Biomass and stem volume estimates for valuable timber species in Mozambique

Accurate aboveground biomass and stem volume estimates are crucial for the management of Mozambique's forests. This study focused on the development of aboveground biomass and stem volume equations for the three most valuable commercial timber species in Mozambique, Afzelia quanzensis Welm. (Chanfuta), Milletia stuhlmannii Taub. (Jambire) and Pterocarpus angolensis D.C. (Umbila). A total of 57 plots were surveyed in three localities: Inhaminga, Mavume and Tome. The diameter at breast height, commercial height, and total height was recorded for all tree species in the surveyed plots. Fifty-eight trees were sampled (24 Chanfuta, 15 Jambire, and 19 Umbila) and used to obtain biomass and volume data by means of destructive methods. Felled trees were subdivided into 5 sections by cutting at 10, 30, 50, 70 and 90% of their total stem height. The recorded data included the top and bottom diameters of each stem section, the length of each section, and the fresh weights of each section as well as the other tree fractions (i.e. branches and leaves). Sub-samples for dry weight and basic wood density determination in the lab were collected from each stem section, at breast height, and from branches and leaves. Biomass values were calculated from the ratios of the dry and fresh weights for each sub-sample. The stem volumes of the sampled trees were estimated from the volumes of the stem sections, which were in turn estimated using Smalian's formula. Biomass and volume data were fitted using non-linear power equations. Diameter at breast height was the best predictor of the total and stem biomass (R2≥0.89), while diameter and height best explained the stem volume data (R2≥0.94). \n \nJambire was found to have the highest biomass of the three species and Umbila the lowest. The stems of Chanfuta and Jambire accounted for the majority of their total biomass but the branches accounted for most of the biomass of Umbila. The commercial stem length accounted for between 30% and 70% of the total length, indicating that commercial logging could produce substantial quantities of biomass residues that could be used for other purposes such as the generation of bioenergy. This would reduce the need to fell forests for energy in Mozambique. Future studies focusing on site-specific biomass and volume estimates as well as annual growth estimates will be required to improve the quality of the estimates presented herein and to support the planning and utilization of Mozambique's forest resources.