New Zealand Plants and their Story
Chapter V. — The Vegetation of the Coast
The Vegetation of the Coast.
General remarks—Adaptations of coastal plants—Physical and physiological dryness—Plants of sandy and rocky shores—Seaweeds—Sandhills—Reclamation of dunes—The wonderful mangrove—Coastal shrubberies—A natural post-card—The coastal veronica—Vegetation of rocks and cliffs—Salt meadows and salt marshes—Stephen Island, the home of the tuatara—The Three Kings and Poor Knights Islands.
A coast-line between four and five thousand miles in length, extending from nearly the latitude of Sydney in the north to far beyond that of the southernmost point of Tasmania in the south, may well furnish a great deal of diversity in both species and societies of plants. The varieties of stations for plant-life are also augmented by the physical features of the shore. In some places calm fiords, flanked by towering, precipitous mountains, stretch far inland; in others an ironbound coast faces the ocean storms. There are long stretches of level shore—of gravel or of sand—extensive estuaries, and tidal rivers. In short, the two main Islands, together with Stewart Island, present a diversified coast not surpassed in variety of physical features by any other of equal size.
Adaptations of Coastal Plants.
Latitude being left out of the question, in all parts of the world coastal vegetation, both in its form and distribution, depends upon certain factors. Of these, salt in the soil and exposure to sea-spray and violent winds are of prime importance. Wherever they occur, genuine seaside plants have various features in common. The most important of these are contrivances to regulate the water-supply, the commonest of which is succulence of leaf and stem, one or both. This succulence is caused by the presence of special tissues which serve for water-storage. Many New Zealand coastal plants exhibit this feature. The ice-plant (Mesembryanthemum australe, pig's-face, horokaka), which so frequently drapes the coastal cliffs page 64with its pale-green leaves, and bears rather large rose-coloured flowers, is a pleasing and familiar, example (fig. 25). This species must not be confused with the Hottentot fig (M. edule), a native of South Africa, now naturalised on many sandhills, but which possesses leaves still "fatter" than those of its indigenous sister, and bears larger and yellow-coloured flowers. Other common coastal succulents are: Salicornia australis (fig. 26), a stem-succulent common in salt meadows, and Suaeda maritima, a leaf-succulent, usually growing in rather wetter ground.
Succulence has been shown experimentally to be brought about by excess of salt in the soil, and certain plants to which salt is not a deadly poison can be made artificially succulent. Some of the introduced plants of this country, as, e.g., the spotted catchfly (Silene anglica, var. quinquevulnera), acquire much fatter leaves when growing near the sea than inland.page 65 page 66
That plants growing in wet stations, such as salt meadows and marshes, should be furnished with appliances to combat drought appears very remarkable. The truth seems to be that for some reason not yet sufficiently explained, although many theories are rife, the plant dare not, use too much brackish water, and so is actually in the same position as a plant of a desert region. When dealing with the bog vegetation it will be seen that it, too, is in a similar condition, and so is that in the neighbourhood of solfataias and the like.
Schimper has summed up these conditions in an excellent manner, pointing out that two kinds of dryness exist. These he has named "physical" and "physiological." Physical dryness arises from want of water in the soil, but a physiologically dry soil may contain any amount of water, but yet of such a quality that its plant inhabitants cannot use it. To quote a common example, the sea is physiologically dry, so far as man is concerned. Physiological dryness alone concerns plant-distribution.
Sandy and Rocky Shores; Seaweeds.
Sandy shores are common enough on the New Zealand coast; and as these, when sufficiently firm, are patronised as playgrounds for our children and ourselves, something as to their plants may be of interest. Such, a shore may sometimes be quite without plants, except for the remains of seaweeds which mark the high-tide limit. Where the shore is sheltered, the shore convolvulus (Calystegia Soldanetta) (fig. 27), with its, lilac-striped flowers, is often present. Here, too, is the home of the tiny buttercup (Ranunculus acaulis), its leaves of three small succulent leaflets flat on the sand, and its little yellow flower buried right up to its neck. The New Zealand spinach (Tetragonia expansa), the succulent Atriplex Billardieri, and the prickly Salsola Kali are also plants of the shore.
Gravelly and rocky shores are richer in plant-life than sandy ones, since they are much more stable. On them in some places a dock (Rumex neglectus) is common. This has a rather stout creeping stem, which enables the plant to make considerable patches on the gravelly shore, where it grows far more luxuriantly than on the peaty ground which it also inhabits. On the stony shore of Foveaux Strait a small plant of the cress family (Lepidium tenuicaule) puts down an enormously long root in quest of the fresh water which flows seaward beneath the stones.page 67
Where rocks jut out into the sea, forming pools, there the beautiful red seaweeds have their home; but where the sea dashes with fury, the huge brown ones are found. As two of these are so frequently cast up on the shore, they, at any rate, must be known to most who are acquainted with the seaside. The one (Macrocystis Dubenii) grows to an immense size, and its leaves float upon the surface of the sea by means of their small bladders full of air, while, dozens of feet below, the cord-like stems are anchored firmly to the rocky floor of the ocean. The other (D'Urvillaea utilis) is found in rougher water, its stouter stem showing a honeycomb-like structure when cut into. D'Urvillaea gets its name from the Admiral D'Urville mentioned in Chapter II. By the Stewart Island Maoris its "leaves" are made into bags for holding the preserved mutton-birds.
In the calm waters of the West Coast Sounds, where not too deep, are flower-gardens of the sea, whose loveliness can be seen for considerable depths through the transparent water. Generally speaking, the depth of water determines the distribution of seaweeds. Thus the green ones are found in the shallowest pools, and the red in the deepest, while the brown occupy a position midway, and some of these may be seen writhing like snakes over the glistening rocks at low water (fig. 2). Some seaweeds behave like the perching-plants of the forest, and have taken up their abode on other species.
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.
Fig. 28.—General view of a Wandering Dune occupying ground formerly good grazing-land. Dune-area of western Wellington.
Lands Department.] [Photo, L. Cockayne.
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.
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.
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 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).
Fig. 32.—Heath of Sand-plain. In front, the Wild-irishman (Discaria toumatou).
Lands Department.] [Photo, L. Cockayne.
Let us leave the dunes, and, in imagination, sail up one of those wide estuaries in the west of the Auckland, Province—Hokianga or Kaipara Harbour, or one of the tidal rivers of the east—the Whangarei, for instance. If it is high tide, we shall see on either side of the stream a belt of close-growing, dull-coloured, small trees, rising out of the turbid water. These consist of the mangrove (Avicennia officinalis), and the sight is one almost unknown in any other land outside the tropics. It is, in fact, one of the natural wonders of New Zealand.
Now, quite undeservedly, the mangrove has got a bad reputation. A mangrove swamp is supposed to represent all that is most hideous on earth—alligators in crowds, a fearsome odour, crabs waiting to pick such of the victim's bones as are left by the alligators, malaria, and deadly microbes in vast abundance. Even in the tropics this picture has been shown to be absurd, and in New Zealand the mangrove belt is quite a pleasing feature of the northern rivers. It is also a most beneficial plant, as it materially assists in turning muddy useless shores into good dry land.
Moreover, the mangrove is one of the most noteworthy plants in nature. As our boat proceeds up the river the tide has turned, and the slimy flats, where the mangrove is rooted, come into view. There, projecting out of the mud, are thousands of upright bodies, 6 in. or so in length, looking much like stout asparagus-shoots. One might feel sure these were young mangroves. But they are nothing of the sort, strange as it may seem. They are roots, which, instead of passing downwards to anchor the trees, grow upwards into the air. On being examined, they are found to consist largely of a very porous tissue. Plants, like animals, cannot live without oxygen. They need to breathe just as much as we human beings do; without air they would die of suffocation. In the soft mud is little of the life-giving gas hence the necessity for the mangrove to obtain a supply for its ordinary roots. This it does with these erect organs, which are the veritable lungs of the tree. Of course, the aerial parts of the mangrove, like those of any other tree, procure oxygen by means of the small pores in the leaves and minute openings in their bark.
The beautiful inlets of Stewart Island derive their charm in large measure from the assemblage of trees and shrubs along the water's edge, especially when the southern rata (Metrosideros lucida), its boughs almost dipping into the water, has burst into flaming crimson. In similar situations the inuka (Dracophyllum longifolium) and the smaller New Zealand flax (Phormium Cookianum) are common.
Where the coastal scrub of Stewart Island is densest, it has received the name of "mutton-bird scrub." This consists largely of the puheritaiko, a very fine shrubby groundsel (Senecio rotundifolius) (fig. 33), which makes an excellent garden plant even as far north as Auckland. The leaf is frequently 4 in. or more in diameter, and is covered so closely with a mat of buff-coloured hairs on the under-surface that it can be written upon. The leaf may thus be made to serve as a post-card, which can be posted at the most southerly office in Australasia—that on the Isle of Ulva, in Paterson Inlet.
Fig. 34.—The Purple-flowered Daisy-tree (Olearia angustifolia), growing at the Neck, Stewart Island. The tree on left is 10 ft. tall, its trunk 1 ft. 3 in. in diameter, and the rounded crown 21 ft. through.
Lands Department.] [Photo, L. Cockayne.
Veronica elliptica, the coastal shrubby veronica, mentioned above, deserves a few words. In the first place, it is one of our South American connections. When fairly sheltered it is a fine upright-growing shrub, covered closely on its outer twigs with rather thick palish-green small leaves. Like all the other veronicas, its flowers have only two stamens. The corolla is at first bright purple, but soon fades to white. The scent of the flowers is delicious. It is abundant in the Auckland and Campbell Islands, the Snares, Stewart Island, the west coast of the South Island, and the east coast to about as far north as Dunedin. From the remainder of the South Island it is absent, but appears again on the shore of Cook Strait at Titahi Bay, near Wellington. Strange to say, it extends no farther to the north, though it grows freely from seeds, and may be cultivated at any point on the New Zealand coast.
Vegetation of Cliffs and Rocks.
Fig. 36.—Pohutukawa growing as erect many-stemmed Tree in School-grounds, Kawakawa, East Cape.
[Photo, L. Cockayne.
Some adventurous flower
On savage crag-side grown
Seems nourished hour by hour
From its wild self alone.
Growing in company with O. insignis is Phormium Cookianum, its leaves drooping from the cliff; the delightful Veronica Hulkeana, with varnished green leaves, whose masses of delicate lilac flowers have earned for it the name of New Zealand lilac; and the aniseed (Angelica Gingidium).
The only member of the gourd family in New Zealand is at the present time quite rare on the mainland, and it may be best seen on some of the outlying islands of the north. On the Little Barrier, at the foot of the cliffs, it is abundant, scrambling over the kawa-kawa (Macropiper excelsum), or ascending to the topmost branches of the pohutukawas.
Certain ferns are peculiar to the coast, and are frequent on the cliffs. The most widely spread is the sea-spleenwort (Asplenium obtusatum).The coastal hard-fern (Blechnum durum) occurs only in the southern part of the South Island and in Stewart Island, but it is abundant also in the New Zealand subantarctic islands and the Chathams. All the coastal ferns have very thick and stiff leaves.
The Salt Meadows and Salt Marshes.
Along the banks of tidal rivers and estuaries there is frequently low ground covered at flood tide with brackish water, or, where higher, subject merely to a periodical submerging. Of both such situations the covering is fairly uniform throughout New Zealand. Colonies of rush-like plants form the bulk of the vegetation. The most striking is the rush-like Leptocarpus simplex, whose stiff, reddish, jointed stems, a yard or more tall, render it very conspicuous. It belongs to a family (Restionaceae) confined almost entirely to South Africa and Australia. A true rush (Juncus maritimus, var. australiensis) is also very common, but it has not been found south of Timaru. Dotted over the salt meadow, or growing in close masses, is the shrubby ribbonwood (Plagianthus divaricalus), a shrub of a dense habit, and made up of slender, wiry, dark-coloured interlacing twigs covered page 81with narrow leaves, most of which it casts off in the autumn. Its relationship to the beautiful lacebarks and ribbonwoods is indeed concealed in its habit, but revealed in the structure of its minute flowers and fruit, as well as in its tough bark.
On the drier ground of the salt meadow are a number of creeping, turf-making plants, mostly with long roots and small thick leaves. The chief of these are Samolus repens, a white-flowered plant of the primrose family, but not a bit like a primrose; Selliera radicans, which has a curious corolla, looking as if a portion had been removed, also white; Cotula dioica, with aromatic leaves and yellowish button-like flower-heads; and Atropis stricta, a small grass. In some places, but by no means everywhere, growing in the pools or streams, is a beautiful musk (Mimulus repens). Its flowers are bright lilac in colour, with an orange throat. Extremely abundant also in some localities (e.g., on the northern shores of Cook Strait), and dotting the ground everywhere, is the pretty relative of the last-mentioned, Mazus pumilio. The curious Eryngium vesiculosum, a plant of the carrot family, which can increase enormously by means of runners, and so become a weed, is an occasional salt-meadow plant.
Where the water cannot get away, and the ground is never dry, and uncovered only at low tide, will be found a salt marsh. In the wettest places colonies of the great bulrush (Scirpus lacustris) will be present, but only where the water is not too salt. More salt-enduring is the smaller Scirpus maritimus. Leptocarpus simplex will generally be the dominant plant, and will cover many acres to the exclusion of all else. A sedge, Car ex litorosa, is peculiar to the salt marsh. Many of the plants mentioned above also occur, specially Juncus maritimus. These salt-marsh plants are of considerable economic importance, as they help to build up solid ground in estuaries, and also to maintain the banks of tidal rivers.
Botany of the Small Coastal Islands.
The small islands near the coast are of extreme botanical interest, and sometimes of great beauty. Some are quite in their virgin condition, while others have been changed by man, especially where the lighthouse-keepers lead their solitary lives.
Fig. 37.—Interior of Forest of Stephen Island, showing spreading limbs of the Kohekohe (Dysoxylum spectabile). The slender upright stems are those of Macropiper excelsum.
Lands Department.] [Photo, L. Cockayne.
Open Bay Island, off the coast of south Westland, is in its virgin state. It would be an unpleasant experience to pass a night there, since in its peaty soil, honeycombed by the holes of petrels, veritable leeches and wetas of huge size and formidable aspect abound. The vegetation consists of a most impenetrable scrub of kiekie (Freycinetia Banksii), almost the last survivor of a forest which must have clothed these islands long ago, when connected with the mainland of Westland. Very interesting, too, must be the Three Kings, where Mr. T. F. Cheese-man found abundance of that magnificent tree, supposed to be almost extinct, the puka (Meryta Sinclairii).
Only a brief reference can be made to the Poor Knights, recently visited for the first time by Captain Bollons and the author, where the big snail, Placostylis Hongii, is still abundant, and where the arborescent vegetation consists largely of Suttonia divaricata, an unexpected plant. Nor can the coastal meadows of Southland, white with gentian and eyebright, be described, nor the cliff vegetation of the Nuggets, where an alpine celmisia clothes the barren rock; nor many other charming spots, lapped by the many-voiced ocean. Sufficient, however, has been said to show that we need not climb into the clouds to find our wild flowers, and that those who are wont to take their pleasure sadly by the seashore may find there a field of new interest.
* The seed leaves are green, and so they supply the growing plant with additional food-material of their own manufacture.