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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.

AbstractFifteen populations of the naturalised grass, Agrostis capillaris, sampled from southern New Zealand, were examined for responses to a range of levels of light, fertility, and water availability. Populations from open, dry areas had genetically low, but plastic, allocation to shoots. Populations from shady areas were more upright than average, and had greater leaf areas, whereas a lawn population was prostrate, but had high allocation to shoots. There was evidence of genecological variation in response to the marked site differences in soil-water availability. Population-based variation in specific leaf area was correlated with rainfall and soil nitrogen and phosphate levels. Differences between populations in other characters did not correlate with environmental trends. Responses indicate some adaptation of populations to their local environments in New Zealand, but also high within-population variation and some instances of nonadaptation. Plasticity is high — as much as 80% of the total variation between treatments — as is typical for a weedy, invasive species. Plasticity, coupled with some genecological differentiation, seems the most likely explanation for the widespread distribution, both spatially and ecologically, of Agrostis capillarisin New Zealand.