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Causes and impacts of land degradation and desertification: a case study of Sudan

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https://www.eduzhai.net/ International Journal of A griculture and Forestry 2013, 3(2): 40-51 DOI: 10.5923/j.ijaf.20130302.03 Causes and Impacts of Land Degradation and Desertification: Case Study of the Sudan Omar A. Abdi1, Edinam K. Glover2,*, Olavi Luukkanen1 1Department of Forest Sciences, Viikki Tropical Resources Institute, P.O. Box 28, FI- 00014 University of Helsinki, Finland 2Faculty of Law, P.O. Box 4, FI – 00014 University of Helsinki, Finland Abstract Desertification, a phenomenon referring to land degradation in arid, semi-arid and dry sub-humid regions as a result of climatic variations and human activities, is considered as one of the most severe environmental and socio-economic problems o f recent times. The p rincipal aim o f th is study was to exp lore the impacts of desertification, degradation and drought on both the natural resources and man's livelihood in the Sudan and to suggest appropriate forest resource management interventions. The study was based on a fact finding tour in the Sudan and data collection on drought trends as reflected in ra infa ll trends in the study area, and on trends concerning the productivity of natural resources. Information was also comp iled fro m existing records on rainfall, forest land cover, forest stocking, rangelands and carrying capacity and on agricultural p roductivity and population trends. Results showed that in rain-fed agricultural zones in the Sudan, deep ploughing and leveling of the surface soil caused an increase in its susceptibility to wind erosion, wh ich, in turn, has led to a severe decline in its fertility and, in some places, the formation of sand dunes. The implications of these trends on the natural resource base include environmental degradation, food insecurity and aggravation of inco me inequalit ies among the Sudanese producers. The study has suggested Agroforestry technology as a potential solution to this continued problem of declining ru ral ag ricu ltural production in the Sudan. Keywords Agroforestry, Desertificat ion, Drought, Drylands, Natural Resources, Rainfall Trends, Sudan 1. Introduction The term Sahel (an Arabic word for shore) is used to refer to the semi-arid zone to the south of Sahara desert. It is one of the world’s warmest regions, with a short summer rainy season of three months[1,2]. Climatologically, the Sahel is characterized by frequent droughts - low, poorly distributed and high ly variable monthly and seasonal unpredictab le rain fall. A rid , semi-arid and d ry sub -hu mid zon es are characterized by, low and erratic ra infall that does not exceed 700 mm p er an nu m, p erio d ic d rou ghts , an d d ifferent combinations of vegetational cover and soils. Inter-annual rainfall varies fro m 50-100% in the arid zones of the world with averages o f up to 350 mm. In the semi-arid zones, inter-annual rainfall varies fro m 20-50% with averages of up to 700 mm. Reg ard ing livelihoo ds systems , generally speaking, light pastoral use is possible in arid areas whilst rain-fed agriculture is not usually possible. In semi-arid areas agricu ltural harvests are likely to be irregu lar, although grazing is satisfactory[3,4]. The dry sub-humid areas receive higher amounts o f rain fall than the other cat egories of * Corresponding author: eddie.glover@helsinki.fi (Edinam K. Glover) Published online at https://www.eduzhai.net Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved drylands which can reach more than 800 mm annually. Drylands are characterized by high maximu m temperatures and large temperature differences between day and night. Other climatic characteristics include strong winds, and low humid ity. These are reflected in an increased vapour pressure deficit with imp licat ions for water use efficiency, transpiration, and evaporation. Drylands are frequently subjected to drought which is the main limiting factor on bio mass production and crop yields. Hu man induced factors such as overcultivation, overgrazing and other forms of inappropriate land use, when practiced under the conditions prevailing in the drylands, may result in significant degradation of vegetation and, soil leach ing and in many cases, in desertification[5]. Against this backdrop, this study was conducted to explore the impacts of desertification, degradation and drought on both the natural resources and man's livelihood in the Sudan. Data for this study was derived fro m both primary data (observation) and secondary data or a review of re levant literature, and a co mpilation of other available information on drought trends as reflected in rainfall trends in the study area, and on trends concerning the productivity of natural resources in the wider context of land degradation and desertification. Information was also comp iled fro m existing records on rainfall, forest land cover, forest stocking, rangelands and carrying capacity and on agricultural International Journal of A griculture and Forestry 2013, 3(2): 40-51 41 productivity and population trends. 2. Dryland Problems Many drylands show clear evidence of environmental degradation. Drought and unreliable and variab le rains are a recurrent problem. Even without climate change, the drylands face a daunting array of threats including population pressure, social changes such as the settlement of traditionally no madic peoples, and exp loit ive agricultural and grazing practices that increase deforestation, soil erosion, salinization and water depletion. Many political and institutional proble ms have conspired to degrade 20% of the world 's drylands, including 22% of Asia's susceptible drylands, and 25% of A frica's. Land degradation and desertificat ion conistitute one of the most serious environmental proble ms fac ing the world today. Desertification threatens the drylands of Sub-Saharan Africa more than any other region in the world. Once the vegetational cover is removed, the fragile soils are exposed to winds and battering rains. Erosion is inevitable. Early storms are often accompanied by strong winds. Wind speeds exceeding 100 km/hour have been recorded at ICRISAT is Sahelian Centre in Niger. According to[6], b lowing sand subjects seedlings to abrasion and often results in their being completely covered by sand, causing serious problems for crop establishment. In many areas desertification takes dramat ic forms, such as, shifting sand dunes that move on to villages and fields, the format ion of deep gullies, and crusts that seal the soil`s surface and markedly increase runoff. Desertification has been described as self-propagating[7] and it feeds on itself as expanding areas become useless for crops or livestock, whilst the pressure on the islands of remain ing fertile land that remain increases. Farming is taken beyond the limits of sustainable rain-fed agriculture. Whole families, sometimes whole v illages, migrate to better-watered areas. As[8] classifies about 75% of the world 's drylands as degraded. Examp les of dryland degradation include salinizat ion and the loss of vegetation or water resources. One of the greatest threats is desertification, which robs the land of its soil, biodiversity, and productivity. The spread of desertification results in a degraded landscape. Millions of people may be forced to leave the land when it can no longer sustain them. Pressures fro m human and livestock populations coupled with the effects of recurrent drought have led to a serious degradation of vegetational cover, erosion, and the depletion of soil fertility on a large scale in many parts of sub-Saharan Africa. 2.1. Land Degradati on Land degradation is, usually, the result of co mp lex inter-relationships between biophysical and socio-economic issues which affect many people and their land, specially in the tropics and developing countries. The term land degradation involves both soil and vegetation degradation. Soil degradation refers to negative changes in the physical, chemical, and biological properties of the soil, whereas vegetation degradation is the reduction in the number of species and the vegetational composition. Usually land degradation is described in terms of the loss in natural resources (soil, water, fauna and flora) or in the biophysical process by which it functions. Soil can be eroded, salinized or impoverished. Water can be lost through evapotranspiration, evaporation, infiltration, run-off, pollution, or overuse. As habitats diminish, so also do the abundance, uniqueness and diversity of liv ing things[9,10]. Many factors contribute to land degradation. Since the essence of the dryland`s environment is climate variability, the successful use of drylands requires a balance of capability, utilizat ion, and resilience. Land degradation occurs when this balance is lost. The causes of dry land degradation are complex, and may be the product of anthropogenic or climat ic factors, such as the impact of drought and desiccation on ecosystems, the overgrazing of these rangelands, unsustainable land-tenure rights, the undervaluation of land resources, and pricing failures, and numerous other social and economic processes (table 1). The link between desertificat ion and poverty is direct and intimate and affects all those who depend on the land as a basic resource, whether for crops, livestock, or fuel-wood. Poverty is the main reason for the steady decline in rural incomes resulting in co mp lex demographic, econo mic, and social changes. Table 1. Causes of dryland degradation[9] FACT ORS RESULT S Dro ught s Livestock Crops Fires Boreholes Lo cust s Human factors Extent, frequency, and severity Pressure “too long” Encroachment on grazing lands Natural and deliberately lit Too many and too close together Extent, frequency, and severity of outbreaks Social, economic, and political 42 Omar A. Abdi et al.: Causes and I mpacts of Land Degradation and Desertification: Case Study of the Sudan 2.2. Desertificati on Desertification has been defined as land degradation in arid, semi-arid, and dry sub-humid areas resulting fro m various factors, including climatic variations and human activities[11]. Another definition of desertification is the spread of desert-like conditions of lo w b iological productivity due to human impact under climat ic v ariatio n s [12 ,1 3, 1 4] . It is estimated that three-fourths of drylands have suffered fro m some degree of desertification[15,16,17,18]. The removal of vegetation cover exacerbates desertification and accelerates soil erosion which causes reduced soil fert ility and eventually renders the land on productive; a situation that has often lead to the assumption that it is a human induced process which leads to the depletion of soil nutrients and a reduction of b iological p roductivity. Desertificat ion is one of the central problems that pose very real and severe challenges to the sustainable development of the dry land`s ecosystem. Rain fall variability both in time and space, coupled with the inherent ecological frag ility of the dry lands, weakens the resilience of the ecosystem and its ability to return to its original condition. According to[19,20], desertification has been with us for thousands of years, but it did not receive attention for a very long time. It was not until the twentieth century that governments and people in general finally realized that land degradation and desertificat ion threatened their future. The desertification of land resources endangers basic production systems as well as natural ecosystems. It places about one billion people in 110 countries at risk, main ly in developing reg io n s . In the Sahel, the slash and burning of natural forests and bush lands in order to clear land for agriculture is considered one of the main causes of deforestation and vegetation re moval that contributes significantly to desertification. Man can either destroy his environment or be constructive and solve problems that occur within it. By increasing the population of perennials in the agricultural zone, farmers become agents for the stabilization of their land. They can then live in harmony with their environ ment in a symbiot ic relationship where the land benefits fro m man’s presence through the increased number of perennials. Furthermore, man benefits fro m h is active control of desertificat ion. 3. Desertification and Land Degradation in the Sudan Desertification and land degradation are a mong the central problems fo r the sustainable development of the dryland ecosystem, especially in the case of the Sudan (Figure 1). Recurring droughts and land degradation are closely lin ked. While drought increases soil degradation, soil degradation, in turn, magnifies the impact of drought. Study Site Figure 1. Map of Sudan showing the study area International Journal of A griculture and Forestry 2013, 3(2): 40-51 43 According to[21] land degradation, due to natural causes, is assumed to occur at a rate, which is almost equal to the rate of natural rehabilitation. However human-related factors account for accelerated forms of land degradation. Over cultivation of croplands, overgrazing of range and pastoral lands, slash and burn techniques, shifting cultivation, inappropriate use of irrigation water (salinizat ion) and industrial pollution are some of the factors which can cause degradation (see Figure 2). Desertification and degradation also expand outwards fro m focal points, usually associated with human or livestock concentrations, especially, around watering points. A study in western Sudan has shown a steady increase of bare soil around boreholes over time, increasing fro m 20% to 55% in 30 years[22,23,24]. It also showed that in the east Kordofan district of western Sudan, with an area of about 29,000 square km, there were 150 boreholes, many of which supplied overlapping grazing areas, which have had great impact on the deterioration and degradation of the ecosystem. In the case of the Sudan population pressure is increasing in areas with very limited natural resources. Colonalization of the Sudan also brought about urban development and roads, transport, education, hospitals, and piped water. Th is resulted in a slow migration of people away fro m rural areas in order to take advantage of urban facilities. Th is increased the concentration of people and livestock around urban areas and drastically increased the pressure on the surrounding land for cropping, grazing, and fuel. It is, therefore, significant, that highly populated areas and livestock watering points were the places where signs of desertificat ion in the Sudano-Sahelian first became apparent[25]. Desertification is considered one of the main factors that cause the migration of rural populations to urban centers; thus, creating so-called “environ mental refugees”[26]. As reported by[27] the impact of land degradation manifests itself in different fo rms (e.g. see Figure 3). Fi gure 2. Schemat ic represent at ion of the combined forces causing desert ificat ion in t he Sudan: desert ificat ion in t he Sudan is the combinat ion of both natural and human factors 44 Omar A. Abdi et al.: Causes and I mpacts of Land Degradation and Desertification: Case Study of the Sudan Figure 3. Degraded land at El Rawashda in Gedaref State of the Sudan (Photo: Edinam Glover) In the case of the Sahel in general and the Sudan in particular, co mmunal o wnership with-well defined structures, based on traditional institutions is still appropriate in many situations, and therefore suggests a policy of stabilizing those communally-owned resources which are most vulnerable to land degradation[21]. Po lit ical and social instability have a strong bearing on land degradation in most parts of the dry Sahel. Civ il strife in southern Sudan and Somalia for examp le, has led to the displacement of large numbers of people to Kenya. So me of these people have been settled in refugee camps thus adding to the problem of an increasing population in the affected areas. The Kenyan Govern ment has housed most of these refugees in two major refugee settlements, namely, in the Kaku ma and Dadaab camps. At present, the Kakuma camp is home to 70,958 refugees fro m 9 d ifferent countries with 72% co ming fro m Sudan and 22% fro m So malia[28] According to[29,30] the degradation of vegetation on overstocked pastures takes place both quantitatively and qualitatively, useful species disappear and are replaced by unpalatable species, for examp le, the poisonous scrub Calotropis procera (iushar) has spread widely on exhausted soils. Unpalatable plants, such as cassia acutifolia (senna senna), Acanthospermum hispidum (horab hausa), and Guiera senegalensis (Gubeish) occupy vast areas and replace former, palatable pasture grasses, such as Cenchrus biflorus (haskanit), and the Eragrostris species and Aristida s p ecies . The old stable dune belt (Qo z) is the main rain-fed cultivation zone in Darfu r and Ko rdofan. In the Sudan rangelands occupy approximately 50% of the country's area. They cover many ecological zones, namely, the desert, semi-desert, and low rainfall savannah. They produce about 80% of animal feed requirements. Livestock rearing ranks after crop production as a major economic activity. Crop production and animal husbandry together form the back bone of Sudan’s economy. Livestock production is widely practiced under a trad itional system. The govern ment has realized the potential of animal resources for earning foreign exchange. Moreover, natural g rasses and herbs play a significant ro le in soil conservation, watershed protection, desertification control, carbon sequestration, maintaining biodiversity, providing medicines, and in the release of plant nutrient elements during the process of humificat ion and mineralizat ion of decomposed grass roots[31, 32] Open grazing is the common practice, which has many disadvantages. This is mainly due to the fact that grazing and animal rearing is practiced under communal ownership which lacks control and management and often leads to the degradation of vegetation and soil and results in social conflicts. Attempts have been made to change the traditional pattern, by calling for a ranching system as an approach for livestock raising in the Abufas reserved range (1960s), the Geraih El Sahra settlement scheme (late 60s), on the Barbanusa ranch (early 70s) and Gazelle Gawazat e xperimental ranch (mid 70s) and on the Elodaya communal improved range (early 80s), all of which aimed to improve rangeland in order to bridge the aforementioned deficit. Figures 4 and 5 illustrate the situation in the Sudan during the early 1980s and up to 2002. Despite the fact that rainfall has decreased, the vegetation cover is in the process of recovering. However, there is tremendous pressure from grazing, especially by goats. In other areas, on the clay plain, there is a continuing land degradation process.[33], estimated that overgrazing accounts for 47% of the clearance of natural vegetation, whereas mechanized cropping and woodcutting, and urban demand for charcoal account for 22% and 19% respectively. The increasing need for wood for construction and fuel in the Sudan may accelerate the trend of woodland destruction. International Journal of A griculture and Forestry 2013, 3(2): 40-51 45 Figure 4. The impact of desertification (moving sand), on houses in Nile state, Sudan (Photo: Mohamed El Fadl) Figure 5. The result of desertification, 2002 (Photo: Mohamed El Fadl. Nile State, Awateeb village) 4. Rainfall Patterns of the Sahel and the Sudan Results from various sources indicated that the Sahel region is renowned for its twin environmental problems of drought and desertificat ion. Evidence fro m various reports[34, 35, 36, 37, 38, 39, 40], indicated a downward rainfa ll trend.[41,42], reported that the documentary records based on the last 70 years show a slight decline in rainfall fro m 1955 and acute drought in 1968 and rain fall below average up to 1973. Th is decline in rainfall results in the familiar pattern of vegetation degradation, soil erosion, and decreased crop yields and livestock productivity coupled with an increase in migrat ions of people. Generally, a ma rked and progressive deterioration of ra infa ll has occurred since the mid-1960s culminating in the mid-1980s. These patterns can be seen from the annual rainfall series in the study area (see Figure 6). 46 Omar A. Abdi et al.: Causes and I mpacts of Land Degradation and Desertification: Case Study of the Sudan Figure 6. Annual rainfall time series expected as seven-year running means in the following locations in the Sudan: (a) (●) Juba; (■), Wau; (▼), Malakal.(b) (●), Ed Damazin;(■), El Gedarif; (▼), Nyala; (▲), El Obeid; (c) (●), El Fasher; (■) Kassala; (▼), Wad Medani; (d) (●), Shambat; (■), Dongola; (▼), Port Sudan. Source:[42] Rainfall variability on a time scale fro m years to days is as much a characteristic of climate as the total amount of rainfall recorded. Low values, however, do not necessarily lead to drought; nor is drought necessarily associated with low rainfall. The reality is that in drylands rainfall is fluctuating, and therefore good and bad years will continue to occur. Some regional patterns of rainfall can be exp ressed in terms of variability, trends (upward or downward), and persistence. Even allowing for the differences between countries in individual years, the period 1960-1993 has experienced widely d ifferent conditions fro m year to year. The years from 1960 to 1963 were among the wettest of the period, while the seventies and eighties experienced, for the most part, lower rainfall. The downward trend fro m 1960 to 1970 affected the whole continent, but only had a negative impact on food production in the low rainfall areas. The years 1973, 1984, and 1992 were bad, while 1963, and, to a lesser extent 1989 were remarkable years in that almost the whole continent experienced above average conditions. The year 1973 was interesting in that it constituted the first poor year after a run of good years. As such, it caught most countries unprepared. In contrast, the impact of 1984, which was more severe than 1973 in climatologically terms, was less serious for the economies of many countries wh ich was also the race in the Sahel. In 1973 almost all the African countries suffered, north and south alike. The Sahel area, including the Sudan is one of the driest and most variable in Africa. Runs of dry years and runs of wet years are a typical feature of the climate of the countries, in this sudano-Sahelian group where extreme years (either good or bad) are more likely than average ones. There is a misconception about the term among many scholars who think it means the sea shore. The Sahelian zone lies between the Sahara in the north and the Sudanese zone in the south. It is spreads in a fringe along the desert fro m the Atlantic Ocean to Ethiopia, So malia, and Kenya. The Sahelian zone passes progressively into the desert in the north as rainfall decreases and in the south it is rep laced gradually by the savannah. There is a belief that desertification in the Sahelian belt is spreading southwards at the rate of 6-10 km per year. The Sudano-Sahelian zone experienced a downward trend in rainfall until 1988, wh ich was followed by a series of about-average years. The worst drought years were 1983 and 1984, but severe droughts were also recorded in 1972, 1973, and 1977 (see Figure. 7). Deficiencies in the nu mber, quality, and length of rainfall records make it extremely difficult to construct an accurate chronology of precipitation behavior in the Sudan as a whole. Nevertheless, it is possible to make some observations about rainfall behavior during this century. The declining trend in rainfall is expected to continue in the Sahel region[43, 44, 45]. In the first half of the century, and especially in the first decade, the climate of the Sudan was probably drier than it had been during the second half of the nineteenth century. The s ingle driest five-year period recorded in Khartoum in the 20th century was centered on 1912 with 101 mm.[46] pointed out that 1913 was a part icularly d ry year, with the isohyets 150 km or more south of their mean positions; the Nile flood was the poorest during the period of modern records. The available data suggests that annual rainfall International Journal of A griculture and Forestry 2013, 3(2): 40-51 47 totals below 100 mm must have been co mmon in the Sudan at this time. Fro m 1920 (see Figure 8) the climate became noticeably wetter, with more reliable rainfall fro m year to year and several sequences of years when rainfall exceeded the recent 30-year on averages. At Khartoum the five-year period centered on 1922, with 289.8 mm of rain, was the wettest on record, but at Ed Dueim the wettest period occurred later, with a mean of 428 mm in the five-year period centered on 1938. In 27 out of the 39 years between 1920 and 1956 general precipitation totals were above the long period normal figures. Undoubtedly, agricultural practices and planning decisions that were made during this favorable wet period need to be reviewed in the light of precipitation behavior in the last two decades. Climatic parameters have both a direct and indirect impact on many land degradation processes, especially through their impact on vegetation and soil conditions. Rainfall variab ility is an important factor in d ryland climates[47]. Drought has been shown to be one of the ext reme climat ic stresses that contribute to land degradation processes[48]. Figure 7. Rainfall patterns in the Sahel and the Sudan[44, 45] Figure 8. Rainfall trends in the Sudan from 1900 to 1980 (http://www.unu.edu/unupress/unupbooks) 48 Omar A. Abdi et al.: Causes and I mpacts of Land Degradation and Desertification: Case Study of the Sudan Figure 9. Sahel Precipitation Anomalies 1900-2011 June through Ochober averages over 20-10 N, 20-10 E. 1900-2011 Climatologic. Source: NOAA Global Historical Climatology Network Date[52] 5. Recent Trends in the Sahel Rainfall Regime Figure 9 shows that the general rainfall trend seen in the Sahel was mirrored in the Sudan: the wet 1950s and 1960s were followed by a pro longed dry spell in the Sahel starting in the late 1960s lasting until the early 1990s. The Sahel has remained drier than normal well after 1995. The general trend towards more rain in the Sahel in the 1990s and early 2000s is also seen in the Sudan. Available statistics indicate that current trends in the Sahel rainfall regime led to divergent conclusions: while[49] that the Sahelian drought ended during the 1990s, in a recent co mprehensive review,[50] reported that a rainfall recovery occurred in the northern Sahel (north to 16o N) over 1998–2003 but that this recovery was limited further south. In a study,[51] realized that with respect to the 20-year wet period 1950–1969, the 20-year dry period 1970– 1989 was characterized by a smaller number of rain events of approximately unchanged intensity. It is reported that this decline was especially evident for the core of the rainy season, over western Sahel, dry conditions are still do minant[52]. 6. Effects of the Drought in the Sudan Sudan is frequently subjected to drought, which is the main limiting factor on b io mass production, and crop yields.[53], reported the first serious sign of soil degradation in the Sudan]. He reported that there was rapid deterioration of soil and vegetation were occurring in parts of the Red Sea Hills which he considered as a warning that such problems might be developing elsewhere, particularly around town peripheries and settlement areas in the Kordofan and Darfur Provinces of western Sudan. The population pressure in Sudan appears still to be growing, to judge fro m the growth in area of cultivated land[54]. Nevertheless, a little caution is needed regarding the explanation. Studies of degradation, even in Africa, have not found it easy to relate population densities to degradation. For examp le, in the same part of Sudan to which[55], referred,[56] could find no correlations between population density and degradation. There are several reports, which argue that, growth rates in dryland populations among paternalists at least are not high[57]. In the Sudan, the slash and burning of natural forests and bush lands in order to clear land for agricu lture is considered one of the main causes of deforestation and vegetation removal that contributes significantly to desertificat ion. 7. Agroforestry for Sustainable Land-use in the Sudan In Sudan, the current trend is mainly one of increasing exploitation of the natural resources, leading to over-exploitat ion in large areas, o wing to the lack of alternatives for a growing population. Generally, external inputs such as chemical fert ilizers are either co mparat ively difficult to come by or lacking in the Sudan. The use of these inputs is not lucrative under the present circumstances, and land productivity depends largely on the natural resources. The adverse effect of over-exp loitation is characterized by environmental degradation, scarcity of tree products, marginal crop and pasture yields, removal of vegetation cover by overgrazing[58], soil loss as a result of monocropping, and over-grazing lead ing to erosion, water run-off and loss of topsoil or soil nutrients, and reduction of biodiversity (local disappearance of the most palatable and useful species, fodder trees and most wildlife[59]. Clearly farming systems in the Sudan have come under International Journal of A griculture and Forestry 2013, 3(2): 40-51 49 some stress as the pressure on farm land increases. The challenge now is to look fo r more sustainable ways of farming. It is for this reason that innovative approaches in farming practices are sought all over the world for ‘sustainable’ farming systems. Owing to adverse impacts of land degradation and desertificat ion with consequent decline in agricultural productivity, it is necessary to avail to the farmers a technology that is acceptable to them, as a means of rehabilitating the degraded drylands. One such appropriate method is the use of agroforestry[60]. Thus agroforestry technology has been seen by many as a potential solution to this continued problem o f declining rural agricultural production in the tropics and for that matter, the Sudan[61, 62]. Agroforestry as an "informal" art based on knowledge is an age-old land use principle that has been practiced for thousands of years by farmers all over the world [63, 64]. As the word and concept became generally accepted in international land-use domains, many defin itions of the term were put forward, as described in detail by[65].The definit ion of agroforestry that the World Agroforestry Center (known as the International Center for Research in Agroforestry, ICRAF before 2002) has used since the early 1980s is as follows: “Agroforestry is a collective name for all land-use systems and practices in which woody perennials are deliberately grown on the same land management unit as crops and/or animals. This can be either in some form of spatial arrangement or in a time sequence. To qualify as agroforestry, a given land-use system or practice must permit economic or ecological interactions between the woody and non-woody components”[66]. This definition provides a classification in agrosilvicultural (trees with crops) and silvopastoral (trees with pastures) practices, sequential and simu ltaneous systems in zonal and mixed arrangement o f trees and crops. The aim of agroforestry practice is to provide rural communit ies with timber and wood fuel; control water and wind erosion, imp rove soil fert ility; provide livestock fodder, increase yield; provide income to the rural co mmun ity, thus contributing to rural development[67]. The Forests Act 1989 of the Sudan has already stressed the need to practice agroforestry and obliged large-scale mechanized farmers to leave or to plant a percentage not less than 10% of the total area o f a rain fed pro ject, and a percentage not less than 5% of the total area of an irrigated project, in the form of wind breaks or shelter belts for the purpose of protection and production[68]. Major mu ltipurpose trees that can be grown on agricultural lands in the area include Acacia senegal, Acacia seyal, Eucalyptus and Ziziphus. These trees can protect the soil against erosion. The trees also enhance infiltrat ion of water into the soil. They “mine” nutrients fro m deep soil and make them available to shallower depths through (main ly) litter fall. Measures of soil fert ility have shown increased levels of nitrogen, phosphorous and organic matter under Acacia trees. Increase in crop yields is estimated to be as high as 15%. More research is needed on the critical ro le wind breaks and shelter belts play in increasing agricu ltural p roduction. 8. Conclusions The desertificat ion in the Sudan is the co mbination of both natural and human factors, wh ich results in a decline of productivity or the degradation of natural resources, such as the constant destruction and deterioration of the land, which reduces the usefulness of these areas to man. It is impossible to separate climate-induced factors, wh ich caused environmental changes from land degradation induced by humann activity. In extreme situations, drough or recurrent drought has worsened in the case of the Sahel, and in Sudan in particular. In the Sudan rainfall is the most limiting factor, as it is erratic and unevenly distributed. The people of the Sudan depend, economically, on agricultural crop production and animal husbandry and both practices have a direct impact on dryland degradation. Unsuitable and damaging forms of land use are the main causal factors of land degradation and include: Overcult ivation, overgrazing, shifting cult ivation or slash and burn techniques, tree felling and illegal logging. The nomadic life-style of the rural co mmunit ies located next to forest land has also contributed to the depletion of resources as a result of conflicts amongst themselves and with other stakeholders over scarce resources which are in a fragile condition. Population growth is a major cause of land use-change, as farmers try to grow more food to feed rising numbers of people by increasing either the yield per hectare or the area under cultivation. So current forms of land tenures or the lack of clear landowning policies constrained the imp lementation of sustainable management strategies for controlling or rehabilitating the degraded lands, because there is a tendency to be careless about communally-owned land. Polit ical factors also have great influence on deterioration and land degradation in terms of conflics, corruption, unstable land tenure systems, bad policies, institutional and market fa ilures. REFERENCES [1] Le Houérou, H. N, "The Grazing Land Ecosystems of the African Sahel" , Springer Verlag, Berlin, 1989. [2] Pu, Bing and Kerry H. C, "Role of the West African Westerly Jet in Sahel Rainfall Variations". J. Climate, 25:2880–2896, 2012. [3] Goodin, J.R and Northington D. K, "Arid and semi-arid lands: Characteristics and importance Arid and semi-arid or sub-humid zones are characterized by low erratic rainfall" , 1985. [4] Pardo, G., J. Carero, J. Aiber, C. Zaragoza. Nutrient Evolution in Soil and cereal yield under different fertilizertion Type in Dryland. Nutrient Cycling in Agroecosystems, 84:267-279, 2009. [5] Keller, A. A and Goldstein, R. A, " Impact of carbon storage

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