Analyzing mangrove forest structure and species distribution on a Pacific island

Three surveys of mangrove forests have been conducted on the island of Kosrae, Federated States of Micronesia, in the eastern Caroline Islands of the western Pacific Ocean. The first two surveys were based on a small number of plots: one group of four that were located randomly in 1983-86 and remeasured in 1992, and a group of 12 that were randomly distributed among fringe, riverine, and interior zones in a 1995 survey. A more extensive survey based on measurements of trees found in belt transects randomly located among nine sampling blocks around the island was conducted in 1999 and is the basis for this paper. Among the eleven mangrove tree species encountered, Bruguiera gymnorrhiza, Sonneratia alba, and Rhizophora apiculata had the highest importance values and, along with Nypa fruticans, the widest distribution. There were no significant differences in the distributions of species, basal area, tree density, and silty soils mixed with organic matter. Because of this uniformity, the earlier surveys based on fewer plots represented the importance of major species well, but they were less useful in calling attention to the higher diversity and richness in interior zones and the distinctly smaller trees in the fringe zones. A volume equation is presented for Barringtonia racemosa, a species for which data have so far been unavailable.