nourishment sand and the sand subsequently deposited by the sea by natural
coastal processes (Nielsen 1990). This gradually increased the width of the beach
by 25 m in 24 years. The sand deposited by the sea was quite similar to the beach
sand of the natural barrier in its pH and exchangeable calcium, but differed from
the nourishment sand (Gravesen and Vestergaard 1969; Vestergaard 2006).
The system studied here seems to have behaved like the ‘‘high sediment supply
system’’ described by Carter (1990), which is characterized by progressive seaward formation of several foredunes, each of which develops until the sand supply
from the beach is cut off by the formation of a new foredune ridge. Thus, an
important consequence of the successive seaward formation of the natural dunes
on the beach in the seaside park has been a strongly reduced dynamic of the
landward dunes, which instantly or within a few years stabilized at a dune height
of 3 m DNN. This is typical of the prograding foredune systems such as those
described by among others Carter (Carter 1990; Hesp 1999, 2002).
4.4.2 Immigration of Plant Species
The increase in species richness and development of vegetation in the dunes
studied here includes the sequence of processes characteristic of primary succession in a new area (Bradshaw 1993). Among these processes, dispersal of diaspores
and distance to species sources are essential for the rate and course of the succession
(van der Maarel 1997; del Moral 1998; Walker and del Moral 2003).
In the nourishment sand, no seed bank was present (Hansen and Vestergaard
1986). Thus, apart from the initial planting of A. arenaria, the subsequent
development of the vegetation in the permanent plots was due to natural influx of
diaspores.
The minimum number of species dispersed into the beach and dune system can
be estimated from the number of species that have been recorded in the permanent
plots during the years, i.e., 38 species. Nothing indicates, however, that the influx
of species to the plots has stopped. Thus, the number of species established in the
beach and dune within the total study area (Fig. 4.1) was 55 (Vestergaard 2006),
and in the natural Ølsemagle Revle barrier, 85 species were recorded within
similar beach and dune habitats after about 37 years of development (Gravesen
and Vestergaard 1969), and 102 species after a further 40 years (2008). Based on
the above, it is thus expected that the species number will continue increasing, if
the same trends are maintained during the coming years.
During the study period, the natural habitat of an increasing proportion of the
species recorded is relatively dry, nutrient-poor inland grasslands and other open
inland habitats (Hansen 1981). The source of these species is rather diffuse, but the
species in question are all common and more or less widely distributed in Denmark
(Vestergaard and Hansen 1989). The remaining species are found in coastal habitats. The source of these species was probably the nearby coasts along the bay of
Køge Bugt and the island of Amager (Fig. 4.1). The relative increase in inland
60
P. Vestergaard
coastal processes (Nielsen 1990). This gradually increased the width of the beach
by 25 m in 24 years. The sand deposited by the sea was quite similar to the beach
sand of the natural barrier in its pH and exchangeable calcium, but differed from
the nourishment sand (Gravesen and Vestergaard 1969; Vestergaard 2006).
The system studied here seems to have behaved like the ‘‘high sediment supply
system’’ described by Carter (1990), which is characterized by progressive seaward formation of several foredunes, each of which develops until the sand supply
from the beach is cut off by the formation of a new foredune ridge. Thus, an
important consequence of the successive seaward formation of the natural dunes
on the beach in the seaside park has been a strongly reduced dynamic of the
landward dunes, which instantly or within a few years stabilized at a dune height
of 3 m DNN. This is typical of the prograding foredune systems such as those
described by among others Carter (Carter 1990; Hesp 1999, 2002).
4.4.2 Immigration of Plant Species
The increase in species richness and development of vegetation in the dunes
studied here includes the sequence of processes characteristic of primary succession in a new area (Bradshaw 1993). Among these processes, dispersal of diaspores
and distance to species sources are essential for the rate and course of the succession
(van der Maarel 1997; del Moral 1998; Walker and del Moral 2003).
In the nourishment sand, no seed bank was present (Hansen and Vestergaard
1986). Thus, apart from the initial planting of A. arenaria, the subsequent
development of the vegetation in the permanent plots was due to natural influx of
diaspores.
The minimum number of species dispersed into the beach and dune system can
be estimated from the number of species that have been recorded in the permanent
plots during the years, i.e., 38 species. Nothing indicates, however, that the influx
of species to the plots has stopped. Thus, the number of species established in the
beach and dune within the total study area (Fig. 4.1) was 55 (Vestergaard 2006),
and in the natural Ølsemagle Revle barrier, 85 species were recorded within
similar beach and dune habitats after about 37 years of development (Gravesen
and Vestergaard 1969), and 102 species after a further 40 years (2008). Based on
the above, it is thus expected that the species number will continue increasing, if
the same trends are maintained during the coming years.
During the study period, the natural habitat of an increasing proportion of the
species recorded is relatively dry, nutrient-poor inland grasslands and other open
inland habitats (Hansen 1981). The source of these species is rather diffuse, but the
species in question are all common and more or less widely distributed in Denmark
(Vestergaard and Hansen 1989). The remaining species are found in coastal habitats. The source of these species was probably the nearby coasts along the bay of
Køge Bugt and the island of Amager (Fig. 4.1). The relative increase in inland
60
P. Vestergaard