technical article no. 7 · technical handbook section 7: native vegetation on foredunes 7.2...

INTRODUCTION

Along with other indigenous sand binding species,the Dune Restoration Trust of New Zealand(Dunes Trust) has been continuing with improvingmethods for large-scale establishment of spinifex(Spinifex sericeus R.Br.) for the rehabilitation ofdegraded foredunes. Spinifex is the majorindigenous sand dune grass that occurs onforedunes throughout most of the North Islandand the upper part of the South Island.

Sometimes referred to as silvery sand grass, orkowhangatara, spinifex is the dominant sandbinding plant on the seaward face of the foredune

where its long trailing runners and vigorousgrowth make it an ideal sand dune stabiliser.In many North Island dunes, spinifex forms anear continuous colony for long stretches ofsandy coastline. The ecology, habitat andgrowth of spinifex is given in Dune RestorationTrust Technical Handbook Article No.7.1.

Technical Article No. 7.2

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A local Coast Care Group planting spinifex on a foredune.

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WHY REVEGETATE SAND DUNES?

Sand dunes along most parts of the coast of New Zealand have been highly modified since thetime of earliest human settlement. Degradation of the vegetation cover was initially attributed to

widespread grazing and fire (Cockayne, 1911) and more recently to residential and industrialdevelopment, recreational activities, spread of weeds, localised sand mining, and browsing andtrampling by introduced animals. Inventories of the vegetation of sand dunes of the North Island(Partridge, 1992) and of the South Island and Stewart Island (Johnson, 1992) document someof the continuing widescale degradation of indigenous vegetation communities on coastal dunes.

The Dunes Trust is continuing to support research initiated by the former Coastal Dune VegetationNetwork in improving methods of propagation and large-scale establishment of native sand

binding species on foredunes. Research concentrated, initially, on developing practical techniquesfor establishing two major native sand binding species, spinifex (Bergin, 1999) and pingao (Finicia

spiralis) (Bergin and Herbert, 1998). Both species were identified early last century as majorsand-binding species in the native flora that were widespread and performed an important role

in stabilising foredunes (Cockayne, 1911).

Article No. 7.2 - Spinifex - guidelines

OPTIONS FOR ESTABLISHING SPINIFEX

Early Australian experience and revegetationprogrammes for over a decade in New Zealandhave clearly demonstrated that there are severaloptions for establishing spinifex on bare dunes andfor promoting growth of existing spinifex stands.These include planting of nursery-raised seedlings,establishment of nursery-raised plants derived fromcuttings, direct transplanting of cuttings and directseeding on dunes.

Direct sowing of seed on dunes

Revegetation of dunes by direct seeding has beensuccessfully used in Australia (Soil ConservationService of NSW, 1990; Beach Protection Authorityof Queensland, 1981). The method involves placing2-3 spinifex seedheads into a spade hole up to15 cm deep.

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However, direct sowing has proved to be largelyunsuccessful in New Zealand. Direct sowing of seedon dunes was tested over four years in New Zealandand fewer than 10% of the trial sites contained oneor more plants 12 months after seed was sown intothe sand dune (Bergin, 1999). The poor success inNew Zealand of direct seeding of spinifex comparedto Australia may be related to the colder temperaturesin the former. Success of direct seeding may alsobe limited by the low proportion of sound seed perseedhead. The reasons for this infertility requirefurther research.

Where Coast Care groups are interested in directseeding, sites that are relatively sheltered whereminimal sand movement is expected are likely toincrease the success from direct seeding of spinifexon dunes, especially if seed material that has areasonable proportion of sound seed is used.

Direct sowing of seed on a dune by burying a seedhead. Anecdotalevidence indicates that germination may be better in years whenwarmer temperatures and regular rainfall is experienced.

Spinifex seedling six months after sowing. Top: a sowing spotthat did not receive fertiliser; bottom: several sowing spots whereslow-release fertiliser was used.


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Transplanting of cuttings on dunes

As with direct seeding, the transplanting of cuttings of spinifexhas proved largely unsuccessful in New Zealand. The techniquecommonly used in Australia, where there is up to 50% survival,involves the placing of freshly harvested stolon sections up to1 m long into trenches dug into the foredune.

Most trials and operational programmes using transplantedcuttings in New Zealand have resulted in only 5% survival.Transplanting of stolons is time-consuming in terms of bothcollection and planting and while much of the work is willinglycarried out by volunteers in locally-based Coast Care groups,the effort is often not justified. As for direct seeding, it is likelythe cooler temperatures in New Zealand compared to those innorthern New South Wales and Queensland are contributingto the lack of success.

Nursery-raised plants from cuttings

Due to the difficulties of obtaining local collectionsof seed, plants can be raised from short lengths ofstolons. However, this technique requiresspecialised nursery facilities and with high mortality,it is not considered a practical technique for raisingspinifex on a large scale.

Planting nursery-raised seedlings

Trials and operational programmes haveconsistently shown that the most successful methodfor establishing spinifex on bare foredunes inNew Zealand is by planting nursery-raisedseedlings. For over a decade, hundreds ofthousands of spinifex have been raised each yearin commercial nurseries for planting on foredunesthroughout its natural range. The remainder of thearticle will focus on establishing spinifex by plantingnursery-raised seedlings.

A one metre section of stolon laid in a 20 cm deeptrench. The growing tip will be left exposed aftermost of the stolon is buried.

Planting of nursery-raised seedlings is the best method ofestablishing spinifex on foredunes.


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SEED COLLECTION AND PREPARATION

In New Zealand, collections of spinifex seed can bemade in mid- to late-summer when seedheads arebeginning to detach from parent plants. Preliminaryinvestigations indicate that there is a higherproportion of viable seed collected from femaleplants that are immediately adjacent to male plants(Refer to Technical Article No. 7.1). Seed shouldonly be collected where there are male plants nearby,preferably within 2 m.

Nevertheless, before large quantities of seed arecollected, the proportion of formed seed in aseedhead should be assessed at the collection site.

Large quantities of seedheads can be collected quickly from female plants inlate January and early February and stored in paper bags. Ripe seedheadsshould be largely straw-coloured and can be readily pulled off parent plantswithout pulling out plants.

If several formed seed are found, it is likely thatseedheads collected in the vicinity do contain atleast some formed seed and that collection shouldproceed. Repeat seed testing may be prudent wherelarge quantities of seedheads are being collectedover a large area.

Seedheads are picked by hand from vigorous femaleplants and placed in large hessian sacks. Severalsacks per hour can usually be obtained from mostsites. The easily identified smutted seedheads shouldnot be collected as they do not contain viable seed.

Do not collect seed that is infected with a floralsmut, easily recognised by the swellingpartway along the spines within the seedhead.


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Seed storage

Spinifex seed is stored dry in cool, dark conditionsin either hessian sacks or paper bags. Rodent andbird control is essential. Hanging sacks of seedheadsfrom the rafters of a cool shed has been found tobe a practical means of keeping seed away fromrodents. If seed has been collected while wet, itneeds to be spread out to dry in the sun beforerepacking into sacks. Seedheads become strawcoloured as they dry during storage and they becomeeasier to break up into separate components.Spinifex seed was found to retain some viabilityafter 19 months storage under cool, dry conditons.

Seed viability

Seedheads vary in size, comprising 40-160 spikeletsper seedhead. The number of spikelets per seedheadvaries with site and with year of collection. Theproportion of spikelets containing sound seed isoften relatively low and can also vary betweencollections, ranging from 0-43%.

Seed preparation and sowing

From extensive nursery-based trials, the mostefficient method for raising spinifex in containers isto sow seed by hand directly into the final container.Other methods of sowing whole seedheads, brokenup seedheads with or without chaff, or mechanicallycleaned seed have resulted in poor seedlingemergence and difficulties in transplanting seedlingssuccessfully. Small seedlings appear to beparticularly sensitive to transplanting. Direct sowingof seed where formed seed has been sorted byhand is the preferred method for large-scaleproduction of seedlings.

Pressing the base of each spine between the thumb andforefinger will reveal whether a firm formed seed is present.


Sorting formed seed from spinifex seedheads

Remove the large chaff to reveal the swollen base ofeach spine where the seed is still covered in scales.

First break the seedhead in two.

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Individual spikelets containing formed seed areobtained by firstly pulling the seedhead apart intotwo equal parts (see box). Large pieces of chaff arethen removed. The base of each spine is thenexposed where the seed is enclosed in scales. Seedis assumed to be formed if the swollen base of aspine is firm to the touch. Dissection of a randomsample can be used to confirm presence of formedseed where the white endosperm contents becomesexposed.

Removal of spikelets from seedheads and sortingof spikelets containing sound seed is time-consuming. Where seed formation is low (less thanfive per seedhead) it is impracticable to extract it.

Hundreds of thousands of spinifex areraised in Tinus root trainers within a yearat several nurseries in the Bay of Plenty

for planting in coastal restorationprogrammes throughout the natural range

of the species.

Seedling costs

Seedling costs make up a considerable proportionof expenditure on dune restoration, especially ifvoluntary labour is used. The cost of spinifexseedlings raised in containers will depend on whetherthe time taken to sort viable seed for direct seedinginto individual containers is included in the seedlingprice. Some nurseries suggest that communitygroups or agencies supply sorted formed seed forsowing to reduce nursery costs and other nurseriesuse quiet times during the winter to sort seed.

Currently, nine to 12-month-old seedlings raised inTinus root trainers or similar-sized containers areavailable from North Island nurseries at about $2each.

At a warm coastal nursery in the Bay of Plenty,spinifex is raised to 80 cm high within nine monthsof hand sowing directly in root trainers. Furtherdetails on the propagation of spinifex and the trialsinvestigating a range of treatments are given inBergin (1999).

Propagating seedlings

Spinifex can be raised in a range of containers andfor up to two years in a nursery. However, large-scale commercial operations are now raising spinifexin Tinus or Hillson root trainers.


ESTABLISHING SPINIFEX ON DUNES

Site requirements

Spinifex grows best where sand accumulation occurson the foredune (Maze & Whalley, 1992). Sandburial increases seed, root, shoot and stolondevelopment of spinifex (Hesp, 1991). Spinifexplanting programmes should be focussed on bareareas along the seaward face of the foredune. Oncewell-established, the plants will tolerate someaccumulation of storm-driven sand, although largeamounts if inundation or erosion will reduce survivalrates.

Success of planting programmes will increase wherebeach users are controlled by fencing and provisionof accessways where necessary, fencing to excludegrazing animals and the control of browsing pestssuch as rabbits.

When to plant

Survival and growth of planted sand binders includingspinifex varies considerably from year to year, aswell as from one season to the next (Hesp, 1989).Initial survival is largely dependent on climaticconditions including the incidence and strength ofstorms. Autumn-planted seedlings may be vulnerableto sand accretion or scouring during winter storms,and spring-plantings will succumb if root systemshave not developed and extended into lower sandlevels before early summer. In several years of trialsand over many sites, there has been no significantdifference in growth and survival of autumn and

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spring planted spinifex (e.g., Table 1). Summerplanting should be avoided because the surface ofthe sand is likely to be too hot and dry for survivaland growth of transplants.

Fertilising planted seedlings

Results from planting trials have consistently shownthat applying slow-release fertiliser at plantingsignificantly improves early establishment and growthof spinifex (Bergin et al., 1998). Spinifex seedlingsplanted with fertiliser have produced several stolonswithin a year of planting. The technique involvesincorporating 30 g of slow-release NPK fertiliser tothe sand around the root system as the seedling isplanted.

In a typical trial located in the Coromandel Peninsula,when approximately 30 g of slow-release fertiliserwas mixed into the planting hole, treated plantsshowed improved vigour, growth rate and stolondevelopment within two years (Table 2; Figure 1).Treated plants produced several stolons within oneyear, some extending up to 8 m. In all trials, fertilisedseedlings consistently had darker green colourfoliage. Similar significant increases in growth withfertiliser have been observed in South Island spinifexplanting trials at Taylors Mistake. It is almost certainthat nitrogen from the fertiliser was responsible forthe improved performance. Chronic nitrogendeficiency is a characteristic of unstable coastalsand in New Zealand (Hunter et al., 1991). In allplanting trials, there has been no adverse effect onsurvival with application of fertiliser (Figure 2).


Table 1: Performance of spinifex seedlings planted at Whiritoa Beach South, CoromandelPeninsula.Assessments were made 18 months after spring planting and 2 years after autumn planting

*Vigour score: 1 - weak, 2 - unthrifty, 3 - average, 4 - good, 5 - robust*Plant spread calculated as square root of (length x breadth). Within groups, values followed by the same letter are not significantly different (p=0.05)

AutumnSpring

FeriliserNo feriliser

Sandaccumulation

(cm)

24 a27 b

32 a15 b

Average lengthof stolons

(cm)

167 a74 b

257 a14 b

Root collardiameter

(cm)

13.8 a11.5 b

20.2 a6.6 b

Seedlingvigour*

1 - 5

4.1 a4.0 b

4.7 a3.5 b

Plantspread*

(cm)

44 a41 a

53 a32 a

Height(cm)

40.8 a41.8 a

42.1 a40.6 a

Survival%

83 a84 a

80 a87 a

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These nursery-raised spinifex seedlings were planted at Tairua Beachwith slow-release NPK fertiliser. Planted groups have very high survivaland most plants have runners up to 8 m long within eight months asshown here..

Coast Care groups have used other slow-release N fertiliser types (e.g., Growtabs) with apparent success.Care is required in ensuring only slow-release fertiliser formulations are used. The use of fast-release fertiliserformulations (e.g., Urea - 46% N) incorporated in the planting hole will kill planted seedlings.

A small handful (30 gm) of slow-releaseNPK fertiliser is applied to each seedlingas it is being planted by incorporating thefertiliser in the sand surrounding the intactplug of potting mix and root system.Seedlings are planted deeply with rootcollars placed at least 10 cm below the levelof the sand surface.

Figure 2: Survival of planted spinifex in two trials after oneyear. Bars show standard errors of means.

Figure 1: Average extent of planted spinifex in two trials afterone year. Bars show standard errors of means.

Whiritoa Beach Taylors Mistake

Ave

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Untreated Slow release fertiliser applied

80

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20

40

60

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20

40

60

80

100

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Whiritoa Beach Taylors Mistake

Untreated Slow release fertiliser applied


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MAINTENANCE AND CARE

Regular inspection of planted sites is essential.Although spinifex appears to be less palatable toanimals than pingao, browsing (largely by rabbits)does occur, so an ongoing pest animal controlprogramme is essential.

Most damage of planted spinifex areas is likely tobe from beach users. All planted areas wheredisturbance by beach users is likely will requirefencing, signage and beach accessways wherenecessary.

Plant survival can vary from one year to next andlosses due to occasional high seas or storms mayoccur at any time of the year. Where losses ofspinifex have occurred, replanting during thefollowing autumn to early spring will be necessaryto ensure development of an even vegetation cover.

Maintenance of fencing, accessways and signs will be requiredto protect planted spinifex areas at heavily used beaches.

PLANTING TECHNIQUEAND PATTERN

Spinifex grown in root trainers can beplanted quickly in spade holes. Deepplanting (sand level at least 10 cm abovesurface of potting mix) will maximiseroot contact with moist sand horizonsand result in greater survival and bettergrowth, especially under conditions ofmoderate sand scouring by wind. Theuse of plants at least 60 cm high willallow deep burial.

Spinifex plants are frequently used torepair gaps in the vegetation cover onthe seaward face of the foredune. Gapsor blowouts result from localiseddisturbance and are common aroundaccessways and other high use areas.Large-scale planting of large sectionsof degraded or reshaped foredunes willtake thousands of plants. Plant spacingmust be related to local site factors.Dense colonies with numerous stolonsspreading several metres beyond plotboundaries have developed fromspacings of 50-60 cm with fertilisertreatment. Dense planting on particularlyexposed sites vulnerable to wind erosionwill increase the likelihood of success.In relatively sheltered sites where highsurvival rates and rapid growth areexpected, 1 m spacing may beadequate. The aim is to achieve densecover as rapidly as possible.

Natural populations tend to consist oflarge patches of single sex plants,probably originating vegetatively fromone individual. Large-scale planting ofindividuals grown from seed is likely toresult in more even proportions of maleand female plants within colonies.


REFERENCES

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Beach Protection Authority of Queensland, 1981: Sandspinifex grass. Coastal sand dunes. Their vegetationand management. Beach Protection Authority ofQueensland, Leaflet No. IV-01. 2p.

Bergin, D. 1999: Spinifex on coastal sand dunes.Guidelines for seed collection, propagation andestablishment. Coastal Dune Vegetation NetworkTechnical Bulletin No. 2. New Zealand ForestResearch Institute Limited. 20p.

Bergin, D. O., Herbert, J. W. 1998: Pingao on coastalsand dunes. Guidelines for seed collection,propagation and establishment. Coastal DuneVegetation Network Technical Bulletin No. 1. NewZealand Forest Research Institute Limited. 20p.

Bergin, D. O., Kimberley, M. O.; Ede, F. J. 1998:Revegetation of sand dunes using spinifex (Spinifexsericeus) in New Zealand. Proceeding of New SouthWales Coastal Conference, November 1998,Batemans Bay, NSW, Australia. 6p.

Cockayne, L.1911: Report on the dune areas of NewZealand plants, their geology, botany and reclamation.Parliamentary Paper C. 13. Department of Lands,Wellington, New Zealand. 76p.

Hesp, P. A. 1989: A review of biological andgeomorphological processes involved in the initiationand development of incipient foredunes. Proceedingsof the Royal Society of Edinburgh, 96B: 181-201.

Hesp, P. A. 1991: Ecological processes and plant adaptionson coastal dunes. Journal of Arid Environments, 21:165-191.

Hunter, I.R,; Rodgers, B.E.; Dunningham, A.; Prince,J.M; Thorn, A.J. 1991: An atlas of radiata pinenutrition in New Zealand. New Zealand Ministry ofForestry Forest Research Institute Bulletin No. 165,Rotorua, New Zealand.

Johnson, P. N. 1992: The sand dune and beach vegetationinventory of New Zealand. II. South Island andStewart Island. DSIR Land Resources ScientificReport No. 16. Christchurch, New Zealand. 278p.

Maze, K. M.; Whalley, R. D. B. 1992: Effects of salt sprayand sand burial on Spinifex sericeus R. Br. AustralianJournal of Ecology, 17: 9-19.

Partridge, T. R. 1992: The sand dune and beach vegetationinventory of New Zealand. I. North Island. DSIRLand Resources Scientific Report No. 15.Christchurch, New Zealand. 253p.

Soil Conservation Service of NSW, 1990: Coastal dunemanagement. A manual of coastal dune managementand rehabilitation techniques. Soil ConservationService of NSW, Sydney. 76p.

Spinifex heavily browsed by rabbits. Spinifex seedlings filling a gap in the foredune vegetation cover.


Author: David Bergin, Environmental Restoration Ltd

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technical article no. 7 · technical handbook section 7: native vegetation on foredunes 7.2...

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