Keywords:
onshore barrier dunes
aeolian transport
marram grass
Ammophila arenaria

Contact:  W.H. van der Putten. Netherlands Institute of Ecology. P.O. Box 40. NL-6666 ZG Heteren. The Netherlands. E-mail: putten@cto.nioo.knaw.nl.

Location:  The Netherlands, Oostvoorne – Noordwijk - Oostkapelle

Stabilisation of coastal foredunes with Ammophila arenaria 
Ammophila arenaria (marram grass) is the most important plant species for sand stabilisation in European coastal foredunes. However, in stabilised dunes marram grass often degenerates because of a poor supply of wind-blown sand. The degeneration enhances the susceptibility for wind erosion. If successional species do not become established this leads to the creation of blow outs. Replanted marram grass in blow outs often fails to become established.

Observations
In 1990, the Netherlands Institute of Ecology examined whether management practices such as mowing, fertilising, burning and below-ground cutting of plants may be applied to re-establish the vigour of Ammophila arenaria. Furthermore, it tested the establishment of natural successors of the marram grass. Three locations for field experiments in Oostvoorne, Oostkapelle and Noordwijk were chosen. All sites concerned calcareous foredunes.
In 1993 to 1994 the Netherlands Institute of Ecology together with the University of Amsterdam - Department of Physical Geography and Soil Sience carried out further studies in the coastal foredunes of Voorne and Goeree. The rejuvenation of marram grass on the edges of the blowouts occurs whereas replanting in blow outs itself often fails. They pointed out that this pattern of rejuvenation and non-rejuvenation is due to a process involving soil-borne pathogens and parasites. This hypothesis was investigated in several field and laboratory experiments.

Results
The first study pointed out that densities of the stands of marram grass corresponded with sand depo-sition. No management practice successfully enhanced the tiller densities of the marram grass. Cutting plants below-ground was effective only at the most dense stand.
The establishment of natural successors of Ammophila arenaria hardly showed success either. However, planting may have been more effective than sowing and cuttings produced more tillers than seed-lings. Pre-grown seedlings can be established throughout the whole winter, but bundles of culms can be better planted early in winter. Nearly none of the plants at unfenced plots survived due to rabbit browsing. Fertilisation had a stimulating effect, but the release of nutrients lasted less than one year and stoped after this time. The establishment of Festuca rubra and Elymus athericus could be regarded as most successful.
The second study showed that soil from the root zone of vigorous stands of Ammophila arenaria contained a higher number of fungal propagules and nematodes than soil from deflation zones of blow outs. Nematodes seemed to be strongly affected by wind-driven sand transport which crushed them between sand particles as well as propagules of several fungi. Aggregates of fungi and bacteria, mainly transported attached to soil particles, were broken because of sandblow and fungal hyphae were destroyed. Soil organisms may have been sifted out because of their weight. Growth of marram grass was best in sterilized sand but also improved in blown sand. Plants in stirred sand, which should imitate the blowing process, produced more biomass correlated to the mixing intensity.
Altogether, the only effective way to maintain vigour of Ammophila arenaria is by fresh wind-blown sand to be deposited in the vegetation. Reactivation of blow outs could be a measure to rejuvenate deteriorated stands. In the case of replanting blow outs, Ammophila arenaria should be planted in the centre of the blow out in the bare sand. Sand nourishment will also lead to rejuvenation of the dunes.
 

References

• de Rooij-van der Goes, P.C.E.M., C. van Dijk, W.H. van der Putten & P.D. Jungerius (1997): Effects of sand movement by wind on nematodes and soil-borne fungi in coastal foredunes. Journal of Coastal Conservation 3: 133-142. EUCC. Opulus Press Uppsala. Sweden. (KJc97b).
• van der Putten, W.H. & B.A.M. Peters (1995): Possibilities for management of coastal foredunes with deteriorated stands of Ammophila arenaria (marram grass). Journal of Coastal Conservation 1: 29-39. EUCC. Opulus Press Uppsala. Sweden. (KJc95a).
• see also: The role of marram grass (Ammophila arenaria) in the re-establishment of natural vegetation in coastal fore-dunes, Voorne, The Netherlands.