Concepts in restoration ecology - Restoration Ecology - page 18

community ecology (Palmer et al . 1997; see Chapter
5 in this volume), in particular on the vast amount
of information of species interactions to understand
the processes regulating foodwebs and keystone
species, species richness and community organiza-
tion, sometimes expressed in terms of assembly rules.
From a restoration-ecological perspective, we may
want to know whether and how to identify reference
communities, a subject we will discuss in more detail.
Finally, population ecology and genetics are of inter-
est when populations of rare species are threatened
with extinction and measures have to be taken to
increase population sizes (Montalvo et al . 1997; see
Chapter 6 in this volume). To re-introduce a popula-
tion to a restoration area where target species have
become extinct is one of the most obvious examples
of potential problems in restoration projects (Falk
et al . 1996; see Chapter 7 in this volume). From
a restoration-ecological perspective, new questions
come into focus, such as, how many plants and
animals should be re-introduced and is the genetic
variation sufficient to prevent inbreeding and genetic
drift?
Several of the attributes discussed above were
listed by SER (2002) as criteria for determining
whether and when restoration has been accomplished,
and they will be discussed in the present chapter.
Recently, Walker and Del Moral (2003) illustrated
how current knowledge of primary succession can be
applied for rehabilitation purposes. Challenging new
scientific questions arise from the search for and
testing of new applications. In the following chapters
several aspects will be dealt with in a certain order,
one after the other, but the reader will recall that eco-
logical restoration demands an integrative approach
(see Chapter 1).

intensively for decades cannot easily, if at all, be trans-
formed to the nutrient-poor heathlands that once
covered the landscape. The increased nutrient stocks
in the soil, combined with increased nitrogen deposi-
tion from the air, will cause the development of a much
more productive ecosystem, even when most of the
organic top soil has been removed at great cost
(Verhagen et al . 2003).
Restoration ecology, therefore, often requires the
evaluation of ecological concepts and approaches in
a modern societal context. Higgs (1997) argued that
good restoration requires an expanded view that
includes historical, social, cultural, political, aesthetic
and moral aspects. Indeed, targets for restoration can
be identified by using historical ecological knowledge
(White & Walker 1997, Egan & Howell 2001), but such
targets should be considered to be feasible and cost-
effective as well. Allen and Hoekstra (1987) held the
opinion that the goal of a restoration is not to 'recre-
ate' some ideal pristine ecosystem, but to establish an
ecosystem in which processes can indeed fit into the
available area of land, which is often limited by the
claims of other land users. We cannot just formulate
restoration goals that are unacceptable for other land
users, or that have no backing by politicians and pub-
lic opinion in general. A restoration scientist should
gather as much information as possible on the his-
torical development and anthropogenic transformation
of the ecosystems and landscapes to be restored. This
knowledge is necessary to formulate acceptable goals
in restoration projects (Aronson & Le Floc'h 1996b).
Recently, Ehrenfeld (2000) reviewed the relative
merits and pitfalls associated with specifying restora-
tion goals based on (i) species, (ii) ecosystem functions
and (iii) ecosystem services, showing that ecological
restoration implies the development of a desired eco-
system in a certain area in a societal context.
As in health care, the restoration of damaged eco-
systems should start with a good diagnosis of the
problem, followed by a suitable trajectory to repair
the damage or otherwise eliminate the complaints by
rebuilding new structures. The way towards such a goal
may demand the recognition that there is no one
paradigm or context for setting restoration goals, and
that ecologists need to develop probabilistic laws,
recognizing that developing ecosystems may undergo
rapid transitions between different meta-stable states
(Fig. 2.2). Very often removing a stress or disturbance

2.2 Objectives of ecological restoration:
targets, references and trajectories

The goal of a particular restoration project may
involve the return of an ecosystem to an approxima-
tion of its structural and functional condition before
damage occurred, but it can also include the creation
of a new ecosystem that had never existed before on
the site selected for restoration. For instance, aban-
doned agricultural fields that have been fertilized