Sandhills.

On many parts of the coast, sand is continually being brought on to the shore by the advancing waves. In the neighbourhood of high-water mark the shore soon becomes dry, and the sand is then borne landwards by any wind coming from the sea. Where the sand accumulates faster than it is blown away, a hill, or dune as it is frequently called, is formed. Any obstacle in the path, of the blown sand will also arrest its progress and cause its heaping-up. The dunes of New Zealand are of great extent, and occupy an area of more than three hundred thousand acres. In some parts of the coast the belt of dunes is more than six miles in width, and in the north of the Auckland Province, on the west of Stewart Island, and elsewhere the sandhills attain a height of several hundred feet, though usually they are much lower.

Frequently the dunes are very unstable, and in some places so much so that great areas of moving sand exist. These "wandering page 69dunes" (fig. 28) insidiously advancing inland, do great damage—burying fertile fields, filling up valuable flax-swamps, choking water-courses, and overwhelming forests, plantations, pasture-lands, and even, human dwellings. Happily nature has done much to stop such inroads, and the wandering dunes of New Zealand are chiefly the result of damage done by grazing animals and by burning.

In order that a plant can live on drifting sand it must have the power of binding that unstable compound into a firm mass. Plants

Fig. 28.—General view of a Wandering Dune occupying ground formerly good grazing-land. Dune-area of western Wellington.
Lands Department.] [Photo, L. Cockayne.

with rapidly growing underground stems, which have the power of rooting near the tips of the branches and putting forth new shoots as fast as the old ones are buried, are sand-binding plants par excellence. With - few exceptions, wherever sandhills exist on the globe, such plants accompany them.

In New Zealand there is a most excellent example in the pingao (Scirpus frondosus) (fig. 29). Its thick, rope-like stems, commonly called roots, form a perfect entanglement inside the dune, and its page 70semi-tussocks of stiff, golden-coloured leaves crown many sandhills from the North, Cape to the Bluff. Unfortunately, rabbits and some other animals do not despise this plant, notwithstanding its most unappetising-looking leaves. In consequence, they destroy this natural protector of our shores, which came into being in a land where grazing animals, the moa excepted, were unknown, and so developed no protective adaptations.

The spiny rolling-grass (Spinifex hirsutus), a native of Australia also, is another very important indigenous sand-binder. Its stout

Fig. 29.—Breach in Foredune made by Sea, north of Rangitikei River. The Pingao (Scirpus frondosus) on right.
Lands Department.] [Photo, L. Cockayne.

stems, often many feet in length, at first creep over the surface of the sand, firmly fixing themselves by means of many roots. Finally they are buried, and the tufts of long flexible leaves, covered densely with soft silvery hairs, project out of the sand. The pollen-bearing and ovule-bearing plants are distinct. When the seeds are ripe, the mature inflorescence breaks off, and, borne by the wind, hops on its long spines over the sandy shore like some, huge insect, until, at page 71last falling to pieces, the "seeds" are deposited and finally buried. S. hirsutus naturally builds up fairly stable dunes which in some places have a surface so even as to look like a railway-embankment (fig. 30), as in the case of the dune fronting the shore near Waikanae, in the Wellington Province.

In Europe, America, and elsewhere plants and grazing animals assumed their present forms side by side. The marram-grass of Europe (Ammophila arenaria) is a case in point. This, although naturally

Fig. 30.—Natural and even Foredune built by Wind and the Silvery Sand-grass (Spinifex hirsutus). Coast near Waikanae.
Lands Department.] [Photo, W. H. Field.

little better as a sand-binder than our Scirpus or Spinifex, is of infinitely more value for "reclaiming" our moving sands, since it is not relished as food, and grows rapidly and luxuriantly. With the marram, may be used the lyme-grass (Elymus arenarius), another European sand-binder.

Besides grasses, trees and shrubs are of great service for sand-fixing. Of the latter, the tree-lupin of California (Lupinus arboreus) is a. page 72most valuable plant when used, with, discretion. But the question of dune-fixing is too complex for discussion here, and, so far as New Zealand goes, the matter is still quite in its infancy.

Where the dunes are more stable, other special "sand-plants" are common. Of these, Coprosma acerosa (fig. 31), with wiry, reddish-coloured, interlacing twigs, is found everywhere; and so, too, is Pimelia arenaria, a low-spreading shrub, with pretty silvery leaves and white flowers. Certain species of Cassinia, which belongs to the

Fig. 31.—The Sand-coprosma (Coprosma acerosa) building a Temporary Dunc. Coast of Canterbury.
Lands Department.] [Photo, L. Cockayne.

daisy family, are very frequent features of this society, but they are different in various parts of the Dominion. In the Auckland region it is Cassinia retorta; Taranaki, Hawke's Bay, and the shores of Cook Strait have the tauhinu or cottonwood (C. leptophylla); while farther south the yellow-leaved C. fulvida is the sole representative until the Bluff Hill or certain places on the east of Otago are reached, when C. Vauvilliersii, a common subalpine shrub, puts in an appearance.

Where the force of the wind is less felt, a heath may make its appearance, and the manuka (Leptospermum scoparium), the cabbage-tree (Cordyline australis), the toetoe (Arundo conspicua), the flax (Phormium tenax), and, from the shores' of Cook Strait southwards, the wild-irishman (Discaria toumatou) occur in force (fig. 32).

Hollows in the dune region are very frequent, the sand being blown away until the ground-water is almost reached. Where the water cannot get away there will be swamps and even shallow lakes.

Fig. 32.—Heath of Sand-plain. In front, the Wild-irishman (Discaria toumatou).
Lands Department.] [Photo, L. Cockayne.

In sandy hollows the pioneer plant is a creeping-sedge (Carex pumila), which soon builds miniature dunes. The sand-gunnera (Gunnera arenaria), forming close mats of small pale-green leaves flattened to the ground, is also very abundant in many localities. Such hollows finally become occupied by introduced grasses and plants of the clover family, and these render the dune region of economic importance, though the grazing by sheep and cattle leads in time to instability of the nature-fixed hills and to the filling-up of the hollows.