Environmental Engineering Reference
In-Depth Information
ecosystem are represented' requires attention for the
problematic relationship between ecosystem function-
ing and species richness (see Chapter 2). Ecosystem
functions include productivity, nutrient cycling,
decomposition and so on. In restoration projects that
make use of functional groups, it is often assumed, or
hoped, that the effects of increasing species richness on
ecosystem productivity probably works through
changes in functional diversity. However, there is still
an unsolved dilemma that requires attention. Some
experimental results favour the
redundant - species
hypothesis
(i.e. only a few keystone species contribute
to the productivity of the ecosystem), while others
support the
rivet hypothesis
, whereby almost all or a
minimum number of species essentially contribute to
ecosystem productivity (for further reading, see e.g.
Loreau
et al
. 2002 ).
We agree with the criterion that the restored ecosys-
tem should be 'suitably integrated into a larger ecolo-
gical matrix existing within the landscape, with which
it interacts through abiotic and biotic fl ows and
exchanges'. On this subject, readers should also refer
back to Chapter 4, where the 'Landscape Functional
Analysis' approach was introduced for monitoring and
evaluating ecological restoration projects, and also
study Chapter 5, which presented the basic compo-
nents of modern landscape ecology. Later, readers will
also fi nd much food for thought in Chapters 16-19 on
wetlands, which explicitly illustrate how ecosystems
are open systems embedded within larger landscapes.
One of the most important criteria for ecosystem
restoration as formulated by the
SER Primer
(SER
2004) is that restored ecosystems should be 'resilient'.
The reader will recall from Chapter 2 that the notion
of
resilience
is an emergent characteristic or attribute
of an ecosystem expressing its ability to return to an
earlier steady state after major disturbance. In princi-
ple, the more resilient an ecosystem (or restored eco-
system) is, the faster it returns to the previous steady
state. Here we distinguish more explicitly between
these two aspects of resilience, as they have been
named and defi ned differently by various authors of
differing backgrounds, reviewed by, for example,
Gunderson (2000) and Groffman
et al
. (2006) . Not
recognizing the difference in the practice of ecological
restoration may cause confusion. Resilience in ecologi-
cal systems ( ' ecological resilience ' ) is defi ned as the
ability to return to the previous equilibrium, or as the
magnitude of degradation that can be absorbed before
the ecosystem redefi nes its structure and develops
towards a new equilibrium. Once a system surpasses a
threshold of irreversibility, it is disturbed and may shift
to an alternative steady state, as in the above-mentioned
case of shallow lakes. Resilience in engineering systems
( ' engineering resilience ' ) is defi ned as the return time
to a previous state of relative equilibrium. Only in the
latter case can different 'degrees of ecosystem resil-
ience ' be distinguished.
This brings us to a fi nal take-home message. In this
chapter, we have tried to introduce the foundations of
ecosystem ecology, and point out that
ecosystems
are
considered the central focus of
ecological restora-
tion
. While navigating at the interface between theory
and practice, many readers may sometimes fi nd that
these two poles are incompatible. Indeed, in the resto-
ration ecology literature there is much debate on the
subject; see for example Cabin (2011).
For several reasons, we have chosen in this chapter
not to confi ne ourselves to those parts of ecological
theories about, and insights into, the structure and
functioning of ecosystems that have already been
proven to be applicable to ecological restoration. We
are convinced that gaps between theory and practice
can only be overcome once they have been explicitly
recognized, for example the recognition of problems
related to the applicability of theories of 'resilience'
and 'complexity'. We take the view that basic, curiosity-
driven science and applied science do go together, and
both are needed - from all the relevant disciplines and
professions - in order to tackle the highly complex
problems faced in most situations where ecological res-
toration is necessary. In fact, this is the critical insight
of
transdisciplinarity
and
sustainability science
(Chapters 2 and 22). We welcome and applaud initia-
tives in search of further exploring the important inter-
face between restoration ecology and the ecological
restoration of ecosystems.
ACKNOWLEDGEMENT
We are grateful to James Aronson for his indispensable
and much appreciated editorial contributions to this
chapter.
