Grazing exclosures increase soil organic carbon stock at a rate greater than "4 per 1000" per year across agricultural landscapes in Northern Ethiopia.

The establishment of grazing exclosures is widely practiced to restore degraded agricultural lands and forests. Here, we evaluated the potential of grazing exclosures to contribute to the "4 per 1000" initiative by analyzing the changes in soil organic carbon (SOC) stocks and sequestration (SCS) rates after their establishment on degraded communal grazing lands in Tigray region of Ethiopia. We selected grazing areas that were excluded from grazing for 5 to 24 years across the three agroecological zones of the region and used adjacent open grazing lands (OGLs) as control. Soil samples were collected from two depths (0-15 cm and 15-30 cm) and SOC and aboveground C stocks were quantified in both exclosures and OGLs. The mean SOC stock and SCS rate in exclosures (0-30 cm) were 31 Mg C ha-1 and 3 Mg C ha-1 year-1, which were respectively 166% and 12% higher than that in the OGLs, indicating a positive restoration effect of exclosures on SOC storage. With increasing exclosure age, SOC stock and SCS rate increased in the exclosures but decreased in the OGLs. Higher SOC stock and SCS rate were recorded in 0-15 cm than in 15-30 cm. The relative (i.e., to the SOC stock in OGLs) rates of increase in SOC stocks (70-189‰ year-1) were higher than the 4‰ year-1 and were initially high due to low initial SOC stock but declined over time after a maximum value of SOC stock is reached. Factors such as aboveground biomass, altitude, clay content and precipitation promoted SOC storage in exclosures. Our study highlights the high potential of exclosures for restoring SOC in the 0-30 cm soil depth at a rate greater than the 4‰ value. We argue that practices such as grazing exclosure can be promoted to achieve the climate change mitigation target of the "4‰" initiative.

Conditional payments for carbon sequestration as a local trading game - A case study from a Tanzanian village.

The authors apply the game theory principal agent model in which the principal is a donor who seeks to reduce or sequester harmful emission through a system of conditional payments, whereas the agent is a village community. The purpose is to explore strategic interactions between the two actors in the case of Mlumbilo village in Tanzania. Whereas carbon sequestration at minimum cost is an objective for the principal, the village community aims at maximizing the net present value of income from all types of land use. The application of both a multi-objective bio-economic model with detailed biological data and a bargaining game theory model with asymmetric information revealed that the choice of reference level used as a performance benchmark had major implications for the negotiated prices for CO2. However, the choice of reference level did not affect the cost efficiency of carbon sequestration. Additionally, the outcome of the bargaining model was unique and efficient. The authors conclude that recipient discretion will yield efficient results when the agent trusts that the principal will pay for verified sequestration.