Observations on the ecology and conservation ofAustralopyrum calcis(Triticeae: Gramineae) in New Zealand

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Abstract
The ecology and conservation of the newly described endemic calcicolous grass Australopyrum calcis are outlined. Of the two infraspecific taxa recognised, subsp. calcis is confined to Marlborough on Mesozoic limestone exposed for at least 2 million years, and subsp. optatum is restricted to Canterbury on Tertiary limestones exposed from about the mid Pleistocene. Limestone colluvium and karst landforms such as tor overhangs are the main contemporary habitats of these grasses, and both taxa grow on sparsely vegetated skeletal rendzinas that are strongly alkaline and high in CaCO3 and available phosphorus. Broad-leaved low forest and “grey scrub” form the dominant natural vegetation of these habitats, and the indigenous flora comprises both wide-ranging species and regional or local endemics. Associated naturalised plants include many species recorded from limestones in Europe. The two subspecies tolerate moderate shade, avoid competition, and seem unpalatable to grazing animals. They appear to have retreated to suboptimal environments in small, relatively dry, high-risk refugia now surrounded by aggressive naturalised plants. Both taxa are therefore in danger of extinction, and although they are not constrained by their breeding system, their future in the wild will depend on soundly based practical conservation measures, especially the retention and enhancement of suitable habitats. The so-called calcicolous element of the New Zealand flora is considered to be underestimated in importance because of a rather narrow interpretation of the term. A broader definition is proposed that includes wild plants characteristic not only of limestones but also of other base-rich rocks, such as basalts, schists, and calcareous mudstones. The origin of Australopyrum and its migration to New Zealand are unknown and open to speculation. Available genetic and DNA information indicates a possible Asian origin, and current geological and fossil plant evidence suggests a mid-Tertiary entry to the country, perhaps during the Miocene or even earlier, and possibly involving one immigration event. Of the two taxa, subsp. optatum is considered the younger isolate. However, compared with other grasses such as Poa and Chionochloa, Australopyrum has not succeeded in diversifying in New Zealand environments and is a relict here, in contrast to its comparatively common relatives in Australia. The emergence of strips of Tertiary limestones by fault movements and the erosion of cover deposits is seen as a major factor in the evolution of calcicolous plants, including many new taxa observed during this study. Much of this speciation is regarded as recent, and has probably occurred since the early Pleistocene or even more recently.