Biomass estimation in mangrove forests: a comparison of allometric models incorporating species and structural information

Abstract: Improved estimates of aboveground biomass are required to improve our understanding of the productivity of mangrove forests to support the long-term conservation of these fragile ecosystems which are under threat from many natural and anthropogenic pressures. To understand how individual species affects biomass estimates in mangrove forests, five species-specific and four genus-specific allometric models were developed. Independent tree inventory data were collected from 140 sample plots to compare the aboveground biomass (AGB) among the species-specific models and seven existing frequently used pan-tropical and Sundarbans-specific generic models. The effect of individual tree species was also evaluated using model parameters for wood densities (from individual trees to the whole Sundarbans) and tree heights (individual, plot average and plot top height). All nine species-specific models explained a high percentage of the variance in tree AGB (R² = 0.97 to 0.99) with the diameter at breast height (DBH) and total height (H). At the individual tree level, the generic allometric models overestimated AGB from 22% to 167% compared to the species-specific models. At the plot level, mean AGB varied from 111.36 Mg ha^-1 to 299.48 Mg ha^-1, where AGB significantly differed in all generic models compared to the species-specific models (p < 0.05). Using measured species wood density (WD) in the allometric model showed 4.5% to 9.7% less biomass than WD from a published database. When using plot top height and plot average height rather than measured individual tree height, the AGB was overestimated by 19.5 % and 8.3% (p < 0.05). The study demonstrated that ignoring species-specific information potentially yields significantly different biomass mangrove forests. Tree level measurement from the inventory plots should therefore be included in allometric models to obtain an accurate estimation of forest carbon from the scale of individual trees up to the ecosystem level.

R markdown script: We added two markdown scripts. First one is used to develop species-specific allometric equations and other necessary statistics. In this script, harvested tree data was used from Mahmood et al., 2019. It can be accessed from the original article or with alom_sund_nfi.xlsx

The second script uses primary tree inventory data from the Bangladesh Sundarbans with DBH (Diameter Breast Height), total height, measured wood density and database wood density. There are two files attached here- RDA (inventory_data_sundarabans.rda) and Excel file (inventory_data_sundarbans.xlsx). RDA file is provided to go step by step to produce all maps and tables presented in the article.