Replanting Native Dune Plants

Sand is a difficult place for plants to survive, but some plants have managed to adapt to the environment and play an important role in the creation of sand dunes.

Dune plants are tough critters, surviving salt spray, being flooded by sea water during storms, living on shifting sand, and trying to hang on to precious fresh water that rushes through the sand. They survive high temperatures, low nutrients, and fierce winds.

• On the seaward side of the dunes, Spinifex (Spinifex sericeus) and Pingao (Demoshoenus spiralis) work together to trap wind-blown sand and build the sand dunes.
  
• Pingao are primitive plants, found only in New Zealand. The leaves - a golden green - catch windblown sand and the stems sprout new shoots as the sand covers and uncovers them. The more mobile the sand, the better pingao seems to like it.
  
• Spinifex is silver coloured and grows in the same fluid sand environment of the windward dunes. Found in New Zealand and Australia, the female Spinifex has seedheads with radiating spikes that blow about the beach until they lodge in a suitable spot. Like pingao, it has strong creeping runners (stolons) that help anchor the sand.
  
• On the back of the dunes, more sheltered from the wind, the fleshy pohuehue (Muehlenbeckia complexa) forms a dark green springy mat interspersed with the purple-trumpet flowers and heart-shaped leaves of sand convolvulus (Calystegia solanella). Further back a wealth of other plants are able to colonise the dunes.
  
• As the dunes are stabilised and soil built from decayed vegetation, coastal vegetation is replaced with coastal forests. Some coastal trees, such as the lovely pohutukawa, are important first settlers in back-beach environments.
  

• Dune plants have been unable to survive in areas where cattle and sheep are allowed to graze on them. They are also overpowered by imported plants, such as mirram grass, trampled by people, removed during sand mining and residential development.
  
• Pingao was once common on dunes throughout New Zealand, but now only small, discontinuous patches exist and the population is declining.
  
• Pingao is used by Maori for weaving and a current increase in traditional weaving has helped deplete the grasses. Maori should participate in replanting projects to assure a sustainable resource for weaving. In the past, harvesting of pingao for weaving was governed by Tikanga Maori but today, it is taken indiscriminately. Plants survive best when individual weaving-quality leaves are clipped from the leaf cluster. Cutting or wrenching of the whole leave cluster kills most plants.
  

Replanting Pingao

The New Zealand Forest Research Institute (Private Bag 3020, Rotorura) is working with community dune care groups, the Department of Conservation, and Regional and local councils to help rebuild New Zealand's coastal plants and manage the dune environment. They conduct research into replanting and harvesting of Pingao, Spinifex and other coastal plants.

Pingao is replanted on dunes using nursery-raised seedlings.

Seeds are collected in late December to early January. Collect them after they have ripened and are a golden brown. You will find a few husks on the sand when they are ready. They should easily fall from the husk when rubbed. If the seed is still green it should not be collected. Clip the entire seed head from the plant and put it in a strong plastic bag. Collect from a variety of plants and leave some seed heads on each plant to provide natural seed dispersion.

Later, to remove the seeds, place the seed head in a tray out of the wind, but exposed to the sun. After a few days, put the seeds and husks in a bowl and stir them. The husks will rise to the surface and most can be removed from the seeds.

Put the dried seeds in a plastic bag, seal it well, and put them in your refrigerator. Don't let them freeze. They can stay in a refrigerator no longer than a year. Remove the seed from the plastic bag and soak them in water in early August or September. Drain the water and mix the seed with 3 or 4 times its volume of moist peat.

Seal the seed and peat in a plastic bag with small holes to allow air movement. Replace this in the refrigerator for about 4 weeks. If the seeds germinate, remove them and sow them immediately.

Sow the seeds in wood or plastic seed trays with ventilation holes on the base. Use a lightly compacted seed raising mix of 50% sand and 50% peat. Spread the sead/moist peat mix evenly over the surface and cover with a thin layer of coarse sand. Water the seed tray two or three times a day. Put the trays on sand to allow drainage and prevent waterlogging. The trays should be kept at 15 to 25 degrees C in a glasshouse or conservatory.

The seeds germinate within 4 to 7 weeks. Allow them to grow to 6 or 8 cm high before transplanting to Rootrainer containers. If rootrainers are not available, use propagation tubes or even yoghurt pots. Allow the seeling's roots to descend vertically and fully into the pottong mix. Use a pencil or stick to carefully adjust the roots in the container.

The potting mix should be 25% to 50% coarse pumice or coarse washed sand. this imporves drainage and prevents waterlogging. Use peat and potting mix grade bark for the remainder. Be sure the peat and bark are well decomposed to prevent heating of the soil by composting.

Fertilise with a controlled release capsule such as Osmocote Plus at about 2.5kg per cubic metre of potting mix. 1 to 1.5 kg of dolomite lime can be added per cubic metre of mix and 1 kg of Diammonium phosphate.

Keep in a glasshouse for 4 to 6 weeks. Watering must be regular and temperatures must be below 30 degrees C. The plant containers should be on freely draining survaces such as sand. After 4 to 6 weeks, shift the seedlings to a shaded area.

Plant in the autumn. Move the plants to an exposed site, with full sun and strong winds at least 8 weeks before planting. The plants will change colour from green to golden brown.

Seedlings planted on small, exposed, unstable foredunes with sparse vegetation survive much better than those planted on stabilised, vegetated dunes.

They are planted in groups of 25-30 seedlings at 50X50-cm spacing.

Slow-release NPK fertiliser at 30g per plant is mixed with the sand when the seedling is planted.

Replanting Spinifex

Spinifex (Spinifex sericeus) or kowhangatara, is more common than pingao and is also important in creating and maintaining dunes.

Unlike pingao, spinifex is difficult to grow in nursery from seed and is usually spread by direct seeding and transplanting of cuttings. Trials are continuing at the New Zealand Forest Research Institute for the best methods and times for planting. Initial trials suggest that a high nitrogen fertiliser improves survival and growth.

Wild seeds are sowed in holes 100-mm deep.

Cuttings of runners 600-mm long are put into 200-mm deep trenches with the runner tips exposed.

References

Restoration of native plant communities on sand dunes. Bergin and Herbert 1994. What's new in Forest Research. No. 232. New Zealand Forest Research Institute, Private Bag 3020, Rotorua.

Pingao: seed collection and propagation. by Roger MacGibbon (Native plant specialist).