The number of species found on North Island mountains is only about one-third of that found in the Southern Alps. The general pattern of mountain vegetation is found on Mt. Egmont where mixed rain forest gives place to shorter trees and shrubs; Libocedrus, mountains totara, hebes, shrubs of the daisy family, and tall tussock. Above are the alpine meadows and then the loose scoria in which few plants can maintain a footing. Lichens are prominent and some moss in boggy places. In the chain of the Ruahine-Tararua mountains there is the same general pattern and many of the same species are found.

The Central Plateau

That the type of soil is one of the most important factors in plant association is shown in the volcanic region, as in the Dun Mountain of Nelson. On the eastern slopes of Ruapehu there are extensive areas of scoria and at the base of the mountain much volcanic ash. These slopes have the same aspects as the nearby Kaimanawas, but instead of mixed rain forest, there is on Ruapehu a beech forest showing great variation in leaf form. The plant associations here are patchy, in places sheltered from sun and wind; Nothofagus fusca and N. cliffortioides are predominant. Under beech trees there is often a layer of fallen leaves up to 2 in. deep, in which little undergrowth survives.

The belt of shrubs above is dense and consists of Phyllocladus alpinus, species of Dacrydium, Coprosma, Olearia, Senecio, Hebe, and Nothopanax. Some of these, in upper limits, are prostrate or creeping. Smaller plants are Libertia pulchella, and some species of fern such as Hymenophyllum multifidum, Blechnum, and Polystichum spp. On the western slopes the belt of shrubs above the mixed forest is more like that of the Southern Alps. On Tongariro there are deep gullies, at altitudes of 4,000 to 5,000 ft where better soil has accumulated and growth is more dense. The dominant species is Phyllocladus alpinus with species of Dracophyllum, Nothopanax, Olearia, Coprosma, also Leptospermum scoparium and Gleichinia cunninghamii.

In some cases bogs occur only in certain seasons, and here Luzula colensoi is seen of very much greater size than in its usual habitat of dry scoria. Sphagnum moss occurs in bogs and may become the bed for germination of seed of manuka. Arundo conspicua, Drosera spathula (a carnivorous plant), and species of Carex may be found. As the streams are swift and icy, few algae are found. Close to the banks are Ranunculus rivularia, Celmisias, Juncus, and Epilobium. In hot springs at Ketetahi there are some blue-green algae and the fern, Hystiopteris incisa. On the pumice-covered plateau in the centre of the North Island and on the lower slopes of the three volcanoes, Ruapehu (9,175 ft), Ngauruhoe (7,515 ft) and Tongariro (6,458 ft), there is scrub formation, mainly of manuka (Leptospermum scoparium), with the attractive small shrub Gaultheria oppositifolia (snowberry), as well as G. colensoi and G. paniculata. There are eight species of Gaultheria, all endemic. G. rupestris is widespread in both Islands, and G. subcorymbosa and G. crassa are found on the Ruahine and Tararua Ranges and in the mountains of Nelson. These little shrubs have a profusion of small flowers, but the berries are larger and more showy. In this region is Dracophyllum subulatum, one of the grass trees, which lives on the poor soil of the volcanic plateau, on the Rangitaiki Plains, and in the Ruahine Range. D. stricta and D. recurvum are found in similar localities in the centre of the North Island sub-alpine regions. Other species of the genus are found in South Island sub-alpine regions, or in lowland areas.

Two species of Ranunculus, R. nivicolus, a slender erect herb, and R. carsei, a prostrate hairy shrub, also R. ignis, are found on the three mountains of the central plateau, and also on Mt. Egmont. The willow herbs, species of Epilobium, E. pernitens, E. perplexum, and E. cockaynianum, may be found in pockets of earth on the Ruahine and Tararua Ranges and on Mt. Egmont. The little eyebrights, Euphrasia monroi, and E. tricolor on Ruapehu, Tongariro, and Egmont are partly parasitic in habit. On the scoria slopes of these mountains there is very little vegetation, but several species of Parahebe, P. spathulata with a root of great length and small, succulent, hairy leaves, and P. hookeriana, a much-branched, woody prostrate shrub, do survive. On Mt. Egmont are masses of alpine foxglove Ourisia macrophylla, which is also common on the volcanic plateau and Ruahines, where O. colensoi, O. caespitosa, and O. vulcanica are also found. Another common plant is Celmisia glandulosa, also C. spectabilis in patches of damp ground. C. incana and C. hieracifolia, with Astelia montana, form a conspicuous part of the vegetation of the Ruahine and Tararua Ranges, while the edelweiss, Leucogenes leontopodium, grows in large masses in alpine regions from the centre of the North Island to Canterbury, but the other species, L. grandiceps, is in South Island only. Of the Olearias, O. nummularifolia and O. ilicifolia are widely distributed mountain species. Senecios are very common subalpine plants. The shrubby groundsels, S. eleagnifolius and S. adamsii, are found in the Tararua and Ruahine Ranges but most species occur only in the South Island.

Similar plant covering was found on the slopes of Mt. Tarawera before the eruption of 1886 when large areas were covered by volcanic ash, in some places to a great depth. Where the covering of ashes was but a thin one, the vegetation reappeared in almost its original form, but in other areas there were great changes. Following the eruption very heavy rain caused changes in the land, so that many gullies were formed in the loose soil. Here some new species became established from seed brought by birds or blown by the wind. Masses of toetoe, Arundo conspicua, are now seen, with much tutu, Coraria sarmentosa and cushion plants of Raoulia australis. Some plants described by early botanists have not been found since the eruption: such is the case of Utricularia mairii, one of the unusual bladderworts, found floating in Lake Rotomahana and described in 1872 by T. Kirk and G. Mair.