Land use/ cover changes, driving forces and influence on soil properties in Rib watershed, Ethiopia

Abstract

Land use/cover (LULC) change has resulted from complex interactions of natural phenomena and human activities. Population growth coupled with economic growth has increased the demand of land resources for centuries and causing changes at various levels ranging from local to global scales. Land use practice affects the distribution and supply of soil nutrients to plants by altering soil properties. This study aimed at understanding the magnitude of LULC changes and its drivers. It also attempts to examine the influence of LULC on soil properties in Rib watershed. Satellite imageries of 1986, 1996, 2006, and 2016, field observation and four key informant interviews were employed. In addition, soil samples were taken over natural forest, grazing and cultivated lands in the two agroecological zones (Dega and High Dega) with five replications. The samples were taken at two depths: 0-15cm (surface layer) and 15- 30cm (subsurface layer) and mixed up to obtain composite and representative samples. Household survey was also employed to obtain data on farmers’ perception of drivers of LULC changes. Image analysis was accomplished on ERDAS Imagine and Arc GIS software to detect land use/cover changes. Descriptive statistics, pair-wise ranking technique, Multivariate analysis of variance (MANOVA), and Spearman’s rank correlation coefficient analyses in SPSS were employed. The findings of this study revealed an expansion of cropland and settlement, plantation, and bare land by 39.01, 24.88 and 5.62 ha/year, respectively between 1986 and 2016. On the contrary, natural forest, grassland, and grazing land have decreased by 30, 26.6 and 12.9 ha/ year, respectively. Plantation shows increasing trends in Dega agroecological zone, whereas in the High Dega cultivated/ farmlands & settlements, bare land has increased rapidly at the expenses of other LULC. Significant differences (p<0.05) were also observed in OC, Ca2+, clay, and silt fractions between the soils of natural forest, grazing land, and cultivated in the two agroecologies. Soils of natural forest has higher OC, OC stock and TN. For instance, soils of natural forest has higher OC stock (188.32 Mg/ha) as compared to soils of cultivated lands (72.75 Mg/ha). BD of cultivated land was significantly higher than natural forest and grazing lands. LULC changes were driven by increasing demands for new farmlands and increasing demand for eucalyptus wood in rural and urban centres. Moreover, weakness in law enforcement on natural resource conservation, low level of public participation in watershed management, and low level of livelihood diversification were among the drivers of change. Therefore, the study has suggested that the watershed ought to be enriched with of watershed restoration and natural resource conservation activities.