If Mother Nature has plans, those plans are flexible. She keeps her options open, allows for more than one route to a given location, and we cannot assume that the same circumstances will always produce the same outcome. To digress for a moment: accepting this need not challenge religious or philosophical beliefs about a creator. Nothing in the bible, for instance, specifies exactly how the Judeo-Christian God goes about his/her business, or specifies any single pathways or mechanisms. As a protestant minister I knew well used to say: “Religion is concerned with the ‘why’ questions, and science addresses the ‘how.’”
Indeed. 35 years in the geoscience research business has shown me that that there is no single “right” or “natural” way for the world to be. Any human notions of singular, immanent norms or optima are tied to needs, goals, or perceptions, not scientific laws or relationships. And—again—there is nothing wrong with having such goals, desires, or expectations for nature, any more than there is anything wrong with a farm or a garden. The key is to realize that there is not much point in expecting Earth surface systems to evolve toward and maintain a single specific condition, any more than we would expect a garden to maintain itself without some guidance and intervention.
Why, then, in the face of overwhelming evidence to the contrary do people, scientists and laypersons alike, adhere to worldviews, conceptual frameworks and models based on singular, normative states of Earth systems?
My best guess is based on two propositions: (1) Humans want to impose (or imagine) order and predictability on nature; and (2) certain aspects of environmental systems imply a “balance of nature;” particularly to those (most) of us predisposed to believe in or desire it.
Jonesin’ for Order
Why do we want to find or impose order and predictability in nature? Most fundamentally, I think, it is because creation is vast, complicated, and complex. We have no hope of even getting our heads around it (or parts of it) intuitively, much less achieving any scientific understanding, without simplifying it in some way. Assuming or postulating a normative state is one way of doing this, and a “balanced” state is as good a choice as any and better than most, since it is quite often a logical reference condition, regardless of attitudes about normativity.
There also exists, of course, abundant evidence that hardwiring in our brains and cultural conditioning both compel us to seek orderly patterns. There are neurological, psychological, social, cultural, aesthetic, and pragmatic aspects to this compulsion that are way beyond my expertise. However, I am well convinced that this compulsion exists, in varying degrees and manifestations, in all of us.
Normative equilibria and balance of nature concepts are also often a matter of convenience or practical necessity. We can’t realistically manage rivers, farms, ecosystems or anything else without some sort of target or goal. Choosing these targets is a lot easier when we assume or imagine a single natural or balanced desired state. Conversely, justifying and explaining management goals is easier if you can claim to be doing exactly what nature intended. And sometimes, faced with multiple options and limited information, the assumed normative equilibrium state may be as good a choice as any.
Finally, as scientists, we emphasize what we do understand (or think we understand) and can predict. And balance-of-nature and equilibrium ideas and models do sometimes help us understand and predict. The underlying equilibrium assumptions may be unrealistic, or just plain wrong, but that doesn’t necessarily prevent them from being useful in some situations (I have written about this in the context of soil and fluvial geomorphology here, here, and here). I often use the analogy of the common economic modeling assumption that all participants always act rationally, in their own best fiscal interests, and with perfect knowledge. The fact that this assumption is untrue does not prevent the models from working well in certain situations.
Keeping Up Appearances--of Equilibrium
So we want or need equilibrium and balance, or at least find it to be a convenient fiction. What is it about environmental systems that enable us to think we see it when it is not there, or to think that a balanced state is more normal or common than otherwise, rather than just one of several possible conditions?
First, consider relaxation time equilibrium. Relaxation time is how long a system takes to complete its response to a change or disturbance. In Earth systems relaxation time is always finite, and very often decelerates. That is, the response is often rapid at first, and then quickly or gradually slows to negligible rates. This can readily be interpreted, if one is predisposed to do so, as the system achieving a new steady-state or normative equilibrium. The more likely and logical interpretation, however, is simply that relaxation time has elapsed, and that the new state was not necessarily preordained.
Second, Earth systems do often have buffering capacities, feedback mechanisms and multiple degrees of freedom in responding to changes. These do not necessarily always operate so as to restore or maintain a (single) balanced state, but they do, along with the first-order constraints imposed by general laws, constrain what can happen.
Third, some systems oscillate (not always regularly, of course) between different sorts of imbalance—for instance, aggradation vs. degradation in river systems. Where this occurs, the system must sometimes be in or near the balanced steady-state, and on average will be approaching this state about half the rest of the time. Interpreting this as a system somehow seeking steady state is like saying humans are seeking a state of partial wakefulness (just waking or falling asleep), but you can see it if you believe it.
Fourth, balanced states are often both scale and time dependent. That is, one can always make the focus either vast or tiny enough to find a state of balance, or find some period of history where balance obtains. Even in the most variable systems, you can zoom into ever-shorter periods (or smaller areas) where balance temporarily prevails, and over ever-longer time spans (or broader areas), things often even out. Further, given the long time scales for many Earth systems and the generally episodic nature of change, it is often easy to find times where little or no change is occurring. Therefore, if you really want to find steady-state, you can—I guarantee it.
Finally, as alluded to earlier, model assumptions based on balance-of-nature ideas are often useful, even when the assumptions are untrue.
Taken together, these aspects of nature can easily give an impression of a balance of nature to those who are looking for it.
How I Stopped Worrying and Learned to Love Nonequilibrium
Let me make clear—I am not saying that steady-state and other equilibrium conditions do not exist, or even that they are rare. I am saying that there are often multiple equilibria for a given environmental system, and that equilibria or steady-states are not in general more common, important, or “normal” than disequilibria and nonequilibria. Further, I happily acknowledge, and sometimes make use of, the convenient fiction of steady-state as a reference condition or simplifying model assumption.
Admitting that there is not, or may not be, a balance of nature, does not imply a lack of any kind of order, regularity, or predictability. It does change the context of predictability, but this can be dealt with, as a vast literature on complexity, nonlinear dynamics, nonequilibrium dynamics, multiple stable states, path dependency, and state-and-transition models in geomorphology, ecology, pedology, and other sciences shows.
There are certain aesthetic virtues to symmetry and orderly patterns. Belief in balance and order may bring some inner peace and reassurance. But far more compelling, to me, is the aesthetic joy one can take in the infinite variety of nature, and the fact that each landscape or ecosystem is in some nontrivial respects absolutely unique.
Heraclitus said “you cannot step twice into the same river.” Nature as we view it now or reconstruct it in the past is a historically contingent snapshot. There is no single way that it is or was supposed to be, and more than one possibility for the future. Our world is, therefore, like many of us: not simple to understand, but easy to love.