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.

Photo of the Week – March 1, 2019

The snow on the ground is slowing down some of our plans for March, but I do appreciate the opportunity to do some more winter photography. It’s also nice to have snow around as a way to gauge the kind of animal activity going on in the prairie. As I walked around the Platte River Prairies last weekend, I particularly noted an abundance of small mammal tracks. Once I started noticing and photographing the tracks, I saw more and more, so I just kept photographing them. As a result, I came home with an absurd number of mouse track photos.

No tracks in this photo, but this gives you a feel for what the afternoon was like on Sunday at the Platte River Prairies – attractive diffuse clouds in the sky and sparkling snow on the ground. A perfect day to obsess over a narrow range of photographic subject matter.

I’m only sharing a small subset of those track photos today. It may be difficult for some of you to appreciate the subtle differences between the photos, which, at first glance might appear nearly identical to each other. I tried to provide explanations in the captions for why each image is absolutely unique and worth sharing. It’s not just because I took a lot of very similar photos and felt compelled to justify that by sharing more than just one or two. Seriously, I could have filled the rest of your day with mouse tracks, but I restrained myself. Enjoy.

While I saw a lot of mouse tracks like this, including some that led to burrows in the snow, I didn’t see any evidence of what the mice were eating (if anything) while they were out and about.
This photo is really different from the previous one in that you can see the individual toe prints. Also, the tracks move from top left to bottom right of the frame instead of top right to bottom left…
THIS photo is different from the previous two because it was photographed later in the day when the sun was lower and providing more golden-colored light.
As the sun neared the horizon, I was still taking photos of mouse tracks. And yes, most of the other images were pretty similar to each other. But THIS one has a sun in it!