Getachew Gemtesa’s research while affiliated with Swedish University of Agricultural Sciences and other places

Tree biomass is a key variable for estimating the carbon stock potential of the forest. This study aimed to quantify the belowground biomass (BGB), aboveground biomass (AGB), and carbon stock of Acacia decurrens across stand ages. The study was conducted at four different stand ages (three, four, five, and six year old stands), and it was replicated six times with a total of twenty four sample plots of Acacia decurrens woodlots in Fagita Lekoma district, Awi zone. For both AGB and BGB estimation, 1×1 m subplots were established in the centre of the main plots (10×10 m). For AGB, the sample tree was cut inside the subplots and divided into different components (stem, branch, and leaves). The BGB were taken from two soil depths (0 20 and 20 40 cm), and they were sorted into fine, medium, and coarse roots based on their diameter. From all biomass components, subsamples were taken for dry biomass, and the stem subsamples were dried at 105 °C, while the remaining were dried at 65 °C. The results indicated that both the AGB and BGB of trees varied significantly (p<0.05) across the stand ages and soil depths. The total AGB and stem biomass were significantly higher in six year stands (20480 g m 2) and (16444 g m 2), respectively. The lowest total AGB and stem biomass were observed in the three year stand, ranging from 1657 to 2857 g m 2. From the total biomass, AGB was shared from 87.2 ₋ 92.8%. In addition, within stand ages, 50.6 74.6% of biomass was obtained from stems. Both branch and leaf biomass were significantly (p<0.05) higher in six year stands (2753 g m 2) and (1282 g m 2) than in three years (722 g m 2) and (479 g m 2), respectively. However, no significant (p<0.05) difference was observed between the other age groups. Similarly, stand age significantly (p<0.05) affects coarse roots and total BGB. Significantly higher coarse root (1373 g m 2) and total root masses (1574 g m 2) were found at six year stands. However, stand age had no significant (p<0.05) effect on fine and medium root masses. The root to shoot ratios gradually decreased from 14.9, 10.4, 9.3, and 7.6% for 3, 4, 5, and 6 year old stands, respectively, and on average, 10.6%. This is due to Acacia decurrens having lateral root systems, producing fine roots across stand ages, and allocating more biomass to their AGB after establishment. The total carbon stock of Acacia dicurrens in both AGB and BGB was significantly higher in six years (11027 g m 2) and lowest in three (1636 g m 2). Generally, stand age and soil depth were shown as important factors influencing the AGB and BGB. It has high biomass carbon sequestration potential during the growth period. Further research should be done on the SOC and litter carbon of Acacia decurrens across stand ages.

Correct estimation of tree biomass is important when calculating uptake or emission of CO2 in relation to land-use and land-use change. The objectives of this study were (1) to estimate the root/shoot ratio for the estimation of root biomass based on the above-ground biomass (AGB) of Acacia mearnsii, and (2) to develop allometric equations for the estimation of the above-and below-ground biomass (BGB) of Acacia mearnsii. To estimate the AGB and BGB, twenty-four trees of varying ages (3, 4, 5, and 6 years) were harvested, with six trees per age group. We measured the dry biomass for different tree parts and developed allometric models using tree height (H) and diameter at breast height (DBH) as independent variables. The results showed that the biomass of the stem accounted for 69% of the total biomass, followed by branches (14%), roots (8.1%), and leaves (7.3%). The recorded mean root/shoot ratio was 0.11. The biomass of the stem and coarse roots increased with increasing tree age, while a contrary trend was observed for the other tree components. Each component has its unique allometric model.