Acacia Dominated Area Exclosures Enhance the Carbon Sequestration Potential of Degraded Dryland Forest Ecosystems

Area exclosure is a widely practiced intervention of restoring degraded lands though its impact in sequestering terrestrial and soil carbon is scanty. The study was initiated to investigate the effect of exclosure of different ages on carbon sequestration potential of restoring degraded dryland ecosystems in eastern Tigray, northern Ethiopia. Twelve plots each divided into three layers were randomly selected from 5, 10 and 15 years old exclosures and paired adjacent open grazing land. Tree and shrub biomasses were determined using destructive sampling while herb layer biomass was determined using total harvest. The average total biomass obtained were 13.6, 24.8, 27.1, and 55.5 Mg ha^-1 for open grazing, 5 years, 10 years, and 15 years exclosures respectively. The carbon content of plant species ranged between 48 to 53 percent of a dry biomass. The total carbon stored in the 5 years, 10 years and 15 years age exclosures were 39 Mg C ha^-1, 46.3 Mg C ha^-1, and 64.6 Mg C ha^-1 respectively while in the open grazing land the value was 24.7 Mg C ha^-1. Carbon stock is age dependent and increases with age. The difference in total carbon content between exclosures and open grazing land varied between 14.3-40 Mg C ha^-1. Although it is difficult to extrapolate this result for a longer future, the average annual carbon being sequestered in the oldest exclosure was about 2.7 Mg C ha^-1 yr^-1. In view of improving degraded area and sequestering carbon, area exclosures are promising options.