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Biogeographical context Long Island, in Vitiaz Strait, is 55 km north of New Guinea, 60 km from Umboi Island and 125 km from New Britain. After its explosive caldera-forming eruption in about 1645, Long is being recolonized by animals and plants. Through renewed volcanic activity in the 1950s a new island emerged from Long's caldera lake, 4 km from the nearest lake shore and was recreated by eruptions in 1968. Long Island thus provides the opportunity to study a nested pair of natural colonization sequences. The geological background, eruptive history, course and results of the seventeenth century eruption, and the geographical features and climate of Long Island are summarized. Existing knowledge of Long's recolonization, confined almost entirely to surveys of its avifauna in 1933 and 1972, is reviewed. The geological history of Motmot is outlined, and published knowledge of its colonization by animals and plants from 1968 to 1988 is summarized. The 1999 expedition and aims An expedition to Long Island and Motmot in 1999 set out to investigate the hitherto little-known flora and present vertebrate fauna of Long Island and to survey the entire flora and fauna of Motmot for comparison with the results of previous surveys. The methods used in the 1999 survey are described, and the papers setting out the results briefly introduced. [ABSTRACT FROM AUTHOR]

Aim Long Island erupted catastrophically in c. 1645 with the probable destruction of its entire biota. While several expeditions have visited the island since, no survey of its flora has been published. In 1968 a small island, Motmot, emerged from its caldera lake. Motmot has been surveyed several times but not since 1988. The aim of this study was to investigate the colonization by vascular plants of this interesting nested pair of islands. Location Long Island is 55 km off the northeast coast of Papua New Guinea (PNG) and Motmot lies in its fresh water caldera lake, Lake Wisdom, c. 4 km from the rim of the surrounding volcano. Methods We conducted a complete survey of the vascular plants on Motmot and made ad hoc collections on Long Island, including surveying three small plots, over 15 days in 1999. In addition, we incorporated data from several collections lodged at the regional herbarium in Lae. Data on seed dispersal syndromes and plant habit were obtained from the literature. Results We recorded 305 species of vascular plants from Long Island, but most trees were small and the species diversity was low. Motmot was still very sparsely vegetated and only forty-five species of vascular plants were found. Communities on Motmot were unspecialized and common species widespread. The flora of Motmot was not significantly different from that on Long Island in terms of the number of species amongst higher taxa, seed dispersal syndromes or plant habits. Main conclusions Low rainfall combined with very porous soils may be responsible for the small stature and low diversity of the forest on Long Island's caldera rim. The absence of specialist littoral species on Motmot, as a result of its landlocked situation, is probably responsible for the very slow species recruitment on the island. This community appears to be functionally important for colonization by comparison with other small volcanic islands in a marine situation. [ABSTRACT FROM AUTHOR]