New Zealand Plants and their Story
Chapter I. — The General History of the Plants
The General History of the Plants.
The New Zealand biological region—Special botanical interest of New Zealand —Origin of the flora—Australian and South American connections—A bridge to South America—South American worms, spiders, and fishes—South American plants—The struggle for existence—Grass land versus forest—The kowhai of Chatham Island—Rival theories of evolution—Plant societies.
Lying isolated from neighbouring land-masses far out in the broad Pacific, New Zealand offered conditions for plant-life different from those of most other regions. Its area, greater by far than that of any oceanic group of islands, is sufficient to have allowed the development of a rich vegetation made up of many species. The land of the "Maori and Moa," as a poet has called our land, has long been famous from both the ethnological and zoological standpoints. The remarkable race of aborigines, with their interesting manners and customs, is known far and wide. Scientific men the world over, and many of the general public, for that matter, have an acquaintance more or less intimate with the giant birds of a former age, and their fast-vanishing relatives, the kiwis of to-day.
Origin of the Flora.
Fig. 2.—The Great Brown Seaweed (D'Urvillea utilis), exposed at low water. Dog Island, near Bluff.
Lands Department.] [Photo, L. Cockayne.
Let us in imagination peer into that remote past when New Zealand had finally emerged from the ocean, and when its surface, destitute of all life, was ready to receive its plant and animal immigrants.
Now, it is quite impossible to estimate geological time from figures. When we try to think of millions of years, our minds become confused; and so those long periods during which the earth gradually assumed its present form are designated by certain names representing divisions of geological time. These have been classified according to the fossils contained in the rocks. The divisions are five in number, and are named respectively, beginning with the earliest—the Archaean, the Primary, the Secondary, the Tertiary, and the Quaternary or Recent. These, again, are divided into smaller subdivisions, each, however, still of an unthinkable age.
With the first two great divisions we have nothing to do here. The history of our plants commences at that subdivision of the secondary period known as the Jurassic, when there flourished on the earth in general cycads, ferns, horse-tails, and pine-trees. The ancestors of the present crayfish and molluscs then lived in the seas, and huge reptiles wandered through the moist forests. Those plants which are propagated by means of the minute bodies known as spores—ferns and mosses, for instance—are able to travel vast distances by means of the wind, and, if the conditions are favourable, they soon gain a footing on unoccupied ground. Thus it is quite easy to account for the presence of the same species of the lower groups of plants in many lands far distant from one another. But when one comes to deal with the more highly organized seed-plants, whose seeds could travel over a vast body of water only by the merest chance, and with animals in general, many of which are still less adapted for ocean transit, speculations as to great changes having taken place on the surface of the globe come into play, and former land-connections between regions now separated by the broad ocean have to be assumed.page 5
Without going into details, zoological and botanical statistics and evidence show clearly enough that New Zealand has received its plants from two main sources—(1) the Malay Archipelago and Australia taken together, and (2) South America, together with a problematical land-area" existing in Tertiary times in the Southern Ocean, of which ice-bound Antarctica, and even portions of New Zealand itself may have been parts.
According to geologists, the land-surface of New Zealand underwent great changes during Tertiary times; at one period reduced to quite a small group of islands, and at another, the land having risen hundreds of feet, stretching north, east, and south, and uniting the scattered members of the archipelago to the main islands. How far "Greater New Zealand," as it may be called, extended is a matter of conjecture, but naturalists are generally agreed that it was joined to Australia and the Malay Archipelago by way of New Caledonia and the New Hebrides. The chief.matter in dispute is whether there has ever been an actual land-connection with South America.
Now, although the author has, in certain of his writings, favoured the idea of a New Zealand-South American union, there is a good deal to be said against the view, especially from the geological standpoint. Perhaps the strongest evidence that a "bridge" to South America existed lies, as Dr. W. B. Benham, F.R.S., has shown, in the presence in New Zealand of a family of South American earthworms—animals which certainly could not travel over the ocean. A spider hitherto found only on those distant granite rocks, the Bounty Islands, is allied not to any existing Australian or New Zealand species, but to a South American family. Galaxias, a genus of fresh-water fishes, occurs chiefly in South America and New Zealand, while there is also a species in South Africa. There is much more zoological evidence, but this will give the reader a sufficient idea as to its character.
Evidence derived from a study of plant-distribution can never by itself be regarded as conclusive, since there are various means—such as birds, ocean-currents, floating logs, icebergs, and the wind—by which seeds can be conveyed over the ocean. But the greater the distance to be traversed, the less likely are they to be carried in this manner. Heavy seeds, such as those of the kowhai, could not be blown by the wind for thousands of miles, and yet our plant of that name is identical with one growing in Chile. Our fuchsias, calceolarias, beeches, and a number of other plants have their headquarters in page 6South. America, and must either have come thence to New Zealand, or have reached both, these regions from the old problematical con tinent of the south.
Besides the kowhai, a number of other species are common to New Zealand and Fuegia. The following are some of the more important: Veronica elliptica, a shrubby speedwell, confined to the coast of the South. Island, to one locality north, of Cook Strait, and to the New Zealand subantarctic islands;. Grassula moschata, a rather small succulent plant with, red stems, common on many parts of the South. Island coast, Stewart Island, the subantarctic islands, and Chatham Island; Colobanthus quitensis, a tiny plant of the pink family, occurring in some parts of the South Island mountains; Coriaria ruscifolia, the tutu; Gcurm parviftorum, a pretty white-flowered plant of the subalpine and alpine region;' Luzuriaga marginata (fig. 3), a beautiful little plant, growing amongst moss in forests, and bearing a large white berry, found at sea-level in Southland, Stewart Island, and Westland, but only in subalpine forests in the North Island; two small species of rush, J uncus scheuzerioides and J. novae-zelandiae; one of the wood-rushes, Luzula racemosa; South America two sedges, Carex Darwini var. urolepsis, which up to the present has only been recorded from Chatham Island, and one of large size, C. trifida.
Oxalis magellanica, a pretty white wood-sorrel, occurs in New Zealand, South America, and East Australia. A number of other plants are so closely related as to be virtually common to these three regions. Finally, Macquarie Island is an interesting case, since no fewer than thirteen of its twenty-eight species of ferns and flowering-plants belong to South America or to the chain, of distant subantarctic islands.page 7
Quite recently, through the explorations of the Swedes in the first place and of Sir Ernest Shackleton in the second, it has been proved beyond doubt that forests containing both subtropical and temperate trees existed during Tertiary times in Antarctica. On Seymour Island, which is virtually a part of the antarctic continent, latitude 64° south, the Swedish Antarctic Expedition discovered a number of impressions of leaves in the sandstone rock. These have since been identified, and in some cases the species show strong relationships to plants living at the present time in South America, New Zealand, and Australia. Most interesting to us is the unlooked-for presence of a fossil Knightia allied to the rewarewa (Knightia excelsa), a tree found only in New Zealand, though there are in New Caledonia two other species of the genus, but belonging to a different section. Then, too, there is the genus Drimys, with the living Drimys axillaris (the pepper-tree), and two other New Zealand species; while D. Winteri (the Winter's bark) and D. aromatica are respectively Fuegian and Tasmanian representatives. Laurelia, a genus of only two species—one in Chile, and, the other L. novae-zelandiae, the wellknown puketea of the New Zealand northern forests—occurred in the forests of Tertiary Antarctica. Araucaria braziliana, of subtropical Brazil, and A. Bichvillii, of Australia, are closely related to a fossil araucaria, while the well-known monkey-puzzle tree of Chile (A. imbricata), the Norfolk Island pine (A. excelsa), and certain New Caledonian trees belong to the same genus. Other examples could be cited, but sufficient has been said, to show that the remarkable discoveries of the courageous explorers strengthen the evidence in favour of land-connection between New Zealand, Australia, and South America, while the existence of an ancient antarctic vegetation, correlated, of course, with a much warmer climate, can no longer be denied.
The Struggle for Existence.
Putting on one side the question whether our plants came by land or were conveyed by winds, birds, or water, and granting that they finally got a foothold, it will be seen that soon a struggle would arise between these newcomers for the possession of the soil. Such a strife would be somewhat analogous to that which has taken place between our colonists themselves, and has resulted in riches for some and poverty for others.page 8
Every one who cultivates a garden, however small, has to cope with what are called weeds—i.e., with the plants equipped in some special manner for occupying the soil at the expense of others. A species that can rapidly reproduce itself from seed, or by suckers, creeping stems, and the like, has a great advantage over one of slower propagating-power, and will soon smother it out by force of numbers alone. Some plants have large leaves, which they flatten against the ground, and so occupy at once more than their share of the soil. Others have a peculiar taste, making them objectionable to snails, slugs, or insects, and so triumph over plants liable to the attacks of such animals. But there is no need to multiply instances; any one interested can search for examples, and a most fascinating quest it is.* The advantages in some cases are so small as not to be appreciable by us; but, however slight the benefit, the plant possessing it must conquer in the long-run.
In nature this strife between plants is always in progress—a silent but nevertheless a deadly conflict. The calm aisles of a forest are a battlefield where the trees, shrubs, and more lowly plants strive for the mastery, while at the same time the forest itself wages incessant war with the adjoining grass-land—the one or the other aided by climatic changes, an abundant rainfall favouring the forest and drier conditions the meadow. Thus, when the plant immigrants arrived from the north and from the south, these two bands of invaders from quite different regions, and not attuned to each other, would engage in fierce battle; many would fall, and those escaping would be driven into inhospitable spots.
What may be accepted as traces of such warfare are still to be encountered. For instance, the beech (Nothojagus) forests may be taken as typical of southern South America—of stormy Fuegia, in fact—while the ordinary New Zealand mixed forest represents, in part, one band of subtropical invaders. This latter forest is the common "bush" of New Zealand, extending from the extreme north of the region to the south of Stewart Island, and even to the distant Aucklands. But near Chelsea, a suburb of Auckland City, may be seen some New Zealand beech-trees. Other isolated groups exist farther north, and even reach that most charming spot, the Little Barrier Island. These solitary trees are doubtless remnants of a page 9battalion of the great subantarctic or antarctic plant army, held now in bondage by their northern conquerors. Farther south the beeches are more powerful; but, driven from the fertile land, they occupy the poorer soil of the lowlands or the inhospitable mountainslopes, where they oppose a solid front to the biting blasts.
A remarkable example of the restricted distribution of a tree is shown by the kowhai of Chatham Island. This plant is common on certain volcanic ground near Auckland City. It was formerly extremely abundant in the Catlin's River forest, and in fact is found all over New Zealand, growing in various distinct kinds of soil. But in Chatham Island you may search the forest everywhere and find no trace of this graceful tree except on the limestone country near the edge of that extensive lagoon, the Whanga. There it is abundant, in company with the ordinary trees of a Chatham Island lowland forest, which latter elsewhere occupies volcanic ground. Here, then, is some slight advantage, not yet estimated by science, afforded to the ordinary trees by the volcanic soil which enables them to exclude the kowhai; whereas the limestone soil does not afford this benefit, and there all the trees meet on equal terms, flourishing side by side.
How many plants of which no trace has been found may have existed in New Zealand, and may have been destroyed through changes of conditions leading to some slight advantage for their competitors, none can tell; but that many ancient types of surpassing interest must have so perished is quite well known from such fossil plants as have been found, and amongst which, side by side with existing genera, are others not now to be found in any part of Australasia.
* This matter is gone into again in Chapter IX.
How Plants change their Forms.
It has been shown above how a constant warfare goes on between the plant inhabitants of the most quiescent forest or meadow, and how some survive and others perish. This truth forms the corner stone of the doctrine of evolution. Just as there is no actual stability in the vegetation of a region, so is there none in the individual species. Constant change is the undeviating plan of nature.
The original plant-immigrants settling down in their new home would be exposed to novel conditions of soil and climate, and to con tact with other plants and animals. This new environment would possibly bring about slight changes in the organisms, and in time page 10such small variations would so accumulate that new forms in harmony with the new conditions would arise. Such forms have arisen, and constitute, in large measure, the plants which are peculiar to New Zealand, and form nearly three-fourths of the flora so far as ferns and flowering-plants are concerned. This is stating the main facts of evolution in very general terms; no one really knows how it has come about, though no scientists deny the phenomenon. That is to say, evolution is proved up to the hilt, but its methods are still under discussion.
Three principal, theories are in vogue. The first, of which Darwin and Wallace are the illustrious authors, is known as the theory of natural selection. It takes the well-known fact that all organisms vary in all directions, and considers that if certain variations are beneficial they will persist, and by degrees, in the course of an enormous number of generations, become so intensified that a new species will result. As for the unbeneficial varieties, they will in course of time perish through the conflict with the more fitted.
Quite recently the eminent Dutch botanist, Hugo de Vries, has shown, by numerous far-reaching experiments extending over many years, that certain varieties, differing markedly from the parent in some hereditary characteristics, appear all of a sudden, and that a new species comes at once into the world without the lapse of longyears. If such a species is adapted to its surroundings it will remain: but, if not, it will go to the wall. This is called the mutation theory. Quite a large amount of evidence in favour of this theory is afforded by New Zealand plants, and a most interesting field of study lies in the collecting and growing varieties of variable species, and ascertaining how far such are constant and reproduce themselves "true" from seeds. Phormium, Veronica, Epilobium, Celmisia, and Ranunculus are genera which might with profit be studied experimentally, and which will never be properly understood otherwise.
The plants having come to New Zealand, having fought many battles, and having in numerous cases given rise to new species, their final settling-down might, at the first glance, seem the work of blind chance. Yet it was nothing of the kind.
A seed falling upon any piece of ground would, if it germinated, depend for its subsistence upon its power to make the best of the circumstances. Were other better-equipped plants present, the species in question would be wiped out. Also, were its structure and organs not suitable for living under the conditions provided, it would soon vanish even were there no competition. In consequence, soil and climate exercise a selective power, and so permit various species of plants to live together under a definite set of conditions. Thus have come into being those collections of plants known as plant societies or associations,* which, taken all together, make up the vegetation of New Zealand. These societies are sometimes quite distinct in themselves, but frequently they merge into one times most peculiar ones, which, depend upon the nature of the rock, its steepness, its exposure with regard to wand and rain, and upon its altitude above the sea. Minor societies frequently exist within the larger ones, and, should certain changes take place, may become dominant.
The two most important groups of plant societies are forests and grass-land. There are numerous varieties of both in New Zealand, and some of them are described further on. Another large class consists of those societies which depend upon the presence of an excess of water in the soil, as in swamps and bogs; while some plants float upon the water of streams or lakes, or are quite submerged. Others owe their presence to the very opposite set of circumstances—scarcity of water; and even in humid, New Zealand something like a desert vegetation may be found in not a few places, but its presence depends rather on the nature of the soil than on an insufficient rainfall. Then there are the societies peculiar to the sea-coast, where salt in the soil and exposure to strong winds are important factors. In such places are sandhills, salt meadows and marshes, shingly or sandy beaches, and cliffs. Rocks have societies of their own, and some-page 13times most peculiar ones, which, depend upon the nature of the rock, its steepness, its exposure with regard to wand and rain, and upon its altitude above the sea. Minor societies frequently exist within the larger ones, and, should certain changes take place, may become dominant.
From what has been said, it can be seen how important a part the study of plant societies plays in the investigation of the botany of any region. Those of New Zealand, unlike those of Europe, temperate Asia, and even much of North America, which have been modified out of all recognition through the long occupation of man, are absolutely primeval even yet in many places. But they, too, are rapidly being modified or destroyed altogether in the progress of settlement. In the temperate regions of the Old World there has been, little chance of studying virgin plant societies; the science of botany began too late for such a work. It is to countries like ours that science looks for such special studies as will bring about that advance in knowledge that will shed light upon the methods by which nature planted the great garden of the world.
* Also called by some "plant-formations," but there is no uniformity as yet in the use of this term.
1 Ranunculus Lyattii.
2 Dacrydium laxijolium
3 Myosotidium nobile.
4 Veronica gigantea.
5 Species of Olearia.
6 Polytrichum dendroides and Dawsonia superba.
7 Macrocystis Dnbenii and D'Urvillea utilis.
8 Species of Haastia and Raoulia.