Environmental Engineering Reference
In-Depth Information
the maximum prior biodiversity, within maximized
ecosystem services, then this term is again useful. The
second level is often called
rehabilitation
and con-
sists of the restoration of certain ecosystem functions
(Mitsch & Jørgenson 1989, Wali 1992), such as the
reduction of flood risks by creating the development
of water-retention systems or restarting peat growth
to fix CO
2
in peat layers. This option would make parts
of the landscape as a whole more natural, but it would
not necessarily result in a significant increase in
biodiversity in the whole landscape. The third level
is sometimes called
reclamation
and consists of
attempts to increase biodiversity
per se
. The landscape
as a whole would benefit from an implementation of
such measures on a large scale but it usually does not
contribute much to the protection of endangered red-
list species. The definition given by Bradshaw (2002)
of 'making the land fit for cultivation' is probably the
easiest to comprehend, and most widely applicable.
The above-mentioned goals are generally associated
with different
scales
, especially in densely populated
areas where most restoration activities take place.
Although it is technically sometimes possible to really
recreate some former communities (true restoration)
on a local small scale and at high cost, this is gen-
erally impossible at the landscape scale because of land-
use conflicts, long-distance effects of other activities
and lack of public support. Reclamation is often the
only realistic option at this scale. Rehabilitation
seems to be practical at an intermediate scale, often
as a network within a certain landscape, for example
riparian restoration (Kentula 1997). We suggest that
simple recreation of past species lists is unlikely to
succeed:
process
and
connectivity
must be taken
fully into account, along with
biodiversity
.
A useful way of separating the reclamation and
restoration definitions is to base them on the types
of barrier that need to be crossed. It is possible to
relate these terms to the conceptual arrangement of
degraded, recovering and restored ecosystems in the
light of a schema defined initially by Whisenant
(1999) and further developed by Hobbs and Harris
(2001), as illustrated in Fig. 1.4. Here, a number of
putative stable ecosystem states, from degraded to
intact, are related to ecosystem function. There are
two principal barriers between degraded and restored
(intact) systems. The first are abiotic barriers, which
Abiotic
Biotic
Requires
physical
modification
Requires
biological
modification
Requires
improved
management
Fully
functional
1
2
Ecosystem
attribute
3
4
5
6
Non-
functional
Reclamation
Restoration
Degraded
Ecosystem state
Intact
Fig. 1.4
Relationship between measured ecosystem
attributes, biotic and abiotic barriers, and the processes
of reclamation and restoration (modified from Hobbs &
Harris 2001).
could be a lack of appropriate topology, contaminated
substrate, too-high or -low a groundwater table, little
or no organic matter, etc. These barriers all require
physical modification to bring the systems to a new
level of stability associated with a new 'higher' level
of function. The second barrier is biotic; this may be
as a result of a lack of appropriate species or inter-
action between them and abiotic components. Again,
active modification allows these barriers to be overcome.
We suggest that the first transition is the reclamation
phase and the second is the restoration phase of a pro-
gramme designed to restore ecosystem function and
structure. Rehabilitation may be regarded as the
transition from level 4 to level 3 on Fig. 1.4; that is,
without crossing a significant threshold leading to a
new, self-sustaining, ecosystem trajectory.
This gives us some clear goals to aim at, such as
the re-instatement of a hydrological regime, or re-
introduction of a keystone species. We must go further
than simply measuring one feature or attribute. There
are often conflicting interests from groups favouring
plants, birds or animals, for example. The techniques
designed to restore a species-rich meadow, with late
cutting once a year, may be totally inappropriate
for invertebrate populations, dependent on bare sub-
strates for nesting and nectar plants for feeding: the
late cut turns a feast into a desert overnight.
