The first settlers found a large part of New Zealand covered by forest, but in areas such as North and South Auckland, the central volcanic plateau, and inland Hawke's Bay, burnings by Maoris or volcanic eruptions had resulted in extensive areas of grassland, fern, and scrub. Only in the drier parts of the South Island were there large areas of indigenous grassland at low elevations, and evidence suggests that a good deal of this had been in forest in the not-far-distant past. Forests are of two main types.
This is a sub-tropical rain forest in which growth is extremely luxuriant, with small trees, shrubs, ferns, mosses, and liverworts in abundance. The large canopy trees are evergreen, often clothed with epiphytes and festooned with climbing plants. Groves of tree ferns are a notable feature. Despite its tropical appearance, however, this forest does not compare with that of the tropics proper in diversity of tree species. The most important trees only can be mentioned here; none of them is found in the Campbell Islands, and only Metrosideros umbellata in the Auckland Islands where it appears as gnarled and stunted in growth.
The kauri – Agathis australis (Araucariaceae) – is perhaps the most famous timber tree of New Zealand. It is prominent in forests of North Auckland, the Coromandel Peninsula, and the Barrier Islands, extending to 38° S. The resin is of great value and the digging of kauri gum over large areas shows that these forests must formerly have been of much greater extent. Closely related are two species of Libocedrus (Cupressaceae): L. bidwillii, pahautea, and L. plumosa, kawaka, which are cypress-like trees with bark which falls in long thin strips. These are cone-bearing plants or gymnosperms.
There are representatives of three genera of Podocarpus in New Zealand, also cone-bearing plants and usually dioecious. Podocarpus totara is widely distributed and prominent in central North Island. Most of the totara in Westland is the closely related P. hallii which ascends to higher altitudes. P. spicatus, matai or black pine; P. dacrydioides, kahikatea or white pine; and P. ferrugineus, miro, are common in lowland forest.
Most other large forest trees belong to the flowering plants and include taraire, Beilschmiedia taraire, (Lauraceae), one of the commonest trees of the forest of North Auckland, which disappears at 38° S. Beilschmiedia tawa, also an important tree in North Island forests, occurs locally in the eastern South Island to 42° S.
Metrosideros genus (Myrtaceae) is represented by about 11 endemic species. The best known is M. excelsa, pohutukawa, which grows in coastal forests in the north, and also on Three Kings; it is often grown in gardens and parks for its showy red flowers. M. robusta, northern rata, overtops most forest trees in the North Island and extends to about Greymouth in the South Island. It begins as an epiphyte on a tree such as rimu; finally the host tree dies and the rata replaces it. The southern rata, M. umbellata, is important in montane forests in the South Island, especially in the west. Some species are climbers, with woody rope-like stems, such as M. scandens and M. perforata, which have a general distribution in coastal and lowland forests. Their flowers are red. There is also M. albiflora, the white-flowered species, found mainly in kauri forest. The Leptospermums, too, belong to this family; these are the manukas of lowland to montane marginal forests.
Weinmannia racemosa (Cunoniaceae), the kamahi, is the commonest forest tree, extending from about 38° S to Stewart Island, and is important both in lowland and in montane vegetation. North of 38° S is the less common W. sylvicola, tawhero.
Pittosporaceae is represented by some 25 endemic species, found mainly on the margins of forests. Pittosporum eugenioides (tarata, lemonwood), P. tenuifolium (kohuhu), and P. crassifolium (karo) are attractive trees which are often cultivated.
Of the family Araliaceae, Neopanax is a genus of trees and shrubs showing great variety in the form of leaves; N. arboreum is found in lowland forests throughout and N. colensoi in montane forest. Pseudopanax crassifolium (horoeka, lancewood) is remarkable for the difference between juvenile and adult forms. Schefflera digitata (patete) is another member of this family which is widely distributed.
There are about 45 species of Coprosma (Rubiaceae) which are nearly all endemic and unisexual. C. lucida (karamu) and C. robusta (also known as karamu) are very common in forest shrubland, and C. repens (taupata) is found mainly in coastal regions.
Other trees include Carpodetus serratus (putaputaweta), Aristotelia serrata (makomako, the wine-berry), Plagianthus betulinus (Malvaceae), Melicytus ramiflorus (mahoe, whitey wood, of the violet family), Fuchsia excorticata (kotukutuku or konini) with loose papery bark and small greenish flowers. Two species of Griselinia are endemic: G. littoralis (the broadleaf) and G. lucida (puka, the shining broadleaf), both of which are often epiphytic.
Common ground plants in forest areas are: Microlaena avenacea (Gramineae), Astelia nervosa (Liliaceae), Cardamine heterophylla (Cruciferae), species of Uncinia and Carex (Cyperaceae), Epilobium (Onagraceae), Nertera (Rubiaceae), Hydrocotyle (Umbelliferae), and Ranunculus. The floor of forest of this kind is covered by an abundance of ferns, mosses, and liverworts. The tree ferns Cyathea and Dicksonia have been mentioned. Other genera well represented are: Asplenium, Blechnum, Adiantum, Histiopteris, Hymenophyllum, and Grammitis.
Oliver (1930) listed 50 species in New Zealand which are habitually epiphytic and classifies them as follows: semi-woody pteridophytes 3, filmy ferns 20, tufted ferns 7, creeping ferns 5, succulent herbs 2, orchids 7, and the tussock plants Collospermum hastatum and Astelia solandri. Four shrubs as epiphytes are Senecio kirkii, Griselinia lucida, Pittosporum kirkii, and P. cornifolium. Also prominent are the following lianes and climbers: Freycinetia banksii (kiekie), Rhipogonum scandens (supplejack), and species of Tetrapathaea tetranda (passion-flower), Parsonsia (Maori jasmine), Rubus (bush lawyer), and Clematis. Of particular interest is a group of climbing species of Metrosideros, with a habit apparently unique in the Myrtaceae.
These may be dominated by one or more of the four native evergreen species of Nothofagus, often in association with certain podocarps. Beech species are not found on Stewart Island or Mount Egmont, and are also missing from a large segment of the west coast of the South Island. Beech forest may occur from sea level to timber line and in regions with rainfall as low as 25 in. per annum or as high as 250 in. per annum. Nothofagus truncata (hard beech) is the only species found north of about latitude 37°. It was common on islands in the Hauraki Gulf near Auckland and isolated patches are known in North Auckland. It is important in the Marlborough Sounds and western Nelson and reaches the Taramakau River in Westland. N. fusca (red beech) is closely related to N. truncata and extends from about 37° S to Lake Manapouri (45 ½ S). N. menziesii (silver beech) ranges from about 37° S to the southern limit of the genus in New Zealand and is the only beech found in the forests of the extreme south-east South Island. It is often found at timber line. N. solandri var. solandri (black beech) occurs at lower altitudes from near Lake Taupo to the northern half of the South Island, while N. solandri var. cliffortioides (mountain beech) tends to higher altitudes from the latitude of Taupo to the southern limit of the beeches, although absent from the Tararua Range.
Podocarpus hallii and Dacrydium cupressinum are podocarps commonly associated with beech forest.
The interior of Nothofagus forest is, in general, more open than that of podocarp-dicotylous forest. In wetter areas there is some undergrowth but in the driest forest there is very little vegetation under the dense canopy. Some shrubs and small trees commonly found are Pseudowintera colorata, Coprosma foetidissima and C. pseudocuneata, Neopanax colensoi and N. simplex, Phyllocladus alpinus, Myrsine divaricata, and small-leaved species of Pittosporum. Where there is sufficient moisture, bryophytes and ferns (such as a few species of Blechnum, Hymenophyllum, and Polystichum) carpet the forest floor, with herbaceous plants such as Nertera, Microlaena. There are few lianes or epiphytes, except mosses and lichens.
Climatic change: Holloway (1954) has shown that South Island beeches are invading new areas and that podocarps are failing to regenerate on many sites. He suggests that this was initiated about A.D. 1300 by a fall in mean or effective temperature, which gave the beeches a relative advantage over the podocarps. The long-living podocarps may still persist in situations now unfavourable to them.
Wardle (1963) suggests that climatic deterioration became most intense between A.D. 1600 and 1800, and that more recently increased regeneration of podocarps has occurred.