Art. XV.—Notes of a Botanical Visit to Herekopere Island, Stewart Island.
[Read before the Otago Institute, 4th August, 1914.]
On the 27th November, 1913, I visited this island, which lies in Foveaux Strait, about five or six miles from Half-moon Bay. As it is one of the few islands upon which Senecio Stewartiae grows, and is, moreover, the most northerly known habitat of both that plant and Poa foliosa, a few notes on the plant formations may prove interesting.
We approached the island from the south-west, and thus had an opportunity of viewing its physiognomy from the weather quarter. The coast from this side presents a series of rocky faces, only here and there traversable.
Just above high-water mark the rocks were covered with a white limy substance, but bare of plant covering. Above this white hue, which is washed by waves during high tides, the rocks were clothed with a greygreen mantle, composed principally of Veronica elliptica and Olearia angustifolia, both in full bloom. Here and there a patch of light green betokened the presence of Histiopteris incisa, which forms the main floorcovering of this isolated spot. Where the wind struck less directly a yellow spot or two revealed the existence of Senecio Stewartiae in the formation, the large yellow corymbose heads and dark-green leaves crowded at the ends of the branches contrast ng strongly with the less-marked Veronica elliptica, which formed the basis of the association.
On a nearer approach the beautiful white bloom of Olearia angustifolia irresistibly caught the eye, the great abundance of blooms and the rounded form of the shrubs rendering the plant conspicuous. On this face neither Olearia Colensoi nor Senecio rotundifolius, although abundant elsewhere, were seen, a further evidence of the high wind to which these islands are subject.
Upon landing, a scramble up the steep slopes revealed a dark peaty soil undermined everywhere with burrows of the mutton-birds (Puffinus griseus) and other petrels,* and possessing a damp pungent odour, reminding one of a domestic fowlyard on a wet day. Growing under the Veronica and Olearia bushes were seen numerous isolated plants of Carex trifida, Asplenium obtusatum, and Muehlenbeckia australis, the latter with exceptionally large and succulent leaves but somewhat straggling form. On the rocky faces Poa Astoni was abundant, while here and there in the peaty crevices Senecio lautus, Stellaria parviflora, Tetragonia trigyna, Blechnum durum, and Poa Poppelwellii were noted. A few stunted plants of Rapanea Urvillei were also seen. Farther up some exceptionally strong plants of Asplenium lucidum and A. lanceolatum and Poa Astoni appeared, the two latter growing on a raised mound of their own dead leaves, both plants having the appearance of growing on caudices, the spaces between being bare and peaty and deeply marked with bird-tracks.
Once the top of the slope is reached the island presents a somewhat flat surface, traversed by comparatively open tracks, no doubt made by the thousands of sea-birds which annually breed on the island.
The ground-covering here was chiefly Histiopteris incisa, which grew plentifully but was somewhat stunted in form, the leaves showing evidence in their brown tips of their struggle with the wind.
The taller covering was almost entirely Senecio Stewartiae and Veronica elliptica, while here and there were patches of Rubus australis and Muehlenbeckia australis, with occasional plants of the large-leaved Stilbocarpa Lyallii.
Senecio Stewartiae is an open-branched shrub from 2 to 3½ metres high. Its lanceolate leaves are from 12 cm. to 18 cm. in length, thick and sticky, crowded towards the ends of the branches, and covered beneath with white tomentum.
The plants were in full bloom, and the large handsome flowers made the shrubs very conspicuous objects. This species seems to be the dominating one among the shrubby species on the higher parts of the island. A marked feature of the Veronica elliptica was that the great majority of the plants had white flowers, instead of the usual bluish ones which charac-
[Footnote] * Pelecanoides urinatrix, Prion vittatus, and Prion turtur.
terize it. In certain individual specimens, however, especially in sheltered situations, I noted deep-blue flowers. Here and there near the tracks I noted dull weather-worn patches of Asplenium falcatum, with patches of Muehlenbeckeia complexa, Hierochloe redolens, Pteridium esculentum, and Poa foliosa, with the imported grass Holcus lanatus.
A few specimens of stunted Weinmannia racemosa and Rapanea Urvillei were also noted, along with Dracophyllum longifolium and Coprosma areolata.
At the eastern end of the island, which is the highest part, there appears to have been a fire some time ago. This apparently destroyed the scrub over an area of from 2 to 3 acres. A most interesting result has followed. The whole of the burnt part is now covered with a close and almost pure association of Poa foliosa, the tussocks being close together and about I metre in height, making progress a difficult matter. The grass is growing very strongly, and the flowering-heads are exceedingly numerous and of immense size.
Upon climbing through this grass I discovered numerous young plants of Veronica elliptica and Muehlenbeckia australis, with a few of Rapanea Urvillei and Lepidium oleraceum var. acutidentatum, while the ground was full of the burrows of the petrels. It would appear, therefore, as time goes on, the original plant association of the island will regain possession, and that the Poa foliosa is merely a temporary occupant of the ground.
The extraordinary spreading of this grass, which elsewhere on the island is only found in isolated “tussocks,” suggests the possibility of its having an economical value, which might be worth investigating. At present practically nothing is known of its value as a fodder plant.
The existence of the plant covering depends in the first place upon the high rainfall, the soft peaty soil being very spongy and damp for a considerable depth. On the other hand, there is little doubt that the traffic of the birds materially affects the plant-growth. The ground is everywhere drained and aerated by thousands of tunnels made by the nesting birds, while the soil is richly manured by the constant deposits of these petrels. Most of the plants have large masses of surface roots only, and the loose soil enabled even fairly large specimens to be lifted out of the ground with ease.
The distribution of the species depends chiefly on the wind factor, the only plants that can get a hold on the steep exposed sides being those specially adapted to resist transpiration, notably Olearia angustifolia, Veronica elliptica, and Poa Astoni.
The extraordinary spread of Poa foliosa I attribute to its abundant seeding habit, the rich soil, and the unimpeded light gained by the destruction of the scrub by fire. Its wind-resisting qualities are evident from the manner in which it grows on exposed subantarctic habitats.