VARIATION IN CARBON STOCK ALONG ENVIRONMENTAL GRADIENTS IN GARA-MUKTAR FOREST, WEST HARARGHE ZONE, EASTERN ETHIOPIA

Forests play vital role in combating climate change through carbon sequestration in the atmosphere and serving as a carbon sink in the form of carbon pool systems of forest ecosystems. This study was aimed to estimate carbon stock variation along the environmental gradients and its contribution to climate change mitigation in Gara-Muktar forest, Western Hararghe zone, Eastern Ethiopia. A systematic sampling method of thirty- six quadrant plots having a size of 20m x 20m each distributed along transect lines. To estimate carbon in above ground biomass, diameter at breast height (DBH) of ≥ 5 cm and total height were measured for each tree in the main plot using diameter tape and vertex. Above ground biomass was estimated using allometric equation while below ground biomass was determined based on the ratio of below ground biomass to above ground biomass factor while the litter carbon was estimated by taking 50% of dry biomass. Soil sample was collected using auguring method from each plot with a depth of 0-30cm. Soil organic carbon was analyzed in the laboratory following Walkley-Black method, while bulk density was analyzed using core sampling method. The data was analyzed using R software. The result of study showed that the mean total above and below ground carbon stocks were 156.60t/ha and 31.32t/ha respectively whereas, litter carbon and soil organic carbon stocks were 2.72t/ha and 125.86 t/ha (up to 30cm depth) respectively. The mean total carbon stock density was found to be 316.6 ± 67.15 t ha-1 (ranging from 140.9 to 487.4 t ha-1) from which 49.5% of carbon was contained in the above ground biomass, 9.9% in below ground biomass, 0.9% in litter carbon and 39.8% was stored in soil organic carbon (0-30 cm depth). The carbon stocks in aboveground, belowground, litter biomass and soil organic carbon showed distinct variation along environmental gradients. The aboveground and below ground carbon stock showed a decreasing trend along with increasing altitude, while soil organic carbon and liter carbon showed increasing trend with increasing altitude. Moreover, the carbon pool and stock were significantly different along altitude, whereas the above and belowground carbon stock variation with slope gradient was also significant except soil organic carbon and liter carbon. The above and below ground biomass, soil organic carbon and the total carbon stock were higher on the North-west aspect as compared to other aspects. It can be concluded that Gara-Muktar forest is a reservoir of high carbon, having positive role in contributing to climate change mitigation and the carbon storage capacity in different carbon pools of the forest area varies with altitude, slope and aspect gradients.