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NZ Plants

Pre-history

Erosion on the eastern edge of the supercontinent Gondwana accumulates sediments in the sea in the future area occupied by New Zealand.

Mountain building begins (Tuhua Orogeny), resulting in severe faulting and folding, igneous activity and metamorphism. Isolated segments of land rise above the ocean surface and subside again.

Further erosion of eastern Gondwana takes place, the sediments being washed into a deep sea trench (the New Zealand Geosyncline).

The accumulation of sediments ends with the commencement of another phase of mountain building (Rangitata Orogeny). The resulting ancestral New Zealand landmass is extensive, being situated between the eastern Australian and Antarctica portions of Gondwana. With the absence of an intervening ocean barrier, this landmass is colonized by spore bearing plants (bryophytes, ferns) conifers (kauri, podocarps), flowering plants (southern beeches, proteas) and many animals including the flightless Ratites from the Gondwana continent.

Angiosperms (flowering plants) are widespread but few are in the land mass that will become New Zealand

The New Zealand landmass breaks away from Gondwana and moves eastwards on the Pacific tectonic plate. New Zealand is completely surrounded by water and contains a gondwanian stock of plants and animals

The New Zealand landmass has been eroded to a flat low-lying landscape (the Late Cretaceous Peneplain). For a while birds and seeds are easily able to cross the narrow waters.

During the Oligocene New Zealand is subjected to a long period of submergence and erosion resulting in a narrow archipelago with a few scattered islands. Many plant species are lost. Organic material accumulates in low lying land where western New Zealand is today which will form the coal deposits of Greymouth, Buller and the Waikato.

Land re-emerges from beneath the sea and a period of uplift begins that continues to the present day (Kaikoura Orogeny). The Alpine Fault is developed. Australia and New Zealand move northward. Warm ocean currents open up trans-oceanic migration routes; coconut palms (Cocos spp.) and cabbage trees (Cordyline spp.) become established on the North and South Islands.

The Antarctic continent cools and circum-Antarctic currents and westerly winds become established. This combination of currents and winds transports plants with light or buoyant seeds such as Sophora, Hebe, Eucalyptus, Casuarina, Acacia from the Australian continent to New Zealand

Northward movement continues. New Zealand has mostly attained its current shape of the North and South Islands

A steady uplift of the land produces a continuous northeast-southwest landmass with a backbone of mountainous terrain creating a range of ecological niches. Pumice eruptions in the Rotorua-Taupo region of the North Island begin and continue up to 700 years before present.

Before the Pleistocene ends about 10,000 years ago there are about 20 cooling/warming cycles that result in numerous fluctuations in sea level. Many warmth-requiring plants perish while cold adapted ones such as grasses, shrubs, rushes and sedges spread down to sea level. Extensive forest coverage becomes restricted at times to the northern part of the North Island but patches of forest remain in sheltered lowland locations throughout New Zealand. Beech forest predominates over podocarp forest

Mamaku eruption of pumice and hot gases produces over 225 cubic kilometres of Mamaku Ignimbrite (fused rock particles), covering more than 3,900 square kilometres of the North Island.

Oruanui eruption causes ash to be deposited over 13,000 square kilometres of land, and much of New Zealand receives at least 1 mm of ash, with horizons found in cores offshore. In only a few days more than 800 cubic kilometres of debris is produced.

The peak of the most recent glacial maximum (Otiran glacial) results in cool, windy and harsh climates with continuous forest growth restricted to the far northern parts of New Zealand. Tussock grassland and scrub extends south of present day Auckland down into the South Island. The sea level recedes to 105-135 m below the present level resulting in a continuous land mass from Stewart Island in the south to the tip of the North Island. At the peak of this glaciation temperatures are 5°C below the present mean.

The ice retreats as the climate warms resulting in the loss of many cold-climate plants and the spread of conifer-broadleaf forest. In the absence of mammalian predators flightless birds including moa and kiwi proliferate and reach their zenith. Over eleven species of moa browse the vegetation, consuming twigs, leaves, fruits and seeds of forest trees, shrubs, vines and grassland.

Continued warming raises sea levels; Cook Strait is continuously occupied by water since this time.