Mangroves are important tropical coastal ecosystems providing various ecosystem services such as carbon sequestration, coastal protection, mitigation of storm winds and surges, as well as serving as habitat for various organisms, etc. However, huge areas of mangroves were already lost because of anthropogenic activities such as conversion of mangrove to aquaculture ponds in the last half century. Therefore, numerous countries like the Philippines have made an immense effort to restore the lost mangroves by replanting. One of the threats to mangrove reforestation is the damage caused by burrowing of marine isopods Sphaeroma terebrans, i.e. the holes created by isopods in the mangrove trunk can cause mangrove trees to fall. In the present study, for three mangrove species, Avicennia marina, A. alba, and Sonneratia alba, isopod hole density at the trunk surface and decay extent of trunks were measured at a recovering forest in Batan Estuary, Aklan, Philippines. The trunk decay was evaluated using acoustic tomography by measuring the travel times and attenuation of the sound wave within the focal trunk. Also, we attempted to clarify the relationships among isopod hole density, trunk decay extent and relative height from mean lower low water (MLLW) level. The hole density decreased significantly with increasing time of exposure to the atmosphere (height relative to MLLW). The trunk decay area increased with decreasing relative height above the MLLW level in A. marina, but did not decrease significantly in the other tree species. The relationship between trunk decay volume and hole density was insignificant, but A. marina had a higher trunk decay volume than the other two species. The present results partially supported our hypothesis that trunk decay extent is a function of isopod hole density on the trunk surface, as well as the species of the host tree, i.e. interspecific differences in trunk decay area and volume were detected but the effect of hole density on the trunk decay volume was insignificant. The holes caused by isopods could be a trigger to start the formation of hollow space in the trunks but further research on the other influential parameters, such as tolerances to water quality, xylophagous fungus and physical disturbance, would be necessary to understand the decay process of mangrove trunks considering their interspecific differences.

This study was conducted in the Letkhokkon delta mangrove, Myanmar to establish species-specific allometric models for accurate aboveground biomass estimation, contributing to improved mangrove ecosystem management. We found three mangrove species (Avicennia officinalis, Sonneratia apetala and Sonneratia caseolaris), and the first two species (A. officinalis and S. apetala) were dominant. Results highlighted the distinctive stand structure, species composition, and the low Shannon diversity (H′＝0.734). Using the tree measurable parameters such as diameter at breast height (DBH), height (H) and wood density (ρ), we established several allometric models of aboveground biomass (W＝ax^b) for two dominant species. We selected the best-fit allometric models by model selection parameters. Also, we compared these best-fit models with the previously reported allometric models. Our study found that volumetric parameter (DBH²H) and ρDBH²H gave the best results with relatively higher accuracy than the other explanatory parameters. The study confirmed the importance of ρ in building of site-specific allometric model and also validated the superiority of species-specific models over generalized equations to estimate the biomass accurately. Besides, comparisons with other allometric models for mangroves in Americas, Asia, China and Myanmar emphasized the significance of tailored approaches, considering the influence of ρ on accurate biomass estimation. Wood density showed less significance in species-specific level though ρ was an important variable for generalized models. Applying ANOVA results for model comparison, the current models did not significantly differ from the previous ones. Furthermore, the mean biomass differences of current study were the least variations from the observed data among other models. It pointed out site- and species-specific models reduce the uncertainties of biomass and carbon stock estimations in comparison with the generalized models. Using the best-fit models, aboveground biomass of Avicennia officinalis stand were estimated as 13 Mg ha^－1 and Sonneratia apetala stand, 14 Mg ha^－1 of carbon. In conclusion, our study established the site- and species-specific equations for estimating mangrove biomass in Myanmar, with implications for Greenhouse gas (GHG) accounting and emission reduction.