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The Vegetation of New Zealand

Chapter II. — The Vegetation of the Chatham Islands

Chapter II.
The Vegetation of the Chatham Islands.

General

, The species of vascular plants number at least 257 (pterido-phytes 53, monocotyledons 71 and dicotyledons 133) which belong to 57 families and 152 genera, the largest being the following: — (families) Filices 48, Cyperaceae and Compositae each 24, Gramineae 17, Onagraceae 13 and Umbelliferae 9; (genera) Epilobium 13, Hymenophyllum and Carex each 7, Blechnum, Scirpus and Coprosma each 6 and Asplenium and Lycopodium each 5. The florula consists of 36 endemic species, 218 of New Zealand proper (Endemic 85, Australian 121 of which 31 are cosmopolitan or sub-cosmopolitan, subantarctic South American 3, Polynesian, Lord Howe or Norfolk Island 9), 2 of Subantarctic New Zealand and 1 Australian but confined to the Chathams.

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With regard to the distribution of the 218 species, 161 occur in all three islands of New Zealand proper, 49 in North Island and South Island, 1 in South Island and Stewart Island, 1 in South Island, 5 in North Island only and 1 in Stewart Island only. Nearly all belong to the lowland flora only 30 at most ascending in New Zealand proper to above the forest line. As for the relationship of the Chathams' flora to that of the other outlying islands 38 species occur in the Kermadecs and 52 in the Subantarctic Islands.

The endemic element is remarkable as containing 23 species so closely related to one or more species of New Zealand proper that most of them, at first glance, seem hardly distinct. On the other hand, the endemic genera Coxella and Myosotidium stand out plainly, as also Agropyron Coxii, Geranium Traversii, the 3 shrubby species of Hebe, Olearia Traversii and Cotula Featherstonii and the related C. Renwickii. Endemics of this class seem to be either representatives of an earlier flora, or relics of one belonging originally to New Zealand proper.

The ecological conditions of the Chatham Islands consist of a combination of coastal, rain-forest and subantarctic factors. Thus, at no part of the main island are you distant 7 km. from the sea and the extreme is, in most places less than one half of this. High winds are frequent, especially those from the north-west and south-west. The rainfall (about 90 cm.) is not great, but the number of wet days is excessive, while cloudy skies are frequent. Frost is trivial, snow falls but rarely and a maximum temperature of 24° C. is seldom reached. The soil in many parts consists of peat frequently more than 6 m. in depth and always in a complete state of saturation. There is however, in certain localities, a much more "fertile" soil known locally as "red clay", the outcome from weathering of the volcanic rock. The main features of the vegetation, as will be seen further on, clearly reflect the climatic and edaphic conditions.

The leading physiognomic plants and their life-forms.

Certain physiognomic plants common in New Zealand proper need no further description here, e. g. the various tree-ferns, Pteridium esculentum, Desmoschoenus frondosus, Rhopalostylis sapida, Leptocarpus simplex, Rhipogonum scandens, Phormium tenax, Muehlenbeckia australis, Mesembryanthemum australe and Corynocarpus laevigata. Other species again have life-forms identical with those of their mainland relatives and differ merely in taxonomic characters, e. g. Carex sectoides, Pseudopanax chathamicum, Cyathodes robusta, the species of Dracophyllum, the large-headed species of Olearia and Cotula potentillina. There remain then only the following all endemic except the first, to be considered: — Suttonia chathamica, Myosotidium Hortensia, Hebe gigantea, Coprosma chathamica, Olearia Traversii and Senecio Huntii.

Suttonia chathamica (F. v. Muell.) Mez (Myrsin.) varies from a dense shrub 1 to 2 m. high to a round-headed low tree 4 to 8 m. high with the page 330trunk 30 to 60 cm. diam. covered with dark bark. The leaves vary in size according to the degree of exposure, but in the forest they are obovate, about 5.5 cm. × 3 cm., dull-green, rather thick, coriaceous and crowded at the ends of the twigs.

Myosotidium Hortensia Hook. (Borrag.), the Chatham Island lily, has a stout rootstock 5 cm. diam. which creeps just below the ground-surface, or is partly unburied. The rhubarb-like leaves are in erect rosettes; they are ovate-cordate to reniform, 25 cm. long × 30 cm broad, more or less, and consists of comparatively thin blade strengthened beneath by a stout framework of midrib and veins; the leaf-stalks are stout and about 12 cm. long. The flowers, each about 1.2 cm. diam., the central half of the corolla bright blue and the outer half white, are arranged in dense, sub-globose, many-flowered cymes borne on stout stalks 60 cm. high.

Hebe gigantea Ckn. (Scroph.) is a low forest-tree 4.5 to 9 m. high with an erect trunk 30 cm. or more diam. and a close, rounded crown. The leaves are lanceolate, 7 to 9 cm. long, soft, dull-green and moderately thick. Though like a gigantic form of H. salicifolia, the seedling-form is altogether distinct in its early leaves deeply and coarsely toothed, their margins ciliated, with hooked, white hairs and the strongly pubescent soft, purple stem. Succeeding leaves are larger than the adult; and, although entire are still ciliated and also pubescent on the midrib. Plants more than 60 cm. high maintain the juvenile character.

Coprosma chathamica Ckn. (Rubiac.) is a tree 4.5 to 15 m. high with a trunk 30 to 60 cm. diam. covered with light-brown bark and having oblong, obovate-oblong or lanceolate leaves about 4.9 cm. long, dark-green, somewhat thin, shining above but pale beneath, flat or with the margins more or less incurved. The species is closely related to the Kermadec C. petiolata, to which it was referred by Hooker.

Olearia Traversii (F. v. Muell.) Hook. f. (Compos.), the Chatham akeake, is a small tree 4.5 to 9 m. high with a trunk 30 to 60 cm. diam. covered with pale, rough bark and a rather dense crown. The leaves are opposite, oblong to ovate, 5.5 cm. long or shorter, soft, rather thick, bright-shining-green above and beneath clothed with dense, silky tomentum, as are also the branchlets, inflorescence-branches and involucres.

Senecio Huntii F. v. Muell. (Compos.), the rautini, is a small tree 3 to 6 m. high of the tree-composite type, with a trunk 30 cm., or so, diam. and 20 to 24 leaves in rosettes at the ends of the branchlets. The leaves are lanceolate, sessile about 12 cm. X 3.5 cm., pale but shining green above and greyish-green beneath with short, glandular hairs. The flower-heads, each some 1.3 cm. diam., with 15 to 20 yellow ray-florets, are in massive much-branched, terminal panicles, 10 cm. or more in breadth. Flower-stalks, involucres, branchlets etc. are densely covered with glandular hairs which fill the air with a powerful aromatic scent. Seen from a distance, the foliage page 331forms a bluish semi-spherical mass, but when in full blossom, fully one half is concealed by the brilliant yellow.

The autecology of the plants.

The trees number 20. All are of low stature but at times a few may reach a height of 15 m., or more, 18 are mesophytes and 2 xerophytes or subxerophytes. Their life-forms are as follows: — canopy-tree 9, tuft-tree 6 (ferns 5, palm 1), bamboo-like 1, bushy-tree 2, araliad-form 1, semi-globose 1. Several readily assume the shrub-form, especially Suttonia chathamica and Olearia Traversii. Dracophyllum arboreum is not of the usual fastigiate habit of its congeners and is here included amongst the canopy-trees. It usually commences life as an epiphyte.

Generally, the tree-crowns are denser than those of the same species of the mainland and resemble those of coastal trees. The trunks are slender and straight. The appearance of Hebe and Coprosma, as true forest-trees, must be specially noted. In species or genera strongly heteromorphic in New Zealand proper the phenomenon is exhibited to a very trifling extent, e. g. the juvenile form of Plagianthus chathamicus gives but a hint of the divaricating form. In Pseudopanax chathamicum, the juvenile stage has leaves of an adult type, but it nevertheless persists for some time with straight unbranched stem. Dracophyllum arboreum has broad spreading leaves as juvenile after the manner of D. latifolium but not nearly so broad or large and absolutely distinct from the narrow grass-like leaves of the adult. They appear on reversion-shoots in the crown of the tree and this stage may blossom. The juvenile Coprosma chathamica has much more mesophytic leaves than the adult and they are frequently much larger. The heterophylly &c. of Hebe gigantea has been already described.

Coming now to the leaves of the trees, they may be characterized as follows: compound 7, simple 13, broad 19, narrow 1, very large 6, large 2, medium 12, coriaceous &c. 13, thin 7, glabrous 17, hairy 3; all are evergreen except Plagianthus chathamicus and most likely Edwardsia chathamica.

The flowers of 5 species are more or less showy, 9 have succulent fruits and those of 2 (both endemic) are specially suited for wind-carriage.

The shrubs number 23, of which 12 are xerophytes or sub-xerophytes 11 mesophytes, 3 wandering, 20 spot-bound, 2 very tall, 8 tall, 8 of medium height and 5 of low stature. The life-forms and the number of species to each are as follows: Wandering 3, consisting of: bamboo-form 1 (Sporodanthus), open rooting cushion 1, erect twiggy 1; spot-bound 20, consisting of: tuft-shrub 2 (both ferns), bushy-shrub 5, ericoid-form 4 (fastigiate 2, bushy 1, ball-like 1), twiggy 1 (tall, open, spreading), rhododendron-form 2, divaricating and semi-divaricating 3, straggling 2 (prostrate 1, semi-prostrate 1), open cushion 1 (divaricating).

The leaves of the shrubs (1 species leafless) may be characterized as follows: compound 2, simple 20, broad 14, narrow 8 (needle-like 2), very large 2, large 2, of medium size 7, small 5, very small 6.

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The flowers of 11 species are more or less showy, Olearia semidentata, with its multitudes of brilliant purple ray-florets, being of extraordinary beauty. Eight species have fleshy fruits and in 2 species they are suitable for wind-transit.

Lianes are only represented by 7 common species of New Zealand proper and include 2 root climbers (ferns), 1 scrambler and winder (combined), 2 high-climbing, woody and 2 semi-woody winding-lianes.

Epiphytes number 13 all of which are common also in New Zealand proper. They comprise creeping filmy ferns 5, erect herbaceous ferns 3 (creeping 1, tufted 2), drooping herbaceous fern 1, low creeping fleshy fern 1, low creeping unbranched semi-woody plant 1 and thick-leaved orchids 2.

Parasites are represented only by Gastrodia.

Herbaceous and semi-woody plants number 187 of which 13 are annuals, 174 perennials (herbaceous 137 semi-woody 37), 114 spot-bound, 73 wandering, 145 mesophytes, 4 hygrophytes, 38 xerophytes, 24 very tall, 23 tall, 37 of medium stature, 58 of low stature, and 45 of very low stature.

The life-forms and number of species to each are as follows: — (1) Annuals or biennials 13 consisting of: (a) semi-woody 4, all erect-branching, and (b) herbaceous 9 made up of tufted 2, mat-form 1, erect-branching 5 and prostrate-spreading 1. (2) Perennials 174, consisting of: (a) semi-woody 37 which include (a) spot-bound 26, made up of erect rosette-form 1, erect tufted 3, erect straggling 2, prostrate trailing 1, cushion-form 1, erect-branching 17 and straggling 1; (?) wandering 11 made up of, erect-creeping 4, prostrate-creeping 1 mat-form 6; and (b) herbaceous perennials 137, which include (a) spot-bound 75 made up of, erect-tufted 24 (ferns 4, grass-form 15, and rush-form 5), prostrate-tufted 3, erect unbranched summergreen 2 (ferns), tussocks 12 (grass-form 7, rush-form 3, iris-form 2), earth-orchid form 11, mat-form 4, erect-branching 8, yucca-form 2, straggling 1, rosette-form 8; and (?) wandering 62, made up of carpet-plants 4, turf-makers 1, mat-form 23, erect-creeping 25, sand-binder 1, wiry interlaced 1, iris-form 1, erect rosette-form 2, straggling 2, tufted-grass 1 and Utricularia-form 1.

Coming now to the leaves, they may be characterized as follows: very large 14, large 14, of medium size 30, small 63, very small 58, simple 141, compound 38, broad 106, narrow 73, coriaceous &c. 77, thin 102, glabrous 137 and hairy 42.

Water-plants number 4 and consist of submerged filiform 1, floating-leaved 2 and partly submerged 1.

The plant-communities.

Here, again, in certain cases an account is given of the vegetation of habitats rather than of definite associations.

On sandy shores the leading species were Ranunculus acaulis, Calystegia Soldanella and Myosotidium Hortensia. The last-named was originally extremely abundant and formed a belt just above high-water mark, but it is now extinct in this association.

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On stony shores beyond the reach of sheep, pigs &c. Myosotidium forms broad colonies which are a remarkable and beautiful spectacle. Its huge leaves have the laminae bent so as to be funnel-shaped and thus an ample supply of water is conducted to the roots during light showers. Other common plants of the association are: — Urtica australis forming thickets 30 to 35 cm. high, its stems 1.5 cm. diam. and leaves 15 X 10 cm.; Rumex neglectus, Ranunculus acaulis, Lilaeopsis novae-zelandiae, Selliera radicans and Cotula potentillina.

Sand-dunes of great extent occupy a large part of the coast-line. The unstable and partly stable dunes bear a plant-covering similar to that of New Zealand proper with Desmoschoenus spiralis and its accompanying species except that Spinifex hirsutus is absent. Where the sand is stable comes dune-forest made up, near the sea, entirely of Olearia Traversii and Suttonia chathamica, but further inland other trees occur.

Where sand has blown on to flat rock-ledges the endemic Sonchus grandifolius1 grows luxuriantly (Fig. 95), and, in its company the endemic creeping, xerophytic grass Festuca Coxii, Salicornia australis, Apium prostratum and Samolus repens var. procumbens.

Cliff and rock vegetation is by no means uniform. A rocky coast-line is a frequent feature especially in the south of the main island and of the smaller islands. Where there is a maximum of spray the endemic Hebe chathamica'2 is characteristic and its companion-plants are: Mesembryan-themum australe, Apium prostratum, Salicornia australis, Senecio radiolatus, stunted Olearia Traversii and the endemic Geranium Traversii, but this last seems hardly so tolerant of salt. Blechnum durum, in less halophytic stations, forms extensive pure colonies.

Near the margin of the great lagoon, there are limestone cliffs, in many places, which, at one time purely littoral, now bear a covering partly coastal, partly inland. The most striking plants is the endemic Hebe Dieffenbachii3. Other common plants of this association are Adiantum affine (in hollows), Phormium tenax, Geranium Traversii, Linum monogynum var. chathamicum, Acaena novae-zelandiae, Leucopogon parviflorus and Senecio lautus.

1 1) A summergreen herb with thick, juicy rhizome, great oblong, pinnatifid or pinnate, palegreen, thick, hard leaves, 30 to 60 cm. long and large flower-head protected by extremely thick, spinous bracts.

2 2) A shrub with rather thick main-stem, issuing from a crevice, and giving off numerous, supple, slender branches which trail over the rock or hang downwards. The elliptic leaves, 2 to 2.5 cm. long, are rather thick, fleshy, pale-green and more or less downy. There are many distinct forms of the "species" and such are probably jordanons, crosses between such, and crosses with Hebe Dieffenbachii and H. Dorrien-Smithii.

3 3) A shrub with far-extending branches, much stouter than those of chathamica, but nevertheless extremely pliant, and thick, fleshy, pale-green, linear-oblong leaves, 6.5 cm. long, confined to the ends of the branches.

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Frequently, flattish rock is covered with peat which varies considerably in depth. In such places, a turf may be formed out of a close growth of Scirpus cernuus, Triglochin striata var. filifolia, Ranunculus acaulis, Lilaeopsis novae-zelandiae, Pratia arenaria and Selliera radicans. Mesembryanthemum australe is characteristic and may form pure stands. In the north of the island, where the peat is deep, and where certain petrels burrow, are extensive colonies of the endemic Cotula Featherstonii1 while alongside are great clumps of Myosotidium and sheets of Mesembryanthemum. In the south of Chatham Island, and on Pitt Island, there is still to be seen the one time more widely-spread endemic Coxella Dieffenbachii2.

Salt-meadows were originally common. Unfortunately, I saw none in their virgin state but W. Martin has very kindly given me details from his field notes which show that the association is dominated by Juncus maritimus var. australiensis and all the halophytes of the florula are present.

In shallow water containing more or less salt there is abundance of Ruppia maritima.

Inland rocks support no special rock plants. The most frequent are the following: — Cyclophorus serpens, Polypodium diversifolium, Asplenium flaccidum, Phormium tenax, Earina autumnalis, Linum monogynum var. chathamicum., Cyathodes robusta, Hebe Dorrien-Smithii, Coprosma sp. (probably undescribed) and Olearia chathamica.

Lakes and sluggish streams of dark peaty water are abundant but water-plants are few and scarce. The sole species recorded so far are Potamogeton Cheesemanii, Polygonum serrulatum, Ranunculus rivularis, Callitriche Muelleri and Myriophyllum elatinoides.

Swamp is essentially a lowland association. In the deepest water, but rarely mixed, grow Leptocarpus simplex and Carex sectoides. Where shallower there is a scrub of Coprosma propinqua (dominant), Blechnum procerum, Arundo conspicua, Deschampsia caespitosa, Carex Darwinii var. urolepis, Phormium, Astelia nervosa (or undescribed species), Epilobium pallidiflorum and E. chionanthum. As the swamp becomes drier small trees or shrubs appear, especially, Coriaria arborea, the endemic Pseudopanax chathamicum, Dracophyllum arboreum and Suttonia Coxii. Hymenanthera chathamica and Senecio Huntii also occur to some extent.

Bog associations are specially characteristic both in the lowlands and on the tableland. Lowland bog has been greatly modified by draining, burning and trampling of stock, so that as it was doubtless similar to the

1 1) A biennial herb, 15 to 30 cm. high, greyish in colour and rather like Matthiola incana. Its leaves are oblong-or obovate-spathulate 2 to 5 cm. long, soft, pubescent and in rosettes at the ends of the naked branches. The life-form is quite different from that of the genus in general.

2 2) A perennial herb of the Aciphylla-form., but the leaves are neither rigid nor spinous. The flower-stalk measures 60 cm. or more and the leaves are 30 to 60 cm. long.

page 335tableland association, the latter, being quite virgin in places is alone dealt with here.

The soil consists of peat which varies considerably in its water-content, this latter being reflected in the vegetation, so that the following successive subassociations can be defined: Sphagnum bog; Sporodanthus-Olearia bog; Olearia-Dracophyllum bog, and pure Dracophyllum bog, which is a connecting-link between bog and forest.

In sphagnum bog a species of Sphagnum forms large, rounded cushions on which grow in the wettest portions, Scirpus inundatus and a species of Carex. Where a little drier are Hierochloe redolens, Pratio, arenaria and the endemic grass Poa chathamica. Other associated plants are, Gleichenia circinata, Heleocharis Cunninghamii, Drosera binata, Myriophyllum pedunculatum, and Utricularia monanthos. The Gleichenia frequently establishes wide colonies. Tiny plants of Dracophyllum paludosum and Olearia semi-dentata in bloom are not uncommon.

Sporodanthus-Olearia bog follows Sphagnum bog, as soon as the ground becomes a shade drier. The soil is peat, fully saturated with water, and, at a depth of 20 cm. it has the consistency of porridge. The vegetation is extremely dense and consists of Sporodanthus Traversii mixed and entangled with Olearia semidentata and Dracophyllum paludosum, the mass averaging perhaps 1.5 m. in depth.

Olearia-Dracophyllum bog which succeeds the last-described as the ground becomes drier, consists of about an equal amount of the Olearia and Dracophyllum while in open places are Poa chathamica, Drosera binata, Gentiana chathamica and the Utricularia. Possibly Phormium was originally an important constituent. When the Olearia is in full bloom the brilliant purple flower-heads, in hundreds on every bush, render these Chatham Islands' bogs wonderfully beautiful.

Pure Dracophyllum bog is a distinct transition between bog and forest. D. paludosum 1.6 m. high is dominant and mixed with it here and there are trees of D. arboreum while juvenile plants of this latter equalling D. paludosum in height, but distinguished by their broad leaves, are abundant. On the ground grow Poa chathamica, Gentiana chathamica, Pratia arenaria and seedlings of both species of Dracophyllum.

Forest occupies a very considerable part of both the main island and Pitt Island. There are two classes, lowland and upland; the first distin-guished by the dominance of Corynocarpus and an abundance of Rhopalo-stylis and Olearia Traversii, and the second by the absence of the above three trees, the dominance of Senecio Huntii and Dracophyllum arboreum, and, with the exception of Hebe gigantea, a smaller percentage of the other forest-trees than in the lowlands. Shrubs, such a common feature of New Zealand forest, are absent, and the tallest undergrowth consists mainly of the 5 tree-ferns (Dicksonia squarrosa, D. fibrosa, Cyathea Cunning-page 336hamii and C. medullaris) and, in some localities, the stems of the liane Rhipogonum. On the floor are many of the usual New Zealand forest-ferns. The lowland forest is generally quite low (6 to 13 m.) and the roof is flat and close, the trees being of equal height. So too, is upland forest low and flat-roofed, except where Dracophyllum arboreum raises its foliage above the general level. Filmy-ferns occur in both classes of forest, but they are most abundant in the upland and may carpet the ground or hide the tree-trunks or fern-trunks. Forest on limestone near the large lagoon is distinguished by the presence of Edwardsia chathamica, but according to W. Martin it occurs elsewhere to some extent. Lowland forest is really ecologically equivalent to Corynocarpus coastal forest of New Zealand proper.

Heath, in exposed situations, succeeds bog as the ground finally becomes fairly dry, or, in many places at the present time, it has seized the ground from which forest has been eradicated by fire. There are two classes of the formation, shrub-heath and bracken-heath.

Shrub-heath is distinguished by the presence of the eriocoid shrubs Leucopogon parviflorus and Cyathodes robusta, the rush-like Scirpus nodosus and the Iris-like Libertia peregrina. Pimelea arenaria, or an allied species, is common in some places. Other species are Pteridium esculentum, Deyeuxia Forsteri, Danthonia semiannularis, Acaena novae-zelandiae, Pratia arenaria, Helichrysum filicaule and Gnaphalium japonicum.

Bracken-heath frequently consists of pure Pteridium esculentum forming dense thickets and attaining a height of more than 1.5 m.; where more open, various plants of shrub-heath gain a footing and there are transitions between the two associations.