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5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Performance of exclosure

Performance of exclosure in restoring soil fertility and ecological requirements, e.g., Acacia saligna, Acacia seyal, Aloe ferox, Eucalyptus camaldulensis, Euclea schimperi in the mild zone while Acacia asak, Carissa edulis, Cupressus lusitanica, Erica arborea, Eucalyptus globulus, Euphorbia abyssinica, Hagenia abyssinica, Juniperus procera in the cool zone. 7.2.2 Sampling and analysis Site selection Site selection and sample collection was done between May and July 2010. The criteria used to select the study district includes: i) availability of different-aged exclosures and control sites adjacent or near to the respective exclosures, ii) availability of exclosures in different agro-ecological zones, and iii) comparable or similar exclosures management levels. Based on the selection criteria, discussions and consultation took place with the Agriculture and Rural Development Offices (ARDO) in North Wello zone to identify study districts. During the selection process, out of districts in the North Wello zone, the Kobo, Gubalafto and Habru districts were shortlisted. Further discussions and reconnaissance visits were made in the shortlisted districts to identify a representative site. Accordingly, Gubalafto district was selected for the study. In the following, agro-ecological zones were delineated on a 1:50,000 scale topographic map. Then exclosures in different agro-ecological zones were identified and located on the map. The cool and mild zones cover a large area (72%) of the district and because most exclosures are located within these zones. Thus, these zones were determined for the sampling. Then, 18 exclosures aged between 8 and 27 years were identified. Because of budget and time reasons, out of the 18 exclosures, 10 exclosures were screened and revisited. Finally, among these, exclosures with similar age and comparable management level and topography were selected: the Lenche-Dima and Ayda-Tig exclosures in the mild zone and the Zendo-Girat and Abo-Dur exclosures in the cool zone (Figure 7.1). The Lenche-Dima and Zendo-Girat exclosures were 10 years old, while the Ayda-Tig and Abo-Dur exclosures were 27 years old. The exclosures have been closed since 1982 and 1999, respectively. Open areas adjacent to the exclosures that have been influenced by free livestock grazing and firewood collection were selected as a control. 104

Performance of exclosure in restoring soil fertility In order to assess the possible impact of topography on the variability of the performance of exclosures with respect to soil fertility restoration, each sampling site was further divided in three landscape positions, i.e., upper, middle and lower (Figure 7.3). The landscape positions were determined based on site observations and contour lines on the topographic map. The upper landscape position of the exclosure receives little or no runoff, the middle landscape position is partly erosion zone that receives runoff from the upper slope and generates cumulated runoff to the lower landscape position. Finally, sampling points were plotted on topographic maps (1:50,000 scale), and coordinates of each point were calculated from the map to facilitate the transfer of the points on the ground. Figure 7.3 Abo-Dur exclosure sampling plots across the slope positions (a) and Abo-Dur exclosure within Gubalafto district (b) Soil sampling and analysis Following identification of sampling sites in the mild and cool agro-ecological zones, each site was further subdivided into three landscape positions. A 1:5,000 scale base map was prepared for each sampling site (exclosure). These maps were used to 105

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