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

Kermadec Islands

Kermadec Islands

The Kermadecs are a row of small islands about 1000 km north-east of New Zealand. The largest and northernmost island is Raoul at 29°S, but it measures only about 10 km by 8 km with a highest point of 520 m. It is a volcano which is active from time to time. Macauley Island, the next island to the south, is only 2 km long, and the southernmost island with a significant flora, Curtis, is even smaller.

With the warm, humid climate, forest is the predominant vegetation cover.173 On Raoul Island Oliver174 distinguished a lower altitude 'dry' forest and above 2–300 m a higher altitude 'wet' forest. Metrosideros kermadecensis, up to 20 m tall, dominates the canopy of the lower forest. Karakas (Corynocarpus laevigatus) and ngaios (Myoporum obscurum, closely page 217related to M. laetum) also reach 20 m in height in sheltered places; considerably greater dimensions than they usually attain in New Zealand. There is a rather sparse subcanopy dominated by Myrsine kermadecensis but also with mahoe (Melicytus ramiflorus), ngaio, karaka, Melicope ternata, Coprosma acutifolia, the nikau palm relative Rhopalostylis baueri var. cheesemanii (sometimes forming picturesque groves), Cyathea milnei, and the endemic Homalanthus polyandrus, now increasing markedly owing to the great reduction in numbers of goats. The fern Pteris comans, up to 2 m high, is the commonest plant of the forest floor (although in many places the introduced aroid Alocasia macrorhiza is dominant), but there are also a number of other ferns and the large leaved form of kawakawa (Macropiper excelsum f. psittacorum) along the north side.

The upper or 'wet' forest is mostly about 10 m high and comprises the same species as the lower forest with the addition of Ascarina lucida var. lanceolata, which dominates the understorey, and, in a few places, the tree fern Cyathea kermadecensis. C. kermadecensis occasionally forms impressive groves where some specimens, according to Oliver, have trunk bases 1–2 m in diameter. The forest floor and trunks and branches of trees are covered with mosses and ferns. Common epiphytes familiar to New Zealanders are the ferns Thymatosorus diversifolius, Pyrrosia serpens, Asplenium flaccidum and Hymenophyllam demissum. Much rarer are Lycopodium varium, Tmesipteris lanceolata and Trichomanes venosum. There are no lianes in the Kermadec forests and no large epiphytes apart from the occasional Pseudopanax arboreus var. kermadecensis and Metrosideros kermadecensis. The only other flowering plant epiphyte is Peperomia urvilleana.

Close to the sea in many places, as in New Zealand, is a dense shrubbery of the ngaio relative Myoporum obscurum. Probably ngaio shrubbery was the dominant vegetation on Macauley Island, but the fires of early whalers and the activities of goats have almost eliminated the woody vegetation of that island.

In open, mostly rocky coastal habitats are a number of herbaceous plants, including a few ferns. Most of these grow in similar sites in New Zealand. Coprosma petiolata is a common endemic coastal shrub.

The total vascular flora of the Kermadecs is 113 species. Eighteen species and three varieties are considered to be endemic and those with New Zealand affinities are Coprosma petiolata and C. acutifolia, the tree ferns Cyathea milnei and C. kermadecensis, Pseudopanax arboreus var. kermadecensis (close to the New Zealand variety and like it sometimes a tree page 218fern epiphyte), Metrosideros kermadecensis, (known as the Kermadec pohutukawa in cultivation in New Zealand; it has shorter, more rounded leaves than pohutukawa (M. excelsa)), Myoporum obscurum, Hebe breviracemosa (now probably extinct) and the palm Rhopalostylis baueri var. cheesemanii.

About 80 of the 113 Kermadec species are shared with New Zealand, but as many of them are also to be found elsewhere in the Pacific and in eastern Australia, they have not necessarily all been derived from New Zealand.

The Kermadec Islands have arisen as volcanoes in isolation and it seems likely that their flora has resulted from long distance dispersal, with New Zealand probably the most important source.