Environmental Engineering Reference
In-Depth Information
frequency as the mean number of events per time period, return interval, cycle
or turnover time, rotation period as the mean time to disturb an area equivalent
to the study area, predictability, area disturbed, magnitude of intensity and
severity, and synergism as a measure of the effects on the occurrence of other
disturbances. In each case disturbance statements have to be specified for both
the spatial and temporal scale..
This notion of disturbance provides a provisional concept only. In the
proceeding examinations further insights will expand the notion of disturbance
putting it into relation to other concepts, such as ecosystem resilience or the
adaptive cycle. If ecosystem resilience - which represents the main topic of
this thesis - is conceived from an operational perspective the disturbance
regime provides the to what part of the ecosystem resilience analysis.
There is another important point with respect to the two distinct resilience
definitions. Although being only a different aspect of ―stability‖ the emphasis
on one of the two distinct stability properties - ecosystem resilience or
engineering resilience - can be decisive. It can result in different views of
nature, different basic assumptions e.g. the debate about alternate stable
regimes, different views on stability itself and as an outcome of the whole to a
different environmental management which is characterized by entirely
different methods. The Resilience Alliance considers ecosystem resilience to
be the more valuable concept both theoretically as well as operationally.
1.2.
E
NVIRONMENT
R
ESILIENCE
The resilience of an ecological system relates to the functioning of the
system, rather than the stability of its component populations, or even the
ability to maintain a steady ecological state [23] Resilience in ecological
systems is not easily observed, and there seems at present to be no agreed
relationship, for example, between the diversity of ecosystems and their
resilience Thus many tropical terrestrial ecosystems have stable and diverse
populations but are relatively low in resilience, while similar ecosystems in
temperate regions with apparently low diversity can exhibit greater resilience.
Coastal and estuarine ecosystems are typically of low species diversity since
they experience periodic physical changes and have a high degree of organism
mobility. Resilience can be defined in many ways. It is the buffer capacity or
the ability of a system to absorb perturbations, or the magnitude of disturbance
that can be absorbed before a system changes its structure by changing the
variables and processes that control behaviour By contrast other definitions of
