Current State of Ammophila arenaria (Marram Grass) Distribution in the Eastern Cape, South Africa, and the Possible Effect of the Grass on the Dune System Dynamics

Abstract

The principal aim of this paper is to show that marram grass is not an invasive alien in South Africa although it affects the dune dynamics as a useful pioneer species in the dune successional process. The historical perspective of marram introduction as a dune stabiliser and the studies and conclusions reached from our European Union funded project, INVASS, in the 1990s and early 2000s is presented. Although these studies showed that marram was non-invasive, this was not clearly carried through to the authorities, and the use of the grass as a dune stabiliser was limited without a special permit. This prompted a survey of the current situation of marram on dune sites in the Eastern Cape. Along with earlier (1980s) data on the dunes, 69 relevés with 66 species abundance from sites along the Eastern Cape shoreline were assembled. These data were analysed with Detrended Correspondence Analysis to show the relationships of the samples (relevés) and species in a 2-dimensional scatter diagram. The survey showed that there are four dune sites where marram grass is no longer present, due to either marram being out of its climatic range, erosion of sand under storm conditions which made the habitat unsuitable, or in one case where marram simply disappeared. Marram often remains in other sites where three to five dune pioneer species were recorded. On some dunes, although marram is the most abundant dune pioneer, it is never dominant in the dune environment but has a presence of as much as 75% at any site. The eight pioneer species are widely dispersed on the DCA scatter diagram, while the shrub species characterising the Coastal Scrub are tightly clustered, showing that all the pioneer dune communities behave similarly in the dune successional series. The conclusion from these studies is that marram grass does not always persist in the dune systems. If marram does persist, it does not compete and behaves identically to the indigenous species as a dune pioneer. These studies show that marram grass is a non-invasive species that can be successfully used in dune stabilisation on Cape dunes.

Keywords: coastal management; dune systems; invasive alien plants; marram grass.

Figure 1

Distribution of Ammophila arenaria (marram grass) in the Eastern Cape, area B. Size of the dots shown in the map below indicates the area planted in hectares, see scale above. There was no area of >100 ha in this region (modified from Hertling [1]).

Figure 2

Abundance of Ammophila arenaria (marram grass) and seven other pioneer dune species sampled in 9 sites along the Eastern Cape coast. (Site 3 = Hamburg; 4 = Mtati Mouth, 7 = Kleinemonde; 8 = Port Alfred; 9 = Kenton; 14 = Port Elizabeth, Summerstrand; 16 = Sardinia Bay; 17 = Paradise Beach; 21 = Oyster Bay. For full names of species, see Table 3 above and in the text.).

Figure 3

Scatter plot of all the 64 species of the coastal dunes in the Eastern Cape sites on the first two axes produced by Detrended Correspondence Analysis. See Table 3 for species names listed in full.

Figure 4

(A) Clumps of Agropyron distichum (sea wheat) on a wind eroded dune at Kenton-on-Sea. Note the exposed elongated rhizomes. (B) A young sea wheat plant in the wet sand.

Figure 5

(A) Ammophila arenaria (marram grass) at Oyster Bay being replaced by shrubs with coastal scrub in the distance. (B) Ehrharta villosa (pypgras) at Hamburg on the rear dunes, where it is replaced by shrubs such as Passerina rigida (dune string).

Figure 6

Scatter plot of all the 69 relevés of the coastal dunes in the Eastern Cape sites on the first two axes produced by Detrended Correspondence Analysis. The four communities are shown, and their perimeters designated. The arrows show that the successional pathways and some dominant pioneer species are positioned where they are most abundant. The three pioneer communities are dominated by the three species indicated: early coastal scrub—Ehrharta villosa (pink); dune pioneer communities of hummock or foredunes—Ammophila arenaria (green); and early dune pioneer communities—Agropyron distichum (blue). The communities are shown roughly as closest and farthest distance from the shoreline from right to left.

Figure 7

(A) St Francis Bay Main Beach that has completely eroded due to inappropriate stabilisation of the dune field that provided the sand supply. Holiday homes are in danger of collapse, as they are positioned just above the eroding dunes shown here (see Lubke 1988). (B) Maitland River Mouth where marram grass has never been introduced but any dune pioneers would have little chance of becoming established due to the exposed nature of the undisturbed dunes and the high wind velocities achieved in this area.

Figure 8

Moribund Ammophila arenaria with its erect rhizomes that grow up as the drift sands are deposited.

Figure 9

Marram grass planted at Hout Bay in 2017, near Cape Town to prevent sand from blowing onto the car park at the harbour (photo: Ted Avis). This project won the South African Landscapers Institute’s (SALI 2020) top award for excellence in landscaping, out of more than 100 projects submitted.