The Vegetation of New Zealand
Chapter IV. — The Plant Communities
The Plant Communities.
New Zealand as a whole, owing to its high average rainfall of a fairly even distribution all the year round, and its equable climate,, was originally covered from north to south with a close mantle of forest, except where the edaphic conditions were antagonistic, or the rainfall insufficient to meet the demand of the various factors influencing transpiration, especially wind. Even yet, settlement notwithstanding, considerable areas are clothed with noble forest, extending in no few places from virtually page 147high water-mark to the subalpine belt. In north-western Auckland, in the East Cape district, on the Volcanic Plateau and the adjacent Wanganui coastal plain, on the slopes of the North Island mountains, on most of the land west of the Southern Alps and on the east up to the average limit reached by the westerly rain, in parts of the South Otago and Stewart districts, forests still exist in no whit different from those visited by the early botanists1, or, as yet so little modified by artificially-wild, grazing and browsing animals as to be virtually primeval. Nevertheless, to give an accurate account of the New Zealand forests is no longer possible and, day by day, a reliable presentation of the subject becomes more difficult. Thanks, however, to the assistance of the State Forest Service, and to my connection therewith, during the last few years I have had an opportunity to study the forests more closely than previously, so that the details given here replace for the most part those of the first edition of this work. The main difficulty has been to draw the line between a general account of the forests as a whole and one attempting to deal with the many details which close study has revealed — details which, if too much stressed, would hide the really important facts and give a blurred picture rather than a clear vision of the great tree-community of New Zealand.
The forest, as a whole, comes into the same class as tropical rain-forest, but it can be naturally divided into subtropical rain-forest — a hygrophytie formation — and subantarctic rain-forest — a formation more or less mesophytic in character, and with Nothofagus dominant. Speaking in general terms, the lowland-tree associations — even those of swamps — are mostly subtropical rain-forest, the species of Nothofagus being absent over wide areas or, if present, only occasionally forming pure associations.
1 1) Thanks to the Scenery Preservation Act of 1903, many areas in these localities, and elsewhere, have been permanently set aside for the preservation of the indigenous plants and animals. There are also several national parks of great extent and climatic reserves on the mountains that serve a similar purpose.
The life-forms of lowland-lower hills' forest and the number of species to each are as follows: — trees 108, shrubs 59, herbs 43, grass-like plants 24, semi-woody plants 5, lianes 26 (excluding ferns), epiphytes 17 (excluding ferns), parasites 13, ferns 90 (tree-ferns 8, filmy ferns 25).
So far as physiognomy is concerned, there is a considerable resemblance between the various forest associations throughout their lowland range, but one rather ecological than floristic. This likeness is owing to the following circumstances: — (1) The presence of podocarps with one or other of their species frequently dominating. (2.) The great abundance of tree-ferns. (3.) The vast number of ground-ferns (Fig. 32) many of which are of wide distribution, and the presence throughout in quantity of Asplenium bulbiferum, Blechnum procerum and B. discolor. (4.) The presence in profusion of the lianes Muehlenbeckia australis, Rhipogonum scandens, Metrosideros hypericifolia and Rubus australis. (5.) The density of the undergrowth and the presence therein of certain low trees or tall shrubs, especially Carpodetus serratus, Pittosporum tenuifolium, Melicytus ramiflorus, Myrtus pedunculata, Nothopanax arboreum, Schefflera digitata, Pseudopanax crassifolium var. unifoliolatum, Suttonia australis and Coprosma robusta. (6.) The abundance of filmy-ferns, mosses, liverworts and, if not too dense, large foliaceous lichens.
Ecological conditions in general governing lowland-lower hills' forest.
Leaving on one side all special details concerning the ecological factors, the following are of prime importance, so far as the lowland-lower hills' communities are concerned: — (1.) A rainfall (except in the case of semiswamp forest) exceeding 90 cm. distributed more or less equally throughout the year. (2.) A sufficient supply of available water at all seasons in the surface-soil. (3.) A winter temperature not falling below —10° C. (4.) The peculiar conditions brought about by the plants themselves, which define, in large measure, the wind, light, heat, air-moisture, soil-moisture and humus factors. These last-mentioned conditions come gradually during the development of forest and render possible the various phases of succession. Usually, the rainfall is far greater than as given above, but with its increase neither the ecological nor the floristic composition of a forest is greatly affected. The even distribution of rainy days throughout the year is a matter of especial importance, for a drought of several months' duration will actually cause the death of several endemic species of trees. As for the heat factor, each species has its special requirements and limitations, and the degree of cold, cited above, is far greater than many plants can tolerate.
The light relation of each species is fundamental with regard to the structure of forest, and it is the main factor regulating succession, as will be seen further on. Here it need only be pointed out that the species page 149differ greatly in their shade-tolerating capacities, and that they range from those which demand bright light to those which grow only in deep shade, by way of species which tolerate many different degrees of illumination.
New Zealand forest as a whole is most catholic in regard to the nature of the soil it, and perhaps nearly all its members, can occupy, though the latter may have individual "preferences" in certain localities for a particular soil. Forests of much the same floristic and ecological character occupy soils where the underlying rock is greywacke, granite, volcanic rocks of various kinds, calcareous rocks of different categories, and mica-schist; in short, pretty well all the geological formations which form the land-surface of the region. Further, forest occurs on stiff clays, rich alluvial soil, shingly river-bed, ancient morainic deposits, pumice and other volcanic ash, sanddunes, badly-drained ground and shallow swamps.
The ecological conditions of any forest-area are far from uniform. Much depends upon the topography, — slopes ridges, flats and gullies, each possesses its special plant-covering in harmony with the differences in groundwater, depth of humus, air-moisture, light-intensity and shelter from wind. An interesting case is presented by the forest of the Wanganui coastal plain, where, on the slopes, there is hygrophytic tawa (Beilschmiedia tawa) forest and on the ridges a pure semi-xerophytic association of Nothofagus Solandri, even if these trees be almost in single file.
Distribution of the species.
A census of the forest species shows that North Island contains 357 species (pteridophytes 95, spermophytes 262) but in proceeding from north to south 46 either do not reach lat. 38° or extend but a short distance beyond, South Island 312 (pteridophytes 87, spermophytes 225) of which in proceeding from north to south 69 do not reach or hardly overstep lat. 42° on the west or lat. 44° on the east, and Stewart Island 147. About 150 species extend throughout most of North and South Islands, 110 of which extend to Stewart Island.
With regard to the individual species, each has its latitudinal limit, so that in proceeding from north to south, or vice versa, species drop out or come in, but from about lat. 38° there is chiefly a more or less gradual dropping out. A few species (about 8) are confined to the north of lat. 36° or somewhat beyond, e. g., Microlaena Carsei, Dacrydium Kirkii, Pittosporum pimeleoides, P. reflexum (and the hybrids between the two last), Ackama rosaefolia (greatly resembling juvenile Weinmannia sylvicola), that great swarm of hybrids and jordanons — Alseuosmia and Colensoa physaloides. Then in the Thames subdistrict a considerable change occurs in the forest various common southern plants having joined the community, but they are confined usually to the montane belt, e. g. Hymenophyllum pulcherrimum, H. peltatum, Trichomanes Lyallii, Lindsaya viridis, Blechnum Patersonii var. elongatum, B. vulcanicum, B. penna marina, the physiognomic Polystichum vestitum, Phyllocladus alpinus, Uncinia ferruginea, Enargea parviflora, Cor-page 150dyline indivisa, Nothofagus fusca (confused by most writers with N. truncate), N. Menziesii, Elytranthe tetrapetala, Weinmannia racemosa, Aristotelia fruticosa, Nothopanax simplex, N. Colensoi, Coprosma foetidissima, C. Colensoi. Perhaps the most striking feature of this list is the sudden appearance (or halt in their northern march) of trees and shrubs of high physiognomic importance whose structure certainly should not have forbidden their reaching further north.
The neighbourhood of latitude 38° south, as emphasized more than once in this book, is a highly critical point in regard to plant distribution, some northern species hardly reaching it, but others overstepping it and extending, for a greater or lesser distance, into the East Cape and Egmont-Wanganui districts. The following is a selection of characteristic forest species belonging to this class: — Lygodium articulatum, Phyllocladus glaucus, Agathis australis, Persoonia toru, Beilschmiedia taraire (but as a common species this has gone out long before), Litsaea calicaris, Ixerba brexioides, Quintinia serrata, Weinmannia sylvicola, Metrosideros albiflora, M. carminea (diffusa), Corokia buddleoides and Vitex lucens. But this discarding of species is balanced, so far as forest is concerned, by the incoming of others, some of them local endemics (e. g. Polypodium novae-zelandiae, Pittosporum Ralphii, Edwardsio tetraptera, Coprosma tenuifolia and Jovellana Sinclairii), and the remainder with a more or less wide range to the south, the following being specially important:—Alsophila Colensoi, Hypolepis Millefolium, Podocarpus alpinus (mainly subalpine until the North-western district) Nothofagus Solandri, N. cliffortioides, Elytranthe Colensoi, Hoheria sexstylosa, Coprosma Banksii (X C. colbanksii appears), and Shatvia paniculata. This forest from lat. 38° southwards, so soon as its far northern plants are cast aside, extends not only throughout the remainder of North Island but occupies much of the Sounds-Nelson and North-western districts, the forest communities of these two districts being marked off from those typical of South Island generally by the following North Island species:— (lianes) Blechnum filiforme, Freycinetia Banksii, Metrosideros scandens, M. perforata, M. Colensoi, (the palm) Rhopalostylis sapida (trees and tall shrubs), Knightia excelsa, Laurelia novaezelandiae, Suttonia salicina, Beilschmiedia tawa, Dysoxylum spectabile, Metrosideros robusta, Myrtus bullata, X. M. bullobcordata, Melicope ternata, XM. tersimplex, Olearia rani, Coprosma grandifolia and Brachyglottis repanda. Certainly a few of these species extend to the Western and even the Fiord districts and to Banks Peninsula, but the forests of the last two cannot be grouped along with those of the southern North Island, the Sounds-Nelson and the North-western districts.
General principles governing succession.
The most important principle underlying succession in New Zealand forests is the relation of the different species to light; also, the gradual incoming of humus on the forest-floor from decay of leaves, dead wood &c. is of fundamental importance, leading page 151as it does to the formation of seed-beds, and the essential station for the establishment of the all-important hygrophytic fern and bryophyte content of the floor vegetation together with many other species dependent on those conditions which humus supplies. Thus in the forest near Lake Rotoma (VP.), where in 1886 the floor was covered with volcanic ash by the eruption of Mount Tarawera, even yet the customary filmy fern-bryophyte mats are absent. Subsidiary to the foregoing are the individual edaphic and biotic (more especially influence of plant on plant) relations but these make themselves manifest rather in diversity of composition and structure of the undergrowth than in succession as a whole. That is to say, there are minor successions within the actual general successions. The latter, in fact, are governed by the tall trees which for the time are dominant. This statement is made more plain when discussing the life-history of various types of forest.
To observe the actual beginnings of certain classes of primeval forest is hardly possible at the present time, all there is to go on being: (1.) the composition and structure of belts of shrubs or small trees at the margin of forest, (2.) the progress of events in Leptospermum shrubland, (3.) young trees or shrubs invading Pteridium heath or tussock-grassland, (4.) succession on river-bed or river-terrace culminating in forest, (5.) swamp-succession terminating in forest, and (6) regeneration or reinstatement after forest is destroyed or damaged. Succession after burning, so far as those forests near active volcanoes are concerned, must be very similar to what happened when such volcanoes were far more active than at present, and probably certain pieces of forest on the Volcanic Plateau, or even Mount Egmont, originated after destruction of the original forest by fire, and this must have taken place again and again, even where now there are only extinct volcanoes (the Tarawera eruption is a case in point). Fire thus may be not an artificial but a natural agent. In what follows, all of the above cases are taken into consideration, though whether induced successions are identical with natural successions (except perhaps fire) no one can say.
Forest species may be grouped into: (1.) light-demanding, (2.) shadetolerating, and (3.) shade-demanding, the second class consisting of species which are more or less indifferent in regard to excess of light or shade. To be sure, there are many grades in each class but, for the purposes of a general account of succession, the light-demanding and the shade-tolerating come together, and it is these which form the earliest stages of forest. Thus, the extreme light-demanders which get established will be augmented by species able to endure a little shade, and so on until true forest with its undergrowth of shade-demanding and shade-tolerating species has come into being. This process is by no means rapid, since the majority of the trees, as already explained, are of comparatively slow growth.
The next principle to grasp is that the tall trees doniating forest page 152and forming its roof, as seedlings and saplings are partly light-demanding and partly shade-tolerating or shade-demanding, the first class being evidently suitable for temporary successions and the other two for climaxes.
The most extreme light-demanding species concerned with the establishment of forest are the shrub (or small tree), Leptospermum scoparium, and the fern, Pteridium esculentum, but both frequently grow so thickly that, until open spaces come into being, few other species, if any, can gain a footing. Next in importance, though it is difficult to say what part it played in primitive New Zealand, is the small, fast-growing tree, Aristotelia serrata, which so commonly forms more or less pure associations after forest is felled but is quite rare in adult forest. The following are other lightdemanding or, some of them, shade-tolerating species which become established in bright light: Histiopteris incisa, Paesia scaberula, Gleichenia microphylla, G. circinata (Filic), Lycopodium volubile, L. densum (Lycop.), Agathis australis (Araucariac), all species of Podocarpus, all species of Dacrydium (D. intermedium and D. Colensoi tolerate a good deal of shade), the species of Phyllocladus (Podocarpac), Gahnia pauciflora, (Cyperac), Cordyline Banksii, C. indivisa, Dianella intermedia (Liliac), all species of Nothofagus (Fagac), Persoonia torn, Knightia excelsa (Proteac), the forest species of Muehlenbeckia (Polygonac.), Quintinia acutifolia, Carpodetus serratus (Saxifrag.), species of Pittosporum of the "tenuifolia" group (Pittosporac), the species of Weinmannia, Ackama rosaefolia (Cunoniac), the climbing species of Rubus (Rosac), the arboreal species of Edwardsia (Legum.), Coriaria arborea (Coriariac), Pennantia corymbosa (Icaciniac), Aristotelia fruticosa (Elaeocarp.), Plagianthus betulinus, the species of Hoheria (Malvac), Melicytus ramiflorus (Violac), Leptospermum ericoides, Myrtus bullata, M. obcordata (Myrtac), Fuchsia excorticata, F. perscandens (Onagrac), Nothopanax anomalum, N. arboreum, N. Colensoi, Pseudopanax crassifolium (Araliac), Griselinia littoralis, Corokia Cotoneaster (Comae), Cyathodes acerosa, Leucopogon fasciculatus (Epacrid.), Suttonia australis, S. divaricata (Myrsinac), Geniostoma Ugustrifolium (Loganiac), the species of Parsonsia (Apocynac), Hebe salicifolia (Scroph.), Myoporum laetum (Myoporac), Coprosma lucida, C. robusta, C. propinqua, C. rhamnoides, C. arborea, C. parviflora (Rubiac), Olearia rani, Helichrysum glomeratum and Brachyglottis repanda (Compos.). With regard to some in the above list, and others omitted, their toleration of bright light is usually more or less dependent on the air being fairly moist.
Tree-ferns (Fig. 23), so important in forest undergrowth generally, tolerate a good deal of light, as may be seen where large colonies of Cyathea medullaris have been established in the open by means of spores (SA., EW.). But C. dealbata is the commonest tree-fern in early stages of forest.
Coming now to actual succession, sufficient is not known and may page 153never be known as to the sequence, composition and duration of the various successions of forest which, by degrees, lead to a more or less stable climax-association. For one thing, so many minor successions in one and the same piece of forest becloud the general progress. Thus it seems to me, though this statement may eventually be disproved, there is rather a general move towards a climax except in the earlier stages of associations of light-demanding and light-tolerating species, than well-marked associations (successions), the one succeeding (replacing) the other.
The first contribution in New Zealand to this fundamental question of succession in forest was my account of the development of kauri forest (1908:30, 31). Later, in the first edition of this work, I put forward with some hesitation the view that the general podocarp forest of North Island was turning by degrees into a climax with the tawa (Beilschmiedia tawa) dominant, and that the podocarps of South Island forest, to the south of lat, 42°, would be eventually replaced by Weinmannia racemosa. Independently, E. H. Wilson (1921:235) has expressed the opinion that the kauri and podocarps were being gradually replaced by broad-leaved dicotylous trees. E. B. Levy (1923) has added strong proof to my tawa theory and L. M. Ellis (Director, State Forest Service) has told me of a definite and striking example of replacement by tawa he had observed in the Volcanic Plateau district. But special details regarding the life-history of lowland forest are given below when dealing with the different groups.
Principles upon which the classification of New Zealand forests is based.
The primary classification of the forest communities into subtropical and snbantarctic rain-forest, suggested by me (1926:7) at first thought seems sound enough. But there are wide areas covered by mixed forest where podocarps, the usual broad-leaved dicotylous trees and Nothofagus are present in abundance, and where the forest interior is almost, if not quite, as hygrophytic as that of subtropical rain-forest. It also seems easy to separate the forests on altitudinal lines, but here again a difficulty arises, for certain North Island high-mountain forests, extending from 900 m. to 1200 m. altitude, are but little different from some of those of the lowland Fiord district.
It is the secondary divisions which are the main stumbling-block. Naturally two important points are their floristic composition and ecological features. The former certainly depends largely on latitude and local endemism but, ecologically, there is little difference between a North Island and Stewart Island forest; so, too, with their, structure. Two features, however, stand out for subtropical rain-forest: that is, it is composed so far as trees go partly of Podocarpaceae, Cupressaceae or Araucariaceae, and partly of broad-leaved dicotylous trees. Unfortunately, for purposes of classification, there is every intermediate stage between a pure podocarp or kauri community and one made up of dicotylous trees alone. Again, a genetic page 154classification suggests itself, but here, too, intermediate stages occur inter calated in one and the same piece of forest.
In what follows, latitudinal and altitudinal distribution of species, structure, special ecology and life-histories have all been taken into consideration. It would have been easy to have made many subdivisions but I have carefully avoided doing so. The subject is treated rather in a general manner, the main object having been to attempt the presentation of an accurate picture of the remarkable New Zealand rain-forest unblurred by superfluous details.
b. The forest communities.
1. Subtropical rain-forest of broad-leaved dicotylous trees and conifers.
Sub-tropical rain-forest associations possess so many features in common that, in order to avoid repetition, the following details are submitted.
The trees, shrubs and ferns, with a few trifling exceptions, are evergreen. As viewed from without, the evergreen character of the trees and the general absence of bright greens gives, when seen from a distance, a sombre aspect to the forest, while the density of their growth altogether masks the height of the trees. But a closer view reveals the varied greens and it is not difficult in some instances to recognize certain species from their colour alone, especially in low, even forests of dry ground. An outside view, too, reveals but little of the tropical character of the forest. A few tree-ferns may raise their crowns of spreading, feathery leaves above the greenery, or in North Island and the Sounds-Nelson and North-western districts, nikau palms (Rhopalostylis sapida) peep forth, but that is all. But push through the bolt of shrubs, or low trees, that may fringe its outskirts, and the vision within will be novel enough to one acquainted only with the temperate forests of the northern hemisphere.
Massive trunks, unbranched for many metres, meet the eye, some covered so thickly with lianes and epiphytes, many of which are ferns and bryophytes, that their bark is invisible. Open spaces are few or wanting. Young trees, shrubs of many kinds and tree-ferns 5 to 10 m. tall, growing in clumps or isolated, closely fill the gaps between the tree-trunks. Ropelike stems of lianes depend from the forest-roof swinging in the air, or lie sprawling upon the ground. The bases of the trees are not infrequently swollen and irregular, while their roots spread far and wide over the surface, at times half-buried, or, here and there, arching into the air, and covered with seedling trees an shrubs, ferns of goodly size, mantles of mosses and liverworts, lichens and sheets of pellucid Hymenophyllaceae. Fallen trees, in various stages of decay lie everywhere, and these too, hidden by a garb of water-holding greenery, are the home of seedlings innu-page 155merable. The actual forest-floor is most uneven; rotting logs, fallen branches, raised roots, ferns frequently with short trunks and mounds of humus covered with bryophytes and filmy-ferns make walking laborious. Progress generally is considerably retarded, too, not merely by the abovementioned obstacles, or by the close-growing shrubs or spreading branches, but a coarse network of the almost black, stiff stems of the liliaceous liane, Rhipogonum scandens, forms entanglements beneath which one is compelled at times to crawl on hands and knees. In other places where there is a good deal of light, the hooked prickles on the midribs of Rubus australis, catching a garment, may hold one fast. Furthermore, even on level ground, there are water-courses, here and there, and near these the density of the undergrowth increases, lateral branches from the trees on either side meet and become entangled, the growth of ferns becomes thicker, so that progress is well nigh impossible. In hilly forest, the density of gullies is still more intensified.
The close growth, which I have attempted to describe, is in harmony with the moist, equable climate, but regulated by the density of the forestroof. Everywhere is the effect of that complex of factors evoked by the forest itself manifest in the plant-forms. Shrubs, which in the open would be rounded and symmetrical, put forth long, slender stems, that, liane-like, lean against other trees and gain support. Young trees have frequently much-reduced lateral branches and long, straight, slender main-stems. In some this habit is hereditary, and thus the curious juvenile form of Pseudopanax crassifolium var. unifolialatum may be an "adaptation" to the forest-life.
On the trunks of most of the trees that do not shed their bark in great flakes, and right up on the highest branches, are not only an abundance of true lianes and epiphytes (Fig. 27), but seedlings of trees and shrubs, ground ferns of many species and hosts of mosses and liverworts. The trunks of tree-ferns, too, are a favourite station for many plants. Even the slender branches of shrubs may be deeply moss-covered while leaves themselves may be the home of various small bryophytes.
Certain forests are not nearly so dense or hygrophytic as described above, nor do they exhibit so fully the various peculiarities as cited, but such occupy drier ground than usual, and even then show unmistakeably their tropical facies.
In every type of New Zealand rain-forest the vegetation is in several distinct layers (stories), each with a definite light-relation. Where the tallest trees are present the uppermost layer (story) consists of their crowns, in some places those of the Podocarpaceae or, in certain associations, Metrosideros robusta, one or other of the two species of Weinmannia, Beilschmiedia tawa, B. taraire or species of Nothofagus. Trees of a medium size form the next layer, while growing in their crowns, as also in those of the upper page 156story, are the flowering parts of the lianes and in forests of North Island type the more massive epiphytes (e. g. species of Astelia, Griselinia lucida Pittosporum cornifolium, young Metrosideros robusta). The upper layer does not, as a rule, make a continuous roof, so the light-relation, but not the windrelation, of these two highest stories is not very different. The third layer is formed by the smaller trees, tallest shrubs, and tall tree-ferns, while in many North Island forests and the Sounds-Nelson and North-western districts, the mkau-palm is conspicuous. Next comes the fourth layer, consisting of the smaller ferns, prostrate or low shrubs, decumbent lianes, tussocks of Gahnia or Astelia and young plants of various kinds. Finally, there is the layer of actual floor-plants, which is largely made up of small ferns (mostly Hymenophyllaceae) and bryophytes, important genera of which are: (Hepaticae) Aneura, Symphyogyna, Monoclea, Treubia, Chiloscyphus, Frullania, Mastigobryum, Lepidozia, Schistochila, Trichacolea, Plagiochila, Tylimanthus, Madotheca; (Musci) Leucoloma, Dicranoloma, Leucobryum, Leptostomum, Hymenodon, Bryum, Echinodium, Ptychomnion, Weymouthia, Mniodendron, Sciadocladus, Lembophyllum, Distichophyllum, Hypopterygium, Cyathophorum, Rhacopilum, Mniadelphus.
β. Kauri (Agathis australis) - broad leaved dicotylous - tree forest.
Forest of this class is distinguished by the presence of more or less Agathis australis together with certain other tall trees especially Beilschmiedia tawa, B. taraire (one or both), Weinmannia sylvicola, Metrosideros robusta and some (or all) of the usual podocarps. Certain" species, rare or wanting elsewhere, except in the Auckland districts, are present, of which (excluding those belonging particularly to the kauri subassociation the following are common or characteristic: — Blechnum Fraseri, Lygodium articulatum, Dacrydium Kirkii, Mida salicifolia, M. myrtifolia, the hybrids between these two, Litsaea calicaris, Melicytus macrophyllus, Dracophyllum latifolium and the polymorphic Alseuosmiae.
The number of species belonging to the community is 231 (pteridophytes 67, spermophytes 164) which belong to 55 families and 117 genera. Lists of the most important species are given when dealing with the associations &c.
The high value of the timber together with the inflammability of damaged (not virgin!) kauri forest, has led to an enormous reduction in area of the community, so that, except where reserved, a dozen or so years from now will see it virtually gone for ever. But, extensive as were these forests of present-day New Zealand, they were but the remains or successors of more ancient communities, their site plainly marked by abundance of kauri-resin or in places tree-trunks beneath the surface of the ground. Why these ancient forests vanished none can say, but Chaeles Darwin who page 157visited a kauri forest in 1835 writes in his Voyage of the Beagle in regard to the fernlands near the Bay of Islands, "Some of the residents think that all this extensive open country originally was covered with forests, and that is has been cleared by fire". Probably this surmise is true enough for certain localities, but it can hardly be accepted as a general principle.
The forest-area, before the interference of man, extended from a line joining Doubtless and Ahipara Bays in the north to the Auckland Isthmus in the south, together with the Barrier Islands and the lower slopes of the Thames Mountains. Kauri forest is essentially an association of the lowlands and lower hills and generally does not ascend to much over 400 m. Nor can it tolerate wet ground, so that its abundant remains in lowland bogs indicates change of level in the land-surface (cf. Cheeseman 1897 a: 344).
Partly because of its great monetary value and partly because of the dominating appearance of the lordly kauri, the community, no matter its composition, is generally designated "kauri forest". This, however, is a misnomer, for the kauri itself occurs, either as solitary individuals or as large or quite small groups, situated in the general forest-mass, but clearly defined through the presence of the mighty tree unlike any other and the astonishing uniformity in composition of its associated plants.
(2.) Kauri forest in a wide sense.
Although there are changes in regard to latitude, and many differences in the relative abundance of species, the whole kauri-forest community may be considered one association and may be conveniently divided into several subassociations.
As a rule the soil occupied by kauri forest is of poor quality from the agricultural standpoint, a fact emphasised by its occupation after the forest is removed by second-class or usually pasture of a much worse character. But there are various local differences of soil within most of the forest areas and these are reflected by the vegetation, dominance of kauri indicating the least "fertile" soil.
The kauri (Agathis australis) subassociation.
This plant-community is distinguished by the dominance of Agathis australis and its remarkable assemblage of associated species. The number of kauri trees present range from a close growth of such to isolated trees here and there. The associated species are as follows: — Cyathea dealbata, Dicksonia lanata (sometimes extremely common), Blechnum Fraseri, Gahnia xanthocarpa, Astelia trinervia, Freycinetia Banksii, Mida salicifolia, M. myrtifolia, Weinmannia sylvicola (juvenile), Phebalium nudum, Dysoxylum spectabile (juvenile), Metrosideros scandens, M. albiflora, Nothopanax arboreum, Dracophyllum latifolium, Leucopogon fasciculatus, Geniostoma ligustrifolium, Coprosma grandifolia, Alseuosmia macrophylla and Senecio Kirkii.
The subassociation owes its very characteristic physiognomy partly page 158to the dense tussock-thickets of Gahnia-Astelia (Fig. 34) and partly to the form of the kauri itself. Where it extends over a wide area, the undergrowth is not thick. The kauri-trunks, usually shining-grey, but sometimes reddish, rise up on all sides, as far as the eye can pierce, as massive colums 1 to 3 m. diam., unbranched for 20 m. or more (Fig. 35). Round the base of each tree is a mound of humus, formed from the shed bark, occupied by small tussocks of Astelia trinervia, sprawling Metrosideris scandens and Senecio Kirkii. Rising up between the giant trunks may be multitudes of the straight stems of Beilschmiedia taraire thrusting their sparse heads of foliage up to the lower branches of the kauris (Fig. 36.), or B. tawa with its irregular thicker trunk, bryophyte-covered, may be abundant. Between the trees there will be a rather low, open undergrowth consisting of (the first three species being dominant): Cyathea dealbata (trunks 1 m. or less). Dicksonia lanata (25 cm. high, in colonies, the green fronds arching outwards, their blackish stems shining with a metallic lustre), juvenile Weinmannia sylvicola with yellowish-green pinnate leaves, black-stemmed Wintera axillaris, slender Dysoxylum, graceful young Beilschmiedia tawa, Melicytus macrophyllus, Suttonia salicina, Coprosma grandifolia, stemless Rhopalostylis, Alseuosmia macrophylla, A. quercifolia, A. Banksii, A. linariifolia, if they be species, and the hybrid swarm in which all take a part, and juvenile Podocarpus ferrugineus. On the ground will be trailing Freycinetia, straggling Lygodium (also winding round the young trees), extensive colonies of Blechnum Fraseri, and in some localities the low straggling shrubs Pittosporum pimeleoides, P. reflexum and their hybrids, and the fern Schizaea dichotoma. High above all rise up the mighty spreading limbs of the kauris (Fig. 37) and extending to these lace-like foliage of Beilschmiedia tawa, or the darker, denser heads of B. taraire. Lianes are not numerous, an occasional Freycinetia or Lygodium ascend the Beilschmiedia trees, but the kauri itself, owing to its bark-shedding habit, remains inviolate.
Much more common than such extensive kauri communities are groves, large or small, or solitary trees, scattered through the forest mass. The kauri trees generally are 20 m. or more distant and the intervening space is occupied by an extremely thick Gahnia-Astelia thicket containing also Freycinetia, Metrosideros scandens, M. albiflora, Phebalium nudum, Senecio Kirkii and all the other species already cited as prominent members of the subassociation. Obviously these shrubs &c. are wanting where the GahniaAstelia is densest (Fig. 34 but only A. trinervia in the picture).
The taraire (Beilschmiedia taraire) snbassociation.
In this subassociation the kauri is absent and B. taraire dominant. It occurs in its full development to the north of lat. 36° south. The taraire trees are about 15 m. high, 3 m. or so apart and their crowns are small but dense. Generally the roof is fairly open. Metrosideros robusta is common and as usual conspicuous through its most irregular trunk full of hollows filled with humus page 159supporting so many bryophytes, filmy ferns; herbaceous ferns and shrubs that its brownish, furrowed bark is hidden by the wealth of greenery. Frequently, the trunk leans out of the perpendicular in which case it will support a dense growth of immense asteliads right to the forks of its great twisted branches in the forest-roof. Other common trees are: — Podocarpus totara, P. ferrugineus, Dacrydium cupressinum, Phyllocladus trichomanoides, Knightia excelsa, Dysoxylum spectabile, Beilschmiedia tawa and Weinmannia sylvicola. Much rarer, and not in all localities, are the following: — Libocedrus plumosa, Dacrydium Kirkii, D. Colensoi and Phyllocladus glaucus.
The undergrowth, in many places, is not dense, but it varies greatly in this regard according to the intensity of the light. In many parts, it consists of a more or less thick growth of the following young forest-trees, low trees, shrubs and tree-ferns: — Knightia, Dysoxylum, Beilschmiedia taraire (these three with a long, straight main-stem and few lateral branches). Wintera axillaris, Pittosporum tenuifolium, Melicytus macrophyllus, Myrtus bullata, Nothopanax arboreum, Pseudopanax crassifolium var. unifoliolatum or occasionally var. trifoliolatum, Suttonia australis, S. salicina, Geniostoma ligustrifolium, Coprosma grandifolia, C. arborea (in dry ground), Alseuosmia macrophylla, Olearia rani, Cyathea medullaris, and C. dealbata. In other parts, there is a thicket of tussocks of Gahnia xanthocarpa, G. setifolia, and Astelia trinervia, mixed with entangled stems of Rhipogonum scandens and Freycinetia Banksii.
The palm, Rhopalostylis sapida, is often abundant, its life-form rendering it specially conspicuous. Tree-trunks are draped thickly by climbing species of Metrosideros or the fern Blechnum filiforme; shrubs and slender trees are festooned and bound together by the twining leaf-spindles of Lygodium articulatum; on horizontal branches are masses of Astelia Solandri and long tassels of Lycopodium Billardieri swing in the air (Fig. 27). Asplenium flaccidum, A. adiantoides, Dendrobium Cunninghami, Pittosporum cornifolium and the thick-leaved P. Kirkii are also common epiphytes.
Open spaces of the forest-floor are occupied by mats of vivid-green Hymenophyllum demissum, Freycinetia, juvenile Blechnum filiforme, rooting Metrosideros hypericifolia, seedlings of trees and shrubs and various bryophytes Fallen trees are thickly covered with translucent Hymenophyllum dilatatum, its fronds 30 cm. long and Trichomanes reniforme dark-green when old, but emerald when young.
The tawa (Beilschmiedia tawa) subassociation.
This subassociation is distinguished by the dominance of Beilschmiedia tawa. It occurs to some extent along with the last-described community but, south of lat. 36°, it is the leading broad-leaved tree association. At one time it was dominant on the Waitakerei Hills and Thames Mountains, but in these localities the primitive forest has been in large measure destroyed while the remnant is usually greatly modified.page 160
Thanks to an early paper of Cheeseman's (1871:270), it is possible to give some account of the original vast forest on the Waitakerei Hills, since he examined a portion of it before it had been seriously interfered with.
The dominant tree was Beilschmiedia tawa which "probably formed three-fifths of the forest". The other most abundant trees were Agathis, Dacrydium cupressinum, Elaeocarpus dentatus, Knightia, Litsaea calicaris, Metrosideros robusta, Pittosporum tenuifolium and Suttonia australis. The undergrowth was dense and consisted of Alseuosmia macrophylla (abundant), species of Gahnia, Astelia and Coprosma, Rhipogonum, Myrtus bullata and Senecio Kirkii; Hymenophyllaceae, ferns in general, and bryophytes were very plentiful.
The originally extensive forests of the Thames subdistrict, except on the Little Barrier Island, Mount Te Aroha and a few other localities, are altogether gone or much modified. Some light is thrown on the original plant-covering by the writings of T. Kirk (1870:89) and J. Adams (1884:385; 1888:32). Without going into details, the forest was much as already described, but Beilschmiedia taraire and Dicksonia lanata were scarce.
Pukatea (Laurelia noyae-zelandiae)-nikau (Rhopalostylis sapida) subassociation.
What follows refers only to the Waipoua forest (south of Hokianga Harbour—NA.), but doubtless somewhat similar combinations occurred throughout the plant-association.
The subassociation is confined to moist gulleys. Beilschmiedia taraire is rare or absent and Laurelia novae-zelandiae the common tree; the palm, generally trunkless, may be so abundant as to dominate. The following are characteristic: — Dicksonia squarrosa (tree-fern), Dryopteris pennigera (here with a trunk), Asplenium bulbiferum, mats of Hymenophyllum demissum, Rhipogonum, Elatostema rugosum (the succulent stems with their bronzy leaves raised 1 m. above the ground and occupying many square metres), creeping juvenile Rubus schmidelioides and the araliad shrub or tree Schefflera digitata. On shaded banks of streams is Trichomanes rigidum, its dark fronds covered with small epiphytic mosses.
Life-history of Agathis-dicotylous forest.
To trace the beginnings of "kauri forest" the outskirts of the association must be studied where the latter abuts on the contiguous Leptospermum shrubland, or the Pteridium, fernland. Information is also to be procured where regeneration or reinstatement is in progress, the kauri forest having been cut down or burnt. In order to find out the successions which the forest undergoes up to its socalled "climax", it is necessary to carefully investigate its interior, and to ascertain the light-demanding and shade-enduring capacity of the principal species. As regards the four leading trees, Agathis is strongly ligth-demanding, the two species of Beilschmiedia are strongly shade-tolerating and Weinmannia sylvicola grows vigorously both in sun and shade.
In many places where the forest and the Leptospermum shrubland meet, page 161there is a temporary association (the primary succession), made up of certain shrubland and forest species, including seedling and sapling Agathis, the composition of the association being somewhat as follows: — Cyathea dealbata, Blechnum Fraseri, Loxsoma Cunninghamii (local), Lycopodium densum, L. volubile, Gahnia xanthocarpa, juvenile, Podocarpus totara, Dacrydium cupressinum, Phyllocladus trichomanoides, Persoonia toru (specially characteristic), Knightia excelsa, Weinmannia sylvicola (juvenile), Melicytus ramiflorus, Leptospermum scoparium (dominant), L. ericoides (occasionally subdominant), Nothopanax arboreum, Leucopogon fasciculatus, Geniostoma ligustrifolium, Coprosma robusta, Olearia rani, Brachyglottis repanda and Senecio Kirkii. An interesting feature of this transitional forest is. the presence of young kauri and young podocarps in much greater abundance than these occur in the forest-interior.
Where kauri forest has been destroyed on the Waitakerei Hills it is frequently succeeded by Leptospermum scoparium which, after it has attained a considerable size, lets in sufficient light for light-requiring seedlings to gain a footing. The succession developing below the Leptospermum is much as already given. Phyllocladus trichomanoides is the commonest seedling tree, but there is plenty of Agathis. Certain floor-plants are antagonistic to the settlement of trees, e. g. Schoenus brevifolius, Gleichenia microphylla, Blechnum procerum, B. Fraseri and Lycopodium densum.
As the Leptospermum grows taller, much more light is let in and eventually the podocarps, kauri and other trees overtop it and it is doomed. Next the sapling forest-trees form a more or less close canopy and shadetolerating species enter the community, e. g. the species of Beilschmiedia, Dracophyllum latifolium and various shrubs and ferns.
The forest having matured, beneath its roof-canopy shade-tolerating trees have slowly developed, ready, at any moment, to replace any mature tree which falls (Fig. 36). On the other hand, there are no kauri seedlings in the dense forest. The adult kauris after some hundreds of years reach maturity, and by degrees they die and falling are replaced by the then slender trees of Beilschmiedia taraire and B. tawa, or it may be Weinmannia sylvicola, these forming the dominant members of the final succession (climax succession).
γ. Podocarp-broad leaved dicotylous forest of dry ground.
This class of forest is one in which broad-leaved dicotylous trees play a leading part in many places but in others certain podocarps occur either more or less evenly dotted here and there or make a close subassociation. In other words, the broad-leaved trees form the groundwork of the community within which the podocarps are inserted. In what follows the name of this class is shortened to "podocarp-dicotylous forest."page 162
As for the floristic composition of this group of associations, taking its whole range, it embraces almost all the 385 forest species, but in North Island and the north and north-west of South Island it is far richer in species than further to the south.
The following are the most common of the species which occur throughout this class of forest: — Hymenophyllum rarum, H. sanguinolentum, H. dilatatum, H. demissum, H. scabrum, H. flabellatum, H. tunbridgense, H. multifidum, H. bivalve, Trichomanes venosum, Eemitelia Smithii, Dicksonia spuarrosa, Polystichum hispidum, P. adiantiforme, Dryopteris pennigera, Asplenium adiantoides, A. bulbiferum, A. lucidum, A. flaccidum, Blechnum discolor, B. lanceolatum, B. procerum, B. fluviatile, Hypolepis rugosula, Adiantum affine, Histiopteris incisa, Polypodium Billardieri, P. grammitidis, P diversifolium, Cyclophorus serpens, Leptopteris hymenophylloides (Filices), Lycopodium Billardieri (Lycopod.), Tmesipteris tannensis (Psilotac), Podocarpus Hallii, P. ferrugineus, P. spicatus, P. dacrydioides, Dacrydium cupressinum (Podocarp.), Microlaena avenacea (Gramin.), Uncinia caespitosa, U. uncinata, U. leptostachya, Carex dissita (Cyperac), Rhipogonum scandens, Astelia nervosa var. sylvestris (Liliac), Dendrobium Cunninghamii, Earina mucronata, E. autumnalis, Pterostylis Banksii, P. graminea, Corysanthes macrantha (Orchid.), Urtica incisa (Urticac), Muehlenbeckia complexa, M. australis (Polygonac), Stellaria parviflora (Caryoph.), Clematis indivisa, Ranunculus hirtus (Ranun.), Cardamine heterophylla (Crucif.), Carpodetus serratus (Saxifrag.), Rubus australis, R. schmidelioides (Rosac), Coriaria arborea (Coriariac), Aristotelia serrata, Elaeocarpus Hookerianus (Elaeocarp.), Plagianthus betulinus (Malvac), Melicytus ramiflorus (Violac), Leptospermum scoparium, Metrosideros hypericifolia (Myrtac), Epilobium pubens, E, rotundifolium, Fuchsia excorticata (Onagrac), Schefflera digitata, Pseudopanax crassifolium var. unifoliolatum (Araliac), Hydrocotyle americana, H. novae-zelandiae (Umbel.), Griselinia littoralis (Cornac), Cyathodes acerosa (Epacrid.), Suttonia australis, S. divaricata (Myrsinac), Parsonsia heterophylla (Apocynac), Calystegia tuguriorum (ConvoL), Coprosma lucida, C. rotundifolia, C. areolata, C. rhamnoides, Nertera dichondrifolia (Rubiac), Erechtites prenanthoides (Compos.).
The forest under consideration extends, but not continuously, from the extreme north of North Island to the south of Stewart Island, but in the conception of such forest the subassociations of kauri forest, excepting the kaun subassociation, should properly be included. Leaving these out of j consideration, podocarp-dicotylous forest of the Auckland districts is altoj gether confined — swamp-forest being excluded — to the montane belt For the rest of North Island, the community originally occupied most of the soil, its continuity being broken only by areas where the edaphic conditions were unfavourable, particularly swamp and poor soil, but in this regard are many exceptions. In South Island, wide areas in the North-western and Fio d districts are occupied by a mixture of the forest under consideration page 163and that where Nothofagus dominates. On the other hand, there are pure podocarp-dicotylous forests in the Sounds-Nelson distrct, wihile in the Western district, from its northern boundary (R. Taramakau) for about 161 km., there are continuous pure forests of this class. On the east of South Island up to the Dividing Range, the rainfall of the North-eastern, Eastern and North Otago districts is not generally sufficient for any class of forest except semi-swamp forest to establish itself naturally, so in these districts forests (here including all classes except the last-named) occur only near the coast where mountainous (Seaward Kaikoura Mountains, Banks Peninsula), or in gullies, or sheltered places, at the base of the foothills (Mount Oxford, Mount Peel, Orari Gorge, Geraldine, Raincliffe, Waimate). In the South Otago district, however, the forest under consideration followed the coast-line (in most places it has been destroyed) and extended inland for a considerable distance in the south. Finally, lowland-montane Stewart Island in large part is occupied by the last-mentioned class of forest.
The life-forms of podocarp-dicotylous, forest have been considered when treating of forest in general.
(2.) The podocarp communities.
It already has been pointed out that the podocarp content of podocarp-dicotylous forest of dry ground varies from an occasional tree here and there to subassociations or associations of such magnitude that the term "podocarp forest" is no misnomer.
The leading podocarps which form more or less pure stands, and may make even associations, are (1.) the rimu (Dacrydium cupressinum), (2.) the totara (Podocarpus totara — at low levels, P. Hallii — at higher levels usually), (3.) the matai P. spicatus. Also the miro (P. ferrugineus) and the kahikatea (P. dacrydioides) are present but usually in much smaller numbers.
All the podocarps require a good deal of light for their early development and without such their growth is either extremely slow or impossible. P. totara is the most light-demanding and probably P. spicatus the least. Excess of wind, and bright sunshine, is unfavourable, but P. totara can tolerate far more of either than the other species. The astonishing number of nodules on their roots may be a factor in allowing these podocarps to occupy a class of soil not favourable for other tall trees (see E. H. Wilson, 1921:236 and Yeates, 1924:124), but judging from the distribution of the forest-trees in general this is hardly likely, and various species (e. g, Podocarpus nivalis, Dacrydium Bidwillii) may occupy xerophytic stations.
Rimu. (Dacrydium eupressinum) communities.
These are distinguished by the dominance of D. cupressinum, but other podocarps, and some broadleaved trees, are generally present.
The floristic character of the communities changes greatly in proceeding page 164from north to south, but this is dealt with when treating of the broadleaved dicotylous-tree communities.
Rimu forest, if it may be so called, extends from the high land south of Hokianga Harbour to Stewart Island, but there Weinmannia racemosa is present in equal or greater quantity. In the Auckland districts it does not occur at much below 600 m. altitude and even in the East Cape and Volcanic Plateau districts it is an upland community. In the Western district, at the present time, there is a great deal of rimu forest (Fig. 38) and the rimu is particularly tall, but not of excessive girth.
The physiognomy of the forest needs but little description, since that already given for New Zealand rain-forest in general applies quite well. The one striking and peculiar feature is dependent on the rimu itself with its long, straight trunk crowned by a rather small yellowish-green head of drooping-shoots.
Totara (Podocarpus totara, P. Hallii—at times) communities.
"Totara forest" is podocarp forest in which either P. totara or P. Hallii, or both, are dominant. The association is more xerophytic than that of Dacrydium cupressinum, the species being able to occupy dry ground or exposed positions where the latter would perish. At the same time, it must be pointed out that totara to a varying extent is nearly always present in podocarp-dicotylous forest and may equal the rimu in importance, in which case there would be a rimu-totara association.
At the present time it is not possible to state accurately the distribution of those forests where totara dominated or was present in abundance. Campbell-Walker (1877) in his account of forest distribution in New Zealand defined a "central or totara district", which included all the forest-lands of the East Cape, Volcanic Plateau and Ruahine-Cook districts. Now although his area as a whole certainly contained abundant totara (Podocarpus totara) yet there were also rimu, kahikatea and other forestcommunities and it is probable that the actual totara associations or subassociations were limited, as now, to the Volcanic Plateau from the north and west of Lake Taupo to the main-trunk line and to portions of the East Cape district. Elsewhere there were most likely rimu-totara and rimutotara-matai associations. In South Island totara forest appears to have been almost restricted to the Eastern district, although both species are of wide distribution and certainly occurred in considerable quantities in all the districts, except North Otago, while in the Western P. Hallii is the dominant species of the lower subalpine forest and in Stewart Island the only one.
At one time totara forest was much more widespread in the Eastern and North Otago districts than is now the case, but how long ago this was who can say? All we know is that totara logs lay on the ground in abundance in Central Otago and parts of Canterbury now treeless There is no page 165clue as to what caused the destruction of these ancient forests. The story goes that there was a vast forest-fire in pre-European days, but it is almost impossible to see how this could cause such wholesale and absolute destruction or why the fallen logs remained. Still more remarkable is the fact of a forest still, undestroyed, marking the limit of the western rainfall (Fig. 39). The climate, too, where those tree-remains lie, is distinctly too dry for the natural occupation by totara forest and I can only conclude with Speight (1911: 417) that the forest came into existence during a much wetter period than the present. This also would account for the rarity of Dacrydium cupressinum on Banks Peninsula, the wet post-glacial period leading to the replacement of a primitive Nothofagus forest by one with D. cupressinum dominant, but the latter during a subsequent drier period, in its turn, being replaced by Podocarpus totara.
Wherever totara forest is situated, its composition is similar to that of other adjacent rain-forest associations. A brief description of the association (now destroyed) at an altitude of some 300 m. near Taumarunui will give some idea of the forest as it occurred in the most extensive area of its distribution.
The soil was pumice mixed near the surface with a good deal of humus. Besides the dominant P. totara there was much P. spicatus. The podocarps formed the upper tier of foliage; their straight, columnar trunks were a striking feature, those of P. totara bearing but a scanty covering of bryophytes, its outer bark hanging in long strips. Some of the other foresttrees were Knightia excelsa, Beilschmiedia tawa (abundant), Carpodetus serratus, Weinmannia racemosa, Pennantia corymbosa, Alectryon excelsum, Hoheria sexstylosa, Melicytus ramiflorus, Fuchsia excorticata, Nothopanax arboreum, Suttonia australis, Olea montana and Brachyglottis repanda. Most of the above also occurred as shrubs or young trees of undergrowth in which likewise amongst others, were the following: — Paratrophis microphylla (very common), Aristotelia serrata, Myrtus pedunculata, Schefflera digitata (dominant in some places), Coprosma rotundifolia and Rhabdothamnus Solandri. In some gullies of this particular community were hundreds of young plants of Schefflera 30 cm. or so high, associated with various ground-ferns, especially Dryopteris pennigera. The chief tree-fern, liane and epiphyte respectively were Cyathea dealbata, Metrosideros hypericifolia and Astelia Solandri. Bryophytes and Hymenophyllaceae were plentiful.
The forest of Banks Peninsula, now almost gone, originally consisted largely of a Podocarpus totara association, but in places P. spicatus was dominant, except on certain slopes facing north and in the subalpine belt. In the deeper gullies, where there were permanent streams, was a wealth of ferns including Hymenophyllaceae but according to Armstrong's list (1880: 346), and to recent observations, only 2 or 3 species of the latter were at all plentiful. On many slopes and in the waterless stony gullies, the forest page 166was of a dry character, as evidenced by the abundance of Pellaea rotundifolia and Polystichum Richardi. Certain negative features help to define the forest as a whole. Thus the following, some of which extend much further to the south in the west of the island were absent: — Trichomanes reniforme, Lindsaya cuneata, Freycinetia Banksii, Astelia Cunninghamii, Ascarina lucida, Weinmannia racemosa, Metrosideros lucida, Metrosideros scandens, Nothopanax Edgerleyi and Suttonia salicina, while Rhopalostylis, though present in a few places, was generally wanting. On the other hand, the elsewhere rare liane Senecio sciadophilus is still abundant, Tetrapathaea tetrandra is not uncommon, the rare Teucridium parvifolium is plentiful, the semiliane Microlaena polynoda is fairly frequent and Cyathea medullaris, Australina pusilla, Corynocarpus laevigata, Pseudopanax ferox and Olearia fragrantissima were occasionally present.
Matai (Podocarpus spicatus) communities.
To what extent Podocarpus spieatus formed communities, more or less pure throughout its range, it is now impossible to state. It is rare in many forest-areas and, even where common, hardly forms even a colony.
A portion of the Mount Peel podocarp forest seems according to H. H. Allan (1926: 40, 41) to be an exception to the above statement. Thus for the forest of the upper terrace flats he writes "In general P. spicatus is dominant with P. totara and P. dacrydioides in lesser amounts". On the driest ground P. totara dominates. Also, even yet, a P. spieatus association exists on certain parts of the Southland Plain, the trees close together, rather stunted and their crowns more spreading than usual. According to Roberts (Kensington 1909: 52), P. spieatus forms small societies on the flats of nearly all the Westland rivers as far south as the Cascade River. He mentions also stunted trees, 2.4 m, diam. with "short bunched trunks dividing into several long, heavy branches".
P. spieatus now extremely rare in Stewart Island, must have been dominant or subdominant for the remains of trees, probably dead for 300 to 400 years, lie abundantly upon the forest-floor, but frequently embraced by the trunk, originally the root, of a mature Weinmannia racemosa (Fig. 29).
(3.) The broad-leaved dicotylous tree communities.
The forests here dealt with are those occasionally composed almost entirely of broad-leaved dicotylous trees, but generally with more or less podocarps present, which usually play a minor part, so far as tall trees are concerned but, as already shown, they may make communities of different grades within the general forest-mass or even compose the greater part of the latter; or, again, podocarps and dicotylous trees be about equal in number. There are, indeed, no hard and fast lines, so that much of the classification proposed by any one can hardly fail to be of an artificial character, or it may be detailed to excess and useless for practical purposes.page 167
The forest communities under consideration, unlike those of kauri or podocarp, are composed of dominant trees which when young are either shade-tolerating or epiphytic, so that, under certain circumstances they are able to replace the conifers: this is gone into under another head. Thus, the forests they eventually govern are climax successions.
Obviously the distribution of these broad-leaved dicotylous forests are those of lowland-montane forest in general as already described. At one time they occupied an area far greater than now, owing to their having been destroyed, year by year, over wide areas to give place to artificial grassland as described in Part III, whereas forests containing an abundance of podocarps — swamp-forest excepted — are removed much more slowly through saw-milling and their damaged remnants may persist for many years.
Unlike the podocarps, which thrive equally well from the north of North Island to Stewart Island, the dominant broad-leaved trees differ in their frost-tolerating capacity, so that the communities are climatic.
Tawa (Beilschmiedia tawa) communities.
The dominant tree is B. tawa already discribed in Chapter II of this section. The undergrowth and species are those of subtropical rain-forest of North Island and the Sounds Nelson district.
It extends from the north of North Island to the Sounds-Nelson district, In North Island it ascends to 600 m., or more. Cook Strait notwithstanding, the forests on both sides of this apparently natural obstacle to distribution are of similar composition — a minor distinction being the occasional presence in Sounds-Nelson of the herbs Poranthera microphylla and Scutellaria novaezelandiae.
Frequently, but in the southern part of its range more especially, tawa forest comes into contact with Nothofagus forest, but the latter, in general is confined to the more barren, dry slopes or ridges, while the tawa is in the gullies and the rich alluvial soil of the flat ground.
Seen from a distance, the tawa trees are of a rather unpleasing grey colour; nevertheless, at a close view with the crowns of tree-ferns peeping out of the dense undergrowth with its vivid greens, the scene is pleasing enough.
Unlike the outskirts of kauri or podocarp-dicotylous forest and Nothofagus forest, few seedlings of the dominant tree are to be seen there, but under the forest-roof or the canopy of small trees of the next story, in open places there will be seedlings in their hundreds; tawa saplings, too, are a frequent feature of the undergrowth.
1 1) A beautiful shade-demanding tree of slow growth, 6 to 12 m. high with darkgreen, glossy, serrate, narrow-lanceolate leayes ± 12 em. long, arrenged in wher s near the apices of the branches and bearing in early summer abundance of white flowers about 2.5 diam. arranged in terminal panicles.
Kamahi (Weinmannia racemosa) communities.
These are distinguished by the dominance of W. racemosa (already described in Chapter II of this section), or there may be a good deal of Dacrydium cupressinum dotted about or in colonies, while there are almost always some of the other podocarps.
Weinmannia forest is of wide distribution and extends from the Mamaku Plateau in the north to Stewart Island, thanks to the frost-tolerating capacity of the tree and its ready establishment. Thus, as already explained it rarely commences life as a terrestial plant, but begins as an epiphyte upon a tree-fern stem, or as a seedling upon some fallen moss-covered trunk. The epiphytic habit is most advantageous in dense forest, for not only does the seedling escape competition with the floor plants, but is in a better position than most with regard to light. As the seedling grows into a tree its roots embrace its host or the fallen tree and eventually growing together function as the base of the trunk (Fig. 29.). Probably Weinmannia racemosa is the commonest massive forest-tree in New Zealand, though most who work in the forest would select Dacrydium cupressinum for that honour, but rather by reason of its being a timber-tree with which they are specially concerned than because of its relative abundance in forests generally. Frequently, valuable so-called "rimu" milling-forest contains twice as much or considerably more kamahi then rimu.
Weinmannia racemosa forest is both lowland and montane, the species itself ascending into the subalpine belt. As for its composition, that of North Island, and the north-east of South Island (SN.), is similar to that of the podocarp-dicotylous forests already dealt with. But in the Northwestern and Western districts, certain species rare or wanting elsewhere enter in, particularly Ascarina lucida2 and Quintinia acutifolia3 as also much juvenile Elaeocarpus Hookerianus of divaricating form4 Generally there is more or less Dacrydium cupressinum or indeed it may dominate.
1 1) A rather smaller tree than Ixerba with pale, rather thin, greenish-yellow, narrowoblong leaves ± 12 cm. long and their margins crinkled.
2 Ascarina lucida is a low, bushy-tree with almost black bark and green, extremely glossy, oblong serrate leaves 2.5 to 5 cm. long.
3 Quintinia acutifolia is a small, rather fastigiate tree of slender habit and abundant leaves of oblong type 7.5 to 12 cm. long, yellowish with green veins and midrib. The flowers are pale lilac and arranged, in many-flowered racemes about 10 cm. long.
4 Other important shrubs etc. of the undergrowth are small Podocarpus ferrugineus, Carpodetus, juvenile Pseudopanax crassifolium var. unifoliolatum, Schefflera digitata and Coprosma foetidissima.
From any lowland-forest association of the eastern and southern parts of South Island and from that of Stewart Island the association is distinguished by the presence in abundance of the lianes Freycinetia and Metrosideros scandens and the epiphyte Astelia Cunninghamii and by the absence of Pittosporum eugenioides and P. tenuifolium. Bryophytes, though not building cushions, are abundant enough to be of prime physiognomic importance, especially Weymouthia mollis and the larger W. Billardieri hanging from slender branches or twigs and, on the forest-floor, Plagiochila glgantea and other species of the genus, extensive mats of the pale-green Trichocolea tomentella frequently glistening with drops of water and species of Schistochila. Ferns are extremely abundant on the forest-floor including colonies of Gleichenia Cunninghamii (Fig. 40.), abundant Leptopteris superba and Blechnum nigrum (in the darkest places).
In the South Otago and Stewart districts, the Dacrydium-Weinmannia forest is much the same for both districts, so that one description will suffice for the two. Generally some Metrosideros lucida is present and, at times, in such abundance, especially near the sea or on hillsides, that it equals the other two trees.
The dominant shrub of the undergrowth is Coprosma foetidissima and C. Colensoi and C. Astoni are common as also the hybrids between the three. Rhipogonum is the only important liane. Asteliads, as epiphytes, are absent but Dendrobium Cunninghamii is still plentiful and Griselinia littoralis replaces its epiphytic relative of the north. Hemitelia is the prevalent tree-fern, and, as ground ferns Blechnum discolor, B. procerum and at times, Leptopteris superba make extensive colonies. In the north of the South Otago district Weinmannia was virtually absent in the originally extensive forest-area. Pittosporum tenuifolium, P. eugenoides and Nothopanax arboreum are absent in Stewart Island, the place of the first-named being filled by P. fasciculatum and of the last by N. Colensoi.
Northern rata (Metrosideros robusta) forest.
A forest or a minor community of this class is distinguished by Metrosideros robusta — that huge tree of most irregular form, owing to its epiphytic origin — its spreading limbs bearing veritable gardens of shrubs, ferns, a pendent lycopod, and one or two great asteliads. Its composition is similar to that of the rimu forest which it has replaced or is replacing, as will be seen below. Weinmannia racemosa and Beilschmiedia tawa are usually important trees. The base of the northern-rata will be covered with various Hymenophyllaceae (e. g. Trichomanes reniforme and Hymenophyllum flabellatum in dense mats), bryophytes (including cushions of Leucobryum candidum) and many seedling trees and shrubs. Where the forest is montane, or upper lowland, there probably will be a good deal of the beautiful Senecio Kirkii on the base of the rata, its leaves soft, dark-green and fleshy and the snow-white flowerheads, each 3 cm. diam., in great abundance.
Southern-rata (Metrosideros lucida) forest.
This is distinguished by the dominance of M. lucida, but frequently there is an equal amount of Weinmannia racemosa, and such would be "southern rata-kamahi forest". The community belongs esentially to South Island, with its chief development in the North-western, Western, South Otago, Stewart and perhaps Fiord districts;, being in the first two districts an upper lowland and montane forest and in the others frequently coastal and semi-coastal as well as montane.
In the Western district at above 450 m. altitude M. lucida becomes dominant and the lowland podocarps gradually decrease in numbers. Weinmannia racemosa is so plentiful in places as to dominate. Quintinia acutifolia is conspicuous through its somewhat fastigiate habit as a sapling and the yellowish leaves blotched with purple but pale beneath. Many of the lowland shrubs and ferns are present. The undergrowth is dense, especially in gullies. Bryophytes (species of Gottschea, Schistochila, Aneura, Mniodendron, Plagiochila, Lembophyllum &c.) and Hymenophyllaceae abound. Leptopteris superba forms extensive colonies.
At the Franz Josef Glacier, the terminal face of which descends to 213 m., the southern-rata association comes on to the ice-worn rocks at a few metres from the ice on either side of the glacier. The forest here, the roof of which has the characteristic billowy appearance, consists principally of the following: — Metrosideros lucida and Weinmannia racemosa (the dominant canopy trees), Carpodetus serratus, Coriaria arborea, Aristotelia serrata, Hoheria glabrata, Melicytus ramiflorus, Pseudopanax crassifolium var. unifoliolatum, Schefflera digitata, Griselinia littoralis, Hebe salicifolia, Coprosma lucida, Olearia arborescens and 0. avicenniaefolia. The pteridophytes include Hemitelia Smithii (tree-fern, but here of low stature), several Hymenophyllaceae, Hypolepis tenuifolia, Histiopteris incisa, Blechnum procerum, B. lanceolatum, Asplenium bulbiferum, A. flaccidum, Polystichum vestitum, Polypodium diversifolium, P. Billardieri and Lycopodium volubile.
In Stewart Island, southern-rata forest, except close to the shores of the inlets, or on small islands therein, is a montane community. In exposed places the trunk may be prostrate or semi-prostrate as in Lord Auckland Island. The undergrowth is that of ordinary Stewart Island forest.
On Mount Peel (E.) according to H. H. Allan (1926: 44) M. lucida forms a subassociation on "rocky knolls and slopes with a western aspect", the tree attaining a height of about 7 m. The undergrowth is sparse and is partly made up of Cyathodes acerosa, Coprosma parviflora, C. rhamnoides and Suttonia australis.
Forest communities off minor importance.
Rewa rewa (Knightia) association is by no means a common community. It is recognized even at a distance by the fastigiate habit of the dominant K. excelsa with its page 171dark-coloured foliage. The association occurs in various parts of North Islands on very steep, barren hill faces, and on the sides of deep, narrow gullies.
Near the Rotoma Saddle, on the steep ridge beyond which lies the R. Tarawera, there is a fine example of a Knightia association. Mixed here and there with the Knightia are occasional trees of Beilschmiedia tawa, but Leptospermum ericoides is far more abundant. As for the undergrowth, it is that of ordinary forest of the vicinity but obviously it cannot be rich in bryophytes.
The puriri (Vitex lucens) association is well-marked and distingusihed by the dominance of V. lucens. It was evidently once common on volcanic soil in the North Auckland district, but the value of the puriri for fencing posts &c, has led to a great reduction in its area. Vitex lucens itself is a most handsome tree, 12 to 18 m. high with a massive, freqently irregular trunk and much-spreading rounded crown with large digitate leaves on petioles some 10 cm. long, and 3 to 5 dark-green, smooth, glossy, oblong leaflets, the largest measuring 7.5 cm. long, or more. Besides Vitex the following were common members of the association: — Podocarpus totara, Beilschmiedia taraire, Dysoxylun spectabile and Melicytus ramiflorus. Asteliads were in abundance on the puriri. This account is inadequate, but I have seen only much-reduced and damaged examples of the association.
On river-banks there are communities of small trees; here associations on deep alluvial soil are alone noted, those of stony river-bed being dealt with further on under another heading. The associations often form a fringe along the bank - which may or may not be connected with an adjacent forest-mass.
The following are the principal species of the above habitat for all New Zealand proper: — Blechnum procerum, Dryopteris pennigera, Cordyline australis, Paratrophis microphylla, Muehlenbeckia australis, Beilschmiedia tawa, Carpodetus serratus, Pittosporum tenuifolium, P. Ralphii, Ackama rosaefolia, Rubus schmidelioides and its var. coloratus. R. subpauperatus, Edwardsia, tetraptera, E. chathamica, E. microphylla, Melicope simplex, Coriaria arborea, Pennantia corymbosa, Aristotelia serrata, the species of Hoheria (subgen. Euhoheria), Plagianthus betulinus, Hymenanthera dentata var. angustifolia, Melicytus ramiflorus, M. micranthus, Myrtus bullata, M. obcordata, X M. bullobcordata, Leptospermum scoparium, L. ericoides, Fuchsia excorticata, F. perscandens and the hybrids between the last two, Nothopanax arboreum, N. anomalum, Pseudopanax crassifolium var. unifoliolatum, Suttonia australis, the species of Parsonsia and their hybrids, Teucridium parviflorum, Hebe salicifolia in a wide sense, Coprosma robusta, C. propinqua, X C. prorobusta, C. rotundifolia, Olearia Hectori and 0. fragrantissima.
The species of Hoheria and Edwardsia according to their distribution and Plagianthus betulinus are specially characteristic. In the East Cape page 172district E. tetraptera (little more than a shrub), Pittosporum Ralphii and Hoheria sexstylosa are companion-plants. H. dentata var. angustifolia (may be an endemic species) is characteristic of the river-bank association on the Southland Plain and Olearia Hectori may occur also. The river-bed forest of the Western district, described further on under another head, is a closelyrelated association, but one with a quite different life-history.
(4.) The life-history of podocarp-dicotylous broad-leaved forest of dry ground.
The early beginnings of the forest under consideration have already been explained in the general introduction to forest, so far as my limited knowledge of the subject goes. Also it has been pointed out that it is not possible to give an account of the various successions, for with the exceptions dealt with below, it seems to be rather a gradual process, except in the earlier stages, leading up to a climax than a series of temporary associations terminating in such a climax — but this statement, opposed to i accepted ecological teaching, may be due perhaps to my ignorance rather than to the real facts of the case.
As already seen, the two distinct groups of associations or subassociationis which stand out are those composed respectively of podocarps and broadleaved dicotylous trees. Owing to the podocarps being light-demanding they become members of the forest earlier than the bulk of the other trees. Also, theoretically, podocarp forests should have been in existence long before dicotylous trees were evolved. Be this as it may, podocarps, along with certain dicotylous trees and shrubs, are important members of the youngest forest associations (successions). Notwithstanding their slow growth, and because it is little if any slower than that of the tall or medium-sized dicotylous trees, the podocarps reach a height which cannot be overtaken by the later arriving dicotylous competitors, e. g. Beilschmiedia tawa. Thus, in young forest, there will always have been a strong podocarp element and, in the early history of those forests of which the present are the direct descendents, the podocarps would be supreme. JSTor, even yet, are they readily supplanted by their rivals, for most of the species can exist as "lingerers" for many years, ready to grow with considerable vigour as soon as light is let in to the interior of the forest through the falling of some over-mature tree.
When in the course of its development, the light within the young forest becomes more subdued, the various shade-tolerating trees, shrubs, and ferns put in an appearance. These, so long as the undergrowth does not become too dense, even for them, will grow at a fair pace and, as low trees &c, thrive beneath the forest roof. By degrees, too, with decrease of light, the shade-demanding species will enter the community.
Within the forest there is great competition between the species. Where page 173there is sufficient light, colonies of tree-ferns (these are by no means purely shade-plants) are readily established, and these forbid the presence of seedlings through the dense shade they cast. Favoured by rather dry ground, wide breadths of open forest-floor are rapidly occupied by colonies of Blechnum discolor which are hostile to the incoming of all seedlings. Certain lianes, particularly Rhipogonum scandens, destroy the shrubs and young trees which they embrace and entanglements of naked liane-stems result.
In many North Island forests, hundreds of seedlings of Beilschmiedia tawa are to be seen in the more open places, thanks to the high germinatingpower of the seeds, the large fruits of which lie where they fall, and the shade-tolerating capacity of the young plants. With but few competitors, the advantage is greatly on the side of the young tawas, some of which grow into saplings; indeed, sapling tawas often form o considerable percentage of the undergrowth, while, beneath them, there may be seedling tawas in profusion. Forest of this class is potential tawa forest. In fact, every transition can be observed from pure podocarp forest to that where the podocarps are altogether wanting over a wide area, and where nearly all the tall trees are Beilschmiedia tawa.
In certain North Island tree communities the tawa is far less in evidence, but the podocarps — particularly Dacrydium cupressinum (rimu) — have an openly-declared enemy in Metrosideros robusta (northern-rata), which as an epiphyte — thanks to its minute seeds — so readily gains a footing on the boughs of the rimu. Very soon the humus made by the epiphytic asteliads &c, that is the soil on which the northern-rata's seeds have germinated, becomes insufficient for the rapidly-growing shrub and this puts down roots which, in course of time, reacn the ground and eventually crush and kill their host, and growing together form an enormous trunk irregular in shape. This replacement of rimu forest can be seen at every stage of progress in many forest-areas up to the southern limit reached by the northern-rata.
Within the forest a similar phenomenon takes place when tree-ferns are attacked by Nothopanax arboreum (also the other small trees of this genus) as an epiphyte and colonies of this small tree are frequent which have originated in this manner.
The establishment of a Weinmannia racemosa (kamahi) climax takes place in somewhat the same manner as that of the semiepiphytes cited above. The tree itself begins life, (1.) as a seedling upon the ground, in which case it rarely reaches beyond the shrub-stage, (2.) as an epiphyte on the trunk of a tree-fern, and (3.) the seedling develops upon a fallen tree-trunk. It is the last two cases which concern the incoming of the Weinmannia climax-association, for, in both, the light is sufficient for the fairly rapid development of the young tree, both the fallen trunk and the tree-fern indicating an open roof-canopy.page 174
On Banks Peninsula and certain other places where sapling tall trees ready to replace the podocarps are few in numbers, it seems probable that the climax-forest is made up of various shade-demanding or shade-tolerating small trees.
On the slopes of gullies tall trees are absent. There is sufficient illumination for light-demanding species, and such portions of a forest may be considered migratory climaxes. In such, Fuchsia exorticata plays an important part; other common members of the community are Rhipogonum scandens, Muehlenbeckia australis, Weinmannia racemosa (as a small bushy tree), Aristotelia serrata, Melicytus ramiflorus and Schefflera digitata.
δ. Podocarp-dicotylous broad-leaved tree forest of wet ground.
Though taken here together for convenience' sake two classes of different ecological status are included, the one forest of wide distribution occupying ground of a swampy character and the other that of a boggy nature, more or less sphagnum being usually present, and of local and restricted distribution. To the first category belongs kahikatea (Podocarpus dacrydioides) semi-swamp forest, and, to the second, communities called collectively "bog-forest" — a misnomer, to some extent, since one association occurs on fairly dry ground — where the small podocarps, Dacrydium Colensoi or D. intermedium, dominate.
Kahikatea (Podoearpus dacrydioides) semi-swamp forest.
This class of forest is distinguished by the strong dominance of P. dacrydioides which may be almost the sole tree.
The flora consists of about 138 species which belong to 41 families and 69 genera but Filices 32 species, Rubiaceae 13 species and Cyperaceae 10 species are the only families of floristic importance and of genera Coprosma heads the list with 11 species only.
The species belong to these 3 categories (1.) those which hardly occur in any other community, here termed "semi-obligate"; (2.) those which are very common but thrive equally well in dry ground forest, here termed "facultative"; and (3.) those which are comparatively rare and occur usually in the driest stations such forest can provide. The following is a list of the more common species belonging to classes (1) and (2): — (semi-obligate) Laurelia novae-zelandiae, Eugenia maire, Coprosma tenuicaulis, C. rigida; (facultative) Dicksonia squarrosa, Dryopteris pennigera, Asplenium bulbi ferum, Blechnum procerum, B. fluviatile, Podocarpus dacrydioides, P. spicatus, Freycinetia Banksii, Microlaena avenacea, Gahnia xanthocarpa, Rhipogonum scandens, Astelia nervosa var. grandis, Rhopalostylis sapida, Paratrophis microphylla, Elatostema rugosum, Muehlenbeckia complexa, Wintera axillaris, W. colorata, Carpodetus serratus, Rubus schmidelioides, Melicope simplex, Melicytus micranthus, Leptospermum scoparium, Myrtus pedunculata, Nothopanax anomalum, Schefflera digitata, Pseudopanax crassi-page 175folium var. unifoliolatum, Hydrocotyle americana, Suttonia divaricata, Geniostoma ligustrifolium, Coprosma robusta, C. spathulata, C. rotundifolia and C. areolata.
Kahikatea forest occurs in the lowland belt from the extreme north of North Island to Foveaux Strait, but is wanting in the North Otago district and Stewart Island (merely a few trees of Podocarpus dacrydioides).
The life-forms of the formation, taking all the species together with the number of species to each are as fellows: — trees 31, shrubs 22, lianes 15, epiphytes 27 (ferns 16), herbs &c. 12, grass-like plants 11, herbaceous ferns 12, earth-orchids 6, parasites 2.
The forest under consideration is distinctly a lowland community which attains its greatest development near those large rivers which overflow their banks, though small typical areas occur anywhere on low-lying swampy ground even, indeed, in dune-hollows. Although there are still wide areas of virgin forest, the great demand of late years for the timber of P. dacrydioides for butter-boxes has led to great destruction and in a few years, except in localities difficult of access, the association will be eradicated and the land it occupied turned into pasture, for the soil it occupies, if it can be drained at a reasonable price, is eminently suitable for dairy farms. Like most formations of a wide range, there is considerable floristic change in proceeding from north to south. Unlike rain-forest in general, kahikatea forest is not dependent on a considerable rainfall, nevertheless it shows the general characters of the true rain-forest — but it can hardly be included as an association of such and is here dealt with as a distinct formation.
The term "semi-swamp" defines the ecological conditions of the forest Many parts of the floor are too wet for most forest-species, for pools usually abound, out of which project the moss-covered pneumatophores of Laurelia should that species be present. But the many fallen tree-trunks offer a position where non-swamp species can be established. Also., the floor, in part, is subject only to periodical flooding, and in places it is always comparatively dry; indeed, fairly typical kahikatea forest is to be found on comparatively well-drained land where forest of dry ground might be expected (Fig. 23). Of course, the conditions for epiphytes are the same as in dry-ground forest, except that some of the trees such specially favour are absent, e. g., Metrosideros robusta.
The physiognomy of the formation is unlike that of any other New Zealand forest. The innumerable kahikatea trees stand up, side by side, straight and unbranched for three-fourths of their length, or more, looking like masts of the sailing-ships of other days. Their great height (over 30 m. is common but 60 m. has been recorded) and the closeness of their growth masks their diameter, but many may exceed 1.2 m. The head of branches and foliage is most scanty but in North Island semi-swamp forest it bears a surprising number of huge clumps of Astelia Solandri (Fig. 41). Within page 176the forest there is not the usual dense undergrowth of drier subtropical forest, but this is far from being wanting on the drier ground. The most striking feature of the shrubs is the divaricating-form of so many, some of that habit being, indeed, virtually confined to semi-swamp forest. Also, in North Island and the north of South Island, tree-trunks hidden by Freycinetia, and the ground closely covered by this liane, are a striking feature.
In order to gain a fair idea of the associations a brief description of certain pieces of forest occurring at different latitudes is next presented.
Near the Northern Wairoa River the trees were more than 24 m. high with their trunks altogether hidden in many cases by Freycinetia. The ground in many parts was quite covered with the last-named together with much Dryopteris pennigera and Carex virgata, the whole forming a close undergrowth out of which rose vast numbers of Rhopalostylis sapida, 9 to 12 m. high, their trunks naked and crowns sometimes touching. The general low tree and shrub vegetation was sparse and consisted chiefly of Paratrophis microphylla, sparingly-branched Beilschmiedia taraire, twiggy Carpodetus serratus, slender Dysoxylum spectabile, small Eugenia maire, low Laurelia novae-zelandiae, Schefflera digitata and some Coprosma rigida and C. spa-thulata. In places there was a moderate amount of Rhipogonum. The leading ferns were Cyathea dealbata and C. medullaris (a little), Blechnum procerum, B. filiforme, Polypodium pustulatum (on raised tree-roots) and Asplenium bulhiferum. The soil was extremely wet; pools of water abounded; there was much soft mud. Podocarpus dacrydioides was much buttressed and its roots often raised high above the ground.
On the Manawatu coastal plain (RC.) semi-swamp forest was originally greatly in evidence. Happily a few remnants in an almost virgin state are still to be seen. Thus, in a piece of such forest not far from Levin (fortunately a Scenic Reserve), there is a tangle of roots on the wet floor and a dense jungly undergrowth, hardly penetrable, which consists principally of the following: — slender stems of Freycinetia, small Dicksonia squarrosa, here and there sapling Laurelia, Carpodetus with naked stems for their lower two-thirds, but above with short flexuous branches. Suttonia australis somewhat similar in form, many black stems of Rhipogonum scandens, erect, sparsely-branched Geniostoma, many small ferns on the raised lateral roots of the trees, tussocks of Gahnia xanthocarpa, much large-leaved Asplenium bulbiferum, juvenile Rubus schmidelioides (on floor and tree roots) and in greater or smaller numbers Blechnum procerum, Asplenium adiantoides, XJncinia ferruginea, Melicytus ramiflorus, Eugenia maire, Metrosideros hypericifolia (on roots), Suttonia salicina and Coprosma grandifolia. Where the ground is wet rise up huge, much-buttressed trunks of Laurelia, its farextending roots putting forth abundant pneumatophores. Finally, there are the straight trunks of Podocarpus dacrydioides and their crowns full of Astelia Solandri looking like huge birds' nests.page 177
In the North-western district the undergrowth may consist largely of Wintera colorata, Carpodetus serratus, Nothopanax anomalum, Pseudopanax crassifolium var. unifoliolatum, Myrtus pedunculata, Coprosma tenuicaulis and C. rotundifolia. As ground plants, tall Blechnum procerum, Astelia nervosa var. sylvestris and Microlaena avenacea are everywhere and Nertera dichondraefolia and N. depressa are common. The slender trunks of the smaller trees and shrubs are thickly clad with liverworts. Dicksonia squarrosa is the dominant tree-fern and there is some Hemitelia Smithii.
In the Western district very large areas of semi-swamp forest occur on the coastal plain. The trunks of Podocarpus dacrydioides are draped with Freycinetia Banksii and on their boughs are masses of epiphytes1 Blechnum procerum is abundant in the undergrowth and reaches 1.5 m. in height. All the species cited for North-western semi-swamp forest are present and a number of others, all of which are doubtless more or less common in the forest just mentioned. One of them, Coprosma tenuicaulis, extends as far south as Ross, and probably further.2
In the Eastern district, at the time of settlement by the European, there were several areas of kahikatea forest at no great distance inland, but all except a small piece near Christchurch3 were cut down years ago. At an earlier date, the extensive swamps, now farmland, were occupied by forest, for they contained abundant remains of trees. The above treeassociation, the last of its special kind in the world, is still quite vigorous, and although it has been drained, seedling Podocarpus dacrydioides are produced by thousands. The species number 694 (trees 22, shrubs 12, lianes 12, parasites 3, herbs 17, ferns 13) and there are 2 hybrid swarms5 Besides the dominant P. dacrydioides there is abundance of Elaeocarpus Hookerianus and some E. dentatus, P. spicatus and P. totara are also present. Paratrophis microphylla is very plentiful. The association is no longer primitive, since it contains certain non-forest species, others of exotic origin, and the relative abundance of the species of the undergrowth is certainly very different from what is was originally.
1 Astelia Cunninghamii, Dendrobiuni Cunninghamii, Lycopodium Billardieri and its var. gracile (probably a species), Asplenium adiantoides.
2 Polystichum vestitum, Leptopteris superba, Hemitelia Smithii, Wintera colorata Rubus schmidelioides, Melicytus lanceolatus, Coprosma parviflora, C. foetidissima.
3 Part of the forest was generously given "to the people a few years ago by its owners, the Deans family, who had religiously preserved it from the earliest days of settlement.
4 An estimate somewhat less than given in Riccarton Bush (Christchurch N. Z., 1924), a booklet published by the Riccarton Bush Trustees, since the hybrids are dealt with as species, and certain species not belonging to the forest proper are included.
5 There is a wonderful polymorphic swarm of Coprosma propinqua × robusta, which has evidently come into being since some of the undergrowth was removed. Also there are many distinct hybrids between Fuchsia excorticata (a tree) and F. perscandens (a liane).
Life-history of semi-swamp forest.
During the continuous occupation of permanent, stationary shallow-water by plants, as described later under the head "Swamp Vegetation", there is a gradual procession of events, the species by their death and decay slowly converting the substratum into loose, dark-coloured soil which, by degrees, becomes occupied by a shrubassociation. Later, seedling trees enter the association of which perhaps the first-comer is Cordyline australis which can build up that special community, here designated Cordyline swamp-forest. Though, undoubtedly, such, in some places, is truly indigenous, it is now generally an indigenousinduced community arising after kahikatea forest has been felled, and, in such a case, there will be a good deal of Typha. Indigenous Cordyline swamp-forest of North Island is distinguished by the presence of Astelia nervosa var. grandis in abundance, and the divaricating-shrubs Melicytus micranthus, Nothopanax anomalum, Coprosma tenuicaulis and C. rigida.
The succession just described, is not always the beginning of kahikatea forest for, as soon as the ground is dry enough for its seeds to germinate and the seedlings to grow, Podocarpus dacrydioides puts in an appearance, it being essentially light-demanding. After this, or at the same time, all those members of the final community which are light-tolerant and can become established on the wettest ground, by degrees, will come in and, later, those which live on the trees themselves, or which can grow only on fairly dry ground or require considerable shade.
Semi-swamp forest may also arise from the frequent flooding of dicotylous-podocarp forest, in which case only the water-tolerating species will persist. Between pure kahikatea forest and the adjacent dry forest, if such be present, are various intermediate combinations, and it is rather the tall trees of the latter which are wanting than the plants of the undergrowth, since although pools of water lie everywhere, there is always more or less moderately dry ground. Moreover, fallen logs cumber the ground and these provide a station for the non-swamp tolerating species as also a place where seeds can germinate. In short, the distribution and combination of species within the forest is regulated by the water-content of the soil.
Bog-forest and related communities.
Under this head come those communities, generally of small extent, where one or other of the lesser podocarps dominate. For the lowlands there are two groups of associations, dominated respectively by Dacrydium Colensoi and D. intermedium.
Silver-pine (Dacrydium Colensoi) bog-forest is a small group of associations where D. Colensoi1 is usually present in considerable quantity. Sphagnum jnay or may not be a member of the association.
1 Dacrydium Colensoi is a small cupressoid tree from 6 to 15 m. high with a pyramidal head of slender branchlets covered with scale-like, densely imbricating, very small, thick leaves and a straight trunk ± 60 cm. diam. The juvenile form is furnished with spreading juniper-like, narrow-linear subulate leaves ± 1.2 mm. long, while the semi-juvenile is longpersisting and the leaves are triangular, flat, ± 4 mm. long and more or less distichous. The type was collected from a tree growing in the North Auckland district, which may not be identical with the tree under consideration here, which is D. westlandicum T. Kirk.
The community occurs, (1.) as a montane association in the Volcanic Plateau district either on the flanks of Mount Ruapehu or in its neighbourhood, and (2.) as a lowland association to the west of the Southern Alps.
The montane bog-forest of the Volcanic Plateau differs in composition in various localities, but its structure and floristic content is usually somewhat as follows: — Dacrydium Colensoi is dotted about, its trunk slender and from 30 cm., or less, to about 50 cm. diam., and its crown fastigiate; there is also small Libocedrus Bidwillii, stunted Podocarpus Hallii and irregularly-branched Phyllocladus alpinus, as a small tree, its spreading branches deeply covered with bryophytes. The undergrowth is frequently dense; it consists of Phyllocladus alpinus, tussocks of Gahnia pauciflora, Astelia nervosa var. sylvestris, bushy Weinmannia racemosa, Myrtus pedunculata, Coprosma foetidissima, C. Colensoi and Alseuosmia quercifolia or an unnamed species. The floor is irregular and on it are many bryophytes, together with Enargea parviflora and Libertia pulchella. Usually, the trees are not more than 12 m. high and the undergrowth 3 in. Generally, the ground is wetter than that of the surrounding forest in which it forms isolated areas, and it may be very wet indeed and with more or less sphagnum.
The silver-pine associations of the Western district can hardly be properly described at the present time, since the greater part has been much modified by the saw-miller1 Therefore I am limiting my account to one piece of virgin forest I had an opportunity to visit in January 1927.
The association in question varies from Dacrydium Colensoi, strongly dominant but mixed with a little Phyllocladus alpinus of the same size and habit, to a combination where Weinmannia racemosa is far more abundant, the structure more open and the silver-pine larger and with more spreading heads. Where the silver-pine is most abundant, the trunks (bearing small hepatics and small foliaceous lichens) are extremely straight and the heads scanty.
The undergrowth is quite open; it consists of Myrtus pedunculata (dominant), Blechnum procerum, some Trichomanes reniforme, Phyllocladus alpinus, an occasional young Dacrydium cupressinum, young Podocarpus dacrydioides, P. Hallii, a fair amount of juvenile Elaeocarpus Hookerianus, small Weinmannia racemosa, a little Quintinia acutifolia and Coprosma foetidissima.
1 1) The timber is of extreme durability and greatly in demand for railway-sleepers. This has led to its being taken from the forest long before the latter is being cut by the saw-miller so that in apparently virgin forest all the silver-pine of marketable size has been removed, and where but few trees have been cut down, and the smaller ones left standing, the association can readily be mistaken for virgin forest.
The subsoil is stony, being old water-borne moraine readily given to the formation of iron-pan. The upper soil is peaty and open; pools of water fill the hollows but, though wet enough, water cannot readily be wrung out of the soil by the hand. The surface of the ground is most uneven and covered with many dead twigs and leaves. There is no sphagnum and no seedlings of silver-pine.
As for the origin of silver-pine forest I can say nothing about that of the Volcanic Plateau, nor much that is really pertinent regarding that of the Western district. The only clue (a better knowledge of the virgin association and of the forest which surrounds it should tell far more) is the regeneration of Dacrydium Colensoi which is common enough where the forest has been felled.
Where this has taken place and the ground is favourable for the formation of iron-pan, sphagnum-bogs quite primitive in appearance, are rather quickly established. Such are a common feature of the district, and where they occupy a wide area, one is never certain whether they are primitive or induced.
On such induced-bog, sooner or later, various bog-tolerating, light-demanding young trees and shrubs settle down, the first arrival being usually Leptospermum scoparium and in its shade various species can be established including, if the light be sufficient, the silver-pine. But the presence of Leptospermum is not an essential, and Dacrydium Colensoi forms extensive colonies in the full light which eventually, if the far more rapidly-growing Quintinia acutifolia did not suppress them would form more or less pure silver-pine forest.
Regenerating bog-forest may also be seen within the general mass of podocarp forest where young silver-pine trees have been left after the large ones have been felled. Such forest, too perhaps, may sometimes not be regeneration but an early succession. Leptospermum scoparium may be dominant and Dacrydium Colensoi, Podocarpus nivalis, P. acutifolius, and Phyllocladus alpinus plentiful. More or less sphagnum will be present.
As to the genetic relation of silver-pine forest to that of dicotylouspodocarp forest, obviously nothing definite can be said. Most likely the silver-pine association is one purely edaphic, perhaps depending, in the first instance, on bog conditions, and with death of the silver-pines and the drying of the ground, it would be replaced by a podocarp or even a Weinmannia association. In this case, the isolated silver-pine trees, or clumps, in the general forest-mass would be relics of former bog-forest. That bog-forest was an early succession over wide areas to be followed by podocarp-dicotylous forest seems highly improbable, for the origin and methods of extending the area of the latter are fairly well known, as will be seen for one class when dealing with river-bed forest.page 181
Yellow-pine (Dacrydium intermedium) bog-forest is distinguished by the dominance of Dacrydium intermedium, a small tree ecologically equivalent and similar in appearance to D. Colensoi, but extending much further to the south. In North Island, there appears to be no lowland yellow-pine association. In South Island, associations occur in the North-western and Fiord districts, and in Stewart Island, where the maximum development of this class of vegetation apparently occurs.
Yellow-pine forest is not confined to boggy ground. Thus, near the shore of Lake Manapouri, an association is met with composed of Dacrydium intermedium, small D. cupressinum, Nothofagus cliffortioides and Metrosideros lucida.
As for the association of the forest in question in the North-western district I have no satisfactory details1 Townson speaks of the species as being abundant from sea-level to 1200 m. altitude (1906: 421), so it should surely be dominant in places.
The yellow-pine association of Stewart Island extends from the Freshwater Valley to the extreme south of the island, and occurs either on very wet soil or in positions exposed to furious gales.
The association is clearly characterized by the abundance of the slender yellowish-green dimorphic D. intermedium, its shoots weeping when juvenile, the presence of great globe-like bryophyte cushions of Dicranoloma Billardieri and Plagiochila gigantea in extreme abundance measuring 60 cm. X 60 cm. (Fig. 42), the rich profusion of other mosses and liverworts, and the numerous green tussocks of Gahnia procera. The tree-trunks are slender and close together; Coprosma foetidissima, so characteristic of the adjacent drier forest, is rare; neither tree-ferns nor ordinary ground-ferns are numerous, though in gullies there is plenty of Leptopteris superba. The floor, where the moss-cushions do not become dominant, is quite green or yellowish-green with the thick bryophyte carpet2 which also clothes the tree-bases and quite encircles the slender trunks.
1 1) My notes for a certain piece of forest on the lower slopes of Mount Rochfort (NW.), at about 300 m. altitude, give in the sequence as written the following composition &c.: — Dacrydium intermedium, Gahnia procera, Dracophyllum latifolium, Phyllocladus alpinus, Metrosideros lucida, Weinmannia racemosa, Trichomanes reniforme, Blechnum procerum, Suttonia divaricata, Gleichenia Cunninghamii, Quintinia acutifolia, Dianella intermedia, Nothopanax Colensoi, Elaeocarpus Hookerianus, Astelia Cockaynei.
2 The following are some of the specially important species: — (Hepaticae) Aneura eriocaula, A. equitexta, Mastigobryum Mooreanum, Lepidozia Taylori, Plagiochila deltoidea, P. ramosissima, P. strombifolia, Schistochila ciliata, S. nobilis, S. marginata, Trichocolea lanata and T. tomentella; (Musci) Dicranoloma Menziesii, D. platycaulon, Hypopterygium novae-seelandiae, Lembophyllum cochlearifolium, Mniodendron comatum, M. comosum and Sciadocladus Menziesii. The moss-cushions are filled with a network of roots from the adjacent trees, which thus procure purer water than from the peaty substratum (here root-tubercles as an "adaptation" for "sour" soil would be useless).
The more common woody plants of the undergrowth are: — young Dacrydium intermedium, young Weinmannia racemosa, Myrtus pedunculata, Nothopanax Edgerleyi, N. simplex, Griselinia littoralis, Cyathodes acerosa, Suttonia divaricata and Coprosma Colensoi. Small trees of Podocarpus Hallii and Dacrydium biforme are often present; Enargea parviflora grows in plenty on the bryophyte cushions; the flat-leaved grass Microlaena avenacea is plentiful; there are extensive colonies of the plagiotropous fern Gleichenia Cunninghamii more than 60 cm. high, while the other common ferns are Blechnum procerum and B. discolor.
Recently C. M. Smith made the important discovery of the same association in the southern part of the Fiord District not very far from Foveaux Strait. He wrote me that it occurred "in large tracts west of the Waitutu" and that Dacrydium biforme is scattered through the association.
2. Subantarctic Rain-forest.
Here all the montane Nothofagus associations of South Island are excluded and in North Island only those of the Thames subdistrict receive consideration. These excluded communities are dealt with further on along with the subalpine Nothofagus forest. Even from the western portion of the North-western district to the south of the Fiord district, and including the west of the South Otago district, the lowland Nothofagus associations are of a subalpine rather than a lowland character, and this becomes intensified as one proceeds south, as will be seen when treating of the forest of the North-western and Fiord districts.
The community under consideration is distinguished by the dominance of one or more species of Nothofagus, and the rarity of other tall trees. Nevertheless, especially in the west of South Island, there are forests where the subtropical and subantarctic forest-trees are equal in number, such communities grading gradually into pure forest of either class, as the case may be.
In North Island and the Sounds-Nelson district (South Island), Nothofagus truncata and N. Solandri dominate, but in the west and south of South Island the dominant trees are N. Menziesii, N. fusca and N. cliffortioides, all of which or one only being present. The hybrid swarms × N. Cliffusca and × N. soltruncata are widely distributed and sometimes dominate small areas.
The floristic composition of lowland Nothofagus forest, taking it in its entire range, differs but little from its subalpine congener, as dealt with in Section III. Chapter IV. Special distinctions are noted when discussing the composition of the associations. So, too, the life-forms need no consideration here.
Subantarctic forest is first met with in the Thames subdistrict, whence it follows the dividing-range of North Island and near Cook Strait occurs page 183almost at sea-level. It is found also to some extent in the broken country to the east of the Egmont-Wanganui district. In South Island an association, almost identical with that of the southern Ruahine-Cook district, occurs in the Sounds-Nelson district and extends to the eastern part of the North-western district. To the west of the Tasman Mountains and the Southern Alps, excepting from the R. Taramakau to the R. Paringa, pure or mixed Nothofagus forest extends to the south coast, and eastwards passes for a considerable distance into the South Otago district1
The Nothofagus communities may be naturally classified in terms of the dominance of any species of that genus. But a better conception of this class of forest, as a whole, is to be gained as follows from an account of typical portions of the community in proceeding from north to south.
Montane Nothofagus Forest of the Mamaku Plateau.
This is distinguished by the dominance of Nothofagus Menziesii and N. fusca, and the presence of the small tree, Phyllocladus glaucus; there is also a little N. truncata. Weinmannia racemosa dominates in some places and, in others, Beilschmiedia tawa is abundant. Ixerba brexioides, both juvenile and adult, occur in the undergrowth and Quintinia serrata and Alseuosmia macrophylla are plentiful. Where the roof-canopy is open there is abundance of young Nothofagi.
Besides the species already cited, the following are common: — Hymenophyllum scabrum, H. flabellatum, H. multifidum, Trichomanes reniforme, Dicksonia squarrosa, Blechnum discolor, Leptopteris superba, Gahnia pauciflora, Astelia nervosa var. sylvestris, Wintera colorata, Wintera axillaris, Carpodetus serratus, Elaeocarpus dentatus, Melicytus lanceolatus, Myrtus pedunculata, Nothopanax arboreum, N. Edgerleyi, N. anomalum, Suttonia salicina, Coprosma grandifolia and Senecio Kirkii.
The presence of Nothofagus forest on the Mamaku Plateau, together with that of Phyllocladus glaucus, according to B. C. Aston, N. Z. Journ. Agric. XXXII (1926) 369, 374, depends upon the nature of the soil which is a "sandy loam" distinct from the "air-borne sandy silts bearing the typical tawa-rimu forest of the kind most resistent to climatic severity".
Nothofagus Solandri-truncata association.
Forest of this class is distinguished by the dominance of Nothofagus Solandri and N. truncata. Frequently it grows side by side with dicotylous-podocarp forest, the latter occupying gullies and flat ground and the former the ridges or wherever the soil is "poorest".
1 1) There are some patches of lowland Nothofagus forest in the east of the Northeastern district, also at one time there were such on Banks Peninsula, and even yet such forest exists in a number of places in the neighbourhood of Dunedin (recently made known by J. S. Thomson and Simpson); and the vicinity of Catlins River.
In some parts of the class of forest under consideration Dacrydium cupressinum, or other podocarps, occur in limited quantity, and there are transitions leading to dicotylous-podocarp forest.
The association just described is that of the southern Ruahine-Cook district and the Sounds-Nelson district. An association similar in character was at one time common at the base of the Ruahine Mountains, and that on sandstone ridges in the Egmont-Wanganui district is probably similar.
Lowland Nothofagus forest in the west of the North-western district.
The Nothofagus forest in this area is by no means uniform in its composition. N. fusca, N. Menziesii, N. cliffortioides and some N. truncata may all be present, or either of the first two be the sole tree, or N. cliffortioides be present in about equal quantity.
The associations occur both in river-valleys and on hillsides, but on the most "fertile" soil there is dicotylous-podocarp forest containing more or less Nothofagus.
Owing to the wet climate, the undergrowth is similar to that of the neighbouring dicotylous-podocarp forest, following being characteristic species: — Alsophila Colensoi, Polystichum vestitum, Leptopteris superba, Quintinia acutifolia (but not everywhere), Wintera colorata, Pittosporum divaricatum (but not everywhere), Viola filicaulis, Myrtus pedunculata, Nothopanax simplex, N. anomalum, Suttonia divaricata, Coprosma foetidissima and Nertera dichondraefolia — all, except perhaps the last, being common lower-subalpine species.
On the floor, mats of N. dichondraefolia and bryophytes are common. Large foliaceous lichens (species of Sticta &c.) abound on tree-trunks and twigs (e. g. those of Myrtus pedunculata). The undergrowth consists of low trees with slender trunks, twiggy shrubs covered with epiphytic bryophytes, occasional tree-ferns (Hemitelia Smithii, Dicksonia spuarrosa), and, according to the light-intensity, more or less sapling Nothofagi.
Lowland Nothofagus forest of the Fiord district.
Generally Nothofagus Menziesii is the sole tall tree, but there is usually more or less N. cliffortioides. In the western part of the district, there is much dico-page 185tylous-podocarp forest, but in the eastern part pure Nothofagus forest rules, though, in some localities, podocarps are not altogether absent. From Lake Te Anau southwards, N. Menziesii is dominant, though generally mixed with more or less N. cliffortioides. Certain species, commonly subalpine, occur in the undergrowth, particularly: — Hoheria glabrata, Pseudopanax lineare. Archeria Traversii var. australis, Phyllocladus alpinus and Coprosma ciliata, but the most important species are Coprosma foetidissima, Wintera colorata, Nothopanax anomalum, N. simplex, many hybrids of the swarm N. simpanomalum, Coprosma Colensoi, C. Astoni and hybrids between the last two and C. foetidissima. On the floor is a deep covering of bryophytes, mats of Nertera dichondraefolia, Enargea parviflora and Libertia pulchella.
When Nothofagus fusca is present, it is rather as colonies than as the dominant of a subassociatien (Fig. 43). But so much of the Fiord district is unknown, that statements based on a few localities are most likely misleading.
Nothofagus Menziesii forest of the South Otago district.
This association is similar to the N. Menziesii association of the eastern Fiord district of which it is a continuation, but it lacks the true high-mountain element, and it contains fewer mats &c. of liverworts. In places, there is a small amount of N. cliffortioides.
The association is mostly confined to the western part of the district, and originally extended from the Longwood Range — where, to some extent, it is generally mixed with podocarps — to its junction with the Fiord forest-covering.
A number of areas of N. Menziesii forest occur near Dunedin which have recently been studied intensively by J. Simpson and J. S. Thomson. One on the Silver Peaks is a good many square kilometres in area. On the whole, the species are much the same as those of dicotylous-podocarp forest, but podocarps are wanting. The undergrowth also is far more open. Simpson and Thomson consider the areas as relics of a primitive Nothofagus forest and they supply strong evidence supporting this view.
— Forest in which other dicotylous trees are present as well as one ore more species of Nothofagus, together with podocarps, are common troughout the range of Nothofagus. They are most abundant in the north and west of South Island, together with the South Otago district. Either the dicotylous-podocarp element may dominate or Nothofagus.
Ecologically, such mixed forests are more hygrophytic than pure Nothofagus forest and, when the trees of the two classes are in about equal proportion, there is little to distinguish the community from the ordinary subtropical forest of the locality. Weinmannia racemosa is generally abundant and may dominate just as in so many dicotylous-podocarp associations.
As to the origin of these mixed forests, speculation comes into play. It page 186is well known that, although the species of Nothofagus can grow under more unfavourable conditions (poor soil, moderate rainfall, heavy wind, "sour" ground) than the tall podocarps, yet they thrive best with good soil and a moist climate; in fact, there is nothing, so far as their "likes" and "dislikes" go, to hinder them from always growing in subtropical forest. But, where the latter is fully established, there is not light enough in its interior for any species of Nothofagus to gain a footing. Once there, however, and if sufficient light is let into the forest, the Nothofagus is better able to take advantage of the situation than any other tall tree, thanks to its comparatively rapid growth and its light-demanding nature. In mixed forest in the North-western district, when a podocarp falls, seedlings of one or other of the species of Nothofagus generally take possession of the ground. Certainly, if shade-tolerating saplings already occupy the soil, the Nothofagus can do little, so that progress towards replacement will be slow enough. Nevertheless, it is not unreasonable to assume that in mixed forest generally Nothofagus has a good chance of being the climax. Certain forests show such change in progress, e. g., almost pure Nothofagus forest near Lake Te Anau with a few trees of Dacrydium cupressinum, or the miserable "suppressed" saplings of Podocarpus Hallii in so many Nothofagus forests near L. Wakatipu. Indeed such replacement by Nothofagus is no uncommon thing. This phenomenon depends upon the rapid growth of a light-demanding tree, just as the Beilschmiedia tawa succession depends upon the shade-tolerating habit in the presence of slow-growing, light-demanding podocarps. The same result — eventual dominance — is thus attained by species of opposite ecological properties and requirements!
3. Shrubland and Fernland.
By shrubland is meant any community in which tall trees are absent and shrubs dominant; and by fernland a community consisting chiefly of Pteridium esculentum.
Judging from the above definitions two distinct classes of vegetation are to be dealt with here. This is true enough, but the most wide-spread group of shrubland is so intimately connected with fernland — either passing into the other again and again — that they must be treated under the same head.
The shrubs which play a part in one or more of the shrubland communities belong to at least 113 species (including 6 hybrid swarms) which fall into 27 families and 40 genera, the largest of which are: (families) Compositae 14 species, Rubiaceae 12 and Myrtaceae, Epacridaceae and Scrophulariaceae each 9; (genera) Coprosma 12, Hebe 9, Olearia 8, Carmichaelia and Pimelea each. 5.page 187
At the present time, the greater part of the shrubland is either modified or indigenous-induced, notwithstanding that wide areas look primitive enough. Though a comparative examination of the communities in all parts of the islands places them in the categories of primitive, modified and indigenousinduced, the first is constantly aped by other two. Thus, there is shrubland and fernland, each apparently a climax-community, but such must be separated into indigenous-induced and primitive, as in the case of Leptospermum shrubland and Pteridium fernland, or either may be an early stage of forest, and this, again, induced or primitive.
As for the associations, they may be either climatic or edaphic. The former may be dependant chiefly on latitudinal or altitudinal change, yet it may also be brought about by a certain increase in subantarctic conditions. On the other hand, edaphic shrubland may be extremely restricted in its distribution, as is that of magnesian soil (Fig. 44); or it may be dependant upon the physical character of the substratum, and be of wide range, as in the case of pumice, river-bed, gravel-plain and river-terrace.
Physiognomically (but this of course is really ecological), shrubland falls into the classes of (1.) ericoid-shrubland, (2.) scrub, and (3.) the incipient forest already mentioned, which frequently is ericoid in nature.
With regard to habitat shrubland occurs on almost any class of soil and in all climates, from the wettest to the driest. But, it must be borne in mind that wide areas of both fernland and shrubland are now in existence where such would be absent or extremely rare in primitive New Zealand.
b. Leptospermum-Pteridium (manuka-bracken) communities.
The communities dealt with under this head are distinguished by the presence of species of Leptospermum — usually L. scoparium — and Pteridium esculentum, either of which may be dominant or pure, or the two may be mixed together. The communities thus range from shrubland to fernland by way of many combinations of the two classes.
The species for the whole group of communities number about 126 (pteridophytes 11, monocotyledons 43, dicotyledons 72), but the estimate could be considerably increased by taking in various species which invade an association at its junction with forest or tussock-grassland. The families and genera number 41 and 73 respectively, the following being the largest: — Graminae 15 species, Orchidaceae and Compositae 13 each, Cyperaceae 9; the genus Thelymitra 6.
Many of the species play little or no part in the structure of the vegetation but the following are of particular importance in one or more of the associations: — Pteridium esculentum, Gleichenia microphylla (Filic.), Paspalum scrobiculatum, Danthonia pilosa, D. semiannularis (Gramin.), Schoenus brevifolius, S, tendo, Gahnia gahniaeformis (Cyperac), Dianella page 188intermedia, Phormium tenax, P. Colensoi (Liliac.), Persoonia torn (Proteac.), Weinmannia sylvicola (Cunon.), Rubus australis in a wide sense, Acaena novae-zelandiae, A. sanguisorbae var. pusilla, the hybrids between the last two (Rosac), Coriaria sarmentosa (Coriariac.), Discaria toumatou, Pomaderris elliptica, P. Edgerleyi, P. phylicaefolia (Rhamnac), Pimelea virgata, P. prostrata in a wide sense (Thymel.), Leptospermum scoparium, L. ericoides (Myrtac.), Halorrhagis erecta (Halorrhag.), Gaultheria antipoda, G. oppositifolia, the hybrids between the last two (Ericac.), Cyathodes acerosa, Leucopogon Fraseri, L. fasciculatus, Dracophyllum Urvilleanum, D. subulatum (Epacrid.), Hebe macrocarpa, H. salicifolia in a wide sense, X H. macrosala, H. diosmaefolia (Scroph.), Cassinia leptophylla, C. fulvida, Olearia furfuracea (Compos.).
Leptospermum - Pteridium communities occur throughout New Zealand proper and are frequently of such extent (many square kilometres at a time) as to dominate the landscape. At the present time their wide range is chiefly due to the action of man, the communities being largely stages of succession (indigenous-induced) following the destruction of forest. Thus, both Pteridium and L. scoparium are of far greater importance in the general plant-covering than prior to the arrival of the white man. All the same, it is wrong to imagine that similar or allied communities did not occur in primeval New Zealand. On the contrary, during the frequent volcanic outbursts, even now not entirely a thing of the past, much forest must have been set on fire, and bracken and manuka associations come into being then as now; indeed, so recently as 1886, this was the case. Further, there are wide areas of a Pteridium association in the neighbourhood of the Otago lakes, near the junction of the comparatively dry and extremely wet districts, the presence of which can best be explained on the supposition of their having gradually replaced forest during a period of decreasing rainfall on the east of the Southern Alps. If the foregoing ideas are correct, then it is clear that man has unwittingly reproduced on a great scale an ancient type of vegetation. But there is this fundamental difference, that in primeval New Zealand the shrubland or fernland would generally revert to forest, whereas, at the present time, this is hindered by the introduced grazinganimal factor and by the purposeful conversion of these waste lands into valuable pasture by means of fire and the grazing of cattle (see Part III).
Coming next to the life-forms of the species, they and the number of species to each are as follows: — trees 3, shrubs 42, herbs 27, semi-woody plants 14, grass-form 23, rush-form 2, lianes 7, parasites 2, ferns 6. Amongst the shrubs are certain trees remaining in the juvenile form; tussocks number 15.
The communities under consideration occur under most diverse conditions. In areas of high precipitation and of the maximum dryness they are equally present. As for soil, it may be alluvial of various kinds, clays, page 189loess, sand, gravel, calcareous or non-calcareous and pumice of different sorts. Though frequently dominant on poor soils this is rather from absence of the competitors which have ousted them from soils more fertile than for any preference for those less fertile. The water-content of the substratum differs greatly according to rainfall and its water-holding capacity, and fluctuates considerably both at different seasons and even brief periods. In certain localities, bog-conditions are present and it is not easy to draw the line between shrubland proper and bog-shrubland.
β. Ericoid shrubland.
1. Leptospermum (manuka) shrubland.
The group to be considered under the above name is distinguished by the dominance of Leptospermum scoparium which may be almost pure or have mixed with it various species of forest, fernland or grassland. The species differ considerably according to botanical districts and also decrease in number from the north to the southernmost range of the group.
Leptospermum shrubland — generally indigenous-induced — is physiognomic in most parts of New Zealand proper, but is particularly in evidence in the Auckland, Volcanic Plateau, south-eastern East Cape and western Sounds-Nelson districts. It varies from low forest, containing many forest-species, which, if let alone, would turn into the type of forest it adjoins, to a dense or open shrubland, the height of which depends partly on the nature of the soil and partly on the time when it was last burned.
At first, the shrubland consists of great numbers of slender young Leptospermum, of fastigiate habit, growing so close together that the entry of other species is difficult, nor is there sufficient light for the development of a distinct undergrowth. But, by degrees, as the Leptospermum grows, a vast number are suppressed and the survivors— now fairly tall, and eventually small trees — branch, and sufficient light enters for the germination of seeds of trees, shrubs &c., but not for the Leptospermum itself, for it is strongly light-demanding. Finally, as the taller-growing species cut off the light, the Leptospermum is doomed. Thus, in primitive New Zealand, except in areas adjacent to active volcanoes, more or less permanent associations of L. scoparium must have been rare and confined to swamps, windswept stations, dunes, acid soils, and unfavourable habitats in general. Uninterfered with, its companion plants, if trees, will wipe out the Leptospermum, but if burned or cut down, its seedlings arise in their thousands and no other species can compete; moreover the seedlings, when only ± 5 cm. high flower and produce viable seed.
In what follows an account is given seriatim of various outstanding groups of associations.
Auckland manuka shrubland.
This association is distinguished by the presence of certain species cited below, most of which are absent south of page 190lat. 38°, It frequently intergrades with bog, so that the line between the two may be difficult or impossible to fix. Also, it is greatly modified by man yet, except for the abundance of certain exotic Australian shrubs, the species must be much as they were in the unaltered association and the structure in places not markedly different.
The species number more than 80, the following of which, absent in southern shrubland, are more or less common in this association: — Lycopodium densum, L. cernuum, Phylloglossum Drummondii, Paspalum scrobiculatum, Schoenus tendo, Lepidosperma laterale, Cordyline pumilio, Thelymitra pulchella, T. pauciflora, T. aemula, T. imberbis, Prasophyllum pumilum, Caladenia exigua, Persoonia torn, Cassytha paniculata, Weinmannia sylvicola, Carmichaelia australis, Pomaderris elliptica, P. Edgerleyi, Leptospermum lineatum, L. scoparium var. incanum, Ealorrhagis incana, Hebe diosmaefolia, Lagenophora lanata, and Olearia furfuracea.
The association covers much of those deep, clay soils that form so large a part of the surface of the Auckland districts. At one time kauri forest occupied this ground as evidenced by the abundance of fossil resin and even undecayed logs beneath the surface. The clay varies in colour from brick-red, by way of orange and yellow, to almost white, this latter being especially barren. In winter it becomes saturated with water, but, in summer, baked by the sun, it is extremely dry and opens out into many cracks. Hollows and low-lying ground are always filled with peaty water or at least remain permanently wet providing where wettest bog-conditions; here their vegetation is dealt with further on under the heading "bog".
A typical area of this shrubland in its modified condition shows many level breadths of Leptospermum scoparium, in one or other of its varieties, varying from perhaps 3 m. to a few centimetres in height. Where tall, the plants are crowded with long, straight, bare, blackish stems and small heads of short leaf-bearing branches. Frequently there is a more or less dense undergrowth of the green rushlike stems of Schoenus tendo mixed with and overtopped by the yellowish-green pine-like Lycopodium densum, or they may grow separately. Probably there will also be some Pteridium, Pomaderris phylicaefolia and Leucopogon fasciculatus.
The great number of seeds, and their ready germination after fire bring seedlings of Leptospermum in their thousands, while at the same time other members of the association reproduce themselves, though in smaller numbers. Where, for example, the Leptospermum is 1 m. high, Dracophyllum Urvilleanum raises its slender, branched stem 50 to 90 cm. above the dull mass of foliage. So too, Epacris pauciflora, but it is not quite so tall. Also the rush-like stems of the Schoenus pierce through the close growth, but these not as seedlings but as new shoots from the undamaged rhizome. Sometimes the fire encourages the growth of pure Pteridium, for its rhizome being unhurt by fire, new leaves are rapidly put forth which check the establishment of seedlings.page 191
Where the ground is dry and the plants of Leptospermum further apart, Pomaderris phylicaefolia is abundant, green flat-stemmed tussocks of Lepidosperma laterale stand here and there and in some localities Pomaderris elliptica and P. Edgerleyi (Fig. 45) are characteristic as also Lycopodium densum and L. cernuum, especially the former. Gleichenia microphylla often climbs over the bushes of Leptospermum1 When the varied forms and colouring of these plants are considered, it can be understood that this type of shrubland is far from being a monotonous spectacle.
When the shrubland is near a forest there are, to the north of the Northern Wairoa River, many young non-flowering trees of Weinmannia sylvicola with yellowish-green, long, pinnate leaves and frequently young trees of Knightia; while occasionally a stunted kauri may be encountered. Near the coast, more especially, Olearia furfuracea, most showy with its masses of white flower-heads, gives a special character to the association, and it is often accompanied by the small tree Persoonia toru2
Volcanic Plateau (pumice) manuka shrubland.
This association is distinguished by the presence, in many parts of Dracophyllum subulatum in abundance and more or less Gaultheria oppositifolia.
The substratum is pumice with more or less humus on the surface which can retain but little moisture owing to the porosity of the pumice, so notwithstanding a fairly high rainfall and many rainy days, tolerably strong xerophytic conditions are provided. Burning has been rife, but this is only what happened again and again in the days of volcanic activity.
1 1) The following are also common nembers of the association: — Lindsaya linearis, Danthonia pilosa, D. semiannularis, Gahnia gahniaeformis, Cordyline pumilio, Dianella intermedia, Drosera auriculata, Leptospermum ericoides, Pimelea prostrata, Leucopogon Fraseri, and Cyathodes acerosa.
2 The following interesting plants are of restricted distribution: — Gleichenia flabellata with its semi-horizontal, glossy green pinnae may occupy several sq. metres at a time; Todea barbara, its short, massive trunk hidden by the close semi-globular mass of Osmunda-like leaves grows in open places amongst Leptospermum, it is confined to the far north; Cassinia amoena is restricted to the North Cape Hill; Hebe diosmaefolia makes pure stands in some localities; Loxsoma Cunninghamii grows in shade of Leptospermum near margins of forests; Cassytha paniculata binds shrub to shrub with its slender, twine-like stems, it is confined to the far north.
3 Probably distinct from the common variety of South Island.
4 An erect dull-coloured shrub, 60 cm. high, with slender, twiggy, fastigiate branches, small, erect, coriaceous, pungent, very narrow leaves 4 to 6 cm. long and deeply-descending roots.
Solfatara manuka shrubland.
Where pumice shrubland comes into close proximity with steam from fumaroles, and the soil contains more or less sulphur &c., the association becomes open and by degrees the species give out, excepting Leptospermum ericoides and Leucopogon fasciculatus, the former becoming a prostrate rooting shrub, but the latter remaining erect. When surrounding boiling-mud holes, the shrubs are luxuriant and erect. Lycopodium cernuum tolerates far more hot steam, heated soil and fumes than any other shrubland species.
Southern North Island manuka shrubland.
The shrubland is nearly all indigenous-induced. It is mainly distinguished from that further to the north by the absence of the northern local endemics and so is much poorer in species. When in proximity to forest, it contains various forest-species, in fact, it is an early stage in forest-succession. Some of the constituents of such shrubland are: Gahnia setifolia, G. pauciflora, G. gahniaeformis, Cladium Vauthiera, Dianella intermedia, various earth-orchids, Nothofagus Solandri (if near Nothofagus forest), Clematis Colensoi or C. hexasepala, juvenile Weinmannia racemosa, Rubus australis, Coriaria arborea, Leptospermum scoparium (dominant), Nothopanax arboreum, juvenile Pseudopanax crassifolium var. unifoliolatum, Gaultheria antipoda, Dracophyllum Urvilleanum (occasionally), Cyathodes acerosa, Leucopogon fasciculatus, Hebe salicifolia (one or other of its jordanons), Coprosma robusta, C. lucida, C. rhamnoides.
South Island manuka shrubland.
1 1) The eruption of Tarawera, 42 years ago, covered a vast area of pumice shrubland with more or less thick covering of volcanic ash. Near the centre of eruption the vegetation was buried to a depth of many metres so that quite new ground was available for colonization. Nineteen years after the eruption I paid a special visit to the new ground. Rain, early on, had carved the loose slopes into gully-like channels 9 m. or more deep and these were filled with a close growth of Arundo conspicua mixed in places with Coriaria sarmentosa this latter forming green patches. The flatter ground contained only plants here and there of which Danthonia semiannularis and Deyeuxia avenoides var. brachyantha were dominant. A species of Cladonia, another lichen, a moss or two, Pteridium, Weinmannia racemosa, Gaultheria antipoda, G. oppositifolia, and Raoulia tenuicaulis were also present. There was a good deal of the introduced Trifolium, repens, T. minus, Holcus lanatus and Eypochaeris radicata, but they had probably been sown by man. Deducting those species from Aston's list (1916 b.: 309–311) which were re-established from plants damaged but not killed, together with other purely forest species, the number of species established on the really bare ground is only 47 all of which came from the immediate neighbourhood.
The comparatively low rainfall, frequent hot winds, and the porous substratum of rounded stones favoured the presence of primitive manuka shrubland (now usually modified by burning) on the gravel plains and valleys of the North-eastern and Eastern districts.
The almost pure subsoil of gravel and sand is capped by a varying amount of surface-soil consisting of loess — it may be clayey — mixed with 20 to 50 per cent of stones. Although apparently flat, the surface consists of hollows and ridges. Both Leptospermum scoparium and L. ericoides are present. Where the shrubs are close, there is a good deal of Hypnum on the ground, and to this in part the humus-content of the soil is due. The spinous Discaria toumatou and the yellow-leaved Cassinia fulvida are common. In open spaces, in the most stony areas, there are abundant silvery mats of Raoulia lutescens, some R. tenuicaulis, and cushions of Scleranthus biflorus.
Magneslan soil shrubland.
This association is distinguished by the presence of Olearia serpentina — a moderate-sized, small-leaved divaricating shrub closely allied to 0. virgata — and the dominance usually of Leptospermum scoparium. It occupies the lowland-montane portion of the Mineral Belt1 where the sail contains more magnesia than most species can tolerate, but where the magnesia is least in evidence there may be stunted Nothofagus forest.
1 1) The belt is a narrow, frequently stony tract, consisting of peridotite and serpentine rocks, extending for about 96 km. from D'Urville Island to the western part of the Sounds-Nelson district with its widest part (about 5 km.) in the vicinity of the Dun Mountain (Fig. 44.). The vegetation of the belt both in its associations and life forms presents a striking contrast to that of the adjacent luxuriant forests. The transition from forest to Mineral belt vegetation is hardly to be seen, each standing out distinct. Not only does the magnesian soil influence the associations but it changes the life-forms, so that trees beyond its influence are merely shrubs on the belt (the spp. of Nothofagus, Griselinia littoralis). Taking the whole altitudinal range of the belt, the following species or well-marked varieties are apparently confined thereto, most, however, being subalpine: — Poa sp. related to P. acicularifolia, Festuca species hitherto placed in the F. novae-zelandiae linneon, Pimelea Suteri, Myosotis Monroi, probably an unnamed species of Hebe, Cassinia albida var. serpentina and Olearia serpentina — a certain indicator of the magnesian soil at all altitudes.
On Red Hill, at an altitude of 150 m. to 360 m. there is a far-richer vegetation and larger florula. The following is a rather full list of the species: — Blechnum procerum, Pteridium esculentum, Lycopodium varium, Poa Colensoi, Cladium Vauthiera, Schoenus pauciflorus, Gahnia pauciflora, Phormium Colensoi, Cordyline Banksii, Libertia ixioides, Thelymitra (of the longifolia group), Clematis marata, Weinmannia racemosa, Melicope simplex, (leaves very small), Aristotelia fruticosa, Pimelea Gnidia in a wide sense, Leptospermum scoparium, L. ericoides, Halorrhagis erecta, Pseudopanax crassifolium var. unifoliolatum (rare), Nothopanax arboreum, N. anomalum, Corokia Cotoneaster, Griselinia littoralis, Gaultheria antipoda, Cyathodes acerosa, Leucopogon fasciculatus, Dracophyllum longifolium (rare), Suttonia chathamica (rare), Hebe angustifolia, H. salicifolia var. Atkinsonii, Hebe probably a distinct species, Hebe hybrids an enormous swarm now being studied genetically, Coprosma parviflora, Cassinia albida var. serpentina and Shawia paniculata.
The shrubland forms a narrow belt on a ridge and separates two pieces of Nothofagus forest. Where at its richest L. scoparium is about 4.5 m. high, much-branched or with several naked trunks. Colonies of green-leaved Gahnia pauciflora, numerous bushes here and there of Phormium Colensoi. and green thickets of the hybrid forms of Hebe add brightness to the association, which is increased when the latter and Pimelea Gnidia are in bloom. This remarkable community was first discovered by A. W. Wastney, who later conducted me to it, but to him the discovery of the wonderful swarm of Hebe hybrids is alone due.
2. Cassinia shrubland.
This is dominated by the presence of one or other of the species of Cassinia, indeed, it may consist of little else.
Though frequent, both near the coast and inland to the montane or even the lower subalpine belt, the community is nearly always indigenousinduced. In parts of North Island and the Sounds-Nelson district, it occupies wide areas where forest has been felled and burned or burned standing. This extension of its range inland is due to its wind-borne seeds, their strong viability and the rapid growth of the seedlings.
These indigenous-induced communities do not concern this part of the book, but, on certain South Island river-beds, there appears to be modified Cassinia shrubland, and some in the montane belt may be of the same character.
In such semi-virgin scrub there is generally little else besides the local species of Cassinia and their hybrids, so numerous that they may outnumber page 195the species. There are also the ground-plants of open spaces but such are mostly species of invaded Raoulia or tussock-grassland communities.
γ. Pteridium (bracken) fernland.
Fernland is distinguished by the complete dominance of Pteridium esculentum. Except where the bracken has been burned repeatedly and heavily grazed by cattle, the members of the association are very few, the most important species being Coriaria sarmentosa. This paucity of species arises from the fact that, except in specially exposed situations, Pteridium is more or less evergreen in New Zealand, so there is no vernal groundvegetation as in Europe, indeed the close growth of the leaves inhibits all undergrowth except in open places. Luxuriant fern-heath is frequently more than 1.5 m. high. Such will be quite pure, the floor will be bare, but there will be an abundance of dead fronds.
In the Auckland districts, and other localities, where shrubland and fernland intergrade, the latter may contain more or less shrubs which have come from the former. In the wide girdles of fernland extending round some of the Otago lakes the exotic Hypericum Androsaemum and H. perforatum are occasionally common, they having entered the association by way of bare ground due to burning.
From the economic standpoint, Pteridium esculentum — though indigenous — is far and away the worst weed which the farmer has to combat.
Scrub of a subalpine character.
This is distinguished by the dominance of shrubs usually found in high-mountain shrubland, particularly species of Olearia and divaricating-shrubs.
It occurs in the wettest parts of South Island, principally upon the sides of river-terraces, and is ecologically equivalent to river-terrace scrub of the montane and lower subalpine belts. From the latter, it differs floristically to some considerable extent, and ecologically in its members being upright and not nearly so much tangled together.
Taking old river-bed and terrace scrub of the Western district, the following are the most important species: -—Podocarpus Hallii, P. acutifolius, Muehlenbeckia australis (liane), Rubus schmidelioides var. coloratus (liane), Carmichaelia arborea, Coriaria sarmentosa, Aristotelia fruticosa, Plagianthus betulinus, Nothopanax Colensoi, N. anomalum, Pseudopanax crassifolium var. unifoliolatum, Griselinia littoralis, Hebe salicifolia var. communis, Coprosma robusta, C. propinqua, C. rugosa, Olearia avicenniaefolia, O. ilicifolia, O. macrodonta (perhaps O. arborescens × ilicifolia) and O. arborescens and as undergrowth, Polystichum vestitum, Blechnum vulcanicum, B. fluviatile, B. penna, marina and occasionally Rubus parvus.page 196
In the west part of the South Otago district a scrub, allied to the last, consists chiefly of divaricating-shrubs, including Olearia virgata.
In the inland part of the North Otago district there is a good deal of scrub with Olearia lineata — a small, twiggy, semi-weeping tree — dominant, accompanied by Muehlenbeckia complexa (liane), Rubus subpauperatus (liane), Discaria toumatou, one or two species of Carmichaelia, Coprosma virescens and Olearia odorata; the exotic Sambucus niger and Rosa Eglanteria have also joined this association.
4. Water Associations.
Under the above head are included associations of plants specially adapted to the aquatic-life and occupying permanent still or flowing freshwater. Here, only the vascular-plants are dealt with, not because there is any lack of fresh-water algae or bryophytes, but the former have been but little studied as yet, while nothing is known of their synecology. The total number of species is 25 (pteridophytes 4, spermophytes 21), which belong to 12 families and 14 genera, and comprise 5 free-swimming plants, 9 soilrooted and leaf-floating, 7 submerged and 4 amphibious, but some come into more than one of these classes.
On still waters throughout all New Zealand, Stewart Island excepted, the floating water-fern, Azolla rubra, the individual plants only 1.2 to 2.5 cm. long, forms close, red sheets several centimetres thick quite hiding the water-surface, and, which, by the inexperienced, might be mistaken for dry ground. Such an Azolla association is generally quite pure, though it may occupy the water-surface of open swamp. The two floating species of Utricularia (U. protrusa, V. Mairii) are extremely rare, the former having been observed only on Lake Tongonge in the far north and Lake Waihi (Waikato) and the latter may be extinct as it was noted only in the Lake Rotomahana which was destroyed by the eruption of Tarawera. U. protrusa forms floating colonies 60 cm. or more across.
Where the water is comparatively still and shallow, as near the margins of lakes and slow-flowing rivers, or on the surfaces of ponds and shallow streams, there are frequently wide breadths of the brownish, long-petioled leaves of Potamogeton Cheesemanii, their coriaceous, oblong blades some 2.5 cm. long, while, beneath the surface, there are, in abundance, the shortpetioled, translucent, ribbon-like leaves generally slowly moving with the current. In similar stations are the amphibious Myriophyllum elatinoides and M. propinquum forming masses of floating stems with submerged finelycut leaves, but having also aereal stems with entire leaves. Callitriche verna is another species of still water.
The submerged water-plants, some of which have been dealt with as coastal, are as follows:—Pilularia Novae-Zealandiae, Potamogeton ochreatus, page 197P. pectinatus, Zannichellia palustris, Ruppia maritima and with these may perhaps be included Ranunculus Limosella and Glossostigma elatinoides.
5. Swamp vegetation.
Swamp vegetation is composed of tall and medium-sized monocotylous herbs, especially Typha angustifolia (in a wide sense) and Phormium tenax (in many jordanons and hybrids), together with more or less herbaceous and shrubby dicotyledons which "tolerate", or "prefer", for their growingplace permanent shallow water, overlying loose peaty soil. Such vegetation is the New Zealand representative of the "Niedermoor" of German and the "Fen" and "Carr" of English ecologists.
Except forest, no other class of vegetation has been so greatly altered by man or so completely eradicated, but there are still some examples fairly primitive, whilst comparative studies enable a general idea of New Zealand swamps to be gained, even if it be no longer possible to secure certain details. Perhaps the most interesting feature at the present time is the life-history of commercial Phormium "swamps", dealt with in Part III, which are purely indigenous-induced associations but presenting a truly primitive physiognomy.
The swamp-flora, excluding aquatics, consists of 74 species (obligate 37), belonging to 18 families and 37 genera, the largest of which are: (families) Cyperaceae 28 species, Juncaceae 5 and Gramineae, Liliaceae, Onagraceae and Scrophulariaceae 4 each; (genera) Carex 10, Scirpus 6, Cladium and Juncus 5 each. The following are common species of wide distribution:— Blechnum procerum (Filic.), the 2 vars. of Typha angustifolia (Typhac.), Hierochloe redolens, Arundo conspicua (Gramin.), Cladium glomeratum. C, teretifolium, Carex virgata, C. secta, C. Oederi var. catarractae (Cyperac.), Juncus holoschoenus, J. prismatocarpus (Juncac.), Cordyline australis, Phormium tenax (Liliac.) Leptospermum scoparium (Myrtac.), Epilobium pallidiflorum (Onagrac.), Gratiola peruviana, Hebe salicifolia (in a wide sense) (Scroph.), Coprosma robusta, C. propinqua, × C. prorobusta (Rubiac.), Olearia virgata (Compos.).
Swamp communities occur here and there throughout the lowland and montane belts occupying from wide to quite trifling areas. The habitat originates in various ways, gradual occupation of lake by aquatic plants in the first case and swamp-species in the second; or from rivers frequently and regulary overflowing their banks, or from changes in the shore-line cutting off the sea from salt-swamp, whereupon the habitat, as its saltcontent lessens, is occupied by fresh-water species, amongst the earliest colonists being Scirpus lacustris, Typha and Phormium. As time goes on, for swamp generally through the decay of the dead plants, in course of time, considerable page 198accumulation of peat takes place, a sour soil is produced and bog-conditions may follow; but, on the other hand, swamp-tolerating shrubs, and then trees may enter the association, and, as already described, first swamp-forest and then ordinary forest form a climax. Also, of course, there may be the reverse.
Coming next to the life-forms of swamp, they and the number of species to each are as follows: — trees 1, shrubs 10, herbs 21, lianes 1, grasslike plants 17, rush-like plants 21, ferns 3.
There are many changes in the composition of swamp-vegetation in accordance with change in latitude, owing chiefly to the different frost-enduring capacity of the species. As for the associations, many are really successions leading from aquatic vegetation, by way of herb-swamp, shrubswamp and semi-swamp forest to subtropical rain-forest — the climax. But these stages, as migratory associations are always in existence so they are best treated as distinct entities, which indeed they are.
b. Monocotylous herb swamp.
Raupo (Typha) communities.
—This group of associations is distinguished by the dominance of the great, bull-rush (raupo) Typha angustifolia (in a wide sense). Frequently there are dotted about in the shallowest water or near the margin stunted plants of Phormium tenax. The chief changes in the community as a whole depend upon latitude and altitude.
Raupo associations extend throughout New Zealand — Stewart Island excepted — from sea-level to 750 m. altitude and they occupy soils of many kinds, including sand, so long as they are covered with water all the year round.
The following species abundant in the Auckland districts occur also to some extent in the rest of North Island, but are rare or absent in South Island: — Sparganium subglobosum (also rare NW.), Isachne australis, Heleocharis sphacelata (occasionally west of South Island and Stewart Island), and Cladium articulatum.
1 1) A perennial herb 30–60 cm. high with a creeping, rooting, flexible, hollow stem which finally ascends, and branching but little, bears thin, yellowish-green blotched lanceolate leaves, 8 cm long by 1.5 cm. broad.
2 A perennial rush-like herb with stout, creeping, stoloniferous rhizome and stout, cylindrical, hollow, erect, septate stems 60–90 cm. high.
In South Island, raupo swamp contains fewer species, otherwise its physiognomy and ecology are the same. At an altitude of from 550 to 750 m. in South Island, where there is a grassland-climate it may contain in addition to Typha a girdle of Carex secta in the shallower water and also C. subdola and C. ternaria. Change to drier conditions in such swamp, if there is sufficient rainfall will bring in sphagnum bog.
— In these, as the name indicates, P. tenax dominates. At the present time quite a wrong estimate might be gained as to the relative importance of this association as compared with that of Typha in primeval New Zealand, since many of the extensive areas of Phormium swamp that now exist have arisen through the draining of raupo-Phormium-swamp where Typha was easily dominant. But areas large and small persist in many places where the natural transition from pure Typha to dominant Phormium can be seen.
Where the Phormium is dense, its masses of rhizomes monopolise the surface and its frequently more or less drooping leaves cut off the light. But where there are open spaces, the usual swamp-plants of the particular locality are present. Where the water is fairly deep Carex secta or C. virgata, may be abundant and Blechnum procerum be important in the undergrowth. On the drier ground there may be colonies of the great tussocks of Arundo conspicua. Shrubs are generally present more or less, especially Leptospermum scoparium, Hebe salicifolia, Coprosma propinqua, C. robusta and × C. prorobusta, these the fore-runners of shrub-swamp. Where there is open water, there may be colonies of Azolla or Lemna minor, or floating Potamogeton, Ranunculus macropus, R. rivularis or Cotula coronopifolia.
Phormium tenax and Arundo conspicua frequently form narrow girdles on the margins of rivers. Here too, or elsewhere, where there is muddy ground subject to frequent wetting, may grow Tillaea Sinclairii, Myriophyllum propinquum (as land-plant), Elatine gratioloides, Limosella aquatica and Gratiola peruviana.
Nigger-head (Carex secta) communities.
Here shock-headed masses of C. secta are dominant raised above the water on their "massive" trunks, 60 cm. to 2.4 m. high. Such trunks both raise the living portion of the Carex high above the water and afford a station for Blechnum procerum, Hydrocotyle pterocarpa, Hierochloe redolens and seedling shrubs. Niggerhead swamp contains many ordinary swamp-plants and many transitions occur between it and Phormium or raupo swamp.
Stewart Island swamps.
As far as the swamps of Stewart Island have been investigated, they are closely related to bog. The main point of importance is that the coastal Leptocarpus simplex (also occurs in swamp near lake Brunner — NW.) is often dominant making pure colonies. In other places Cladium glomeratum and Carex ternaria respectively form close masses. Other species of importance are Blechnum procerum (stunted), Carex stellulata, several common species of Hydrocotyle, and where wettest, Carex secta.
Swamps of this class have their greatest development where the snow-rivers have produced deltas at the heads of large lakes (e. g. L. Pukaki, L. Wakatipu), and in some of the intermontane basins.
As in lowland swamps, distribution of the species is governed by the depth of the water, so that Typha occupies the deepest part and where more shallow Carex secta, Phormiwn tenax, Cladium teretifolium or C. glomeratum while, in the very shallow water, and wet ground adjacent, there is a varied assemblage1, which belongs rather to bog than swamp, certain species of which rarely descend to the lowlands; Carex Gaudichaudiana (also lowland) is a specially important constituent.
c. Shrub swamp.
This is to be distinguished by the presence of shrubs in considerable numbers of which Leptospermum scoparium is nearly always dominant and frequently forms a close growth of straight, slender stems. Cordyline australis is usually an accompanying plant, and as already seen when dealing with forest, it may make a pure low-tree association. Other shrubs of the community are Carmichaelia divaricata (NW.), C. gracilis very rare — E., NO.), C. arborea (W., F.), Eugenia maire (North Island), Pseudopanax crassifolium var. unifoliolatum, Griselinia littoralis (west of South Island), Hebe salicifolia in a wide sense and its var. paludosa (W.), the species of Coprosma already cited and Olearia laxiflora (NW.).
1 Carex ternaria, Schoenus pauciflorus, Juncus polyanthemos, Luzula campestris — one or other of its many jordanons, Rumex flexuosus, Montia fontana, Potentilla anserina var. anserinoides, Geranium microphyllum, Viola Cunninghamii, Ealorrhagis micrantha, Hydroctyle novae-zelandiae var. montana, Oreomyrrhis andicola in a wide [unclear: sense], Mazus radicans, Plantago triandra, Asperula perpusilia, Celmisia longifolia in a wide sense, Cotula dioica var. montana, Gnaphalium paludosum.
Shrub-swamp may also be a stage in the retrogressive evolution of swamp from semi-swamp forest, in which case, at first, many forest plants would persist for a time. Leptospermum swamp strongly favours the presence of Sphagnum and thus is readily transformed into the different ecological category of bog, or the bog-moss, the Leptospermum and its accompanying plants, be a relic of a former bog-community.
d. Associations of warm-water, or of hot ground exposed to steam.
According to Setcpiell, various Schizomycetes flourish in the numerous hot-water pools of the Volcanic Plateau, but none can endure a higher temperature than 75° C. Where, the heat is moderate, there Cyanophyceae occur. On shrubs, constantly exposed to steam, the twigs become deeply coated with the orange-red alga Chroolepus aureus.
The following ferns and lycopods grow luxuriantly near hot-water streams, their roots in strongly heated soil and their aereal parts exposed to steam: — Histiopteris incisa, Dryopteris gongylodes, D. dentata, Nephrolepis cordifolia, Gleichenia linearis, G. circinata, Schizaea dichotoma, Lycopodium cernuum and Psilotum triquetrum; Histiopteris incisa and Lycopodium cernuum are of extremely common occurrence, the latter constantly hugging the warm around round steam vents, but the other species are of local distribution.
On the sides of the boiling wells which supply the Boiling River (Otumakokori Stream) Dryopteris dentata, Nephrolepis cordifolia and Gleichenia linearis grow n great abundance in a hot atmosphere always saturated with moisture1.
Hot water swamps contain many ordinary swamps-plants, e. g.: Typha, Scirpus lacustris, Heleocharis sphacelata, Cladium articulatum, Carex ternaria, together with Dryopteris dentata. The latter, according to Kirk, formerly covered acres of the swamp on either side of the warm river connecting lakes Rotomahana and Tarawera, "its dull green fronds sometimes five feet high and seven inches across but in this state it is usually barren". The same fern grew in abundance also on the "White Terrace", covering "the thin crust overlying the scalding mud and from its erect, rigid habit and the strict sori-laden pinnules presenting a forcible contrast to the luxuriant swamp form".
1 1) For further particulars see Hochstetter (1867: 402) and Kirk (1873: 336), but the statements as to all these "hot-water" ferns being confined to such a station is now known to be incorrect, only Nephrolepis and Gleichenia linearis being so restricted. The 2 species of Dryopteris are of limited distribution in the North Auckland district and the Schizaea is an occasional denizen of the kauri subassociation.
6. Bog Vegetation (Communities of sphagnum and its associated plants).
Various kinds of sphagnum are the special feature of bog vegetation and with such are associated species of Gleicherda, Lycopodium, Cladium, Carex, also Hypolaena lateriflora and species of Drosera and Utricularia. But the associations differ considerably in various localities and, even sphagnum may occur only to a limited extent, or at times be wanting.
The total number of species in the lowland portion of the formation is about 110 (pteridophytes 13, conifers 2, monocotyledons 42, dicotyledons 43) which belong to 27 families and 67 genera, but 24 species are confined to Stewart Island. The most widely-spread vascular species are the following: — Gleichenia microphylla (Filic.), Cladium teretifolium, C. glomeratum, C. Vauthiera (Cyperac.), Hypolaena lateriflora (Restionac.), Drosera spathulata, D. binata (Droserac.), Leptospermum scoparium (Myrtac.), Halorrhagis micrantha (Halorrhag.), Centella uniflora (Umbel.), and Pratia angulata (Campan.).
Wherever there is a soil which remains saturated with water at all seasons, a bog association of some kind will be present. But, although there may be shallow pools here and there, the entire surface must not be permanently covered. According to the average degree of wetness, so will the plant-covering vary, Sphagnum bog occupying the wettest and shrub bog the driest ground.
The amount of peat present regulates the species to some degree, but to a lesser extent than would be imagined. Where the peat-content is scanty, pakihi bog occurs and forms a connecting link with Leptospermum shrubland. Bog appears to originate in various ways, e. g.: from lake by way of monocotylous-herb swamp; from frequent floods causing swamp in the first place; from water lying in wet hollows; from an excessive rainfall on flat badly-drained ground and from Sphagnum settling on the forestfloor in a wet climate.
Obviously an abundant rain-fall, a comparatively low summer temperature and frequent cloudy skies favour bog which is thus a common feature of the west and south of South Island and Stewart Island. In North Island, extensive Sphagnum bogs were present on the Waikato Plain, but these were edaphic rather than climatic and arose in swamps caused by overflow of the river and defective drainage. So, too with certain bogs, now reclaimed, on the Canterbury Plain, where the climate is hostile to bog. Hollows in the Auckland gumlands are occupied by bog, and it is a matter of choice whether to call a good deal of the vegetation shrubland or bog.
Well-developed bog shows a distinct succession of vegetation. First, comes Sphagnum bog; it is succeeded by various related combinations of species in which rush-like Cyperaceae and the xerophytic Gleichenia circinata page 203with its plagiotropic pinnae and their pouch-like segments, is dominant. Finally, this is followed by shrubland or low forest, which latter may be replaced by high forest.
The life-forms are varied and include the following: — ericoid-shrub, creeping-shrub with underground stem, rush-form, grass-form, tussock-form, cushion-form, prostrate creeping-herb, Gleichenia-form, rosette-herb, summer green tuberous-form. Generally speaking xerophytic structure is present to a considerable degree. The far-creeping stem of certain species is a most important characteristic, leading, as it does, to enormous vegetative increase and consequent dominance of a particular species over a wide area.
Many bog species, especially in South Island, are also subalpine or alpine, while the bogs of Port Pegasus, Stewart Island are virtually identical with those at 600 m. altitude, and upwards.
The various groups of associations are next to be considered but the treatment, as for most other formations, is far from exhaustive.
This group is distinguished by the presence of Sphagnum, usually in a considerable amount, and the dominance of Gleichenia circinata (G. dicarpa of Cheeseman's Manual), or G. alpina.
The distribution of this class of bog coincides with that of lowland bog in general. It occurs in wet places amongst Leptospermum shrubland, in open places in forest (especially west and south of South Island), and as a stage in succession from lake to forest following swamp; even yet, this can be seen in various localities.
The amount of Sphagnum varies much in different places. Frequently, there are pale straw-or cream-colored cushions separated from on another by dark, soft peaty ground where coffee-coloured water lies. Or, development has advanced, the cushions grow into one another forming a continuous covering of soft moss saturated with water, except after a period of drought when the surface may be dry. Almost always there are a number of species growing on the moss, some of which will be absent elsewhere on the bog, for the upper surface of the cushion contains a purer water than bog-soil in general. Between the Sphagnum and its occupants there is a "struggle" for the mastery, for the moss by its upward growth tends to bury any plant whose upward growth is too slow.
The following are common on Sphagnum-cushions throughout:—Blechnum procerum, Gleichenia circinata, Cladium teretifolium, C. Vauthiera, Hypolaena lateriflora, Drosera binata, D. spathulata, Leptospermum scoparium, Halorrhagis micrantha, Centella uniflora.
Where Sphagnum is either absent, or in scattered patches, and the soil consists of soft, wet peat, a low green carpet of Gleichenia circinata frequently covers many square metres of ground, and as it can be recognized from a considerable distance, it is the physiognomic indication, par excellence, of the association. In other places, the rush-form is physiognomic, the page 204species being Cladium teretifolium, or C. glomeratum, plants of wetter ground than the Gleichenia from which they stand distinguished by their darker green. In other places again, wide areas are occupied by Hypolaena lateriflora, a restiaceous plant with slender wiry, flexuose, leafless, semi-prostate steins which frequently form thick brownish masses 60 cm. to 1 m. in depth, mixed or unmixed with the Cladium.
In the north of the North Auckland district, and the Waikato subdistrict, the bamboo-like Sporodanthus Traversii (stems erect, up to 3 m high, crowded, stout, flexible) was originally dominant in certain bogs and made a distinct subassociation.
The bog-vegetation is generally stratified, the fern and sedges, already mentioned, forming the upper layers, or where both occur, the sedges overtop the fern. The ground-layer may consist of low-growing creeping species of Lycopodium. This is the case in the Western district where L. ramulosum, flattened close to the soil, covers extensive areas. Further north L, laterale of similar form, but with more erect stems, is the common bog-species.
On bare places as well as on Sphagnum are the tiny red rosette of Drosera spathulata pressed closely to the substratum. Several species of Utricularia are common, e. g. U. delicatula (NA., SA.), the flowers white with a yellow eye, and U. novae-zelandia (North Island, E. in South Island), its flowers pale purple but in South Island generally it is the beautiful U. monanthos with bright purple flowers and yellow eye.
The bogs of South Otago, but especially those of Stewart Island, are remarkable for the number of high-mountain plants they contain. For instance, in the latter, there is an association at sea-level equivalent to that of a high-mountain bog, as the following list clearly shows: — Gleichenia alpina, Microlaena Thomsoni, Oreobolus pectinatus, Carpha alpina (also SO.), Chrysobactron Gibbsii, Astelia linearis, Gaimardia ciliata, Caltha novae-zelandiae, Geum leiospermum, Drapetes Bieffenbachii, Actinotus suffocata, Cyathodes empetrifolia (also SO.), Dracophyllum rosmarinifolium (=D. politum), D. Pearsonii, Pentachondra pumila, Liparophyllum Gunnii, Hebe buxifolia, Oreostylidium subulatum (also SO.), Donatia novae-zelandiae (also SO. but rire), Celmisia argentea and C. linearis. In South Otago bog, Thelymitra uniflora, Gunnera prorepens (leaves often almost black) and the wiry Gaultheria perplexa are characteristic, but they are of wide range. In both South Otago and Stewart Island, Danthonia Raoulii var. rubra become established on Sphagnum-Gleichenia bog and tussock-bog results, which, as the habitat becomes. drier, changes into tussock-grassland. Analogous is the occupation of bog in the Western district by the great tussocks of Gahnia rigida which may take complete possession but the ralationship here is with forest and not with tussock-grassland.
This group is distinguished by the dominance of Leptospermum scoparium accompanied by Gleichenia, Hypolaena and other page 205plants found in the formation. Even on such bogs, as already described, there is usually more or less Leptospermum scoparium, and then it is only a question of time for this to become dominant and shrubland-bog established. Beneath the Leptospermum a good many of the bog species continue to thrive, thanks it may be to some epharmonic change. Thus Hypolaena and Gleichenia become semi-lianes and Lycopodium ramulosum grows erect, increases its stature and almost ceases to develop sporophylls. Or shrublandbog may be distinguished, as in some parts of Stewart Island or South Otago by the presence of the following shrubs either in clumps or dotted about, rather than by the dominance of Leptospermum:—Dracophyllum longifolium, Coprosma parviflora, C. rhamnoides, Hebe buxifolia, Cassinia Vauvilliersii, Olearia virgata.
Near Lake Manapouri to the east there is an extensive shrubland-bog. There is a great depth of peat. Dracophyllum Urvilleanum (one of its varieties) forms so close a mass that nothing else can be seen at even a short distance away. Within the scrub there is Sphagnum, Hypolaena, Cladium teretifolium, Oreobolus strictus and other bog species.
A rather remarkable association occurs in those flat, badly-drained areas of the North-western and Western districts known by the Maori name of "Pakihi". All that I have studied have been burned repeatedly, and. although the vegetation bears a primitive stamp through the absence usually of introduced plants, one can but guess at the composition and arrangement of the primitive vegetation.
The soil-conditions are different from those of true bog. The ground is frequently ancient coastal terrace, and the subsoil consists altogether of stones which through the presence of "iron pan" are impervious to water. The upper soil is clay capped by a layer of peat, usually quite thin, though this may be wanting. Generally, the ground is extremely wet. Where Leptospermum does not dominate the covering is a combination of Cladium teretifolium, C. glomeratum, C. capillaceum (at times), C. Vauthiera, Hypolaena lateriflora and Gleichenia circinata, just as ordinary peat-bog, in fact. Lycopodium ramulosum is abundant, and there may be Gahnia tussocks.
On the pakihis of the North-western district the North Island Epacris pauciflora is abundant. Liparophyllum Gunnii, and Gentiana Townsoni are plentiful. The very local Siphonidium longiflorum is common in places. Sphagnum is dotted about in certain parts, but is absent over wide areas, nor does it seem to be making peat. Leptospermum at all stages of development is everywhere. In the extreme north of the district there is a good deal of Lycopodium cernuum, a species otherwise wanting from a little to the south of latitude 38°.
Doubtless much pakihi is indigenous-induced, following the removal of forest, but the native name proves that there was a primitive bog association, yet it was one in which peat was virtually absent.
7. River-bed vegetation.
The vegetation of river-bed proper is distinguished by its open character and the presence of mats or low cushions of species of Raoulia and Epilobium the latter both creeping and erect.
Leaving out of consideration the semi-climax and climax associations, since they belong to other plant-formations, the communities of river-bed proper contain obout 66 species (pteridophytes 3, monocotyledons 9, dicotyledons 54) belonging to 24 families and 38 genera, the only group of any size being the Compositae with 15 species. No list is given of the common species as they are all cited in what follows.
The habitat (Fig. 1) here called "river-bed" is characteristic of those shingle plains formed by the various streams which still bear their stony burden from the lofty ranges. These beds extend from the sea-coast far into the mountains. Their greatest development is to the east of the Divide in South Island, though on the west, although shorter, they are still considerable. In North Island river-bed is much less in evidence.
Between the vegetation of river-bed at different altitudinal belts it is not easy to draw the line; ecological differences are slight, and many species occur throughout. Rainfall is the chief factor that governs the combinations; thus in South Island the humid west favours the presence of plants in the lowlands which are purely subalpine in the drier east.
Terraces in most places bound the lowland and montane river-beds, while these latter may be 1.6 km. in width. It is obvious that as the stony plains themselves have been subject to inundation in all parts during their formation, the vegetation-dynamics of river-bed at the present time must be very similar to that of the plains during their construction.
Typical river-bed consists of a more or less flat expanse of stones which vary considerably in size and are mixed with a large but varying proportion of sand and silt. The river-proper wanders from side to side of the bed in anastomosing streams, its path restricted only by the terraces or adjacent mountains slopes. During the frequent floods, the streams may change their course, so turning stable ground into flood-plain, but rendering the abandoned stony bed fit for plant-colonization. Moreover, the stream may cut into its bed, and terraces, such as now exist far from the river's influence, but whose surfaces are ancient flood-plains, be in process of formation. Thus it can be seen that various associations will exist, each marking a certain phase in the development of the land-surface, commencing with the peopling of the bed as the water recedes, and ending with the vegetation of the oldest flood-plain, the climax-association of the east being shrubland or tussock-grassland and of the west forest.
The ecological conditions are comparatively simple. The stony sub-page 207stratum favours rapid drainage, the water-content close to the surface being extremely small. At a depth of about 30 cm. there is always a certain amount of moisture; the stones themselves assist in reducing evaporation; the sand and silt hold water to some extent; and doubtless the water-table is near enough, even on the highest parts of the bed, to allow deep-rooting plants water in abundance. Were this not so, the extensive plantations of the Canterbury Plain, where the rainfall is low, could not exist. At first, there is a total absence of humus and but little of nutritive salts. When the sky is cloudless, the plants are exposed to an extremely bright light and the stones become burning hot. The wind, hemmed in between terraces, or adjacent mountain-slopes, sweeps over the ground with great force, but its effect is mitigated somewhat by the unevenness of the bed and its larger stones, which afford both shelter and shade. On the east, the hot, dry North-west wind not only causes excessive transpiration, but the course of the river is marked by great clouds of silt and finer sand high in the air. The rainfall is a factor of moment though much less than in the case of retentive soils nor does it affect the subterranean water-supply, which is regulated by the downpour on the mountains.
In many localities, the vegetation is much altered, especially by continuous thickets of the introduced Ulex europaeus and Cytisus scoparius, but, although various foreign species generally occur where these plants do not dominate, much river-bed is still primitive enough to allow accurate conclusions to be drawn as to its original character.
As for the life-forms of the 66 species, 14 are shrubs, 41 herbs or semiwoody plants, 8 of the grass-form, 1 of the rush-form and 2 ferns. Amongst the above are represented mat-forming plants (often circular); prostrate creeping and rooting herbs; low shrubs with leafless green stems; and ericoid shrubs. Raoulia lutescens and Scleranthus biflorus are cushion plants.
b. Unstable river-bed formation.
Here there is only the one community — the Epilobium-Raoulia formation — which is distinguished by the presence of Epilobium pedunculare, and in South Island, E. melanocaulon and E. microphyllum — though these two may be absent at below 300 m. altitude — together with Raoulia tenuicaulis.
The formation (it is complete in itself and not an initial succession) occupies that portion of the river-bed subject to frequent flooding and eventually complete overthrowing. However, there must be stability enough to allow the windborne seeds of the Epilobia and Raouliae to gain a footing, germinate, and produce mature plants. Both E. pedunculare and R. tenuicaulis have creeping rooting stems which hug the ground. The latter grows rapidly, owing to its mesophytic juvenile form and its reversion-shoots; it forms flat, green or silvery patches 60 cm. or far more diam. (Fig. 46). A few plants of R. australis may also be present.
c. The communities of stable river-bed.
In the case of stable river-bed, the substratum lies beyond the reach of ordinary floods. Its vegetation is an initial succession which leads, according to the climate of the locality, to tussock-grassland, shrubland or forest as its climax. The substratum varies considerably according as its surface is stony or silty, the stones, often coated with a dark lichen, may be packed as closely as if paved.
The eastern South Island Raoulia association.
The association is distinguished by the presence of mats or low cushions of species of Raoulia. They attain their greatest development in the North-eastern and Eastern districts and what follows refers to these alone. Generally, there is far more stony ground than plants. Low, silvery, dense flat cushions of Raoulia lutescens are everywhere, their cushion-form arising from a gradual filling of the plant with wind-borne silt. Great dull-green patches of the shrubby Muehlenbeckia axillaris are common, and the leafless, grey-coloured rushlike stems of M. ephedroides, of similar habit, may be present. Raoulia australis, looser in habit than R. lutescens, will be abundant both on silty and stony ground. Somewhat older bed may contain large colonies of Carmichaelia nana, its flat, leafless, vertical stems close together and a few centimetres tall. The larger, thicker stemmed C. Monroi, usually subalpine, may occasionally be present. On the older parts of the bed there will be many large irregular patches of Raoulia Monroi, distinguished by its folded, silvery, distichous small leaves. Thickets of Cassinia fulvida may abound or of C. albida (NE.), and where both species are present there will be a polymorphic hybrid swarm. Patches of Racromitrium lanuginosum are frequent. Besides the species cited above the following are more or less abundant: — Scirpus nodosus, Scleranthus biflorus, Tillaea Sieberiana, Carmichaelia subulata, Oxalis corniculata, Geranium sessiliflorum var. glabrum, Epilobium nerterioides, Daucus brachiatus, Leucopogon Fraseri, Gnaphalium japonicum, G. collinum, Cotula perpusilla.
The later history of the association is dealt with further on under the heading tussock-grassland.
Low isolated dunes, or short ridges, are frequent here and there on river-bed (E.). They are simply collections of the blown sand and silt. Usually they are fixed by vegetation. The small tree Edwardsia microphylla was originally common. Phormium tenax, Arundo conspicua and Cassinia fulvida are abundant. The species of Raoulia are generally absent. The introduced Lupinus arboreus has complete possession in some localities.
Groves of trees &c. on eastern river-bed.
In some places, even yet, small groves of trees are to be met with, especially at the base of a high terrace. Edwardsia microphylla will be dominant, accompanied probably by Cordyline australis, Pittosporum tenuifolium, Melicytus ramiflorus, Fuchsia page 209excorticata, Nothopanax arboreum and Griselinia littoralis, while Rubus australis var. glaber, Muehlenbeckia australis and Parsonsia heterophylla may be abundant as lianes loading the trees with greenery.
Phormium-Arundo-Cordyline swamp and slowly-flowing streams or ponds with aquatic and swamp vegetation are common enough on river-beds, but they are identical with similar associations elsewhere and need no description.
The western South Island Raoulia association.
This is distinguished by the absence of many of the eastern xerophytes and the presence of Mazus radicans, Acaena Sanguisorbae var. sericeinitens and species of Coriaria and their numerous, polymorphic hybrids. Frequently the vegetation is closed. Here the association of the Western district is alone considered.
The following are the important species: — Carex comans, Muehlenbeckia axillaris, Ranunculus foliosus (sometimes), Acaena Sanguisorbae var. sericeinitens, A. inermis, Coriaria sarmentosa, C. lurida, X C. sarlurida, Pimelea prostrata var. repens, Epilobium pedunculate, Hydrocotyle novaezelandiae, Mazus radicans, Veronica Lyallii (common in montane belt, but rare et sea-level), Coprosma rugosa, C. brunnea, Nertera depressa, Wahlenbergia albomarginata, Pratia angulata, Helichrysum filicaule, H. bellidioides, Cotula squalida, Raoulia glabra (sometimes), R. australis, R. tenuicaulis.
The station, thanks to the frequent downpour, is mesophytic notwithstanding the coarse, stony substratum. Rocks far larger than on eastern river-bed are present. Hot dry winds are virtually unknown; frosts are never heavy.
On older river-bed shrubs come in and there is a procession of events leading eventually to forest, an account of which is next presented.
Western river-bed forest.
This is distinguished by the close growth of low slender trees and the presence of species wanting or rare in the adjacent lowland forest e. g. Rubus schmidelioides var. coloratus, Coriaria arborea, Pennantia corymbosa, Aristotelia serrata, Plagianthus betulinus and Coprosma rotundifolia, as a tree. Here only the association of the Western district receives consideration. The species may be seen from what follows.
The ground is level und traversed by numerous streams. The upper soil consists of humus beneath which is merely river-shingle. The vegetation is in three layers — the floor-plants, the small tree-ferns and shrubs and the low trees. The association is 4.5 to 6 m. high. Slender tree-trunks not exceeding 15 cm. diam. are the rule; they may be erect or more or less leaning and draped with a moos-mantle, while from their branches hangs the pale moos Weymouthia Billardieri. Coprosma rotundifolia, elsewhere usually a shrub, is the dominant tree, and it grows in such profusion at times as to make pure stands. Besides the trees already mentioned, page 210the following are common: — Carpodetus serratus, Melicytus ramiflorus, Fuchsia excorticata, Pseudopanax crassifolium var. unifoliolatum and Griselinia littoralis. Podocarpus acutifolius and Weinmannia racemosa may occur.
The second tier consists of young forest-trees, the Coprosma-form dominating together with small Dicksonia squarrosa and Hemitelia Smithii and the semi-tree-ferns Polystichum vestitum and Dryopteris pennigera. On the floor are mosses, liverworts, the liane Metrosideros hypericifolia (creeping), Blechnum procerum and B. fluviatile.
The lianes Rubus schmidelioides var. coloratus, Metrosideros hypericifolia and Polypodium diversifolium are common, the two latter being especially abundant on tree-fern stems. The filmy ferns, Hymenophyllum scabrum, H. sanguinolentum and Trichomanes reniforme cover the leaning trunks, particularly of Griselinia littoralis. Polypodium grammitidis, P. Billardieri and the orchid Earina mucronata are fairly common as epiphytes.
At an altitude of some 300 m. on river-bed in the Western district there is an association closely allied to subalpine totara forest, although that of the adjacent slopes is Weinmannia-Metrosideros and that of swamps Podocarpus dacrydioides.
Podocarpus Hallii, Phyllocladus alpinus (a tree) and Pseudopanax crassifolium var. unifoliolatum are dominant (Fig. 48) and Libocedrus Bidwillii sub-dominant. The forest is low, the trees &c. are erect. The under-growth consists principally of Polystichum vestitum, Pittosporum divaricatum, Aristotelia fruticosa, Nothopanax simplex, N. anomalum, Suttonia divaricata, Coprosma rotundifolia, C. propinqua, Olearia ilicifolia and O. avicenniaefolia. There is also some Wintera colorata, Carpodetus, Pittosporum Colensoi (Fig. 47), Pennantia, Myrtus pedunculata and Griselinia littoralis. Rubus schmidelioides var. coloratus is the sole liane.
North Island river-bed.
Generally the habitat is narrow and the species few. The following are probably the most important: Epilobium pedunculare, Hebe salicifolia (in a wide sense), Veronica catarractae var. resembling the type, V. lanceolata, V. diffusa, Raoulia tenuicaulis, Gnaphalium keriense and Cassinia leptophylla.
The natural grasslands of New Zealand differ essentially from meadows of the Old World. Green, flat-leaved, turf-forming grasses do not rule, in their stead is brown tussock composed of closely-bunched often filiform rolled leaves and slender oulms. Frequently, and probably always in the primitive associations, the tussocks grew so closely as to hide such smaller plants as might be present.
Grassland is for more abundant in South Island than in North Island.page 211
It is absent in the north of the island except at the southern boundary of the South Auckland district, its place being taken by shrubland, fernland or bog. Further south, it occurs in the subalpine belt of the high mountains; also, at a lower level, on the flat parts of the Volcanic Plateau, and to the east of the central mountain chain, through, there, most if not all is of indigenous-induced origin. In South Island, it occupies wide areas to the east of the Divide and extends in places from sea-level to perhaps 1500 m. altitude, being indeed the most striking physiognomic feature of the vegetation.
The tussock-grasslands are by no means virgin, yet, to the inexperienced eye, they seem primitive enough. By far the greater part has been modified by sheep-farming since the "fifties" of last century and subjected to the periodical burning which that type of agriculture is considered to demand. Then, from the end of the "seventies" it has been exposed nearly everywhere to the depredations of rabbits but in numbers differing in different areas. Taking all the above into consideration, the marvel is that the tussock-grassland has been so little changed. Certainly, in the lowlands, much has been ploughed and replaced by artificial pastures of European grasses, or by farmlands of short-rotation crops. In some localities, the association is indigenous-induced, it having replaced Nothofagus cliffortioides forest after the latter was burned. There is also some evidence already dealt with that considerable areas of apparently primeval tussock-grassland owe their origin to the burning of forest long ago, such evidence being based partly on Maori tradition and partly on the actual presence of burnt trees on the hillsides of Canterbury, Central Otago, and elsewhere.
There are two distinct types of tussock-grassland, the one where comparatively small tussock-grasses dominate, here called "Low tussock-grassland", and the other where far larger, more massive tussocks are dominant, here called "Tall tussock-grassland".
In preparing what follows, it has seemed best not to restrict the account of these two formations to their occurrence in the lowlands, but to deal with them up to that level on the mountains where they begin to receive a reinforcement from the true high-mountain species sufficient to alter their floristic and ecological condition.
b. The plant-formations and groups of associations.
1. Low (Festuca-Poa) tussock-grassland.
This highly-important plant-formation is distinguished by the presence of the medium-sized tussock-grasses in such quantity as to frequently touch one another — it may be with the tips of the leaves only — and to conceal most of the other species except on a close examination. The dominant tussocks are Festuca novae-zelandiae, Poa caespitosa and, in some places, P. intermedia and, in primitive New Zealand, Agro-page 212pyron scabrum 1 (in a wide sense). At the present time, as far as I know, there are no examples of the primitive formation, nevertheless by means of comparative studies, carried out over the whole formation, it does not seem impossible to reconstruct the community in one's mind.
The low tussock grassland indigenous flora consists of 216 species (pteridophytes 10, monocotyledons 66 and dicotyledons 140) belonging to 38 families and 104 genera, the largest being, (families) Gramineae 36, Compositae 35, Cyperaceae, Leguminosae and Onagraceae 11 each, Umbelliferae 9, Rosaceae 8; (genera) Poa and Epilobium 11 each, Carmichaelia 9, Deyeuxia 8, Carex, Acaena and Raoulia 7 each. There are also at least 16 hybrid swarms.
Many of the species included in the above statistics play no part in the structure of the communities, but the following are either of prime-importance in that regard or are wide-spread and abundant: — Dichelachne crinita, Danthonia pilosa, D. semiannularis, Poa caespitosa, P. Colensoi, P. intermedia, Festuca novae-zelandiae, Agropyron scabrum (Gramin.), Carex Colensoi, C. lucida, C. breviculmis (Cyperac.), Luzula campestris (in a very wide sense), L. ulophylla (Juncac.), Chrysobactron Hookeri (in a wide sense) (Liliac.), Muehlenbeckia axillaris (Polygonac.), the 2 vars. of Scleranthus biflorus (Caryoph.), Ranunculus multiscapus (Ranun.), Acaena microphylla, A. inermis, × A. microinermis, A. Sanguisorbae var. pilosa (Rosac.), Carmichaelia subulata (Legum.), the vars. of Geranium sessiliflorum (Geraniac.), Oxalis corniculata in a wide sense (Oxalidac.), Coriaria sarmentosa (Coriariac.), Discaria toumatou (Rhamnac.), Viola Cunninghamii (Violac.), Pinelea prostrata in a wide sense (Thymel.), Epilobium Hectori, E. pedunculare in a wide sense, E. novae-zelandiae (Onagrac), Hydrocotyle novae-zelandiae in a wide sense, Oreomyrrhis Colensoi, O. ramosa, Aciphylla Colensoi, A. squarrosa, Anisotome aromatica, Daucus brachiatus, Angelica montana — in the primitive formation (Umbel.), Leucopogon Fraseri (Epacrid.), Convolvulus erubescens, Dichondra repens (Convol.). Plantago Raoulii, P. spathulata (Plantag.), the vars. of Coprosma Petriei, Nertera setulosa (Rubiac.), Wahlenbergia albomarginata, the forms of W. gracilis (Campan.), Vittadinia australis, Celmisia longifolia, Gnaphalium Traversii, G. luteo-album, G. japonicum, G. collinum, Raoulia subsericea, R. glabra, Helichrysum bellidioides, H. filicaule, Craspedia uniflora in a wide sense, Cotula squalida, Lagenophora petiolata, L. cuneata, Brachycome Sinclairii, Senecio bellidioides and Microseris Forsteri (Compos.).
1 1) This statement is based on the facts that all the forms of this grass being far more palatable than the Festuca or the Poa — knowledge recently acquired by experiments carried out by W. D. Reid and myself — has been eaten out where not protected, and that when open pasture is fenced securely from grazing animals the Agropyron appears once more in true tussock-form. The species itself is a compound one made up of many jordanons, differing greatly in colour and of two types, the one a true tussock and the other creeping and mat-like.
In any consideration of the formation the exotic species cannot be omitted. These number about 74, which belong to 21 families and 54 genera, the most important being the following: Gramineae 20 species, Compositae 11, Caryophyllaceae 8 and Leguminosae 6. None of the genera contain more than 4 species1.
In the wet North-western district with its forest climate, the formation is confined to stony montane valleys (old flood-plains). In North Island, it occurs to some extent in the montane belt of the Volcanic Plateau.
The life-forms of the formation (216 species) are as follows: trees 2, shrubs 31, tussocks 13, other plants of the grass-form 43, herbs 90, semi-woody plants 30, ferns 7; and 16 of the foregoing are summergreen, 131 mesophytes and 85 sub-xerophytes or xerophytes.
As in the case of forest, the low tussock-grassland formation is present, in its full development, in a wide range of climates and soils, but with this difference, that forest cannot be established except with a fairly high rainfall and many rainy days, whereas low tussock-grassland has much the same composition and structure in climates ranging from an annual rainfall of 225 cm. to 35 cm., nor is this all, for where growing under conditions antagonistic to the natural establishment of forest, violent hot winds may be frequent, as also long periods of drought and a summerheat constantly above 26° C. in the shade, while 38° is not unknown. Evidently, the mesophytes growing in the protection of the tussocks escape much of these severe conditions, but the tussocks themselves and the shrubs which considerably overtop them (species of Carmichaelia, Discaria toumatou) are exposed not only to the semi-arid climate just described but to one of extreme humidity and to every degree of transition from the one to the other. Hence, the old idea — still more or less current — that the tussock-form of these dominant grasses had been evolved in order to combat xerophytic conditions, must be abandoned. And this dictum is strongly supported by the fact, dealt with below, that various turf-making grasses and other life-forms make extensive colonies — no shade or shelter being available — under the dry tussock grassland environment.
1 Festuca rubra var. fallax — has been sown largely, Anthoxanthum odoratum, Agrostis tenuis, A. alba, Holcus lanatus, Aira caryophyllea, Dactylis glomerata, frequently sown, Poa annua, P. pratensis, Rumex Acetosella, Silene anglica, Cerastium glomeratum, C. triviale, Stellaria media, Arenaria serpyllifolia, Sagina apetala, Rosa Eglanteria, Ulex europaeus, Cytisus scoparius, Trifolium arvense, T. repens, T. dubium, Geranium molle, Erodium cicutarium, Linum marginale, Centaurium umbellatum, Myosotis arvensis, Prunella vulgaris, Veronica agrestis, Plantago lanceolata, P. major, Achillea Millefolium, Cnicus lanceolatus, Crepis capillaris, Hypochoeris radicata. Many of the above merely occur on the bare ground, so they are rather invaders bent on making a new formation than real colonists.
Montane grassland is richer in species, certain plants common at a higher altitude being present. The following assist in modifiyng its physiognomy at a near view: — Poa Colensoi, Scleranthus biflorus, Acaena Sanguisorba var. pilosa, Pimelea prostrata var. repens, Aciphylla Colensoi, Plantago spathulata, Wahlenbergia albomarginata, Brachycome Sinclairii, Celmisia spectabilis, Raoulia subsericea and Senecio bellidioides.
Life-history of the formation.
1 1) The first account of this was given by the author (1911b.) but it dealt with the subalpine belt. Subsequent papers treating of the subject are Cockayne and Foweraker (1916: 175–76) and Foweraker (1917: 4.5.), both relating to montane river-bed; see also Cockayne, L. (1926: 356 and Fig. 59.).
2 Raoulia tenuicaulis, R. lutescens, R. australis, R. apice-nigra, R. Monroi, R. Haastii and R. Parkii.
3 Prostrate shrub with far-creeping, matted, rooting underground-stems, forming large, circular patches; the leaves are very small, oblong to oblong-orbicular, glabrous and more or less coriaceous.
Obviously, the early colonizers of mats &c. must be light-tolerating species, but, except in the case of rapidly-growing large plants, to be shade-tolerating also is an advantage. For, as the seedling tussock-grasses increase in size they cut off the light, so that in time only those species which possess the dual property of tolerating both bright light and more or less shade survive. But the shelter afforded by the incoming tussocks makes the bare patches between them more suitable for seed germination, so that the vegetation by degrees becomes closed. Finally, as there is no uniformity in the habitat — old flood-plain though it be — but many transitions from wet places to those more stony and drier than the average, there comes a distribution of the species in accordance with such differences, the most xerophytic occupying the dry stony ground1 and mesophytes on the more silty and moister. In course of time, too, the species themselves modify the habitat through slowly adding humus to the soil.
Besides the species indubitably belonging to the formation there are others of a different class. Thus, an important succession following the river-bed stage is Discaria toumatou thicket. Now, though this spinous shrub dotted about the grassland is a characteristic feature, it must be considered rather a relic of the former shrub-association than a true member of the grassland, the shrub-association, as it died with age, being replaced by the tussock community. Also, other species may, by invasion, become established here and there, the forerunners of unrelated associations, especially species of Cassinia, or if near forest species of Nothofagus. So, too, with Pteridium esculentum and Coriaria sarmentosa — these really members of fern-heath —, Cordyline australis and Phormium tenax. Aspect plays an all-important part in delimiting these invaders, one which is sunny favouring Pteridium and one moister and more shady Phormium.
The foregoing sketches only the life-history of those low tussock-grassland associations on ancient river-bed, fans and the like, so that extensive portion of the formation covering hillsides has now to be considered. At the present time, the early, and successive stages of development can no longer be seen. The best clue is to be gained from studying what is taking place on the bare ground — plentiful enough — which has come into being through sheep-grazing, burning the tussocks and the attacks of rabbits.
1 1) A distinct community is confined to the most stony ground — really a piece of the old river-bed association not converted into grassland — consisting chiefly of Muehlenbeckia axillaris, Carmichaelia nana, Raoulia Monroi and Cotula perpusilla. It is again referred to further on.
These damaged areas — the major part of the formation — are occupied by different species in harmony with the amount of damage done, the nature of the soil and the climate. The effect of the last is so marked, that although low tussock-grassland as a whole is of a uniform physiognomy and composition, the actual procession of successions can hardly have been everywhere the same. This stands out clearly in semi-arid Central Otago (NO.), as will be seen in Part III. However, the general principle seems to be that regeneration — and one may presume the same for primitive establishment — depends upon the ground being occupied, first of all, by mat-plants or low cushion-plants of which the following appear to be the most important so far as montane low tussock-grassland is concerned: — Muehlenbeckia axillaris, Acaena inermis, Coprosma Petriei, Raoulia subsericea and R. glabra. Badly-damaged tussocks also provide an acceptable station for colonization and so, too, both tall and low-growing open shrubs while, in the latter, many grasses become established and form nuclei for seed-dissemination; Discaria toumatou and Hymenanthera alpina continually function in this regard.
Primitive low tussock-grassland.
At the present time no association, or even portion of such, can claim to be truly primitive, through many areas look as if they were so. Probably the outstanding differences between the primitive and modified grassland are, (1.) that the tussocks were very close together in the primitive formation and that the smaller species were represented by far fewer individuals and belonged rather to stages of succession than to the climax, (2.) that species of higher palatability1 for sheep than Poa caespitosa or Festuca novae-zelandiae were common, especially Angelica montana2 (now extremely rare), and the varieties of Agropyron scabrum. There would also be (3.) far more Aciphylla squarrosa in the lowland belt and, in the montane, more A. Colensoi. Probably (4.) the invasion of shrubs and of fernland had not commenced.
Modified lowland low tussock-grassland.
This association extends on the piedmont alluvial plains and adjacent hillsides from the R. Wairau to the southern limit of the formation. Though essentially belonging to the drier parts of South Island, it occurs to a limited extent where the rainfall is excessive.
1 1) The matter of relative palatability of tussock-grassland plants was studied in considerable detail by W. D. Reid and myself, both by experiment and field observations. The results are in perfect accordance with the present composition of low tussock-grassland.
2 C. E. Christensen informed me that, where the grassland near Lake Tennyson (NE.) had been fenced from stock and rabbits by a "rabbit-proof" fence, Angelica montana was in similar abundance to what it was in the early days, as described by old settlers.
The grassland of the Canterbury Plain (E.) has been greatly modified or swept away by agriculture. As for its flora, it seems clear that the species cited for the formation as common would be abundant. In addition, there are a few species of restricted distribution1
Low tussock-grass of semi-arid habitat.
In its most extreme form this association occurs in the valleys and on the lower mountain-slopes of the upper Clutha basin (NO.), and extends to almost the average westerly rainfall. At the present time the species number about 74, but doubtless there were more in the primitive association. An association similar in character, but floristically richer, clothes much of the lower Mackenzie basin-plain and the lower Waitaki valley.
In the virgin association, even in the most arid part, there appears to have been as close a covering of the tussocks of Festuca novae-zelandiae and Poa caespitosa as in the low tussock-grassland generally. Many forms of Agropyron scabrum were abundant2 The following are either confined to the association or extremely rare elsewhere: — Acaena Buchanani, Carmichaelia Petriei, C. curta, C. compacta, Pimelea aridula, P. sericeo-villosa, a most distinct var. of Convolvulus erubescens or an undescribed species and various forms of Myosotis pygmaea. At the present time, in many places there is hardly a hint of the original plant-covering, but one of lindigenous-induced origin rules in its stead. An account of this remarkable state of affairs is given in Part III.
Montane low tussock-grasslantjL
This falls into two classes of, (1) where Festuca novae-zelandiae is dominant, and (2.) where Poa intermedia is extremely abundant and may dominate.
1 Scirpus nodosus, Hypoxis pusilla, Muehlenbeckia ephedroides (stony ground, a relic from river-bed), Carmichaelia nana, (as for the last-named but far commoner), Raoulia Monroi (associated with C. nana, also a river-bed relic), Cotula Haastii (far more abundant on the Port Hills and perhaps confined thereto), C. filiformis (not seen on the Canterbury Plain since it was collected by Haast, but occurs in a few places on the Hanmer Plains).
2 This reconstruction of the association has been made possible through research carried out for The New Zealand Department of Agriculture by the author, and especially by an examination of areas fenced from sheep and rabbits, and through a series of experiments carried out by the author on an area of maximum depletion where the regeneration of the pasture could be observed in relation to aspect, altitude, the moisture-content of the soil and competition between species. For a brief account see Cockayne, L. (1926: 355–361).
(Class 2.) Poa intermedia grassland occurs on the mica-schist mountains (NO., SO.) where, owing to the absence of shingle-slip, grassland with but few true high-mountain species, ascends on some mountains to 1200 m., or much higher. Its chief characteristics are the presence of Poa intermedia in abundance and a good deal of Agropyron scabrum and Festuca novae-zelandiae, and its florula being more that of lowland, than of montane grassland.
2. Tall tussock-grassland.
Tall tussock-grassland is characterized by the dominance of either Danthonia Raoulii var. rubra or var. flavescens1 together with certain low-growing shrubs semi-woody plants and herbs which tolerate wet, sour-soil. At the present time most of such grassland is more or less modified, while, over wide areas, it has been converted into farms. Ecologically it falls into two groups of associations dominated respectively by D. Raoulii var. rubra and D. Raoulii var. flavescens.
Its indigenous flora consists of 57 species (pteridophytes 3, monocotyledons 18, dicotyledons 36) belonging to 22 families and 50 genera, the largest being Gaultheria with 3 species only.
1 1) Taxonomically, the group of which D. Raoulii Steud. is the type is in a state of great confusion, owing to the two distinct jordanons D. Raoulii var. rubra Ckn. (= D. Raoulii Steud. in Man. N. Z. Flora, ed. 2, p. 174, in part) and D. flavescens Hook f. and a vast number of hybrids between the two being united together by New Zealand botanists under the name D. Raoulii. There may also be other jordanons in the mixture. It is not unlikely that D. Raoulii Steud. (D. rigida Raoul) is identical with D. flavescens Hook. f. Under the circumstances, in order to avoid confusion, I am here dividing the group into D. Raoulii var. rubra Ckn. ined. (= the forms with narrow reddish leaves — "red-tussock") and var. flavescens (Hook, f.) Hack. ex Cheesem. (= the forms with broad, green leaves — "snow-grass"), since I do not know what is really the type of D. Raoulii. Both, I consider valid compound species.
The life-forms may be classified as follows: — shrubs 12, herbs 25, semi-woody plants 5, grass-form 9, rush-form 4, ferns 2.
The physiognomy of the vegetation depends upon the great size of the tussocks, their reddish or green colour, as the case may be, and dense growth; except for an occasional shrub raised above the tussock all else is hidden. Thus, the habitat is far from uniform, and this is reflected in the tier of species subject to violent winds and, at times, strong light, and in the ground layer where the air is still, usually moist and the light comparatively dim.
The Danthonia Raoulii yar. rnbra (red-tussock) association.
This falls into 3 subassociations — (1.) that of the Southland Plain, (2.) the Stewart Island and (3.) the lower montane. All are intimately related to bog and appear to be that formation changed by the incoming of the tall Danthonia, its subsequent dominance and the consequent suppression of such species as could not tolerate the diminution of light caused by the close growth of the tussocks.
The following are the principal species of the Southland Plain sub-association:—Blechnum penna marina, B. procerum, Danthonia Raoulii var. rubra, Hypolaena lateriflora, Astelia Cockaynei, Herpolirion novae-zelandiae, Thelymitra uniflora, Carmichaelia virgata, Geranium microphyllum, Halorrhagis micrantha, Centella uniflora, Gaultheria depressa, G. perplexa, Cyathodes empetrifolia, Gentiana Grisebachii in a wide sense, Plantago Raoulii in a wide sense, Coprosma parviflora and Lagenophora petiolata. Species of minor importance are Cladium Vauthiera, Oreobolus pectinatus, Gunnera mixta, G. prorepens, Nertera depressa, Helichrysum bellidioides and H. filicaule.
The chief ecological factor is the wet, sour, peaty soil which results from the frequent cold, south-westerly rain. But, as already seen, the tall species are subject to different conditions from those growing more or less close to the ground, in fact the community is a combination of grassland and bog.
The Stewart Island subassociation contains nearly all the above species and, in addition, the following which are either absent or rare in the community last described: — Lindsaya linearis, Lycopodium ramulosum, Microlaena Thomsoni, Gaimardia ciliata, Ranunculus Kirkii, Geum leiospermum, Actinotus suffocata, Liparophyllum Gunnii and Hebe buxifolia in a wide sense. Hypolaena lateriflora and Leptocarpus simplex frequently fill the spaces between the tussocks and exclude the smaller species.page 220
The lower montane subassociation, in addition to many of the bog plants, contains species of drier ground — the habitat ranging from semi-bog conditions to those supplied by fairly well-drained ground — e. g.: Uncinia rubra, Geranium sessiliflorum var. glabrum, Viola Cunninghamii (also a bog plant), Aciphylla squarrosa (also a bog plant), A. Colensoi, Leucopogon Fraseri, Wahlenbergia albomarginata, Celmisia longiflora, Raoulia subsericea, Craspedia unifiora in a wide sense, Senecio southlandicus; Herpolirion and Oreostylidium subulatum are common.
Danthonia Raoulii var. flavescens association.
This occurs on the hill-slopes of the northern part of the South Otago district. Fire has almost wiped it out of existence and its former presence is only betrayed by isolated plants of D. Raoulii var. flavescens or patches here and there which look quite out of place. As to its original composition, I can say nothing, but a well-marked bright-green variety of Aciphylla squarrosa — using this name in a very wide sense — is frequently an accompanying plant.
9. Rock vegetation.
The group of associations dealt with here is distinguished by the presence of certain species confined, or almost so? to a rock-habitat, together with various epiphytes, root-climbing lianes, xerophytes and sub-xerophytes of the neighbourhood of a rock association, and such mesophytes as epharmonically can colonize rock.
The species number about 193 (pteridophytes 31, monocotyledons 30, dicotyledons 132) which belong to 40 families and 102 genera, the largest being the following: — (families) Compositae 32 species, Filices 31, Scrophulariaceae 15, Myrtaceae 9, Onagraceae 8; (genera.) Hebe 11, Epilobium and Metrosideros 7 each and Coprosma 6. The following are common species of wide range: Adiantum affine, Cheilanthes Sieberi, Asplenium flaccidum, Pteridium esculentum, Polystichum Richardi, Polypodium diversifolium, Cyclophorus serpens (Filic.), Dichelachne crinita, Danthonia pilosa, D. semiannularis, Poa caespitosa, Festuca novae-zelandiae, Agropyron scabrum (Gramin.), Scirpus nodosus (Cyperac.), various vars. of Luzula campestris (June.), Cordyline australis, Phormium tenax, P. Colensoi (Liliac.), Thelymitra longifolia in a wide sense (Orchid.), Muehlenbeckia complexa in a wide sense (Polygonac.), Scleranthus biflorus (Caryoph.), Acaena novae-zelandiae, A. Sanguisorbae var. pusilla, Rubus australis in a wide sense (Rosac.), Oxalis corniculata (Oxalidac.), Leptospermum scoparium, Metrosideros hypericifolia (Myrtac.), Epilobium pubens, E. nummularifolium (Onagrac.), Griselinia littoralis (Cornac.), Dichondra repens (Convolv.), various vars. of Hebe salicifolia (Scroph.), Coprosma robusta (Rubiac.), Wahlenbergia gracilis in a wide sense (Campan.), Lagenophora pumila, Shawia paniculata, Helichrysum glomeratum, Brachyglottts repanda (Compos.).
Rock-vegetation does not play nearly so important a part in the lowland-page 221lower hills belt as in those of the coast and the high mountains, for it is absent in those wide areas, the gravel-plains of both islands, the northern gumlands, the Waikato plain, the Egmont-Wanganui coastal plain, the even pumice land of the Volcanic Plateau, and is but little in evidence on some of the lower hills. By far the greatest development is in river-gorges and narrow valleys, also near some of the large lakes and in the highest part of the lowland belt, but there the associations are usually only a continuation of those at a higher level.
As elsewhere, rock offers most diverse ecological conditions for plant-colonization, the most outstanding differences being due to the degree of wetness of the rock which is, in part correlated with position in regard to illumination. Really, in most associations so-called, there are several distinct communities according to the nature of the substratum, especially with regard to the slope of the rock, the amount and depth of the soil other than pure rock, and the aspect in regard to sun, shade and the prevailing wind. Evidently, then, any attempt to deal here with all the combinations of species is out of the question, all that is attempted is a general account of the principal communities according to latitudinal range and some particulars about special rock-species.
The life-forms of the 193 species are as follows: — shrubs including dwarfed trees and woody lianes 70, herbs and semi-woody plants 77, grass-form 15, rush-form 1 and ferns 30.
Communities of the Auckland districts.
The most important rock-plants are as follows: — Asplenium flaccidum, Polypodium diversifolium, Cyclophorus serpens, Blechnum procerum, Poa anceps, Cladium Sinclairii (often dominant), Cordyline Banksii, Phormium tenax, P. Colensoi, Astelia Solandri (often dominant), Astelia Cunninghamii var. Hookeriana (abundant on old lava flows), Bulbophyllum pygmaeum, Earina mucronata, Peperomia Urvilleana, Elatostema rugosum (wet rocks), Rubus australis, Coriaria arborea, Leptospermum scoparium, Metrosideros carminea (sometimes dominant), M. perforata, Griselinia lucida, Gaultheria antipoda, Cyathodes acerosa, Leucopogon fasciculatus, Hebe salicifolia in a wide sense, H. macrocarpa, Nertera Cunninghamii (wet rocks), Olearia furfuracea, Celmisia Adamsii (Thames subdistrict and near Whangarei), Gnaphaliuwn keriense (wet rocks), Brachyglottis repanda.
Communities for the rest of North Island.
On volcanic conglomerate near L. Rotoma (VP.), and doubtless elsewhere in the destrict, there is a well-marked association dominated by the beautiful Gaultheria oppositifolia, G. antipoda var. erecta and a polymorphic swarm of hybrids between the two. Other species in the association are Pteridium esculentum, Blechnum procerum., Gahnia gahniaeformis, Danthonia pilosa, Coriaria arborea, Weinmannia racemosa (stunted), Dracophyllum Sinclairii and rather narrow-leaved Hebe salicifolia.page 222
In the East Cape district, rocks in the drip of water are clad with a luxuriant growth of Jovellana Sinclairii1 and probably wide breadths of Gnaphalium subrigidum or G. keriense. A very common association throughout North Island in river-gorges is that of Blechnum procerum2, Cladium Sinclairii and Gnaphalium keriense with shrubs, especially Hebe salicifolia, projecting outwards or downwards. On drier rocks, in the full sunlight, the small tuft-tree Cordyline Banksii may form close masses accompanied by Poa anceps (a most common rock-plant throughout North Island), Hebe salicifolia, Brachyglottis repanda and other shrubs.
The vegetation of the soft marl ("papa") cliffs of the many deep gorges of the Wanganui coastal-plain is perhaps the most important rock-association of North Island and represents, on a vaster scale, that briefly described above, where Blechnum procerum dominates. Taking the gorge of the Wanganui itself, there are many kilometres of cliff, sometimes sloping and sometimes perpendicular. Above comes low Beilschmiedia tawa forest, beneath wich there may be a belt of shrubs and beneath this again the true cliff-covering consisting above of masses of the drooping, smooth, flat, pale-green, grass-like leaves of Cladium Sinclairii 1 m. or so long by 2 cm. wide and great breadths of the huge leaves of Blechnum procerum, this the physiognomic plant. If the position is specially wet and shaded, pure yellowish-green colonies of Elatostema rugosum are characteristic. Nearer the base of the cliff is great abundance of Gnaphalium keriense mixed with Hebe lanceolata and beneath this again Adiantum affine with stunted fronds. Phormium Colensoi is abundant in places. Senecio latifolius is common where the rock is wet, and, in a few localities, the allied S. Turneri3 is to be found; also Ourisia macrophylla and Euphrasia cuneata add to the floral display.
In the Ruahine-Cook district the following showy species occur on rock in gorges piercing the Tararua Mountains: — Carmichaelia odorata, Jovellana repens, Hebe salicifolia var. angustissima, Veronica lanceolata, a species of Craspedia with small flower-heads and Olearia Cheesemanii.
1 1) Stem creeping and rooting, finally erect, 15 to 45 cm. tall; leaves thin, pubescent, long-petioled, ovate with blade 2.5 to 7.5 cm. long; flowers rather showy, white spotted purple.
2 The great pinnate leaves 90 cm. to even 3 m. in length project downwards; each keeping so clear of those adjacent that the whole covering makes an ideal mosaic. These close mantles of B. procerum are a striking feature of New Zealand everywhere on the banks of moist gulleys and give a most characteristic stamp to the scenery.
3 S. Turneri has a long creeping stem and bright-green, cordate leaves 15 cm. long with stalks 15 to 30 cm. It is conspicuous where it occurs, but, so far as known, it is of local distribution though extending from the Wanganui to the Mokau River.
South Island rock communities.
Rock in the Sounds-Nelson district is frequently distinguished by the presence of Hebe angustifolia with which may be associated Polypodium diversifolium, Asplenium flaccidwn, stunted Nothofagus Solandri, Muehlenbeckia complexa var. microphylla, Coriaria arborea, Melicytus ramiflorus, Leptospermum scoparium, Epilobium pubens, E. junceum, Cyathodes acerosa, Coprosma robusta and Hebe salicifolia var. Atkinsonii. On the rocky banks of the Pelorus River, Hebe rigidula and H. divaricata are common.
In the North-eastern district, generally on limestone but sometimes on greywacke, exposed to the full sunshine is perhaps the most remarkable rock-association of the region with its assemblage of species bearing most striking flowers. It is distinguished by the monotypic Pachystegia insignis 1 which is accompanied by the following though rarely are all present at the same time: — Hebe Hulkeana 2, Senecio Monroi 3, Linum monogynum, with its delicate white petals, the golden-flowered Ranunculus lobulatus, the silvery-leaved, white-flowered Celmisia Monroi, the purple Notospartium torulosum or the pink N. Carmichaeliae, the pale-lilac Wahlenbergia Mat-thewsii and a number of other species4 not restricted to this association though common members.
1 P. insignis is a stout low-growing-shrub of straggling habit. The sparsely-branching stems are grey or black, exceedingly stiff and bear at the extremities short, open rosettes of 6 to 7 obovate, thick, fleshy leaves each about 9.5 cm. long, shining green above, and clad beneath with dense, felt-like, buff tomentum. The roots pass far down into the rock. The shrub grows on the driest and steepest rock-faces. The flowers are in large hemispherical heads, 5 to 7.5 cm. diam., with yellow disc and white rays; the species apparently consists of several jordanons.
2 An erect shrub about 60 cm. high with slender branches, dark-green shining coarsely-serrate broad leaves 2.5 to 5 cm. long and a much-branched panicle up to 15 cm. long, bearing numerous soft-lilac flowers, but the colour ranges to white.
3 A dense, semi-globose, much-branched shrub up to 90 cm. high, its leaves about 2.5 cm. long, narrow-oblong wrinkled, crenate, thick, green above, white tomentose beneath and terminal corymbs of many golden-rayed flower-heads.
4 Phormium Colensoi, Angelica montana, Anisotome aromatica (a distinct jordanon), Coriaria sarmentosa and, in places, Shawia paniculata and S. coriacea, and the hybrids between them.
At the lower Waimakariri Gorge (E.) there is a rich rock-vegetation consisting of the usual xerophytic shrubs, but of special interest is the occurrence of the usually coastal Rhagodia nutans and Angelica geniculata and the strongly xerophytic fern Gymnogramme rutaefolia.
Limestone rocks have usually a very open vegetation made up with but few exceptions — e. g. Asplenium anomodon, Anisotome patula — of species growing equally well on non-calcareous rock. In the north of the Eastern and south of the North-eastern districts, common members of the association are Asplenium anomodon, Adiantum affine, Clematis afoliata — tangled masses of leafless rush-like stems and flowers greenish-yellow, fragrant — and Olearia avicenniaefolia. Near Oamaru (NO.) the rocks possess a scanty community consisting of: — Asplenium anomodon, A. Hookerianum, Epilobium junceum, Anisotome patula, and in shallow gullies, Cordyline australis, Discaria, Melicytus ramiflorus, Myoporum laetum and Coprosma propinqua. Further south at Clifton (west of SO.) the rock carries the Asplenium, Blechnum lanceolatum, Cordyline australis, Hymenanthera alpina, Edwardsia microphylla, Griselinia littoralis, Hebe salicifolia var. communis, Pimelea prostrata, Anisotome patula, and Coprosma propinqua. Near Greymouth (south of NW.), in a far wetter climate for limestone than any of the foregoing, there is Cordyline Banksii, Poly podium diversifolium, Hebe salicifolia, Olearia avicenniaefolia and Brachyglottis repanda (on dry ledges) and Asplenium lucidum, Epilobium rotundifolium, Lagenophora pumila, Craspedia uniflora var. and Gnaphalium Lyallii (where water drips).
In the semi-arid part of the North Otago district, dry mica-schist rocks are distinguished by the locally-endemic, straggling Hebe pimeleoides var. rupestris — wiry stems, small glaucous leaves, blue flowers — and the silky-haired Pimelea aridula, accompanied by Cheilanthes Sieberi, Poa intermedia, Agropyrum scabrum, Scleranthus biflorus, Rubus subpauperatus, Discaria toumatou, Corokia Cotoneaster and Hymenanthera alpina (Fig. 82). Increased rain brings in Leptospermum scoparium.