5 years ago

Die Wirksamkeit von Boden

Die Wirksamkeit von Boden

Land use-land cover and

Land use-land cover and normalized difference vegetation index changes in Wello Table 4.3 LULC dynamics of North and South Wello zones LULC in 2000 LULC in 2009 Change LULC classes Ha % Ha % 2009-2000 Cultivated land/others 1787300 59.6 1758800 58.6 -0.9 Forest 295600 9.8 274400 9.1 -0.7 Degraded woody vegetation 590900 19.7 202000 6.7 -13.0 Grassland/woody grassland 323100 10.8 761500 25.4 14.6 Water bodies 3900 0.13 3800 0.13 nil Total 3000800 100 3000500 100 Note: The slight difference between the two totals (300 ha) is area estimation rounding error incurred by the software (ArcGIS) and due to rounding of the output. But the error is too small to change the analysis result. The LULC dynamics of the area depicted spatio-temporal variability. For example, forest cover change showed remarkable spatial variability (Figure 4.2). Although steep lands (mountains, gorges and hills) are distributed over the entire area, there were considerable improvements in the eastern escarpment. On the other hand, scattered groves and thin strips of forest depicted on the 2000 image in the northeast, southeast and central part of the study area were fully or partly destroyed by 2009 images. The forests occupied steep slopes along river courses and mountainsides. Generally, forests/vegetation showed improvement in density and area coverage on the eastern escarpments and mountains. The forest cover improvements were observed in areas where their coverage was originally better and conservation had been practiced regardless of topographic similarity between the different parts. However, rate and extent of forest cover change was very small as compared to the land lacking vegetation cover. On the other hand, considerable grassland/woody grassland cover changes indicate achievement of restoration interventions. The woody grassland represents new exclosures undergoing rehabilitation. At an early age, exclosures are dominated by nonwoody vegetation such as scrubs, herbs and grasses (Descheemaerker et al. 2006; Kalinina et al. 2009; Mekuria et al. 2011). As a result, the signature is similar to that of grassland. Vegetation succession on degraded land after exclosure followed the order of non woody vegetation (grasses, herbaceous plants and shrubs), woody grassland, mixed trees and forests dominated by limited tree species (Figure 4.3). The vegetation restoration pattern on degraded land following exclosure resembles that reported by Kalinina et al. (2009) and Descheemaerker et al. (2006). Newly established exclosures 44

Land use-land cover and normalized difference vegetation index changes in Wello show considerably improved vegetation cover on steep landscapes within a few years time. Figure 4.3 Exclosure vegetation change across time: (a) 10 years old (woody grassland), and (b) 27 years old (forest) The DEM-generated slope map reveals that about 10% of the land has slopes of over 60%. Forest cover in the study area accounts for nearly 9% (Table 4.3 and Figure 4.4). The field observations also verified that very steep slopes, except rocky areas, were largely covered by forest. It was also observed that old exclosures developed to forest with over 60% canopy cover (Figure 4.3 b). The comparison of slopes, LULC maps and field observations showed that the forest occupied very steep landscapes. Nonetheless, vegetation restoration and succession depend on site-specific biophysical and climatic conditions such as soil seed reserve, soil depth, rockiness, rainfall and temperature (Carla et al. 2003; Descheemaeker et al. 2006; Oba et al. 2006). Carla et al. (2003) also reported that restoration is inversely related to degradation. Generally, the slope and LULC maps indicate that very steep landscape (slope >60%) were dominantly covered by forest, while woody grassland occupied steep landscape (slopes 30% to 60%). Woody grassland was observed on new exclosures that were undergoing succession from degraded vegetation remnants to forest. The time interval in which degraded lands develop to forest through self-restoration due to exclosure depends on climatic conditions and bio-physical potential of the area (Descheemaerker et al. 2006). 45

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