5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

General introduction

General introduction livestock population is high (Hurni 1987; Bhan 1988; El-Swaify 1997; Sonneveld and Keyzer 2003). The highlands, which account for 45% of the total country landmass, support about 85% of the human and 75% of the livestock population. In order to secure their livelihoods and feed their livestock, people have exploited the natural resources to a maximum and also used marginal lands for cultivation and grazing (Woldesemait 1983; Hurni 1993). This has resulted in rapid deforestation, severe soil erosion and alarming environmental degradation (Hurni 1993; EFAP 1994; Tefera et al. 2002; Tamene et al. 2006; Nyssen et al. 2009). For example, over 80% of the forest cover was destroyed between 1900 and 1960 (Pohjonen and Pukkala 1990; EFAP 1994). Consequently, the Ethiopia highlands have experienced extensive land-use/land-cover (LULC) dynamics, and in particular, the area of cultivated land has increased rapidly. The land degradation problem has had serious consequences in Ethiopia such as occurrence of persistent food insecurity, economic losses and various environmental hazards such as recurrent drought (Shiferaw and Holden 1999; Tekle 1999). Deforestation and conversion of marginal land to agriculture has been followed by severe soil erosion that has caused crop production losses, which in turn result in economic losses (Bojö and Cassels 1995). For example, due to soil and nutrient loss through erosion, Ethiopia has been annually losing about US$ 106 million (Bojö and Cassels 1995). To circumvent this problem, the Government of Ethiopia has taken different measures such as policy interventions, conducted studies, and implemented massive soil and water conservation (SWC) and capacity building programs, especially after the severe drought of the failed 1974/75 and 1984/85 rainy seasons (Hurni 1993; Shiferaw and Holden 1999; Tilahun 2006). Soil and water conservation measures were implemented largely in the drought-affected areas, including in Wello (Tekle 1999; Badege 2001). The interventions were focused on both mechanical and biological measures (Tamene et al. 2006; Babulo et al. 2009). The major mechanical measures include construction of bunds, check dams, micro-basins and hillside terraces. The biological measures include enclosure of degraded land from human and animal interferences (exclosures), tree seedling production, planting of tree seedlings on farmlands (agro-forestry), afforestation, and tree plantations around the homesteads and tree plantation in exclosures as enrichment to the natural regeneration (Badege 2001; Feoli et al. 2002; Mekuria et al. 2011). The intention of the interventions was to reduce 2

General introduction soil erosion, restore soil fertility, rehabilitate degraded lands, improve micro-climate, improve agricultural production and productivity and restore environmental condition (Vancampenhout et al. 2006; Bewket 2007; Mekuria et al. 2007). Despite the massive mobilization of resources for SWC, only very few studies have been done to analyze the impacts of the measures with respect to restoration of degraded lands. Beside the insufficiency of the studies, they are also not interdisciplinary, and in some cases the conclusions are contradictory. For example, Bewket (2007) reported that SWC measures were inefficient in reducing soil erosion and restoring soil fertility, while Hengsdijk et al. (2005) criticized the validity of his model. Similarly, Eshatu (2004) reported that planted forest did not result in significant changes in organic carbon, nitrogen and soil-organic matter inputs and did not improved soil fertility during a 25-year forest growth. Conversely, other studies indicated a positive contribution of SWC measures to the reduction of soil erosion, conservation of soil moisture, and restoration of vegetation cover and diversity (e.g., Asefa et al. 2003; Hengsdijk et al. 2005; Vancampenhout et al. 2006; Mekuria et al. 2007; Gebreegziabher et al. 2009). For example, Mekuria et al. (2007) reported significant soil fertility restoration in 5- to 10-year-old exclosures. In spite of these facts, policies, decisions, and planning and implementation of SWC measures have been based on very few case studies and general recommendations of small-scale national level studies like riverbasin master-plan development studies. In addition, most plot-based studies are focused on assessing the severity of soil erosion in physical terms and lack information on the impact of SWC on soil fertility and agricultural production. They also have gaps regarding the effect of the service time and difference in agro-ecological and topographic conditions. Furthermore, SWC structures construction demands huge resources (finance, labour, materials and equipment), and the adoption and recommendations of the SWC interventions should be justified by empirically proven evidence (Badege 2001; Amsalu and de Graaff 2007; Nyssen et al. 2007). In order to fill this information gap and support the country’s effort in combating land degradation, a study that assesses the effectiveness and variability of conservation/land management measures is of paramount importance. 3

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