This ecoregion extends from North Cape as far south as Kāwhia in the west. It curls around the eastern coastal strip to East Cape.
Warm and moist
These northern lowlands of the North Island are surrounded by warm subtropical waters. They enjoy a mild, moist climate with warm summers and few winter frosts. Winters are much wetter than summers, and although there is a regular summer dry spell, severe drought is uncommon.
Rocks and soils
The basement rocks are highly variable, with sedimentary sandstones, mudstones and limestones. However, most prominent ranges, including the mountainous Coromandel Peninsula, have formed from intermittent basaltic and rhyolitic volcanic activity over the past 25 million years. A large part of the west coast is formed from sand dunes.
Compared with most of the country, northern New Zealand is tectonically stable, so the landforms are old. Deep leaching of soils has resulted in clay lying over deeply weathered rock, often bright red because of the high iron oxide content, but lacking essential nutrients. In contrast, soils derived from volcanic rocks are often very fertile.
The moist, warm, temperate climate encouraged the growth of the country’s most species-rich and complex forests. Most of New Zealand’s conifer species are found here, including massive kauri trees (Agathis australis). These grow in stands that tower over conifers and broadleaf trees.
A tangle of forest
In An account of New Zealand (1835) the English missionary William Yate described the dense North Island forests:
‘The whole of the earth is completely matted with roots; and those of the smaller trees frequently pass over those of the larger, and seem to draw their sustenation from their more sturdy and gigantic neighbours: and such is the rankness of the foliage, from the ground to the tops of the highest trees, that the eye can penetrate only a few feet before it, into the deep umbrageous recesses of the woods.’ 1
These impressive forests dominated the landscape before being converted to the pasture and scrub typical of Northland today.
Warm coastal bays and inshore islands are covered with broadleaf forest, including large-leaved trees such as kohekohe (Dysoxylum spectabile) and nīkau (Rhopalostylis sapida), New Zealand’s only palm tree.
More than 100 species of trees and shrubs are endemic to this region – they do not grow naturally anywhere else.
Some are abundant in the forest canopy, such as taraire (Beilschmiedia tarairi) and makaka (Ackama rosifolia). Others are just a handful of plants in scattered locations – for example the white-flowered rātā of North Cape (Metrosideros bartletti) and the large-leaved puka (Meryta sinclairi) found on a few headlands and islands.
Many trees have close relatives that are common further south – for example, the northern tawhero (Weinmannia silvicola) gives way to kāmahi (W. racemosa) in the south, and taraire to tawa (Beilschmiedia tawa).
A feature of the northern landscape is its vast gumlands – areas of infertile soil covered with stunted scrub. This is where tracts of kauri forest grew, before humans arrived and lit fires, destroying the forests. Kauri’s acid leaf litter tends to form poor soils.