The biogeochemistry of phosphorus after the first century of soil development on Rakata Island, Krakatau, Indonesia

This study examined the accumulation of organic carbon (C) and fractions ofsoil phosphorus (P) in soils developing in volcanic ash deposited in the1883 eruption of Krakatau. Organic C has accumulated at rates of 45 to 127g/m²/yr during 110 years of soil development, resulting inprofiles with as much as 14 kgC/m². Most soil P is found inthe HCl-extractable forms, representing apatite. A loss of HCl-extractableP from the surface horizons is associated with a marked accumulation ofNaOH-extractable organic P bound to Al. A bioassay with hill rice suggeststhat P is limiting to plant growth in these soils, perhaps as a result ofthe rapid accumulation of P in organic forms.     

Genetic Evidence for Natural Hybridization between Species of Dioecious Ficus on Island Populations1

Natural hybrids between Ficus septica and two closely related dioecious species, F. fistulosa and F. hispida, were confirmed using amplified fragment length polymorphisms (AFLP) and chloroplast DNA markers. Ficus species have a highly species‐specific pollination mutualism with agaonid wasps. Therefore, the identification of cases in which breakdown in this sophisticated system occurs and the circumstances under which it happens is of interest. Various studies have confirmed that Ficus species are able to hybridize and that pollinator‐specificity breakdown can occur under certain conditions. This study is the first example in which hybrid identity and the presence of hybrids in the natural distribution of parental species for Ficus have been confirmed with molecular markers. Hybrid individuals were identified on three island locations in the Sunda Strait region of Indonesia. These findings support Janzen's (1979) hypothesis that breakdown in pollinator specificity is more likely to occur on islands. We hypothesized that hybrid events could occur when the population size of pollinator wasps was small or had been small in one of the parental species. Later generation hybrids were identified, indicating that backcrossing and introgression did occur to some extent and that therefore, hybrids could be fertile. The small number of hybrids found indicated that there was little effect of hybridization on parental species integrity over the study area. Although hybrid individuals were not common, their presence at multiple sites indicated that the hybridization events reported here were not isolated incidences. Chloroplast DNA haplotypes of hybrids were not derived solely from one species, suggesting that the seed donor was not of the same parental species in all hybridization events.     

A phytosociological study of a forest area in the humid tropics (Ujung Kulon,West Java,Indonesia)

A vegetation survey was carried out in the Ujung Kulon nature reserve (West Java, Indonesia). Particular attention was paid to the altitudinal zoning of the vegetation, to succession and to the applicability of the phytosociological approach in forests of the humid tropics. The altitudinal zoning provides a clear example of the telescope effect: low, isolated mountain complexes surrounded by sea reflect the vegetation zoning of higher mountains in a condensed, telescoped way. The pattern of primary forests, secondary forests and rattan-dominated shrublands can be explained by the former shifting cultivation practice and the impact of ash rains following the notorious eruption of the nearby volcano Krakatau in 1883. The arguments against the phytosociological approach in the humid tropics are found to be invalid. The minimal area concept does not cause great problems if used in a practical sense and if plants of all age classes and all terrestrial growth forms are included in the relevé.     

Stand Biomass and Tree Mortality from Permanent Forest Plots on Krakatau,Indonesia, 1989–19951

Forest closure on the three original Krakatau Islands (Panjang, Rakata, and Sertung) took place ca 1930, about 50 yr after the apparent sterilization of the islands due to volcanic eruptions. Two permanent forest plots were established on each of these islands in 1989. A full enumeration of these plots, of two additional Rakata plots, and of two “mainland”plots from the Ujung Kulon National Park, West Java, was undertaken in 1992. These data provide the first estimates of aboveground biomass from Krakatau. The values reported for Krakatau are below the local West Javan figures, with considerable variation occurring within the islands. In 1992, the fourth Krakatau island, Anak Krakatau, began an eruption sequence which continued through the study period, depositing ash on the study sites of Panjang and Sertung. A further partial survey of these plots in 1994–1995 revealed a significant increase in mortality since the volcanic activity recommenced, with an increase in deaths of larger stems. Although Rakata has not been influenced directly by volcanism, three sites surveyed on Rakata in 1994–1995 have experienced increased tree mortality, in two cases as a consequence of storm damage and in particular, of lightning strikes. Stand dynamics on Krakatau thus appear to be strongly influenced by episodic environmental disturbance with varying degrees of dependence on the volcanic activity of Anak Krakatau.     

Chance and determinism in the development of isolated communities

• 1 In the colonization of an island by potentially interacting species both the severity of the competition between them and the length of the interval between their arrivals should affect the likelihood of the second species becoming established. Between‐island variation in priority and the interval between colonizations will depend on the dispersal rates of the two species.
• 2 We predict that early colonization should be relatively deterministic, whereas later in the colonization process both the sequence of arrivals and the interval between them will be more variable.
• 3 Possible instances of both deterministic and stochastic stages in community development are identified in the colonization of the Krakatau islands by zoochorous forest trees and large zoochorous lianes.

     

The rebuilding of an isolated rain forestassemblage: how disharmonicis the flora of Krakatau?

The compositional balance of the flora of the Krakatau Islands, Indonesia, is examined in order to identify taxonomic and/or ecological groups which are under-represented in this recovering island ecosystem in relation to regional analogues and potential source areas in the Sunda Strait (Ujung Kulon and Sebesi Island). Interpretations are conditioned by the limited availability of comparative data, the uncertainty surrounding dispersal classifications, the problem of determining habitat suitability for missing elements, and thus the unsuitability of a formal statistical approach. Analysis by dispersal syndrome supports predictions that species with large, winged, wind-scattered propagules, or those with no particular dispersal potential, are under-sampled. However, some species with winged propagules have colonized, in most cases probably by thalassochory (sea-dispersal). Although zoochorous (animal-dispersed) trees and shrubs are well represented on Krakatau, those large-seeded species which are primarily dependent on dispersal by animals other than birds are under-represented. Large-seeded zoochores are probably highly dependent on two species of Ducula (large fruit-pigeons) for transport to Krakatau and their colonization has been relatively slow. Comparison with Christmas and Jarak Islands yields differing degrees of overlap for thalassochorous, zoochorous, and anemochorous (wind-dispersed) spermatophytes and for pteridophytes, interpretable in terms of dispersability and size of the respective species pools. Particular families and genera can be identified which are seemingly under-sampled on Krakatau, as can some which are over-represented in relation to the principal comparative site, the Ujung Kulon peninsular, West Java. The latter are mostly very small-seeded wind-dispersed epiphytic herbs (especially orchids). Ferns are also very well represented in relation to the West Javan source pool. It is concluded that the flora of Krakatau remains disharmonic, in a predictable fashion, although it is certainly becoming less so. The data provide empirical evidence for the abilities of particular functional guilds of rain forest plants to disperse across significant barriers: the implications of these findings are discussed in relation to current concerns with forest fragmentation in the tropics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pollinating fig wasps: genetic consequences of island recolonization

The levels of genetic diversity and gene flow may influence the long-term persistence of populations. Using microsatellite markers, we investigated genetic diversity and genetic differentiation in island (Krakatau archipelago, Indonesia) and mainland (Java and Sumatra, Indonesia) populations of Liporrhopalum tentacularis and Ceratosolen bisulcatus, the fig wasp pollinators of two dioecious Ficus (fig tree) species. Genetic diversity in Krakatau archipelago populations was similar to that found on the mainland. Population differentiation between mainland coastal sites and the Krakatau islands was weak in both wasp species, indicating that the intervening 40 km across open sea may not be a barrier for wasp gene flow (dispersal) and colonization of the islands. Surprisingly, mainland populations of the fig waSPS may be more genetically isolated than the islands, as gene flow between populations on the Javan mainland differed between the two wasp species. Contrasting growth forms and relative 'immunity' to the effects of deforestation in their host fig trees may account for these differences.