LAND USE LAND COVER DYNAMICS, AND RESTORATION OF DEGRADED LANDS IN THE CENTRAL DRY LOWLANDS OF ETHIOPIA

Abstract

In the central dry lowland areas of Ethiopia, rehabilitation of the natural resource-base in degraded lands through area exclosures has become a necessary intervention. A better comprehending and quantitative analysis of the tempo-spatial dynamics of land use land cover and the effect of exclosures on restoration of degraded landscapes soil properties are critically important. Thus, this study was conducted at Kewet district, central dry lowlands of Ethiopia, to analyze the trends of land use land cover changes, investigate changes in selected soil properties with a main focus on soil organic carbon (SOC) and total nitrogen (TN) stock along exclosures’ age and slope positions, and to provide empirical evidence on the effects of area exclosure on seasonal litterfall production, C and N flux, and associated nutrients inputs to the soil in an age sequence. Supervised classification using the maximum likelihood classifier was employed to quantify LULC change. Soil samples were collected from three slope positions of three purposively selected exclosures with different ages and one adjacent open grazing land for analysis of pertinent soil properties. Leaf litterfall production was recorded by 0.25 m2 litter traps from systematically laid line transects along the exclosures and adjacent open grazing land. The LULC analysis between 1995 to 2017 showed that shrubland cover occupied the largest portion next to cultivated land and it showed a net decrease of 29.2%. Over the past twenty-two years, bare land continuously increased from 3.06 to 12.26% cover. However, forest cover showed a net increase of 18.2%. Age of exclosure showed a significant (p < 0.05) effect on soil bulk density, contents of sand, clay, SOC, TN, available phosphorus (Av.P), CEC, and exchangeable Mg2+ and K+. Higher available water content (173 mm/m) was obtained in the 20-year-old exclosure. Soil organic carbon stock ranged from 15.76 Mg ha-1 in the 20-yearold age exclosure to 18.43 Mg ha-1 in the 15-year-old exclosure. Total nitrogen stock value ranged from 1.18 Mg ha-1 (15-year-old exclosure) to 1.79 Mg ha-1 (20-year-old exclosure). The SOC content of macroaggregates (> 250 μm) and microaggregates (< 250 μm) ranged from 2.40 to 2.85 and 3.18 to 3.36, respectively (p < 0.05) between different ages of exclosures and adjacent open grazing land. Soil organic carbon, TN, and Av.P increased from 2.58 to 3.37%, 0.24 to 0.34%, and 27 to 34 mg kg-1, respectively from 5 to 20-year-old exclosure. Yet, the influence of exclosures’ age on soil bulk density, available water content, and electrical conductivity was not significant. The mean weight diameter (MWD) and water-stable xviii aggregates (WSA) ranged from 2.57 to 3.03 mm and 74.58 to 81.35% in the 5-year and 20- year-old exclosures, respectively. Mean monthly leaf litterfall production was significantly (p < 0.05) higher (22 g m-2) in the 20-year-old exclosure than was in the adjacent open grazing land (9 g m-2). Total annual leaf litterfall ranged from 107.3 g m-2 (grazing land) to 266.24 g m-2 (20-year-old exclosure). Except for C, no significant differences in leaf litterfall nutrients i.e., N, P, K, Ca, and Mg concentration, were observed. The annual leaf litterfall associated C and N input ranged from 1073 - 2662 and 27 – 68 kg ha-1 year-1, respectively. The empirical evidence from this study indicates that area exclosures can improve some of the dynamic soil properties of open degraded grazing lands in the dry lowlands of Ethiopia. Generally, exclosures can be suitable tools to rehabilitate degraded lands and bring overall ecological restoration. To improve the effectiveness of exclosures and for a better understanding of SOC and TN dynamics in these exclosures, further research on soil organisms and the contribution of dominant tree species in litter production along the age of exclosure is recommended.