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Northwestern part of New Zealand's South Island

This is a region with outstanding natural values and large areas of protected land, principally within Kahurangi National Park. Approximately 95 percent of the land above 600 m retains an almost unmodified natural cover, and the diversity of life, landform, and habitat is the highest in New Zealand. The coastline is relatively unmodified, and it contains many contiguous sequences of indigenous vegetation.

  • Scientific Code
    (AA0404)
  • Ecoregion Category
    Australasia
  • Size
    5,600 square miles
  • Status
    Relatively Stable/Intact
  • Habitats

Description
Location and General Description
In the Tertiary era, this part of the country was low-lying and often covered by sea. Over time, faulted sections of land were lifted up but were again eroded away until finally the present mountain ranges formed more than 1 million years ago. This complicated ontogeny has given the region a diverse range of landforms and rock types. The western coastal fringe is a montage of old marine and river terraces interspersed with layers of limestone. The most visible of these lowland escarpments are found at Punakaiki (with its popular ‘Pancake Rocks’) and Oparara, further to the north. The central area contains older sedimentary rocks, and a mix of hard granite, gneiss, ultramafics, and marble, with occasional bands of overlying limestone (Soons and Selby 1982). The oldest landforms, the remnants of large peneplains, can be seen in the Gouland Downs and Mt Arthur Tablelands. Tertiary rocks overlie other peneplains to form spectacular high altitude moors like the Thousand Acre Plateau. Fossils are abundant and include 540 million year old trilobites in the Cobb Valley, and Permian fossils that firmly link New Zealand to the ancient land mass of Gondwana (Department of Conservation 2001). The area was partially glaciated during the Pleistocene Ice Ages; remnant landforms include U-shaped valleys, cirques, and outwash terraces.

The area to the south, closer to the Alpine Fault and other nearby fractures, is seismically active and the region has experienced some major earth movements in recent times (e.g. the Inagahua earthquake of 1929). As a consequence, landslips and other signs of earthquake damage are common in the region’s mountains and new landscape features are regularly created. For example, the Maruia Falls were formed when a landslide redirected the Maruia River to a new course.

The region has the largest and most diverse karst landscapes in New Zealand. Karst features occur from sea level to the alpine zone in comparatively young limestone and in older metamorphosed marble. Features of particular note are Waikoropupu Springs, fed by a huge marble aquifer from the Pikikiruna Range, and the glaciated alpine karst of Mt Owen. The upland karst areas contain the deepest cave currently known in the Southern hemisphere (889 m), and the longest caves in the country (39 km) (Department of Conservation 1996).

Rainfall is high in the uplands to the west (5,000 mm annum) but this decreases to 1,600 mm in eastern parts of the region. The vegetation is generally dense and relatively unmodified. Half of New Zealand’s 2,450 plant species are found in the region and, despite the relatively small amount of alpine habitat, the percentage of alpine flora is as high as 80 percent (Molloy 1994). Ninety-five percent of the land above 600 m remains covered in tall forest and alpine tussock herbfield (Department of Conservation 1996). The forests in eastern parts of the region are primarily beech (Nothofagus spp.). Podocarp forests with a rich understory of ferns, vines, and shrubs are located around the coastal fringe and the western ramparts. At least 38, or 12 percent, of the country’s 320 nationally threatened plants occur within the region, and threatened plants include 18 of the 75 regionally endemic species.

The coastline is sheltered to the northeast and exposed on the west. Abel Tasman National Park, which occupies the northeastern corner of the region, has beautiful golden beaches with granite-derived sand lying between some important unmodified estuaries. The vegetation reflects a history of fires and land clearance, but the forest is regenerating well, especially in damp gullies where a rich variety of plants can be found. Black beech (Nothofagus solandri solandri) dominates the drier ridges. Continuing westward along the coast, there are a number of other natural estuarine systems and important habitats for waders and seabirds. Of particular note are Whanganui Inlet and Farewell Spit.

Biodiversity Features
The varied landscape creates numerous different habitats, supporting many different creatures. It is particularly suitable for birds like the kaka (Nestor meridionalis VU), kereru or New Zealand wood pigeon (Hemiphaga novaeseelandia) and falcon (Falco novaeseelandiae) that range widely in search of seasonal food sources (Hilton-Taylor 2000). The relatively unmodified uplands are a stronghold for many bird species like the great spotted kiwi (Apteryx haastii VU) and blue duck (Hymenolaimus malacorhynchos VU), now gone from more modified lowland areas.

Farewell Spit, at the tip of the northern coast, is the longest sandspit in the country with the largest intertidal sandflat system. It is an important staging post and feeding area for about 90 bird species, mainly migratory and local waders. Godwits (Limosa lapponica baueri), knots (Calidris caanutus ), and turnstones (Arenaria interpres) are the most commonly seen species. Paparoa National Park, on the west coast, has the only mainland breeding colony of the endemic Westland black petrel (Procellaria westlandica VU). It is one of only a few places in the world where petrels of any sort breed on the mainland.

Studies have shown the top part of the South Island (which includes this region) to be particularly rich in invertebrate species (Department of Conservation 2001). The cool wet montane beech forests and sub-alpine tussocks of the northwest are home to about 29 of 64 known species of giant land snails (Powelliphanta spp). Members of the Rhytididae family of snails which have Gondwana origins going back 200 million years (Molloy 1994). These carnivorous snails feed on native worms which are closely related to species found on other Gondwana fragments, like Australia and South America.

The western coastal fringe is important as the ecological sequences are essentially intact from the water’s edge to alpine herbfields. The coastal forest is very diverse and includes northern rata (Metrosideros robusta), karaka (Corynocarpus laevigatus), and the nikau palm (Rhopalostylis sapida). The latter is the country’s only indigenous palm and is the world’s southernmost member of the Palm family (Dawson 1988).

The plants that grow on wet infertile granite-based soils are characterized by yellow pine (Halocarpus biforme) and Dracophyllum species, some of which are endemic (e.g., D. townsonii and D. traversii). The lime-rich karst ecosystems (within Kahurangi and Abel Tasman National Parks) support a more diverse range of species including many that are rare and/or endemic. Almost 50 percent of the endemic plants in the region are limited to marble or limestone substrates (Department of Conservation 2001). Below ground there is an even more specialized fauna including 20 different types of cave weta (from the Rhaphidophoidae family), 15 types of endemic carabid beetle and New Zealand’s largest spider, the Nelson Cave spider (Spelungula cavernicola), with a 12 cm leg span. The Nelson spider belongs to the primitive Gradungulidae family, the last survivor of the various spider groups that thrived millions of years ago (Meads 1990).

About 6 percent of the region’s alpine species are confined to the area (e.g., Celmisia dallii) while others (e.g., Celmisia traversii) are seen again only in Fiordland – another Ice age zone of refuge (Mark & Adams 1986). This unusual distribution pattern mimics the Westland ‘beech gap’ and is again due to the presence of large, destructive ice sheets over Westland during the Pleistocene Ice Age. In comparison, only 2 percent of alpine species are confined to the very extensive alpine areas of Canterbury/Otago and Westland.

Current Status
Ninety percent of the region’s uplands (above 600 m) are legally protected, principally in Kahurangi National Park, New Zealand's newest national park and, at 4,520 km2, one of the largest. Paparoa National Park (300 km2), on the west coast, was created in 1987. It includes a full range of ecosystems, from coast to mountain tops. The third, and smallest, of the region’s national parks is Abel Tasman (225 km2). It is more modified than most of New Zealand’s national parks, and its value lies more in its scenic values and estuaries than its intact ecosystems.

The coastline is relatively unmodified and contains some important wildlife habitats. Some sections are protected within the various national parks. Farewell Spit is protected as a nature reserve (the strictest category of conservation protection in New Zealand) and, in addition, has been designated a Wetland of International Importance under the UN Ramsar Convention (Molloy 1994).

Because it is not economically feasible to carry out effective control of all species throughout the region control work currently tends to focus on the species that pose the greatest risk and the areas that are most at risk. In general, most effort goes into possum control but some funding is available for controlling goats, pigs, mustelids, rodents, chamois, deer, and wasps (Dix and Napp 1999).

Types and Severity of Threats
Introduced ground-dwelling browsers include red and fallow deer (Cervus elaphus and Dama dama), chamois (Rupicapra rupicapra), hares (Lepus europaeus occidentalis) and goats (Capra hircus). All cause damage to the forest understory and alpine vegetation, and reduce regeneration by browsing on seedlings. Cave and karst areas are particularly vulnerable to browsing damage through vegetation removal and trampling/erosion (Department of Conservation 2001). Commercial hunting of deer has helped minimize the problem in alpine and subalpine areas where they can be shot from helicopters. Possums (Trichosurus vulpecula) cause widespread dieback in the canopy. Few introduced weeds have penetrated the region’s interior but they are present around the margins. Gorse (Ulex europaeus) is the most invasive and has reached more pristine areas such as the Gouland Downs.

Feral pigs (Sus scrofa) rarely occur in large enough numbers to damage the vegetation however, like rats (Rattus rattus, R. norvegicus), possums, and stoats (Mustela erminea), they do prey on Powelliphanta snails, other invertebrates, and the eggs of ground-nesting birds (Department of Conservation 2001).

The Kahurangi area has historically been of interest to mining operations because of its unique geology and mineralization. In general, mining is prohibited or restricted in national parks; however, it is currently possible to apply for mining access to Kahurangi National Park, although the required management practices would make large scale operations very difficult. It is likely that efforts will be made to include Kahurangi into the Crown Minerals Act 1991 to give it the same protection as other existing national parks (Department of Conservation 2001).

Karst landscapes and ecosystems in unprotected area (or in areas surrounded by eveloped land) can be threatened by land clearance, siltation, and pollution. The majority of karst areas within the region are largely protected from this large-scale damage but as ‘wild caves’ they are still at risk of being degraded by recreational use. Visitor impacts are virtually irreparable and to some extent inevitable (Bunting & Balks 2001); even a foot print can remain, perhaps for decades, if not centuries. Management strategies such as controlling visitor numbers or closing access to caves, are options that can be used to keep damage within acceptable levels.

Fire is a threat, as it is in most of New Zealand, where the indigenous flora is not adapted to regular fires. The regenerative forests of Abel Tasman National Park are probably the most prone to fires and because the soils are granite-based and infertile it is difficult for plants to reestablish.

Justification of Ecoregion Delineation
This ecoregion has fairly good correspondence with Wardle’s (1991) ‘Western Nelson’ botanical province. The northern half of this ecoregion makes up the ‘North-west Nelson’ Centre of Plant Diversity (Given 1995). Much of this region is included in the ‘South Island of New Zealand’ Endemic Bird Area (Stattersfield et al 1998).

References
Bunting, B. and M. Balks. 2001. A quantitative method for assessing the impact of recreational cave use on the physical environment of wild caves. Australasian cave and karst management association journal. 44: 10 – 18.

Dawson, J. 1988. Forest vines to snow tussock: the story of New Zealand’s plants. Victoria University Press. Wellington.

Department of Conservation. 2001. The Conservation requirements of New Zealand’s nationally threatened invertebrates. Threatened species occasional publication: 20. Biodiversity Recovery Unit. Wellington.

Department of Conservation. 1996. Conservation Management Strategy, Nelson/Marlborough Conservancy. Management Plan Series No. 10. Nelson/Marlborough Conservancy. Nelson. Conservancy. Department of Conservation. 2001. Kahurangi National Park Management Plan. Management Plan Series: 12. Nelson/Marlborough

Dix, J. and G. Napp. 1999. Nelson/Marlbrough Conservancy summary of pest control operations and outcome monitoring. Workshop proceedings: Outcome monitoring – animal pests. Pages 161–179 in science and research internal report 170. Wellington.

Given, R. 1995. North-west Nelson. Pages 510 – 512 in S. D. Davis, V. H. Heywood and A. C. Hamilton. editors. Centres of Plant Diversity. Volume 2. Asia, Australasia, and the Pacific. WWF/IUCN, IUCN Publications Unit, Cambridge, UK.

Hilton-Taylor, C. 2000. The IUCN 2000 Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.

Mark A.F. and N.M. Adams. 1986. New Zealand alpine plants (revised edition). Reed Methuen. Auckland.

Meads, M. 1990. Forgotten fauna. DSIR Publishing. Wellington.

Molloy, L. 1994. Wild New Zealand. New Holland Publishers. London.

Soons, J. and M. Selby, editors. 1982. Landforms of New Zealand. Longman Paul, Auckland.

Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wedge. 1998. Endemic Bird Areas of the World. Priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International, Cambridge, United Kingdom.

Wardle, P. 1991. Vegetation of New Zealand. Cambridge University Press, Cambridge, United Kingdom.

Prepared by: Sonia Frimmel
Reviewed by:

 

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