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

136 Karel Prach et al.
nutrient availability increases, remaining high even when such sites are rewetted
(Eschner and Liste 1995). It is impossible to predict whether such systems will
redevelop into nutrient-poor mires or develop into a more productive alternative
stable state (cf. Scheffer 1990). However, where the altered topsoil has been
removed to expose nondegraded layers and the system rewetted, it has been
possible to restore target communities with low-productivity (Pfadenhauer et al.
2001, van der Hoek 2005).
Restoration is particularly difficult on large-scale, surface-mined Sphagnum
bogs, even when unaltered peat layers are left (Money 1995). The most likely
reason for this lack of success is the inability to maintain stable water levels
in leftover remnants (Giller and Wheeler 1988, Joosten 1993). If stable water
levels can be achieved, bog succession can be rapid, taking only 10–20 years
on floating rafts that fluctuate with the water table (van Diggelen et al. 1996,
Beltman et al. 1996b). The intensity of restoration management required depends
on the damage inflicted on the system. Low-quality woodland (Pinus
sylvestris, Picea abies, Betula spp.) usually develops after large-scale industrial
peat harvesting unless the water table is manipulated (Salonen et al. 1992,
Prach and Pyˇsek 2001). Where peat has been extracted in a traditional manner
(i.e., shallow and without deep drainage), unassisted succession is usually
successful (Joosten 1993).
Base-rich fens are also affected by extraneous factors, especially longdistance
hydrological interference that redirects groundwater flow patterns and
results in changed hydrochemical conditions. A decrease in upwelling, base-rich
groundwater normally leads to acidification of the top soil, and also to increased
water level fluctuations. Succession will not, therefore, lead to the reestablishment
of low-production fen communities (Wolejko et al. 1994, Wassen et al.
1996, van Diggelen and Grootjans 1999), unless the previous hydrological
system is restored. If this is not the case there will be very rapid succession
toward bogs, even in calcareous landscapes (Jasnowski and Kowalski 1978). In
contrast, the life span of calciphilous pioneer communities in dune slacks can
be extended for many decades in a Ca-poor landscape by upwelling, Ca-rich
groundwater (Lammerts and Grootjans 1998).
A second situation where base-rich fen vegetation develops quickly without
much active intervention is in former peat cuttings which have become filled
with base-rich ground and surface water. As long as the rafts are still thin, the
pH remains high enough for basophilous species, but after it has achieved a
certain thickness it becomes isolated from the underlying water body and pH
starts to decrease. In medium-sized turf ponds (1 ha) this phase is normally
reached within a few decades (van Wirdum 1995, van Diggelen et al. 1996).
This phase can be prolonged if rainwater is removed artificially by a shallow
drainage system (Beltman et al. 1995), or the process can be started by new
cuttings (Beltman et al. 1996a).
Salt marshes are an even more extreme type of wetland ecosystem with two
major constraints for plant growth: (1) low oxygen availability, and (2) high
salt concentration. Only a few species are adapted to these extremes but all
are very characteristic and are mostly restricted to this habitat. The majority of
salt marshes in the temperate zone have been managed (Bakker et al. 1997).
Mature salt marshes used to be artificially enclosed with banks for grazing but
over the last 25 years this management has reduced and grazing has diminished
(Esselink 2000). The consequence is a reduction in salt-marsh pioneer