Rain forest composition and patterns of secondary succession in the Vava'uIsland Group, Tonga

The Vava'u island group, Tonga, comprises ca. 60 limestone islands on a sin gle submarine platform overlain with rich soils derived from tephra deposit s from nearby volcanic islands. The island group has moderate topographic r elief (215 m) and is characterized by plateaus and steep cliffs. Humans set tled in Tonga ca. 3000 yr ago and have exploited the flatter terrain for ag riculture since that time. We conducted the first survey of forest composit ion in Vava'u, sampling remnant patches of late-successional forest as well as stands in various stages of secondary succession following agricultural abandonment. Plant species composition did not vary greatly with elevation over this short gradient, in contrast with patterns found on 'Eua, a highe r island in Tonga. The most significant environmental gradient affecting sp ecies composition was coastal or maritime influence. However, the greatest variation in species composition and structure appeared to be related to sp ecies turnover during secondary succession, and we hypothesize a sequence o f species replacements. Secondary forest begins to resemble late-succession al forest in 30 - 50 yr in terms of structure and native species richness a nd therefore is of significant conservation value.