Tag Archives: grassland

The Show Must Go On

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Almost a decade ago, I wrote about two competing metaphors for prairie restoration. I suggested we view prairie restoration like the reconstruction of a city after a disaster rather than like the restoration of an historic building.  We need to concentrate on the roles and functions of prairie ecosystems rather than how closely a restored patch of prairie resembled what it used to be in the past.

Today, I’m hoping to stimulate conversation about the difficult decisions we face as we try to conserve prairies in the face of rapid climate change.  One conservation planning approach is to focus on conserving the stage, not the actors.  It advocates prioritization of sites with geophysical diversity because those abiotic conditions influence habitat heterogeneity, which supports biodiversity.  The hope is that we might be able to conserve “an abiotically diverse ‘stage’ upon which evolution will play out and support many actors (biodiversity).”

The varied topography and the habitat size and connectivity found in Flint Hills of Kansas makes it a ‘stage’ that can potentially sustain biodiversity – but only with thoughtful, persistent, and adaptive management.

I think the ‘conserve the stage’ approach has merit, but it’s just a first step, especially for prairie conservation.  We don’t just want to save the stage; we want to make sure the show goes on.  Thus, I present to you a long (and potentially ridiculous) metaphor for prairie conservation that builds upon the ‘conserve the stage’ approach.

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Every actor in a theatrical production plays a role that helps tell a story.  Likewise, every species in a prairie plays a role that contributes to the overall functioning of the ecosystem.  In a healthy and resilient prairie, all the key roles in are filled. 

Fortunately, there is a lot of redundancy built into prairie communities.  We have lots of species that provide pollination, seed dispersal, nutrient cycling, and all the other essential functions that keep prairies going.  We have a big cast, or maybe a big actors’ union.

Today’s prairie ‘show’ already looks different than it did in the past.  Prairie landscapes are fragmented, invasive species have joined the cast, and the climate is changing.  Those and other factors mean that some actors who played key roles in the past are no longer part of the show, at least at some venues.  Other actors remain in the cast but don’t play their roles as effectively as they used to.  Despite those changes, there are still really good versions of the prairie show being presented on various stages, though the versions vary quite a bit from place to place.

To keep the show going, we, as producers and directors, have to be creative and adaptable.  We face really difficult decisions, especially when it comes to actors who aren’t well suited for their roles anymore.  Continuing to direct the show with those actors as the main focus can weaken the performance of others and drag the whole production down. 

Making changes to the cast of a show comes with a lot of risk, however.  We don’t have a lot of experience with that process and we’re likely to make mistakes. Fortunately, in most cases, there are existing cast members that have the potential to adapt their roles and take on new challenges.  With some guidance, those actors will find new ways to collaborate with each other and put on a show that might not be exactly the same as we’re used to but will still have a plot we can follow and enjoy.

More frequent and severe flooding is occurring as a result of climate change. That increased flooding will likely affect which plant and animal species will persist in low-lying prairies like this one. Can we predict those changes and help guide them in ways that don’t lead to reduced biodiversity?

If more drastic actions are needed, we might recognize that some actors are on their way out and start training understudies who can gradually take over roles as needed.  If necessary, we might decide to recruit actors that are playing diminished roles on other stages and bring them in to rejuvenate their careers in a more suitable situation.  Similarly, we might help some of our own long-term stars find new opportunities elsewhere, rather than just watching them slowly fade away. 

In some cases, the world around us might force major a rewriting of the show itself.  We might find ourselves directing a shrubland or woodland production rather than a prairie show.  That doesn’t mean the show will stop or become less important, but it will require a different approach, a significantly altered cast, and a lot of adaptation by all involved.  However, if we stick with the mantra of ‘The Show Must Go On’, we’ll need to figure out how to adjust on the fly and sustain as much biodiversity and ecological function as we can.

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Ok, I have to break away from this tedious metaphor.  The real point here is that we can’t afford to be so invested in current or past versions of our prairies that we don’t allow them to adapt to changing conditions.  At the risk of sliding back into my metaphor, there are lots of old movies and plays that don’t hold up well today.  Jokes that used to be funny 20 or 30 years ago aren’t funny today.  Old references don’t land with new audiences.  In most cases, the basic stories themselves are still solid – they just need to be adapted for today’s world.  Prairies and their species also exist in a different world than they used to, and that world continues to change (very quickly) around them.

The resilience and function of prairies is highly dependent upon biodiversity, which depends upon habitat size and heterogeneity, along with other factors.  Maintaining high biodiversity in prairies that exist in fragmented landscapes comes with huge challenges, which are compounded by a rapidly changing climate.  Plant and animal communities aren’t the same as they were in the past and they’ll continue to change over the next few decades and beyond.  In fragmented landscapes, unless we take an active role, those alterations will largely take place in isolation, with limited opportunities for species to travel between one prairie fragment and another.  Even in landscapes with large contiguous grasslands, we’ll need to be very thoughtful about how we shepherd those prairie communities through the coming years.

These tent caterpillars probably aren’t causing serious impacts to this patch of wild plum, despite appearances. How will climate change, habitat fragmentation, and increased woody encroachment affect this insect species and its impacts on other species in the future? (This is just a random example – I’m not saying tent caterpillars are going to become a major problem!)

It’s really hard to look at the prairies we know best and imagine them with a different composition of species.  We’re used to measuring stewardship success by our ability to sustain the status quo.  Watching the population of a species diminish in size – or disappear entirely – feels like a major failure.  Most of us have also looked skeptically at any new species that show up in a prairie, worrying about potential negative impacts of that species on the existing community. 

I don’t have a lot of answers to the big questions we face.  I’m certainly not ready to lay out a plan or advocate for a particular approach to managing these changing prairies.  As I did in another recent post, I’m mainly trying to get some conversation going on this topic. 

The best I can do right now is offer a few ideas for discussion.  For example, I think we might be smart to reevaluate the way we look at our objectives for prairie management.  Instead of trying to maintain the current composition of plants and animals, maybe we should focus more on biodiversity and less on which particular species are present or abundant within those communities.  (That doesn’t mean we welcome invasive species, by the way.  Any species – plant, animal, or otherwise – that acts to reduce biodiversity is still a problem.)  

I also think we need more serious conversation about when to resist ‘state changes’ like the transition from grassland to shrubland and when to facilitate those transformations, while trying to preserve as much biodiversity and productivity as we can.  Again, I have little to offer in terms of specifics, but it seems clear that we’re not going to be able to stave off those state changes forever in at least some places.  Let’s start thinking about contingencies instead of just waiting for those sites to collapse.

There’s a lot of woody encroachment in this prairie. The number of trees in the surrounding landscape and a changing climate are both spurring that invasion. At what point does the fight against this kind of encroachment become fruitless? What do we do then?

Finally, it’s never been more important to find opportunities to enlarge and reconnect prairie fragments through prairie restoration.  The chances are slim that a small, isolated prairie fragment is going to adapt well to a rapidly changing world.  Growing the size of those fragments by restoring adjacent patches should be a top priority.  Can we find new approaches for creating those restoration opportunities in strategic locations? As we do that restoration work, we should also continue to test and discuss seed sourcing strategies, including the regional admixture approach, to see if we can further bolster the adaptive capacity of those small sites.

We’ll be figuring this out as we go, and we’ll surely screw some things up, but we can’t afford to just continue reacting.  At the very least, we need to be thinking ahead about the changes that are taking place and how those will affect prairies.  In some cases, we should probably be ‘acting ahead’ to guide state transitions, migration of species, or simply changes in species composition within individual prairie sites. 

What we can’t afford to do is live in the past.  We’re hurtling into the future whether we like it or not.  Let’s make sure we bring prairies along with us.

What we know about managing soil carbon in prairies – a complete (but disappointing) guide

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I’ve delayed writing a post about soil carbon and soil health in prairies for years because I haven’t been able to figure out how to do it.  It’s a difficult subject to write about because we (scientists) know disappointingly little about the subject.  In fact, I thought seriously about making this blog post nothing but a title and a single hyphenated word of text.  Something like this:

<<< >>>

What do we know about prairie management and soil health?

Diddly-squat.

<<< >>>

The idea made me chuckle, but based on my experience telling jokes at home, I probably would have been the only one laughing.  Most of you would have felt disappointed because you were hoping for some helpful information.  Well, join the club.  I’m fortunate to know quite a few brilliant people who are well-educated on the subject of soils, soil carbon, soil health (whatever that is – definitions vary wildly), and related topics.  However, my numerous queries to them about how we should manage prairies to improve or sustain soil health have pretty much yielded me diddly-squat.

 That’s not completely true, of course, but it’s also not much of an exaggeration.  We know much more about how farming practices affect soils in crop land than we do about how fire, grazing, or other management affects soils in prairies.  There are actual useful tips farmers can use to improve their soil productivity and health – e.g., “don’t till your field more than necessary.”  People can use that information to do good.  Wouldn’t it be great to have something similar for prairie management?

Soils are an integral part of prairie ecology but they stay hidden below ground where it is hard to know what they’re up to. We need to better understand how our management strategies affect soils in order to better conserve prairies.

In just a minute, I’m going to give you some useful information about soil carbon in prairies, but trust me, it’s not going to be very satisfying.  You might ask yourself why I would even write a blog post if there isn’t much information on my chosen topic.  Good question.  There are two reasons.  First, a lot of people ask me about it.  Second, there is a whole lot of mythology and just bad information out there about soil health and grasslands, and I’m getting increasingly frustrated by that. 

If you hear someone talk about how some kind of grassland management strategy (fire, grazing, etc.) affects soil health or soil carbon sequestration, be skeptical.  Remember that loud confident voices aren’t necessarily right, and anecdotal results or even data from a single prairie, farm, or ranch operation can be biased, wrong, or at least minimally extrapolatable.  I’m not saying someone who loudly advocates for a particular approach is being dishonest.  I’m just saying that it would be smart to do some searching for peer-reviewed research that backs up any claim before you invest in a new strategy.

How does fire frequency affect soil carbon? The answer is not fully known, and what we do know is very complex.

Ok, I’ve written nearly 500 words without giving you any useful information.  Here are the few statements about soil carbon and soil organic matter in prairies that seem to be generally agreed upon by most soil experts I’ve talked to, including several I reached out to while working on this post: 

Soil organic matter is added to grassland soil primarily through roots, their exudates (substances secreted into the soil by roots), and root turnover.

Experts are quick to point out that this can be less true in other ecosystems, including forests, and that even in grasslands, there are other important sources of soil carbon, including charcoal (aka biochar) from fires.  Regardless, it’s really important to understand the important contributions of plant roots when you think about soil organic matter in prairies. Inputs from grass litter aboveground (vegetative matter from previous growing seasons) can also add to soil organic matter.  However, there is general skepticism among soil scientists that the trampling of grass litter by livestock (for example, in mob grazing or similar intensive rotational grazing systems) has much influence on overall levels of soil organic matter. 

Most experts seem to agree that moderate grazing can be positive for soil carbon, at least when compared to chronic overgrazing or letting prairies sit idle. However, there’s clearly much more to investigate along those lines.

The amount of total soil carbon changes very slowly in prairies. 

Never-cultivated prairies tend to have high levels of organic matter because production has exceeded decomposition for a very long time. In these prairies, increases in soil carbon are hard to detect because of how much carbon is already present.  Picture how little the waterline in a nearly-full bathtub changes when you dump in a cup of water.  Prairies that have been re-planted in former crop land start with lower carbon levels (much less water in the bathtub) and so often show more marked changes in soil carbon over time.  However, those rates of change can be highly variable between sites.

In addition, the amount of soil carbon in soils is not uniformly distributed within the soil profile (the vertical section of soil from the surface down to underlying rock).  For example, there tends to be more carbon nearer the surface where grass roots are most concentrated.  Also, the rate at which soil carbon levels change can vary quite a bit by depth, which can make it hard to get good measurements of the overall trends. 

To make things more complicated, not all organic matter is equally decomposable. Some soil organic matter is labile; it is decomposed by soil microbes and plants can take up the released nutrients.  Other forms of carbon are harder to decompose (e.g., charcoal) or inaccessible to microbes (organic matter bound onto soil minerals or within aggregations of soil particles). These recalcitrant forms can be stored in soils for longer time periods (centuries!) and are much less a part of the active carbon cycle.  As a result, changes in total soil carbon may not directly reflect how soil functions or processes are changing.

Researchers are trying to catch us up, but it’s going to be a while before we can link soil impacts to many of our common prairie management techniques.

Soil health is a term that isn’t well defined or, perhaps, even useful in grasslands. The term works better in crop land, where it can be an indicator of soil fertility (though it is still often defined and applied quite variably within that context).

This is also where I reiterate the disappointing news about how little is known about how various prairie management strategies affect specific soil traits or qualities.  There’s a lot of research ongoing, and eventually we’ll learn a lot more than we know now.  Impacts of prescribed fire on soils has been studied a lot, but the impacts vary with geography, soil productivity and depth, frequency of burning, and other factors.  In some cases, fire can increase root production and turnover enough to make up for the carbon that goes up in smoke, but that also depends upon how often fires occur and other factors.  

When grazing is added to that mix, it becomes even more difficult to predict impacts on soils.  Consistent overgrazing is probably bad for soil organic matter and most belowground functions, but we don’t know much beyond that.  There is some evidence that moderate grazing might create more soil carbon than no grazing, but again, that seems to vary a lot by geography and soil type.  I know of at least one study currently looking at how different grazing systems might affect soil carbon, but it’s going to take many years of research at many locations to get us much useful information about how something like patch-burn grazing might vary from a deferred rotation or traditional continuous grazing system in terms of impacts on soil organic matter.

At this point, it appears that high levels of soil carbon are linked to high plant species diversity, along with productivity.  It seems fair to assume, then, that managing for plant species diversity should be good for soil carbon – as long as that management doesn’t reduce overall productivity.  Probably.  Hopefully.  With lots of caveats and assumptions in need of testing.  You get the idea.

Maintaining plant diversity is probably a no-regrets strategy for managing prairie soils, and it is clearly good for many other aspects of prairie ecology. However, there are lots of ways to promote plant diversity, and they are probably not all equal in terms of how they affect soil carbon.

Plowing up prairies is bad for soils.

This is the one statement that seems to garner easy consensus among soil experts!  We might not know as much as we’d like about how various fire and grazing treatments affect prairies soils, but there is no question that soil carbon decreases immediately and precipitously when grasslands are tilled up.  Furthermore, the recovery of that carbon if/when grassland vegetation is reestablished can take many decades or centuries.  Protect prairies, folks.

Thank you to Clare Kazanski, John Blair, Hannah Birge, Sara Baer and Stephen Wood for their patient and generous guidance, review, and instruction on this topic and post.  They gave me excellent (if sometimes conflicting) input, based on their own research and that of others.  Any errors in this post are definitely mine, not theirs.