RANGITOTO REVISITED

New Zealand Listener, Volume 14, Issue 357, 26 April 1946, Page 18

RANGITOTO REVISITED

(Written for "The Listener" by Dr.

R. A.

FALLA

Director

of the Canterbury Museum)

URING a recent holiday visit to Auckland, it was suggested by some friends that we should make a pilgrimage to Rangitoto Island. It was familiar ground to Auckland naturalists and holidaymakers before the war, but having been closed as a defence area, it was bound to appeal with new fresh. ness when again accessible. There are few outlines more familiar to many New Zealanders than this extinct volcano with its symmetrical cone, and sombre shades contrasting with the contour-and colour of the surrounding coast. To those who pass it by, or know it only as a landmark, it leaves an impression, like a cut-out in stage scenery, of height and length, but no depth.. The plant cover seems so uniform and dark that it is difficult to know whether it is low scrub or dense forest, and it is safe to say that any guess about the details and close-up appearance will be wide of ‘the mark. It is necessary to go there to find out exactly what the surface looks like. One may find good descriptions of the island and the volcanic origin by real ‘geologists like Professor J. A. Bartrum, while several botanists have done full justice to the peculiarities of its plant life in readable popular descriptions. It is to such sources that one should go for facts that are both full and accurate: this article deals only with the more salient features of the island as they strike a visitor, and so perhaps will contain little of novelty for those who know the place well. Only "Yesterday" " The first thing to attract notice is the surface itself. No cliffs here; practically no sandy beaches; no soil or earth in its many familiar forms; nothing but solidified lava like a mass of coke, or rather metallic slag from a gigantic furnace. From its appearance it might almost

have had its molten flow arrested as lately as yesterday. In a sense it was only yesterday as geological time is reckoned,. for Rangitoto is one of the youngest of many cones throughout the world that serve as classic types for students of vulcanology. It is not a smooth surface, for the gas-pitted lava as it hardened has been cracked and tumbled by the last of the pressure before the flow subsided. It is incredibly rough going, and anybody who feels tempted for any reason to explore off the main tracks and roads should develop some of the technique of the fire-walker if footwear is intended to last out the trip. The regular tracks, however, are good and permit exploration half-way round the long foreshore or up the mile and a-half to the summit. On the first part of the

summit track the natural contour of the lava flow makes for the easiest of grades, imperceptible at first and steepening gradually until the rim of the original lava cone is reached. This is not the summit: it is the point that looks like a humped shoulder in a distant view of the island, and it marks the top rim of the original mass of slow-flowing lava. Within its basin rises the scoria cone, the fine debris and heavier ash thrown up into the air by the violence of the eruptions and settled back into a steeper cone. On the slopes of this the grade is stiffer until the summit is reached. It overlooks another crater cavity. Unique Vegetation Just how long Rangitoto has been in this condition is not known, but it has possibly been active within a matter of

centuries. At any rate atmosphere and climatic conditions have as yet done little to alter the primitive surface. The only conspicuous agent of change is the vegetation. It is unique in character, so much so that most eminent botanists visiting New Zealand have made a point of inspecting it. The several features and problems that engage their attention can hardly be dealt with here, but some of the unusual features are plain to anyone who has cultivated a habit of observation. In most places, and in ordinary conditions, a pre-requisite for the growth of plants is soil. But here is a place with practically no soil, and yet it is remarkably well covered with trees and shrubs. By comparison with other areas of native bush there is no great variety,

The dominant plant is the pohutukawa. As may be seen on any cliff and headland, this tree has an amazing root system, much of it along the top of the ground, pushing* outward rather than downward for support and nourishment. On the inhospitable lava of Rangitoto this tendency must be exercised to the full-the sensitive and exploring roottips, hundreds of them, pushing into the pits in the lava that may hold a little moisture. Cavities below can accommodate still more and in time a formidable root system supports a large tree. Centuries of accumulation of leafmould have gradually filled up surface hollows, the shade has allowed a growth of moss to bind it, and other seediings have found a place to start. On a level parade ground surfaced with fine scoria we found a patchy sward, consisting not of grass, but of seedling trees of five different kinds, pohutukawa in the majority. On the established patches of bush the undergrowth includes some of the hardier ferns and even the delicate-looking kidney fern in profusion. Not Much to Drink The problem of moisture is the main factor limiting plant grewth, for there | are of course no streams, and it is not surprising that a large percentage of the plants are xerophytic, i.e., adapted in some way for conserving what moisture they can get. Pohutukawa leaves for example have a furry surface on the underside of the leaf which acts in that way. Of plants with highly polished fleshy leaves, serving the same purpose, the most conspicuous on Rangitoto is broadleaf. It is the species which elsewhere grows mainly as an epiphyte on the branches of larger trees, but the Rangitoto specimens start from the rock and become trees themselves. There is much more to the story of the plants, but. for that you must go to the competent botanists who have written about it-to non-technical books by Miss M. W. Crookes, Miss Lucy Cranwell, Professor Arnold Wall, and others. . Animal life is not very abundant or ‘conspicuous. There are insects, but mainly those that can live on the trees. For some reason or other Rangitoto is a cicada’s paradise and their stridulating din on a hot day is remarkable. A number of birds live there too, but water

supply is a problem for them and must restrict the number that such an area should support. Australian wallabies were introduced many years ago and are still there. It sees a pity, for the plants have difficulties enough without a browsing mammal to crop off shoots and seedlings. The marine life of the long shore-line is a story in itself, interesting enough to keep marine zoologists happy for hours in its rock pools and its rare, restricted sandy beaches. Altogether, as harbour sentinel or as’ wild life sanctuary, Rangitoto is both unique and satisfying.