Littell's Living Age/Volume 178/Issue 2308/The New Vegetation of Krakatao
The great volcanic eruption of Krakatao in August, 1883, will be fresh in most memories. It was at one time reported that the island had totally disappeared, but this was not so. Previous to the eruption, however, it was covered with a luxuriant vegetation, no trace of which existed after the event.
Dr. M. Treub, the director of the botanic garden at Buitenzorg, Java, when at Kew last year informed the writer that he had visited the island the previous year, and intended publishing the results of his botanical investigations. This he has now done,[1] and as the derivation of insular floras is a subject of great interest to many persons, the substance of Dr. Treub’s communication deserves a place in Nature.
The existing portion of Krakatao Island is about three miles across, and has the form of a mountain rising out of the sea. On one side it is nearly perpendicular almost to the summit of the peak, which has an altitude of about twenty-five hundred feet, and on the other it presents a steep slope. It is situated ten miles-distant from the Island of Sibesie, the nearest point where there is terrestrial vegetation; twenty miles from Sumatra, and twenty-one miles from Java. Verlaten and Lang Islands, lying much nearer Krakatao, were utterly desolated and denuded of their vegetation by the great catastrophe, and were still absolutely bare in 1886.
With regard to the total destruction of vegetable life in the island, Dr. Treub asserts that there can be no doubt; the most durable seed and the best protected rhizome must have lost all vitality during the intense heat, and not a germ was left. The whole island from the summit of the peak down to the water’s edge is now covered with a layer of cinders and pumice stone, varying from one to sixty metres in thickness. Furthermore, the possibility of the new vegetation having been conveyed thither by man is out of the question, because the island is uninhabited, uninhabitable, and difficult of access.
Therefore, the present vegetation must be due to other agencies, of which three different ones may have operated — namely, winds, waves, and birds.
Now, as to the composition of the vegetation met with on Krakatao by Dr. Treub in June, 1886, nearly three years after the eruption, the bulk consisted of ferns with isolated plants of phanerogams, both on the shore and on the mountain itself. Eleven species of ferns were collected, and some of them were already common. They are all species of wide distribution, and it may be of interest to give their names: Gymnogramme calomelanos, Acrostichum scandens, Blechnum orientale, Acrostichum aureum, Pteris longifolia, Nephrolepis exaltata, Nephrodium calcaratum, N. flaccidum, Pteris aquilina, P. marginata and Onichium auratum.
It is not at all surprising that the spores of the foregoing and many other ferns should have been carried to the island by winds; but, as Dr. Treub remarks, it is almost incomprehensible that they should grow under such extraordinarily disadvantageous conditions. Chemically and physically the volcanic matter covering the island is as sterile as could well be, yet the prothallia of ferns readily developed. A closer investigation, however, revealed the fact that ferns were not the first organisms in the new vegetation of Krakatao, the cinders and pumice stone being almost everywhere covered with a thin coating of Cyanophyceæ (fresh-water algæ) belonging to the genera Lyngbya, Tolypothrix, etc., — altogether six species. The presence of these algæ gives the surface of the soil a gelatinous and hygroscopic property, in the absence of which Dr. Treub doubts the possibility of fern growth. Thus these microscopic organisms prepare the soil for the ferns, much as the latter provide the conditions under which the seeds of phanerogams can germinate and grow.
The phanerogamic element (flowering plants) of the new vegetation consisted, on the shore, of young plants of Galophyllum inophyllum, Cerbera odollam, Hernandia sonora, Scævoia Kænigii, Ipomcæ pescapræ, a species of Erythrina, two species of Cyperaceæ, and Gymnothrix elegans. With the exception of Gymnothrix elegans, a common grass in Java, all the plants named are among those which take possession of newly raised coral islands.
In the interior of the island, on the mountain itself, Dr. Treub discovered Scævola Kænigii, Tournefortia argentea, a species of Wollastonia, a species of Senecio, two species of Conyza, Phragmites Roxburghii, and Gymnotkrix elegans.
In addition to the foregoing phanerogains, Dr. Treub observed on the seacoast seeds or fruits of Heritiera littoralis, Terminalia catappa, Cocos nucifera, Barringtonia speciosa, and Pandanus. These also are among the commonest seashore and coral-island trees throughout the Malayan Archipelago and Polynesia.
A more interesting record of the processes of a new flora can hardly be imagined, especially that in relation to the preparation of the soil by microscopic sporiferous plants. Of course this is not a new discovery; but it is perhaps the first actual observation of the renewal of the vegetation of a volcanic island.
Dr. Treub intends visiting Krakatao again, and reporting fully on the progress of the new flora, and his report will doubtless be looked forward to with great interest.
Notes
[edit]- ↑ Annales du Jardin Botanique de Buitenzorg, vii., pp. 213-23, with a sketch map.