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

Chapter 5 Succession and Restoration of Drained Fens 109
occurring on fen sites because these groups contain species with large as well
as small seeds. The results of this study also reveal that in the long run, species
richness could increase again if the systems develop to alder carrs.
Our simulation results have shown that the indicators of the carbon and nitrogen
cycle and the nutrient balances show different patterns of change for
the three successional seres selected. In the seres A and B, abandonment led
to a continuous increase of NNM, N-leaching, and denitrification from stage I
up to stage IV. In addition, microbial soil respiration increased. These differences
were probably due to lower soil moisture caused by higher water used
to support higher net primary production of the late successional stages. As a
consequence, abandonment without rewetting could have negative effects on
the functional properties of these systems. In the successional sere C, the decrease
of fertilization reduces the risk of nutrient losses from the systems. Here
the simulated N-leaching rate was much lower in successional stages II and III
compared with stage I. On the other hand, it can be assumed, that the functional
properties of the nitrogen budget would drastically get worse, if the systems
change to drained alder carrs. NNM and N-leaching increased and N-balance
became more negative. This effect can be explained by lower water tables in
alder carrs compared with the intermediate successional stages of this sere.
The simulation results concerning the effects of abandonment on seminatural
fen ecosystems are based only on changes of vegetation structure during
succession. However, long-term physical changes to drained fen areas (such as
a continuous closure of ditches by plants) can result in the rise of local water
tables. These kinds of process were not considered in the simulations.
5.4.3 Effects of Rewetting on Ecosystem Structure and Function
Raising water levels up to the soil surface in drained wet pastures resulted in
a decrease and later an increase in species richness. Roth et al. (1999) also
observed the initial development from wet pastures to tall sedge reeds after
rewetting. However, the success of rewetting strongly depends on the hydrological
system and the quality of the available water (Grootjans et al. 2002).
Rewetting intensively drained, eutrophic fen areas with precipitation water or
stream water often results in the development of shallow lakes due to surface
soil compaction. In this case, the succession will start with aquatic plants and
will continue with the development of reeds beginning from the riparian zones
of the lakes. In most areas, high nutrient concentrations in the stream water
lead only to the establishment of eutrophic systems and common plant species.
Asada et al. (2005) observed the expansion of the eutrophic reed species Typha
latifolia in a flooded Canadian wetland consisting of bogs and surrounding drier
peatlands after raising water levels up to 1.3 m. On the other hand, rewetting of
wet pastures in discharge fen areas with deep, nutrient-poor groundwater enhances
the potential for the establishment of mesotrophic fen species (Grootjans
et al. 1996, Kieckbusch et al. 2006).
The simulation results indicate that raising water levels up to the soil surface
in wet pastures efficiently reduces net nitrogen mineralization, nitrogen
leaching, and microbial soil respiration if tall sedge reeds develop. Decreased
nitrogen availability after rewetting due to lower mineralization rates are detected
in the studies of Berendse et al. (1994), Updegraff et al. (1995), and
van Duren et al. (1998; see Chapter 6), but other studies show no decrease