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A fundamental concept in considering ecological resilience is that while stability is defined as a system near to an equilibrium state that we might consider the reference condition, resilience is most often thought of as the amount of disturbance a system can be subjected to before a change in state occurs (Gunderson 2000). A certain amount of caution should be exercised in not interpreting this equilibrium state as good ecological status (GES), as the environment could already have been significantly affected and thus already be in an altered stability domain. Folke (2003) illustrates in figure 3.5 how humans can drive a decrease in resilience that ultimately leads the ecosystem into a different state, termed ‘stability domain’. As phosphorus accumulates in the soil and mud of the lake system the stability domain is reduced and the subsequent pressure of flooding or over exploitation of predators causes the system to shift into a turbid eutrophied water state.

Figure 3.5 Shifts between states in lakes from human-induced reduction of resilience

1 – free flowing river   2 – regulation, over-exploi-      3 – decreased variability         4 – regulated water-
                                     tation of flow, pollution            increased episodes of low,       course with low
                                                                                 flow, drought and flooding       genetic diversity

Source: ETC/ICM, Based on Folke 2003
Note: The figure is an illustration using the ball and cup view of stability. Valleys are stability domains and balls the system, with arrows indicating disturbance. Engineering resilience is defined by the slopes, while ecological resilience is the width of the stability domain (Gunderson 2000).

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