Salt
marshes develop in close interaction of hydrodynamic processes with
vegetation development and can be distinguished in relation to their
geomorphologic features. On the islands, four types could be
distinguished. Barrier-connected salt marshes develop on the lee
side of the sand dune system of the barrier islands. Green beaches
are salt marshes which developed on the North Sea side of the
islands. In addition to the categories in the 1999 QSR, salt marshes
in summer polders and in de-embanked summer polders have been
included.
On the mainland,
foreland marsh (including the estuarine salt marshes), salt marshes
in summer polders and de-embanked (summer) polders are the main salt
marsh types. Most foreland marshes have been developed from
sedimentation fields protected by brushwood groynes. As a special
case, the salt marshes in St. Peter-Ording (Schleswig-Holstein) and
Skallingen (Denmark) have been added as barrier-connected type,
because they have developed in the shelter of a beach-barrier system
comparable to the barrier islands.
Hallig salt
marshes have been accreted on surviving parts of marshes flooded in
the past and are highly exposed to wave energy. They represent a
separate type as they resemble more the mainland foreland type.
Distribution and size of salt marsh types
A trilateral
overview of the surface area for the different types is given in
Table 1 and Figure 1. The border between the pioneer zone and bare
soil is chosen at 5% coverage (10% in Schl-Holst). This is based on
practical reasons when mapping with aerial photos.
Table 1:
Recent extent
(ha) of salt marshes in different parts of the Wadden Sea specified
according to their geomorphology. The areas include the pioneer
zone, except for Denmark. The pioneer zone has been defined as the
area where pioneer vegetation cover ≥ 5%; in Schleswig-Holstein,
this threshold value was 10%. On the islands, de-embanked
summerpolders may be added to the back-barrier marshes; on the
mainland to the foreland-type salt marshes (source QSR 2009)
Figure 1:
Overview of the
total area of salt marshes and summerpolders in different parts of
the Wadden Sea specified according to their morphology. Same data as
Table 1. See this table for further explanation.
Land use and
management of salt marshes
In
general, the intensive agricultural exploitation of salt marshes
observed has decreased since the mid 1980s. Today, large areas of
the salt marsh are grazed moderately, often for nature conservation
purposes, for example for geese management on the Halligen in
Schleswig-Holstein.
By
comparing the recent situation with information from the 1980s (Kempf
et al., 1987), the last Wadden Sea wide review available, a
decrease of intensively used areas could be observed (Fig. 2). In
using these historical figures, it has to be taken into account
that, because of methodological differences, the figures by Kempf
et al. (1987) cannot be compared directly with the figures
compiled later and from other sources. However, they give an
indication about the general trend since the 1980s.
Figure 2:
Development of land use by
livestock grazing in the Wadden Sea mainland salt marshes,
comparison between data from the 1980s and recent data (period
1999/2002) (source: QSR 2004)
