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 Figure 4.5 Mean NDVI values in dry periods (January to April) 2000 to 2010 The analysis was simplified by visualizing NDVI values with increasing and decreasing values in two colors (Figure 4.6a). Similar to the mean values, the temporal NDVI change over time showed an increasing trend in some parts, while larger areas showed a declining trend (Figure 4.6a). The statistical analysis (t-test) revealed that temporal NDVI slope changes were predominantly insignificant, while some areas showed significant differences at P = 0.05 and 0.1 (Figure 4.6b). Areas showing significant inter-annual NDVI change could have shown difference at higher probability level, if the analysis was done since the period exclosure practice has been started in the area. However, due to lack of data (MODIS NDVI data is available since 2000) the analysis covered the period after 2000. 48

Land use-land cover and normalized difference vegetation index changes in Wello Note: (-) show decreasing and (+) increasing trend Figure 4.6 NDVI changes between 2000 and 2010 (January to April): (a) crude NDVI change, and (b) NDVI change by significant level In order to identify the area showing vegetation decline or improvement as proxy indicator of restoration and/or degradation, spatio-temporal NDVI changes were further analyzed. The analysis indicates that the vegetation signature particularly in the central, central east and southeastern area showed an increasing trend, while the eastern, northwestern and southwestern parts showed a declining trend (Figure 4.6b). In relative terms, areas showing a significant NDVI decline (P = 0.05) cover a considerably larger area as compared to areas showing a significant (P = 0.05) NDVI improvement. Areas with non-significant NDVI (slight decline and gain) cover a larger proportion of the study area of which areas showing a declining trend are larger (Figure 4.6b). Higher NDVI values, which help to identify the state of the perennial vegetation remaining green throughout the year, could indicate vegetation degradation or restoration. This holds true where vegetation is not dominated by species with shading leaves in dry periods. In the study area, annual vegetation of the highlands is dominated by evergreen species, while the midlands and lowlands are dominated by acacia species that flourish 49

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