Environmental Engineering Reference
In-Depth Information
been evoked as a reason to restore, at least until
recently. Indeed, restorative activities undertaken in
this pragmatic spirit are most often referred to as
rehabilitation, in the sense given to this term in
Chapter 1 and in the SER Primer (SER 2002). But this
should assuredly not be taken as a hierarchical level
of lesser importance or difficulty as has often been
done in the past. Indeed, from a global-society point
of view the contrary is probably true.
The third reason to restore encompasses the first
two reasons and seeks to reconcile them. Ecosystem
goods and services, the life-sustaining products of
our stock of natural capital (Jurdant
et al.
1977,
Costanza & Daly 1992, Daily 1997, Clewell 2000a, Daly
& Farley 2004) are best assured by ecosystems that
are functioning in a healthy fashion, in the broad
sense that ecosystem health was defined in Chapter 1
(Cairns 1993, Daily & Ellison 2002).
reason 1, above), but also has positive functional or
dynamic effects at the level of ecosystems. For ex-
ample, an increase in species richness can contribute
to an increase in ecosystem productivity (the rivet
hypothesis; see Fig. 4.3 in this volume). But it is of
course important to distinguish between native and
introduced species, and also to consider the timeframe
of most relevance when considering productivity. In
restoration ecology, species richness cannot without
risk be considered in neutral terms in the sense of
Hubbell's (2001) neutral theory of biodiversity.
Indeed, a first pertinent question of a general nature
is: in a given situation, how do biodiversity changes
-
losses
, at genetic, specific or ecological levels,
gains
, of invasive or introduced species, or intention-
ally reintroduced natives - affect ecosystem func-
tioning and ecosystem integration in landscapes and
bioregions? This is of course a relatively long-
standing issue in ecology (Schulze & Mooney 1993,
Ernest & Brown 2001, Kinzig
et al.
2001, Giller &
O'Donavan 2002, Loreau
et al.
2002, inter alia), but
one which can clearly be much further elucidated
in the context of ecological restoration projects than
anywhere else. Similarly, it is important to enquire
in each specific situation where restoration is being
considered, do species numbers really matter? Are some
species redundant? Do
driver
,
passenger
or
keystone
species
really exist, and if so how do they interact
with each other? Does redundancy really exist, as some
suggest, in natural or socio-ecological systems? This
broad issue was touched upon in Chapter 2 in this
volume. Here we shall refer to a state-of-the-art ana-
lysis presented by Lawler
et al.
(2001), who identified
four unresolved issues.
16.2 Eight hot topics
What are the major challenges to ecological modelling
and theory from the twin points of view of the
science and the practice of ecological restoration?
In the broad context, at least eight hot topics in
theoretical ecology should be mentioned, with special
emphasis on the ecosystem and landscape levels,
where disproportionately little work has been done to
date in ecology.
1
Biodiversity and its role in ecosystem functioning.
2
Assembly rules and the structuring of ecosystems.
3
Ecotones, ecoclines and landscape boundaries.
4
Ecosystem resilience.
5
Ecosystem health and integrity.
6
Emerging ecosystems.
7
Socio-ecological systems and their relevance to the
setting of restoration objectives and references.
8
Linkages, re-integration and the science of sustain-
ability and ecosystem services.
1
The relationship between ecosystem functioning
and biodiversity is not well-enough established to
use as an argument for preserving biodiversity.
2
Ecosystem functioning forms an asymptote with
species richness at a relatively low number of
species.
3
Because randomly assembled communities show
that biodiversity influences ecosystem functioning,
species identity may be unimportant in some cases.
4
Dominant species may be solely responsible for
correlations between biodiversity and ecosystem
functioning.
16.2.1 Biodiversity and its role in
ecosystem functioning
It has frequently been suggested that an increase
of biodiversity has not only an intrinsic value (see
