Anak Krakatau's vegetation and flora circa 1991, with observations on a decade of development and change

Ecological surveys were conducted over the period 1989 to 1991 on the island of Anak Krakatau. The aims of the study were to detail a key phase of rapid change in the vegetation succession and plant colonization of this young volcano and to compare results with those from earlier studies.Floristic composition was determined by reconaissance of all vegetated areas during the period 1989 to 1991. Colonization has been rapid since 1983 with 53 species newly recorded for Anak Krakatau, comprising 8 Pteridophyta and 45 Angiospermae. Of the latter, a significant element (13) were of species believed to be human-dispersed. Comparison of all floral surveys has revealed a core of strand-line and pioneer colonists which has been common to each restart of colonization. The sea-dispersed component is already comparable in size to that of Rakata and is thought unlikely to increase significantly from this point. The accumulation of animal-dispersed species of interior habitats has only recently begun to pick up speed.Vegetation was characterised by means of plot-based sampling, including the establishment of three permanent plots, and by mapping at the whole-island scale. Variation in composition within the island is discussed, with particular reference to the three vegetated forelands. Anak Krakatau now supports the most extensive and advanced vegetation in its disrupted 61-year history. A more or less closed cover extends along the eastern/north-eastern coast-line, but the xeric interior remains only sparsely vegetated. It is concluded that because of volcanic disturbance a base-line for ecosystem development on Anak Krakatau cannot be calculated but that the pattern of change is not inconsistent with significant disturbance ca. 1972 and the subsequent relaxation of these peculiar environmental constraints.