The secret to stabilising and saving our sand dunes

Posted on September 27, 2016

Coastal sand dunes are some of the least understood and degraded natural ecosystems in New Zealand. Every day we are harming these sensitive ecosystems through our recreational activities, uncontrolled livestock damage, housing developments and beach mining.   Instead, we should be restoring them through revegetation to buffer the land from wind and storms and fencing them off to protect ecologically sensitive seabird nesting areas.

New Zealand’s native dune plants are worth protecting. The endemic plant species that grow on them tolerate high velocity sand blasting and thrive on regular doses of salt spray and on being buried alive. They grow in a low nutrient soil medium, tolerate extremely dry conditions and tolerate vastly varying temperatures from below 0-40°c. They produce leaves and roots that actively stabilise and trap moving sand and provide a natural environment for native insects, animals and birds. They also add rich colour and texture to the dune environment.

There are four main zones in a coastal area.

The ‘sand dune’ zone is the first 10-20m above the high tide mark to the top of the first dune crest. It is a particularly hostile area for plant survival. Plants that grow in this zone are typically low growing and can cope with salty soils and salt laden sea spray. These species trap the sand blowing in the wind and drop it onto the sand dune where they are growing. This reduces the inland creep of sand dunes and maintains the smooth and gentle contour of the sand dune.

Key species in the ‘sand dune’ zone include:

The ‘groundcover’ zone is the 20-50m wide band behind the ‘sand dune’ zone. These are the next sand dunes behind the first sand dune that are typically covered in groundcover species. These dunes are usually slightly more sheltered from the wind, and have some moisture and organic matter in the sandy soil. This zone has a mixture of ground cover plant species and salt tolerant grasses and rushes. Shore spurge and tauhinu will grow in this area, as will the species that grow on the ‘sand dune’ zone.

Key species in the ‘groundcover’ zone include:

  • Muehlenbeckia complexa (Pohuehue or wire vine)
  • Coprosma acerosa (Tarakupenga or sand coprosma)
  • Euphorbia glauca (Waiū-o-kahukura or shore spurge)
  • Isolepis/Ficinia nodosa (Wīwī or knobby clubrush)
  • Ozothamnus leptophylla (Tauhinu)
  • Disphyma australe (Horokaka or NZ ice plant)
  • Lachnagrostis billardierei (Perehia or sand wind grass)
  • Apium prostratum (Tutae koau or shore celery)
  • Tetragonia trigyna (Kokihi or beach spinach and NZ spinach)

The ‘short shrub’ zone is the area that is typically 50-200m (or even wider on large sand dunes) behind the ‘groundcover’ zone. The ‘short shrub’ zone is typically well covered in plant species including coastal grasses, rushes and flaxes and many short bushy shrub species that produce succulent berries and other seeds, providing a rich food source for birds, insects and lizards. This zone is more sheltered and has a higher moisture and organic content in the sandy soil. Species that grow in the ‘groundcover’ zone will also grow in the ‘short shrub’ zone.

Key species in the ‘short shrub’ zone include:

The ‘coastal forest’ zone is the 200-500m wide band of coastal forest behind the ‘short shrub’ zone. The ‘coastal forest’ zone is still subjected to some onshore wind but has a considerably higher moisture and organic content in the soil. Soil temperatures are lower so many shrub and tree species will establish here. This is the area where building subdivisions are being constructed, so a good mix of these species is desirable. Plant species that grow in the ‘groundcover’ and ‘short shrub’ zones will also thrive in the ‘coastal forest’ zone.

Key species in the ‘coastal forest’ zone include:

For more detailed information on coastal sand dune restoration and suitable species, see https://www.boprc.govt.nz/media/289195/lab-2a-advanced-ppt.pdf