Grazing management and carbon sequestration in the Dry Lowland Rangelands of Southern Ethiopia

Abstract

ABSTRACT Rangelands occupy more than half of the terrestrial ecosystems and their management has a significant impact on the global carbon cycle. They are often managed for pasture and forage for livestock. This study examined impact of grazing management practices on biomass and carbon stock in dry lowland rangelands. A systematic transect sampling was applied to measure vegetation data, and to collect soil and herbaceous samples from the field. Allometric and species-specific equations were used to determine the woody biomass. Herbaceous biomass and soil carbon were analyzed in a laboratory. The results showed that herbaceous vegetation accounted for 5–15% of the total carbon stock while the woody vegetation accounted only for 0.3–1% of the total carbon stock. The soil is the largest carbon pool holding more than 90 % of the total carbon. Enclosures and bush clearing favored more herbaceous growth and changed the vegetation dynamics. As a result, the grasslands sequestered significantly high (P < 0.05) amount of soil carbon compared to the bush lands and the tree savannah. The management practices improved total carbon sequestration by 12.2%—26% in the system. There is high seasonal dynamics in the herbaceous carbon with a significant increase (P < 0.5) during the wet season. Soil carbon showed an inverse relationship with stem density, soil bulk density and slope. Rainfall and altitude have a positive influence on soil carbon. Total carbon stock in the managed rangelands was 19.8% higher than in the unmanaged rangelands. It can be concluded that enclosures and bush clearing enhance soil carbon sequestration. At the estimated annual sequestration rate of 1.6–3.5 t CO2e ha−1 yr−1 into the soil and 2.2–5.6 t CO2e ha−1 yr−1 into the total carbon stock in the system, the rangelands can make significant contribution to climate change mitigation.