Concepts in restoration ecology - Restoration Ecology - page 23

Ulanowicz (1997) argued that ecosystem health
relates to how well an ecosystem is functioning at a
given point in time, while ecosystem integrity can only
be evaluated over a longer time period, including the
ability of a system to deal with unforeseen circum-
stances in the future. Indeed, whereas in the use of
the term ecosystem health the focus is on ecosystem
functioning, the term ecosystem integrity includes
a strong biodiversity component. It is the state or
condition of an ecosystem that displays the biodiver-
sity characteristics of a reference system, expressed
in terms of species composition and community
structure (SER 2002). We recognize that ecosystem
functioning and species richness are not independent
ecosystem characteristics; there is an increasing body
of literature on functions of species richness (see
Waide et al . 1999 for a review, and Loreau et al . 2002).
A stable ecosystem may be resistant to invasions of
alien species that ultimately can disturb the system.
Although this is already quite a difficult matter to deal
with in a strictly ecological sense, it becomes even more
complicated in confrontation with other disciplines.
Nevertheless, 'increasing our understanding of these
interactions will involve more active collaboration
between the ecological, social and health sciences'
(Rapport et al . 1998).

distinguished five major drivers of biodiversity
change, with different relative importances in each of
the biomes: (i) changes in land use, (ii) atmospheric
CO 2 concentration, (iii) nitrogen deposition and acid
rain, (iv) climate and (v) biotic exchanges (introduc-
tion of aliens).
The issue of restoring biodiversity is central in the
field of restoration ecology (Falk et al . 1996). Divers-
ity or variability is characteristic of life on Earth and
can be observed at different biological levels. Here we
focus on (i) taxonomic diversity at the level of eco-
logical communities: among species of plants, animals
and/or micro-organisms, and (ii) genetic diversity at
the species level: among individuals and populations
within a species.

2.4.1 Biodiversity at the community level

Bakker et al . (2000) recommended the expression of
biodiversity not in general terms, but rather in terms
of specific diversities of plants, birds, insects, etc. to
enable an adequate monitoring and evaluation. This
is in line with the definition of communities as
adopted in Chapter 5. How can restoration ecology
cope with the community as an ecological entity?
The species pool concept has been revisited for the
purposes of ecological restoration, and we have seen a
renewed interest in topics such as functional groups,
keystone species and indicator species.

2.4 The biodiversity approach

The term biodiversity (biological diversity) emerged
in the 1980s as a general catchword for the whole
variety of life on Earth (Gaston 1996a), but from a
scientific point of view biodiversity has existed since
the emergence of life on Earth over 3500 million years
ago. Since then, through the process of speciation and
(mass) extinction, new species have appeared and
others become extinct (Hsü 1986, Wilson 1994). This
resulted in the biodiversity encountered by modern
humans since their appearance on Earth some 200,000
years before the present. Concern about biodiversity
during recent centuries is mainly based on human
impact and its decline. It has become a scientific issue
since the worldwide adoption of the Convention on
Biological Diversity, which arose from the Rio
Declaration on Environment and Development (UN
1992a) and Agenda 21 (UN 1992b; see also WCMC
1992, Groombridge & Jenkins 2000). Sala et al . (2000)

The species pool

A regional species pool is defined within a biogeo-
graphic region, extending over spatial scales many
orders of magnitude larger than those of the local com-
munity. Local communities assemble from this pool
through a series of filters, or stages. Pärtel et al . (1996)
and Zobel et al . (1998) related the concept of species
pools to plant community types and applied it to
restoration ecology to identify the 'target community'.
They considered a species pool as an ecological spe-
cies group selected from a flora and distinguished three
levels according to the following spatial scale (Fig. 2.4).

1 Regional species pool : the set of species occurring
in a certain biogeographic or climatic region which
are potential members of the target community.