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Alpine plants

by  Hugh Wilson

A rich assemblage of plants has evolved and diversified in New Zealand’s high mountains, where some grow wedged into rock crevices or anchored to scree slopes. A fifth of New Zealand’s flowering plants – 500 species – grow exclusively in rugged, cold alpine environments.


Alpine New Zealand

New Zealand’s alpine area totals about 30,000 square kilometres (about 11% of the country). Most is in the South Island, where several mountain peaks in the Southern Alps are higher than 3,000 metres. In the North Island, alpine terrain is limited to the volcanoes of the central plateau (Ruapehu, Ngāuruhoe and Tongariro), Mt Taranaki (Mt Egmont) to the west, Hikurangi to the east, and the crest of the axial ranges Kaweka, Kaimanawa, Ruahine and Tararua.

Alpine defined

The word ‘alpine’ is often used loosely to refer to anything to do with high mountains. Ecologists use the word to mean land above the upper altitudinal limit of trees. Strictly defined, it means the altitudinal zone between the timberline and the permanent snowline. Above that is ‘nival’.

Altitude zones

There are distinct bands of vegetation from the foot of a high mountain to its summit. Dark green forest gives way to tawny grassland, above which is apparently barren rock. Higher still, some of the rock is hidden beneath snow and ice.

Abrupt and gradual timberlines

The timberline or treeline (‘bushline’ to New Zealanders) – the highest elevation where trees can grow – is often a sharp ecological boundary. In New Zealand, timberlines formed by southern beech (Nothofagus) are typically abrupt – quite tall beech trees give way suddenly to tussock grassland.

Where beech is absent, such as on Mt Taranaki and in central Westland, the timberline can be gradual. Trees such as thin-bark tōtara (Podocarpus hallii) and rātā (Metrosideros umbellata) diminish in stature until they intermingle with subalpine scrub. Key members of subalpine scrub include shrub daisies such as leatherwood (Olearia colensoi) and Brachyglottis species, turpentine shrubs (Dracophyllum species), Hebe species and small-leaved, highly branched Coprosma species. Subalpine scrub and alpine grassland often intermix – tongues of grassland grow down into subalpine scrub, while spurs of low scrub and shrubland advance upwards.

Temperature threshold

It is not known why beech timberlines are so abrupt. New Zealand botanist Peter Wardle has argued that the critical factor is whether the growing season is long and warm enough for young shoots to finish growing and become sufficiently hardened to withstand the cold winter that follows. With increasing altitude, a tree’s ability to harden decreases. A common factor at timberlines throughout the world is that the mean temperature of the warmest month is about 10˚C.

The alpine belt

In the central region of New Zealand’s Southern Alps the alpine belt extends from 1,250 metres (timberline) to 2,000 metres (permanent snowline). In warmer, more northern parts of New Zealand, the lower limit of the alpine zone rises to 1,500 metres. On Stewart Island it descends to about 900 metres. At even more southerly latitudes in the subantarctic islands, the lower limit of the alpine zone is at sea level.

Low altitude alpines

Here and there, alpine plants grow at altitudes much lower than would be expected on the basis of temperature alone. For example, on Mt Moehau, at the northern tip of the Coromandel Peninsula, they occur at 892 metres. With a latitude of 36˚30’ south, the expected timberline would be at 1,750 metres. On Stewart Island, alpine vegetation descends almost to sea level in a few places, and is extensive on infertile, poorly drained, windswept uplands. On both Mt Moehau and Stewart Island, features of the soil (especially low fertility) and of climate other than temperature (especially wind) inhibit competition from taller-growing plants.


Alpine grasslands and wetlands

Environmental factors

A low average temperature is the defining characteristic of alpine zones. Other environmental factors vary widely. Differences in rainfall, cloud cover, aspect, rock type, soil fertility and drainage mean that alpine vegetation across New Zealand is diverse. For simplicity, however, the country’s alpine plants can be grouped into four main vegetation and habitat types:

  • grassland
  • wetland
  • stable rock
  • rock debris.

Alpine grassland

Unlike the short, summer-green alpine grassland in many other parts of the world, those in New Zealand are dominated by large, long-lived, evergreen tussocks of Chionochloa, collectively known as snow tussock. Some alpine grasslands are formed by shorter, evergreen grass species, notably in the genera Chionochloa, Poa and Rytidosperma.

Which grass dominates is determined by a complex set of interacting variables. These include seasonal rainfall levels (mostly an east–west gradient), north–south species distribution patterns, soil characteristics, how long snow lies on the ground, and disturbances such as avalanches.

Shrub associates

Short-statured shrubs are associated with the grasses, especially in the lower half of the alpine zone. They include snow tōtara (Podocarpus nivalis), a number of Hebe and Coprosma species, and some heath and heath-like shrubs (Gaultheria, Archeria, Leucopogon and Dracophyllum).

Herbaceous associates

Many herbaceous flowering plants grow between the snow tussocks. Among them are numerous species of mountain daisy (Celmisia), spaniard (Aciphylla), Anisotome, buttercup (Ranunculus), Ourisia, eyebright (Euphrasia), Parahebe and gentian (Gentianella). Compared with continental alpine areas the flowering season in New Zealand is prolonged. Some buttercup and marsh marigold (Psychrophila) species are in full flower from November to December, Celmisia daisies bloom from December to March with a peak in January, and gentians flower from late January into April.

Alpine wetlands

In waterlogged and aquatic sites (lakes, tarns, bogs, marshes and swamps) the shape of the land prevents water from draining away, or water is supplied continuously from higher ground (flushes, streams and waterfalls). Widespread in alpine wetlands are mosses (including peat-forming Sphagnum), liverworts, sedges, rushes, golden-flowered lilies (Bulbinella species), white and pink-flowering willowherb (Epilobium macropus) and algae.

In the South Island a distinctive orange-brown, glossy alpine rush (Marsippospermum gracile) is often the dominant species where there is more or less continuous seepage in high-altitude grasslands. It is visible from afar.

Carnivorous bog plants

Sundews (Drosera species) obtain essential nutrients, especially nitrates, from infertile, acidic, waterlogged bog sites by trapping and digesting small insects. They use specialised, flypaper-like leaves that are covered with sticky glandular hairs. Of six native sundews, three are alpine.

Cushion bogs

Wetlands where cushion-forming plants such as comb sedge (Oreobolus pectinatus) dominate are known as cushion bogs. They are extensive in areas where alpine terrain was planed and hollowed by glacier ice in the last glaciation but which has been free of ice for thousands of years. On the eastern side of the central Southern Alps, glaciation was so extensive and the ice retreat so relatively recent that a number of characteristic alpine bog species including alpine bog cushion (Donatia novae-zelandiae) and pygmy pine (Lepidothamnus laxifolius) are absent.


Alpine rock vegetation

Stable rock

Alpine rock often looks barren from a distance, yet it supports a rich array of plant life, including many flowering herbaceous and sub-shrubby species, grasses, mosses and lichens.

The remarkable cushions of vegetable sheep (Raoulia and Haastia species) have adapted to avoid drying out on rock at high altitude. These plants are in effect highly compressed shrubs, their multiple branches ending in tightly packed rosettes of tiny, woolly leaves. This forms a hard, continuous surface that minimises water evaporation. Rain penetrates quite easily, saturating the peaty core, with its numerous fine roots. These roots take up water to supplement that taken up by the main roots, which anchor the plant to the rock.

New Zealand edelweiss

New Zealand edelweiss is probably the most characteristic, abundant and widespread of all the alpine rock dwellers. North Island edelweiss (Leucogenes leontopodium) occurs from Mt Hikurangi down to the northern South Island. South Island edelweiss (Leucogenes grandiceps) is found throughout the South Island and on Stewart Island. Their strong resemblance to the famous Swiss edelweiss (Leontopodium alpinum) is more than skin deep – despite growing on opposite sides of the earth, all these edelweiss species are botanically related.

Rock debris

Areas of fragmented rock such as fellfield, scree, moraine, bouldery torrent beds and shingle river beds are major parts of New Zealand’s mountain landscapes. Most look bare from all but the closest vantage points. But everywhere plants are colonising the debris. Mosses and lichens are often abundant. Among flowering plants, the genera Epilobium, Raoulia, Haastia, Ranunculus and Poa are well represented. They constantly risk being destroyed by moving rock.

Fellfield

Fellfield is the most stable of the debris habitats. A characteristic plant form on these alpine rock deserts is the cushion. Many unrelated plants (Hectorella, Raoulia, Haastia, Chionohebe, Kelleria, Phyllachne, Colobanthus and Luzula) have evolved the cushion form to make the best use of the microclimate close to the ground, and to resist damage by wind or abrasion.

Scree

Least stable is scree. About a dozen specialised scree dwellers are virtually confined to huge shingle slides on South Island ranges east of the main divide. Despite their botanical diversity, they share many features. They are small, have fleshy, waxy, blue-grey leaves, and have well-developed underground parts that lie within the firm, fine-grained layer immediately beneath the mobile surface stones.

The specialised scree plants belong to several unrelated plant families, such as the willow herbs (Epilobium, family Onagraceae), buttercups (Ranunculus, Ranunculaceae), Lignocarpa (Apiaceae), Stellaria (Caryophyllaceae), penwipers (Notothlaspi, Brassicaceae), harebells (Wahlenbergia, Campanulaceae), Lobelia (Lobeliaceae), and button daisies (Leptinella, Asteraceae).

Scree adaptations

It remains uncertain how these plants survive in the precarious shingle. One hypothesis is that they photosynthesise rapidly and send food down quickly into their underground parts. Water is never lacking on the scree sub-surface, and because the leaves of scree plants are mostly water, they are expendable – it is not a great loss if the fleshy shoots are torn off by moving stones.

This hypothesis may explain why nearly all scree plants fail to extend west into mountains with high levels of rainfall. The lower temperatures and reduced light intensities there would result in growth rates too low to compensate for losses due to scree movement.

The blue-grey colouring and waxy coating of leaves protect against high light intensities and temperature extremes (although not against drought, and not as camouflage against the stones).


Highest of all

Not all of the area above the perennial snowline is permanently snow-covered. Snow accumulates in some places and is cleared rapidly from steep rock by gravity, wind and sun.

Aoraki/Mt Cook

In the Mt Cook region there are flowering plants found only on rock above glacier neves. Ranunculus grahamii appears to be restricted to the central alps, but has never been reported west of the main divide. It reaches altitudes of nearly 3,000 metres, along with Parahebe birleyi and Hebe epacridea. Some other vascular plants found high above the snowline include Myosotis suavis, Pachycladon enysii, Poa novae-zelandiae, Colobanthus buchananii, Raoulia youngii and several species of Epilobium. One species of fern, Grammitis poeppigiana, reaches an altitude of at least 2,600 metres – higher than any other New Zealand fern.

Rock crannies

One might expect the cushion form to be well represented among flowering plants at the highest altitude, but few are cushions or mats. High-altitude plants live in crannies in solid rock. Such sheltered places are probably where frozen water first becomes available in usable liquid form. Most of the highest altitude cranny plants are relatively soft, herbaceous or sub-shrubby, as in other high mountains of the world.

High altitude plant records

Buttercups are the flowering plant champions of high-altitude growth in New Zealand and elsewhere. In the European Alps the glacier buttercup Ranunculus glacialis grows to about 4,300 metres. The record is shared by Ranunculus lobatus and a scree plant belonging to the mustard family, Ermania himalayensis – both are found at 6,400 metres in the Himalayas.

Summit lichens

No ferns or seed plants have been noted above 3,000 metres in New Zealand. Mosses, lichens and algae go higher, just as they extend much closer to the poles than any vascular species. At least 15 species of lichen have been identified from the Summit Rocks area of Aoraki/Mt Cook, at 3,500 metres.

Red snow

Even the perennial snowfields are far from lifeless. As in other parts of the world, bright reddish-pink flushes on the melting surface of summer snow reveal themselves under the microscope to be millions of one-celled algae (Chlainomonas kolii), swimming for a time in the surface film of water round the ice granules. When the cells enter their resting stage, they mask their green photosynthetic colouring with protective red pigments.


New Zealand’s alpine flora and its origins

New Zealand has about 2,500 native vascular plant species (seed plants, ferns and lycophytes). About 500 of these belong exclusively to the high mountains, with another 100 at lower altitudes only under certain circumstances. This makes 600 alpine, subalpine or nival species, belonging to 45 families and about 120 genera. Another 350 or so species are found both in the lowlands and highlands, bringing the mountain flora to a total of nearly 1,000 species.

Origins

The origin of New Zealand’s high altitude plants is something of a mystery. The mountains are geologically young and geographically isolated. Most of the alpine species occur nowhere else, although there are affinities to plant life in Australia, New Guinea and South America.

The movements that produced today’s uplifted land began only a few million years ago. Before that, for tens of millions of years, the New Zealand region was low-lying and warm. There were mountains earlier still, in early Cretaceous times more than 100 million years ago, before New Zealand split from the supercontinent Gondwana. But these mountains had been worn away by late Cretaceous and early Tertiary times. A Cretaceous mountain flora could not have survived such a long period of warmth and low relief. From what, then, has New Zealand’s unique modern mountain flora developed? There are several possibilities, probably all of which played a part.

Adaptable survivors

One possibility is that a few cool-climate plants survived on infertile upland soils. Some of the Cretaceous mountain flora may have been able to adapt to warmth and low altitude, and then expand into the new mountain habitats of the Pleistocene period. Even if the Cretaceous mountain vegetation was almost extinguished, lowland plants may have given rise to innumerable new species when mountain habitats became unoccupied. Certainly many high altitude plants have close relatives in the lowlands. But others do not. Hectorella caespitosa, for example, a high-altitude cushion plant, is never found below the alpine zone and its only known relative is found in the Kerguelen Islands in the subantarctic. For Hectorella at least, we must assume it survived through the warm period of the Tertiary on cooler lands further south.

Long-distance arrivals

Another possibility is that ancestral forms have reached New Zealand by long-distance dispersal across the sea, mostly from or via Australia. A few migrant species could have evolved explosively to fill unoccupied niches on the rising mountains. Willowherbs (genus Epilobium) are an example. Its worldwide distribution and taxonomy means it could not have originated in New Zealand, but there are a large number of native species there. Many of these are mountain plants, but all are so closely related that it seems certain they evolved from a single ancestor in the geologically recent past.


Survival

Alpine beauties

Alpine plants are unique because they can grow and reproduce in low temperatures. Many of the adaptations underpinning this ability are features admired by gardeners. The plants are miniature and compact, yet often have disproportionately large flowers – even small plants need to attract pollinating insects or birds (few, except grasses, sedges and rushes, risk relying on the wind).

Adaptive features of alpine plants

As well as large flowers, alpine plants have other features that assist their survival:

  • Leaves are often woolly to help trap heat, reduce transpiration, and protect against wind, abrasion, and ultraviolet radiation.
  • Their optimum rates for photosynthesis and respiration are at lower temperatures than for low-altitude plants.
  • They are long-lived. There are very few alpine annuals. Perennials can store more energy and are not obliged to reproduce every year.
  • Flower buds are typically formed in the preceding summer, if it has been warm enough. Whether or not the bud flowers or is aborted is determined by the temperature of the current summer.
  • Some produce anti-freeze chemicals (soluble carbohydrates) that prevent their cells from freezing when temperatures drop below 0°C.

White flowers

New Zealand's alpine flowers are notable for their lack of colour. After white, yellow is the most frequent hue, although much less common. The proportion of white flowering alpine plants in New Zealand is 77% – about twice the world average. Genera and families with colourfully-flowered species in other parts of the world (for example, Gentianaceae, Asteraceae, Myosotis and Ourisia) are represented mainly or exclusively by white-flowered species in New Zealand.

‘My darling specimens’

On his first trip to the alpine herb fields of the Ruahine Range in 1845, missionary botanist William Colenso was astonished at the richness and beauty of the flowering plants that grew there. He collected many specimens and stowed them in his jacket, shirt and hat for safekeeping. He recorded, ‘I was wholly occupied with my darling specimens … only getting about 2 hours sleep towards morning’. 1

Insect pollinators

The prevalence of white flowers seems to be related to New Zealand’s lack of specialised insect pollinators. Flower colour attracts certain pollinators – for example, long-tongued bees respond especially to blue and ultraviolet. New Zealand has no native species of long-tongued bees – the chief pollinators are flies, moths and short-tongued bees, which visit a wide range of flowers. Colour is a cost to the plant in terms of resources and genetic coding, and if colour has no advantage, then in severe alpine environments evolution tends to select against it. White, bowl-shaped flowers attract as many insect pollinators as possible in areas where pollinators are scarce.

Footnotes
  1. William Colenso, In Memoriam. An account of visits to, and crossings over, the Ruahine Mountain Range, Hawke’s Bay, New Zealand. Napier: Daily Telegraph, 1884, p. 22. › Back

Alpine invaders

The New Zealand alpine zone is less disturbed, and less compromised by introduced plants and animals, than many other native ecosystems. Māori settlement probably had minimal impact on alpine areas, although some large browsing birds were reduced or eliminated.

Browsing mammals

European settlement had a much greater impact. Some introduced plants are now abundant and widespread. The introduction of browsing mammals (tahr, chamois, red deer, sheep and hares) has proved harmful to native plants. Once the palatable alpine herbs, tussocks and shrubs are selectively eaten, they are replaced by unpalatable plants such as speargrasses (Aciphylla species), mountain daisies (Celmisia species), fescue tussock (Festuca novae-zelandiae) and bristle tussock (Rytidosperma setifolium). Sheep have been grazed up into the alpine zone on South Island runs since the 1840s, but much of the higher land has now been retired from grazing, and wild sheep do not live at such altitudes. Chamois and tahr, introduced to South Island mountains in the early 20th century, and red deer, introduced in the mid-19th century, quickly established wild herds. As well as eating alpine plants, they trample vegetation and contribute to soil erosion in the mountains.

Alpine weeds

Some introduced plants are now naturalised and abundant in the alpine zone, including catsear (Hypochoeris radicata), hawkweed (Hieracium species, especially H. praealtum), sheep’s sorrel (Rumex acetosella) and the grass browntop (Agrostis capillaris). These European natives are not confined to the alpine zone – they are opportunistic, with a wide altitudinal range in both Europe and New Zealand.

Global warming

The effects of global warming can be expected to show up clearly on high mountains, with likely elevation of tree- and snowlines, invasion upwards by lower-altitude species, and possibly major disruption and change to alpine ecology.


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How to cite this page: Hugh Wilson, 'Alpine plants', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/alpine-plants/print (accessed 20 March 2019)

Story by Hugh Wilson, published 24 Sep 2007