CHAPTER 5
We even enter the domain of philosophy, and speculate on the fundamental nature of the association, regard it as the basic unit of vegetation, call it an organism, and compare different areas of the same sort of vegetation to a species.—Gleason 1926
As an organism, the formation arises, grows, matures, and dies. . . . The climax formation is the adult organism, of which all initial and medial stages are but stages of development.—Clements 1936
The ordinary citizen today assumes that science knows what makes the community clock tick; the scientist is equally sure that he does not. He knows that the biotic mechanism is so complex that its workings may never be fully understood.—Leopold 1949
The grassland is complete in itself, a relatively stabilized product of nature, the outgrowth of climate, soil, vegetation, animals, and microorganisms, all interacting together.—Malin 1967
It appears fairly certain that there can be no final victory for either, there can only be periods of varying duration in which prairie or forest holds the ground won by the favor of the changing climate cycle.—Weaver 1968
A first principle is that chance and change are the rule, the future is as unpredictable to other organisms as it is to us, and natural disturbance is too frequent for equilibrium models to be useful.—Drury 1998
EVERY TIME THE PUP AND I visit a prairie, even ones we think we know like the back of our hand, or paw, we see something different. Every trip is unique for any of a dozen different reasons. While I can generally predict that there will be a lot of sunflowers and asters blooming in the late summer, I don’t know exactly how many or exactly where they will be. I have no idea what birds we might flush from the grass. There’s a lot of uncertainty at the beginning of every prairie visit.
Previous chapters provided a longer-term historical context for how dynamic the prairie landscape was, and still is. The prairie is also very dynamic over short time periods and small areas. Researchers in the prairies in the first half of the twentieth century largely influenced how scientists around the world thought about ecosystems. It still influences how many non-scientists perceive ecosystems today.
The three factors that largely determine the diversity and productivity of the prairie are fire, grazing, and weather extremes, especially periodic drought. Ecologists call these events disturbances. One of the most often cited definitions of an ecological disturbance is “any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment” (Pickett and White 1985). The disturbance would destroy or damage much of the existing vegetation and would be especially destructive of the most dominant species. (Think about a forest fire killing mature pine trees in the Intermountain West.)
“Disturbance” definitely has a different context in social and scientific settings. Disturbance may have a negative social context, such as hearing on the news about a domestic disturbance. In his landmark book Man and Nature, George Perkins Marsh (1864) wrote, “But man everywhere is a disturbing agent. Wherever he plants his foot, the harmonies of nature are turned to discord.” In this mindset, humans and nature are separated. Only humans were able to disrupt things, and only humans caused problems in the natural world.
Kansas and the great plains were largely in their primeval state, one hundred years ago. A balance among plants and animals, between each species and its parasites and predators, has been established through the ages, which was, until the coming of man, but little disturbed. (R. C. Smith 1932)
Man alone can destroy the stability of the climax [plant community]. (Clements 1936)
In the past, and often still today, we wanted nature to be a peaceful, harmonious place. Bambi, Thumper, Flower, and Friend Owl all dance and frolic together. We wanted processes and ecosystems to be at equilibrium and for all things to be in balance and stable. We wanted nature to be predictable. We wanted nature to be simple enough that we can understand it and predict what will happen next. That’s all comforting. It gives us at least a little sense of control. This mindset probably expresses itself most clearly in the phrase “balance of nature” (Edgerton 1973; Simberloff 2014).
Unlike “disturbance,” the word “balance” has a positive connotation. However, nature isn’t in balance, well-balanced, out of balance, unbalanced, or imbalanced. Nor can we through our actions or inactions get nature back into balance. We just shouldn’t use the words “nature” and “balance” together.
Modern ecologists are more of the view that “the idea of ‘balance’ has had a cultural and religious connotation rather than a strict scientific foundation” (Wu and Loucks 1995). That said, a quick search of titles shows a number of books published relatively recently with some version of “balance of nature” in the title or subtitle. This seems to be an idea we don’t want to let go of culturally.
The “balance of nature” term and concept may have been one of the areas where Aldo Leopold, and many others, struggled. At various times he wrote that ecologists “accept it only with reservations” (1939), and that “this figure of speech fails to describe accurately what little we know” (1949). That said, Leopold used phrases such as “internal processes must balance” and “an internally balanced community” (1949).
Along with the idea of balance are the ideas of stability and equilibrium. And here we can connect back directly to the prairie. Frederic Clements was one of the leading plant ecologists of the early 1900s and did much of his work in the prairies of Nebraska. He interpreted his research findings to show that undisturbed prairies were stable. John Weaver, another well-known ecologist, was a student of Clements and also conducted his research in Nebraska grasslands.
It can still be confidently affirmed that stabilization is the universal tendency of all vegetation under the ruling climate. (Clements 1936)
The great stability of the prairie . . . denotes a high degree of equilibrium between vegetation, soil, and climate. (Weaver 1968)
Stability leads up to the concept of ecological succession, or what happens to the plant community over time after a disturbance. In theory, there is a predictable and orderly sequence of species that dominate the disturbed area over time. Eventually, the original, pre-disturbance, or climax plant community once again dominates the area, and the vegetation becomes stable and at equilibrium. Henry Cowles first described this process in 1901 from his work at the Indiana Dunes in northwest Indiana.
In Clements’s view, Plant Community 1 is composed of Species A, B, and C and develops immediately after a disturbance. After a period of time, it is replaced by Plant Community 2, composed of Species D, E, and F. Eventually the site will reach a point where the Plant Community is dominated by Species X, Y, and Z. From then on, Species X, Y, and Z will replace X, Y, and Z when a plant dies. This is the stable climax plant community that is at equilibrium. As importantly, the timing and sequence of species and formations after the disturbance should be somewhat predictable.
Clements took the idea of plant succession and the sequential replacement of one plant community by another one step further. He stated that plant communities functioned as a superorganism.
Like other but simpler organisms, each climax not only has its own growth and development in terms of primary and secondary succession, but it has also evolved out of a preceding climax. (Clements 1936)
Hence prairie is much more than land covered with grass. It is a slowly evolved, highly complex organic entity, centuries old. It approaches the eternal. (Weaver 1954)
Not everyone bought into the ecosystem as organism viewpoint. One can hear the tension some of these ideas created within the scientific community. Comparing a plant community to an organism is a “flight of the imagination” (Braun-Blanquet 1932). Put another way, “there is no need to weary the reader with a list of the points in which the biotic community does not resemble the single animal or plant. They are so obvious and so numerous” (Tansley 1935). That said, writers such as Aldo Leopold and others make frequent use of the “land organism” or related wording as a metaphor for ecosystems.
The next related concept is cooperation. Again, cooperation is a social construct. There are examples of the elements of nature seeming to work together such as a fungi and algae living together to form a lichen or Rhizobium bacteria in the root nodules of legumes.
Charles Darwin made it clear that life was about struggle, against both the elements and other organisms. Is the prairie a cooperative effort or a bloody field of battle? Compare the following quotes from Aldo Leopold.
This biota, through ten thousand years of living and dying, burning and growing, preying and fleeing, freezing and thawing, built that dark and bloody ground we call prairie. (Leopold 1949)
Any prairie is a model cooperative commonwealth. (Leopold 1999)
Likewise, we can compare the following quotes from John Weaver’s Prairie Plants and Their Environment.
The beauty and quiet calm of the grassland should not obscure the fact that the prairie is both a field of battle that is centuries old and a field in which the conflicting species, never wholly victorious nor entirely vanquished, each year renew the struggle.
The great stability of the prairie, resulting in part from the long lifespan of many species, denotes a high degree of equilibrium between vegetation, soil, and climate. (Weaver 1968)
Is the prairie a dark and bloody ground or a cooperative commonwealth? Is the prairie a field of battle or a place of stability and equilibrium? It doesn’t seem like it can be both. We can most easily see that battle between forests and prairies, but each grass and forb on the prairie fights its own battle with neighbors.
One may see in the oak openings of Wisconsin the area in which the fight is still doubtful, where in some spots the forest is advancing on the prairie, in others receding before it. (Quick 1925)
The grass and trees went to war, and they are still fighting for the land. (Peattie 1938)
The average battle line between prairie and forest was about where it is now, and the net outcome of the battle was a draw. (Leopold 1949)
Leopold’s quote almost makes it seem like the battle is over and each side signed a truce. The other two quotes give a more evolutionary and ecologically more accurate description of a battle that continues on.
It’s interesting how many times words like fight, battle, and war show up in the prairie literature. That doesn’t sound very cooperative. That historic struggle can lead to patterns that are sometimes difficult to understand today.
[T]he prairie species practice “team work” underground by distributing their root-systems to cover all levels. (Leopold 1949)
Species don’t practice teamwork in rooting depths, or anything else. We’re all familiar with the phrase “nature red in tooth and claw,” which was actually written by the poet Alfred, Lord Tennyson. If nature is red in tooth and claw, it is also dark of shade and deep of root. Charles Darwin gave us the phrase “struggle for existence” and his contemporary Herbert Spencer coined the phrase “survival of the fittest.”
Over evolutionary time, fighting tooth and claw, or leaf and root, each species finds the best ways they can avoid competition for light, nutrients, water, and pollinators. Each species has diverged in these characteristics to avoid or minimize competition from other species. This is called the “ghost of competitions past” (Connell 1980). The two species aren’t competing today, because they’ve already fought those battles and figured out how to avoid each other. Today, it may look like they aren’t competing and are cooperating.
Donald Worster (1990) wrote, “We look for cooperation in nature and we only find competition. . . . We hope for order and discern only a mishmash of conjoined species, all seeking their own advantage in utter disregard for others.” Battle line, battle, fight, war, mishmash, and utter disregard do not sound like the plant community behaving as an organism or cooperating together. Nor does it make the natural world seem stable, balanced, or at equilibrium.
The following quotes perfectly illustrate two different strategies. There is no ideal situation in the natural world. Species can avoid competition by living in a harsh environment. Or a species can avoid a harsh environment by living in a competitive environment.
Only gravel ridges are poor enough to offer pasques full elbowroom in April sun. They endure snows, sleets, and bitter winds for the privilege of blooming alone. (Leopold 1949)
In June as many as a dozen species may burst their buds on a single day. (Leopold 1949)
Pasqueflower grows and blooms when it is cold, when there’s a good chance of late spring snowstorms, when there aren’t a lot of pollinators, and on hilltops with poor soils and low water availability. Those aren’t ideal conditions, but it allows this species to escape competition. In contrast, in June there’s still moisture from the spring rains, it’s warm but not yet hot. However, these plants face intense competition for pollinators. These plants have a benign climate, unlike pasqueflower, but face intense competition that pasqueflower doesn’t have to deal with. These are two strategies, but neither is perfect or ideal.
Henry Gleason was a midwestern prairie plant ecologist in the early 1900s. He developed what became the Individualistic Hypothesis. According to Gleason’s theory, each point in space and each time period along a successional sequence is a far less predictable sequence of species or communities than what Clements hypothesized.
Gleason’s theories conclude that the natural world is less predictable than it is according to the Clementsian view. After a disturbance, there will be a sequence of species at a location, but the exact order of species isn’t always predictable. Each species comes and goes individually without close association with other species. Much of Gleason’s world was based on probabilities and randomness, not comfortable ideas if one is looking for stability, equilibrium, and predictability in the world.
The vegetation of every spot of ground is therefore also continually in a state of flux, showing constant variation in the kinds of species present, in the number of individuals of each. (Gleason 1939)
Although academic debate goes back to the 1930s, there was a small revolution in ecology in the 1960s and 1970s. Ecology became much messier, fuzzier, and unpredictable, with a lot more uncertainty. Scientists started to see ecological disturbances as driving and maintaining ecosystems, not disrupting them. Imagine an area with no disturbance. The most competitive and aggressive species will crowd out the others and diversity will be low. Imagine another area that is facing frequent, intense, large-scale disturbances. Only the weediest, most ruderal species will be able to survive all those stresses and diversity will be low. (Typically “weed” is equated to an invasive species. A ruderal species is a native species that does well in highly disturbed environments, such as Canada goldenrod in a road ditch.)
Now imagine an area where there are some disturbances, but they aren’t too frequent, too large, or too severe. There’s just enough disturbance to knock back the dominant plants that crowd out other species, but not enough disturbance to eliminate a large number of species. These areas will have a higher level of diversity than undisturbed or heavily disturbed areas. This is known as the Intermediate Disturbance Hypothesis (Connell 1978).
Then add a spatial component. One area hasn’t been disturbed in ten years; one area burned five years ago; and in one area cattle grazed last year. Now each area has a different disturbance history, type of disturbance, and time since disturbance. Each area will have a slightly different plant community or dominant species due to those disturbances. Added together, the diversity across the larger area should be relatively high.
This probably describes the prairie before Euro-American settlement. Bison grazed the prairie, but they moved around and didn’t graze every area every year. Fires were common, but not every acre burned every year. Floods periodically disturbed areas along creeks and rivers. Droughts occasionally affected entire regions. At the smaller scale, badgers and ground squirrels made burrows and dirt mounds. All of these are unpredictable in both space and time.
Much of the research conducted historically was designed with a more Clementsian, balanced viewpoint. In more recent decades things have changed. The following quotes demonstrate just how complicated and intricate all the interactions on and in the prairie are.
Within the transitional zone [tallgrass prairie] no single set of environmental factors explains the mosaic pattern of vegetation. The environmental factors influencing the vegetation operate in concert, with the relative importance of each factor and the interactions of these factors varying in time and space. (R. C. Anderson 1983)
Their [Wu and Loucks 1995] argument, that the classical equilibrium view in ecology has failed to provide a useful predictive model of most natural systems because of the rarity of equilibrium conditions in nature, is certainly true for grasslands. In contrast, elements of the nonequilibrium models they reviewed—such as the focus on transient dynamics, stochastic processes, fluctuations in environmental variables as dominant processes, the important role of historical factors, nonlinear interactions, sensitivity to critical changes that cross threshold boundaries, and inherently low predictability—are the features that make nonequilibrium models ideal for interpreting grassland dynamics. (Knapp and Seastedt 1998)
That all seems complex, unpredictable, and full of jargon, but that’s the idea. It’s complicated. In other words, the more (we think) we know, the less we can predict. If all that wasn’t confusing enough, they go on a few pages later to state:
Put another way, what truly makes the tallgrass prairie a challenging system to study is the high frequency of switching between limiting factors during and among years. Fire, herbivores, and climatic extremes all influence, and their effects are influenced by, this variation in supply and demand for essential resources. (Knapp and Seastedt 1998)
Each of those factors, fire, grazing, and climate extremes, are disturbances. It’s these, and other, disturbances acting at different times, different frequencies, different intensities, and different sizes that makes the prairie so complex and dynamic.
To make the prairie more complex than most ecosystems, the limiting factor is frequently changing. Deserts are hot and dry. Tundra is cold. The understory of coniferous forests is dark. However, in the prairie, light, water, temperature, and other factors can vary from spot to spot and year to year, so the limiting resources are constantly changing in space and time. Frequently, it’s the history of disturbance and the most recent disturbance that determine the limiting factor at that spot at this time. Taking this one step further, studying the changes in the vegetation, and the reason behind those changes, may be more useful and informative than studying the vegetation itself.
[V]egetation is constantly undergoing various kinds of change, but the increasing habit of concentrating attention on these changes instead of studying the plant communities as if they were static entities is leading to a far deeper insight into the vegetation. (Tansley 1935)
Currently, ecological interests have shifted from seeking similarity for the purpose of classification to understanding variability within the context of natural disturbances. (Collins and Glenn 1995)
Today, most ecologists think that we live in a more Gleasonian than Clementsian world. However, that’s not to say that ecologists have completely abandoned Clements’s ideas (Tansley 1935). Although the super-organism idea has led to criticism, Clements’s ideas still have many positive influences on how modern scientists understand plant communities (Collins and Glenn 1995). So let’s go back to Leopold’s land organism. He was drafting these chapters through the late 1930s and into the 1940s. Gleason’s work and the research of Shimek, Tansley, and others, demonstrate that there were different viewpoints out there.
Was Leopold out of touch with science when he wrote about the land organism? Did he get this wrong? No, he was not wrong, but he wasn’t right either.
Although Gleason’s ideas were present in the 1940s, they weren’t widely adopted. Through the 1940s scientists were still taking an equilibrium view of the world. When it came to Gleason’s theory, “most simply ignored it” (McIntosh 1975) and “few American ecologists publicly agreed with it or even seemed to notice it” (Barbour 1995). However, Barbour also states that “prior to the 1950s nature was simplistic and deterministic; after the 1950s nature became complex, fuzzy-edged, and probabilistic.” Likewise, “ecology was basically a study of equilibrium, harmony, and order; it had been so from its beginning. Today . . . it has become a study of disturbance, disharmony, and chaos” (Worster 1990). So, Leopold was reflecting mainstream science, at the time. It’s just that the times have changed.
Things are changing all the time and there’s a lot we don’t know or understand. How do we develop policies and management plans built on change, uncertainty, unpredictability, disturbance, and chaos? No matter how much or how long any person or group studies an area, there’s still a lot to learn. Indeed, at the end of a career studying or managing the prairie, most have far more questions than answers. And every time we think we have something figured out, the prairie will do something to confuse us.
I have looked for a prairie remnant that I could manage, where I could apply unfettered what I think I have learned. (Drobney 1999)
Note the phrase “think I have learned.” Every time you think you know something, the prairie is going to surprise you.
Conversing with the Dead
I’VE NEVER UNDERSTOOD WHY, but people like to know other people’s favorites. What’s your favorite color, or song, or movie?
Who’s your favorite Beatle? What’s your favorite bird? What’s your favorite prairie flower? When asked this, I always say I’ll have to think about it and then try to change the subject.
I suppose that if threatened with bodily harm, I could name two or three of my favorite birds and flowers. Really, they are all pretty interesting in their own way. Two of those flowers would probably be pasqueflower and shooting stars, and another would be hoary puccoons. I like them all for personal and probably irrational reasons, but they are my reasons.
In writing about the Illinois and Iowa prairies, Leopold describes “a narrow thread of sod” between the road and toppling fences. He also describes a cemetery that “flashes by,” presumably due to its small size. He writes that the cemeteries’ borders were “alight with prairie puccoons.” However, across the rest of the landscape other species, mostly invasive, provide a splash of yellow that puccoons once provided. He ends the paragraph with a sorrowful “puccoons converse only with the dead.”
There may be two possible ways to interpret this line. First, puccoons are found only in native prairie and much of the native prairie left in Illinois and Iowa is in pioneer cemeteries. The second interpretation is a little more complicated. Cemeteries, especially older cemeteries, are rather static. They don’t change much.
It’s relating puccoons to a static prairie that I would like to politely argue with Leopold about. Puccoons are a species that are difficult to restore and therefore seeing them almost always indicates a remnant of native prairie.
Even in the highest quality native prairies, puccoons often do best at small disturbances, such as the bare ground left from small mammal burrowing. When it comes to ditches, the place I often see puccoons is right on the edge of road, where gravel meets grass. After snowy winters when the township snowplows have been out in force, puccoons are often most common in spots where the plow blade scraped off the top bit of soil.
So, while puccoons do indicate either a high-quality plant community, or at least an area where a few species have hung on, relating them to the relatively static conditions found in old cemeteries may do a disservice to the natural history of this species. This is a species that is often dependent on some level of disturbance. This also tells me that puccoons may not be the best competitors and hang on best where they have a little elbow room. Puccoons are dependent on disturbance and change, and don’t do well in any static or stable situation, where they are soon crowded out.
This is not to argue that snowplows are a prairie’s best friend. However, it is an attempt to show that burrowing animals, grazing, and in some cases human mechanical disturbances can be beneficial to some species and can help maintain the overall diversity and dynamics of the prairie.
Puccoons were abundant at my undergraduate research site, a sandy area along the Wabash River. I still remember checking small mammal traps at dawn and seeing the dew glistening on the puccoons. I recorded them at Spinn Prairie on my last trip to an Indiana prairie as a college student.
Since I moved to Minnesota, puccoons have always been one of the species I most rely on to show me where there might be some remnant prairie in a field corner or ditch. If I see puccoons, I stop and look. More often than not, I’m rewarded with some prairie violet, blue-eyed grass, pasqueflower, prairie smoke, and other prairie species hanging on in that narrow thread of sod.