Rakiura Island temperate forests
Stewart Island temperate forests. Source: C.Michael Hogan
The Rakiura Island temperate forests ecoregion is a geographically small area comprised by Rakiura Island (also known as Stewart Island) and neighbouring smaller islands; this ecoregion is a southerly refuge for many of New Zealand's endemic species. Its large tracts of wilderness and mist-drenched forests provide insight into what mainland New Zealand was like before the arrival of humans. The Podocarp/Mixed broadleaf forests here are thought to be some of the most ancient continuously stable forests in the world, dating in continuity for tens of millions of years before present. This circumstance is due to the relative geographic isolation and lack of prehistoric settlement by humans.
This is considered the southernmost rainforest in the world, with dense forests of podocarps and hardwoods. Endemic and threatened birds of the mainland thrive here, such as the flightless kakapo (Strigops habroptilus), a large, nocturnal parrot that was completely extirpated from the mainland and later rediscovered here. A large portion of the island is protected, and while some pests have been introduced, the island has largely been spared the devastating alien species introductions of the mainland.
Location and General Description
WWF Rakiura, also known as Stewart Island, lies about 25 kilometers (km) south of the South Island of New Zealand. The 1700 square-kilometer (km2) island is separated from the mainland by the shallow Foveaux Strait, but has been connected to the South Island during past glacial periods, most recently about 14,000 years ago. Stewart Island is hilly and wet, with little flat ground. Mean annual rainfall varies from 1000 millimetres (mm) to 3000 mm depending on altitude, and rainless periods of more than two weeks are uncommon. The highest peak, Mt. Anglem, rises to 975 metres (m) above sea level. The island is composed primarily of diorite gneiss and granite, which decays rapidly to clay. The clay soil is not very fertile, but the wet conditions, mild temperatures, and humus from decaying vegetation allow forest to thrive across the island. The main factors limiting the forest cover on Rakiura Island are wind and salt spray. This ecoregion also includes the Snares Islands, a 3.3 km2 island group located 105 km southwest of Rakiura. The Snares are volcanic in origin, and consist of one main island and several rocky islets. Climatic conditions are similar to Rakiura.
Podocarp-hardwood forests dominate the lowlands of Rakiura Island, but give way to sub-alpine manuka (Leptospermum scoparium) scrub above 300 m. The dominant lowland trees are rimu (Dacrydium cupressinum), kamahi (Weinmannia racemosa), and southern rata or ironwood (Metrosideros umbellata). There are more than 50 other tree and shrub species in the forest, including Senecio spp., daisy-trees (Olearia spp.), and Coprosma spp. Cushion plants, liverworts, mosses, and the fern Blechnum discolor are all common in the understory. The tree trunks are draped with orchids (e.g. Dendrobium cunninghamii) and ferns such as Hymenophyllum dilatatum, Polystichum adiantiforme, Polypodium diversifolium, and Asplenium flaccidum. Due to its small size, only 20 plant taxa are native to the Snares Islands. On the main island of the Snares, Hebe elliptica grows around coastal fringes, while Olearia lyallii forms central stands reaching up to nine m in height.
Biodiversity Features
Podocarp/Mixed broadleaf forest, Ulva Island. @C.Michael Hogan Rakiura Island has a lush and distinctive vegetation. The forest here is largely undisturbed by humans, and provides an interesting perspective on what forests on the New Zealand mainland might once have been like. There are few endemic plant species on Rakiura, and the island is more notable for the species that are not found here despite being commonin similar habitats on mainland New Zealand. Strikingly, there are no Nothofagus spp., Libocedrus bidwillii, or Phyllocladus alpinus present on the island. The podocarps and hardwoods are thought to have been reestablished at the end of the last ice age by birds, but southern beech Nothofagus spp. rely on freshwater stream dispersal, which would have been prevented by the rising Foveaux Strait.
Rakiura Island is well known for its rich birdlife. The island become a haven for mainland species, and some unique subspecies, in the wake of European colonization of New Zealand. European settlers brought a whole range of introduced predators to New Zealand, including cats (Felis silvestris), rats (Rattus exulans, R. norvegicus, R. rattus), stoats (Mustela erminea), ferrets (M. furo), weasels (M. nivalis), and hedgehogs (Erinaceus europaeus), which together drove many New Zealand birds to the brink of extinction. Fortunately for the avifauna of Rakiura Island, ferrets, weasels, and stoats were never introduced there, and populations of cats and rats were largely confined to the small human settlement area near Half Moon Bay.
As a result, bird populations on Rakiura fared much better than those on the neighboring South Island, and flightless birds like the Stewart Island kiwi (Apteryx australis lawryi) are still found here. The kakapo (Strigops habroptilus), the world's only flightless, nocturnal parrot, was extirpated from the mainland by introduced predators but survived on Stewart Island until 1997, at which point the last few individuals were translocated to smaller, predator-free islands for more intensive management. The kakapo is now listed as "extinct in the wild" by the IUCN, but approximately 56 individuals survive on government-owned offshore islands. Other species such as the endemic laughing owl (Sceloglaux albifacies EX) are probably now extinct. The Stewart Island shag (Phalacrocorax chalconotus VU) is found on Rakiura and the southeastern region of South Island. Extant endemics on Rakiura and its offshore islets include subspecies of southern robin (Petroica australis rakiura), weka (Gallirallus australis scotti), and fernbird (Bowdleria punctata stewartiana), as well as a leaf-veined slug, a Paryphanta spp., and the harlequin gecko (Hoplodactylus nebulosis). The harlequin gecko is commonly found among subalpine cushion plants and is one of the world's southernmost lizard species.
The Snares group is known for its thriving seabird populations, with 23 different species sighted here. No predatory land mammals have been introduced to the Snares Islands and the total seabird population is estimated to equal that of Great Britain and Ireland, with 2.75 million breeding pairs of sooty shearwaters (Puffinus griseus) alone. The Snares crested penguin (Eudyptes robustus VU) is restricted to these islands, as is a subspecies of New Zealand snipe (Coenocorypha aucklandica huegeli). C.a. iredalei was endemic to Stewart Island, but died out when weka (Gallirallus australis) and rats (Rattus rattus) were introduced.
Current Status
Crown fern on forest floor, Ulva Island. @C.Michael Hogan Almost 93 percent of Rakiura Island is owned by the New Zealand government, and over half is designated as either a nature reserve or scenic reserve. The level of protection on the island is excellent, and all of the major habitats are included in the current reserve system. The New Zealand government is currently considering a proposal to turn much of Rakiura into a National Park, to unify the present mosaic of land management activities and give Rakiura a higher public profile. Human settlements on the island have always been small, and have had a very limited impact on the vegetation of the island.
Although there was some logging activity on Rakiura between 1860 and 1930, it was mostly confined to the area around Half Moon Bay and Paterson Inlet so that the majority of Rakiura Island still supports intact native forest. Some of the smaller islands surrounding Rakiura are also protected and serve as refuges for highly endangered species such as the kakapo and the South Island subspecies of saddleback (Philesturnus carunculatus carunculatus), which was nearly extirpated from Rakiura by the arrival of rats. The Snares are uninhabited and wholly protected as a National Park. Landings are restricted by a permit system. There is a concerted effort to trap and eliminate alien species of mammalian predators (e.g. stoats, rats); in addition there are several areas of predator control fences that prohibit movement of such aliens from the areas that have been effectively cleared from these predators. One such major fence is in the vicinity of the populated area of Half Moon Bay.
Types and Severity of Threats
Rakiura (Stewart) Island, New Zealand. @ Susanne Peck
The main conservation concern on Rakiura Island, as in much of New Zealand, is the impact of introduced species. Introduced deer (Odocoileus virginianus) and brush-tailed possums (Trichosurus vulpecula) browse heavily on native vegetation, and have significantly affected both the understory and the canopy of Rakiura's forests. Introduced cats have had a devastating effect on the native birds and were instrumental in the decline of the kakapo on Rakiura Island. They continue to pose a threat to the Stewart Island kiwi. Introduced rats are also a problem, but fortunately no ferrets or stoats have ever been released on the island. There are currently no introduced predatory land mammals on the Snares, and preservation of the unique fauna found here is contingent upon the total restriction of alien species introductions.
Justification of Ecoregion Delineation
These islands off the southern coast of New Zealand are considered botanically connected to the mainland. However, they are designated a separate ecoregion due to their long isolation from the mainland, endemic flora, and very different history of human settlement in comparison to the mainland.
Further Reading
- For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
- Clout, M.N. and D.V. Merton. 1998. Saving the Kakapo: the conservation of the world's most peculiar parrot. Bird Conservation International, 8:281-296.
- Cockayne, L. 1909. Report on a botanical survey of Stewart Island. Department of Lands, New Zealand.
- Heather, B. D. and H. A. Robertson. 1997. The Field Guide to the Birds of New Zealand. Oxford University Press, Oxford, United Kingdom. ISBN: 0198501463
- Hilton-Taylor, C. 2000. 1998. The 2000 IUCN Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom. ISBN: 2831705657
- McGlone, M.S. and H.D. Wilson. 1996. Holocene vegetation and climate of Stewart Island, New Zealand. New Zealand Journal of Botany, 34:369-388.
- Molloy, L. 1994. Wild New Zealand. New Zealand Department of Conservation/MIT Press, Cambridge, Massachusetts. ISBN: 0262133040
- Powlesland, R.G., B. D. Lloyd, H. A. Best, and D. V. Merton. 1992. Breeding Biology of the Kakapo, Strigops habroptilus, on Stewart Island, New Zealand. Ibis, 134:361-373.
- Wardle, P. 1991. Vegetation of New Zealand. Cambridge University Press, Cambridge, United Kingdom. ISBN: 0521258731
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