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Forest Vines to Snow Tussocks: The Story of New Zealand Plants

Cushion Moorland

Cushion Moorland145

Most New Zealand mountains are steep with narrow ridges and distinct peaks, but in central and north Otago in the south of the South Island there are a number of quite different block mountains, bounded by faults, with flat, plateau-like summits dotted with prominent rocky tors (Fig. 113). During the last glaciation when the winds were strong and much of the landscape was open with little plant cover, dust storms would have been frequent and sometimes quite deep deposits of dust, known as loess, would have built up on the hills and mountains. On the loess mantling the flat tops of the Otago mountains, cushion moorland page 193
Figure 114 Close up of cushion moorland. A silvery cushion of Anisotome imbricata surrounded by species of Dracophyllum and Raoulia.Photo: J. W. Dawson.

Figure 114 Close up of cushion moorland. A silvery cushion of Anisotome imbricata surrounded by species of Dracophyllum and Raoulia.
Photo: J. W. Dawson.

forms a low but more or less continuous cover. Conditions here are at least as severe as those of the fellfield, with strong, cold gales from the south, heavy snow in winter and frequent severe frosts. Over a 5 year period on the Old Man Range at 1590 m there were on average 113 ice days, 179 freeze-thaw days and only 73 frost-free days per year.

In this type of vegetation small cushion plants are characteristic, with Dracophyllum muscoides the most common, but also the silvery Raoulia hectorii, Anisotome imbricata (Umbelliferae) with dense silver-grey hairs (Fig. 114) and Phyllachne rubra. Small rosette herbs grow in and between the cushions including Anisotome lanuginosa (also with dense matted silver-grey hairs obscuring the leaves) and the small spaniard Aciphylla hectorii. A few small grasses, sedges and luzulas of the rush family may also be present, and small grey lichens are often an important component.

As a result of freeze/thaw action the surface of the cushion moorland is often shaped on level areas into a very regular pattern of hummocks and hollows, which tend to elongate into alternating ridges and trenches on slopes.