Plant succession and dune dynamics on actively prograding dunes, Whatipu Beach, northern New Zealand

Whatipu Beach, north Manukau Harbour, Auckland, has prograded episodically over 1.5 centuries. Sand dune vegetation is quantitatively described, and related to successional stage, local environment, and progradation dynamics. Foredunes, with fine, mobile, infertile sand, occupy the most recently prograded areas and are partially vegetated by native species. Instead of a dune slack, a stream which changed course to flow between dune ridges has created wet "sand river" vegetation. Relict fore-dunes and a dune slack persist inland of the sand river, disrupting a lineal spatial sequence, as do rear dune wetlands. Less-mobile grass and shrub communities, derived from Ammophila arenaria dunes, occupy surfaces >50 years old. No climax communities are present. In contrast to spatial analogues, the Whatipu dunes demonstrate how rapidly succession proceeds in response to the formation of new habitat, while freshwater movements generate non-seral sand-river communities. Succession is modified by invading exotics and by the absence of many disturbance-intolerant native shrub species. Coastal progradation rates at Whatipu indicate that shrubland develops within 50 years, suggesting that spatial analogues of dune succession can mis-represent the longevity of early seral stages. These unusual successional patterns on dateable surfaces, and the presence of rare flora and fauna, make Whatipu Beach important for conservation.