Variation in environmental characteristics and vegetation in high-rainfall mangrove forests, Kosrae, Micronesia

Understanding differences among fringe, riverine, and basin zones in mangrove forests may assist mangrove scientists in clarifying the relationships between tree distributions and environmental characteristics, and may assist resource managers in designing appropriate management policies for these important wetlands. This study examined differences in soil redox potential and porewater salinity as well as in characteristics and distribution of hardwood mangrove trees among these zones on the island of Kosrae in the Federated States of Micronesia. Neither porewater salinity nor soil redox potential differed significantly among the three types of forests. High annual rainfall (5000-6000 mm/year) and, perhaps. high rates of groundwater flow and surface runoff, may buffer these forests from extremes in salinity. Zonation of trees was not readily apparent, with Sonneratia alba J. Smith, Bruguiera gymnorrhiza (L.) Lamk., and Rhizophora apiculata Bl. dominant in volume and/or density in all three zones. Tree heights were significantly shorter in fringe forests than in basin forests. Growing conditions appear to vary among the three zones, but other environmental characteristics may be responsible. Data on regeneration patterns suggest that resource managers should restrict harvesting in fringe and riverine zones and attempt to increase regeneration of S. alba in basin zones where large gaps are formed.