Rebound effects

Many naturally growing phenomena tend to be subject to so called rebound effects.

Think of bacteria in a Petri dish with some kind of content that is not beneficial to the bacteria but also not completely lethal. Only if bacteria manage to evolve a mutation that adapts to the conditions in the Petri dish and becomes able to subsist on its contents, the population will grow. This successful adaptation however might soon lead to an over-exploitation of the resource. Once the population reaches the carrying capacity of its environment, conditions can become unsafe again. A successive adaptive effort is needed. The conditions that once were beneficial for growth do not need to be beneficial in future. They can become sub-optimal just because they once were optimal. Growth hence can cycle or spiral.

Rebound effects

The adaptive cycle

In the late 1970ies the ecologist Crawford Stanley (Buzz) Holling together with colleagues suggested a heuristic model for explaining periodic devastation and recovering cycles of forests and other ecosystems. The so called adaptive cycle model is an essential aspect in Holling's famous concept of resilience. The idea is that living systems tend to cycle through four principal phases: exploitation (r), consolidation (K), destruction (Ώ) and reorganization (α).

Adaptive cycle

A forest for instance develops from pioneer species slowly exploiting resources (r) to a state with large trees and various undergrowth species (K). In this phase, biomass and dead organic matter accumulates and makes the system gradually more vulnerable. The probability for fires or pests increases (Ώ). These disturbances may release accumulated nutrients or may let the sunlight reach the forest bottom. A phase of reorganization announces the start of a new cycle (α).

The reorganization phase may be seen as a window of opportunities for new developments. New species for instance may get a chance to enter the ecosystem, such as the decline of the dinosaurs opened a window for the spread of mammals.

The cycle shows two distinct phases: a slow forward loop, characterized by two phases of growing (r and K), and an unpredictable and rather rapid back loop of destruction and a new beginning (Ώ and α). Both loops together make the system adaptive.

Holling emphasized that such adaptive cycles can be found at all scales in ecosystems. And disturbances may propagate across scales, letting transformations on small scale trigger cascading avalanches on large scale. Holling's book Panarchy interprets numerous examples of such adaptive cycles.

In the 1980ies Holling and others expanded the model of the adaptive cycle to active adaptive management stressing that the reorganization phase in the cycle could be strategically prepared or supported, for instance by inducing or allowing for a degree of disorder in organization. Today, small forest fires for instance are often not extinguished or sometimes even intentionally sparked, in order to burn loose undergrowth that otherwise would accumulate and attract big fires. In economic management philosophy too it has become a common conception that it is good to "shake the tree" from time to time in order to promote innovation. In terms of attractor theory, one could illustrate this by attempts to keep the slopes of the attractor basin from becoming too steep in the processes of exploitation and consolidation, so that the system can shift to alternative attractors when needed. 

Clark W.C. / Munn R.E. (1986) (eds.) The Resilience of Terrestrial Ecosystems. Local Surprise and Global Change. Cambridge UP.

Gunderson L. / Holling C.S. (2001). Panarchy. Understanding Transformation in Human and Natural Systems. Island Press Washington DC.

Walker B.H. / Salt D. (2006). Resilient thinking. Sustaining Ecosystems and People in a Changing World. Island Press Washington DC.