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The Renewal, Growth, Birth, and Death of Ecological Communities

Perhaps I have been in the game too long to be sympathetic to "Chicken Little" stories of catastrophe. In 1969 Time magazine entitled an article "The New Jeremiahs" and featured six scientists who were prophesying doom—an environmental doom that may have been novel then but that is familiar now. I remember they included Paul Ehrlich, Barry Commoner, Ken Watt, and—me! Now, twenty-five years later, I find the articles that repeat the same litany of doom to be not necessarily wrong, but tiresome, unconvincing, and weak.

What is really disturbing is that they ignore the remarkable advances, learning, and understanding that have occurred in the intervening years. They ignore the opportunities for conversations among and actions by previously polarized individuals that increase both understanding and the ability to develop and apply integrated and adaptive policies. The topics revolve around five interrelated themes—regional resource management and development, ecosystem restoration, sustainable development, global change, and biodiversity. Population growth and technology drive them all.

The last twenty years have seen a stunning advance in understanding how the planet has evolved and functions. The reconstruction of the composition of our atmosphere over the last 160,000 years (using bubbles trapped in the Vostok ice core from Antarctica) and its correlation with climate (using proxy biological and chemical signals) can be seen as an engrossing tour de force of international science. It is also useful for politicians. It tells them that the present concentration of carbon dioxide in our atmosphere is higher than it has been for the last 160,000 years.

However narrow the mainstream of molecular biology might be, it too has yielded techniques that now are transforming the evolutionary, ecological, and conservation sciences. Is it true that we can trace all human mitochondrial DNA back to an "Eve" in Africa? Biologists now can certainly unravel affinities in related groups of species and individuals and can join the geophysicists in compelling reconstructions of the past. At the least, molecular biology can help put our present problems in a perspective—from the role of past extinctions to present declines in biodiversity.

But we must recognize what this means and the challenge it presents. The relevant biophysical processes operate over an enormous scale, potentially from soil processes operating with time constants of hours or days in meter-square patches; to ecosystem successional processes of decades to centuries covering tens to thousands of square kilometers; to global biotic processes involved in the regulation and isolation of elements like carbon, which have time lags of millennia and a global impact. This is why satellite imagery, remote sensing, and geographic information systems, now routinely available to analyze patterns, are of such major consequence. Computer advances have made it possible to visualize complexity in both space and time. It is a picture of discontinuous behavior, of multiple stable states, of the interaction between slow forces that accumulate environmental capital and fast processes that slowly exploit, suddenly release, and renew the capital. It is as far a cry from public perceptions of fragile, stable, and equilibrium nature as could be imagined (see box: "Five Paradigms of Nature"). And that knowledge too is useful. It is the foundation for the regional experiments in adaptive policy design and management that are as much examples of institutional learning as they are of using science for public policy.

On Theory

"Don't give me academic theory; give me practical advice and actions!" That's what I heard, appropriately, in the certainty of the 1970s. But at a time of confusion, such as the 1990s, promising and relevant theory is the only antidote to dated ideology or belief. And the intriguing paradoxes that have emerged—by applying past incomplete theories of equilibrium, of gradual change, and of control—have set a foundation for new theories of discontinuous change and evolution. Oddly, one of the most practical things we could recommend now is massive support for the expansion of new theory.

The intensity and global nature of the changes now taking place are moving the planet and its occupants into totally new behavior. In this transformation some consequences can be predicted, others will be uncertain, and still others will be unpredictable. It is essential to be guided by theories of change that can contain short- and long-term changes, gradual and abrupt ones, and dynamic and structural ones. The theories will determine the questions we ask, the problems we perceive, the data we collect and analyze, and the policies and actions we initiate. Theories that do not match the problem can be at best delusions and at worst dangerous.

The discovery of the hole in the ozone layer is an example. It was not detected initially by satellite imagery, because the smoothing algorithm applied to the data assumed that abrupt changes could only be caused by instrument glitches. The implicit theory presumed gradual, continuous change in atmospheric chemistry and chemical composition.

There are also many examples of theories that have had more disastrous consequences. One recent example is the devastating events in the Sahel of Africa. External changes in precipitation were partially responsible for the collapse, but such changes have occurred and been absorbed before. The response was exaggerated by increased vulnerability of a culture and ecosystem caused, in part, by development aid that broke the patterns of nomadic movement and social adaptations that had evolved in these semi-arid savannas. No adequate theory was utilized to relate the resilience of local ecosystems and the adaptive flexibility of people to drought and the migrations of people and animals.

Regional changes such as the Sahel's and the anticipated global ones make the world we are entering one of surprises, with consequences that threaten to overwhelm the adaptive capacities of individuals, business, and government. Investing in the development and testing of usable and useful theory is therefore not an academic luxury, but a practical necessity, particularly at times of such profound change.

The New Four-Phase Model

The traditional view of ecosystem succession has been seen as: exploitation, in which rapid colonization of recently disturbed areas is emphasized, and conservation, in which slow accumulation and storage of energy and materials are emphasized. An economist might use such labels as market and innovation for the exploitation phase and monopolist or hierarchy for the conservation phase.

But revisions in understanding indicate that two additional functions are needed. The first can be called release, or creative destruction , a term borrowed from the economist Schumpeter, in which the tightly bound accumulation of biomass and nutrients becomes increasingly fragile (overconnected, in systems terms) until it is suddenly released by agents such as forest fires, insect pests, or intense pulses of grazing. The second is one of reorganization, in which soil processes of mobilization and immobilization minimize nutrient loss and reorganize nutrients to become available for the next phase of exploitation. An economist might use such labels as invention and reinvestment for this stage.

During this four-phase "infinity sign" cycle (see figure on previous page), biological time flows unevenly: from the exploitation phase, slowly to conservation, very rapidly to release, rapidly to reorganization, and rapidly back to exploitation. During the slow sequence from exploitation to conservation, connectedness and stability increase and a "capital" of nutrients and biomass is slowly accumulated. That capital becomes more and more tightly bound, preventing other competitors from utilizing the accumulated capital until the system eventually becomes so overconnected that rapid change is triggered. The agents of disturbance might be wind, fire, disease, insect outbreak, or a combination of these. The stored capital is suddenly released and the tight organization is lost to allow the released capital to be reorganized to initiate the cycle again.

This pattern, though drawn as continuous loops, is actually discontinuous. It depends on changing multistable states to trigger and to organize the release and reorganization functions. Instabilities and chaotic behavior trigger the release phase, which then proceeds in the reorganization phase, where stability begins to be reestablished. In short, chaos emerges from order, and order emerges from chaos! Resilience and recovery are determined by the fast release (or creative destruction) and reorganization sequence, whereas stability and productivity are determined by the slow exploitation and conservation sequence.

Moreover, there is a nested set of such cycles, each with its own range of scales (see figure). In the typical boreal forest, for example, fresh needles cycle yearly; the crown of foliage cycles with a decadal period; and trees, gaps, and stands cycle at a period of about a century or more. The result is a hierarchy in which each level has its own distinct spatial and temporal attributes.

A critical feature of such hierarchies is the asymmetric interactions between levels. In particular, the larger, slower levels maintain constraints within which faster levels operate. In that sense, therefore, slower levels control faster ones. If that is the only asymmetry, however, it would be impossible for organisms to exert control over slower environmental variables. This is the criticism that many geologists make of the Gaia theory: How could slow geomorphic processes possibly be affected by fast biological ones? However, it is not broadly recognized that the birth, growth, death, and renewal cycle transforms hierarchies from fixed static structures to dynamic entities whose levels are vulnerable to small disturbances at certain critical times in the cycle. That represents a transient but important bottom-up asymmetry.

There are two key phases in which slower and larger ecosystems components become briefly vulnerable to dramatic transformation because of small events and fast processes. One occurs as the system slowly moves toward maturity, when it becomes overconnected and brittle . There are tight competitive relations among the plant species. The system is highly stable (i.e., fast return times in the face of small disturbances), but from a resilience perspective, the domain over which stabilizing forces can operate becomes increasingly small. Vulnerability comes from such loss of resilience. The system becomes an accident waiting to happen.

In the boreal forest, for example, the accident might be a contagious fire that becomes increasingly likely as the amount, extent, and flammability of fuel accumulate. Or it could be a spreading insect outbreak triggered as increasing amounts of foliage both increase food and habitat for defoliating insects and decrease the efficiency of search by their vertebrate predators. It is also the phase where, in human organizations, the rebellion of aggressive interest groups can precipitate an inexorable demand for change.

During the reorganization phase, small and fast variables can also dominate slow and large ones. The system is underconnected, with weak organization and weak regulation. As a consequence, it is the phase most affected by probabilistic events that allow a diversity of entrained species, as well as exotic invaders, to become established. On the one hand, it is the phase most vulnerable to erosion and to the loss of accumulated capital. On the other hand, it is the stage from which jumps to unexpectedly different and possibly more productive systems are possible. Instability comes from a loss of regulation, rather than from the brittleness of reduced resilience. It is the phase in a system—ecological or human—where the individual or small groups of individuals can make the greatest structural change for the future.

This new view of alternative phases in a cycle of birth, growth, death, and renewal seems to underlie any complex adaptive system—ecological certainly; maybe human, institutional, and societal as well. The four-phase system, and viewing Nature and human institutions on multiple scales of time and space, are two of my proposed foundations for new theory. Does such a view have generality? Does it suggest what to do, and equally important, what not to do? If so, then a possible foundation exists to turn sustainable development from an oxymoron into a plan of action.