Monday, September 5, 2016

Emergence and fire on the prairie

My son brought to my attention an Econtalk podcast  that has an interesting discussion of emergence. Here is some of the transcript.
I've become so fascinated by the prairie as a metaphor for emergent order. And some things have to emerge and grow in an organic way. And I've referenced this book--it's by Shona Brown and Kathleen Eisenhardt; it's called Competing on the Edge. It's actually a management book. It's not about emergent order per se, and it's not about wildlife or prairies literally. 
[Here is a long but beautiful quote from the book].
Imagine yourself at O'Hare at a far different time, not in 1998 but in 1898, or even in 1798, before the patchwork quilt of roads, fences, and farms had changed the Midwestern landscape forever. Around you would be an abundance of plants, long grasses of various colors, a pallette of flowers, some trees. You'd see the original "amber waves of grain." If waited a little while, you'd also see a variety of animals going about their daily ritual. You would be enjoying a living, breathing prairie that stretched a thousand miles to the Rocky Mountains. It's an ecological system that today is virtually extinct. 
Suppose you were given the task of recreating that prairie as it was 200 years ago. Assume you have no budget constraints. Also assume you cannot buy the prairie, but rather that you have to create your own. As you think about how you'd approach the problem, jot down the key steps to your solution. 
If you are like most people, at least our friends, you probably came up with a list that is something like this: 
Step 1. Buy a plot of land where prairie likely thrived in the past. For example, on the outskirts of Chicago--O'Hare. 
Step 2. Check the libraries. Look for old photos of the prairie. Obtain the most complete list available of all the plant and animal members of a prairie ecosystem. 
Step 3. Collect samples of all the relevant species, e.g., seeds of plants, male and female pairs of animals. 
Step 4. Clear the plot of land and plant your seeds, along with a few trees. 
Step 5. Release the animals into the plot of land. 
Step 6. Watch and wait. 
Perhaps you added a few steps with more intervention, like fertilization or watering. But overall, you likely suggested some kind of approach that we will loosely call "Assemble." That is, the steps you listed were to clear out your workspace, get the component plants and animals, lay out the blueprint, follow the directions, and start assembling. You'd then piece together the various components of the prairie and hope that somehow a prairie emerges. The approach is quite reasonable. It seems intuitively correct. If you were assembling a car, house, or a toaster, it would probably work. All you'd have to do is to assemble the components of the desired system on a reasonably attractive plot of land, and eventually a prairie would emerge. It makes sense, right? 
Wrong. Assembly doesn't work. At least, not for a prairie. A prairie is something that grows. It has to start small. It has pieces that interact and build on each other. Once it's up and running, the prairie works as a complex system. It is dependent on the intricate interaction of all the components of the system. A prairie cannot be brought to life with one abracadabra, one wave of the magic wand. 
Ecologists have in fact experimented with trying to grow prairies. Early experimenters took the assemble approach. But they ran into complications. Urban weeds are one such complication. Relative to most prairie species, these noxious weeds are aggressive and fast-growing. Given a chance, these tough weeds will muscle out the more timid prairie species and prohibit them from thriving. Knowing this, early ecologists began their work by clearing their field of weeds and then planting prairie grass seeds. Then the prairie flourished, right? Wrong. The prairie never emerged from these cleared plots. What happened? The problem with this logic is that the first plants to sprout and grow in a freshly cleared field, the most aggressive, fast-growing weeds. So even though the prairie seeds are planted first, the urban weeds that go over the cleared so and the prairie never took hold. 
... In later experiments, ecologists extended the grow-not-assemble approach. In particular, one successful experiment in Illinois, a college grew a prairie savannah--a prairie with trees--that began by planting a sample of choice prairie savannah weeds, seeds, and wooded weed-filled fields on the outskirts of Chicago. 
Butterflies came back, with the savannah.... As the experiments continued, ecologists learned more lessons about recreating prairies. They learned that order matters. Reversing the introduction of one species and another, e.g., reversing the order of entry of two predators, alters the ecosystem that emerges. Adding or subtracting of species also alters the system, affecting its final states and its resilience to change. Perhaps the most subtle lesson to learn was that not all of the essential ingredients to growing a prairie savannah are visible at the end. Ecologists learned this lesson when they were stymied in their efforts. They were close to creating a prairie, but something was not quite right. Half-breed prairies were being created. A mixture of prairie and non-prairie species. The experiments didn't seem to be capable of evolving into that final step of a pure prairie. Ecologists searched for key components of a prairie that might be missing. But this was the whole problem: they were searching for something that they thought should be there but wasn't. Instead, ecologists should have been looking for something that had been there, but did not stay. In other words, a fleeting member of the prairie system, a missing link. 
Was there a missing link that was not present in the mature prairie but was essential to growing it? Yes--that missing link was fire. Initially, ecologists failed to introduce fire into their experimental prairie systems because its presence is not explicit in the final product. It was not an immediately obvious candidate to be deliberately added. Moreover, although ecologists were trying to mimic nature and minimally manage the fields of emerging prairie, the incidence of wildfires was far lower than it would have been in a true, natural setting. Without fire, ecologists could not create the elusive, pure-bred prairie. Fire triggers certain prairie seeds to sprout and eliminates many fire-intolerant urban plants. Without fire, there is no prairie.
What do we learn about emergence?
The sum is greater than the parts.
The prairie is a lot more than the individual components that you see today.

Are there some lessons here for self assembly of material systems and biomimetics?


  1. In my view the example given here is not a very strong example of emergence; one could argue with the same validity that assembly works, but that not all ingredients were used.
    Or that "prairie" is not a state variable (i.e. even if you put all the flora and fauna in, that does not guarantee you get the same outcome).

    Bottomline: "the prairie is more than the components we see today" does not prove it's an emergent phenomenon.

    So, thinking about it, my hypothesis (lesson, discussion opener, ...) would be: despite being self-assembled, the state of self-assembled systems need not be equilibrium states, and may be path variables.
    Maybe this goes against first intuition, but self-organization (producing self-organized order, i.e. emergence) is indeed often far from equilibrium - though (self-organized) thermodynamic ground states obviously are ordered one way or the other (hence order parameter).

    Aside: I do think ecosystems are emergent steady states, and I do think self-organization is a better term because assembly carries a connotation of top-down building. Emergence means emerging order, and order is (somewhat) synonymous with organization.

    My 2 cents...

    1. Thanks for your thoughtful comment.

      I think you have sharpened some of the issues.