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.
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.
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 (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.