Community Resilience to Climate Change: Theory, Research and Practice

55 the backward switch happens at much lower nutrient level than the forward switch. Thus, often reduction of the nutrient level to values at which the lake used to be clear and vegetated will not lead to restoration of that state (Dent et al. 2002). Correspondingly, in a descriptive sense the resilience of an ecological system can be defined as “the magnitude of disturbance that can be absorbed before the system shifts to another basin of attraction” (cf. Class 2 in Table 1; Gunderson and Holling 2002, Bellwood et al. 2004, Nyström 2006). In addition, some authors distinguish several characteristics or aspects of resilience, respectively (cf. Class 2a and 2b in Table 1). The descriptive ecological definitions described above (Class 1–4 in Table 1) differ with respect to the criteria they provide as means to determine if a system is resilient and to what degree. In this article we focus on the extended-ecological definition of resilience in order to point to the concept of slow controlling variables, which can be used to operationalize resilience, and thus to the importance of a quantitative and measurable approach to resilience. Fig. 1. Bifurcation diagram of a system described by a fast variable and a slow variable: the stable regimes are given by the blue and green solid lines and the boundary of the basins of attraction, i.e., unstable state, by the dashed line. ET1 and ET2 represent ecological threshold points (modified from Scheffer and Carpenter 2003) Indeed, a crucial question for scientific progress is: are there any possibilities to estimate or measure the resilience of an ecosystem? Any operational interpretation of resilience means to specify resilience “to what” and “of what” (cf., Class 4 in Table 1; Carpenter et al. 2001) and channels into a comprehensive resilience analysis (Walker et al. 2002, Brand 2005). This also means to inquire which of the criteria for resilience described in definition Classes 1–4 are in fact meant as criteria that must be measured to assess and/ or quantify the resilience of an ecosystem. The”to-what part” of the analysis explicates to what exactly a certain regime of an ecosystem should be resilient. This corresponds to specifying the disturbance regime, e.g., the kind of disturbances, their frequency, and intensity (Pickett and White 1985, White and Jentsch 2001), which may include both human disturbances, e.g., pollution pulses or habitat fragmentation, and natural disturbances, e.g., hurricanes or floods, as well as possible multiplicative effects (Vinebrooke et al. 2004). The subsequent “of-what part” explicates the specific regime that is meant to be resilient to the identified disturbance regime. This part of the analysis is comprised of several steps. Step one means to assess which ecosystem processes or ecosystem services (see Jax 2005) of the regime are of primary concern on which spatial and temporal scale (Walker et al. 2002). Step two explicates the self- identity of the selected regime delimited in step one. This includes explicating the precise boundary of the regime, the set of variables of interest, and the expected internal degree of relationships, as well as the component resolution (Jax et al. 1998, 2006, Cumming et al. 2005). Step one and step two are dependent on societal values or normative judgments and should therefore incorporate environmental assessment procedures and participative deliberations (Plachter 1994, Jax and Rozzi 2004).