The extent of soil organic carbon and total nitrogen in forest fragments of the central highlands of Ethiopia

摘要

Deforestation and degradation are currently affecting the ecosystem services of forests. Among the ecosystem services affected by deforestation and degradation are the amount of soil organic carbon (SOC) and total nitrogen (TN) stored in forest soils which have greater impacts in global climate change. This study aimed at examining the amount of SOC and TN in the forest fragments which were separated from the continuous tracts of forests of Jibat and Chillimo through fragmentation processes over four decades. We have sampled soils from 15 forest fragments of Chillimo and Jibat in the central highlands of Ethiopia. The soil samples obtained in two separate soil depths (0–30 and 30–60?cm) were bulked, dried, and sieved for analysis. Our results have shown that the two sites (Jibat and Chillimo forest fragments) differed in their SOC and TN contents. While the values for Jibat were found to be 29.89?Mg/ha of SOC and 2.84?Mg/ha for TN, it was 14.06?Mg/ha of SOC and 1.40?Mg/ha for TN for Chillimo. When all forest fragment soil samples were bulked together, Jibat site had twice the value of SOC and TN than Chillimo. When disaggregated on the basis of each fragments, there existed differences in SOC (1.86?Mg/ha and 42.15?Mg/ha) and TN (0.24?Mg/ha and 4.23?Mg/ha) values. Among the forest fragments, fragment four (F4) had the highest Relative Soil Improvement Index (RSII) value of 3826.82% and fragment fifteen (F15) had the lowest RSII value (726.87%) which indicated that the former had a better quality of soil properties than the latter. SOC and TN differed across sampled fragments and sites. Variations in soil properties are the reflections of inherent soil parent material, aboveground vegetation, human interferences, and other physical factors. Such differences could be very important for identifying intervention measures for restoration and enhancing ecosystem services of those fragments.