Resilience, Ecological

Natural systems are dynamic, complex, and interdependent. Ecological resilience describes the amount of change such a system can undergo and still remain within the same state. This definition is also referred to as engineering resilience, since it concentrates on stability at a presumed point of equilibrium, resistance to a disturbance, and the speed of return to equilibrium.

As applied to ecosystems, or to integrated systems of people and the natural environment, ecological resilience therefore has three defining characteristics: the amount of change a system can undergo and still retain the same controls on function and structure, the degree to which a system is capable of self-organization, and the ability to build and increase the capacity for learning.

The key concepts to explain ecological resilience are nonlinearity, adaptive cycles, panarchy, adaptability, and transformability. Nonlinearity can be illustrated by a ball in a basin. The state of this twodimensional system is the ball. Its dynamics cause it to move to the bottom of the basin. The system can change regimes either by the state changing, or through changes in the shape of the basin.

Ecological systems are never static, and they tend to move through four recurring phases, known as adaptive cycles, the second key concept. Generally, the pattern of change is a sequence from a rapid growth phase (exploitation) through a conservation phase in which resources are increasingly unavailable, followed by a release phase that quickly moves into a phase of reorganization, and then into another growth phase. For example, a tropical rain forest may be afforested, established, destroyed by a fire, then regrow again. Multiple possible transitions among the four phases are possible and the pattern may not reflect a cycle. The growth and conservation phases together constitute a relatively long developmental period with fairly predictable, constrained dynamics; the release and reorganization phases constitute a rapid, chaotic period during which capitals (natural, human, social, built, and financial) tend to be lost and novelty can succeed.

The third element is panarchy. Adaptive cycles never occur only on one scale, but all systems exist and function at multiple scales of space, time, and social organization, and the interactions across scales are fundamentally important in determining the dynamics of the system at any particular focal scale. This interacting set of hierarchically structured scales has been termed a panarchy.

Fourth, adapatability is the capacity of systems to alternate regimes (sometimes called adaptive capacity). It involves either or both of the following two abilities: The ability to determine the trajectory of the system state (the position within its current basin of attraction), and the ability to alter the shape of the basins, that is, move the positions of thresholds or make the system more or less resistant to perturbation. The abilities to affect both of these are determined by a combination of attributes of both the social domain and the ecosystem.

The fifth and final key concept of ecological resilience is transformability. In cases where a system is already in an undesirable regime and efforts to get it back into a desirable regime are no longer possible (or worse, make the undesirable basin larger), one option for resolving the predicament is transformation to a different kind of system—new variables, new ways of making a living, different scales—a different panarchy.

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