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The Frisian islands (Southern North Sea) have extensive island tails, i.e. the entire downdrift side of an island consisting of salt marshes, dunes, beaches and beach plains, and green beaches. Currently, large parts of these tails are ageing and losing dynamics, partly due to human influence. This may mean a loss of young stages on the long term, and current management is not enough to counteract this. To aid the development of new interventions aiming at (re)introducing natural dynamics, a conceptual model of island-tail development under natural and disturbed conditions was developed, based on existing data, field visits and literature. The development of an island tail follows the general pattern of biogeomorphic succession. The first phase consists of a bare beach plain. In the second phase, embryonic dunes form. In the third phase, green beaches, dunes and salt marshes form, including drainage by creeks and washovers. In the fourth phase, vegetation succession continues and the morphology stabilises. Human interference (such as sand dikes and embankments) reduces natural dynamics and increases succession speed, leading to a reduction in the diversity in landforms and vegetation types. Both for natural and human-influenced island tails, succession is the dominant process and large-scale rejuvenation only occurs spontaneously when large-scale processes cause erosion or sedimentation. Island tails cannot be kept permanently in a young successional stage by reintroducing natural dynamics through management interventions, as biogeomorphic succession is dominant. However, such interventions may result in local and temporal rejuvenation when tailored to the specific situation.

A field survey of the infection of dune plants by vesicular-arbuscular mycorrhiza (VAM) has been madein the coastal sand dunes of the province of North Holland, The Netherlands. Winter annual grasses and herbs are not or nearly not affected, whereas perennial plants, especially the grasses Agrostis stolonifera and Calamgrostis epigeios have a high degree of VAM infection. Seasonal changes of the infection degreegenerallyoccur; the highest infection is found in summer.In greenhouseexperimentsat 20°C infectioncould be induced in the dune annual Phleum arenarium by Glomus fasciculatum and G. mosseae. The dune annual Aira praecox, however, could not beinfected. This result is discussed in relation to seasonal development and temperature demands ofVAM.In greenhouse experiments with Calamagrostis epigeios, infection by Glomus fasciculatum and G.mosseae had no positive effect on growth of, or phosphorus supply to C. epigeios. Both Glomus species cause differential translocation of phosphorus and potassium from roots to shoots of C. epigeios.The ecological importance of these results is discussed in relation to the hypothesis of drought protectionand nutrient translocation by VAM.

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