4.2.3 Plant Data Analysis
The species diversity in the permanent plots was expressed by the number of
species as well as by the Shannon–Wiener diversity index. These measures were
found to be highly significantly positively correlated (Fig. 4.3). Therefore, the
discussion of the trends in plant diversity development presented here will be
based on the number of species per plot.
For each of the dunes, the correlation between the number of species per plot
and the following dune attributes was investigated: number of years since establishment, dune height, distance to the sea, and total plant cover. The plant species
were classified according to their life forms (Raunkiær 1907, 1934), and diaspore
dispersal strategy, following Andersen (1993).
The frequency and Hult–Sernander cover data were combined into a 1–9 cover–
abundance scale (Vestergaard 2006). Based on this scale, the species composition
of the relevées was subjected to TWINSPAN classification analysis, cut levels
0–2–4–6–8, using the program PC-ORD (McCune and Mefford 1999).
4.3 Results
4.3.1 Change in Dune Morphology 1978–2002
The morphology of the landward part of the initial man-made dune remained fairly
unchanged during the study period, while in other parts, the morphology changed
substantially (Fig. 4.2).
In the seaward part of the initial dune, a net accumulation of up to approximately 0.4–0.5 m of windblown sand was recorded. On the beach, new foredune
ridges, parallel to the initial dune, gradually developed, supported by A. arenaria,
which spread from the planting in the initial dune, as well as by other duneforming grasses. Thus, in the inner part of the beach, the dune, represented by
‘‘dune 2,’’ accreted rapidly (0.15 m year
-1 ) to about the same height as the top of
the initial dune, +3 m DNN (Figs. 4.4, and 4.5). After 1990, this dune stabilized,
and the height did not change significantly. On the outer part of the beach, another
new dune, represented by ‘‘dune 3,’’ developed, albeit a little more slowly
(0.1 m year
-1 ). In 2002 this dune was about 0.5 m lower than ‘‘dune 2.’’
The total width of the beach–dune system increased from approximately 75 m
in 1978 to 100 m in 2002, owing to the accretion of additional beach formed by
less calcareous marine sand (Vestergaard 2006). On this beach, a low dune, represented by ‘‘dune 4,’’ had developed in 2002 (Figs. 4.2, and 4.4). This propagation and development of new foredunes is similar to those examined by for
example Hesp (1989) and McLean and Shen (2006).
54
P. Vestergaard
The species diversity in the permanent plots was expressed by the number of
species as well as by the Shannon–Wiener diversity index. These measures were
found to be highly significantly positively correlated (Fig. 4.3). Therefore, the
discussion of the trends in plant diversity development presented here will be
based on the number of species per plot.
For each of the dunes, the correlation between the number of species per plot
and the following dune attributes was investigated: number of years since establishment, dune height, distance to the sea, and total plant cover. The plant species
were classified according to their life forms (Raunkiær 1907, 1934), and diaspore
dispersal strategy, following Andersen (1993).
The frequency and Hult–Sernander cover data were combined into a 1–9 cover–
abundance scale (Vestergaard 2006). Based on this scale, the species composition
of the relevées was subjected to TWINSPAN classification analysis, cut levels
0–2–4–6–8, using the program PC-ORD (McCune and Mefford 1999).
4.3 Results
4.3.1 Change in Dune Morphology 1978–2002
The morphology of the landward part of the initial man-made dune remained fairly
unchanged during the study period, while in other parts, the morphology changed
substantially (Fig. 4.2).
In the seaward part of the initial dune, a net accumulation of up to approximately 0.4–0.5 m of windblown sand was recorded. On the beach, new foredune
ridges, parallel to the initial dune, gradually developed, supported by A. arenaria,
which spread from the planting in the initial dune, as well as by other duneforming grasses. Thus, in the inner part of the beach, the dune, represented by
‘‘dune 2,’’ accreted rapidly (0.15 m year
-1 ) to about the same height as the top of
the initial dune, +3 m DNN (Figs. 4.4, and 4.5). After 1990, this dune stabilized,
and the height did not change significantly. On the outer part of the beach, another
new dune, represented by ‘‘dune 3,’’ developed, albeit a little more slowly
(0.1 m year
-1 ). In 2002 this dune was about 0.5 m lower than ‘‘dune 2.’’
The total width of the beach–dune system increased from approximately 75 m
in 1978 to 100 m in 2002, owing to the accretion of additional beach formed by
less calcareous marine sand (Vestergaard 2006). On this beach, a low dune, represented by ‘‘dune 4,’’ had developed in 2002 (Figs. 4.2, and 4.4). This propagation and development of new foredunes is similar to those examined by for
example Hesp (1989) and McLean and Shen (2006).
54
P. Vestergaard