Specks in the sea
Off northern New Zealand lie a number of isolated island groups:
- Norfolk Island (governed by Australia, but closer ecologically to New Zealand)
- Kermadec Islands
- Three Kings Islands
- Poor Knights Islands.
Norfolk Island and the Kermadec group were formed by volcanic eruptions. Both are true oceanic islands (islands rising from the deep sea floor). They are comparatively young: the earliest Norfolk Island rocks date from about 3 million years ago, and the Kermadec Island eruptions from around a million years ago.
The Three Kings rocks date back to the Cretaceous period (around 120 million years ago) and have been separated from the mainland for 10–15 million years.
The Poor Knights are younger – roughly 5 million years old – and have been separated for a much shorter time.
Even as recently as the last glaciation 20,000 years ago, when the sea level was 120 metres lower, all the islands remained isolated. This separation has allowed endemic species to evolve.
Climate and vegetation
All have warm, temperate, moist climates and originally had generally low but dense coastal forest and scrub cover. They share many of these features with coastal Northland.
Pacific and New Zealand links
While representing just a small fraction (75 square kilometres) of the New Zealand landmass, these islands are of great interest to scientists. The offshore islands have been stepping stones between the mainland and the Pacific Islands, their species forming part of an interchange between New Zealand and the tropical Pacific. Some mainland animals and plants, such as the red-flowered rātā (Metrosideros species), have dispersed northward to the Pacific Islands, while species such as hibiscus have dispersed south to New Zealand.
Endemics: species found nowhere else
Norfolk Island has a range of unique species, including:
- the tall Norfolk Island pine (Araucaria heterophylla)
- the Norfolk Island palm (Rhopalostylis baueri)
- a gecko and skink
- land birds (for example, the Norfolk Island kākā and pigeon) closely related to New Zealand species
- a number of flightless rails.
The Kermadecs are younger than Norfolk Island, and have been formed by volcanic activity. They have a smaller range of endemic species. This includes a pōhutukawa tree (Metrosideros kermadecensis) and palm (Rhopalostylis baueri var. cheesemanii), and an extinct megapode (a large ground-dwelling bird).
Although the Three Kings are only 53 kilometres north of the mainland, many of their species are endemic – notably the tree Pennantia baylisiana and a single specimen in the wild of the white-flowered vine Tecomanthe speciosa, which is widely cultivated in New Zealand gardens.
The Poor Knights are much closer to the mainland, and have few endemic species, notably the spectacular, red-flowered Poor Knights lily (Xeronema callistemon).
Impact of rats
All the northern islands originally had abundant and diverse marine bird life, especially petrels, but rats have largely wiped them out.