[HCG28-P01] Forest structure and site environments of a mangrove community in the surface erosion area possibly caused by rapid sea-level rise on Pohnpei Island, Micronesia.
Keywords:Mangrove community, Surface erosion, Sea-level rise, Mangrove peat
The plot is situated behind a R. stylosa community with about 30 m depth. Four species, Bruguiera gymnorrhiza, R. apiculata, Xylocarpus granatum and Sonneratia alba, were identified in the plot. Number of each species were 116, 40, 17 and 13, respectively. Tree density was calculated at 715 trees/ha. 90 % of R. apiculata trees were shrub with smaller than 5 cm in diameter. Diameter of B. gymnorrhiza and X. granatum show unimodal distribution whose mode is 20.0 to 29.9 cm and 30.0 to 39.9 cm, respectively, while S. alba shows inhomogeneous distribution between 20 and 90 cm in diameter. Aboveground biomasses were calculated at 256 t/ha for B. gymnorrhiza, 173 t/ha for S. alba, 94 t/ha for X. granatum and 25 t/ha for R. apiculata. Substrata consists of mangrove peat, which shows that former dominant species was Rhizophora sp. Ground elevation in the plot was between -57 and +19 cm. Area above mean sea level sparsely distributed around 100 m line, which indicates that surface erosion is surely progressing. At the base of B. gymnorrhiza trees, the buttress roots and the like of prop roots under the buttress roots were exposed by the surface erosion and the gaps between ground surface and its buttress root appeared. The average gap height reached 43 cm between 0 and 20 m line, 31 cm between 110 and 130 m line, which suggest that the amount of erosion possibly decrease with distance from seaward forest edge.