Abstract
Community-led watershed development activities, including the establishment of exclosures (areas where both livestock and farming activities are excluded) on degraded communal grazing land, have become a common practice in Ethiopia since the 1990s. However, it is not yet fully understood how these exclosures change soil organic carbon and total soil nitrogen in different soil types and under different agroecologies. A meta-analysis using data gathered from the most relevant peer reviewed articles from Ethiopian exclosure systems was conducted to assess the variation in the effects of exclosures on soil carbon and nitrogen and to investigate the factors controlling change. The results demonstrate that after 16 years, exclosures can increase soil organic carbon and total soil nitrogen up to an effect size greater than two. This is moderated by soil type, exclosure age, landscape position and agroecology. More effective restoration of soil carbon was observed in less developed Leptosols and Cambisols than in more developed Luvisols, and in drier than more humid agroecologies. The results suggest that soil type and agroecology should be taken into consideration when planning and implementing exclosures on degraded communal grazing land. The findings of this study provide base line information for the future expansion of exclosures, and guide where to focus implementation. They also provide criteria to be used when planning and establishing exclosures to restore soil carbon and nitrogen. In addition, the results generated through this meta-analysis provide better understanding of the spatial and temporal variation of the effectiveness of exclosures to restore soil carbon and nitrogen.
Highlights
Land degradation, resulting in long-term loss of ecosystem services, is one of the world’s most pressing environmental problems (IPBES, 2018)
Regional differences were observed within Ethiopia in terms of the efforts made to understand the effects of exclosures on soil organic C and total soil N, and variables such as vegetation composition and diversity (Figure 1)
The results showed that most of the studies were conducted in areas dominated by Cambisols and Luvisols followed by Leptosols and Vertisols (Figure 3). This could be attributed to the large coverage of these soil types in Ethiopia (Jones et al, 2013)
Summary
Land degradation, resulting in long-term loss of ecosystem services, is one of the world’s most pressing environmental problems (IPBES, 2018). A report on progress toward achieving Sustainable Development Goal (SDG) 15 (life on earth) indicated that 20% of the Earth’s total land area was degraded between 2000 and 2015, resulting in a significant loss of key services underpinning food production, clean water and emissions of greenhouse gases (SDG Report, 2019). Agroecologies, and economies are affected by land degradation It may pose a serious threat to food production and rural livelihoods in poor and densely populated areas of the developing world (Global Mechanism of the UNCCD et al, 2019). As in other developing countries, land resources in Ethiopia are facing intense degradation due to deforestation, soil erosion, agricultural land expansion, and overgrazing (Nyssen et al, 2004).
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