WSNL 1997-1

M. Stock

Salt Marsh Management in the National Park "Schleswig Holsteinisches Wattenmeer"

Martin Stock, National Park Office Schleswig-Holstein Wadden Sea, Tönning, FRG

INTRODUCTION

The special living conditions in Wadden Sea salt marshes give rise to the development of a characteristic vegetation and fauna which serves as an irreplaceable genetic resource. Marine and terrestrial biotic communities intermingle in the Wadden Sea salt marshes.

The salt marshes are furthermore important in terms of coastal and dike protection, as they absorb wave energy. This function is of significance with regard to a rising sea level (e.g. Dijkema 1994). These marshes are at the same time the scene of a conflict between the interests of coastal protection, agriculture, tourism and nature conservation (e.g. Kiehl & Stock 1994).

MANAGEMENT AIMS - GENERAL CONSIDERATIONS

The internationally acknowledged overriding management objective is the maintenance of at least the present size of the salt marshes. This goal was established for example in 1986 at the WWF Wadden Sea Conference (Kempf et al. 1987) and in the recommendations made by the Rømø Conference (Oevesen 1990). It is also emphasized in the regional nature conservation and National Park Laws in Germany. It forms the basis for the ban on further embankment work and the demand for an increase in the area salt marshes. Besides this general objective, there are further objectives of relevance to nature conservation, on which various management recommendations depend in accordance with the weighing they are given.

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M. Stock

BIODIVERSITY ? ... OR ...

The concept of biodiversity in salt marshes is characterized by the promotion of "target communities" with a high species richness through the maintenance or creation of a high variation in abiotic conditions (e.g. Bakker et al. 1993). With a view to preserving the greatest possible diversity, the authors call for low intensity grazing of the salt marshes. In the opinion of Bakker (1993), however, natural salt marshes which have never been grazed should, however, remain so in order to give priority to natural succession.

Structural diversity: The term "structural diversity of salt marshes" is, however, rarely defined precisely. It is widely used to refer to the following aspects:

Salt marshes with a wide variety of geomorphological structures are ones with a natural drainage system, featuring for example tidal channels with shallow gradual and steep abrupt slopes, raised channel edges, salt pans and other non-draining areas. As a result of the numerous microhabitats, the diversity of species may be somewhat greater than in salt marshes with few morphological structures. Artificially created salt marshes with their regular channel system feature a uniform morphological structure and therefore more evenly balanced habitat factors. In areas where ditches have no longer been constructed for many years, the diversity of geomorphological structures increases again when ditches start to meander, steep ditch edges wear down or non-draining old arms are formed by the collapse of ditch edges and sedimentation.

In lower salt marsh zones, the greatest small scale variation in vegetation height is to be found in non-grazed areas, which can thus be classed as possessing a variety of vegetation structures. In areas of extensive sheep grazing, the small-scale differences are less pronounced in the lower marsh zone. When considered on the scale of several hundred meters, however, gradients can be observed between low vegetation in areas close to and high vegetation further away from the dike.

A diversity of geomorphological and vegetational structures, summarized as habitat diversity, promotes the development of a diversity of invertebrate fauna characteristic of salt marshes. Various salt marsh fauna species are dependent on special structures and microhabitats. Thus, for example, numerous phytophagous insects are directly reliant on the formation of specific structural elements of vegetation such as stems or floral organs.

The above examples illustrate that both used and unused salt marshes can be described as having a variety of structures depending on the parameters and scales chosen for consideration. The use of the term "structural diversity" therefore has to be clearly defined in the context of discussions on objectives.

WSNL 1997-1

M. Stock

... NATURAL DYNAMICS!

The undisturbed course of natural processes is the declared prime objective of the Schleswig-Holstein, Niedersachsen and Hamburg National Park laws. Against this background, the cessation of sheep grazing and a considerable extensification of coastal protection measures, particularly with regard to the construction of brushwood groynes and draining in foreshore salt marshes, are recommended for nature conservation reasons.

Natural salt marshes largely free from human influence are worthy of protection in the Wadden Sea region on account of their small total area and the special features associated with them.

Despite having been created by coastal protection measures, foreshore salt marshes subjected to draining can be largely given over to natural sedimentation and erosion processes (Kiehl & Stock 1994, Kiehl et al. 96). As the preservation of the salt marshes is the overriding objective in the Wadden Sea, the construction of land reclamation works cannot be avoided in areas at risk from erosion. This in turn restricts the natural character of such areas.

If draining is considerably reduced and grazing discontinued, even artificial foreshore salt marshes will develop into more natural systems they can, however, never become natural salt marshes.

In consequence, the cessation of grazing and the reduction of draining within salt marshes will allow the establishment of a structural and a species diversity on a large scale which is determined by the dynamic processes effecting each specific site.

By contrast, the cessation of anthropogenic coastal protection activities in areas with a high sedimentation rate allows new natural salt marshes to form. The promotion of sedimentation within sedimentation fields can also promote the development of near-natural salt marshes in areas with lower sedimentation rates if artificial draining is dispensed with and a natural drainage system allowed to form.

WSNL 1997-1

M. Stock

CONCLUSIONS

The particular desirability of and necessity for the protection of all salt marshes along the Wadden Sea coast are reflected in a number of laws and recommendations (§ 20c BNatSchG; § 15a LNatSchG; National Park Laws; Trilateral Ministerial Declaration, Esbjerg and Leeuwarden). Consequently, any protection oriented concept should also incorporate all salt marshes irrespective of their current protection status.

The protection of all salt marsh types in the German part of the Wadden Sea is governed by the guiding principle of "natural dynamic processes".

The guiding principle applied to salt marshes should lead to an area with tidal channels which are allowed to meander naturally, a geomorphological structure typical of the habitat and a distribution of plant communities as well as a the corresponding fauna determined by dynamic processes of the specific site

A first step to realize this aim is the large scale cessation grazing. The second stage involves more or less complete discontinuation of the maintenance of the artificial drainage channels in salt marshes. Coastal protection activities to safeguard the existing foreshore are to be reduced to a minimum and become more compatible with nature.

When implementing this guiding principle it is absolutely essential to give continued priority to the coastal protection. If natural dynamic processes are allowed to take place, a monitoring program is necessary to observe the future development of the marshes both with regard to the establishment of flora and fauna and with respect to changes in the morphological structure due to sedimentation and erosion. In SH, such a concept was implemented in 1995 (Melff 1995).

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M. Stock

A MANAGEMENT PLAN FOR THE SALT MARSHES IN SH

In order to harmonize the coastal defence strategies and the environmental objectives on salt marshes, a "salt marsh - working group" was initialized in 1993. The target of the group was to establish common principles for the future protection and management of salt marshes in the light of the overriding objectives mentioned above. The plan has a validity of about 10 years. However, a continuous evaluation of its efficiency and environmental tolerance on the basis of a monitoring program is intended. If necessary, the plan can be adjusted.

The common principles are as follows:

• The common goal of coastal defence as well as of environmental authorities is the preservation of existing salt marshes and the creation of new marshes in areas where no salt marshes exist in front of the sea dikes.
• The techniques used to reach this goal depend upon local circumstances. They will be carried out as ecological sound as possible. Where local circumstances allow, technical measures will not be used.

These management aims have further been transferred into regional management plans at a scale of 1:10.000.

In existing salt marshes, only those techniques are to be applied which prevent possible edge erosion by creation of brushwood groynes. Furthermore, the main drainage channels and the drainage of the foot of the dike are to be guaranteed (Fig. 1).

At specific sites, intensive sheep grazing is to be allowed to maintain a short sward for the cultivation of salt marsh turf for dike repairs. Most of the existing salt marshes will, therefore, in future, no longer be grazed or drained in a systematic way.

Fig. 1. Coastal protection measures in an existing salt marsh. Current practice and future development. The stippled salt marsh zone will not be grazed anymore

In the developing salt marshes, a differentiated system, divided into a salt marsh -, an accretion - and a turbulence zone is aimed at (Fig. 2). A developing salt marsh turns, per definition, into an "existing" salt marsh when a 200 m wide salt marsh zone is established.

Fig. 2 Coastal protection measures in a developing salt marsh.

In some sheltered areas, all management techniques have been abandoned. These areas will be monitored carefully in order to study the development and renaturation of artificial salt marshes (Fig. 3). Furthermore, the program allows for the timely recognition of negative developments so that, if necessary, the appropriate measures can be undertaken.

Fig. 3 (left). Sheltered salt marsh areas where all management techniques have been abandoned.

The monitoring program supplies the necessary data for a well- founded estimation of the efficiency of the techniques applied, as well as a thorough checking of the environmental tolerance and necessity of environmental measures in the area. In addition, this program functions as an early warning system for the effects of possible climatic changes and their impact on the salt marshes.

A set of reference areas and reference profiles are chosen to represent all different environmental circumstances within the SH part of the Wadden Sea. The program consists of a list of different technical, hydrographic, morphologic, sedimentological and biologic parameters which are to be measured every two to five years. Additionally, every five years, a CIR-aerial survey will be carried out to gather mainly biological and morphological data.

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REFERENCES

BAKKER, J.P., J. DE LEEUW, K.S. DIJKEMA, P.C. LEENDERTSE, H.H.T. PRINS & J. ROZEMA (1993): Salt marshes along the coast of the Netherlands. - Hydrobiologia 265: 73-95.

BAKKER, J.P. (1993): Strategies for grazing management on salt marshes. - WSNL 1/93: 8-10.

DIJKEMA, K.J. (1994): Auswirkung des Meeresspiegelanstiegs auf die Salzwiesen. - In: Lozán, J.L., E. Rachor, K. Reise, H. von Westernhagen & W. Lenz (Hrsg.): Warnsignale aus dem Wattenmeer. - Blackwell, Berlin: 196-200.

KEMPF, N., J. LAMP & P. PROKOSCH (1987): Salzwiesen: Geformt von Küstenschutz, Landwirtschaft oder Natur? - Tagungsbericht WWF Heft 1.

KIEHL, K. & M. STOCK (1994): Natur- oder Kulturlandschaft? Wattenmeersalzwiesen zwischen den Ansprüchen von Naturschutz, Küstenschutz und Landwirtschaft. - In: Lozán, J.L., E. Rachor, K. Reise, H. von Westernhagen & W. Lenz (Hrsg.): Warnsignale aus dem Wattenmeer. - Blackwell, Berlin: 190-196.

KIEHL, K., I. EISCHEID, S. GETTNER & J. WALTER (1996): Impact of different sheep grazing intensities on saltmarsh vegetation in northern Germany. - J. Veg. Sci. 7: 99-106.

MELFF (1995): Vorlandmanagement in Schleswig Holstein. - Endbericht der MELFF/MNU Arbeitsgruppe "Vorland" - Kiel.

OEVESEN, C.H. (1990): Saltmarsh management in the wadden sea region. - Proc. 2nd trilateral Working Conference, Rømø, Denmark. Ministry of the Environment. The National Forestry Agency. 203 p.

Authors address:
Landesamt für den Nationalpark Schleswig Holsteinisches Wattenmeer
Schloßgarten 1
D - 25832 Tönning