THE REESTABLISHMENT OF THE FLORA ON KRAKATAU

When the island was first visited by a geological expedition two months after the eruption, the whole surface was buried under a layer of ashes and pumice averaging thirty meters in depth, and in some places as much as sixty meters. Thus, of course, every trace of life must have been quite annihilated and the sterilization was complete. An analysis of the ashes showed that, except for phosphorus and nitrogen, all of the elements necessary for plant life were present. (See Ernst, p. 50.) Ernst suggests that the other elements necessary for the establishment of a new flora were conveyed from the mainland in the form of dust, and that as a result of the intense electrical activity which accompanies the almost daily rains of the equatorial region, the atmospheric nitrogen is oxidized into the nitric and nitrous acids which furnish the necessary nitrogen. This with the salts and traces of organic matter in the ashes would have been sufficient in a very short time to allow the establishment of the first micro-organisms upon the island.

The first botanical expedition, as already stated, was made under the direction of Professor Treub in 1886, three years after the eruption. During this interval a considerable number of plants had already established themselves upon the island. The most important fact brought out by this trip was the great importance of the blue-green algae in the early establishment of the new vegetation. Thin blackish, slimy films, formed by a number of species of Oscillatoria and other blue-green forms, were found in great quantity coating the surface. of the ashes, and the gelatinous matrix of these low plants offered a substratum which was favorable for the germination of the spores of ferns and even for the seeds of a few phanerogams. It was found that the colonization of the island was quite as marked in the interior and upon the high cone as it was along the shore, but the plants of the interior of the island were for the most part

quite different. A remarkable fact was the great preponderance of ferns in the new flora. In the period of three years no less than eleven species had established themselves and formed the predominant feature of the new vegetation. In our visit to the north side of the island, where the reestablishment of the vegetation, as we have seen, was less advanced than on the south side, this preponderance of ferns was very marked, whereas in the other parts of the island they have been to a very great part supplanted by the phænogamous immigrants and several species seem to have disappeared. In the drift zone of the beach Treub found nine species of seedling plants, and in the central part of the island eight, two of which were the same as those upon the shore. Of the remaining six, four were composites and two grasses, all forms which would be distributed readily by the wind. These phanerogams, however, were far less numerous as individuals than were the ferns.

A series of visits to the islands was projected by Treub, but unfortunately the plan could not be carried out, and it was not until 1897 that a second expedition visited Krakatau. This second expedition was also under Treub's direction. In the interval of more than ten years that had elapsed since the first visit the number of plants had greatly increased and most of the island was covered with vegetation which began to show the characteristic formations which are now so conspicuous. The "Pescapra" formation, i. e., the beach zone characterized by the predominance of Ipomoea pes-capra, was well established, but the belt of strand forest now so marked upon the southern side of the island was entirely wanting in Krakatau, but the beginning of such a forest was found upon the neighboring Verlaten Island. Almost no trees were met with, and even shrubby plants were not numerThe grassy "steppe" lying between the beach and the base of the cone was conspicuous and probably not very different from its present condition. The total number of vascular plants collected on this second ex

ous.

pedition amounted to sixty-two, of which twelve were pteridophytes and fifty phanerogams. The ferns still predominated in number of individuals.

A third party visited the island in 1905, but the results of this expedition have not yet been published.

A very full account of the present flora is given by Ernst (pp. 37 to 48). In the three expeditions the results of which have been published a total of 137 species is recorded. While a very large majority of these are phanerogams, representatives of all the principal groups of plants have been collected. In the earlier expeditions the preponderance of ferns, as we have seen, was very noticeable, but at present this is not the case and they have largely given place to the more aggressive phanerogams. We collected only six species of ferns and one of Lycopodium, the wide spread L. cernuum, while on the first and second expeditions eleven species were noted, and although it is true that we failed to reach the center of the island, where in all probability other species would have been encountered, it may be noted that we collected seventy-three species of phanerogams against forty-eight species recorded at the time of the second expedition.

Of the lower plants only two species of mosses have been collected and a single species of antheroceros (this was found only on the second expedition). We found the two species of mosses growing fairly abundantly, but no liverworts. Whether the latter grow in the central part of the island remains to be seen, but it is highly probable that some of the very numerous species of Java and Sumatra will be found there. The scarcity of bryophytes is remarkable, as it is generally assumed that their spores are readily disseminated; and the contrast with the ferns which so quickly colonized the island is most striking. Three species of fleshy fungi have been collected and a considerable number of species of diatoms and blue-green alga were among the earliest settlers of the island.

Professor Ernst made some interesting studies on the

459 bacteria, collecting from several places samples of soil which were placed in sterilized tubes. These were examined by Dr. E. De Kruyff, bacteriologist of the Agricultural Department at Buitenzorg, and the soil was found to contain the usual proportion of bacterial forms, both ordinary soil bacteria and putrefactive types. An interesting discovery was the presence of a new aerobic nitrogen-fixing bacterium, which was named Bacterium krakataui. B. radicicola is present in abundance in the root tubercles of the numerous leguminous plants which now abound on the island. It is evident that the different kinds of bacteria must have very early established a foothold upon the sterilized island surface and were no doubt among the factors which rendered the establishment of the higher types of vegetation possible.

A most interesting find was a single thrifty female specimen of Cycas circinalis. This tree had a trunk nearly two meters in height, and the size of the plant suggested that it was a survivor of the original flora; but Ernst states that this is impossible, as the portion of the island where it is growing belongs to the new shore formed since the eruption.

AGENTS IN DISTRIBUTION

Ernst has treated very fully the question of the agents by which most of the members of the new flora were introduced (pages 53 to 68). There seems no doubt that the earliest immigrants-bacteria, blue-green algæ, ferns and mosses, were wind borne, and the same is probably true of the first phanerogams found upon the island, composites and grasses, but other agents have been active in transporting seeds and fruits to the shore of the devastated island, and of these the ocean currents have probably been most important. There is no question that the fruits and seeds of the strand plants are probably all water borne, and Ernst called attention to the important part played by driftwood in introducing new plants whose seeds might have been lodged in the crevices in the

bark, or he even suggests the possibility of young plants being transported on uprooted trees. The shore of the island is covered with masses of logs and fragments of trees which might very well have brought with them not only vegetable immigrants, but animals as well. An interesting case was that of the two species of fleshy fungi, Polystictus, which were found growing upon logs lying on the shore, and whose mycelium almost certainly had been growing in the logs before they were drifted out to

sea.

Birds have undoubtedly also played their part in the introduction of seeds, especially those of fleshy fruits such as the species of Vitis, common near the shore, and several species of figs found somewhat further inland.

The rapid development of the vegetation in the nine years between the visit to the island in 1897 and our visit in 1906, and especially the great increase in the forest vegetation, makes it evident that before very long the forest which originally covered the island will be again in possession. Already the belt of forest along the shore is working inland, and it is to be expected that the patches of forest in the ravines flanking the cone in the interior of the island are spreading shoreward, so that in the course of time the intermediate belt of grassy land will probably be completely obliterated and the forest will once more be in undisputed possession of the entire island.