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.
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.