Art. XXVIII.—Notes on the Plant-covering of Pukeokaoka, Stewart Island.
[Read before the Otago Institute, 7th September, 1915.]
Pukeokaoka is one of the mutton-bird islands situated in Foveaux Strait. It lies about ten miles from Half-moon Bay, and is passed on the trip from Bluff to Stewart Island. It is roughly triangular in shape, and its greatest diameter is only about half a mile. It lies between Motunui and Here-kopere, and is less than half a mile from the former and about one mile from the latter.
On the 1st January, 1915, I spent some hours on the island, accompanied by my son, noting its vegetation. As the plant-covering differs considerably from that of Herekopere, a short description of it may prove of interest.
The name Pukeokaoka was, according to Mr. J. Bragg, given to this scrap of land by the Maoris because of the abundance on the island of the tree-nettle Urtica ferox. This plant is called “ongaonga” in the North, but the name is hardened to “okaoka” in the South. “Pukeokaoka” should therefore be translated “nettle hill,” a reasonable enough designation for this island. The sides of the island are rocky, and consist of steep cliffs in several places. These are covered with vegetation. On the east side there is a rough accumulation of large boulders, and it was on these that we landed.
Approaching the shore, the physiognomy shows a dull grey-green colour, with a smooth surface, although here and there can be seen a green patch. This dull colour is brought about by the abundance of Olearia angustifolia which fringes the water, and must m its season be a mass of white from its beautiful blossoms The greener patches consist of Veronica elliptica, which is also fairly abundant on the cliff-side. Where the cliffs are steep, or a slip has occurred, great curtains of Tetragonia trigyna mantle the surface, the reddish stems, and, where exposed to strong light, the red leaves, contrasting strongly with the surrounding plants
Senecio rotundifolius is common in this association, and on a closer view Stilbocarpa Lyallii peeps through in patches, its large leaves giving a striking characteristic to the physiognomic appearance.
The usual shore fern Asplenium obtusatum is also common among the undergrowth, and Apium prostratum is not infrequent On the steeper cliffis Mesembryanthemum australe is common, its reddish stems and pink flowers contrasting beautifully with its dark-green succulent leaves
On a more open part of the cliff-side the association consisted of Poa Astoni, Linum monogynum, Gnaphalium luteo-album, and Sonchus littoralis, all growing very rankly, chiefly on account of the nesting habits of the various petrels which frequent the island. The petrel-burrows serve to dram and aerate the soil, while their droppings enrich it very much.
As the hill was ascended Senecio lautus became common, and a few plants of Scirpus nodosus (?) were noted, together with a mixed association consisting of Coprosma lucida, Rapanea Urvillei, Pittosporum Colensoi, Erechtites prenanthoides, Sonchus littoralis, and Polypodium diversifolium. At first these plants were very stunted, showing the effect of the strong wind, but as the top of the hill was reached they became taller, and a forest association commenced.
Among the scrub for considerable areas the floor-covering consisted of Polypodium diversifolium as a pure association. On the edge of the forest the scrub was about 12 ft. tall, and consisted chiefly of Rapanea Urvillei, Coprosma lucida, C. areolata, together with the ferns Asplenium lucidum
and Polystichum vestitum, and the climbing-plants Rhipogonum scandens and Rubus australis. The floor of the forest was covered for considerable areas with Polystichum vestitum, Asplenium lucidum, and Stilbocarpa Lyallii, and occasional patches of Blechnum durum from 8 ft. to 10 ft. in diameter were seen.
The forest consisted of Metrosideros lucida, Schefflera digitata, Pittosporum Colensoi, Aristotelia racemosa, Fuchsia excorticata, Melicytus lanceolatus, Nothopanax Edgerleyi, Griselinia littoralis, Carpodetus serratus, and Veronica elliptica. The undergrowth was 3 ft. or 4 ft. high, and consisted of Asplenium bulbiferum, A. flaccidum, A. scleroprium, A. lucidum, Polystichum vestitum, and Polypodium diversifolium, while Rhipogonum scandens was common.
The interior of this forest presents a tangled mass of Rhipogonum, through which can be seen the crooked trunks of the forest-trees, grey with lichens and mosses. Metrosideros lucida grows about 30 ft. high, and Coprosma areolata here forms a straight tree about 20 ft. high, with a trunk 6 in. in diameter. Urtica ferox was also growing rankly in this forest. It was about 6 ft. tall, and had leaves 9 in. or 10 in. long, including the petiole of 2 in. to 3 in. The only tree-fern was Dicksonia squarrosa. Epiphytes were not common, but consisted principally of the ferns Asplenium flaccidum and Polypodium diversifolium. A. lucidum was noted growing on Dicksonia squarrosa and also on the sloping trunks of Metrosideros lucida.
Near a cliff-edge I noted Hypolepis tenuifolia, Calystegia tuguriorum, Stellaria media, Apium prostratum, Carex trifida, and Poa imbecilla. On this steep side Urtica ferox was also very plentiful, associated with Muehlenbeckia australis.
At the northern end of the island there is a steep cliff exposed less to the prevailing south-west wind and subject to more direct sunlight. The principal vegetation here consisted of Veronica elliptica (common), Apium prostratum (in patches), Mesembyranthemum australe (plentiful), with quantities of Tetragonia trigyna, Muehlenbeckia australis, Linum monogynum, and Poa Astoni. Several strong-growing patches of Hierochloe redolens in full bloom were also noted, with Sonchus littoralis, Dichelachne crinita, Halorrhagis erecta, and Lepidium oleraceum var. acutidentatum. Throughout these plants the burrows of the petrels were very plentiful.
The top of this island is almost flat, and is perhaps less than 200 ft high. The peat seems much drier than on Herekopere, and is apparently deeper. There does not, on the whole, appear to be nearly so much evidence of bird traffic, except on the steep sides. The difference in the vegetation is quite marked, inasmuch as there is here a “forest” association which is entirely absent from Herekopere. (See my “Notes of a Botanical Visit to Herekopere Island,” Trans. N.Z. Inst., vol. 47, pp. 142–44, 1915.)
The absence of Poa foliosa and Senecio Stewartiae from Pukeokaoka is also strange, as these plants are a marked feature of Herekopere, only about a mile distant. Possibly they grow here also, and were overlooked by me; but, if so, they are certainly rare. The only way I can account for the absence of these plants is by suggesting that the close forest formation of Pukeokaoka has prevented them getting a hold. Poa foliosa seems to be present on all the exposed parts of the mutton-bird islands where the scrub is unable to exist, but does not grow where the light has not full access. The restricted habitat of these plants is of more than passing interest.
As the plants noted are all mentioned in the text, I have not appended a list.