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

112 Joachim Schrautzer et al.
development potential of degenerated fens may be limited in many situations.
Moreover, we found no field experiments in which hay-making of degenerated
fens leads to the development of small sedge reeds with a full range of their
characteristic (and mostly threatened) species. This phenomenon has complex
reasons. First of all, the seed density in the soil generally decreases rapidly
if the current vegetation does not continually add new seeds (Jensen 1998).
In the case of Scheuchzerio-Caricetea species, short seed longevity cannot be
used to explain the absence of these species as argued by other authors (Bekker
et al. 1998b). The results of the burial experiments clearly reveal that most
Scheuchzerio-Caricetea species build up a long-term persistent seed bank. Another
reason for unsuccessful attempts to reestablish these species is that it is
difficult to restore the hydrological system of fen areas (van Diggelen et al.
1994, Grootjans et al. 1996). Results of Runhaar et al. (1996) have shown that
long-term hydrological changes at the landscape scale might be responsible for
the decrease of target species in the long run as observed by Bakker (1989).
Moreover, it should be taken into account that the changes of physical soil parameters
at the sites caused by intensive drainage are almost irreversible (Zeitz
1992). The reversibility of compaction in drained peat soils after rewetting is
low. Blankenburg et al. (2001) measured reswelling rates of 2–18 Vol. % in
different peat soils.
5.4.5 Development of Species Richness After Grazing
Without Fertilization
Extensive broadscale grazing has currently been introduced as a new strategy
for the preservation of open landscapes in many parts of Europe (Finck et al.
2001). The main conservation objective of such projects is the development
of a mosaic of different successional stages to offer suitable habitat conditions
for many species and the development of high species richness. Moreover,
broadscale grazing systems are considered as a cost-effective alternative to
other management strategies such as mowing without fertilization (Härdtle et al.
2001). However, cattle grazing in species-rich wet grasslands have been rejected
for many years as a useful measure to maintain species richness (Bakker and
Grootjans 1991, Schrautzer and Wiebe 1993). One important argument used
against extensive grazing in fen areas was that cattle prefer to graze dry places
within the wetland, leading to undergrazing in wet areas, which promotes the
development of tall-growing, species-poor vegetation.
The results presented here show that broadscale grazing maintains species
richness in wet meadows and enhances the biodiversity of degraded fen ecosystems.
However, the increase in species richness was due to increases in common
grassland species. Grazing seems to be an effective management measure in
species-rich, small sedge reeds as well. Based on the results of an indirect successional
analysis, Stammel et al. (2003) detected that, despite a 15% lower
mean species number in the grazed compared to the mown site, there were no
differences in numbers of characteristic fen species.
Finally, it has to be taken into account that the limited reestablishment of
target species in mowing and grazing experiments is probably also related
to the absence of dispersal vectors in the cultural landscape of northwestern
Europe and central Europe (Bakker et al. 1996). Dispersal of our target species