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Shrublands

by  Maggy Wassilieff

Large areas of New Zealand are shrublands – a mix of plants, often including mānuka, kānuka, mingimingi and daisies. Many native shrubs have a wiry, small-leaved growth form. Some shrublands are a temporary stage in forest regeneration, while others are permanent.


New Zealand’s shrublands and scrub

New Zealand has an abundance of twiggy shrubs. They grow in various combinations from the coast to alpine slopes, forming shrubland and scrub communities.

Shrublands occur alone, or mixed with grassland and forest, over some 7.5 million hectares – 28% of New Zealand. Some are temporary, forming one stage in the development of forests. Others are permanent, growing in harsh environments where trees fail to prosper – exposed coasts, wetlands, infertile soils, alpine areas, and very dry hill country.

Shrublands in New Zealand include:

  • mānuka shrublands, which have an important role in forest regeneration
  • alpine shrublands, found above the treeline in mountain areas
  • matagouri scrub, which occurs among the South Island’s tussock grasslands
  • heathlands, found on very infertile soils.

Shrub or scrub?

Shrubland is open vegetation where shrubs are the tallest plants; scrub is denser, with a continuous or near-continuous canopy of shrubs and small trees. Both are usually differentiated from bush – a New Zealand term for tall native forest.

What is a shrub?

A shrub is a small woody plant, usually with multiple stems that start close to the ground. There is no clear distinction between a small tree and a large shrub. Some species may take a shrub form when growing in exposed conditions, but develop into a small tree in moist sheltered situations.

New Zealand shrubs

New Zealand has around 445 native shrub species, more than twice the number of native trees. Just over a third (155) are uncommon or threatened. One, Logania depressa, is assumed to be extinct.

Around 230 shrubs have small leaves (less than 2 centimetres long). Of these, about 60 have an unusual, densely branched growth form that seems to be peculiar to New Zealand and is called divaricate, filiramulate or zigzag growth.

Lost shrub

The prostrate shrub Logania depressa was collected just once – by the missionary and botanist William Colenso in 1847, east of Waiōuru in the central North Island. Despite further searches, it has never been found since. The area where it grew has been damaged by fire and browsing animals, and much of it is now covered by Lake Moawhango, formed by a hydroelectric dam.

Reasons for divaricate form

Divaricating shrubs have small leaves and wiry, interlacing branches, set at wide angles. Why this habit occurs in at least 17 plant families in New Zealand is uncertain. Some biologists think that divaricates evolved from large-leaved relatives in response to cold, frosty and windy environments during the Pleistocene ice ages. Others suggest that the form was an adaptation against excessive browsing by moa – large flightless herbivorous birds, now extinct, that lived in open country and forests.

Common adaptations

With a few exceptions in very dry periods, New Zealand’s shrubs are evergreen – they hold their leaves year-round. Many have features that help them survive in dry, windy environments by preventing excessive transpiration (evaporation of water from the leaf):

  • They have a dense network of interlacing branches, with small leaves held in the interior of the shrub.
  • Leaves are leathery, waxy on top, and often covered in hairs (tomentum) underneath.
  • Vertical, needle-shaped leaves are held at the tips of stiff, upright branches.
  • Leaves are reduced to scale-like structures, and are closely pressed to the branch stems.
  • The edges of the leaf curl inwards on the underside.

Plants in New Zealand’s shrublands

Although shrublands are extremely varied in their species composition throughout New Zealand, some generalisations can be made. Dominant or common plants include:

  • divaricating shrubs
  • the heath family (Ericaceae)
  • small conifers
  • shrub daisies
  • hebe and coprosma species
  • introduced shrubs, especially in the lowlands.

Lowland and hill country shrublands

On the lowland plains and in the hill country, most shrublands are secondary growth – they occur on sites that were formerly forest. In the absence of disturbance (fire and heavy browsing by mammals), the forests regenerate.

Mānuka shrublands

Mānuka (Leptospermum scoparium) is the most abundant and versatile native shrub in New Zealand. It is a variable species, usually growing to 3–5 metres in height, but capable of persisting in a dwarfed form (10–30 centimetres tall) in exposed or infertile situations.

Mānuka shrublands occur in two distinct ecological settings:

  • permanent shrublands, on infertile, dry, exposed, or poorly drained soils
  • temporary shrublands on disturbed sites that formerly carried forest, as one stage in forest regeneration.

In moist, low-altitude areas that were once forest, mānuka is an important pioneer plant, starting forest regeneration. It forms dense shrublands that persist for decades (30–70 years, depending on the location), but are later replaced by tall forest.

In the lowlands and fertile hill country, mānuka is often accompanied by kānuka (Kunzea ericoides). This long-lived tree overtops mānuka, forming firstly a tall scrub cover, and then a forest. Areas of regenerating mānuka and kānuka scrub cover some 3 million hectares – especially in moist hill country where farming is marginal.

Although fire usually kills mānuka shrubs, it promotes seeding. On its branches, mānuka often has unopened fruit capsules, which split open in a fire and release thousands of tiny light seeds.

Broadleaved scrub

Broadleaved shrublands and scrub develop on moderately fertile and fertile soils. They usually comprise fast-growing, short-lived trees such as wineberry (Aristotelia serrata), rangiora (Brachyglottis repanda), māhoe (Melicytus ramiflorus), five-finger (Pseudopanax arboreus) and tree ferns. Near the coast, ngaio (Myoporum laetum) and taupata (Coprosma repens) are often present. At higher altitudes, the dominant tree species are pigeonwood (Hedycarya arborea), kāmahi (Weinmannia racemosa) and broadleaf (Griselinia littoralis). Broadleaved scrub is usually a stage in the regeneration of mixed conifer–broadleaf forest.

Coastal shrublands

Tauhinu (Ozothamnus leptophyllus) is a small, bluish-grey shrub daisy. It forms temporary shrublands that last for 15–20 years on coastal farmlands. Close to forest, tauhinu shrublands quickly revert to broadleaved scrub. Away from forest, they often develop into a mixed shrubland of small-leaved twiggy plants, known as grey scrub.

Gorse and Scotch broom

The introduced shrubs gorse (Ulex europaeus) and Scotch broom (Cytisus scoparius) form young regenerating shrublands covering 800,000 hectares of New Zealand. They are especially prominent on low-producing hill pastures and gravel flood plains. Gorse and broom are able to ‘fix’ atmospheric nitrogen and change it into a useable form, which gives them an advantage over most native shrubs. Both gorse and broom have seeds that stay viable for years when buried in soil or deep litter.

Unlike most native shrubs, gorse resprouts after fire, so it soon dominates native plants on sites that have been frequently burnt. Broom tolerates drier and frostier sites than gorse, and is especially common on the east coast of the South Island.

If left undisturbed, gorse and broom shrublands are invaded by native tree seedlings, which eventually overtop the shrubs and develop into mixed broadleaved forests.


Mountain shrublands

Alpine shrublands

Above the treeline, the forest suddenly gives way to shrubland or grassland. Alpine shrubs grow as a dense band of scrub up to 200 metres above subalpine forest, or as a mosaic with tussock grasses and alpine herbs. With increasing altitude and exposure to wind, shrublands become stunted, and comprise dwarf and prostrate shrubs less than half a metre tall. On the highest mountains, conditions are too severe even for shrubs, and shrublands are replaced by grasslands or alpine herbfields.

The broadest and most impenetrable bands of alpine shrublands grow on the wet western side of the mountains, especially those that experience frequent fogs.

Common alpine shrubs include species of hebe, Dracophyllum, shrub daisies and coprosma, along with Ozothamnus vauvilliersii, snow tōtara (Podocarpus nivalis), bog pine (Halocarpus bidwillii), mountain toatoa (Phyllocladus alpinus) and mountain flax (Phormium cookianum).

In the South Island and on Mt Taranaki (Mt Egmont), mountain lacebark (Hoheria lyallii) forms tall shrublands and low forests on old slip faces and in gullies. It is one of New Zealand’s few deciduous plants.

Under or over

In the 1930s, before deer opened up tracks through leatherwood scrub, a botanist noted that the only way to get through it was ‘to worm one’s way along the ground or even walk upon the top of the shrubs’. 1

Leatherwood scrub

On the wet western sides of the mountains, leatherwood scrub often forms a near-impenetrable band just above the treeline. The broadest stretches grow above subalpine broadleaf forest, which is not found as high as beech forest.

Leatherwood scrub is dominated by one or more shrub daisies with broad, tough leaves. The main species is tūpari (Olearia colensoi), found from Mt Hikurangi in the North Island to Stewart Island in the south. It is a stoutly branched, chest-high shrub with semi-prostrate stems which seriously impede trampers’ progress. Tūpari’s serrated leaves are broad and leathery, glossy above and clad in long woolly hairs underneath.

Tūpari is absent from Mt Taranaki, but a lookalike shrub daisy, Brachyglottis elaeagnifolia, forms leatherwood scrub there. In the Ruahine Range, Brachyglottis elaeagnifolia often grows with tūpari. In the South Island Brachyglottis rotundifolia, another leathery-leafed shrub daisy, is usually present with tūpari and īnanga (Dracophyllum longifolium) in the leatherwood zone.

Muttonbird scrub

Muttonbird scrub, found around the coasts of the southern South Island and on Stewart Island and the Snares Islands, closely resembles leatherwood scrub. It is also dominated by one or two leathery-leaved shrub daisies, Olearia lyallii and Brachyglottis rotundifolia. It is named muttonbird scrub because the soils underneath are usually riddled with the burrows of a native petrel (Puffinus griseus), known as muttonbird, sooty shearwater or tītī.

Heather shrubland

Scotch heather (Calluna vulgaris) shrubland covers 52 square kilometres of the northern and western side of Tongariro National Park, in the central North Island. Heather was planted deliberately from 1912 to 1922, and spread rapidly through native red tussock grassland, especially after the tussock was burnt, up to 1,650 metres altitude.

In the absence of fire, mānuka and īnanga invade and overtop heather. This succession to native shrubland is fairly rapid on hill slopes (within 38 years), but slow on frosty basin flats (more than 75 years).

Footnotes
  1. V. D. Zotov, and others, ‘An outline of the vegetation and flora of the Tararua mountains.’ Transactions and Proceedings of the Royal Society of New Zealand 68 (1938–1939), http://rsnz.natlib.govt.nz/volume/rsnz_68/rsnz_68_02_001890.html › Back

Shrublands of dry country

The eastern South Island and Central Otago lie in the ‘rain shadow’ of the central mountain ranges – they have low rainfalls and dry soils. Before humans arrived in New Zealand, these areas were clothed in forests and tall scrub. They have been frequently burnt and heavily grazed, which few native woody plants can survive, so grasslands and shrublands now dominate. All but the most fire-tolerant and unpalatable plant species are gone from the slopes and valleys.

Kānuka scrub

Kānuka (Kunzea ericoides) is found in the drier areas of the eastern South Island. Like mānuka, it is a pioneer plant (able to grow on cleared land). In some areas, it is replaced by broad-leaved forest trees after 100 years or so. However, in the driest locations of Central Otago, kānuka is a permanent part of the vegetation, and has formed open woodlands along with kōwhai (Sophora microphylla) and Hall’s tōtara (Podocarpus hallii).

Matagouri scrub

Matagouri (Discaria toumatou), also known as wild Irishman and tūmatakuru, is widespread in semi-arid and moderate rainfall regions of the South Island below 1,000 metres.

The only native plant with thorns, it forms sparse to dense shrublands among short-tussock grasslands. Common associates include other small-leaved, highly branched shrubs such as mingimingi (Coprosma propinqua), porcupine shrub (Melicytus alpinus), native brooms (Carmichaelia species) and sweet briar (Rosa rubiginosa). Although plentiful now, matagouri was even more so in the mid-1800s when it grew up to 6 metres high among tall tussock. Matagouri can resprout after a fire, but frequent burning, heavy sheep grazing and rabbit browsing have reduced its spread.

Sweet briar

The introduced sweet briar rose (Rosa rubiginosa) is the other common prickly shrub on the South Island’s east coast. With matagouri, it occupied about 1 million hectares of dry South Island country in the 1970s (when the area was last measured).

Sweet briar has been in New Zealand since the early days of European settlement. By 1900 it had spread through much of the South Island sheep country, and was declared a noxious weed. It favours fertile sites and quickly colonises disturbed open ground. It sprouts numerous, thorny stems, forming impenetrable thickets 2–3 metres tall.

Grey scrub

Grey scrub – a mix of small-leaved, dark twiggy plants – is widespread in dry areas, frosty river terraces and exposed hill country. Although it always includes mingimingi, the other species vary around the country. At least 25 different coprosma species could be present, along with a number of small-leaved pittosporum and olearia species. Grey scrub always includes climbing plants such as pōhuehue (Muehlenbeckia complexa), native jasmine (Parsonsia heterophylla) and clematis, their stems winding through the twiggy shrubs.


Heathlands

Heathlands occur on very infertile soils. These widespread soils are found on diverse landforms, in areas from subtropical Northland to the cool-climate subantarctic islands. They support low-growing (1–2-metre-tall) plants, mainly evergreen shrubs with small, hard leaves (sclerophylls). Many of these belong to the heath family (Ericaceae). In other countries, this type of vegetation is known as heathland. In New Zealand it is also called gumland and pakihi.

Mānuka is usually present, often dominating or sharing the canopy with one or more species of Dracophyllum. The understorey plants are usually grass-like sedges and rush-like plants from the restiad family.

Where to find heathlands

  • gumlands on podzol soils – Northland
  • heathlands on peat – Waikato lowlands, southern South Island, Stewart Island, Chatham, Campbell and Auckland islands
  • heathlands on young volcanic materials – central Volcanic Plateau
  • heathlands on wet mineral soils – mountains, glacial outwash surfaces, hill country.

Fire and heathlands

Many heathlands, especially in lowland areas, formed and expanded after Polynesian and European settlers cleared forests using fire.

In dry periods, heathlands are susceptible to fire. Most heathland species are poorly adapted to frequent fires, although mānuka seeding is promoted by burning, and mountain flax, sedges and some ferns can resprout from underground root stocks.

Gumlands

Gumlands are areas where kauri forests previously grew, and were named after the valuable kauri gum found in their soils. In 1840 gumlands covered about 300,000 hectares of northern New Zealand – but today few remain, as most have been converted to farmland.

In gumlands mānuka is the dominant plant, along with kūmarahou (Pomaderris kumeraho), sedges, and heath shrubs (Dracophyllum lessonianum, Leucopogon fasciculatus and Epacris pauciflora).

Peat bog heathlands

Heathlands developed on peat bogs in the Waikato, but most have been burnt or drained and turned into farmland. They carried a cover of mānuka and bamboo rush (Sporodanthus ferrugineus), under which grew Schoenus brevifolius, Baumea teretifolia and wire rush.

The peat bog heathlands of the Chatham, Auckland and Campbell islands are dominated by Dracophyllum species.

Volcanic Plateau heathlands

Mānuka and Dracophyllum dominate on young volcanic soils in the central North Island, which have been burnt many times. The soils dry out in summer, summer frosts are frequent, and forest is slow to regenerate. The introduced Scotch heather, Calluna vulgaris, dominates in the north-western part. Since the 1920s, heathlands on the Volcanic Plateau have been greatly reduced through pine planting and agriculture.

Subalpine and alpine heathlands

Dracophyllum scrub grows in wet mountain areas of both main islands, above the treeline. It often forms a mosaic with tall tussock grasslands, or a richer subalpine scrub of conifers, shrub daisies, coprosma and hebe species, mountain flax and shrubs, depending on the location.

Pakihi heathlands

The wet, leached soils of the western South Island support an open shrub vegetation known as pakihi – a Māori word that originally meant open country.

Pakihi vegetation is similar to that of the northern gumlands. Mānuka grows above a layer of sedges, ring ferns and wire-rush. Some sites are long-standing, while others developed after forests were burnt and cleared. A taller shrubland of celery pine, mānuka, silver pine, kāmahi and Quintinia often develops at the margin between forest and pakihi.


Importance of shrublands

Valuable ecosystems

Long despised as scrub weeds by farmers, native shrubs are slowly gaining acceptance as a valuable part of the landscape. Shrublands harbour a rich mix of native plants, animals and fungi. These vary around the country, and are mostly not well documented.

Invertebrates and fungi

The rich invertebrate life of native shrublands is slowly being revealed. In a small grazed reserve in Central Otago, 280 different species (spiders, insects, crustaceans, millipedes, snails and worms) were found on and under 30 plants of Olearia bullata, a shrub daisy, and mingimingi (Coprosma propinqua). Small-leaved divaricating olearia species support a complex array of lichens, mosses and algae on their twigs and stems. These are food for the larvae of 41 moth species known only in New Zealand.

At least 700 species of native fungi are found in mānuka shrublands, where they live in a beneficial association with mānuka.

Birds and lizards

Open shrublands provide shelter and a nesting habitat for banded dotterels and the New Zealand pipit. New Zealand falcons hunt in shrub country, and green finches, hedge sparrows and brown creepers nest in subalpine shrubs. Kea feed on fruit and insects in subalpine scrub.

A number of skinks and geckos also inhabit shrublands. They eat small invertebrates, and seasonal fruits from the shrubs. Lizards spread seeds in shrublands, especially those of coprosma fruits, a favourite food.

Beneficial effects of shrublands

On steep, erosion-prone soils, shrublands protect the land against slips.

Secondary shrublands, of both native and introduced plants, provide shelter and act as a nursery for regenerating forest. They are an effective carbon store, holding around 15.5 tonnes of carbon per hectare. This increases to about 212 tonnes of carbon per hectare as the shrublands develop into mature forest. Carbon accumulation by mānuka is similar to that of fast-growing pine plantations.

Mānuka and kānuka are major sources of honey. Some mānuka honey with high antibacterial activity is used in a range of medical products. Kānuka scrub can be sustainably harvested as firewood, although in the early 2000s, mānuka and kānuka firewood for sale was from clearfelled stands.

Disappearing shrublands

There are no national regulations for the protection of shrublands, apart from those covered by the Resource Management Act. Between 1997 and 2002, 12,415 hectares of native shrubland and scrub were cleared for pasture or conversion to forestry.


External links and sources

More suggestions and sources


How to cite this page: Maggy Wassilieff, 'Shrublands', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/shrublands/print (accessed 21 May 2019)

Story by Maggy Wassilieff, published 24 Sep 2007