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Some General Observations on the Bryophytes of Stewart Island.
The climatic conditions are such that from sea-level to approximately 1,500 ft. altitude the surface of Stewart Island is clothed with dense forest or scrub, with the exception of the river valleys of the Freshwater and Rakiahua Rivers, the Mason Bay Flats in the west, and the Toi-toi Flats in the south-east. The open tops of the mountains are either rocky or covered with moorland. Throughout this area mosses and hepatics are prolific and frequently physiognomic, especially in the south of the island, where conspicuous moss and liverwort cushions of large size frequently cover the
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ground or encircle the stems and trunks of trees. Similar cushions are conspicuous in the upper forest zone and in the manuka belts.
The presence on the island of thousands of deer over a period of many years has resulted in great changes in the forest interior; for whereas it was formerly impossible to see more than a few yards ahead owing to the density of fern and shrub and lianes, it is to-day possible in the same areas to see a hundred yards or more. Asplenium bulbiferum, Leptopteris superba, and other ferns are to-day rare in localities where formerly they were common or even dominant, and seedlings on the forest floor are rarely numerous. Nevertheless, it is difficult as yet to detect any marked or probable changes in the bryophyte flora of the areas visited. Though more than a third of New Zealand's indigenous mosses have now been detected in Stewart Island, the writer is convinced that the total will ultimately be found to be considerably higher. A considerable increase in the hepatic flora may also be expected when the southern portion of the island is investigated.
The progressive increase in rainfall and decrease in the annual hours of sunshine from the north-east to the south and west is reflected in a decrease in the fern flora and in a progressive increase in the hepatic content of the bryophytic flora as well as by an increasing tendency for both mosses and hepatics as well as phanerogams to adopt the cushion form. Whereas in the Half Moon Bay area the trees do not carry a conspicuous epiphytic flora or at most a thin cover of filmy-ferns, mosses, hepatics, and crustose lichens, in much of the Port Pegasus area, every tree and shrub is heavily clothed with cushions of moss or hepatic and with conspicuous foliose lichens. How far the species-content differs in the two areas remains to be determined, but it can be stated that some species do become increasingly common or scarce as progress is made from north to south.
Cockayne, referring to the moss and liverwort cushions, named but two, viz., Dicranoloma billardieri and Plagiochila gigantea (or P. ramosissima?). However, the cushion-forming habit is adopted by many species under the climatic stimulus of strong winds, dull skies, brief hours of sunshine, and heavy rainfall. Thus near the summit of Pryse Peak, on the south side of Paterson Inlet, the following plants formed individual or composite cushions of large size:
Mosses: Dicranoloma billardieri, D. plurisetum, D. robustum (uncommon), and Ptychomnion aciculare.
Hepatics: Bazzania involuta, Bazzania sp., Acromastigum anisostomum, Chiloscyphus billardieri, C. beckettianus (?), C. decipiens, Lophocolea australis, Plagiochila gigantea, P. ramosissima, P. lyallii, Riccardia sp., Schistochila glaucescens, S. pinnatifolia.
On these cushions which cover the forest floor, the roots and lower portions of the trees, and fallen logs and tree-ferns, seedlings of most of the surrounding trees and shrubs take root and develop. Usnea and the drooping elfin mosses (Weymouthia cochlearifolium var. billardieri and W. mollis) which form such an arresting feature of subalpine forests on the mainland and, indeed, of many lowland
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forests also, are nowhere conspicuous in the areas examined, though both are usually present. The presence near the summit of Table Hill in soil pockets on the rocks of Dendroligotrichum dendroides, Plagiochila ramosissima, and Holomitrium perichaetiale which normally are forest-frequenting species is noteworthy, as here there is no forest or scrub. The paucity of sunshine and low light intensity in this fog-invested area is doubtless a factor leading to this result. Macromitrium longirostré occurs both on maritime and subalpine rocks.
Certain mosses believed rare on the mainland are surprisingly common on Stewart Island. Thus Macromitrium caducipilum and Isopterygium limatum are two of the commonest epiphytes. Both I have recently found to be not uncommon in forests near Bluff and Invercargill, but elsewhere in New Zealand they are met with very infrequently. Tetraphidopsis pusilla is an endemic moss which I found much more commonly on Stewart Island than in any other area save near Stratford in the North Island. On coastal banks Eriopus apiculatus was frequently noted by me, yet elsewhere in New Zealand it is of rare occurrence save possibly on the Otago coastline. Blindia tenuifolia, once deemed rare on the mainland, is quite abundant on all mountains investigated in Stewart Island (e.g., Mount Anglem, Thomson Range, Table Hill, Mount Rakiahua).
On the other hand, certain mosses described by Hooker as “common throughout the islands” (e.g., Echinodium hispidum and Distichophyllum microcarpum) have not been seen at all by me in the areas visited and can scarcely be considered common.
Cockayne has pointed out that Tmesipteris tannensis, normally an epiphyte, frequently grows on the ground in Stewart Island. This observation applies equally to such mosses as Holomitrium perichaetiale, Isopterygium limatum, Rhizogonium novae-hollandiae, Stereodon chrysogaster, and even to Hymenodon piliferus, once noted on the detritus at the base of a tree-fern, and Weymouthia cochlearifolia twice observed on the rocky banks of forest streams. The moss Schlotheimia campbelliana hitherto known only from the Campbell Islands grows plentifully on Stewart Island.
Sphagnae are abundant on the moors, in manuka thickets, in wet spots in the forest, on swampy areas, and even on sand-dunes near Mason Bay, and comprise four main species and a variable collection of forms belonging to the cuspidata group, which Mr. Sainsbury recommends be listed as Sphagnum cuspidatum until this perplexing genus undergoes modern revision. Several species of Campylopus (C. clavatus, C. bicolor, C. introflexus, C. appressifolius) are the most frequent associates.