Allometric Equations for Aboveground and Belowground Biomass Estimations in an Evergreen Forest in Vietnam

Assessment of a Cocoa-Based Agroforestry System in the Southwest of Colombia

Cocoa-based agroforests play an important role in farmer livelihood and the global environment; however, despite these facts, their low yields and tree aging put at risk their fate. This project investigated the carbon storage potential, productivity, and economics of different agroforestry arrangements of cocoa (Theobroma cacao) with Melina (Gmelina arborea) trees, in the southwest of Colombia. We established the experiment under a Randomized Complete Blocks design with seven treatments and three repetitions. Different allometric models were tested. Allometric models were made for G. arborea trees with dbh, ranging between 30.24 and 50.11 cm. The total carbon accumulation fluctuated between 49.2 (Treatment 4) and 88.5 t ha−1 (Treatment 2), soil organic matter (SOM) ranged between 9 and 17%, bulk density decreased from 0.83 to 0.77 g cm−3. Cocoa yield ranged between 311 kg ha−1 year−1 (Treatment 7, traditional farm) and 922 kg ha−1 year−1 (Treatment 6). Treatment 6 showed the best performance with a net present value (NPV) of COP 1,446,467 (US $337.6), an internal rate of return (IRR) of 42%, and a cost-benefit ratio (B/C) of 1.67%. The benefits of AFS were also evidenced in some of the physical and chemical soil properties. Despite local marginality, these cocoa agroforest arrangements are a viable alternative to improve the traditional (local) cocoa systems because cacao agroforest arrangements increased cacao yield and carbon storage becoming a suitable alternative to improve traditional systems.

Biomass allometric equation and expansion factor for a mountain moist evergreen forest in Mozambique

BACKGROUND

Worldwide, forests are an important carbon sink and thus are key to mitigate the effects of climate change. Mountain moist evergreen forests in Mozambique are threatened by agricultural expansion, uncontrolled logging, and firewood collection, thus compromising their role in carbon sequestration. There is lack of local tools for above-ground biomass (AGB) estimation of mountain moist evergreen forest, hence carbon emissions from deforestation and forest degradation are not adequately known. This study aimed to develop biomass allometric equations (BAE) and biomass expansion factor (BEF) for the estimation of total above-ground carbon stock in mountain moist evergreen forest.

METHODS

The destructive method was used, whereby 39 trees were felled and measured for diameter at breast height (DBH), total height and the commercial height. We determined the wood basic density, the total dry weight and merchantable timber volume by Smalian's formula. Six biomass allometric models were fitted using non-linear least square regression. The BEF was determined based on the relationship between bole stem dry weight and total dry weight of the tree. To estimate the mean AGB of the forest, a forest inventory was conducted using 27 temporary square plots. The applicability of Marzoli's volume equation was compared with Smalian's volume equation in order to check whether Marzoli's volume from national forest inventory can be used to predict AGB using BEF.

RESULTS

The best model was the power model with only DBH as predictor variable, which provided an estimated mean AGB of 291 ± 141 Mg ha^-1 (mean ± 95% confidence level). The mean wood basic density of sampled trees was 0.715 ± 0.182 g cm^-3. The average BEF was of 2.05 ± 0.15 and the estimated mean AGB of 387 ± 126 Mg ha^-1. The BAE from miombo woodland within the vicinity of the study area underestimates the AGB for all sampled trees. Chave et al.'s pantropical equation of moist forest did not fit to the Moribane Forest Reserve, while Brown's equation of moist forest had a good fit to the Moribane Forest Reserve, having generated 1.2% of bias, very close to that generated by the selected model of this study. BEF showed to be reliable when combined with stand mean volume from Marzoli's National Forestry Inventory equation.

CONCLUSION

The BAE and the BEF function developed in this study can be used to estimate the AGB of the mountain moist evergreen forests at Moribane Forest Reserve in Mozambique. However, the use of the biomass allometric model should be preferable when DBH information is available.

Biomass dynamics in a logged forest: the role of wood density

Wood density (WD) is believed to be a key trait in driving growth strategies of tropical forest species, and as it entails the amount of mass per volume of wood, it also tends to correlate with forest carbon stocks. Yet there is relatively little information on how interspecific variation in WD correlates with biomass dynamics at the species and population level. We determined changes in biomass in permanent plots in a logged forest in Vietnam from 2004 to 2012, a period representing the last 8 years of a 30 years logging cycle. We measured diameter at breast height (DBH) and estimated aboveground biomass (AGB) growth, mortality, and net AGB increment (the difference between AGB gains and losses through growth and mortality) per species at the individual and population (i.e. corrected for species abundance) level, and correlated these with WD. At the population level, mean net AGB increment rates were 6.47 Mg ha-1 year-1 resulting from a mean AGB growth of 8.30 Mg ha-1 year-1, AGB recruitment of 0.67 Mg ha-1 year-1 and AGB losses through mortality of 2.50 Mg ha-1 year-1. Across species there was a negative relationship between WD and mortality rate, WD and DBH growth rate, and a positive relationship between WD and tree standing biomass. Standing biomass in turn was positively related to AGB growth, and net AGB increment both at the individual and population level. Our findings support the view that high wood density species contribute more to total biomass and indirectly to biomass increment than low wood density species in tropical forests. Maintaining high wood density species thus has potential to increase biomass recovery and carbon sequestration after logging.