Tag Archives: resilience

Diversity, Redundancy, and Resilience

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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

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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.