32 PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 16, 1969

MANAWATU S~ND PLAIN VEGETATION

A. E. ESLER

Botany Division. D.S.l.R"Palmen.ton North

INTRODUCfION

Sand plains are low-lying areas where wet sandnear the water-table is exposed by wind. In theliterature the plant communities of sand plainshaye received only brief menIion (Cockayne 1911,1928; Pegg 1914; Carnahan 1957; Moore & Adams1963). Along the Manawatu coast some sand plaincommunities have retained their identity unin-fluenced by the factors which have altered the com-position and vigour of almost all other New Zea-land vegetation, They remain both in spite of. andbecause of. the extreme environment. The speciesare not equally attuned to the environment of thesand country and each expresses its responses, inpart, by its pattern of distribution.This paper examines these patterns in relation to

the position of the water-table, which has a criticalinfluence because of the limited"ability of the sandto slore water or to lift it above the water-table inappreciable amounts.

THE HABITAT

Sand is deposited in large quantities along theprograding Manawatu coast and is carried inlandabout two miles by lhe strong, prevailing on-shorewinds. This belt of sand has probably never beenstable but movement was accelerated last centuryby cattle grazing on the dunes. Spinifex hirsutus,the most palatable plant and the most importantstabilizing sp~cies on the foredune, was eliminated(Wilson 1959). Its reintroduction by artificial seed-ing and the establishment of marram brought adegree of stabilily, but the dunes are still veryactive.

From a...,rialphotos it is apparent that there havebeen gross changes in the pattern of deposition ofsand in the last 25 years. In 1942 the foredune wasundeveloped between Foxton and Himatangi Beachand a mass of jrregular dunes extended far inland.These dunes enclosed small, wet flats mostly about30 chains from the sea, and a few nearer the shore.Since 1942 a more defined topography has deve-

loped. The foredune now forms a ridge about 25 ft.high but breached in many places. Long, paralleldunes running 113° E. of true north extend inlandand join transverse dunes. almost barchan innature, to form basins (Fig. I). It is convenient toregard lhis dune-and-basin topography as an incip-ient parabolic dune system hindered in its develop-ment by a surfeit of sand and a deficiency of vege-tation. This conception is complicated by the over-lapping of dunes further inland in a belt one-half totwo miles from the beach and parallel to it, butbeyond this belt the parabolic formations becomevery pronounced.

Each basin has short irregular dunes adjacent tothe blow-outs of lhe foredune. These tail off intoridges and hummocks a few feet high over most ofthe central part of the basin. In part, these undula-tions are relics left after deflation of. the largerdunes which previously occupied the area, butsome have formed from recent accumulations.Against the longitudinal dunes on the northern

and soulhern margins of each basin sand hasdeflated to near the water-table and lateral sandplains have developed. These are moist in summerbut in rainy periods water flows several inches deepacross the surface which slopes 12 feet per miletowarQ the coast. Water gathers at deplhs of a footor more in the lower reaches against the shortirregular dunes. On the eastern margin of eachbasin the water-table is usually exposed at the baseof the windsweep of the transverse dunes. In someplaces low sand ridges reslrict movement of surfacewaler from the terminal sand plains to create pondssufficiently permanent to support Typha and thesnail, Limnaea stagnalis.The topography is slatic only in winter. In drier

periods sand moves over the basin and the encom~passing dimes. The longitudinal. dunes, beinghigher lhan the foredune, are little'protected by itand the moving sand is only slightly impeded bythe very sparse cover of Desmoschoenus spiralis.Spinifex and marram. The lateral sand plains areinfluenced by this sand moving off lhe dune flanks.Sand accumulates on lhe wet surface until dryingis sufficient 10 allow it to be driven away by wind,but in high winds the sand races across the surface

ESLER: MANAWATU SAND PLAIN VEGETATION 33

FIGURE 1. Form of typical Himatangi sand ba;'in. Wind data are for Ohakea.

wilhout being deposited. except where plants forma barrier.Some terminal sand plains are migratory in dry

windy wealher. Sand from the centre of the basingathers on the windward side and is removed fromthe other side unless yegetation is well establishedaround the plains.

THE PLANT COMMUNITY

There are fewer lhan 20 significant plant specieson these sand plains but they make a complex com.munity because of their diversily of tolerances andrequirements. There are obligate water plants andplants normally growing on higher ground restrict.ed here in their distribution by the wetness of thehabilat. Others. although not typical water plants,are dependent on this wet habitat for perpetuationby seed. Still others have a wide ecological ampli.tude and grow on the plains and on the dunes.Thus is brought together an assemblage of plantssome specific to the habitat and others usuallyassociated with many different habitats.

.

The most striking feature of the community isthe zonation and the limited intermingling of someof the species. Moisture is the main factor deter.mining the presence or absence of species but thepaltern is modified by yarying tolerance of deposi.

tion and removal of sand. It is apparent that posi.tion of the water.table is crilieal to the success ofmany species because the sandy substrate wilhouttopsoil is not very effective in supplying the waterrequirements of plants. Fluctuations of the water-table make it difficult to detennine the limitingfactors with certainty. The critical period for obli.gate water plants is in summer. Some other speciesare restricted to higher ground because they do nottolerate periods of submersion in winter.

THE INVESTIGATION

In the summer of 1967.68 a dumpy level andstaff were used to record the altitudes of 290 samp.ling points relative to the datum line taken as theestimated mean water-table in summer. At each ofthe sampling points, which were arranged in tra.verses parallel to the coast and in grids, the specieswithin a radius of 2.2 ft. were recorded with noteson lhe habitat. The study area was about half amile south of Himatangi Beach in a basin of thetype described above.

RESULTS

Figure 2 shows the altitudinal distribution of themajor sand plain species in relation to mean sum-mer water.table in this particular sileo Limosella

PROCEEDINGS OF THE NEW ZEALAND ECOLOGICAL SOCIETY, VOL. 16, 1969

linea/a and Myriophyllum vatschii exist in a verynarrow habitat range and u3ually occur together,tolerating large quantities of sand blowing acrossthe surface ,in summer and dense mats of filamen-tous algae blanketing the surface in shallow walerin winter and spring.Eleocharis nea-zelandica, Ranunculu.\' acau/is

and Sirpus cernuus thrive on the moist sand. All ofthese are less than one inch tall and the environ-ment is not greatly changed by their presence. Thesmall amount of sand that accumulates is removedwhen the surface dries sufficiently to allow mobil-ity. Eleocharis and Ranunculus almost invariablyoccur on sites with moving sand but Scirpuscernuus is less specific.Carex pumila grows on the wet parts of the sand

plains and extends to about 2 ft. above lhe meansummer water-table onto adjoining fresh accumula-tions of sand. No other plant of lhe plains hasgreater abilily to gather sand, a feature which leadsto its own extinction where the sand supply isplentiful. Variations in vigour and seeding capacitywithin a single patch suggest response to differencesin micro-habitat. This offers an interesting line ofresearch.

FIGURE2. Dis.tribution of plantJ relative to mean summer water-table. S=seedling only.

Selliera radicanJ is the most widespread of thesand plain species and also occupies moist sitesnear the foredune where few other species grow. Ittolerates submersion in winter and can survivewhere lhe water-table is more than 2 ft. below lhesurface in summer.Leptocarpus similiJ establishes from seed where

the waler-table is near the surface most of the yearand not more than a foot below it in summer. Ifmassive movement of sand does not occur thespecies spreads extensively by rhizomes to becomedominant in other communities. The same habitatfavours Epilobium billardierianum and Lobeliaanceps. De.veuxia billardieri usually grows withthem but is not confined to the same habitat. Itoccurs also on the dunes wherever other plantsarrest the sand movement sufficiently to allow seed-lings to establish.The remaining species in Figure 2 are character-

istic dune plants. There are two reasons for thepresence of Desmoschoenus and marram (Ammo-phila arenaria) on the sand plains. Firstly, theolder plants are relics of the vegetation of the duneswhich covered the area before deflation. Secondly,the sand plains provide suilable conditions for the

34

Myrio.phyllum

Limosella

Eleocharis

Ranunculus

'~&<1

Scirpus~~'~i

cernuus.'W.

e=Carex

.on,,"

Selrr~ra

EpilobiumlLepto-carpus

lobelia

.",'"Deyeuxia

....,

Desmo- I

IschoenusI

Ammophila'

Gnap~~liuml

,-,-,-",

SCit£us

nodosus

I Ca~$:inia

seedlings of both species. The success of these duneplants in this environment depends on their abilityto accumulate sand. Even in the most favourablecircumstances Desmoschoenus is a poor collectorand binder. Few seedlings survive on the sandplains. Marram, on the other hand, establishesfreely. Seedlings occur most abundantly on theflanks of the longitudinal dunes where they collectsand to form low berms which sometimes developinto subsidiary lateral dunes. Seedlings also estab-lish on similar moist habitats at the base of the slipface of transverse dunes advancing across wet flats.Here marram slows the movement of the sand andplays a part in revegetation of the dune. However,marram seedlings are palatable and establishmentis hindered by rabbits. Thus rabbits, although fewin number, may playa significant part in shapingthe topography of the sand country.The effects of water-table on the distribution of

Gnaphalium luteo-album is apparent from theaggregations of plants on what look like "high-tide marks" following contours around the lowhummocks. It reaches a little closer than seedlingsof Cassinia leptophylla to the mean summer water-table but has much more limited range on thedunes.

. .

Scirpus nodosus seedlings occur in abundanceon the sand plains, but this species is less depend-ent than Desrnoschoenus and marram on a high-water-table for germination of its seeds.On some terminal sand plains there are greater

complexities brought about by ponding and thegrowth of filamentous and globular algae whichform a skin over the sand when the water Jeve!falls. These areas support a much larger flora witha high proportion of exotics. The sand plains nearthe foredune, on the other hand, have a smallerrange of species because of the greater effect ofmoving sand and the wider fluctuation in the water-table between summer and winter. Here. Sellieraradicans and Carex pumila are the major species.Other sand plain species such as Lilaeopsis orbi-

cularis, Gunnera arenaria and Triglochin striatumhave not received mention in this account. Theywere present in the study area but not in sufficientquantity to give reliable information on theirrequirements and tolerances. The only exotic plantof note. other than marram, is Leontodon taraxa~coMes. It occurs on the low hummocks and extendsdown to the mean summer water-table.

SUCCESSION

Natural changes in sand plain vegetation are

ESLER: MANAWATU SAND PLAIN VEGETATION 35

towards extinction by advancing dunes or by sandaccumulated by marram, or towards Leptocarpuscommunities. Pioneer sand plain vegetation of the

type described above remains while Leptocarpus isabsent or is in lhe early stages of invasion. OnceeSlablished, Leptocarpus arrests sand movement atthe margins of the plaiDs. At the same time Scirpusnodosus occupies the margins of the hummockswhich, having their supply of sand cut off, are oftenlevelled by wind. Nearly all other pioneer plantsdisappear as the sand surface becomes shaded andstable. These are replaced by Schoenus nitenswhich makes its appearance soon after Lepto-carpus becomes domjnant. Juncus maritimus var.australiensis appears in some places and later,Cortaderia toetoe. followed by Phormium tel1ax.At the Leptocarpus stage of succession organic

matter begins to accumulate and in time this formsa topsoil two or three inches deep and overlyinggrey sand. Sand plain soils of this nature are gleyedyellow-brown sands and have been mapped in theHokio series by Cowie and Smith (1958) andCowie (1967).' As these soils are sufficientlydeveloped for agricultural use the native vegetationhas been replaced by pasture and there is noevidence remaining of later successional stages.

ACKNOWLEDGEMENTS

I am grateful to 1. M. Stewart, Department of Landsand Survey. Palmerston North, to H. J. Esler for hisstimulating interest 'and assistance in the field and toMrs M. J. A. Bulfin and R. M. Greenwood for help inthe preparation of this paper.

REFERENCES

CARNAHAN. J. A. 1957. Botany of the Manawatu sandcountry. Proc. N.Z. Eco!' Soc. 5: 17-18.

COCKAYNE,L. 1911. Report on the cune-areas of NewZealand, their geology. botany and reclamation.Append. J. N.Z. House Repres. C 13: 1-76.

COCKAYNE,L 1928. The vegetation of New Zealand. inDie vegetation der Erde XIV. Engelman, Leipzig.(2nd Edit.)

COWIE,J. D. 1967. Soils of the Manawatu-Rangitikei sandcountry. N.Z. Soil Bur. Bull. 29. Govt. Printer,Wellington.

COWIE,J. D., and SMITH, B. A. J. 1958. Soils and agricul-ture of Oroua Downs, Taikorea, and Glen Orouadistricts, Manawatu County. N.Z. Soil BUr. Bull. 16.Govt. Printer, Wellington.

MOORE,L. B., and ADAMS, N. M. 1963. Plants of the NewZealand Coast. P.aul's Book Arcade, Auckland andHamilton. .

PEGG, E. J. 1914. An ecological study of some NewZealand sand.dune plants. Trans. N.Z. lnst. 46:150-177.

WILSON, R. A. ]959. Fifty years' farming on sand coun-try. Keeling and Mundy, Palmerston North.