Blue Lake in the west Sabine valley, from Moss Pass. Beech forests form a dense coat in the valleys to about 1400 m (4593'). The upper slopes of the mountains are sharp and dissected and show many signs of recent glaciation. The altitudes of the summit ridges are fairly uniform throughout the park, between 2100 and 2300 m (6890-7545'). Photo NC.

Nelson Lakes National Park was formed in 1956 as the ninth national park in New Zealand. The inclusion of the Glenroy and Matakitaki Valleys in 1983 was the largest of several additions since its creation. This is a mountainous area of long ranges separated by deeply gouged and densely forested valleys. Many other features left from the last glacial period remain in the landscape, like the two lakes (Rotoroa and Rotoiti) after which the park is named. While Nelson Lakes National park has a good network of tracks and huts, a feeling of remoteness and wilderness also prevails in the park.

Geological setting
Nelson Lakes National Park is located in the northern part of the Southern Alps. Its north-western boundary follows the Alpine Fault (apart from the bulge of Lake Rotoroa). The path of the fault is clearly shown in several little valleys (Station Creek, Bulls Creek), and by the markedly higher altitudes immediately to its south-east.
The mountains of the park are almost entirely made of the two main rock types of the Southern Alps: greywacke and argillites (Torlesse Supergroup) in the St Arnaud and Travers ranges, schists of the Haast Schist Group in the Misery and Ella ranges. A variety of older rocks of volcanic, intrusive and sedimentary origins are found immediately west of the Alpine Fault.
No glaciers exist at present in the park, but the landscape was intensely sculpted by the glaciers of the latest ice ages. Many glacial landforms remain, such as lakes Rotoiti and Rotoroa, the moraine on which St Arnaud is located, cirques like Cupola Basin, and many others.

Climatic conditions
The ranges to the west of Nelson Lakes National Park provide shelter against the prevailing westerly weather systems, so that climatic condition in the park are less severe than elsewhere in the Southern Alps.
Precipitation is higher in the western parts, and decreases eastward: 1800 mm/year (71 in.) at Lake Rotoroa, 1550 mm/year (61 in.) at Lake Rotoiti. Likewise, over 4000 mm/year (157 in.) on the tops of the Emily Ranges in the west, 2500 mm (98 in.) further east in the St Arnaud Range. Precipitation decreases even more further east, as can be seen in the dry lands that stretch towards the Kaikoura Ranges.
Temperatures are mild and vary within a narrow range between winter and summer: at Lake Rotoiti 600 m (1968') above sea level mean summer temperature is 15 degrees C (with highs up to 30 degrees C), and mean winter temperature is 4 degrees C (with lows down to -10 degrees C).
The weather in the park is changeable and difficult to predict, due mainly to the often quick succession of cold and warm fronts brought by the westerly weather system, as well as the local disturbances generated by the mountains.

Forests
Beech forests dominate the lower landscape of Nelson Lakes National Park. Podocarp forest, mixed with beech, is restricted to the lower and wetter areas around Lake Rotoroa. Major species present are kahikatea, miro, matai, rimu.
All four species of beech are present. Red beech and silver beech share the lower, warmer and more fertile areas, with hard beech less common, in the less fertile areas. Mountain beech and silver beech extend up to the treeline, at about 1400 m (4590') above sea level.
The treeline is itself a striking feature in the park, as it stretches in straight line, as if drawn artificially, along the valley sides.

Vegetation above the bushline
  The alpine scrub zone immediately above the treeline is patchy in the park, because in many areas it was destroyed by fire or grazing. Dracophyllum, celery pine, snow totara (Podocarpus nivalis), mountain flax, can be found in some areas.
Snow tussock (Chinochloa) grasslands dominate the rest of the vegetation above this shrubland, with four main species: C. pallens, C. flavescens, C. rubra and C. australis.
  Interspersed among them are many other species of alpine plants, such as spaniards (Aciphyllum), mountain daisies (Celmisia), mountain buttercups (Ranunculus), gentians, Ourisia, Senecio.
  Vegetation is sparse above 1700 m (5577'), though various species of vegetable sheep thrive, and South Island edelweiss, gentians and hebes grow in sheltered spots.

Birds
 Beech forests are not rich in flowers or nectar, so provide habitats mostly to insectivorous birds.
In Nelson Lakes National Park many insects feed on the honeydew secreted by a scale insect living off the sap of trees. In turn they provide food for birds such as fantails and tomtits. The honeydew is also a source of sugar appreciated by birds, especially in winter.
Birds of the beech forests include robins, riflemen, silvereyes, grey warblers, tuis and bellbirds. Kakas and parakeets also feed on insects, kakas in particular using their sharp beak to rip the bark off trees and dig out larvae.

Native New Zealand pigeons are especially attracted to the podocarp forests, where they feed on the fruits of miro and kahikatea, and on the nectar of the flowers of the kowhai.

Harriers, New Zealand falcon and morepork (the native owl) can be seen or heard throughout the park.

Above the bush line, Nelson Lakes National Park is home to the rock wren, the only truly alpine bird in New Zealand. Keas and pipits are also commonly found in that zone.

The park's lakes and streams provide habitat for many aquatic birds. Paradise shelducks and native grey ducks are common. By contrast the numbers of New Zealand scaup have dwindled, like those of the endangered blue duck which has been driven to the most remote alpine streams.
The lakes and main rivers are home to shags, herons, gulls and kingfishers. They are joined in summer by migrants such as South Island pied oystercatchers, pied stilts, banded dotterels, spur-winged plovers.

Other native fauna
  There are many species of invertebrates in the park: native wasp, spiders, moths, butterflies, weevils, wetas. The beech forests sustain several species of defoliators and wood borers, such as the mountain beech moth caterpillar Proteodes canifex, the beetle Nascioides enysi, and the three species of Platypus pinhole borers.
  Above the bushline there is an abundance of grasshoppers.
  In the waters of the lakes live native eels (Anguilla diffenbachii) and several species of galaxiid fish (the whitebait family), including G. divergens and G. brevipinnis.

Honeydew
  Honeydew is the product of the small female sooty beech scale insect, Ultracoelostoma assimile. This insect lives inside the bark of trees, protected in a waxy cuticle. It feeds on the sapwood, and sends out its sugary byproducts via a long thin translucid tube protruding out of the bark. In the beech forests the trees are covered by multitudes of such tubes with their sweet droplets, on which depend the lives of many species of insects and birds.
 
Introduced animals
  Rats, mice, opossums, stoats and in some areas pigs live in the forest.
Red deer, chamois and hares live above the tree line.
As elsewhere in New Zealand introduced animals have had a destructive impact on the indigenous flora and fauna.
   The numbers of red deer and chamois were drastically reduced in the past decades and remain under control.
  On the estern side of Lake Rotoiti, near St Arnaud, the Department of Conservation has created a 'mainland island', in order to remove all exotic predators and restore a healthy native fauna and flora.