Effect of Land Use and Land Cover Changes on Soil Erosion in Ethiopia

Land degradation is one of a serious agricultural problem that posed severe threat to food production and the livelihood of peoples in Ethiopia. It resulted in high economic loss and threat in natural environment. The country loses about $106 million annually through soil and nutrient loss. Soil degradation is the one and the major form of land degradation that have been stayed for long period as the bottlenecks of the country’s economy and human wellbeing. The economic loss soil degradation in the form of soil erosion and nutrient depletion only from the highlands of the country is about10-11% of agricultural gross domestic products. Soil erosion is one of the major causes of soil degradation in the country. The annual soil loss rate on average is about 42 tones/ha for croplands, and up to 300 tones/ha in extreme cases. The average total soil loss of the country is estimated as 12 ton/ha/year, which varied based on land cover types. Ethiopia historically passed signifi cant dynamics in land use/land cover since long ago to date. Land use and land cover changes and degradation are increasing at alarming rate generally throughout the country. The change in land use types played a signifi cant role in this increased rate of soil erosion in Ethiopia. Cultivated lands showed continuously increasing trend at the expense of forest and grasslands. The rapidly increasing population has led to a declining availability of cultivable land and a very high rate of soil erosion. The objective of this review paper is to view the effect of Land Use-Land Cover change in soil erosion in Ethiopia Review Article Effect of Land Use and Land Cover Changes on Soil Erosion in Ethiopia Bekele Tsegaye* Areka Agricultural Research Center, Southern Agricultural Research Institute, Ethiopia Received: 21 December, 2018 Accepted: 10 May, 2019 Published: 13 May, 2019 *Corresponding author: Bekele Tsegaye, Areka Agricultural Research Center, Southern Agricultural Research Institute, P.O. Box: 79, Areka, Ethiopia, Tel: +251911893571; Fax: +251465520502; E-mail:


Introduction
Land degradation has become an important concern generally in the world, and the same is true specifi cally in Ethiopia, because of its implications for food security and the environment. Ethiopia is known for its historic agriculture, but also for the associated, widespread, and ongoing land degradation [1]. Land degradation is one of a serious agricultural problem that posed severe threat to current and potential food production and the livelihood of peoples in Ethiopia [2,3]. Some studies before few years indicated as the annual costs of land degradation relate to soil erosion and nutrients loss from agricultural and grazing lands is estimated at about $106 million from a combination of soil and nutrient loss [4,5]. Due to the favorable climatic conditions and fertile soils, known to be the oldest settled high land areas of the country land degradation stems from the historical development of agriculture and human settlement in these areas and latter progressively increased with signifi cant rate [6]. The shortage of land, rapid growth of population and demand for increased food production intensifi ed the pressure on the land and aggravated the process of land degradation [7].
There is no doubt that the major cause for land degradation in Ethiopia is known as inappropriate use of land for different economic activities. Human activities contributing to land degradation such as deforestation, removal of natural vegetation, overgrazing, and agricultural intensifi cation without erosion control measures sustained for long period by deteriorating land [8]. Girma, indicated the major causes of land degradation in Ethiopia as rapid population increase, severe soil loss, deforestation, low vegetative cover and unbalanced crop and livestock production. Besides the human induced causes, factors such as land topography, ecology, rainfall, land cover and soil types counted as being as proximate and underlying causes of land degradation in Ethiopia (Ayalnen, 2003, cited in . Large areas abandoned or managed at low levels productivity and affecting 20-50% of the land and some 6 -11 million people each year and continued till present as the greatest threat to the survival of the nation [9].
Soil degradation is the key component of land degradation, and there is almost no form of land that does not include soil degradation [10]. Many defi nitions are given for the term 'soil degradation'. It is the decline in soil quality leading to a reduction in other components of land resources (e.g. vegetation, water, and air) [8]. Soil degradation is a narrower term for declining soil quality, encompassing the deterioration in physical (e.g., soil erosion, compaction, and waterlogging), chemical (e.g., nutrient depletion and acidifi cation) and biological (e.g., soil organic matter decline and depletion of soil DOI: http://doi.org/10.17352/2455-815X.000038 fauna) attributes of the soil [11,12]. In Ethiopia different forms of soil degradation have been stayed as the bottlenecks of the country's economy and human wellbeing. Approximately, 17% of the potential agricultural Gross Domestic Product (GDP) is being lost because of soil degradation [13]. In Drechsel and Gyiele, cited in Berry et al., it was indicated as the annual economic loss of the country because of soil degradation in the form of soil erosion and nutrient depletion as 10-11% of agricultural gross domestic products from the highlands of the country. In these highlands of the country, soil degradation reached at the level of severe which led to lower yield or higher costs of inputs so that the food security of present and future generations is being threatened, as the smallholder farmers in the area largely depend upon the land for their livelihood [14,8].
Soil erosion is one of the major causes of soil degradation along with soil compaction, low organic matter, loss of soil structure, poor internal drainage, salinization, and soil acidity problems [15][16][17]. Soil erosion is a physical process that causes land and soil degradation, and refers to the displacement of soil particles by water, wind and/or forces associated with farming activities such as tillage that eventually results in reduction in soil productivity due to physical loss of topsoil, reduction in rooting depth, removal of plant nutrients, and loss of water.
Topsoil, which is high in organic matter, fertility and soil life, is relocated elsewhere "on-site" where it builds up over time and results in onsite effect such as reduces cropland productivity or is carried "off-site" where it fi lls in drainage channels and results in offsite effect like contribution to the pollution of adjacent watercourses, wetlands and lakes. The rapid growth of demand for food related with population growth increased the need for cultivated land that in turn put pressure on land and leading to loosening of soil structure and cohesion which made the soil easily lost by erosion [18].
In Ethiopia, soil erosion by water is the dominant degradation process and occurs particularly on cropland, with annual soil loss rates on average of 42 tones/ha for croplands, and up to 300 tones/ha in extreme cases [19]. The average total soil loss of the country before some three decades was estimated as 12 tone/ha/year which varied based on land cover types as high as 70 ton/ha/year in unproductive lands to as low as 1 ton/ha/year in forest lands [20]. Despite the fact that the country's government effort in massive and vast participation in prevention of soil erosion through implementation of different soil and water conservation works [21][22][23], there are still reports as the soil rate of the country is still increasing.
Though the estimate was in smaller area size, different land use defi nition than Huri (1989) and mainly focused on cropping lands, still the average soil loss rate of the country is about 18 ton/ha/year and nearly 1 billion tones of suspended sediments originating from human-induced soil erosion still reach the rivers every year [1].
The change in land use types played a signifi cant role in this increased rate of soil erosion in Ethiopia. Cultivated lands showed continuously increasing trend at the expense of forest and grasslands over the last four decades [24,25]. Land use change is the conversion of land use due to human intervention for various purposes, such as for agriculture, settlement, transportation, infrastructure and manufacturing, parks, recreation uses, mining and fi shery [26,27]. In Ethiopia, the rapidly increasing population has led to a declining availability of cultivable land and a very high rate of soil erosion [28].
In general term, the historic land use and land cover change in Ethiopia had induced great impact on biodiversity, water resources, forest and local livelihoods of the country [22]. Due to deforestation and permanent removal of other vegetation in Ethiopian highlands before some few years, about 27.5 million ha of the areas examined showed signifi cant signs of accelerated soil erosion, while about 14.5 million ha of land were considered the 'worst affected areas' and were recommended to be abandoned [29]. Therefore, from this we can see the close relationship between land use-land cover change with soil erosion narrow view and land degradation in general.

Objective
The objective of this review paper is to view the effect of Land Use-Land Cover (LuLc) change in soil erosion in Ethiopia.

Some basic concepts
It is important to defi ne and distinguish related concepts such as land degradation, soil degradation, and soil erosion, as these are sometimes (incorrectly) used interchangeably. One should understand where the terms are different and again their relationships for ease and standard communication. The other confusing terms are also the terms 'land use' and 'land cover'. In some cases the two terms used interchangeably which does not means that the terms are one and the same in all cases.
Land degradation is a broad term, refl ecting the fact that land itself is a broad term, including more than just the soil.
The U.N. Convention to Combat Desertifi cation defi nes land as "the terrestrial bio-productive system that comprises soil, vegetation, other biota, and the ecological and hydrological processes that operate within the system", and land degradation as "reduction or loss of the biological or economic productivity and complexity of rainfed cropland, irrigated cropland, or range, pasture, forest and woodlands resulting from processes such as (i) soil erosion caused by wind and/or water; (ii) deterioration of the physical, biological or economic properties of the soil; and (iii) long-term loss of natural vegetation" [30]. In Fitzpatrick, land degradation is also defi ned as is the systematic decline in the quality of land resulting from a mismatch between land use and land quality. Land degradation is defi ned as the temporary or permanent decline in the productive capacity of the land, and the diminution of the productive potential, including its major land uses (e.g., rain-fed arable, irrigation, forests), its farming systems (e.g., smallholder subsistence), and its value as an economic resource [31]. UNCCD also defi nes land degradation as a persistent decline in the ability of a ecosystem to provide goods and services associated with primary production [32].
Therefore, land degradation is more general term that it is a 'situation' or 'from' of land that do not stand alone that caused by other factors such as soil erosion, acidifi cation, pollution, etc. It is a complex phenomenon infl uenced by natural and socio-economic factors.
Soil degradation is a narrower term, and one form of land degradation, for declining soil quality, encompassing the deterioration in physical, chemical and biological attributes of the soil [11]. Soil compaction, low organic matter, loss of soil structure, poor internal drainage, salinisation and soil acidity problems are other serious soil degradation conditions that can accelerate the soil erosion process [18]. Soil degradation refers to the decline in a soil's inherent capacity to perform environmental and socio-economic functions. The problem usually caused by many factors including excessive tillage, inappropriate crop rotations, excessive grazing or crop residue removal, deforestation, mining, construction and urban sprawl [33]. Some soil degradation processes are natural phenomena but they are exacerbated by all kinds of unsustainable human uses. Causes of degradation include deforestation, overgrazing, agricultural practices, overexploitation of the vegetative cover, and industrial activities.
Soil erosion is one of the causes of soil degradation and it refers to the wearing away of a fi eld's topsoil by the natural physical forces of water and wind. Topsoil, which is rich in organic matter, high fertility and soil life, is relocated elsewhere "on-site" where it builds up over time or is carried "off-site" where it fi lls in drainage channels [18]. The different forms of

Soil Erosion in Ethiopia
Soil erosion is recognized as one of the most serious causes of soil degradation in Ethiopia [34,15,16,35] and hence in highland areas of the country the crop yield and soil fertility levels are extremely low [36]. Continued soil erosion seriously threatens peoples' livelihoods, especially in highland parts of the country, where arable land is a very scarce resource [37]. Annually about 2 billion cubic meter top soil loss is reported for the country [1,6,38]. Ethiopia losses over 1.5 billion tons of topsoil annually only from the highlands due to erosion [8]. The average annual soil loss rates from crop lands estimated as 42 tones/ha, and ranged up to 300 tones/ha in extreme cases [19]. Especially the productive highland parts of the country, which characterized by rugged topography, densely populated, intensive cultivation and that host large proportion of people and livestock, harmed highly with problem of land degradation [22,39,40]. About 43% of the total highland areas of Ethiopia are highly affected by soil erosion with an estimated average annual loss of 20 ton per hectare and measured annual amounts of more than 300 ton per hectare on specifi c plots [41,42]. Only the Blue Nile basin of the country loses fertile soils with a rate of 131 million ton per year [35]. Not only the highlands, but also the dry lowland areas of the country have also been identifi ed as vulnerable to the problem of land degradation [43].
In Ethiopia the annual costs of land degradation relate to soil erosion and nutrients loss from agricultural and grazing lands is estimated at about $106 million (about 3% of agricultural GDP) from a combination of soil and nutrient loss [4,5]. The food security of present and future generations is being threatened due to soil erosion, as the smallholder farmers in the area largely depend upon the soil for their livelihood, and farmers are changing land use from cropland to plantation forest (e.g., Eucalyptus globulus) responding to soil degradation mainly by soil erosion [8]. Bojo and Cassells (1995)

Land Use-Land Cover dynamics in Ethiopia
Understanding the dynamics in land use/land cover change is increasingly important issue in study of environmental change for assessing and fi guring the current resource status and planning sustainable resource management options. Not only the dynamics but also knowing the direction of dynamics, the cause and how this change is benefi ting or harming the natural environment and the people is very important. It is claimed that there is constant change in land cover-land use with interaction of human being and resulted in modifi cation of environment and its service. A land cover change, particularly deforestation, has become a global concern, with dynamic implication for human livelihood system [54]. Natural land covers have been transformed to agricultural lands and urban areas to meet the increasing demands for food, water, consumption of goods and other public utilities for over six billion people worldwide (Amare and Kameswara, 2011, cited in Amare and Gebeyehu, 2017).
Land use conversion due to increasing human and livestock population is a common experience in eastern African countries like Ethiopia through inappropriate agricultural practices and high human and livestock population pressure that led to sever land degradation in the country (Alemu, 2015, cited in Mammo et al., 2018). Land use dynamics is one of the major environmental problems in Ethiopia. Estimates of deforestation in Ethiopia, which is mainly for expansion of rain fed agriculture, vary from 80,000 to 200,000 ha per annum (EPA, 1997, cited in Temesgen et al., 2014). The highland parts of the country which cover the major portion of the country (40% of the total area of the country), characterized by high human and livestock population pressure, high land fragmentation, rapid expansion of agricultural land extensive cultivation eventually resulted in high land degradation [28]. Land use and land cover changes and degradation are increasing at alarming rate in the highlands of Ethiopia [55] that led to the transformation of natural habitats to other land use types [56]. Farmers often push onto steeper and steeper slopes for crop farming which can only give yields for a few years before the soil is washed away. Rapid population growth which resulted in rapid agricultural expansion at the expense of the forest resource and free grazing system aggravates the depletion of the ecosystem including soil erosion and water resource degradation [57].
Though the fi gurative nationwide change information in land use/land cover is limited, there are different watershed and basin wide reports. In Gumara watershed of Lake Tana basin forest land, shrub land, grass land and wetland declined by 85.30, 91.39, 76.15 and 72.54 %, respectively, within 28 years [58]. The cultivated land and settlements increased by 15.4 and 9.9%, respectively, at the expense of shrub land and grazing lands in Gilgel Tekeze watershed in the highlands of Northern Ethiopia within 28 years [59]. The cultivated was increased by 7054.6 ha while grass, wetland and bush lands decreased by 4846.5, 511.9 and 3376 ha, respectively, in Koga watershed of North Western Ethiopia for demand for cultivated land and fuel wood [60]. There was 59% increment in cultivated land at the expense of grass, shrub and forest lands and a decrease of 25.5%, 14% and 20.5% of grass, shrub and forest land within 37 years in Huluka watershed of Central Rift Valley of Ethiopia [61]. The forest coverage became smaller and more fragmented and declined from 202.6 ha to 101h between years 1985 and 2011 due to an extensive and massive clearance of forests and grasslands in Lake Haramaya Watershed [62].
In Ethiopia, previous studies reported that there have been considerable land use/land cover changes in different

Land Use/Land cover change and soil erosion in Ethiopia
Land use/land cover changes and land degradation are highly interrelated [67,68] because usually the changes are associated with deforestation, biodiversity loss and land degradation [69].
Land cover is one of the factors that determine the rate of soil loss due to erosion. Belay, stated that land use/land cover changes towards cultivated land aggravate soil erosion problems unless proper management is undertaken. A study by Hurni and Ludi, also reveals that human land use around the Simen Mountains National Park has accelerated the degradation of vegetation and soils. Changes in land use/land cover has signifi cant impacts on the socioeconomic and environmental systems functioning with tradeoffs for sustainability, food security, biodiversity and the vulnerability of people [70].
Most of land use/land cover change in Ethiopia is in the form of changing forest and shrub lands to cultivation [71].
Removal of vegetation cover means exposing the land to soil erosion because process accelerates removal of soil particles and increased sheet, rill and gully erosions by reducing the protection of soil cover. In the highlands of Ethiopia, signifi cant land cover changes have been observed since the last century due to a long history of agricultural practices and human settlement that recently resulted in high population pressure including unsustainable practices and depletion of the natural resources including soil [24,34]. This resulted in the soil degradation, mainly in the form of soil erosion, to be in worse sate. The estimate in mid 1980s by FAO, indicated as about half of the highlands' land area of Ethiopia was "signifi cantly eroded" and over one-fourth was "seriously eroded" and over two million hectares of farm lands had reached the "point of no return" in the sense that they are unlikely to sustain economic crop production in the future.
There are different watershed and basin based studies reported the impact of land use/land cover changes in erosion. The study report before few years indicated as Gojam area has undergone dramatic land use and land cover changes, with the result that almost all land units have been converted to cultivated land [24]. The result of Soil Conservation Research Project on 100ha soil loss monitoring catchment in Gojam showed annual soil loss from cultivated lands ranges from 130 to 170 t/ha/yr [72]. Bosshart, reported as the average annual suspended sediment yield from the unconserved parts of the catchment reached 61 t/ha/y, higher than the country average. The 52% increment in cultivated land with the expense of forest and grass lands in Genale watershed, Southern Ethiopia, increased the soil loss rate by 189 percent within 3 decades (1985 to 2015) with predicted soil loss rate of 41 ton/ha/year in year 2015 [73].
Land use and land cover changes and degradation of natural resources, particularly vegetation and soils, are increasing at alarming rate in the highlands of Ethiopia [55]. Most mountainous areas in north western part of the country severely threatened by the agricultural land expansion and livestock overgrazing which would ultimately lead to excessive soil erosion and disrupting hydrological system of the area [57]. The dramatic increase in both livestock and human population due to migration from the surroundings in Abjitata Shala national park area induced high pressure in the environment that resulted in the conversion of natural vegetation, into cultivated and bare lands through overgrazing of natural grasslands, removal of natural shrub for fi re wood, and clearing of forests for construction materials and charcoal making which eventually resulted in changes in land use/land cover and hence vulnerable sloping areas in the area face increased erosion and depletion of nutrients required for vegetative growth [55].
The major impact of land use/land cover changes in the livelihood of rural communities indicated in Belay (2018) include: its impact on land resources with related to land degradation, soil erosion, and productivity decrement; its impacts on environment thereby rural communities' vulnerability to climate vagaries; vulnerability of rural communities towards erratic rain fall and water sources problem with related to the change; impact on access to quality water; its negative impact on livestock rearing which related with grazing land shrinkage for agricultural land expansion, and also its impacts on ecosystem goods and services especially related with deforestation. Therefore, information on land use/land cover changes, its ultimate impact and possibilities for their optimal use is essential for the selection, planning and implementation of land use schemes to meet the increasing demands for basic human needs and welfare. In Ethiopian condition there is an urgent need to design and implement appropriate land management options, coupled with population control and sustainable natural resource use and conservation that meet the need of both present and future generations [74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90].

Summary and Conclusion
Land degradation is one of a serious agricultural problem that posed severe threat to current and potential food production and the livelihood of peoples in Ethiopia. The shortage of land, rapid growth of population and demand for increased food production intensifi ed the pressure on the land and aggravated the process of land degradation. It resulted in high economic loss and threat in natural environment. The country loses about $106 million annually through soil and nutrient loss. Inappropriate use of land contributing to land degradation such as deforestation, removal of natural vegetation, overgrazing, and agricultural intensifi cation without erosion control measures sustained for long period by deteriorating land. Large areas of the country abandoned or managed at low levels productivity and affecting land and the dwelling peoples.
Soil degradation is the one and the major form of land degradation that have been stayed for long period as the bottlenecks of the country's economy and human wellbeing. Approximately, 17% of the potential agricultural Gross Domestic Product of the country is being lost because of soil degradation. The economic loss soil degradation in the form of soil erosion and nutrient depletion only from the highlands of the country is about10-11% of agricultural gross domestic products Soil erosion is one of the major causes of soil degradation in the country. The annual soil loss rate on average is about 42 tones/ha for croplands, and up to 300 tones/ha in extreme cases. The average total soil loss of the country is estimated as 12 tone/ha/year which varied based on land cover types as high as 70 ton/ha/year in unproductive lands still with an indication of increasing trend. About 43% of the total highland areas of Ethiopia are highly affected by soil erosion with an estimated average annual loss of 20 ton per hectare. Annually about 1 to 2 billion soil loss is reported for the country. The country-wise damage of soil erosion in economic term is indicated as losses of USD 1 billion annually. The situation threatened the food security of present and future generations as the smallholder farmers largely depend upon the soil for their livelihood. Out of a total surface area of 112 million hectares, about 27 million hectares are signifi cantly eroded, 14 million hectares are seriously eroded with 2 million hectares have reached the point of no return.
The change in land use types played a signifi cant role in this increased rate of soil erosion in Ethiopia. Cultivated lands showed continuously increasing trend at the expense of forest and grasslands. The rapidly increasing population has led to a declining availability of cultivable land and a very high rate of soil erosion.