Structure of mangrove trees and forests in Micronesia

Volume equations were constructed for five species of mangrove trees on volcanic high islands of Micronesia in the north Pacific Ocean, where islands that span a distance of more than 3000 km from east to west are characterized by a gradient of rainfall from 3080 to 5250 mm/year and a range of typhoon frequency from less than one per century to several per decade. We also calculated mean annual increments for a subset of the trees. The inclusion of very large trees in the data set makes these volume equations unique. For the five most common species, separate volume equations were calculated for each of the two easternmost islands (Kosrae and Pohnpei), the remaining islands (`Western Islands', including Chuuk, Yap, and Palau), and all the islands together (Micronesia). Tree structure differed significantly among the three island groupings and for two species, between Kosrae and Pohnpei, which are only 560 km apart. Mean annual diameter increments for Sonneratia alba and Bruguiera gymnorrhiza indicated significantly faster growth on Kosrae (0.96 and 0.44 cm/year, respectively) than on Pohnpei (0.33 and 0.26 cm/year, respectively). Frequency distributions of diameter size classes on these two islands demonstrated a more even distribution of sizes and more large trees on Kosrae (e.g., up to 3.2 m in diameter for S. alba). Differences in diameter distributions may be attributed to a typhoon that devastated Pohnpei, but not Kosrae, in 1905, but differences in growth rates cannot yet be explained.