, grassland birds are an important component of high quality prairies, but their presence and/or success doesn’t necessarily mean a prairie is high quality.

Now that I’ve spent 1,500 words bashing prairie birds (I really do like birds…) the relevant question is, “What SHOULD we use as indicators of prairie conservation success?”  I wish I had a simple answer.  Part of the answer, of course, depends on how you visualize prairie quality (see my earlier post on this subject) because evaluation needs to reflect objectives.  But if our vision of a high-quality prairie includes species diversity, habitat heterogeneity, and other complexities, our evaluation methods will have to be complex as well.  Figuring out how to “take the pulse” of prairies may be the most important conservation challenge we face, because without that information we can’t design effective conservation strategies.

While we still have a lot to learn about how to take that pulse, it’s clear that we’ll have to do more than just count birds…