Community Resilience to Climate Change: Theory, Research and Practice

54 systems (Anderies et al. 2006). Category III: Normative concept Class 9: Metaphorical definition In a metaphoric interpretation, the concept of resilience means “flexibility over the long term” (Pickett et al. 2004:381) and is viewed as desirable as such. Class 10: Sustainability-related definition Resilience has been suggested as to be one of the guidelines for a conception of strong sustainability (Ott 2001, 2003, Ott and Döring 2004). Hereby the term refers to the maintenance of natural capital in the long-term in order to provide ecosystem services that provide instrumental as well as eudaemonistic values for human society. These ten definitions together represent the intension of the term resilience. Even though they are all related to the original, descriptive concept of resilience, as introduced by Holling (1973), the term has been transformed considerably. The conceptual development of resilience has been recently reviewed by Folke (2006), who made a distinction between an early interpretation of resilience, which focuses on the robustness of systems to withstand shocks while maintaining function, i.e., ecosystem or ecological resilience, social resilience, and a subsequent interpretation, which refers more to the interplay of disturbance and reorganization within a system as well as to transformability, learning and innovation, i.e., social-ecological resilience. Although Folke (2006) points to the change in the specific meaning of resilience our own interpretation of the conceptual development of resilience highlights the distinct use of the concept of resilience within the spectrum of scientific disciplines. Thus, the subsequent sections contrast (a) a clearly specified concept of resilience that is merely used in ecology with (b) a vague and malleable concept of resilience that is used as a communication tool across different scientific disciplines and between science and practice. RESILIENCE AS A DESCRIPTIVE ECOLOGICAL CONCEPT This section describes a descriptive, ecological concept of resilience in more detail. By definition a descriptive concept of resilience excludes normative dimensions. Resilience may be viewed as either desirable or undesirable in a specific case; this depends on the state of concern. This means, a degraded savannah or a polluted lake can be highly resilient but at the same time undesirable from an anthropocentric perspective (Carpenter et al. 2001, Carpenter and Cottingham 2002, Walker et al. 2002). In a descriptive sense, the concept of resilience points to a nonequilibrium view on ecological systems (Wallington et al. 2005), that is, it assumes the existence of alternative stable regimes (Holling 1996). For example, a savannah may exhibit either a locally stable grassy regime or a locally stable woody regime depending on the value of some driving factors, such as rainfall, grazing pressure and fire events (Walker 2002). There is strong evidence that most ecosystem types can exist in alternative stable regimes, for instance lakes, coral reefs, deserts, rangelands, woodlands, and forests (Folke et al. 2004, Walker and Meyers 2004). However, the weight of empirical evidence shows that the relative frequency of the occurrence of alternative stable regimes across systems is higher for systems controlled by environmental adversity, e.g., deserts, arctic tundra, or savannahs, than those controlled by competitive adversity, e.g., forests or coral reefs (Didham 2006). A mathematical model of this behavior termed “bistability” is provided by phase plane and bifurcation diagrams proposed by Ludwig et al. (1997, 2002). Formally a systemexhibits alternative basins of attractionwhen a fast state variable, e.g., annual grasses, macrophytes, responds to changes in a slow variable, e.g., long-lived organisms, nutrient storages, by a backward-folding curve, as shown in Fig. 1. Because of the backward fold, two stable basins overlap, separated by an unstable one over a given range of the slow variable (Scheffer et al. 2001, Scheffer and Carpenter 2003, Schröder et al. 2005). When the system is in a regime on the upper blue branch of the folded curve in Fig. 1, it cannot pass to the lower green branch smoothly. Instead, when the slow variable changes sufficiently to pass the critical value, i.e., the ecological threshold (ET1), a catastrophic transition to the lower branch occurs, either caused by only an incremental change in conditions or due to a bigger disturbance. To induce a switch back to the upper branch it is not sufficient to restore the slow variable to the value before the collapse. Instead, one needs to go back further, beyond the other switch point (ET2), at which the system recovers by shifting back to the upper branch, a pattern known as “hysteresis” (Scheffer and Carpenter 2003, Groffman et al. 2006, Briske et al. 2006). In contrast to a narrow equilibrium view, this indicates the importance of the boundaries of a basin of attraction and the ease or difficulty with which a system could be moved out of this basin (Holling 1973, 1996, Gunderson and Holling 2002). For example, shallow lakes can exhibit two stable regimes with respect to nutrient load, i.e., a clear-water regime with aquatic plants and a turbid regime without vegetation. If the lake is in the clear-water regime, an increase of the nutrient level will lead to a gradual and moderate rise in turbidity until the critical turbidity for plant survival is reached. At this point, vegetation collapses and the lake shifts to the turbid regime. Reduction of nutrients after this catastrophic transition does not result in a return of plants immediately. However,