To the beach-formation belong, amongst the trees and shrubs, Barringtonia speciosa, Calophyllum Inophyllum, Guettarda speciosa, Pemphis acidula, Scævola Kœnigii, Tournefortia argentea, &c., and amongst the creepers and procumbent plants, Canavalia obtusifolia, Ipomœa pes capræ, Triumfetta procumbens, &c. To the mangrove-formation belong the Asiatic and the American species of Rhizophora, and species of Bruguiera, Carapa, Lumnitzera, &c. Amongst the trees that gather around the borders of the mangrove-swamp, constituting the intermediate formation, occur Barringtonia racemosa, Excæcaria Agallocha, Heritiera littoralis, Hibiscus tiliaceus, and several other species, all of them being equally at home on the sandy beach, at the border of a mangrove-swamp, and on the banks of an estuary. The climbers, such as Entada scandens, Mucuna gigantea, Derris uliginosa, &c., belong more to the mangrove and to the intermediate formations than they do to that of the beach. Referring the reader to the more complete lists given in [Note 24], I may remark that it is not always possible to distinguish sharply between the three formations, since some of the plants belong to two, and a tree like Cerbera Odollam may, in different localities, be referred to all three formations. The general distinction, however, prevails in the physiognomy of the coast-flora.
The mangrove-formation comprises, it may be pointed out, many plants other than mangroves, plants that find a home in the mangrove-swamps of Fiji, either within their limits or at their borders. It presents, indeed, a world in itself. When the mangroves establish themselves in a new locality they carry along with them a host of hangers-on, both plants and animals, that only find a home under the favourable conditions of a mangrove-swamp. Thus, the absence of the mangrove-formation from a Pacific island deprives its littoral flora of many very striking features. For this reason the Tahitian shore-flora must seem to a botanist coming from Fiji comparatively tame and monotonous; whilst that of Hawaii, for this and for other reasons to be subsequently mentioned, is still less interesting, and scarcely even gives a character to the coasts.
We are now, therefore, prepared to learn that a large number of the plants other than true mangroves, that thrive in or around the Fijian mangrove-swamp, are not to be found in those Polynesian islands where true mangroves do not exist; and that a law of association here exists. Many of the plants of the intermediate formation are so closely bound up with the mangroves in their life-conditions that they are not to be found where the mangroves are absent, even though their seeds or fruits are pre-eminently fitted for dispersal by the currents. The influence of “station” here rules supreme. This matter will be treated more in detail when discussing the Tahitian and Hawaiian strand-floras in Chapters [VI.] and [VII.]
THE MODES OF DISPERSAL OF THE FIJIAN STRAND-PLANTS.
The predominant influence of the currents having been already established, there remains for consideration the distribution of the floating capacity of the seeds or fruits among the different formations. One can say that almost without exception the seeds or fruits or seedlings of the mangrove and intermediate formations float for long periods. In the case of some of the true mangroves, as in Rhizophora and in Bruguiera, where germination takes place on the tree, it is the seedling that floats, whilst in others, as in Carapa and Lumnitzera, it is the seedvessel that floats. The plants with non-buoyant seeds or fruits that belong to the littoral flora are all confined to the beach formation, but they do not form more than a sixth of the total. Almost all the “good floaters” of the beach-plants are widely spread over the shores of the Pacific and of much of the tropics, and include such familiar species as Barringtonia speciosa, Cæsalpinia Bonducella, Terminalia Katappa, and many others mentioned in the lists of Notes [2] and [24].
When, however, we come to the dozen or so of beach-plants that possess seeds or fruits with little or no floating power, we find that several of them have a limited distribution in the Pacific, such as Acacia laurifolia, Drymispermum Burnettianum, Eugenia Richii, &c., whilst others, such as Casuarina equisetifolia, Tephrosia piscatoria, Triumfetta procumbens, and Wikstrœmia fœtida, are widely spread. This small non-buoyant group of the beach-plants has a nondescript appearance, and it is here that the inland flora is most likely to make its influence felt by additions to the number. It is here indeed that the littoral floras of the tropics mostly differ, the accessions from the inland flora varying in each region. It is in fact the zone of change.
A number of these plants, such as the species of Drymispermum, Eugenia, and Wikstrœmia, have probably been dispersed by frugivorous birds; whilst others, like Triumfetta procumbens, possess fruits that might have been transported in birds’ plumage. From the frequency with which Tephrosia piscatoria is associated on hilltops in Fiji with Fagræa Berteriana and climbing species of Morinda that are well suited for dispersal by frugivorous birds, it seems likely that it is also distributed by birds fond of a drier diet. It is possible that the Polynesians, who much value the wood of Casuarina equisetifolia, have often assisted in dispersing the tree.
The following is a summary of the contents of the chapter.
(1) The extension inland of the Fijian strand-flora is to be attributed to the xerophilous organisation of the plants, and to the exceptionally favourable conditions that are offered to such plants on the plains, and in other scantily vegetated localities, lying usually on the drier sides of the larger islands.
(2) Excluding the mangroves and the plants associated with them in the coast-swamps, there are few littoral plants of the islands of the tropical Pacific that do not extend inland in one region or another.