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Dune lands

by  Carl Walrond

Since the early 1900s, New Zealand has lost 70% of its dune lands – rolling sand hills behind beaches. Seen as waste areas, they were planted with introduced species, or turned into pine forest, golf courses or housing. Today many remaining dunes are being protected and planted with native sand-binding species.


Dunes

Dune lands are piles of wind-blown sand that build up behind beaches in exposed coastal areas. In earlier times, they were seen as wastelands – but today they are recognised as unique environments. Many are protected from development, and are being planted with native sand-binding plants such as pīngao (Desmoschoenus spiralis) and spinifex (Spinifex sericeus), which grow naturally on dunes close to the sea.

How dunes form

Dunes form where there is a good supply of sediment from the sea. Waves deposit sand on the beach, then when the tide retreats, the sand is exposed. Most sand grains are between 0.06 and 0.6 millimetres in diameter – small enough to be moved by the wind. The amount of sand moved increases exponentially with wind speed.

Sand gathers around small obstacles, forming a mound, which builds on itself and eventually becomes a dune. Sand also forms into ripples, which over time develop into ridges and dunes.

Active dune lands

Active dune lands are those where dunes are able to migrate, because they are not completely covered with vegetation and the wind can blow the sand about. Most former dune lands are covered in plants, and the dunes are no longer active.

Dune migration

Dunes have a shallow upwind slope and steeper downwind slope. Wind blows sand along the upwind slope, and then it tips down the steeper downwind slope. As a result, dunes migrate downwind over time. On the Manawatū coast, dune migration rates are some of the world’s highest. Maximum advance rates over one year have been measured as 1–10 metres through forest, 70 metres over low scrub, and 400 metres across grassland.

Remaining dune lands

The larger remaining active dune lands are in Northland (Aupōuri Peninsula, North and South Kaipara peninsulas, Awhitū peninsula), Auckland’s west coast (Manukau Heads), Waikato (Aotea and Kāwhia harbours), the Manawatū coast, Farewell Spit, the Fiordland coast, Southland (Oreti Beach) and Stewart Island (Mason Bay). All are on west-facing coasts, where they are exposed to prevailing winds.

Less extensive dune lands are also found on eastern coasts – such as at Sandfly Bay on Otago Peninsula, and Woodend Beach near the Waimakariri River mouth. In the past, rare localised inland dunes also occurred in Central Otago, around Alexandra and Cromwell, formed from sand deposited by the Clutha River.

Many former dune lands have been taken over by native bush. This is a natural process – before human arrival, sand and vegetation vied for ascendancy in many exposed parts of coastal New Zealand.

Burning sands

In the 1880s in winter, settler families often made all-night watches for frostfish, which washed up on beaches north of Dunedin. One settler recalls: ‘[T]he boys used to set fire to the native grass, and night after night saw patches of the sandhills ablaze. In places the grass disappeared altogether, and at these points the strong north-east wind cut its way through, opening up long hollows through the protecting sandhills and carrying the sand over the flat in long, straight lines, or spreading it out fan-shaped.’ 1

Sand supply

The sand supply that forms dunes may be in a closed system where the sand was formed long ago, or an open system with ongoing inputs of new sand.

The giant dunes of the Aupōuri Peninsula in Northland are an open system. Much of their sand comes from the volcanoes of the central North Island. Over millions of years, sediment from volcanic eruptions has washed down the Waikato River. Coastal currents moved the sediment northwards, forming huge sand deposits, in a process that continues today. The Aupōuri Peninsula is actually a sand deposit (known as a tombolo) that joins the rocks of the mainland with those of Cape Rēinga.

Closed systems have little or no inputs of new sand. For instance, at Pākiri Beach on Auckland’s east coast, coastal erosion and storm waves shift sand from the beaches and dunes to sandbars out at sea. Between storms, smaller waves dump the sand back on the beaches.

Footnotes
  1. Murray Gladstone Thomson, A pakeha’s recollections: the reminiscences of Murray Gladstone Thomson. Wellington, A. H. & A. W. Reed, 1944, p. 44. › Back

The ‘problem’ of drifting sands

Human impact on dunes

It is not known how much Māori influenced the active dune lands, but their fires may have opened up more land to sand movement. From the mid-1800s, settler farmers cleared and burnt sand-binding native grasses, shrubs and small trees near the coast in order to run sheep and cattle. They removed the natural vegetation cover, allowing dunes to move inland.

Increase in dune lands

It is difficult to know the extent of dune lands, as they are continually moving. An 1880 estimate suggested that there were 40,000 hectares of drifting coastal sand. By 1909, the area was thought to have increased to 120,000 hectares. It is uncertain if the growth was entirely due to farming practices – research has shown that dune lands also had natural periods of expansion over the late Holocene (last 10,000 years), so some of the growth may have been natural.

Evil sand

In 1903, Parliament debated the Sand Drift Bill. One legislative councillor, John Rigg, outlined his view of advancing sands on the Kapiti coast:

‘It may be that its onward march may be checked by planting near the sea-shore, and that the evil may be mitigated; but from the sandhills the sand flies in clouds with every wind, and on a windy day it is carried for miles. In the neighbourhood of the sandhills it is with difficulty that you can breathe on such days. Your eyes and nose are full of sand, and the experience is altogether disagreeable.’ 1

The sand threat

Today dune lands are seen as unique ecosystems, but in colonial New Zealand there was a fear of drifting sands. Sand blew about in coastal areas, encroaching onto pastures and even burying a church at Waikanae on the Kapiti coast.

From the 1870s, the threat to productive land was recognised but little was done. In 1908, the government passed the Sand Drift Act – an ineffective tool which did nothing to arrest the drift of sand, but gave the matter official recognition. In places around the coast farmers had already taken things into their own hands and planted introduced marram grass (Ammophila arenaria) to stabilise the dunes. They had some success, but their efforts were piecemeal.

Looking for a solution

The Department of Lands was the first government agency to tackle what was seen as the sand problem. The botanist Leonard Cockayne was asked to write a report, published in 1909. His second report, in 1911, included a section on stabilisation methods. The French had stabilised dunes on the Gascony coast with extensive planting, and this was seen as a solution for New Zealand. Cockayne’s advice guided the government’s approach in the following decades.

The first step was to stabilise sand at the point of supply – the coast. Cockayne pointed out that only continuous vegetation cover would solve the problem, and that this should also be commercially valuable. Trials of sand-binding plants and forest trees were done at the mouths of the Rangitīkei and Waikato rivers, but they were not well funded.

Planting the dunes

During the economic depression of the 1930s, the Public Works Department took over the sand-stabilisation project. Gangs of men lived in camps, planting marram grass and other exotic species. By 1951, when the New Zealand Forest Service took on the job, 9,000–10,000 hectares of dunes had been planted in marram grass and yellow tree lupin (Lupinus arboreus), and 3,800 hectares of forest had been planted.

The Forest Service trialled different types of vegetation and ways of stabilising dunes. They mechanised the planting of marram grass and radiata pine (Pinus radiata), greatly increasing the areas they could cover. By the 1970s, they had a standard approach, starting at the beach and moving inland:

  1. Build fore dunes (dunes close to the sea), using barriers such as mānuka fences and radiata pine prunings.
  2. Plant marram.
  3. Sow yellow tree lupin.
  4. Plant radiata pine on the coastal edge.
  5. Plant commercial forests in the lee of the shelter achieved.

From the 1960s to the 1980s, the Forest Service established pine forests in large areas of Northland, Auckland, Waikato and Manawatū dune lands. These forests have been the largest factor in the reduction of New Zealand’s active dune lands.

Footnotes
  1. New Zealand Parliamentary Debates 126 (1903), p. 590. › Back

Dune lands today

Reduction of dune lands

New Zealand’s area of active dune lands stayed much the same from the early 1900s until the early 1950s, when the government decided to plant many areas in radiata pine. By the early 2000s, only about 30% (39,000 hectares) remained.

One study looked at the loss of active dune lands from the 1950s to the 1990s. It found that the regions with the largest dune land areas also had the biggest reductions (Manawatū by 81%, Northland 76%, Waikato 72% and Auckland 68%). A 1987 study found that 200,000 hectares of sandy, rolling land that had once been dunes was now covered in pasture, pine trees, gorse and other exotic species.

Forests reduced sand drift and provided timber. But there was a growing recognition that dune lands were also attractive landscapes with unique ecosystems.

All on its own

The native sand-binding sedge pīngao is a botanical loner. One ecologist wrote that the plant ‘has no near relatives anywhere in the world — a sign of long, isolated ancestry. Pingao has presided over eons of dune-building and shoreline change.’ 1

Loss of native species

Many exotic plants have invaded dune lands. Marram grass has been planted extensively, and has also spread naturally. It has stabilised dunes, but has also replaced native plants such as pīngao (Desmoschoenus spiralis) and spinifex (Spinifex sericeus).

Plants can also alter the shape and extent of dunes. Marram is a very effective sand binder, creating dunes that are steeper and higher than those covered in pīngao and spinifex. Pīngao actually needs sand movement to survive, so it does not grow on well-stabilised dunes, and is now found mainly on fore dunes (closest to the sea).

Replacing pīngao with marram grass has also changed the habitat of the native katipō spider, which is now considered to be a threatened species.

Impact of development

Links golf courses are sand dunes turned into fairways and greens. Coastal subdivisions have been built on and behind dunes. For example, the coastal Christchurch suburb of Brighton sits immediately behind dunes, which protect it from storms and possible tsunamis.

Remaining dune lands are still under pressure from development. Localised sand mining and building seawalls and groynes can decrease the sand supply. Where vehicles have access to dunes, their tyre tracks can damage plants and animals.

Remaining dune lands

Some of New Zealand’s best preserved active dune lands are at Mason Bay on Stewart Island. They give a good idea of the original nature of these areas. In places, dunes are advancing inland, burying native forest. Downwind of Mason Bay beach, a 14-kilometre dune land extends up to 3 kilometres inland, with sand hills higher than 150 metres. A few bays northwards, at Hellfire Pass Hut, a tongue of sand has been blasted up through the bush, forming dunes 200 metres above sea level.

On the Aupōuri Peninsula in Northland, dune hills rise up more than 150 metres (covering bedrock), and lakes occur where drifting sands have dammed small streams.

On the Manawatū coast, dunes once reached up to 18 kilometres inland, but are now just a narrow coastal strip.

Restoration

The rate of loss has slowed over the 1990s, as some dunes have come under the management of the Department of Conservation. Local and regional authorities were also required to address the protection of dunes under the 1994 New Zealand Coastal Policy Statement.

In many places, restoration groups are replanting active dunes with native sand-binding plants such as pīngao, spinifex and euphorbia. Slopes further from the sea are being planted with native coastal species such as ake ake, ngāio, cabbage tree, flax and hebe. On Stewart Island, the Department of Conservation has used herbicide to kill marram grass and encourage pīngao.

Footnotes
  1. Neville Peat and Erwin Brinkmann, Stewart Island: the last refuge. Auckland: Random House, 1992, p. 52. › Back

External links and sources

More suggestions and sources

More links and websites


How to cite this page: Carl Walrond, 'Dune lands', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/dune-lands/print (accessed 19 July 2018)

Story by Carl Walrond, published 24 Sep 2007