Abstract
Improved estimates of aboveground biomass (AGB) 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 AGB among the species-specific models and seven 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 developed models explained a high percentage of the variance in tree AGB (R 2 = 0.97–0.99) with the diameter at breast height 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%–9.7% less biomass than WD from published databases and other sources. When using plot top height and plot average height rather than measured individual tree height, the AGB was overestimated by 19.5% and underestimated by 8.3% (p < 0.05). The study demonstrates that species-specific allometric models and individual tree measurements benefit biomass estimation in mangrove forests. Tree level measurement from the inventory plots, if available, should be included in allometric models to improve the accuracy of forest biomass estimates, particularly when upscaling individual trees up to the ecosystem level.
Highlights
There has been a global effort to develop accurate and efficient methods to quantify aboveground carbon in mangrove forests (Hutchison et al 2014, Ni-Meister 2015, Baccini et al 2017, Lagomasino et al 2019)
This study developed and tested five species-specific and four genus-specific allometric models for the nine most important species in the Sundarbans
At the individual tree level, the generic allometric models overestimated aboveground biomass (AGB) between 22% and 167% compared to the species-specific models and at the plot level, they showed statistically significant AGB differences compared to the species-specific models (p < 0.05)
Summary
There has been a global effort to develop accurate and efficient methods to quantify aboveground carbon (measured as biomass) in mangrove forests (Hutchison et al 2014, Ni-Meister 2015, Baccini et al 2017, Lagomasino et al 2019). Destructive harvesting of trees provides the most precise estimates of aboveground biomass (AGB), yet is impractical, laborious, costly and often illegal (Komiyama et al 2008, Edwards et al 2019) and so mathematical models have been developed to estimate tree biomass from measured biophysical parameters (tree diameter at breast height (DBH), height (H), or wood density (WD)) (Brown 1997, Komiyama et al 2005, Picard et al 2012, Chave et al 2014). These models are known as allometric models. The choice of appropriate allometric model is critical to reduce uncertainties in the estimation of forest biomass
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