Chapter VIII —133 — Natural Factors 



of a volcanic eruption Krakatau has been considered a particularly 

 suitable subject. Observations on the revegetation of this island have 

 already been made for over 50 years, as a result of which there have 

 been accumulated many scientiiic papers devoted to it. In recent years 

 there have appeared two extensive works (Ernst, 1934; Docters 

 VAN Leeuwen, 1936), reviewing the results of these investigations. 

 Krakatau, one of the Sunda Isles in the Malay Archipelago, is a vol- 

 canic island, approximately 14 sq. mi. in area and located 25 mi. from 

 Java and 23 mi. from Sumatra. In 1883, as a result of a big volcanic 

 eruption, the luxurious vegetation of the island was destroyed by a 

 downpour of hot ashes and stones that covered the entire island in a 

 thick layer. Regarding the former vegetation of the island we have 

 no exact data. It is only known that two weeks prior to the end of the 

 eruption, at a time when in the northern part of the island there could 

 be seen only occasional bare trunks of trees, the whole southern slope 

 comprising the more elevated part of the island was still covered, 

 according to observations of the geologist Verbeek, by dense, green 

 vegetation, and only during the very last moments of the eruption was 

 this part of the island also buried under ashes and pumice. 



Three years after this catastrophe Treub (1888) made a trip to the 

 island for the purpose of studying the new vegetation on it. On the 

 shores of the island he found about 16 different species of flowering 

 plants, and in the interior 8 species of flowering plants (6 of which 

 were not found on the shores) and 11 species of ferns, the latter in 

 abundance. Assuming that all the original flora of the island, in- 

 cluding seeds and underground parts of plants, had been completely 

 destroyed at the time of the eruption and that, due to the uninhabit- 

 ableness of the island, plants could not have been brought by man, 

 Treub came to the conclusion that sea currents and wind, and later 

 also birds, constituted the factors responsible for the stocking of this 

 island with plants. From that time on, Treub's work was regarded 

 as an example par excellence of the significance of natural factors in the 

 dispersal of plants, as proof based on the actual observation of facts, 

 and Treub's final conclusion almost as a law. Since then, from time 

 to time, various investigators have visited Krakatau and published 

 their findings as regards its vegetation. The number of plants col- 

 lected constantly increased, but the mode of their origin on the island 

 did not evoke any doubts. For most of these investigators Treub's 

 premise as to the complete destruction of the vegetation on the island 

 was regarded as an incontrovertible fact. 



In 1929 Backer, who had himself visited Krakatau on numerous 

 occasions and who held the same viewpoint as all the other botanists, 

 undertook a summary of the data of all the investigators of the island's 

 vegetation, a survey of all the results of the various expeditions to the 

 island, including those in which he had personally participated. Hav- 

 ing completed this survey, he was forced to renounce his previous views 

 and to put the whole question in an entirely different light. He found 

 that it was by no means established that all the vegetation of Krakatau 

 had been destroyed by the volcanic eruption of 1883, and he con- 

 cluded, therefore, that the problem of Krakatau can never be solved 

 and should be regarded as without significance for botanical science. 



