Should we Leave Nature Unattended or Assist through Enrichment to Foster Climate Change Mitigation? Exclosure Management in the Highlands of Ethiopia

In order to foster the potential of exclosures to sequester carbon, it is understood that they are increasingly assisted through enrichment planting. To study the impact of the enrichment planting on carbon sequestration process, five exclosures with enrichment planting and five pure naturally regenerated exclosures were selected. Along parallel transects, 20 × 20 m plots were laid at 100 m intervals where all woody vegetations were counted and measured for their diameter and total height. For soil sampling, five subplots at the center and four at each corner of the plots were established. The samples were collected at a depth of 0–0.2 m, and this procedure was repeated for each plot. In this case, when good management practices were implemented (such as Wukro exclosures), significant differences in organic soil carbon above the ground and the total carbon between naturally regenerated and enriched exclosures (P < 0.05) were found. The mean estimates of the above ground carbon, soil carbon, and total carbon were respectively 8.08, 31.04, and 39.12 ton/ha for natural regeneration vs. 7.94, 31.00, and 38.93 ton/ha for enriched regeneration. Lower altitudes had significantly higher soil organic carbon (P < 0.05) than the higher altitudes. However, the slope had an insignificant effect on carbon distribution. Enriched exclosures performed more poorly in carbon sequestration. This was possibly due to the disturbances caused by mass plantation and poor post plantation follow up, since improved performance (P < 0.05) was seen in one enriched exclosure with better management practices.