The swamp formation occurs principally in the lowest portions of the central and northern part of Chatham Island, in the immediate vicinity of lakes, lagoons, or sluggish streams, and is distinctly a transition, in some cases, between lake and forest; indeed, the line of tension may be often observed where swamp and forest plants intermingle. The swamp at the southern end of Lake Huro is easy to examine, and is of especial interest, since it offers every transition from the waters of the lake to the ordinary lowland forest. The vegetation of the swamp seems determined by the average depth of the water which more or less covers its floor. Where the water is deepest there is to all intents and purposes an original formation, for the ground is altogether too boggy to permit the inroads of cattle; but in all other parts the trampling of cattle and horses has consolidated the ground more or less and reduced its water-content, thus making it suitable for other plants, both indigenous and introduced. The floor of the swamp in its unchanged portions consists of black peaty mud, upon which it would probably not be safe to walk. Everywhere are large pools of water, 50 cm., more or less, in depth; while in winter the whole floor of the swamp, I learn from Mr. Cox, is under water. Here there are no shrubs of any kind. The vegetation consists of the curious restiaceous plant Leptocarpus simplex, a well-marked xerophyte, which in New Zealand occurs in salt meadows and sand-dunes (122, p. 119). In this formation Leptocarpus often forms very large patches, to the complete exclusion of every other plant. Growing near but not mixed with the Leptocarpus is Carex secta* in great quantities, its “trunk” composed in large part of dead rhizomes and roots matted together, on the summit of which the living plant, raised out of the water, can avoid excess of moisture, sending its roots far down into the decayed and semi-decayed “trunk.”
As the water of the swamp decreases in quantity the ground becomes quite covered with vegetation and decaying vegetable matter. There the floor is very uneven, with its many mounds of peat and decaying vegetation separated from one another by holes full of water. In such a part of the swamp Coprosma propinqua is very abundant, making a sub-
[Footnote] * Pastor G. Kukenthal, who is preparing an account of the genera Carex and Uncinia for “Das Pflanzenreich,” informs me that he considers C. secta distinct from the European C. paniculata, to which Cheeseman had previously referred it as a variety (8).
formation which occurs so frequently on the island as to have attracted the notice of the settlers, who call it “Mingimingi scrub.” Mixed with the Coprosma are the tall grass Arundo conspicua, Phormium tenax, Carex secta, Carex forsteri(?), Deschampsia cœspitosa, and quantities of Epilobium pallidiflorum, E. billardierianum, E. chionanthum var., and a large species of Astelia which is perhaps new.
As soon as the swamp becomes a shade drier small trees make their appearance, and this point is evidently the line of tension between swamp and forest. The first tree to appear is the xerophytic Olearia traversii; then Dracophyllum arboreum becomes abundant, mixed with Coriaria ruscifolia, Pseudopanax chathamica, and Myrsine coxii. Hymenanthera chathamica and Senecio huntii also occur to some extent. Mixed with this arborescent vegetation are all the swamp plants mentioned before, Leptocarpus simplex excepted, and large quantities of the fern Lomaria procera. Such a “scrub” is often extremely dense, and almost impossible to be traversed. On the banks of Sandstone Creek a very dense formation of this kind, almost in its virgin state, may be seen.
As the water-content of the swamp gradually decreases, through accumulations of vegetable matter becoming peat, so do the trees become more and more numerous, until finally, as in the case of Lake Huro, mentioned above, a true forest makes its appearance. The trees of the formation need not be reduced to mere shrubs; on the contrary, the Pseudopanax, Coriaria, and others, attain in the Huro Swamp a height of 6 m. Wherever a sluggish stream flows through a lowland forest, and at times inundates the neighbouring ground, the character of the forest changes, and a formation of Corynocarpus lœvigata, Coprosma chathamica, Rhopalostylis baueri(?), Hymenanthera chathamica, and Myrsine chathamica changes to one of Myrsine coxii, Dracophyllum arboreum, and Olearia traversii, this latter plant being of more lowly growth than when growing in the drier forest.
Those of the swamp plants which differ little from the New Zealand forms of the same species growing under similar conditions need not be further dealt with here; Dracophyllum arboreum and Senecio huntii are treated of at some length further on, when dealing with the “tableland forest,” so there only remains Myrsine coxii for special mention. This is a rather twiggy shrub, attaining under favourable circumstances a height of 3 m. or 4 m. Its leaves are close together, and form rather a dense mass at the ends of the branches. They are small, averaging about 1.8 cm., including the leaf-stalk, by 8 mm., and are narrow-obovate in shape. The fruit is of a beautiful mauve colour, and was doubtless originally distributed by means of native birds. These latter,
however, are for the most part nearly extinct, so this method of distribution no longer exists. However, as Mr. G. M. Thomson points out for New Zealand, introduced birds (50, p. 317) are now playing a most important rcle in the spread of plants; indeed, they may very well supply the place of the indigenous birds in this particular. Myrsine coxii is the first of all the Chatham Island trees to come into bloom, flowering as it does from the end of July.
Most of the swamp formation of Chatham Island has been much modified through consolidation of the soil consequent on the trampling of cattle and horses, which also destroy the trees which otherwise would seize on the “reclaimed” ground; so instead of following its natural course and becoming a forest the swamp becomes gradually transformed into meadow land, in which certain native and introduced plants which are not destroyed by the grazing of animals become dominant and form a turf.