Site environments and stand structure of the mangrove forests on Pohnpei Island, Micronesia

In order to obtain fundamental data for the prediction of stand productivity and sustainable management, two permanent plots, 1 ha each, were established in two types of mangrove habitats, i.e. estuary and coral reef types, on Pohnpei Island, Micronesia. This paper analyzes the stand structure and the site environments and their relationships. The number of trees in the estuary type was less than half of that in the coral reef type and tree size in the former was larger than in the latter. These differences were attributed to the difference in the age between the forests which was estimated from the thickness of the mangrove peat layers. Distribution of Rhizophora apiculata and Xylocarpus granatum trees may possibly be related to the submergence frequency which affects the soil water content and soil water EC. Large Sonneratia alba trees were widely scattered in both plots. These trees were assumed to have survived by vegetative reproduction in spite of the changes in site environments that have occurred since the mangrove forests were developed at their present site. There were few Bruguiera gymnorrhiza and X. granatum trees with a diameter between 10 and 25 cm in the estuary type. This fact suggests that some environmental changes which disturbed the establishment of B. gymnorrhiza and X. granatum trees, such as a relative rise in sea level, occurred during a certain period of time.