ALLOMETRIC EQUATION FOR ESTIMATING HIGHLAND BAMBOO (Oldeania alpina (K. SCHUM.) STAPLETON) CARBON POOLS ALONG ALTITUDINAL GRADIENTS: THE CASE OF GARAMBA FOREST, SOUTHERN ETHIOPIA

Abstract

Due to a lack of species-site-specific models, information about the carbon (C) stock potential of highland bamboo in various carbon pools is limited. Thus, the objective of this study was to develop an allometric equation for estimating highland bamboo C pools along altitudinal gradients in Garamba forest, southern Ethiopia. Using a systematic design approach, 34 plots were chosen and placed along a transect in the altitude range. Then, bamboo culm diameter at breast height (DBH), height (H) and number of culms were collected. A total of 102 soil samples were collected to determine the soil bulk density and soil organic carbon (SOC) from three different depth classes. A composite 17 litter samples were collected. Besides, a total of 102 bamboo culms covering the full range of sizes were destructively sampled. A subsample of bamboo biomass components and litter were taken to the laboratory to determine the C content. Allometric equations in the form of power models were formulated for all age groups of bamboo by evaluating the statistical relationships of measurable variables (DBH and H) and dry total biomass (TB). The best models were validated by leave-one-out cross-validation procedures and results were compared based on model performance statistics. The data analysis was performed using R software. The result of the study showed significant (p<0.05) stand density, DBH and height differences between the three altitudinal ranges. The average culm density, DBH and height were 12,120.6 ± 3,560.5 culms ha-1 , 5.1 ± 0.9 cm and 9.2 ± 1.9 m respectively. The study also revealed that the strongest predictor variables for estimating TB for each of the age groups was DBH (R = 0.97). Accordingly, the better performing equations are TBage<1 = 1.005 × 0.107 × D2.167, TBage 1-3 = 1.005 × 0.198 × D2.083, TBage >3 = 1.025 × 0.155 × D2.414 and TBall age = 1.031 × 0.247 × D1.967. Except for SOC, both TB and litter carbons showed a significant variation among altitudinal classes and increased as altitude increases. The mean C stocks in TB, litter and SOC were 41.72 ± 18.59, 0.48 ± 0.17 and 252.60 ± 43.14 t C ha−1 respectively. The C stocks and CO2 equivalent of the Garamba bamboo forest were found to be 293.29 ± 47.25 and 1,076.37 ± 173.42 t C ha−1, respectively. In conclusion, the developed allometric models can be applied to estimate the biomass C storage potential of highland bamboo forests grown in Garamba as well as elsewhere. Garamba highland bamboo forest has significant C stock and sequestration potential. Therefore, sustainable management of these crucial vegetation resources will enhance their role in providing ecosystem services, including climate change mitigation.