International Encyclopedia of Systems and Cybernetics

The capacity of an adapting and/or evolving system to bounce back to dynamic stability after a disturbance.

In a more general meaning, resilience includes the system's ability to create new conditions of fitness for itself whenever necessary.

C.S. HOLLING describes resilience as: "… the ability of a system to maintain its structure and patterns of behaviour in the face of disturbance"… He adds: "The size of the stability domain of residence, the strength of the repulsive forces at the boundary, and the resistance of the domain to contraction are all distinct measures of resilience" (1986).

He also observed: "Resilience determines the persistence of relationships within a system and is a measure of the ability of this system to absorb changes of state variables, driving variables, and parameters, and still persist. In this definition, resilience is the property of the system and persistence or probability of extinction is the result" (1976, p.83).

This condition is as well formulated by T.F.H. ALLEN and T.B. STARR: "The ability of a system to maintain its structure and general patterns of behavior when displaced from its equilibrium condition" (1982, p.276).

These authors add: "More resilient systems are those which can return to an equilibrium condition despite large displacement" (Ibid).

Resilience should thus not be confounded with dynamic stability, even if the latter is generally recovered as a result.

Resilience is in a trade -off relation with stability: some limited instability is a favourable survival condition.

Resilience may be greatly reduced or even suppressed when a system is driven too close to a threshold of instability by excessive pressure. This has been for instance frequently the case after overfishing of some marine or lake species: the population may collapse irreversibly, even if the excessive pressure is belatedy lifted.

However, within reasonable limits, as stated by W.D. GROSSMANN and K.E.F. WATT: "Systems will develop resilience and maintain it only if the environment of the system continually confronts the system with varying challenges. Resilience thus evolves in a way similar to human immune capabilities" (1992, p.16).

The same authors also state that: "… complexity is one perequisite for resilience" (p.22).

In this way the notion of resilience is connected to ASHBY's law of requisite variety: no variety, no resilience… and no viability.

C. HOLLING states: "There are two resilience measures: Since resilience is concerned with probabilities of extinction, first, the overall area of the domain of attraction will in part determine whether chance shifts in state variables will move trajectories outside the domain. Second, the height of the lowest point of the basin of attraction… above equilibrium will be a measure of how much the forces have to be changed before all trajectories move to extinction of one or more of the state variables" (1976, p.86).

G. BROEKSTRA writes: "The new fluctuation paradigm views organizations… as instances of stable chaos or coherent spots of vorticity in a turbulent background… It implies the recognition that resilience rather than stability is crucial for the organizational survival and that resilience implies that the organization is generally far from its equilibrium state" (1992, p.1028).

As also noted by BROEKSTRA, "… all fits are only temporarily effective" (p.1029).

HOLLING has observed that there is a kind of trade-off between resilience and productivity. The latter can be increased, and even much increased, allowing for a loss of resilience, and conversely. At the limit, as stated by C. HOLLING and M. GOLDBERG, it becomes a matter of changing "…the emphasis from maximizing the probability of success to minimizing the chance of disaster. It shifts the concentration from the forces that lead to convergence on equilibrium to the forces that lead to divergence from a boundary. It shifts our interest from increased efficiency to the need for resilience" (1971).