The Solomon Islands and Their Natives

by H. B. Guppy

This description of the vegetation of a coral islet brings me to refer to the manner in which such an islet, which is usually of very recent origin, has become stocked with its plants: and in so doing I shall be treating of a very important matter, the oceanic dispersal of plants. Fortunately for me, my notes and collections relating to this subject had an increased value at the time of my arrival in England, and in this respect I have been able to accomplish one of the principal aims of a young traveller, that of supplying trustworthy materials to those engaged in the particular line of research to which his notes and collections relate.[429]

[429] Mr. Botting Hemsley was on the point of completing his report on the oceanic dispersal of plants in connection with the Botany of the “Challenger” Expedition. Such of my collections, as referred to his work, were placed at his disposal by Sir Joseph Hooker; and my notes were incorporated in volume I. of the Botany of the “Challenger” (Part III. p. 309), to which I must refer my readers who are more specially interested in this subject.

The picturesquely wooded islets of these seas have been stocked through two principal agencies. Winds and currents drift to their shores the fruits and seeds of the littoral trees which ultimately form the margin of the vegetation; whilst the fruit pigeons disgorge the seeds or fruits of those often colossal trees which occupy the interior.

I will first refer to the former of these agencies. Lines of vegetable drift, intermingled with floating pumice, are frequently observable whilst cruising among the islands of the Solomon Group. The floating fruits commonly found belong to the most familiar littoral trees of this region, those of Barringtonia speciosa and Calophyllum inophyllum being especially frequent; and on more than one occasion the solitary fruits of the former were noticed at sea by Lieutenant Oldham and myself at distances of from 130 to 150 miles to the southward of the group, being probably derived from one of the islands of the New Hebrides to the eastward. Other fruits or seeds occurring frequently in the drift are those of Nipa fruticans and of two or more species of Pandanus; numerous beans (species of Mucuna, Canavalia, Dioclea), the long germinated seeds of the mangrove (Rhizophora), an occasional cocoa-nut, the cones of Casuarina equisetifolia, Terminalia catappa, Lumnitzera coccinea, Guettarda speciosa, Ochrosia parviflora, Heritiera littoralis and others.[430]

[430] Other fruits found floating were a second species of Calophyllum, a species of Gomphandra, Harpullia sp., and some Scitamineæ.

The foregoing seeds and seed-vessels with many others may be observed washed up by the waves on the surface of the bare sandy islets or sand-keys, which exhibit the first stage in the growth of those picturesquely wooded coral islets that are ultimately formed on the reefs. On such a sand-key, not more than some 25 or 30 yards across, I have counted as many as 30 different kinds of seeds and fruits, all collected together in the centre, which was only washed over at spring-tides. One of the first trees to establish itself is the mangrove (Rhizophora), which by its reclaiming agency adds to the area of the islet and enables other trees, such as Lumnitzera coccinea, to take up their abode. Pari passu with the seaward extension of the reef, the islet increases in size; and in time the winds and currents bring other fruits and seeds which germinate and form ultimately the belt of littoral trees bordering the beach. In this manner Barringtonia speciosa, Calophyllum inophyllum, Thespesia populnea, Hibiscus tiliaceus, Cerbera odollam, Ochrosia parviflora, Heritiera littoralis, Terminalia catappa, different species of Pandanus, Casuarina equisetifolia, and Cycas circinalis with many others referred to on a previous page, become established. It is worthy of note that the fruits of the great majority of trees which form the margin of the vegetation, whether on the lee or weather side of such an islet, float in salt water.[431] The small cones of the Casuarina however, require a certain amount of drying before they can be transported by the waves. The green fruits of the Cycas usually sink in salt water; but I found that one out of ten specimens floated, an exceptional circumstance which sufficiently accounts for the occurrence of Cycas circinalis on these coral islets.

[431] The results of some experiments I made are given on [page 305].

Whilst through the agency of the winds and currents the waves have stocked the islet with its marginal vegetation, the fruit pigeons have been unconsciously stocking its interior with huge trees, that have sprung from the fruits and seeds they have transported in their crops from the neighbouring coasts and islets. Perched up in the branches of the trees, these birds disgorge the seeds they have brought from other localities; and the rejected seeds and seed-vessels lie strewn on the ground beneath. The soft and often fleshy fruits, on which the fruit pigeons subsist, belong to numerous species of trees. Some of them are as large even as a hen’s egg, as in the case of those of the species of Canarium (“ka-i”) which have a pulpy exterior that is alone digested and retained by the pigeon. The fruits of the banyans and other ficoid trees, which with the Canarium are amongst the most conspicuous trees in the interior of the coral islets, are apparently preferred by the fruit pigeons, since they occur commonly in their crops. A species of Eugenia common in the interior of these islets possesses fruits found in the crops of these birds. Amongst other fruits and seeds on which these pigeons subsist, and which they must transport from one locality to another, are those of a species of Elæocarpus (“toa”), a species of laurel (Litsea), a nutmeg (Myristica), an Achras,[432] one or more species of Areca, and probably a species of Kentia. There is, however, another bird common on these coral islets, the ground pigeon Geophilus nicobaricus, known commonly as the Nicobar pigeon, which transports seeds in its gizzard cavity that on account of their hardness are not fed upon by the ordinary fruit pigeon (Carpophaga). The peculiar structure of the gizzard, which is described on [page 323], enables the Nicobar pigeon to crack seeds that can only be broken by a sharp blow with a stone. I have found inside this organ, the hard red seeds of a leguminous plant, very probably Adenanthera pavonina, of which one seed is occasionally found to be cracked. We may therefore consider that many small hard seeds and seed-vessels, which would be refused by the common fruit pigeon of these islands, are transported from one locality to another in the gizzard cavity of the Nicobar pigeon.

[432] I am indebted to Mr. Charles Moore of Sydney N.S.W., for the identification of this fruit. (Vide also “Journal and Proceedings of the Royal Society, N.S.W.,” XVII., p. 226.)

From the foregoing remarks it may be inferred that the pigeons in these islands play a very important part in the dispersal of plants, to which, as Mr. Botting Hemsley remarks in his report ([page 313]), they have perhaps contributed more than any other animal. In the Solomon Islands the fruit pigeons, as dusk approaches, frequent the islets on the coral reefs in great numbers, and from their unwillingness to leave their roosts in the trees they fall an easy prey to the sportsman. In one afternoon, on one of the islets of Choiseul Bay, 57 birds fell to the guns of Lieutenant Heming and Lieutenant Leeper; and it is to these two officers that I am indebted for my opportunities of collecting the fruits taken from the crops of these pigeons.