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

Chapter 5 Succession and Restoration of Drained Fens 113
is limited in this region by rare donor sites for seeds of these species (Bonn
and Poschlod 1998). Furthermore, important dispersal agents such as regular
flooding in river valleys are lacking due to the extensive construction of dykes.
Based on the results of a greenhouse experiment, van den Broek et al. (2005)
found that Molinietalia and Scheuchzerio-Caricetea species dispersal by hydrochory
was restricted because of relative low buoyancy of their seeds. However,
field investigations in the Eider valley and Estonian river valleys have
shown that many Molinietalia and Scheuchzerio-Caricetea species are spread
by hydrochory (unpublished data K. Voigt, A. Wanner, Ecology Centre of Kiel,
Biological Institute University of Hamburg).
5.5 Conclusions and Recommendations for Restoration Management
In this chapter, we have described the species and abiotic changes in a retrogressive
succession caused by increasing disturbance intensity from alder
carrs to wet meadows, and a progressive succession for three retrogressive
stages back to alder carrs. The results show no clear progressive changes in the
functional indicators following land use intensification or abandonment. Successional
changes and restoration actions are summarized in Fig. 5.11. Each
of these systems fulfills important ecological functions in cultural landscapes
developed over centuries. It seems unwise to favor any of these ecosystems over
any other for nature protection. However, the development from low-productive
mesotrophic wet meadows via eutrophic wet meadows to wet pastures supports
the hypothesis of decreasing indicator values with increasing human impact
and underlines the need to reduce land-use intensity in degraded ecosystems.
During this intensification sequence (see also Müller et al. 2006) the indicators
show the following differences during retrogression:
1. A reduction in biotic heterogeneity.
2. Exergy capture increases with rising productivity (which is the target of the
dominant agricultural landscape management), while entropy production
increases due to better conditions for microbial mineralization, i.e., after
drainage.
3. Efficiency measures decrease with growing land-use intensity as do biotic
and abiotic storage capacities, whereas nutrient loss is maximized by landuse
intensification.
Abandonment of previous agricultural ecosystems often has been recommended
as a nature protection “measure” in terms of reactivating selforganizational
processes (Woodley et al. 1993, Jedicke 1995). If this were the
case, then the indicators should generally show better values due to the reduced
pressure, which potentially allows more pathways for self-organized dynamics.
The results shown in Fig. 5.11 suggest that abandonment in fact improves
the abiotic ecological functions of the ecosystems if successional stages develop
that are characterized by clonal species such as tall sedges or large herbs.
The initial decrease of NNM and nitrogen as well as carbon losses that might
take place if eutrophic wet meadows are abandoned can be explained by the decrease
of fertilization and rising water levels. However, the development of these