Environmental Engineering Reference
In-Depth Information
different structure Resilience, understood in this way, is the ―magnitude of
disturbance that can be absorbed before the system changes its structure by
changing the variables and processes that control behavior‖[16]
Note that both definitions of resilience use several concepts that are hotly
contested among ecologists. For instance, the first definition implies an
assumption of global stability, i.e. an ecosystem has only one equilibrium or
steady state and the focus of study is on slow dynamics near this stable
equilibrium [17]. The second definition presupposes the existence of
alternative stable regimes, i.e. ecological systems can exhibit a shift from one
regime to another that is controlled by a different set of variables [15,16]
Focus of interest are slow dynamics in a region that separates two alternative
stable basins. In order to understand the ecosystem resilience concept entirely
we have to go into these concepts in a more profound way.
The terminology provides a good tool in order to distinguish the two
stability properties which are associated with the term resilience. Definition
corresponds to the property resilience which is defined as ―tendency of a
system to recover or return to (or close to) its original state after a
perturbation‖. Definition matches the property ―robustness‖ or the ―tendency
of a system to remain unchanged, or nearly unchanged, when exposed to
perturbations‖. Hence, the two different definitions of the resilience concept
reflect two different properties of ecological systems: resilience and robustness
or persistence, respectively. Both definitions are contrastive aspects of the
common qualifier ―stability‖.
In the Dictionary of Ecology, Evolution and Systematic [18] the suggested
definitions for stability and resilience both reflect the different usage of
resilience and the confusion of two or even more distinct stability properties.
The authors define stability as ―resistance to change; tendency to remain in, or
return to, an equilibrium state; the ability of populations to withstand
perturbations without marked changes in composition‖ and resilience as ―the
ability of a community to return to a former state after exogenous disturbance;
the capacity to continue functioning after perturbation‖. In this connection,
aspects of robustness and resilience are intermixed. It is important to separate
stability properties meticulously in order to be able to communicate clearly.
The distinction of the two definitions for resilience is also highlighted by
the Resilience Alliance. The research group uses a different terminology and
provides the term engineering resilience for the property resilience and the
term ecosystem resilience or ecological resilience for the stability property
robustness. The term vulnerability is used, in turn, as an antonym for
