Letting nature take its course

The phrase “let nature take its course” is so widely used and accepted, it has gained idiom status.  The idea that nature is self-perpetuating and self-correcting is an attractive one.  The supporting evidence is strong too – I mean, look at how long nature thrived before humans were even a species! 

Unfortunately, the romantic notion that we should just back off and allow natural areas to manage themselves just doesn’t work in today’s world.  Or, to be more accurate, most of us would be uncomfortable with the results of that strategy – especially at individual sites.  Whether you like it or not, the earth today is heavily shaped and manipulated by human activity.  Within that context, deciding to suddenly back away and allow nature handle things on its own comes with some serious repercussions.  It’s akin to taking a bunch of athletic kids, training them for years to be elite volleyball players, and then entering them in a soccer tournament.  They might be great athletes, but they aren’t likely to fare well at a tournament for which they don’t know the rules and don’t have the appropriate skills to succeed.

Prairies like this one depend upon human management for their survival.

This isn’t a post about what would happen to the earth if humans suddenly disappeared.  That story has been told by others, and you can go explore and argue about that story with them.  This is a post about what happens when we walk away from natural areas – prairies, in particular – within the context of the world we inhabit today.  I also want to be clear that this post is not a criticism of the way humans have altered the earth.  There’s plenty to talk about on that topic, but today’s post is about how we manage (or not) natural areas in the contemporary world.

Let’s start by considering some of the ways in which humans have altered the playing field for species and natural communities.  We’ll focus on the grassland landscapes of central North America because that’s the setting most familiar to me.  First and foremost, we’ve converted much of the landscape to intensive agriculture and other human developments.  As a result, once expansive swaths of prairie are now divided into small isolated fragments, limiting the ability of animals and plants to migrate or otherwise move across the landscape.  We’ve brought plants and animals from the opposite side of the globe and released them into this fragmented landscape.  Many of those have become dominant competitors, with the ability to eliminate other species from their territories and reduce biological diversity. 

The fragmented nature of today’s landscape facilitates invasions, which most often occur along boundaries between prairies and nearby land uses, such as roads, crop fields, suburban areas, or other areas where invaders are established.  Introduced species are not the only invaders in this context, however.  Native trees and shrubs, which have battled prairie plants for dominance since the last Ice Age, have been given a huge advantage.  Instead of trying to spread into prairies from a few stream valleys or other fire-resistant sites, they now invade from countless locations – like an army that has dropped millions of paratroopers behind enemy lines.

Invasive grasses have become dominant in this grassland, which is not being actively managed for plant diversity. In addition, the numerous tree lines in the background provide a constant seed source for potential woody plant invasion.

Within our fragmented landscapes, our agricultural and industrial activities have increased the levels of nutrients such as nitrogen and phosphorus – and those chemicals enter prairies through both the water and the air.  We are essentially fertilizing prairies, which might sound positive, but usually favors invasive plants (e.g., reed canarygrass) or makes a few native plants exhibit the same aggressive diversity-reducing traits as invasives.  The inadvertent fertilization of prairies is most intense in areas near crop fields or factories, but the impacts are measurable even at great distances from those sources.

Adding a rapidly-changing climate to all those other stressors just seems unfair, doesn’t it?  We’ve introduced new enemies, provided them (and old foes) with access points and increased competitive advantages, and carved up the landscape to block escape routes and re-supply lines.  Now, we’re turning up the heat and quickly changing the basic growing conditions and living environment within the prairies that have managed to survive to this point. 

But, hey, prairies should be able to handle all that without our help, right?  (Good luck in the soccer tournament, kids!)

Before we address that question, here’s one more consideration.  The last glaciers retreated from central North America thousands of years ago, and tundra and spruce forests gradually gave way to grasslands.  During and after that transition, people have been present and active managers of those grasslands.  Human hunters influenced the composition and behavior of animal communities, and arguably helped eliminate a number of important animal species.  Perhaps most importantly, humans were actively using fire as a management tool (to attract grazing animals, for example) as well as for warfare and other purposes.  Those fires were an essential factor that helped perpetuate grasslands and prevent them from being taken over by encroaching woody vegetation.  As a result, today’s prairies have never been separated from people and human management.    

People have been actively burning prairies in central North America since those prairies first constituted themselves after the last ice age.

So, what would happen to a prairie today if we decided to just leave it alone?  It’s not a hypothetical question – any experienced prairie manager can tell you stories based on their own prairies, or on prairies they’ve watched suffer from insufficient or no management.  The only fires that occur in today’s fragmented landscapes are those set by people.  In the absence of those prescribed fires (or a substitute such as haying or grazing), prairies begin accumulating thatch – the dead stems and leaves from successive years of annual growth of grasses and wildflowers.  Within a few years, that thatch begins to smother many of the plants trying to grow through it.  It also creates inhospitable habitat for most prairie animals.  Biological diversity, an essential component to the resilience and survival of prairie communities, decreases dramatically.

As thatch builds up, so does the competitive pressure from invasive plants and trees.  In my area, for example, smooth brome, reed canarygrass and tall fescue tend to flourish in the absence of management.  They do particularly well in high nitrogen environments, but they also get by just fine without inadvertent fertilization.  In addition, there are numerous tree and shrub species that can quickly take advantage of a lack of fire, including eastern red cedar, white mulberry, honey locust, Siberian elm, smooth sumac, and rough-leaved dogwood. Especially in highly-fragmented landscapes, those and other trees are often growing right on the edges of prairies, and if not, their seeds can easily reach prairies by bird, wind, or other conveyance.  Complete conversion of a diverse prairie to a woodland with a brome understory can happen within a couple of decades or less.

By the end of a growing season, prairies can produce a tremendous amount of vegetative growth, which can accumulate after multiple years (if not burned, grazed, or mowed off) to the point where it greatly inhibits the growth of plants beneath it and provides poor habitat for many animal species.

You might be thinking, “well, sure, I can see how that might happen in a tiny prairie surrounded by cornfields, woodlands, and suburban sprawl, but what about some of the big prairie landscapes of Kansas, Nebraska, or the Dakotas?   Surely those prairies can take care of themselves, right?“

We can argue about whether lightning fires alone would be sufficient to prevent tree encroachment in a huge expanse of prairie.  I feel confident they wouldn’t, but it’s an argument that can be had.  However, invasive species, spurred on by nutrient pollution and climate change, are still going to be a killer threat to biological diversity and the subsequent vitality of those prairies in the absence of human management.  Depending upon location, already-present invasive plant species such as leafy spurge, sericea lespedeza, spotted knapweed, cheatgrass, Kentucky bluegrass, and many others would expand their reach and power to the point where they would dominate large swaths of land, if not entire prairies.  That invasion and dominance would trigger a cascade of other impacts, leading to reduced plant diversity, decreased habitat quality for animals, eventual extirpation of many plant and animal species, and an ecosystem that would be unrecognizable – and undesirable to most of us.

Invasive species, such as crown vetch (Securigera varia), are already present throughout many prairies, but are held in check by constant and thoughtful management. In the absence of that management, prairies would be overrun by these species, losing plant diversity and ecological function as a result.

Anticipating protests, here are couple more quick points.  If you’re an advocate of the broad idea that we should get out of the way and let nature take its course, you might say prairies are an unfair example because they are a transitional ecosystem that relies heavily on disturbances such as fire to avoid becoming a woodland.  That’s fine, but if you look around the world, there are lots of other fire-dependent ecosystems, including many (most?) forests and woodlands.  Most of those also have very long histories of human fire management. 

In addition, woodlands and other ecological communities suffer from invasive species, habitat fragmentation, nutrient overload, and climate change, just as prairies do.  We’ve created a world that puts those natural systems at a disadvantage, and whether we like it or not, they now rely on us to help mitigate those threats.  Arguing about whether human management is natural or not is a moot argument that distracts from the great challenges we face in conservation.  Let’s focus on the important discussions about how best to manage ecosystems, not the settled issue of whether we should be managing in the first place. 

People are an intrinsic part of nature and the world we live in.  That shouldn’t make nature seem any less fascinating or inspiring – in fact, recognizing our interconnection with nature should inspire us even more. We are part of an incredibly complex and beautiful web of interacting species and communities across the glove. As such, it’s up to us to play our roles responsibly.  Just as we don’t exist outside of nature, we also can’t survive without it.

Choosing Your Destination Before You Choose Your Mode of Transport

Last week, I attended a science and stewardship conference of The Nature Conservancy in Madison, Wisconsin.  It was an inspiring and thought-provoking week.  There were a lot of topics that will provide fodder for future blog posts, but I wanted to start with an issue that came up in several sessions.  The topic had to do with setting appropriate objectives for conservation strategies, and for land management in particular.  In short, it’s really important to make sure we’re not setting objectives that are focused on strategies rather than outcomes.

This mixed-grass prairie is managed with both prescribed fire and grazing.  However,  neither fire nor grazing is the objective, they are tools that are strategically employed to create desired outcomes.  Gjerloff Prairie – Prairie Plains Resource Institute

Here’s an illustration of what I mean.  If I was planning a vacation for next summer, I probably wouldn’t start with the following question: “What mode of transportation should I take on my vacation next year?”

Clearly, it’s tough to answer that question without knowing more about the ultimate objectives of the vacation.  Where do I want to go?  What time of year am I going?  How many people are going with me?  If I’m planning to travel from Nebraska to Ireland, I probably won’t be able to do that by bus.  I could conceivably travel by motorcycle (if I had one) to the Rocky Mountains, but probably not if I was going during the winter or planning to take little kids with me.

It seems silly to start by thinking about how to get somewhere before deciding where to go, but as land managers, it’s easy to fall into exactly that mindset.  We sometimes set objectives about using fire or grazing, for example, instead of first defining the outcome we want and then thinking about what tools and strategies might get us there (which may or may not include fire or grazing).  In this post, I’ve provided examples of how this trap can present itself, both to managers of conservation land and private landowners, and some thoughts about how to avoid the trap.

Significant research has helped us understand the kinds of fire and grazing patterns under which North American prairies developed.  For example, in many places, we have a pretty good idea how often a particular site burned, on average, before European settlement.  We also have reasonably good information on the presence, abundance, and behavior of historic grazers.  Based on that information, a land manager could decide that the best management for their prairie would be to reinstate, as closely as possible, the timing and intensity of historic fire and grazing that site likely evolved under. 

Historically, prairies in this region probably burned on an average of every 4-5 years.  However, within that average range, there would have been wide variation.  More importantly, this prairie sits within a very different landscape today, with challenges not faced by those historic prairies.

Patch-burn grazing is often described, for example, as “mimicking historic fire and grazing patterns.”  Mob grazing advocates trumpet (though I’m skeptical) that their system replicates the way bison moved across a landscape.  Some in the Upper Midwest region of North America point to research showing high populations of indigenous people and scarce evidence of abundant bison and argue that their prairies should be managed only with fire.  We can argue about all three of those examples – and many more – but the bigger point is that none of those arguments should determine our management strategies.  Again, we shouldn’t be setting objectives about the strategy we want to use without first identifying the outcome we want.

To make a clunky return to my vacation travel analogy, it would be silly of me to choose horseback as my preferred mode of transportation across the Great Plains to the Rocky Mountains just because it’s what worked several hundred years ago.  Today’s landscape is broken up into countless fenced off private land parcels, which would make cross-country horse travel difficult, to say the least.  In addition, there is a pretty nice set of modern opportunities (roads and vehicles) I can take advantage of nowadays.

Likewise, our prairies exist within a different world today, with a new set of challenges and opportunities.  Mimicking historic disturbance regimes won’t necessarily keep prairies in good shape in a world with habitat fragmentation, massive invasive species pressure, climate change, nitrogen deposition, and other factors.  And speaking of good shape, our first and primary concern should really be to define what “good shape” is, right?  Are we managing for plant diversity or a few rare plants?  Are we trying to sustain diverse bird populations?  Habitat heterogeneity? Is ecological resilience the goal?  If so, what are the factors driving resilience, and how to we sustain those?  There are countless reasonable goals for land managers to choose from, many dependent upon scale, but those goals should be based on the outcome we want.

This annually-hayed prairie maintains high plant diversity but provides only one type of habitat structure for nesting birds and other wildlife species.  Depending upon the objectives for the site, that could be fine, but it very much depends upon what the manager wants to accomplish.

I feel it’s important to say this here:  I am a big proponent of both fire and grazing as management tools – you can find myriad examples of that by searching through my previous blog posts.  However, while I think combining fire and grazing can create some fantastic results, those strategies/results don’t fit all objectives.  More importantly, your particular site may or may not respond well to those kinds of fire and grazing combinations.

Let’s say your primary objective is to provide habitat for as many species of grassland birds as possible.  First, you’ll need a pretty big swath of land – many bird species have minimum habitat size requirements.  Assuming you’ve got sufficient land, the major factor grassland nesting birds respond to is habitat structure.  Some birds prefer tall thatchy structure, others like short/sparse vegetation, and others want something in-between.  A reasonable outcome-based objective might be that you want to provide all three of those habitat types across your prairie each year (and you’ll want to make sure the habitat are being successfully used by a diverse bird community).  Perfect.  Now, how will you create those habitat types?

 Grasshopper sparrows tend to nest in prairies with relatively short structure, but with some thatch (which they use to build nests) along the ground.  Some of the highest abundances of grasshopper sparrows around here are found in relatively heavily-grazed prairie.

Fall or spring fires can create short habitat structure that some birds really like to nest in.  However, some bird species (e.g., grasshopper sparrows) usually like short habitat with a little more thatch in the ground layer than is usually found in recently burned prairies.  Also, while burned areas are short and unburned areas are tall, it’s difficult to create in-between height/density habitats using only fire.  This is where other tools such as mowing and grazing might be helpful.  Mowing can reduce the height of tall vegetation and create short or mid-height structure that grasshopper sparrows, meadowlarks, and other species prefer.  Grazing can do the same and can have the advantage that cattle or bison are selective grazers, eating some plants and leaving others.  This can create structure with both tall and short vegetation mixed together and can also help suppress grasses and allow for greater expression of forbs (broadleaf plants) – something birds such as dickcissels often prefer.

Upland sandpipers prefer to nest where vegetation structure is short, but often move to sites with strong forb cover and a little patchier structure when their chicks become active.

If we’re trying to create optimal bird habitat, then, fire, mowing and grazing might all be useful tools to consider.  It’s important to understand how each tool can be used to affect habitat structure, as well as the potential risks of using each (fire can sometimes kill aboveground animals and stimulate invasive plants, grazers can sometimes target vulnerable plants and create issues via trampling).  With all of that information, you can start putting together strategies that employ the right tools, and then test those strategies against the OUTCOMES you desire.  Notice that the process I’ve just described is independent of the kinds of historic fire returns for your area or whether or not you think grazing was a significant factor in the evolution of regional plant communities.  Define your objective by the outcomes you want and test/adapt strategies based on that objective.

Other examples: At my family prairie, we aren’t using prescribed fire because we’ve been able to use grazing to meet our objectives of habitat heterogeneity and increasing plant diversity, and we use loppers/herbicide to successfully control woody invasion.  In small prairies where preserving particular plant species is the objective, a strategy using only fire or mowing could be most appropriate.  If that small prairie has rare insects or reptiles that are especially vulnerable to fire, maybe mowing is the best tool.  Regardless, the right tools and strategies depend upon the outcome-based objective.

This photo was taken in the burned patch of a patch-burn grazed prairie at Konza prairie, near Manhattan, Kansas.  The grazing created varied habitat structure because of the selective grazing by cattle.  Leadplant and other ungrazed forbs contrast with surrounding short grasses.

For ranchers and farmers who manage prairies, this same objective setting process should apply, but of course those prairies also have to help provide sufficient income to keep a family or business thriving.  Even in those cases, however, it’s still important to start with outcome-based objectives.  Those objectives can include a certain amount of needed income but should also include specific habitat or other ecological objectives.  Once you’ve decided, for example, that you really want to manage in a way that provides a certain amount of quail habitat or provides consistent pollinator resources through the season, you can look for ways to accomplish that while still providing the needed income.  When a conflict between income and habitat objectives arises, you can make the decisions that make sense to you, but at least you’re making those decisions with all the information needed to fully consider the options.

Prescribed fire can be a great tool for accomplishing some objectives, but it can also be difficult to implement for some managers.  While it is an important ecological process in prairies, employing prescribed fire should still be seen as a tool/strategy, rather than as an objective in and of itself.

There are plenty of reasonable prairie management objectives to choose from, but they should be based on outcomes rather than on tools and strategies.  Employing more frequent prescribed fire is not a good objective.  However, using more frequent prescribed fire might be a great strategy to reach a particular outcome.  (It could also be a terrible strategy, depending upon your objective.)  Don’t fall into the trap of choosing your transportation method before you know where you want to go. 

P.S. I’m sure some of you are thinking it, so let me address what might appear to be a weakness of my vacation transportation analogy.  Yes, it’s perfectly fine to start vacation planning by deciding that you want to take a cruise ship or motorcycle if the OUTCOME you really want is to ride on a ship or motorcycle.  If you don’t care where you go, the destination isn’t the outcome, it’s just a by-product of your mode of travel.  Fine.  But I think you understand what I was trying to say, right?  Sure, you could argue that conducting prescribed fires could be your objective if all you want is a legal way to light things on fire and watch them burn.  If that’s your objective, though, you’re not managing prairies, you’re lighting things on fire – and there’s a big difference.  Ok?  Ok.