Resilience

The concepts of resilience and the “resilient city” have gained considerable currency in recent years among urbanists, not only as they relate to ecological sustainability but also in terms of urban disaster planning and adaptations to the anticipated threats of the 21st century, among them peak oil and climate change. While resilience emerged from the ecological sciences in the 1970s, it is now widely discussed in many disciplines, and interest in its application to cities has surged since the September 11, 2001, terrorist attacks, the 2003 North American power blackout, and Hurricane Katrina. The term is sometime [Page 376]used interchangeably with sustainability, and while they may be closely related in practice, they are distinct, both semantically and theoretically. For example, while sustainability is always considered an ecological and social good, a social-ecological phenomenon may be undesirable yet still be quite resilient to change. Resilience is a function of the adaptive capacities found in nature, but when applied to human societies is highly normative and would demand an almost thorough departure from present structures and practices. At the very least, it requires an interventionist state to fund or subsidize infrastructure renewal, which may be politically controversial.

Generally, resilience is understood as the degree to which a complex system is flexible enough to respond and adapt to an externally-imposed force or change, and thus persist over time, while retaining its structure and functions. Conversely, a vulnerable system would be one in which conditions are inflexible, key resources comprise a monoculture, there is little learning capacity, and choices for addressing crises are constrained.

Resilience can be manifested in both ecologies and in human societies: Each are highly complex systems in which the interrelationships and synergies between elements are fundamentally important to their potential resiliency. Indeed, related literature explicitly recognizes social-ecological systems (SES) as the most appropriate unit of analysis, for human societies are indivisible from their biotic bases. Social-ecological systems such as cities cannot therefore be considered resilient unless these adaptive capacities are present not only in the natural environment but also within the full range of social, cultural, economic and political relationships.

The concept of resilience saw its origins during the early 1970s in the ecological sciences. Crawford S. Holling used mathematical models of natural systems to determine what makes them adaptive and resilient. Holling observed that forests have an adaptive cycle of growth, collapse, regeneration, and regrowth. In the growth stage, the ecosystem gathers biomass and becomes increasingly complex and interconnected. Eventually, self-regulation mechanisms kick in, developing efficiencies as specialized organisms fill a range of niches, and the system seeks to conserve these efficiencies. Eventually, however, the forest becomes so oriented to a particular and specific set of environmental circumstances that it can't absorb shocks, be they invasive species or changes to climatic conditions. The introduction of such elements—particularly if they are the result of violent or abrupt change—can therefore cause collapse of the ecosystem. Yet in the wake of this collapse comes the opportunity for new organisms to gain hold, which are not closely interconnected to others at first and can develop on their own. With these new opportunistic organisms come system regeneration and reorganization, as well as the beginning of a new growth stage. The ability of a system to regenerate also depends on the health of larger-scale complex systems in which they reside: If the climate is stable, the forest will regenerate.

...