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

Abstract

Abstract. The Vava'u island group, Tonga, comprises ca. 60 limestone islands on a single submarine platform overlain with rich soils derived from tephra deposits from nearby volcanic islands. The island group has moderate topographic relief (215 m) and is characterized by plateaus and steep cliffs. Humans settled in Tonga ca. 3000 yr ago and have exploited the flatter terrain for agriculture since that time. We conducted the first survey of forest composition 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 higher island in Tonga. The most significant environmental gradient affecting species composition was coastal or maritime influence. However, the greatest variation in species composition and structure appeared to be related to species turnover during secondary succession, and we hypothesize a sequence of species replacements. Secondary forest begins to resemble late‐successional forest in 30–50 yr in terms of structure and native species richness and therefore is of significant conservation value.