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Conifer–broadleaf forests

by  John Dawson

With their rich jumble of tangled vines, perching plants and ferns, New Zealand’s conifer–broadleaf forests resemble tropical rainforest. Majestic trees jut up through the leafy canopy, and the forests are home to native birds, bats, lizards and insects.


Overview and features

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.

Forest structure

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.

Vines galore

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.

Perching plants

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

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

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

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.


Forests of northern New Zealand

Northern New Zealand has a warm climate and moderate rainfall through the year. As a result, northern conifer–broadleaf forests have the most diverse species and growth forms. They include a number of trees and shrubs from tropical plant families.

Lowland forests

In northern lowland areas, rimu is the most common large conifer, growing up through the forest’s roof. Others include mataī (Prumnopitys taxifolia), miro (Prumnopitys ferruginea) and tōtara (Podocarpus totara).

Taraire (Beilschmiedia taraire) is the main broadleaf tree in the forest’s canopy. Other canopy trees include tawa (Beilschmiedia tawa), hīnau (Elaeocarpus dentatus) and maire (Nestegis cunninghamii).

Kohekohe (Dysoxylum spectabile), māhoe (Melicytus ramiflorus) and other smaller trees make up the subcanopy. Like a number of tropical trees, kohekohe produces flower clusters directly from its trunk and branches. New Zealand’s only native palm tree, the nīkau (Rhopalostylis sapida), is also usually present, along with several kinds of tree fern.

The dense shrub layer includes hangehange (Geniostoma ligustrifolium) and species of Alseuosmia shrubs with their perfumed flowers. Many fern species grow on the forest floor along with mosses, lichens, brightly coloured fungi and ground orchids.

Swamp forests

On swampy ground the forest composition changes. There are fewer tree species, and the tallest trees are not rimu, but kahikatea (Dacrycarpus dacrydioides). This conifer can grow over 50 metres tall. It looks similar to rimu, which also has leaves reduced to scales. However, rimu has brownish-green foliage and weeping twig tips, while kahikatea’s leaves are bright green or grey-green and its twig tips point upwards.

Pukatea (Laurelia novae-zelandiae) is a tall flowering tree that grows alongside kahikatea. It has two special features similar to some tropical trees, which help it live in the swampy conditions. Thin triangular flanges (plank buttresses) at the base of its trunk help support the tree in the soft ground. Like mangrove, it forms breathing roots (pneumatophores), which project above the soil and supply air to the waterlogged roots.

Maire tawake or swamp maire (Syzygium maire) is a smaller tree in the swamp forest. It also has breathing roots.

Kauri–broadleaf forests

Kauri (Agathis australis), a conifer and one of the world’s largest trees, grows in the poorest soils of the north. Conifers generally do not take many nutrients from the soil. The kauri is even less demanding than most, and can tolerate the thin soils of ridge crests and other infertile sites.

The trunks of mature kauri are enormous columns from the ground to their huge spreading crowns. Kauri either grow in clumps, or individually, among smaller conifers such as rimu, tōtara, miro and tanekaha (Phyllocladus trichomanoides), emerging above a layer of broadleaf trees.

Kauri forests contain some smaller broadleaf trees, but these are stunted and scattered, so the forest floor is quite well lit. Smaller trees include neinei (Dracophyllum latifolium), with its tufted, sword-like leaves. On the ground are dense groves of kauri grass (Astelia trinervia), a relative of one of the nest epiphytes.


Central and southern forests

Forests of central New Zealand

The climate changes further south in New Zealand, and so do the forests. Temperatures are lower, and in the east it rains less. Species disappear from the conifer–broadleaf forests as they reach their limits of tolerance, and some hardier species enter in.

Tawa replaces taraire as the most common canopy tree in the southern two-thirds of the North Island, the Marlborough Sounds and the Seaward Kaikōura Range. Rimu and northern rātā are common as emergent trees in the moist western and central forests. Mataī and tōtara dominate in the drier forests to the east.

High-altitude forests

In the absence of beech forest, a hardier version of conifer–broadleaf forest grows at high altitudes.

In the North Island this is a relatively low forest dominated by kāmahi (Weinmannia racemosa), kāpuka (Griselinia littoralis), mountain tōtara (Podocarpus hallii) and the attractive conical mountain cedar (Libocedrus bidwillii).

In the South Island, southern rātā (Metrosideros umbellata) and Quintinia acutifolia are prevalent.

Large vines and epiphytes are uncommon. But, especially at highest altitudes, many smaller epiphytes – mosses, liverworts, filmy ferns and lichens – flourish in the cool, moist, misty climate. Every branch and twig is engulfed by these small organisms.

Popular host

A kahikatea tree in South Westland holds the record for hosting the greatest number of plant species. Fifty species of epiphytes and climbers make their home upon the old conifer.

The far south

In the southern South Island and Stewart Island, most of the conifer–broadleaf forests are rimu growing above a canopy of kāmahi and southern rātā. Miro and mountain tōtara are also common conifers. Tree ferns, vines and epiphytes flourish in the wet climate.

Southland has high rainfall and many low-lying sites, so there is extensive swamp forest. As in northern swamp areas, kahikatea is abundant, but its northern associates, pukatea and swamp maire, do not grow this far south.

In the lower half of Stewart Island, yellow-silver pine (Lepidothamnus intermedius) is the dominant tree in swampy sites. It is a small tree and forms a low forest, 6–10 metres tall.


Coastal forest

New Zealand’s coastal forest is made up of plants that can tolerate salty winds from the sea. These forests generally lack large emergent conifers, and have fewer vines and epiphytes. Coastal forest usually has a dense wind-shorn canopy of broadleaf trees, and is not very tall.

Species of the coastal forest

In northern New Zealand, pōhutukawa (Metrosideros excelsa) dominates the coastal forest. Pōhutukawa has many spreading trunks and rough, flaky bark. Masses of aerial roots grow down the trunks or hang in mid-air, and the dark green leaves have woolly undersides. Pōhutukawa often overhang the sea and are splashed by waves.

Karo, ngaio and taupata also grow in coastal forest. Karo (Pittosporum crassifolium) has leaves that are smaller than pōhutukawa’s, but also woolly beneath. Its three-valved seed capsules contain sticky seeds. Ngaio (Myoporum laetum) has leaves that show translucent oil glands when held up to the light. Taupata (Coprosma repens), with its very shiny leaves, is the smallest tree in the coastal forest. In exposed places taupata crouches close to the rocks, but with shelter it grows into an erect shrub.

Away from direct salt spray, several other trees grow. All are related to tropical plants. The handsome pūriri (Vitex lucens) has large compound leaves (made up of a number of leaflets), tubular crimson flowers and large red berries. It is related to the tropical mahogany. Karaka (Corynocarpus laevigatus) is another common coastal tree, and has simple dark green leaves and orange berries the size of small plums.

Underneath, the coastal forest is often fairly open. A thick litter of large leaves and leaflets covers the ground. There may be an undergrowth of kawakawa (Macropiper excelsum), a shrub with distinctive heart-shaped leaves. It is related to Fiji’s kava plant, and the Asian plant that is the source of pepper. Ferns are dotted here and there.

Pōhutukawa and pūriri do not occur naturally further south than Taranaki and the East Cape.

Subantarctic coastal forest

On the subantarctic Auckland Islands, the low coastal forest on sheltered shores is dominated by southern rātā. There are also a few smaller species and some ferns on the forest floor. The dense, wind-smoothed forest roof is a striking sight when the red-flowered rātā is in bloom.


Loss of conifer–broadleaf forests

In the 200–300 years after New Zealand was first settled, Māori burnt about 6.7 million hectares of forest. Another 8 million were logged or burnt by European settlers between 1820 and 1920. Today about 6.2 million hectares (23% of the country) is covered in native forest. Less than half is conifer–broadleaf forest.

The fires of Māori

Before people arrived in New Zealand, occasional fires were started by lightning or volcanic eruption, but the forests grew back soon after. This changed after the Polynesian ancestors of Māori arrived in the 13th century. Fires became more frequent on the dry eastern coasts. Forests which had been burnt repeatedly did not regenerate, and were replaced by grassland or bracken fern.

When Europeans reached the Canterbury Plains they found short tussock grasses, drought-resistant shrubs and herbaceous plants. They assumed that this was the natural cover, because of the drier climate. Later, when ploughing, they found charcoal, and blackened logs and tree stumps in most places. Several different trees were identified. It is clear that in pre-human times, the plains and foothills were covered with conifer–broadleaf forests of mataī and tōtara, with understorey species such as kāpuka and southern rātā.

Māori fires also destroyed kānuka and mountain tōtara forests in Central Otago, and upland conifer forests of kaikawaka (Libocedrus bidwillii) in the Kaimanawa Mountains.

The North Island’s wetter western forests did not burn as easily as the east coast forests. Deforestation by Māori was restricted to coastal strips between Taranaki and Horowhenua, the Auckland area, and the Aupōuri peninsula at the island’s northern tip.

Timber!

Houses were built from kauri and rimu timber. Mataī was used for flooring, and tōtara for piles. Durable tōtara and pūriri became railway sleepers, fence posts and telegraph poles. Kahikatea was used for butter boxes, and rātā and black maire for firewood.

Clearance by Europeans

Europeans started to log and clear kauri forests at the start of the 19th century. At first they used kauri for ships’ spars. Later they logged the trees to get timber for housing, and to clear land for farming. Settlers began clearing forest from coastal areas in the mid-19th century. They worked their way inland as rail and roads developed.

Some timber was used for bridges, houses and heating, but much was wasted. Millers usually felled the most accessible timber trees. Settler farmers followed and burned the remaining forest, then sowed grass. By the end of the 1920s most of the North Island’s kauri and kahikatea forests were gone, and much lowland conifer–broadleaf forest had been turned into pasture.


Native wildlife and forest survival

Originally, New Zealand’s conifer–broadleaf forests supported a rich mix of birds, bats, tuatara, lizards, frogs and giant invertebrates. The plant and animal species had evolved together and were interlinked in terms of feeding and plant regeneration. When people arrived, bringing mammals, they disrupted or destroyed many of these relationships.

The arrival of people and predators

When Polynesians first settled in New Zealand around 1250–1300 AD, they introduced dogs and kiore (the Polynesian rat). They also burnt forests. By the time Europeans arrived, some 35 bird species were extinct. So were three frog species and three lizard species. A number of other species disappeared from the mainland, surviving only on offshore islands. This was due to hunting by people and dogs, predation by kiore, and the loss of forests.

European settlers brought more predators. Ship rats, Norway rats, cats, stoats, ferrets, weasels and possums have all reduced native wildlife populations.

Impact on the forests

Pollination

Some plants rely on a particular animal for pollination, and cannot regenerate without it. Tree fuchsia, rātā, kōwhai and some mistletoe species are pollinated by the nectar-feeding birds tūī, bellbird and hihi. The kiekie vine and the parasitic wood rose (Dactylanthus taylorii) are pollinated by the short-tailed bat.

Seed distribution

Around 70% of New Zealand’s trees, including most species in the conifer–broadleaf forest, have fleshy fruits. The seeds are mainly dispersed by birds, although lizards and bats can also spread seed. Nowadays the main native birds carrying seed from small forest fruits are bellbirds, kererū (New Zealand pigeons), kōkako, silvereyes and tūī.

Kererū, kōkako and weka are the only native birds that can eat large fruits (more than 12 millimetres in diameter). Kōkako and weka now only live in small forest remnants. So only kererū can distribute the seed of the North Island’s large-fruited trees, such as tawa, taraire, karaka, kohekohe and pūriri. Kererū also spread the seeds of another 60 forest plants. Their numbers are decreasing around the country, so the long-term survival of many plants is not assured if kererū continue to decline.


Hononga, rauemi nō waho

More suggestions and sources


How to cite this page: John Dawson, 'Conifer–broadleaf forests', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/conifer-broadleaf-forests/print (accessed 23 September 2019)

Story by John Dawson, published 24 Sep 2007