Types of Vegetation
The distribution of plants in New Zealand is very restricted but this is not surprising when one considers how sudden within a short distance are the changes from sea level to snow line; how the high mountains cause a great variation in rainfall; and how varied are the soil and other conditions in sheltered valleys, on mountain screes, and on wind-swept shores. All types of habitat are found within short distances and each is occupied by distinct types of plants. Many of the plants found in the exposed coastal regions or in high altitudes are xerophytes. The vegetation of the North Island varies much from that of the South Island; it seems that Cook Strait forms a natural barrier to the distribution of many species. Two other definite boundaries seem to be 38° S latitude in the North Island and 42° S latitude in the South Island. In the forests of North Auckland, Great Barrier Island, and Coromandel Peninsula the kauri and taraire are dominant trees, but are not found below 38° S. Tawa is found in central North Island and to 42° S. Plants of general distribution throughout the country are manuka (Leptospermum scoparium) and bracken fern (Pteridium esculentum). A feature of the landscape is the wealth of tree ferns, and the profusion of other ferns within the shady forests has given rise to the use of a fern leaf as a national emblem.
The general aspect of vegetation is that of the conspicuous plants such as the flowering plants and conifers, and the ferns and lycopods. But of importance are the inconspicuous plants: the lichens of barren rocky regions, the mosses and liverworts of the humid interior of the forest, the fungi which are so often overlooked, and the algae both of sea and of fresh water.
The New Zealand forest is typically dark green in all seasons of the year and has little resemblance to forest of similar latitudes in the Northern Hemisphere. Deciduous trees, summer-green herbs, and annual plants are uncommon. Most of the canopy trees are evergreen with thick, tough leaves as Beilschmiedia tawa, B. taraire, and Nothofagus species. A few species of Fuchsia (Onagraceae), Sophora (Leguminosae), Hoheria (Malvaceae), and Aristotelia (Elaeocarpaceae), trees of shorter growth in the sub-canopy layer, have thinner leaves and show deciduous habit in varying degrees.
In lowland vegetation summer-green herbs are of little importance. In some areas are found small orchids (Thelymitra and Pterostylis) and in swampy areas Typha muelleri (fresh water swamps) and Scirpus americanus (salty swamps). In montane tussock grasslands are Coriaria spp., and in alpine meadows Ranunculus lyallii as herbaceous forms, while in higher altitudes on screes on the Southern Alps are found Anisotome carnosula (Umbelliferae) and Ranunculus haastii. In the sub-Antarctic Islands commonly found herbaceous plants are Bulbinella rossii (Liliaceae) and Pleurophyllum criniferum (Compositae). Allan noted the scarcity and unimportance of indigenous annuals.
A common habit of growth is found in divaricating shrubs, with densely tangled branches, small leaves, and inconspicuous flowers. Over 50 species show this habit, of which common examples are Plagianthus divaricatus of coastal salt swamps, Coprosma rhamnoides of forest, Melicope simplex of coast and forest, with Corokia cotoneaster and Sophora prostrata of open hillsides.
Mat and cushion forms of growth are characteristic of two endemic Compositae genera, Raoulia and Haastia, found mainly in the South Island. Large plants of these with their dense growth of leaves, thickly covered with white hairs, have been aptly termed “vegetable sheep”.
In swampy areas are toetoes (Cortaderia spp.), large clumps of native flax (Phormium tenax and P. colensoi), and cabbage trees with great tufts of sword-like leaves (Cordyline spp.).
Of plants showing distinct juvenile and adult forms there are some striking examples in New Zealand. Most noticeable among these is the lancewood (Pseudopanax crassifolium) of which the juvenile form has a slender stem with rigid deflexed leaves of leathery texture and sharply toothed margins, which may be 2 to 3 ft in length. The adult has a thick trunk with a crown of broad, short, erect leaves. The young trees of rimu (Dacrydium cupressinum) is an extremely graceful tree of drooping habit, with tiny leaves closely pressed to the stems, but the older tree is erect, with long straight trunk and a crown of larger leaves. Some plants when young have a divaricating habit, with small leaves, as Pennantia corymbosa and Hoheria angustifolia, but lose this habit in the adult stage and grow erect with larger leaves.
Another form of growth is seen in the tussock country where “bunch grasses” cover large areas. These are referred to as low and tall tussock, red and silver tussock, and snow tussock, and are species of Poa, Festuca, and Chionochloa.
Other areas are referred to as scrub country. These are often regions where forest has been destroyed by man, or by volcanic ash, and the dominant plants now are manuka, bracken fern, tauhinu (Cassinia), and plants of similar type. Where such an area is left undisturbed, especially by introduced animals, natural regeneration of native forest may take place.
Lianes and epiphytes, usually associated with tropical and subtropical forest, are found in great profusion. Climbing by various means are characteristics of such plants as species of Clematis(by means of twining stems or petioles),Tetrapathaea (by means of tendrils), supplejack (Rhipogonum scandens) (by twining), bush lawyer (Rubus australis) (by hooked spines), and the climbing rata (Metrosideros florida) and many ferns (by roots). The perching habit of growth, merely for a place to live, is common among mosses and ferns (Asplenium flaccidum), but there are also many flowering plants such as the perching lilies (Astelia spp.), the perching kohuhu (Pittosporum), and many orchids (Dendrobium and Earina). Some species of Metrosideros and Pittosporum begin life as epiphytes. Metrosideros robusta sends roots towards the ground, and is found later to have almost replaced the tree on which it has germinated. There are few parasites. Elytranthe tetrapetala (the scarlet mistletoe) and Loranthus micranthus (the common New Zealand mistletoe) are woody shrubs which live as semi-parasites. Dactylanthus taylori, pua reinga, is a unique plant which is a root parasite and has been found in the North Island on roots of Pittosporum, Nothofagus, and Coprosma. The parasitic and saprophytic habits are common among the fungi.