Krakatau and its ProblemsAuthor(s): W. B. TurrillSource: New Phytologist, Vol. 34, No. 5 (Dec. 4, 1935), pp. 442-444Published by: Wiley on behalf of the New Phytologist TrustStable URL: http://www.jstor.org/stable/2428286 .

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[442]

KRAKATAU AND ITS PROBLEMS

BY W. B. TURRILL

THE flora and vegetation of islands must always be of particular interest to phytogeographers and ecologists, since problems of

origin and development are in some respects simpler and in others more difficult than for land-locked areas. The history of Krakatau since the great eruption in I883 is familiar to English students largely because of Prof. Seward's translation (Cambridge University Press in I908) of Prof. A. Ernst's account published in Zuirich the previous year. A more recent account by C. A. Backer (published by the author, I930) was also written in English. This latter is a book of three hundred pages under the title The Problem of Krakatao as seen by a Botanist. Backer, in opposition to Treub, Ernst, and most other scientists who have visited the main island since the catastrophe, concluded that it has not been proved, and that it is even improbable that the old vegetation was totally destroyed by the eruption of I883. Backer's arguments are weakened by a dogmatic and unnecessarily polemical style, which, rightly or wrongly, leads the reader to suspect a personal bias of the writer against one or more of the previous investigators. There remains, however, a considerable mass of facts and statements which have to be considered by those who believe that a large and unique example of primary succession can be traced in the new vegetation of Krakatau.

Prof. Ernst has now published (Vjschr. naturf. Ges. Zitrich, 79, I934) a paper of I87 pages on " Das biologische Krakatauproblem ", in which the whole problem is carefully reviewed, data from still more recent investigations are added, and Backer's arguments at least partly met. The paper is illustrated by seven plates and five text-figures and has five and a half pages of references.

There can be no doubt that the existing growing vegetation of what is now Krakatau and the associated smaller islands of Verlaten Eiland and Lang Eiland was mainly if not entirely destroyed in I883. Backer, himself, thinks it most probable that the two smaller islands were completely denuded of living organisms. The crucial matters are whether or not some vegetation survived in ravines on the higher parts of Krakatau, especially on those sides not visited by Treub in i886, and whether on the higher parts of the island the ash covering

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Krakatau and its Problems 443 was sufficiently hot and remained everywhere long enough to kill all seeds and underground plant parts such as deeply seated rhizomes. It is obvious that, half a century after the event, only the statements of earlier investigators and indirect circumstantial evidence are available. The earlier biological investigators were unanimous in concluding that all living organisms were destroyed and that the new flora and fauna immigrated from surrounding land. Their judg- ment was based on close investigation of sanmple areas, which though not so numerous or so extensive as is now known to have been desirable, were, from the standpoint of the main problem, chosen at random. Considerable weight must be given to the published accounts of Treub, Verbeek, and Penzig. The possible survival of seeds or other disseminules under a temporary ash covering on the higher slopes can only be considered by most indirect evidence. Ernst notes that plants with deeply seated rhizomes (Zingiberaceae, Musaceae, Araceae) are even now represented by relatively few species.

It is impossible in a short review to do justice to the evidence, so much of it being matters of detail. While it cannot be proved in any absolutely certain manner that every trace of living organisms was destroyed there can be no doubt that the three existing islands of the group have become clothed with an essentially new vegetation. The greater part of Krakatau itself must now have a vegetation which represents one or other stages of a primary succession. The investigations summarised by Ernst have therefore a peculiar value to ecologists. On the other hand, the problem of complete or in- complete destruction of the former vegetation is of less importance to students of plant dispersal than it would have been had Krakatau been much farther from surrounding land masses. Sebesi Eiland is only I9 km. from Krakatau (and less from Lang Eiland and Verlaten Eiland) and the vegetation on Sebesi Eiland was only partially destroyed. Parts of Java and Sumatra are only 40 km. distant. Transport of disseminules over much greater distances by the common agents of dispersal (birds, wind, water) has been proved by many -independent observations in widely different parts of the world. Phytogeographically Krakatau is of less interest than it is ecologi- cally.

Ernst summarises the existing plant formations, largely on the work of W. M. Docters van Leeuwen, as follows:

(i) The Strand-Zone with the Ipomaea pes-caprae formation, and (2) The Barringtonia wood, both of unequal width and still (up

to I9I9) discontinuous. PHYT. XXXIV. 5 29

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444 W. B. TURRILL

(3) The Casuarina wood here and there in extensive groups. (4) Mixed wood and Macaranga formation, over considerable

areas with a strong development of ferns as undergrowth. (5) The Grass steppe, which in I906 occupied the largest part

of the island, still covers considerable areas. (6) The Cyrtandra formation on the higher slopes, with con-

siderable richness in epiphytes. In addition to coastal changes due to the removal and redeposi-

tion of the mobile strand terrain, with destruction of some of the pioneer vegetation, successional changes are summarised by Ernst. The Casuarina wood is the first woody vegetation to develop on the Krakatau islands, but is the one with the shortest existence, since once it has established itself it is invaded by and soon destroyed by elements of the Barringtonia community which over-shade the light crowns of Casuarina. Another striking successional change is the reduction of the grass steppe area. This formerly dominated in the inner coastal stretches and on the lower slopes of the peak but is being rapidly invaded by forest both from below and from the ravines of the mountain.

Unfortunately early investigators after I883 did not reach the peak and changes in the Cyrtandra forest can only be recorded from I908. It would appear that Cyrtandra sulcata has grown and multi- plied rapidly to produce a rather low but thick wood, which, in habit but not in composition, is now similar to the forests on volcanic peaks in Java and Sumatra. It is probable that the Cyrtandra wood is not a climax at the Lelatively low altitude of the Krakatau peak and it may be expected that in the not far distant future a forest covering will be developed of the same luxuriance and composition as that destroyed in I883.

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