The Bench Strength of Prairies in the Face of Climate Change

In case you hadn’t noticed, the climate is changing.  Things are getting weird, and they’re going to get weirder.  Here in central North America, we’re expecting more and more intense storm events and drought periods in the coming decades.  Scientists are scrambling to figure out how to predict and facilitate the inevitable changes those crazy weather events will bring to natural systems, including prairies.

Fortunately, prairies have been training for this for a very long time.  A few months ago, I wrote a post about the resilience of prairies, and how that resilience is built largely upon the diversity within their ecological communities and the size and connectivity of prairie habitats.  Prairies that are relatively big and still have the majority of their potential plant and animal species are going into this encounter with rapid climate change with what you might call solid bench strength.

Diversity of plants and animals is the keystone to ecological resilience. The Nature Conservancy’s Nachusa Grasslands, Illinois.

In sports, teams want to have lots of available players that represent a broad diversity of skills.  Each opponent they face will have its own individual mix of power, endurance, speed, and other attributes.  A successful team can build a roster for each game that counters their opponent’s strengths, no matter what they are.  The number and quality of their players is a team’s bench strength.

Healthy prairies have great bench strength too.  No matter what gets thrown at them, they can adapt by changing their roster of species.  The speed at which they can drastically change the makeup of their “team” is impressive.  Anyone who has spent many years watching the same prairie has seen this in action, but none of us have seen prairies go through what Professor John Weaver saw back in the 1930’s and 40’s.

Weaver, one of the best known prairie ecologists of all time, had been studying 30 “large typical prairies” across parts of Nebraska, Iowa, Kansas, and Colorado prior to the start of the Dust Bowl era.  His baseline data gave him an invaluable opportunity to document the dramatic changes to the plant communities of those prairies during and after the droughts of the 1930’s.  What he recorded, along with his former student F.W. Albertson, was an incredible testimony to the dynamism and resilience of those prairies.  Their 88 page 1944 publication, entitled “Nature and Degree of Recovery of Grassland from the Great Drought of 1933 to 1940”  encapsulates the bulk of their findings in one place, and is worth a read if you have the time.

In 2012, we got a small glimpse of what Weaver and Albertson saw in the 1930’s, but our drought – while severe – only lasted one year here in Nebraska.
In 2013, the response of the prairie to the 2012 drought included some explosions of wildflowers, including shell leaf penstemon (Penstemon grandiflorus).

One of the biggest plant community shifts Weaver and Albertson documented was the widespread and dramatic death of grasses such as big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), and Kentucky bluegrass (Poa pratensis), and the subsequent rise of other grasses such as prairie dropseed (Sporobolous heterolepis), sand dropseed (Sporobolous cryptandrous), porcupine grass (Stipa spartea), and most of all, western wheatgrass (Pascopyrum smithii).  Western wheatgrass populations exploded throughout the mid to late 1930’s, to the point where many prairies were completely dominated by it, to the near exclusion of other plant species. In fact, in a 1942 publication, Weaver said the following, “The large area of drought-damaged true prairie and native pasture now dominated by western wheat grass and the harmful effects of the successful competition for water of western wheat grass with species of greater forage value present a problem of much scientific interest and great economic importance.”

In other words, as they made massive substitutions within their lineups, prairies were changing so much they became almost unrecognizable, even to those who knew them best.  Weaver and Albertson watched waves of forb species they’d always considered to be of little value become stars on the field, and they and others didn’t quite know how to react.  Daisy fleabane (Erigeron strigosus), Missouri goldenrod (Solidago missouriensis), and heath aster (Aster ericoides) were all examples of wildflowers that suddenly rose to prominence in new and major ways.  The two dismayed scientists described how heath aster, a “nearly worthless native forb,” formed near monocultures across wide swaths of prairie, to the extent that it “ruined many of the prairies…for the production of hay, because of its brush-like growth.”  Others were out of their depths on this too, and Weaver and Albertson reported that “considerable native sod was broken because of the seriousness of this pest.”  In the following sentence, however, they begrudgingly added a short sentence, “Of course, it did protect the soil.”

While Weaver and Albertson considered heath aster to be “nearly worthless” it plays an important role in the prairie, and is an important food source for pollinators in the fall.

Exactly.  While the strategy was foreign and frightening to those who hadn’t seen prairies dealing with these kinds of conditions before, those prairies were just doing what they’ve done many times before – making whatever roster adjustments were necessary to keep functioning at a high level.  In addition to forb species they denigrated as weeds, Weaver and Albertson noted that many wildflowers with “large storage organs”, including bulbs and corms, also greatly expanded their population size during the dust bowl years.  This included species like Violet wood-sorrel (Oxalis violaceae), bracted spiderwort (Tradescantia bracteata), windflower (Anemone caroliniana), and wild garlic (Allium canadense).  Those species and others increased the size of the patches they’d occurred in previously, but also were found “in many new locations.”  Other native forbs that became superabundant in some prairies, especially early in the dust bowl years, included prairie ragwort (Senecio plattensis), white sage (Artemisia ludoviciana), and yarrow (Achillea millefolium).

Windflower (Anemone caroliniana) was one of the wildflowers with “large storage organs” that proliferated during the droughts of the 1930’s.

As rains started to return in the early 1940’s, Weaver and Albertson watched with amazement and renewed optimism as plant communities started “recovering”, which of course meant they were returning to a composition more familiar to the people observing them.  Grasses were often the first to rebound in prairies, including big bluestem, which initially formed large and lush monocultures in many places.  Wildflowers that hadn’t been seen for seven years or more, suddenly appeared everywhere, including blue-eyed grass (Sisyrinchium campestre), which grew “more thickly than if the stands of 7 normal years had been combined.”  Downy gentian (Gentiana puberula), which had been considered rare prior to the big droughts, became much more common in the early 1940’s than Weaver and Albertson had ever seen before, with abundances of “15 or more plants in a space of a few rods”.

Stiff sunflower (Helianthus pauciflorus) returned fairly quickly to “normal abundance” by 1943, as did many others, including silverleaf scurfpea (Pediomelum argophyllum), cream wild indigo (Baptisia bracteata), and buffalo pea (Astragalus crassicarpus).  Prairie violets (Viola pedatifida), pussy toes (Antennaria neglecta),  and others came back more slowly, but returned nevertheless.  Importantly, those returning species didn’t appear to be traveling from long distances.  Instead, they simply re-emerged, either from seeds or underground buds, from where they’d been sitting on the metaphorical bench, awaiting the call to step up to the plate again.

Buffalo pea (Astragalus crassicarpus) and many other wildflowers recovered from the long droughts at a speed that amazed Weaver and Albertson.

The prairies we know today have been through a lot.  In Nebraska and surrounding states, we have specific documentation of the kinds of extreme roster changes prairies can and have made to adjust to the world around them, thanks to the work of John Weaver and F.W. Albertson.  If you have a favorite local prairie, and I hope you do, it’s important to remember that the way it has looked for as long as you’ve known it is only a small sample of what it’s capable of.  Smart teams don’t reveal their secrets before they need to.

As we work to keep prairies healthy through this period of rapid climate change, it’s both useful and reassuring to remember what they’ve been through before.  Today’s prairies certainly have additional challenges to deal with today, compared to the dust bowl days (more invasive species, more landscape fragmentation, etc.), but many should still have sufficient bench strength to make the adjustments they’ll need to make in the coming years.  Our responsibility is to provide management that helps prairies sustain their plant and animal diversity, as well as to protect prairies from additional conversion to cropland or other land uses.  Where possible, restoring prairie habitat around and between prairie fragments can also help build resilience.  In short, we have to allow prairies to do what they do best – adapt and adjust.  Prairies are wily veterans and they’ve been in this game for a long time.  It’s a good bet they’ve still got a few tricks up their sleeve.

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.

Compatibility of Cows, Conservation and Climate Change?

I’ve been asked a number of times why I advocate for cattle grazing in prairies when cattle are such strong contributors to greenhouse gas emissions and rapid climate change.  It’s a fair question, but also a complicated one.  I don’t have a definitive answer, but I can share some of what makes it a thought-provoking subject.  Rather than providing a lot of specific research citations, I’m aiming instead to provide some general information that highlights the complexity of the topic.  Feel free to contribute additional information and perspectives in the comments section below (as long as you keep it constructive and polite).

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Cattle graze among leadplant and prairie clover at Konza Prairie in the Kansas Flint Hills.  What are the ramifications of cattle grazing for greenhouse gas emissions and other contributing factors to climate change?

Cattle: The Downsides

First, here are some reasons people are concerned about the impact of cattle on climate change.  According to the EPA, agriculture is responsible for about 9% of the U.S. greenhouse gas emissions, and beef production makes the largest contribution to that category.  Most of the impact comes not from carbon emissions, but from methane and nitrous oxide, both of which influence climate change more strongly (pound for pound) than does carbon.  “Enteric methane” (cow burps) is a big part of that equation, but so is manure, urine, and application of fertilizers to pastures.  These emissions are bad enough, but there are other negative impacts from beef production as well, including emissions from growing corn and other feed for cattle, emissions from manure in feedlots, water consumption by cattle and feed production, and pollution from sedimentation and nutrient runoff of pastureland.  Reading a list of bad stuff like this, it’s easy to see how people might wonder why I keep talking about grazing like it’s a good thing.

Cattle
Cattle are sometimes their own worst enemy in terms of advocating for their own existence.  I mean, come on, man!  This is just not a good look.

Predecessors to Cattle

As I provide some counterpoints, I’m going to do so from the perspective of the central Great Plains – the area of the world I’m most familiar with.  Outside the Great Plains, the situation varies greatly; there are places in the world where grazing may not be compatible with local ecosystems, for example, and where forest or other land cover types are being converted to pasture.  Here in my part of the country, however, we are in the heart of the historic bison range.  Before Europeans entered the picture in the Great Plains, prairies here were being grazed by bison, elk, pronghorn, and other large animals.  There are many arguments about the size of those historic bison populations, fluctuations in herd size and geographic range over time, and when/where bison impacts were important for prairie ecology.  For the purposes of this discussion, the important point is that cattle (and their emissions) weren’t introduced into a landscape with no history of methane emissions.  Bison were here prior to cattle, and they burped too.

The most cited article I’ve seen on the issue of methane emissions from historic bison populations is by Francis Kelliher and Harry Clark.  They use a fairly standard estimate of 30 million bison across the Great Plains prior to European contact.  Based on their calculations, the methane (CH4) emissions from those bison (2.2 Tg CH4 year-1) are not hugely different from those of today’s 36.5 million cattle across the same geography (2.5 Tg CH4 year-1).  The exact numbers are less important than this basic idea: the prairie ecosystem was contributing large amounts of methane to the atmosphere before humans brought cattle to the Plains.

Of course, feedlots, fertilization, and forage production, along with all the greenhouse gas emissions and other concerns associated with them, were not part of the historic bison landscape.  We definitely have an obligation to examine those aspects of cattle production and do what we can to limit their negative impacts.  In addition, the fact that cattle on native rangeland are producing emissions similar to their bison predecessors doesn’t release us from the responsibility of trying to reduce those emissions where possible.  I’m hopeful that research over the next decade or so will provide us with more guidance on how we might do that.

Bison
Before there were cattle, bison roamed (and burped) across the Plains.

Get Rid of Cattle?

What if we just stopped grazing cattle on the Great Plains?  Well, since the vast majority of the Great Plains is privately owned, grassland still exists primarily because it produces income.  Without cattle production, much of that grassland would likely be converted to row crop agriculture – a scenario that would probably be worse for climate change and would certainly spell disaster for prairie ecosystems.  Some have argued that a majority of the Great Plains should be turned into public land that would support both wildlife and tourism.  There are way too many economic and social issues associated with that for me to deal with here, but from a climate change emissions standpoint, I’m not sure it would solve the problem.  Either cattle would be replaced by bison again (see previous paragraph) or, if bison were not reintroduced, prairies would suffer from the loss of grazing, a major component of ecosystem function (see next paragraphs).

Simply getting rid of cattle altogether is probably not a great strategy for conservation. Plus, how could you get rid of something this cute?
Simply getting rid of cattle altogether is probably not a great strategy for conservation. Besides, how could you get rid of something this cute?

Grazing as a Positive Force

Despite the fact that chronic overgrazing can cause degradation of prairies (loss of plant species and habitat, soil erosion, etc.), grasslands and large grazers evolved together and grazing is still an essential component of grassland ecosystems.  This is especially true in North America’s Great Plains where there are still grasslands large enough to support wide-ranging wildlife species such as grouse and pronghorn.  Grazing, along with fire and drought, is one of the three major forces that affects prairies and prairie species.  For example, large herbivore grazing helps keep grasses from being so competitive that they overwhelm and reduce the diversity of plant communities, something that leads to a cascade of negative and interconnected impacts on pollinators, productivity, wildlife/insect communities, and more.  In addition, grazing alters vegetation structure, creating a wide range of habitat conditions.  Ungrazed prairie provides fairly uniform vegetation structure, even if it is hayed or burned.  Grazed prairie (under the right management) is heterogeneous, with patches of tall/dense vegetation, patches of short/sparse vegetation, and many other habitat types in-between – allowing the widest possible spectrum of prairie wildlife and insect species to thrive.

Maintaining plant and animal diversity, ecosystem function, and ecological resilience within the historic range of American bison would be very difficult without some kind of large ruminant, and in the face of climate change, we need our grasslands to be as resilient as possible.  Resilient grasslands will better adapt and maintain their ecological functions as climate changes, and that means they’ll continue to pull carbon from the atmosphere and store it belowground – an incredibly important part of our global climate change strategy.  While the impact of grazing on carbon storage of grasslands is, in itself, a complex topic, the general scientific consensus seems to be that a moderate level of grazing facilitates more carbon storage than no grazing (and more than chronic overgrazing).

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Strategic cattle grazing can create a variety of wildlife habitat structure types and help sustain plant diversity and ecological diversity.  It can also help maximize carbon storage in grasslands.

The Upshot

In the Great Plains of North America, grazing is an essential part of grassland ecosystems – a component that maintains the ecological health and resilience of prairies.  Cattle have mostly replaced bison as the large ruminant on stage at the moment, but they are filling many of the same basic roles – regulating plant competition and creating wildlife habitat, and also pooping, peeing, and burping.  We absolutely need to find ways to minimize the impacts of today’s grazing on climate change.  Livestock confinement operations, pasture fertilization, forage production, and other related practices provide opportunities for continued improvement.  In addition, some rangeland grazing practices, such as chronic overgrazing, are known to be detrimental, and not just from a climate change standpoint, so that’s an obvious place to focus.  Beyond that, we need to figure out how best to limit methane and nitrous oxide emissions and increase carbon storage on rangeland.  That will likely mean changing techniques for managing cattle in pastures, but also dealing with issues related to pasture fertilization, forage production, forage and animal transportation, feeding operations, and more.

The topic of cattle grazing and climate change is incredibly complex.  There is much more involved than I could possibly cover here, and what I did include is plenty complicated.  I don’t pretend to fully understand all the facets of the issue, but for now, I feel comfortable in my stance that cattle (and/or bison) grazing can be compatible with responsible conservation of our prairies here in the Great Plains.

 

More Information and Acknowledgements

Several scientists from The Nature Conservancy wrote a really helpful piece on the beef supply-chain and its impacts on water, wildlife, and climate.  You can see a summary and get access to the full report here.

Special thanks to Jon Fisher and Joe Fargione, who both helped me refine and improve this post.  Any remaining errors are my fault, not theirs.

 

How Science Works and Why It Matters

As a scientist and science writer, I’m concerned about the way science is perceived by the public.  I think some big misunderstandings about how science works are creating distrust and dismissal of important scientific findings.  That’s a huge problem, and I’d like to try to help fix it.

Let’s start with this: Science is a process that helps us understand and explain the world around us.  That process relies on repeated observations and experiments that continuously change our understanding of how things work.

Scientists often come up with results that conflict with those of other scientists.  That doesn’t indicate that something is wrong; it’s exactly how science is supposed to work.  When scientists disagree about something, more scientists get involved and keep testing ideas until a consensus starts to emerge.  Even at that point, ideas continue to be tested, and either gain more acceptance (because of more supporting evidence) or weaken (because conflicting results are found).

There is no endpoint in science.  Instead, ideas move through various steps of acceptance, depending upon how much evidence is collected to support them.  You can read much more about how the process works here.

We are lucky to have easy access to immense amounts of information today.  However, it can be be very difficult to know which statements are supported by good science and which are just opinions amplified by people with an agenda and a prominent platform.  Today’s world, for example, still includes people who earnestly believe the earth is flat, despite overwhelming evidence to the contrary.

Media coverage of science often increases confusion.  How many times have you heard or read a media story about how a particular substance either cures or causes cancer?  In most cases, the scientist being interviewed tries to explain that their work is just one step in a long process of evidence gathering and doesn’t prove anything by itself.  That scientist might as well be talking to an empty void.  The headline has already told the story and pundits are shaking their heads and complaining about how scientists can’t ever agree.  (Please see paragraph three above.)

Unfortunately, confusion about how science works means the public often doesn’t pay attention when scientists actually do agree on things.  Loud voices can easily sway public opinion on important topics because it’s hard to know who to believe.  Often, we believe those who say things we want to be true.

Let me ask you three questions:

Do you believe that childhood immunizations are safe and effective?

Do you believe that rapid climate change is occurring as a result of human activity?

Do you believe that food derived from products containing Genetically Modified Organisms (GMOs) is safe for human consumption?

The scientific community has clearly and strongly stated that the answer to all three of these questions should be yes.  Despite that, many people will answer yes to one or two of these questions, but not all three.  If you’re one of those people, I have another question for you.

If you trust the scientific community and the scientific process on one or two of these topics, why not on all of them?

This post is not about vaccines, global warming or GMOs.  I’m not trying to tell you what to think. Instead, I’m inviting you TO think.

If you’re a scientist, are you spending enough time thinking about how to talk to a public that is skeptical of science?  Being right isn’t enough when there are louder voices shouting that you’re wrong.  How do you expect the public to find the real story when your results are hidden in subscription-only journals and written in technical jargon-filled language?  What can you, personally, do to help others understand what science is, why it’s important, and what it can tell us?

If you’re someone who believes the science on some topics, but not others, are you comfortable with the reasons behind that?  Do you think science has been polluted by money and agendas, or do you think money and agendas are trying to discredit science?  Have you spent enough time reading articles that contradict your position and evaluating the credentials of those on each side?  Is it possible that long-held beliefs are preventing you from looking at evidence with clear eyes?

While individual scientists may have biases, the scientific process has no agenda other than discovery.  Scientists are strongly incentivized to go against the grain – both employers and journal publishers get most excited by research that contradicts mainstream ideas.  Because of that, ideas that gain overwhelming scientific consensus should be given extra credibility because they have withstood an onslaught of researchers trying to tear them down.

Can scientists be wrong?  Yes, of course – scientists are wrong all the time, and they argue back and forth in pursuit of knowledge.  That’s a good thing.  Saying that science is untrustworthy because not all scientists agree is like saying that we shouldn’t eat fruit because some of it isn’t ripe.

We desperately need credible science in order to survive and thrive on this earth.  Sustaining that credibility is the responsibility of both scientists and the public.  Scientists must provide accessible and clear information about what they’re learning, but the public also needs to be a receptive and discerning audience.

There is a torrent of news and data coming at us every day.  As you process that information, think like a scientist.  Question everything, including your own assumptions.  Form an opinion and then test it by looking for information that might disprove it.  Most importantly, even when you’re confident in your viewpoint, keep your mind open to new evidence and alternate perspectives.

Finally, remember that science is a continual and cumulative process.  Conflicting research results don’t indicate weakness, they drive scientists to keep looking for answers.  Science shouldn’t lose your trust when scientists disagree.  Instead, science should earn your trust when scientists reach consensus.

 

Special thanks to Anna Helzer for helpful feedback on this piece.

Why A Warming Climate Is Making This Spring So Cold (… and Last Spring So Warm)

Melting sea ice might not seem important to those of us living in the middle of a continent.  It is.

Weather and climate have always been complicated and difficult to understand, so it’s no wonder that climate change is a topic that confuses most of us.  The fact that most climate change discourse is more political than scientific these days makes things worse.  It’s hard to have reasonable discussions because most people’s opinions tend to be linked to whichever loud voices they listen to, and few of us understand climate science well enough to draw our own independent conclusions.

The poor groundhog has been a popular scapegoat for this year's cold spring temperatures.  In reality, both this year's cold spring and last year's warm spring are much more strongly tied to global warming and melting arctic ice.
The poor groundhog has been a popular scapegoat for this year’s cold spring temperatures. In reality, both this year’s cold spring and last year’s warm spring are much more strongly tied to global warming and melting arctic ice.

I’m certainly not going to wade into the politics of climate change, and I’m not qualified to get very far into climate science.  However, I did read something recently that clarified some things for me, so I’m hoping it will help you as well.  Thanks to Joel Jorgensen for passing along the article that spawned this post.

One of the most difficult things to understand about global warming is that it can make local temperatures get colder as well as warmer.  Here in Nebraska, we’re experiencing a very cold spring – if you can call it spring – this year, but had a very warm spring in 2012.  How, you might ask, is it possible that both the warm spring of 2012 and the cold spring of 2013 are a result of global warming?

Last year at this time, pussytoes was starting to bloom in our Platte River Prairies.  This year, there's no indication that they're anywhere close to that stage.
Last year at this time, pussytoes was starting to bloom in our Platte River Prairies. This year, there’s no indication that they’re anywhere close to that stage.

Scientists have long suggested that more extreme weather patterns (including warm and cold, wet and dry) are a consequence of global warming, but I’ve never had more than a vague understanding of why.  Apparently climate scientists are still figuring it out too, but new research published by Jennifer Francis and Stephen Vavrus in Geophysical Research Letters seems to help.  After reading a summary of the work in the Omaha World Herald and stumbling through the actual scientific journal article, here is my best shot at explaining the results.

First two pieces of background information you need to understand.  This is based on my own rudimentary understanding of this topic, so please take it as such.

1.  The warming of the Arctic and the subsequent loss of sea ice is reducing the contrast in temperature between the cold Arctic region and the warmer center of the globe.

2. The contrast between warm and cold areas of the globe is a major driver of weather patterns because it creates an imbalance in atmospheric pressure.  The jet stream is the major current of air that tends to run along the boundary between those cold and warm areas (there is actually more than one jet stream, but let’s not get into that). When the jet stream is strong, it moves strongly in a relatively straight west to east direction.  However, when it is weak, it makes large north-south loops as it ambles slowly to the east.

Ok, armed with that background knowledge, here’s what’s happening with global warming.  Arctic air to the north of us is less cold than it used to be, so there is less contrast between that air and the warm air to our south.  That weakens the jet stream, causing it to make large loops as it moves from west to east.  Equally importantly, those loops tend to stay in the same place for a long time.

When Nebraska is inside a southward loop of the jet stream, the jet stream’s current allows lots of cold arctic air to come down from the north.  That’s what is making our 2013 spring so cold.  The opposite is true when we’re inside a northward loop – our weather is dominated by warm air coming up from the south, creating a weather pattern such as the one we saw in 2012.  Because a weak jet stream causes those loops to not only be greater in size, but also to stick around longer weather patterns persist for longer periods than they otherwise would.  If the weather extra warm for a long time, we tend to have drought, but extended weather periods can just as easily lead to flooding, extended cold temperatures, etc. – depending upon whether we’re north or south of the jet stream current.

When we are inside a southward loop of the jet stream (top picture) cold air from the north dominates our weather.  When we are inside a northward loop of the jet stream, warm air moves in from the south.
When we are inside a southward loop of the jet stream (top picture) cold air from the north dominates our weather. When we are inside a northward loop of the jet stream (bottom picture) warm air moves in from the south.

Of course, there is much more to weather and climate than just jet stream loops, so a slower, more wandering jet stream is only part of the story.  In addition, understanding why we’re getting more extreme and extended weather patterns doesn’t change the situation – it just explains it.  I’ve written in the past about some climate change adaptation strategies for those interested in prairie management, restoration, and conservation.  A big part of our responsibility is to make prairies as ecologically resilient as possible.  

Since creating and sustaining resilience in prairies is largely dependent upon factors we’ve been working on for a long time anyway – species diversity, habitat size and redundancy, etc. – not much changes when we add climate change into the mix, except perhaps that we should feel a little more urgency.

Again, I’m no climate scientist, so I’m trying to explain things I barely understand myself.  Please correct me if I’ve mis-stated something or explained things poorly.

Ahead of the Game

Do you suppose we’ll run out of wildflowers before the summer’s over?

I’m only half kidding.  With the extraordinarily warm winter and spring we’ve had, it seems like everything is way ahead of schedule this year, and I really do wonder what will happen as the season progresses.  Most wildflowers are blooming between two and four weeks earlier than average this year.  A few individual plants are even further ahead than that, including the switchgrass plant I saw blooming last week and the patch of flowering Missouri goldenrod I saw yesterday.  Dan Carter at Kansas State University wrote last week to say that in Kansas he’s seen big bluestem blooming – and even heath aster.  Now that’s just crazy.

I photographed this prairie larkspur flower on June 18, 2009. This year, larkspur has already been blooming for a couple of weeks, and looks like it will be done before the 1st of June.

Continue reading

New Information on Tree Invasion in Prairies

One of the biggest challenges of prairie management today is the suppression of woody invaders.  Both native and non-native woody species can spread rapidly in prairie, making it difficult to maintain the open grassy habitat that most prairie species depend upon.

There has been extensive speculation about why shrubs and trees appear to be more aggressive and successful now than in the past.  Fire suppression has been a factor identified by many as a likely cause, but it’s clearly not the only factor because there are examples such as Konza Prairie in Kansas where shrubs have spread strongly under more than 20 years of regular fire application.

Fire can help suppress shrubs, but there are plenty of examples where frequent fire is not sufficient to stop their expansion.

Now, a new study from Konza Prairie may shed some light on at least some of the reasons behind the agressive expansion of shrubs in the Kansas Flint Hills and other mesic tallgrass prairies.  The research paper, written by Zak Ratajczak, Jesse Nippert and others, addresses both the initial survival of new woody plants and the subsequent spread by clonal species (such as dogwood and sumac, which spread by underground rhizomes).  It’s worth reading, and you can find a PDF here.

The question of why woody plants are able to establish more successfully in prairies now than they could several decades or more ago is still largely speculative.  Jesse Nippert explains his reasoning in an interview here.  Changing atmospheric conditions – especially higher nitrogen and carbon levels – are altering the competitive balance in grasslands to favor C3 plants over C4 plants.  Because shrubs like dogwoods (Cornus sp.) are C3 plants, higher levels of nitrogen and carbon in the atmosphere are likely giving them an advantage over C4 plants such as big bluestem and other warm-season native grasses that have historically had a competitive edge in tallgrass prairie.  This could explain why woody plants are surviving their seedling stage more now than they did in the past – but the idea still needs to be tested further.

However, while initial survival of shrub and tree seedlings is one important component of the issue, the research paper by Ratajczak et al. also addresses the subsequent spread of those shrubs – and they do so through field data collection.  They focused their work on the primary shrub species spreading at Konza Prairie – rough-leaved dogwood (Cornus drummundii).  What they found was that while most prairie plant species get the vast majority of their resources from the top foot or so of the soil profile, dogwood plants get almost half of their resources from below that level.  In other words, dogwoods are using resources – especially moisture – that most prairie plants aren’t taking advantage of.  (Yes, most prairie plants do have deep roots, but they typically reserve the use of those deeper roots for periods of drought and rely on their much more abundant shallow roots most of the time.)  Importantly, not only do “parent” stems of dogwood use deep soil water, new stems that are initiated by rhizomes (below-ground stems) do too – probably because they can pull water from their parents until they get their own deep roots established.

Taken together, the two ideas proposed by Ratzjcak, Nippert, and others provide an interesting hypothesis about how today’s shrub invasion may be taking place.  Higher levels of carbon and nitrogen in the atmosphere and/or soil provide a new competitive edge to colonizing woody plants.  That “fertilized” environment overrides the traditional advantage that warm-season grasses have over shrubs, which is that grasses are very good at monopolizing soil resources within the top foot or so of the soil profile.  Today, young woody plants are surviving long enough in that dry upper soil layer to extend their roots into deep moist soil – below where most other prairie plants mine resources.   Once those woody plants tap into that deep soil moisture, their survival is much more assured.  Woody plants that are clonal – such as rough-leaved dogwood and smooth sumac (Rhus glabra) – can then spread by rhizomes, continuing to take advantage of their ability to utilize the deep soil moisture their neighbors aren’t using.

Smooth sumac and flint hills prairie - Kansas. Konza prairie researchers have found that shrub invasion in upland prairies has much less aggressive than in lowlands. Is this because deep soil moisture is less abundant in uplands, reducing the competitive edge to those shrubs?

In addition to the carbon/nitrogen levels and deep soil moisture that both favor shrubs, anyone who has conducted prescribed fires in prairies containing large clones of dogwood or sumac knows that those shrub patches can inhibit the growth of grasses around their edges, reducing the amount of fuel for fires.  In other words, shrub patches can reduce nearby fire intensity – thus greatly reducing the effectiveness of one of the most important threats to their survival.  You really do have to admire their strategies, don’t you?

I think the hypotheses proposed by Ratajczak, Nippert, and their colleagues could explain a good portion of the puzzle.  Atmospheric conditions have certainly changed over recent decades, and that could explain why trees and shrubs have an easier time getting started in grasslands now.  However, the competition for deep soil moisture shouldn’t be much different now than it was historically.  We know there were at least some shrubs in historic prairies – why didn’t they grow into gigantic unstoppable clones?  What controlled their spread that isn’t doing so now?  Was the historic abundance of browsing animals high enough to control those clones?  Are the fewer browsers today simply overwhelmed by the increased number of new clones that are successfully establishing?  Are there other factors we’re not even considering yet?

There are plenty of questions left to answer, but it’s great that we’re moving in the right direction.  Besides the work of Ratazcjak, Nippert, and their colleagues, there are several other projects I’m aware of that are working to investigate the issue of woody invasion of prairies.  There are certainly plenty of us interested in their results!

Ecological Resilience in Prairies: Part 2

This is Part 2 of a two part series on ecological resilience in prairies.  In Part 1, I interviewed Dr. Craig Allen about the basic definition of ecological resilience and then wrote about the relevance and application or resilience to prairie ecosystems.  In Part 2, I explore how ecological resilience can influence the way we restore and manage prairies, and about how much we still have to learn about how to do that.

 

Influencing Resilience through Restoration and Management

Understanding ecological resilience should help us better design restoration and management strategies that build and maintain resilience in prairies.  Using the components of resilience discussed in Part 1, it seems apparent that when restoring (reconstructing) prairies, it’s important to maximize species diversity in seed mixtures.  More importantly, prairie restoration that adds to the size and connectivity of existing prairie remnants should make the entire complex of restored/remnant prairie more resilient (see earlier post on this subject).  Finally, selecting and altering restoration sites, when possible, to include topographic and other habitat type variation – and multiple examples of each type – can also help ensure the resilience of the resulting restored prairie. 

Designing management strategies for prairies that sustains ecological resilience is trickier because we still have much to learn.  We’re far from fully understanding the various stable states prairies may exist in, or flip to, let alone where the thresholds are between those states.  In addition, the level of plasticity, or range of adaptive capacity, of prairies is a subject of great debate right now among prairie ecologists – although the discussion is not usually framed in those terms.  The real question is – How much can prairies change their plant and animal species composition and still remain “in the bowl”? 

As an example, I manage a sand prairie that was hayed annually in the mid-summer for about 20 years before The Nature Conservancy purchased it in 2000.  Over that 20 year period, the plant community in that prairie adjusted to that annual haying regime.  Species such as stiff sunflower, leadplant, and sand cherry became restricted to a few steep slopes where hay equipment couldn’t go.  Early summer grass and forb species became very abundant, but later season flowering plants were less so because they were mowed off around their flowering time each year.  The prairie was a nice quality mixed-grass prairie, with good plant diversity, but definitely had the “look” of an annually-hayed prairie. 

Stiff sunflower has increased in abundance since annual haying ceased.

When we took over the management in 2000, we let the site rest for about 5 years and burned portions of it each year during that time.  Then, we began introducing some combined fire and grazing treatments at different intensities and at varying times of the season.  As a result, the prairie looks fairly different now.  Stiff sunflower and leadplant have spread considerably through the site, re-taking lower slopes where hay equipment had earlier eliminated them.  Cool-season grasses (native and non-native) change in abundance from year to year, but warm-season native grasses are certainly more dominant than they previously were.  Overall forb diversity is about the same as it was, but the relative abundance of many forbs has changed, and those abundances now vary from year to year, rather than remaining fairly stable.

In the context of plasticity, or adaptive capacity, this prairie has demonstrated that the 20 years of haying was not enough to move the plant community into a new stable state from which recovery, if that’s the right word, was not possible.  The community was altered by that haying regime, but upon alteration of that regime, the community composition morphed to match changing conditions – without losing plant diversity.  In other words, assuming that the prairie hasn’t lost anything critical during the 11 years of our management, both the haying regime and our current management have kept the prairie “in the bowl”, though it changed appearance fairly dramatically.  Its adaptive capacity is broad enough to include the “hayed” look and the “crazy Nature Conservancy management” look.  The real test of this, of course, would be to reintroduce haying for another 20 years and see if the plant community reverted back to something very similar to the condition it was in when we purchased it. 

This sand prairie has changed species composition substantially since we switched management from annual haying to a mixture of prescribed fire and grazing.

Here’s another example from my own experience.  We have a 45 acre restored prairie (prairie reconstruction) that was seeded in 1995 by Prairie Plains Resource Institute adjacent to a degraded remnant prairie.  The seed mixture included approximately 150 species of mesic prairie plants, most of which established successfully.  We managed the prairie with periodic spring fire for its first seven years, and then incorporated it into our experimental patch-burn grazing system (light stocking rate).  During nine years of patch-burn grazing management, (6 of which were during a severe drought) the plant species composition in any one place has bounced around quite a bit due to the fire/intense grazing/rest cycles imposed by the patch-burn grazing management system.  Overall, however, the prairie has maintained its mean floristic quality within 95% statistical confidence intervals (I collect annual data which entails calculating floristic quality within 100 1m2 plots and averaging the values across those plots).   Read more about our patch-burn grazing work and results at this restored prairie and others here.

That’s not to say the prairie hasn’t changed – it has.  Some plant species have increased in frequency among my annual data collection plots, some vary in frequency from year to year, and others stay fairly stable.  However, no species has dramatically declined over the time period.  (I wish I had data on other species, particularly insects, but I don’t.)  Perhaps the most interesting, and somewhat concerning, phenomenon has been an increase in the frequency of Kentucky bluegrass in my plot data.  The increase has been fairly steady over the nine years of patch-burn grazing and data collection, and bluegrass is now in about 75% of my 100 1m2 plots, though it rarely looks dominant where it occurs.  To this point, that increasing frequency doesn’t seem to be impacting the overall diversity or floristic quality of the plant community, but that doesn’t mean it won’t at some point.  Two possibilities are: 1) Our management is allowing bluegrass to enter the plant community but remain a minor component, or 2) Kentucky bluegrass is on a steady march of increasing dominance and will eventually turn my restored prairie into the same kind of low-diversity degraded prairie that exists in the adjacent remnant prairie.  I won’t be completely shocked by either scenario, but I have hope that #2 won’t happen because of the way bluegrass is acting in the community to this point.  It’s way too early to know for sure.

Interestingly, I have some large exclosures within this restored prairie that have never had grazing, only prescribed fire at a similar frequency to the grazed portion.  Those exclosures have very little Kentucky bluegrass in them – probably because of both the differing management and the fact that the exclosures are on the far side of the restoration from the neighboring bluegrass-dominated remnant prairie.  However, the exclosures also have much lower plant diversity and mean floristic quality than the grazed portion of the restored prairie.  Visually, they are dominated by warm-season grasses and a few large forbs (e.g., perennial sunflowers).  At this point, I prefer the grazed portion of the prairie because it seems to line up better with my management objectives of maintaining diverse and resilient plant communities (assuming it’s not slowly becoming a bluegrass wasteland). 

This photo was taken when the 1995 prairie seeding was nearing the end of its establishment period (fifth growing season). The prairie has maintained its mean floristic quality (and all of its plant species) through years of patch-burn grazing and drought.

To relate this example back to adaptive capacity, it appears likely that the grazed portion of the restored prairie has the adaptive capacity to retain its integrity as a prairie community through fairly wild fluctuations in species composition as a result of stresses from fire, grazing, and drought.  This is, again, remembering that I’m only evaluating the plant community and that the experiment is far from over.  On the other hand, it appears the exclosed portions of the prairie have lost plant diversity over time.  Whether the communities in those exclosures are still “in the bowl” or in a new stable state of lower diversity is a big question.  To address it, I’m going to open one of them to fire/grazing this coming year and exclude a portion of the currently-grazed prairie and see what happens.  If the two plant communities trade identities to match their new management regimes, I’ll know that both were still “in the bowl” and understand more about the adaptive capacity of our prairies.  If they don’t, that will be equally instructive!

The Upshot

Building and sustaining ecological resilience in prairies may be the most important component of prairie conservation in the coming decades.  Threats from invasive species, habitat fragmentation and detrimental land management practices, compounded by climate change, will make conservation extremely difficult.  Armoring prairies with ecological resilience gives us the best chance of success. 

In order to build that resilience, we first have to understand it better.  It is certainly more complex than the few simple examples I’ve provided.  There are numerous belowground processes and systems we still know relatively little about.  Even aboveground, there are many more questions than answers regarding the way species interact with each other and their environment – and what is required to maintain those interactions.  To gain a better understanding of these natural systems, we have to rely on experimentation and observation.  I think there are essentially two broad questions:

  1. What is the adaptive capacity of prairies, and where are the thresholds between the desired state and other, less desired, stable states?  This will certainly vary between tallgrass and mixed-grass prairies, and between sand prairies and black soil prairies, etc., but there will almost surely be some consistent themes. 
  2. How important is it to keep the ball moving within the bowl?  In other words, are prairies really like our human bodies, in that the more we stress and rest them, the better prepared they are for future stresses?  (Does the bowl shrink if we don’t keep pushing at the edges?)  Or do we just have to keep prairies from being stressed too far in any particular direction? 

 

We can work toward answering these questions with direct experimentation on prairies we manage (similar to my simple experiment with grazing and exclosures in the restored prairie example presented earlier).  In addition, though, we can learn much from prairies that “flip” to less desirable stable states (hopefully not the ones we’re managing!) by documenting as much as we can about what happens to them and why. 

Most importantly, I hope that thinking about ecological resilience with regard to prairies will make you look at the prairies you’re familiar with in a new way.  Seeing prairies as balls rolling around in a bowl makes watching and managing prairies a much different experience than seeing them as a stable “climax community.”  When we expect change, it’s easier for us to perceive change, and the more observant we are, the more we’ll learn.  And goodness knows we have plenty to learn.

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If you’re interested in learning more about ecological resilience, here are some relevant references that Craig Allen recommends (I’m pretty sure it’s just a coincidence that he’s a co-author on all of them).  The Gunderson et al. book reprints a lot of the classic / foundational papers on the subject.    

Sundstrom, S., C. R. Allen and C. Barichievy.  Biodiversity, resilience, and tipping points in ecosystems.   Conservation Biology: in review.

Gunderson, L., C. R. Allen, and C. S. Holling. 2010.  Foundations of Ecological Resilience.  Island Press, New York, NY.  466pp.  

Allen, C. R., L. Gunderson, and A. R. Johnson.  2005.  The use of discontinuities and functional groups to assess relative resilience in complex systems.  Ecosystems 8:958-966.

Forys, E. A., and C. R. Allen.  2002.  Functional group change within and across scales following invasions and extinctions in the Everglades ecosystem.  Ecosystems 5:339-347.

Peterson, G., C. R. Allen, and C. S. Holling.  1998.  Ecological resilience, biodiversity and scale. Ecosystems 1:6-18.

Ecological Resilience in Prairies: Part 1

This is Part 1 of a two part series on ecological resilience in prairies.  Part 1 starts with an interview with Dr. Craig Allen, the Unit Leader of the Nebraska Cooperative Fish and Wildlife Research Unit at the University of Nebraska-Lincoln.  Craig has studied and written extensively about ecological resilience and I’ve been fortunate to collaborate with him on several research projects examining the role of resilience in grasslands.  Following the interview with Craig, I present some of my own thoughts about how to apply the idea of ecological resilience to prairies.  Part 2 builds upon that theme, exploring the relationship between resilience and prairie restoration and management.  I’ve had a hard time finding much written about ecological resilience and prairies – at least not much that can be easily and directly applied to prairie conservation.  This is my attempt to begin a conversation on that subject.  Please chime in with your own thoughts and opinions.

Prairie Ecologist:   Why don’t you start by describing “ecological” resilience?

Allen:  The term resilience has a long history, and has been used in academic fields such as psychology, medicine and engineering.  In psychology and engineering, the term usually refers to the return time to a state of equilibrium following disturbance.  The term “ecological resilience” was forwarded in 1973 by C.S. Holling.  The definition was different than earlier definitions.   Ecological resilience followed from an emerging understanding of multiple stable states.  When a system can occur in more than one state – for example, grasslands can remain grasslands or transition to forest – resilience is a measure of the amount of disturbance required to cause that state change.  A system with low resilience can “flip” into an alternative regime very easily, but very resilient systems can be highly variable while remaining in the same regime.   Resilience is not necessarily a good thing – – degraded systems (like eutrophic lakes) can be very resilient – difficult to change.

Click here to see a graphic illustration of ecological resilience.

Prairie Ecologist:   So, the range of stability quantifies the ability of an ecological system to stay within one stable state.  What influences that range of stability in grasslands?

Allen:   First, it’s important to understand that stability in this context means the ability to stay within a regime (rather than to remain “unchanging”).  In fact, highly variable systems are often more resilient, and thus the term stability is a term to be used cautiously because no ecological systems are strictly “stable”.

We think resilience is influenced by the distribution of functions, functional diversity and response diversity.  A diversity of functions means that the system can cope with a wide range of perturbations.  Think of function as the way an animal or plant species exploits its environment.  For example, an annual nitrogen-fixing plant will respond to drought differently than a perennial.  In addition, two members of the same functional group (e.g. annual nitrogen-fixing plants) may respond differently to a perturbation, so species that have been uncommon in a community may change roles and become common (or “drivers”) under some situations.  In this way, resilience has a lot to do with plasticity, not just at the species level, but within communities.   An ecological community with a high number of species is generally better able to adapt to changing conditions (without “flipping” to another regime) than a similar community with fewer species because of the range of functions those species are capable of performing and the high degree of redundancy and response diversity.

Prairie Ecologist:   What else would you want ecologists and prairie enthusiasts to know about ecological resilience and how it should influence their thinking and strategies in prairies and prairie landscapes?

Allen:
Resilience is quite different from stability, and quite different from efficiency.  In fact, very efficient systems are often not very resilient at all.  When we alter or manage ecological systems to try to optimize a single output (e.g., corn, annual hay, or mid-summer flowers) we are increasing efficiency but decreasing resilience.  Resilience is about getting an “output” across a wide variety of conditions, while optimization and efficiency seek to maximize a narrow range of outputs.

 

Tallgrass prairie at Camp Cornhusker (Boy Scouts of America) near Humboldt, Nebraska. What role does ecological resilience play in the future of prairies?

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APPLYING ECOLOGICAL RESILIENCE TO PRAIRIES

By Chris Helzer

What makes a prairie resilient?

We need to understand the components of ecological resilience in prairie ecosystems before we can design effective restoration and management strategies.  Unfortunately, as Craig has told me, much of what we think about ecological resilience is still theoretical, and we are greatly in need of more experimental studies.  Keep that in mind as you read this, and maybe you can help refine some of these ideas based on your own experiences or through future observations/research. Don’t take my thoughts to be the truth.  I’m trying to lay out the way I understand the ecological resilience of prairies based on my own experiences and those of others I know, but there’s an awful lot I (and others) don’t understand yet.  As always, your comments and thoughts are very welcome.

Species Diversity

Clearly, species diversity plays a role in ecological diversity, and it can be one important indicator of the resilience of a prairie.  However, Craig stresses that comparisons of diversity/resilience should only be made within the same ecological systems.  In other words, just because a tallgrass prairie has higher species diversity doesn’t mean that it’s more resilient than a shortgrass prairie that has fewer species.  However, between two tallgrass prairies where latitude, soil type, and other factors are similar, the one with higher species diversity is likely more ecologically resilient.

Why?  As Craig talked about in my interview with him, species have different ways of interacting with their environments – even species that we categorize together (e.g., annual legumes, perennial cool-season grasses, herbivorous ground beetles, etc).  When something stresses a prairie – such as drought, intensive grazing, or a pest outbreak – some species will be better suited to respond to that stress than others.  The prairie community’s “response” to the stress is that those species better suited to deal with the stress will become more abundant as other species become less abundant.  In a resilient prairie community, the species that increase in abundance will fill at least somewhat similar roles to those that decreased in abundance so that the overall ecological processes in the prairie continue on as before.  Moreover, when a stress in the other direction (e.g., a wet period that follows a drought) occurs in that same resilient prairie, the previously abundant species will regain their dominance under the conditions they are best suited for.  In contrast, a less resilient prairie might experience a drastic shift in its ecological processes in reaction to the same stress, and might not recover its prior composition when conditions change back to what they were.

By the way, I’m presenting these changes as linear – species composition changing in one way and then straight back to the previous condition again – because it makes for easier illustration.  In reality, it’s better to envision a ball rolling around in a constantly moving bowl.  As long as the bowl (the ecological community) remains in the bowl (the stable state) it can theoretically return to a previous point, but it’s unlikely to happen very often.  However, if the ball leaves the bowl because something drastic happens to push it out, it’s very difficult – or impossible – for it to return to the same bowl again. 

Let’s look at a couple examples.  When a prairie experiences drought conditions for a couple consecutive seasons, some plant species will become less abundant – or at least produce fewer flowers – while other species will respond in the opposite way.  In order for pollinator insects to survive those drought years, the flowering species that respond positively to the drought conditions must provide the same kind of opportunities for those insects to get nectar and pollen as the plant species that are now much less abundant.  If there are fewer overall blooms across the prairie, or the size/shape of flower that a particular pollinator needs is not available, pollinator species (and pollination services) will suffer.  That loss of pollination can cascade through the prairie system, affecting seed production by plants, food availability for seed-eating insects and animals, and so on.

Plant species like hairy goldenaster can respond during drought years when other plant species suffer. Maintaining species like that can help a prairie’s resilience to drought.

Herbivores have somewhat similar needs to pollinators.  An insect that feeds on the leaves of warm-season grasses or the flowers of legumes needs suitable leaves or flowers to be available in dry years as well as wet.  Prairies with higher species diversity are more likely to have the redundancy across those plant species categories and provide consistent food sources for those herbivores, regardless of climatic variations.

Prairie Size and Redundancy of Habitats

Besides species diversity, there are other important components of ecological resilience in prairies.  Among those, two interrelated examples are the size of a prairie and the redundancy of its habitat types.  Prairie size has become more of an issue, of course, as many prairies have become fragmented by human development.  Smaller prairies can hold fewer individual plants and animals than larger prairies, making species more vulnerable to local extinction.  Isolation from other prairies makes the situation even worse, because it further increases the likelihood that species will disappear from a particular prairie (butterflies in two prairies close to each other can exchange individuals between sites, helping to compensate when numbers drop in one of the prairies).  Equally important, once a species disappears from an isolated prairie, it’s unlikely to ever recolonize from other prairies.

Small prairies not only have fewer individuals of each species, they tend to have fewer species overall.  This phenomenon is laid out in MacArthur and Wilson’s Theory of Island Biogeography.  Both the lower number of species and the vulnerability of those species to local extinction reduce the overall ecological resilience of small prairies for the reasons explained above.

In addition to the size of a prairie, the number of habitat types it has influences its species diversity.  A prairie that has wet, mesic, and dry habitats is likely to have more species than a prairie that has only one habitat type.  Besides the total number of habitat types, the redundancy of those habitats within a prairie is important as well.  Many species of plants and animals are tied to relatively specific habitat conditions (e.g. sub-irrigated meadows or south-facing dry slopes, etc.) so the boundaries of those habitat types are also the boundaries of populations of those species.  In that way, those habitat types and populations function and interact much like small prairies (island biogeography again).  A prairie that has multiple examples of the same habitat type, especially if they’re close enough for species to interact between them, is more likely to sustain viable populations of the species that rely on those habitats than prairies that have fewer (or more disjunct) examples of each habitat type.  Thus, prairies with multiple examples of habitat types are more resilient, in that they are less likely to suffer species extinctions.  AND – since the number of habitat types is likely to be higher in large prairies than smaller prairies, we’re back to talking about prairie size again.

Examples of Stable States and Thresholds in Prairies

Assuming that ecological resilience is relevant to prairies, it’s extremely important that we learn more about how to recognize the boundaries between current and potential stable states – and how to predict when those thresholds might be crossed.  One fairly obvious example of multiple stable states relative to prairies involves eastern redcedar invasion.  A prairie with a few scattered cedar trees is still a prairie, but at some point, the trees become dense enough that the prairie becomes a woodland.  When the trees are small and scattered, fire can still push the prairie back to a less wooded state (the ball is still in the bowl), but at some point the trees become large enough that they are almost invulnerable to fire, and when the size and density of trees reach a certain point, there is not enough grass beneath them to carry a fire anyway.

Once a prairie has converted to a cedar woodland, everything is different. The woodland obviously hosts a completely different set of species living in it now because most prairie plants, insects, and other animals can’t survive in the dense shade of the cedar trees.  The soils begin to change too, because they are no longer being built and maintained by the annual growth and death of prairie plants – or by the countless species of tiny invertebrates, bacteria, and fungi that drove that process of decomposition.  Both the plants and their decomposers are gone and are replaced by those species that can live under cedar trees.  The seed bank in that soil changes too, because many prairie seeds have a relatively short life span in the soil.

As a result, even if a massive tree clearing operation takes place and removes all of the cedar trees, there are a tremendous number of obstacles that can prevent the site from becoming a prairie anything like the one that previously existed.  The ball is in a different bowl.

When eastern red cedar invasion reaches a certain extent, extensive changes occur, not only to plant species composition, but to ecological processes.

Another change of stable states seems to occur when a prairie plant community loses plant diversity and becomes increasingly dominated by invasive grass species.  I’m not sure whether the loss of plant diversity allows the grasses to gain dominance or the grasses push the other plants out (chicken and egg?) but the phenomenon often occurs as a result of chronic overgrazing and/or broadcast herbicide application.  Once grasses such as smooth brome, Kentucky bluegrass, or tall fescue become dominant, it appears to be nearly impossible to regain plant diversity in those prairies – the ball is in a different bowl again.  As opposed to the cedar example, above, we don’t yet fully understand what makes it so difficult to reverse the loss of plant diversity in this example.  Simply altering management doesn’t seem to have much impact (it’s possible to switch dominance from cool-season invasive grasses to warm-season native grasses, but forb diversity remains low).  Clearly, forbs can’t regain dominance if they and their seeds are no longer present, but even when seed or seedlings are reintroduced, most people have experienced only moderate success – at best –  in regaining some degree of plant diversity.  It’s likely that important insect-plant host and soil microbe-plant host relationships have been broken and that those play a large role in holding back recovery.  It’s also possible that soil nutrient levels have altered (e.g., more nitrogen) in ways that favor continuing invasive grass dominance.  Whatever the reasons, it’s clear that avoiding crossing the threshold into the low diversity/invasive grass dominance state should be a high priority for prairie managers.

This discussion is continued in Part 2 of this two-part blog post.  That post focuses on applying ecological resilience as we restore and manage prairies.

Why Prescribed Fires in Grasslands Don’t Contribute to Global Warming

There are plenty of things to worry about when conducting a prescribed fire.  Is the wind going to change?  Is the smoke going where it’s supposed to?  Will the fire leave sufficient unburned refuges for insects and other animals?

Fortunately, one thing we don’t have to worry about is whether or not the smoke from our fires is contributing to global warming.  It’s true that smoke from prairie fires contains carbon, and that carbon is lifted right into the air.  However, it’s important to step back and look at the bigger picture.

When all is said and done, the smoke from a prairie fire returns much less carbon to the atmosphere than was sequested during the same time period. Even with annual burning, a prairie stores more carbon than it releases.

First, prairies pull more carbon from the ecosystem each year than they release – even if they’re burned annually.  Prairie plants take carbon from their environment and store it beneath the ground as soil organic  carbon.  We’ve long known that prairies build organic soils – that’s why grasslands make such good farmland – but recently that ability has gotten more notice because of its contribution to carbon sequestration efforts.

Second, burning prairies stimulates stronger vegetative growth, which sequesters even more carbon in the soil than if the prairie was unburned.  Spring fires warm the soil and allow prairie plants to start their growth earlier, and removes shade that would otherwise slow plant growth.  In addition, it appears that fires also stimulate soil bacteria that make more nitrogen available to plants.

Third, the carbon that IS released through smoke is not the fossil carbon that is responsible for steeply climbing carbon dioxide levels in the atmosphere.  Smoke from prairie fires contains carbon that was pulled out of the atmosphere within the last few years.  Remembering that much of that carbon is sent down in the the soil by prairie plants, whatever is re-released is simply returning carbon that was already in modern day circulation.  Today’s increasing atmospheric carbon levels are driven by the release of fossil carbon from millions of years ago.  That carbon was stored away in coal and oil deposits until we pulled it out of the ground and released it through combustion.

A nicely succinct (if slightly ornery) synthesis of the reasons prairie fires don’t contribute to global warming was written by Gerould Wilhelm, a widely respected botanist and educator.  You can read that in PDF form here.  GW carbon paper

So – stop worrying about carbon.  Instead, make sure the forecast is still accurate, watch where your smoke is going, and be sure to leave some unburned areas for insects and other animals.

Most importantly, be safe.