When humans first settled in New Zealand around 1250–1300 AD, more than 80% of the land was covered with tall evergreen forests. There were two main types: conifer–broadleaf forest and southern beech (Nothofagus) forest.
Conifer–broadleaf forests extended from northern New Zealand to Stewart Island, occupying most of the lowland and fertile hill country. Much of this forest was later cleared and turned into pasture, so only small areas remain.
The mountains were mostly covered up to the tree-line in beech forest, except for a few areas of conifer–broadleaf forest. These forests are largely intact, because the land was not so accessible or useful for farming.
Conifer and broadleaf
Conifers are an ancient group of plants which reproduce via seeds. They produce cones, but do not flower. Twenty species of conifer are endemic to New Zealand (found nowhere else). The most common in conifer–broadleaf forests are kahikatea, mataī, rimu, tōtara and miro.
Broadleaf is a general term for large-leaved, evergreen flowering trees. There are about 100 species in New Zealand, including kohekohe, tawa and taraire. It is also the common name of a small flowering tree, kāpuka (Griselinia littoralis).
New Zealand’s conifer–broadleaf forests typically have a dense canopy of broadleaf trees, with large conifers jutting up through the canopy.
There are different types of conifer–broadleaf forest in different parts of New Zealand, depending on the growing conditions. Climate, soil, altitude and other factors all affect the plant species that are able to grow.
The most complex, species-rich conifer–broadleaf forest is found in lowland areas. It looks like tropical rainforest, with a layered structure and many vines, perching plants (epiphytes) and ferns. The largest trees are conifer species and northern rātā (Metrosideros robusta).
A fully developed conifer–broadleaf forest has five layers:
- tall trees (mostly conifers) emerging through the forest canopy, 30–50 metres high
- a canopy of broadleaf trees, around 20 metres high
- a subcanopy of tree ferns and small trees, 10–15 metres high
- shrubs and young trees, 1–3 metres high
- ferns, grasses and sedges on the forest floor among carpets of mosses, liverworts and herbaceous plants.
Vines and epiphytes grow throughout the layers.
Abundant vines often cover the tree trunks. Some are slender ferns, but others have woody, cable-like stems. Woody vines include several species of climbing rātā (Metrosideros species); bush lawyers (Rubus species), which have sharp hooks; the native passion vine (Passiflora tetrandra); species of clematis; the bamboo-like supplejack (Ripogonum scandens), which forms near-impenetrable tangles; and kiekie (Freycinetia banksii), most common in swamp forests, which has long narrow leaves with fine-toothed cutting edges.
Conifer–broadleaf forests include many epiphytes – plants that grow by perching on other plants. This diverse group may form veritable gardens in the crowns of the larger trees.
Nest epiphytes look like nests for very large birds. The three New Zealand nest epiphytes belong to the lily family. They have tufts of long, narrow leaves and build up large amounts of dark humus from their own decayed roots and leaves. Several smaller orchids and ferns, and a few small shrubs, also germinate in the soil and litter around nest epiphytes.
Puka (Griselinia lucida) begins life as a seedling within a nest epiphyte. For a few years it gets nutrients and water from the soil and litter around the epiphyte. Later, it sends a fluted root down to the ground for a more reliable source of food and water.
Northern rātā (Metrosideros robusta) starts out as an epiphyte in a tall tree, and later becomes a tall tree itself. It sends down roots to the ground that combine to form a pseudo-trunk when the supporting tree dies. The rātā’s presence probably hastens its host’s death. In much of the lowland conifer–broadleaf forest, rimu (Dacrydium cupressinum) acts as the host for the northern rātā.