Linking Restoration and Ecological Succession (Springer ... - Inecol

Chapter 5 Succession and Restoration of Drained Fens 115
Implementation of appropriate restoration measures in highly degraded fen
ecosystems such as wet pastures that cover more than 90% of the fen areas
of most northern European countries is an important task within the scope of
species and nature protection. Thus, raising the water levels in these systems to
reduce their nutrient losses has to be a priority.
Nutrient budget simulations for an intensively utilized fen area (10% of
the catchment area ) and its surrounding mineral soils (90% of the catchment
area) revealed that the fens contribute more than 90% to the nitrogen output
of the catchment (Müller et al. 2006). Because of the high cost involved, the
degree of rewetting usually depends on the socioeconomic conditions in the
regions concerned. The most effective measure is to raise the water levels
up to the soil surface that then leads to a decrease of NNM and microbial
soil respiration. In the long run, it is possible to develop eutrophic wet alder
carrs that have a higher species richness than the previously intensively used
ecosystems (Fig. 5.11). Rewetting of fen areas with resulting initial development
of shallow lakes is also a recommended measure if reduction of NNM and
purification of polluted surface water is required. However, this measure bears
the risk of increased phosphorus release (Grootjans et al. 2002, Kieckbusch
et al. 2006).
If options to enhance water levels are restricted, measures that aim at the
reestablishment of target species in strongly degraded fens should be introduced.
Field experiments carried out in northwestern Europe have shown that
grazing or mowing without fertilization usually enhances species richness and
the number of target species (Fig. 5.11). Nevertheless, the success of these
processes depends on the duration of these management measures. In our own
field experiments, target species develop well in eutrophic wet meadows and
wet pastures but not for up to 5–10 years. Moreover, the reestablishment of
target species is restricted to Molinietalia species and common Scheuchzerio-
Caricetea species. In contrast, the potential for reestablishment of rare species
is low due usually to missing dispersal vectors, lack of suitable donor sites, and
far-reaching, irreversible soil compaction. Removal of the upper, degraded soil
horizon (sod cutting) is often recommended as a small-scale restoration measure
in highly degraded fens. This measure will enhance habitat conditions for
target species, but is too costly for broadscale use. Consequently, species protection
in fens of northwestern Europe should mainly focus on the maintenance
of species-rich small sedge reeds and wet meadows.
Finally, our results show both irreversible changes on the one hand and
hysteresis effects on the other. Abandonment and self-organizing processes
will not always develop a desired successional stage and technical measures
such as rewetting in abandoned wet pastures are needed.
Acknowledgements: The authors thank Rudy van Diggelen, Werner Härdtle,
David Mackenzie, Roger del Moral, Gert Rosenthal, and especially Joe Walker
for careful reviews of the manuscript.
References
Asada, T., Warner, B. G., and Schiff, S. L. 2005. Effects of shallow flooding on vegetation
and carbon pools in boreal wetlands. Applied Vegetation Science 8:199–208.
Bakker, J. P. 1989. Nature Management by Grazing and Cutting. Dordrecht: Kluwer.