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Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of exclosure

Performance of exclosure in restoring soil fertility production, vegetation type, (Lawrence and Bruce 2005) and OM mineralization (Zhao et al. 2010) As opposed to various studies (e.g., Fu et al. 2003; Moges and Holden 2008; Sariyildiz et al. 2008), most soil properties did not show significant differences with landscape positions of exclosures. The close vicinity of the lower landscape position of the exclosures to settlement, grazing and cultivated lands make this part prone to recurrent livestock and human interference. The physical SWC structures in the exclosures enhanced in-situ soil and water conservation and thereby reduced fertility restoration variation across landscape. From the above analysis the following can be concluded: i. OC and TN restoration rate significantly increased with exclosure age and the restoration rate reduced with time, indicating steady state. Steady state OC and TN differences could be due to change in biomass quantity and quality with exclosure age. Biomass quality and quantity in turn determine OM input and mineralization. ii. Soil fertility significantly varied with agro-ecological zone of the exclosures, where higher soil fertility was observed in the mild than in the cool zone. This could be due to the effect of agro-ecological zone (climate) on vegetation types and OM mineralization. iii. Soil fertility restoration showed insignificant differences with landscape position of the exclosures, which is attributed to conservation complementary effect of physical SWC structures. 120

Implications of soil and water conservation measures for land rehabilitation- a synthesis 8 IMPLICATIONS OF SOIL AND WATER CONSERVATION MEASURES FOR LAND REHABILITATION- A SYNTHESIS 8.1 Introduction In an effort to reduce degradation and restore the degraded lands, soil and water conservation (SWC) measures have played a considerable role in Ethiopia (Gebremichael et al. 2005; Vancampenhout et al. 2006; Nyssen et al. 2007). The empirical analyses presented in the previous chapters provide tangible evidence of the positive impacts of SWC, particularly exclosure and farmland terracing, on soil fertility maintenance and the associated benefits. This chapter presents a synthesis of the implications of SWC measures for land degradation with particular emphasis on exclosure and terracing as analyzed in Chapters 4 to 7. 8.2 Conceptual framework of human-induced land degradation Land degradation reduces the potential of land in providing sustainable ecosystem services. Land degradation gradually takes place over time. However, the manifestation time depends on the land´s resilience to degrading conditions and the intensity of the degrading factors. Factors are also mostly interwoven, and the deleterious effect of one could initiate the other processes. In the present study, cause and effect of land degradation is demonstrated using a conceptual framework (Figure 8.1). Nearly 40% of the study area has slopes over 30% of which 10% are slopes of more than 60% (Chapter 4). Land potential for agricultural use has been limited not only by slope but also by shallow soil depths and rock outcroppings. Moreover, the study area is characterized by high population density and rapid growth rate. The population of the country increased 6-fold from 12 million at the beginning of the 1900 to 74 million in 2007 (Logan 1946; Sørensen and Bekele 2009). Similarly, in the study area, population density and growth rate was also very high. For example, the South Wello population grew by 3.4% between 1970 and 1994 (Tekle 1999). With the population increase, disturbance of natural resources such as forest and other vegetation due to free livestock grazing, expansion of settlement and cultivation increased (Tekle 1999). Forest degradation also increased due to uncontrolled cutting to satisfy the demand for household energy and construction and for income generating purposes (Pohjonen and Pukkala 1990; Feoli et al. 2002). The human and livestock intrusion on 121

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