Abstract
Forest and soils constitute a major terrestrial carbon pool sequestrate and store carbon dioxide (CO2) from the atmosphere. Ethiopia is implementing diverse land management based carbon projects that can help mitigate climate change.
Plantation establishment with exotic or indigenous tree species, and/or area exclosures supplemented with Reforestation /afforestation to restore degraded vegetation and soil are among the major carbon project initiatives in the country. However, the effectiveness of such initiatives in terms of carbon sequestration is not much investigated. This study aims to contribute to such knowledge by investigating carbon sequestration potential of area exclosure supplemented with afforestation of exotic tree plantations in central Ethiopia. The study assessed both biomass and soil carbon stocks. For above-ground biomass estimation, plots of the dimension 10 x 10 m were systematically laid in the exclosure area and adjacent open land, and trees diameter at breast height (DBH) of all trees with size greater than 5cm measured using a caliper. The height of each tree was also measured by using a hypsometer. For soil carbon stock and stock change analysis, soil samples were collected from five plots laid systematically over the area including from adjacent open/bare lands. Soil samples were taken from 0-20 cm and 20-40 cm depths. Soil samples from the same depth were mixed up to make a composite of 300g that was taken to the laboratory for organic carbon analysis. The exclosure afforestation is 8 years since established. The results of the study showed that area exclosure combined with afforestation /reforestation increases biomass carbon but reduces soil carbon, and the later may be temporary. The soil carbon in 0-40cm soil depth was 115.84 ton/ha in the exclosure area compared to 141.46 ton/ha in the open area. The low soil carbon in exclosure may show many things: i) temporary decrease in soil carbon due to site disturbances during planting; ii) original very low level of soil carbon in the exclosure compared to the adjacent site since often most degraded sites are given priority in management, and/or iii) temporary suppression in soil carbon due to microbial activities in decomposition freshly added organic matter that will be followed by increase once decomposable components are exhausted. Overall, the rapid buildup in biomass carbon in the exclosed area will soon lead to an increase in soil carbon too, hence an overall increase in carbon stock in the managed ecosystem than an unmanaged ecosystem. At the current rate, the net carbon gain is 9.62 ton/ha/yr. In conclusion, area exclosures combined with A/R are likely one good solution to ensure carbon-neutral growth in Ethiopia.
Keywords: - Above ground biomass; Afforestation/ Reforestation: land use: Soil Carbon
