Environmental Engineering Reference
In-Depth Information
• material and energy flows, e.g. rates of transmis-
sion within, into and from the ecosystem, between
biotic and abiotic components, change in pool sizes;
• biotic components, e.g. standing crop, species in-
ventories, trophic connection, nutrient pools;
• abiotic components, e.g. nutrient pools, active com-
ponents in nutrient cycling;
• ecosystem architecture, e.g. physical development and
arrangement of the system.
ment of tolerances of key organisms with respect to
environmental conditions. If the ambition level is
rehabilitation or reclamation, the demands are less strict
and one might proceed without reference systems
and just choose the function one likes to enhance. In
that case, however, the line between landscape design
and restoration becomes very thin and we do not
advocate this approach here. Instead we argue that one
should also use references in these cases and aim
to restore certain species and/or functions of an eco-
system that have been lost through human-induced
disturbance.
This encourages due weight to be given to the inter-
ests of a diverse group of stakeholders, but relation-
ships between, for example, biodiversity and functional
stability are not yet clear. The overall problem of what
an ecosystem is remains, leading to boundary prob-
lems, but this can be resolved by taking, for example,
the catchment (watershed) to be the geographical
context in which this activity should take place.
Historical reference ecosystems
One of the most superficially attractive targets for
restoration projects is to re-instate the ecosystem
'prior to degradation' (Egan & Howell 2001). A number
of sources of information may be available to varying
degrees to allow the development of a restoration
prescription, including historic photography, less-
disturbed remnants on-site, similar sites, historical
accounts and museum collections, and palaeoecolo-
gical evidence.
A way of organizing this into types of information
is shown in Table 1.1. Those techniques which rely
on purely human records (historical photography and
records) may not be available for many areas, and the
palaeoecological evidence often begs the question, how
far would you like to go back? All of the methods
which reference the past suffer from what we might
call moving-target syndrome, illustrated in Fig. 1.5.
The original target system would have changed with
time responses to environmental pressures, if left
undisturbed. The question then arises, should our
target prescription be set for where the system was,
or where it would be now? What if key species have
become extinct? We must also recognize the variability
in natural systems in time and space (White & Walker
1997). The landscape, if unconstrained, would be a
shifting mosaic of habitats at different successional
stages, a newly exposed clearing here, a stand of
ancient trees there, carved and renewed by the
interactions of water, fire and sometimes even greater
perturbations such as earthquakes and volcanic erup-
tion. This does not, however, detract from the as-
piration to restore some desirable characteristics of
historical ecosystems, if they are sustainable.
Ecosystem services
We have already outlined the four types of ecosystem
service upon which human society depends - these are
in many ways a combination of species and function
classifications outlined above, but they may be easier
to comprehend for a wider audience. Consequently, if
we can devise suitable targets incorporating all three
latter categories, while giving due weight to the pub-
lic perception of past ecosystems being in some sense
unsullied, there will be a greater chance of ecological
restoration being adopted as a land-ocean manage-
ment process.
1.3.4 Which type of target to choose?
Which restoration target to choose depends on the
level of ambition of the project. If true restoration is
chosen as a goal, a reference ecosystem is essential
as a template for the restoration scheme to be based
upon. The study of reference systems provides several
types of relevant information. They enable the study
and understanding of key processes that are relevant
for the restoration trajectory. They provide some kind
of yardstick that can be used both to estimate the
degree of degradation of a disturbed ecosystem and
the distance between the actual situation and the end
point of the restoration. Finally they enable measure-
