Environmental Engineering Reference
In-Depth Information
are not peat-forming species, they can rapidly form
a highly productive marsh vegetation, suitable for
sustaining large populations of waterfowl. In order to
restore the peat-forming function of the mire the
vegetation should consist of marsh species with less
easily degradable tissue ( Phragmites australis , tall
Carex species; Hartman 1999, Richert et al. 2000).
Flooding is also important for redistribution of seeds
within restoration sites (Danvid & Nilsson 1997,
Jansen et al. 2004, Wheeler et al. 2002). Middleton
(1999) advocates the need for a 'flood pulse' water
regime, which is the natural regime; flooding in
winter and lower water levels in summer. Such a regime
stimulates seed dispersal in winter, allows germina-
tion in spring and prevents desorption of phosphates
and possibly sulphide toxicity in summer (Lamers
et al. 2002).
that resuming the traditional management in pre-
dominantly cultural landscapes produces the best
effects in mires and wetlands that have not been
drained or fertilized. Successful projects have been
executed at sites that have been least affected by inten-
sive agriculture and drainage. Successful restoration
in western Europe is often the result of repairing dam-
age at high costs. From a European perspective the
conservation of still-existing semi-natural ecosystems
is much more cost-effective. Failures to repair damaged
elements of the semi-natural landscape are as numer-
ous as the successes, but they are usually not well
documented. Failures are often caused by an in-
correct diagnosis of the restoration prospects of the site,
lack of knowledge on ecological processes affecting
the site negatively, and expectations that are too high
(lack of knowledge on appropriate references). The
availability of reference communities is, indeed, an
acute problem in target areas where intensive fertil-
ization has taken place for a long time, soil degrada-
tion has occurred and where practically all target species
have disappeared in both the established vegetation
and the seed bank.
9.6 Generalization and concluding
remarks
9.6.1 Successes and failures
In Europe, the restoration of natural mires in a land-
scape that has been used intensively by humans is an
almost impossible task, since hydrological conditions
of natural mires are practically always connected
to large hydrological systems of the surrounding
landscape. In densely populated areas support from
society will be lacking entirely when such goals are
formulated. Targets should be formulated very clearly
in order to obtain political support for restoration
projects (Swart et al. 2001). In practice, natural mire
ecosystems can only be restored on a very local scale,
and although aspects of natural mires may return in
restored wetlands, the new ecosystems will differ
from the ones that have been destroyed in former
times. Restoring semi-natural ecosystems may gain
considerable popular support, particularly in western
Europe, where very few elements of the semi-natural
landscape, shaped by past generations, have remained.
Large sums of money are now being spent to con-
serve and restore species-rich grasslands or wetlands
with large numbers of waterfowl. Restoration projects
aimed at restoring semi-natural ecosystems are
usually considered a success if rare and endangered
species (Red List species) return. It is not surprising
9.6.2 Prospects for the future
Reduction of the amount of N deposition remains
a prerequisite for successful restoration of many
nutrient-poor ecosystems, such as bogs, fens and
several types of fen meadow. In the Netherlands the
atmospheric N deposition has declined ( c .40%) since
1985 and the atmospheric deposition of SO 2 has also
decreased strongly ( c .70%) during the past 20 years.
Freshwater ecosystems have benefited considerably
from drastic reductions of the phosphorus emissions
in the surface water, but in many streams and rivers
the amount of sulphate is still much too high and
causes eutrophication in many terrestrial mire systems
when they are flooded.
The prospects of restoration of damaged ecosys-
tems are relatively good in most western European
countries, since (i) much experience is now available
to repair or even rebuild damaged (semi-natural)
ecosystems, (ii) some of the environmental stress
factors such as sulphate and nitrogen deposition are
decreasing and (iii) public and political support for
restoration is increasing. In eastern and southern
 
Search WWH ::




Custom Search