Boundaries

New Zealand lies in the southwestern Pacific Ocean and encompasses the North Island and South Island, as well as Waiheke Island, Great Barrier Island, Stewart Island/Rakiura Island, and the Chatham Islands. The ecoregion also includes the Auckland Islands and Campbell Island. Within the ecoregion there are three areas of biogeographic distinction, including the northern North Island, central New Zealand, and southern New Zealand. The northern North Island sub-ecoregion consists of the landmass north of the Auckland isthmus. Its southern boundary includes all of the catchments draining Kaipara harbor. The central New Zealand sub-ecoregion is the largest and most geologically diverse unit, and includes all of the catchments entering the Hauraki Gulf. It could arguably be separated into two separate units, although defining a possible boundary within the central portion of the North Island is difficult due to the loss of most freshwater biological evidence. The southern New Zealand sub-ecoregion includes the eastern coast of the South Island from the Hapuku and Kahutara rivers in the north, to Stewart Island in the south, and the Chatham Islands in the east.

Topography

New Zealand lies on the boundary of the Pacific and Australian plates and has a rich tectonic and volcanic history. The northern North Island is centered around a chain of ancient Pliocene islands (7-4 million years (Ma) ago) that have since been connected to the central North Island by sand, volcanic activity, and changes in sea level (Morgan-Richards et al. 2001). The area has been relatively free of major disturbances that mark southern and central New Zealand, although volcanism has had an intermittent influence during the Pleistocene, with localized basaltic eruptions occurring in northeastern Northland as recently as 1300 years ago (Leathwick et al. 2004).

The northern part of central New Zealand contains both the andesitic volcanoes of Taranaki and Tongariro, and the rhyolitic Taupo Volcanic Zone. Eruptions from the latter generally consisted of high-energy, ignimbrite flow material and air-fall tephra deposits. Over the last 50,000 years over thirty-six significant tephra events have been recorded. The largest of these would have affected most of the central and lower North Island and northeastern South Island (Leathwick et al. 2003).

The southern and eastern side of the central New Zealand sub-ecoregion is marked by another area of major historic disturbance, but here glaciation rather than volcanism was the major biogeographic driver. The Southern Alps (highest point at 3754 m) runs lengthwise down the middle of the South Island and forms a natural dispersal barrier between east and west coast rivers. During major glacial periods ice cover at higher elevations was extensive and thought to have occurred almost continuously from Nelson Lakes in the north to southern Fiordland (Leathwick et al 2004). Ice also descended to form piedmont glaciers that covered much of the coastal plain in Westland (Soons 1982), an area devoid of non-diadromous fish species. 

The southern New Zealand sub-ecoregion encompasses a topographically and environmentally diverse part of New Zealand, including eastern slopes of high elevation mountains along the Southern Alps, lower elevation hill country and mountains further east, and extensive inter-montane basins and plains of glacial and/or alluvial origin (Leathwick et al. 2003).

Freshwater habitats

New Zealand’s young and mountainous landscape is home to an exceptional diversity of lakes, most of which originated within the past 20,000 years. Unlike Australia, which has many saline lakes, only Lake Sutton in Otago is naturally saline. Most of the others are volcanic or glacial in origin. Volcanic lakes include Lake Taupo (616 km²), New Zealand’s largest lake, as well as Lakes Rotorua, Rotomahana, Tarawera, and Okareka. Glacial lakes, occupying former glacial valleys, are the most common lakes in New Zealand. They are also the deepest; for example, Lakes Hauroko, Manapouri, and Te Anauall exceed depths over 400 m (Brookes & Hamilton 2009).

Terrestrial habitats

The terrestrial habitats in this ecoregion are diverse, and span four biomes, including temperate broadleaf and mixed forests in the north and west; temperate grasslands, savannas, and shrublands in the southeast; montane grasslands in the Southern Alps; and tundra in the Subantarctic islands. Within these biomes are twelve terrestrial ecoregions, including the North Island temperate forests, South Island temperate forests, Fiordland temperate forests, Rakiura Island temperate forests, Westland temperate forests, Northland temperate kauri forests, Nelson Coast temperate forests, Richmond temperate forests, Westland temperate forests, Cantebury-Otago tussock grasslands, South Island montane grasslands, and Antipodes Subantarctic Islands tundra.

Description of endemic fishes

The archipelago has been isolated from Australia for over 80 million years. The fauna and flora show high levels of endemism and radiation among groups, many of which are thought to be ancient lineages, although recent debate suggests that the biotas’ origin may be more recent and the result of colonization after New Zealand emerged from the sea since the early Miocene (25 Ma: Trewick et al 2007). Endemics are dominated by the genera Galaxias, Gobiomorphus, and Neochanna. Two widespread endemic diadromous species, black flounder (Rhombosolea retiaria) and giant kokopu (Galaxias argenteus), are noticeably absent in the northern North Island, as is dwarf galaxies (G. divergens), the most widespread non-diadromous species.

Justification for delineation

For New Zealand and other islands and island groups, islands were placed in ecoregions on the basis of expert input.