Environmental Engineering Reference
In-Depth Information
Consequently, resilience is of limited use for management aimed to protect
ecosystems. Apart from the challenges associated with defining and measuring
resilience, it might not always be desirable to achieve high resilience of an
ecosystem because it reduces the capability of the system to move to another,
possibly more desirable ecosystem state (Walker et al.
2004
).
The concept of health for an ecosystem, by analogy with human health,
suggests that optimal ('healthy') states for ecosystems could be defined
(Scrimgeour & Wicklum
1996
). Critics of the ecosystem health concept argue
that there are no intrinsically defined optimum states of an ecosystem because
the interactions between parts are not optimised for the functioning of
the whole system (Scrimgeour & Wicklum
1996
; Calow
2000
). Applying the
proposed key attributes (vigour, organisation and resilience) of ecosystem
health would mean, for instance, that oligotrophic lakes (low productivity,
low biodiversity) would be less healthy than productive (higher vigour) and
diverse (higher organisation) eutrophic lakes (Karr
1999
). We agree with Karr
(
1999
) that such definitions of health are hard to defend on scientific grounds
and are of limited use in practical ecosystem management. The concept of
ecosystem health is evolving, and the role of socioeconomic values of ecosys-
tems including their effect on human health is emphasised to various degrees
in more recent definitions (Meyer
1997
; Rapport et al.
1999
). However, no
consistent and integrative definition of this meaning of ecosystem health has
been developed so far.
When we reduce biological integrity and ecosystem health to their essential
parts, two principal concepts emerge: we can either define the quality of an
ecosystem by its resemblance to a reference state with little human influence
(integrity) or by the capacity of an ecosystem to maintain its organisation over
time (ecosystem health). Closeness to a natural state, sometimes explicitly
defined as integrity, has been adopted by various implementations of major
environmental legislation, including the US Clean Water Act and the EU Water
Framework Directive, despite the practical problems associated with the estab-
lishment of the natural reference conditions (Karr
1991
; Lackey
2001
).
The ecosystem health concept requires a definition of a 'normal' or desired
state to be operational. If the natural state is used as benchmark, then the
definition of ecosystem health essentially merges into the concept of ecological
integrity, with a stronger emphasis on stability and resilience. We argue that
there is no objective ecological basis that could justify the sole focus on a
natural reference in the definition of ecological quality, and we concur with
the argument of Freyfogle and Lutz Newton (
2001
) that subjective values of
society are needed to decide whether a particular ecosystem state or ecological
process is good or bad. We do not argue against 'naturalness' as a quality
criterion for ecosystems but we emphasise that the ascription of value to
'naturalness'
is a domain of society and cannot be inferred solely from
