The Kermadecs are true oceanic islands that have never been joined to nearby land masses. When volcanoes emerged from the sea they were bare, and all plants and animals that are now found there had to travel across the ocean or be transported. A distinctive fauna and flora has gradually developed over thousands of years.
Native vegetation is found on all the islands, but it is locally modified by weeds introduced by humans. On Raoul, the only forested island, the dominant canopy species are the Kermadec pōhutukawa (Metrosideros kermadecensis) and the Kermadec nīkau (Rhopalostylis baueri var. cheesemanii), with an understorey of small trees, shrubs and ferns. Māpou is widespread in coastal areas up to 250 metres above sea level, replaced at higher altitudes by hutu.
113 native species or subspecies of vascular plants, of which 23 are endemic, are found in the Kermadecs. The flora is largely derived from New Zealand, and many of the endemic forms have evolved from New Zealand species. The plants that have colonised the islands are well adapted to natural disturbances such as cyclones, landslides and volcanic eruptions.
The Kermadec Islands have no native land mammals, but are home to large colonies of seabirds which nest in the forests or on the coast. 35 bird species are known, at least three of which are unique to the Kermadecs. Important species include the red-tailed tropic bird, the Kermadec parakeet, the masked booby and distinctive species of noddies and terns.
Four seabird species migrate annually to the North Pacific after the breeding season, but the remainder are confined to the South Pacific or do not travel far from their nesting grounds.
Within the forest on Raoul Island the New Zealand tūī is the most common species.
Introduced plants and animals
The introduction of goats, cats and rats to Raoul and Macauley islands had a disastrous effect on both the vegetation and the bird population. A range of exotic plants was introduced to Raoul by settlers, and some of these have spread widely in the warm climate and become weeds. The tī pore (tropical cabbage tree) was probably introduced to the islands by Polynesian voyagers to New Zealand.
Army worms at work
An aroid lily (Alocasia brisbanensis) was introduced to Raoul Island in the 19th century, and has spread explosively to cover the forest floor. There seemed to be no way to remove this weed. But an unexpected consequence of rat eradication was the emergence of the tropical army worm – which is now defoliating the lily plants.
Goats, cats and rats have all been eradicated from both islands in recent years, and there has been an immediate increase in the number and diversity of birds. The Kermadec parakeet has reappeared on Raoul, and new seabird colonies have been established.
Volunteer groups have worked since the 1980s to eradicate weeds from Raoul Island, with considerable success. Work continues to control and eventually remove persistent species such as Mysore thorn, guava, passionfruit and buttercup plant.