Forest Vines to Snow Tussocks: The Story of New Zealand Plants
The Auckland Islands are currently credited with 187 native vascular plant species,160,161 of which perhaps 6 are endemic and a further 22 are page 207found elsewhere only on other subantarctic islands in the New Zealand region.
The relative richness of the Auckland Islands' flora compared with Macquarie reflects partly their lower latitude (51°S); partly their larger size (the main Auckland Island and the barely separated Adams Island are about 50 km long by 10-30 km wide); and partly a less severe climate during the last glaciation which probably allowed some of the previous interglacial flora to survive. The last is also likely to be true of the Campbell and Antipodes Islands.
The Auckland Islands also contrast topographically with Macquarie in having a very indented eastern coastline and, between the glacially steepened valleys, mostly gradual slopes leading up to ridges and distinct peaks, sometimes flat-topped, up to 668 m in altitude (Fig. 116).
The Aucklands are the only islands in the New Zealand subantarctic with forest. Forest forms a narrow zone up to about 50 m above sea level on sheltered shorelines and is dominated by southern rata (Metrosideros umbellata) in association with Dracophyllum longifolium var. cockayneanum and Pseudopanax simplex. Undershrubs are Coprosma foetidissima (stinkwood), the Dracophyllum and Myrsine divaricata, while on the forest floor the ferns Polystichum vestitum, Asplenium scleroprium, and Blechnum page 208durum are abundant in places. Fuchsia excorticata has been recorded from one locality and the tree fern Cyathea smithii from several sheltered north-facing valley sides in the eastern inlets. The trees of this forest are unusual in that the lower parts of their trunks and branches are inclined or even prostrate as a result of wind action. Cockayne162 describes this very graphically: 'Everywhere are the massive prostrate and semi-prostrate trunks of the southern rata, sometimes lying close to the ground, at other times forming great arches, or at others again natural bridges over the deep depressions of the forest floor.'
At a few localities at the north-east tip of the main island and on adjacent islets there is also a coastal forest of the large-leaved Olearia lyallii. This species has increased its range in Port Ross over the past century and may have reached the Auckland Islands from southern New Zealand as recently as early last century.
Above the narrow forest zone there is a wider belt of 'scrub' or shrubland. Some of the scrub species are also found in the forests, but in the shrubland they are reduced to 1-2 m in height and when dominated by Myrsine divaricata they are so dense as to be almost impenetrable. Myrsine divaricata is the dominant species on the upper parts of the valley sides and Dracophyllum longifolium immediately above the rata forest. On some gradual slopes the scrub is arranged in an unusual pattern (Fig 116). It forms narrow strips, more or less parallel to the contours, which alternate with open lanes with a ground cover of low plants including hard cushions of Oreobolus pectinatus, stunted plants of the scrub species, gentians, orchids and scattered tussocks of Chionochloa antarctica.163 We still await a detailed study which might lead to an explanation of this pattern.
Above 300-400 m in altitude the shrubland gives way to a grassland dominated by the large yellow-green tussocks of Chionochloa antarctica. It seems probable that a similar grassland originally occupied the 'lanes' within the shrub zone, but these have been greatly modified by the activities of wild pigs.
Several large herbs were a conspicuous feature of the tussock grass-page 209land particularly at lower elevations and this is still the case in 'Fairchild's Garden' near sea level on Adams Island, where pigs are not present. Cockayne162 describes the area as 'a wonderful collection of stately herbs with immense leaves, and in some cases masses of showy flowers'.
Anisotome latifolia has large, dark green dissected leaves and broad, pink to purple flower heads. Stilbocarpa polaris, already described for Macquarie, may also be common. Two species of Pleurophyllum are conspicuous — P. speciosum (Fig 117) with rosettes of almost circular, pale green longitudinally pleated leaves up to 30 cm in diameter and P criniferum with even longer, but ascending, leaves up to 1 m long. The former has quite large flowers with purple centres and pinkish 'petals', while the latter, although its flower heads may be 1.5 m high, has red, dome-shaped button flowers similar to those of Pleurophyllum hookeri. Towards the upper limits of the garden Pleurophyllum speciosum and Bulbinella rossii become particularly abundant. Bulbinella rossii is much larger than its mainland relatives and has broad arching leaves and large orange-yellow flower heads.
Figure 117 Close up of large herbs on the Auckland Islands. The plants in flower with broad ribbed leaves are Pleurophyllum speciosum. The dissected leaves on the left are Anisotome latifolia and the rounded leaves with toothed margins centre and right are Stilbocarpa polaris. A flower head of the latter appears in the left background. Photo: D. J. Campbell.
At higher altitudes, and also in the 'lanes' at lower altitudes, on very wet, more or less level sites there is a low plant cover of mat or cushion plants including Carpha alpina, Astelia linearis, Oreobolus pectinatus, Centrolepis ciliata and 'glistening green mats' of Damnamenia vernicosa, an endemic genus formerly included in Celmisia.
Some of the exposed summit peaks have a stony mineral soil with little peat development. They support a variety of plants, including Pleurophyllum hookeri which is often common, Plantago aucklandica with its large leaf rosettes, Ranunculus pinguis with unusually large yellow flowers for the size of the plants and Myosotis capitata with brilliant dark blue flowers.