Regeneration and growth of pioneer and shade-tolerant rain forest trees in Tonga

Size distributions were analysed for 25 tree species (4331 individuals) from among those recorded in 64 plots in the Vava'u island group, Kingdom of Tonga, in 1995. These species were assigned to four groups representing their regeneration patterns (association with either gaps or low light microsites as seedlings and/or as larger trees). The distribution of tree diameters was calculated from early- (n = 28) and late-successional (n = 36) plots to determine where the species were regenerating. Six years later 1110 of these trees were remeasured. Average net growth increment was used as an estimate of growth rate, and maximum growth increment as potential growth rate, for each species. Most shade-tolerant, late successional species had low growth rates and a lognormal size distribution in late-successional plots, as expected. One species in this group, however, had the highest estimated average growth rate in the study. The second group of species, found in shade as seedlings but abundant as small trees in early-successional plots (e.g., “mid-successional"), as well as the third group, found in gaps as seedlings but most abundant in late-successional plots, shared high growth rates. The fourth group, pioneer species establishing in large gaps, were not regenerating in late-successional plots but, unexpectedly, had estimated growth rates comparable to the other groups. Tongan rain forest has diverse regeneration functional types, analogous to those found in richer continental tropical forest, but perhaps represented by different numbers of tree species.