desertification in north darfur state4

Click here to load reader

Post on 02-Jul-2015




0 download

Embed Size (px)


Desertification in North Darfur State


  • 1. 35Desertification in North Darfur StateSalih Ahmedai Abdalla, Faculty of Environmental Sciences and Natural ResourcesAl-Fashir University-Sudan 011 011 - 05319115 . 9.0 9115 01 93 . . 931 / . 01 / 9110 -0595 911.1 / 0551 - 059091 % - . 39191 . 01 . - 9111 9111 . 0500 - 9111 0509 - 0595

2. 30-0511 0510 . 0519 - 0515 0551 0555 031 99 % 9111 - 9113 51 % 31 % . - 91 . .AbstractThe climate of North Darfur State is semi-desert and desert to the north. The rainfall in about 200-400 mm with a rainy season of 2 to 2.5 months. It had a population of 2.1 million according to 2003 census and the population growth rate is about 12% per year and the population density from 3 persons /km2 in 1956 to 18 persons / km2 in 2003.Farmers practiced cultivations of millet, sorghum, sesame and groundnuts during the rainy season and they keep livestock. Cultivation of crops reached areas receiving 150 mm and crop rotation is reduced resulting in decrease of soil fertility and yields. The spread of rain-fed cultivation farmers used to cut the trees often fired the bush destroying most trees and seedlings. They used large amount of wood 3. 33for fuel, constructions, tools and fencing. Subsistence needs are considered to be about 250 kg of cereals/person/year. Millet yields in North Darfur State about 60 kg/fed during the period 1973-2004 and for sorghum 111.6 kg/feddan during 1970-1990. Livestock number about 40 million. Average annual deforestation rate was 77% between 2000 -2005 and Darfur has lost more than 30% of forests since Sudan's independence and rapid deforestation is going.The destruction of the vegetation through pearl millet cultivation, overgrazing and clearing of woodlands led to the loosening of the sandy soil and its exposure to the influence of strong winds. The dominant processes are wind and water erosion. The amount of the dust in air has increased. Sand accumulation is often regarded as the actual desert encroachment because the newly formed dunes encroach on settlements and fields.1-Environmental settingGreater Darfur consists of five states North, Central, East, South and West Darfur. North Darfur State lies between latitudes 12 N and 20 N and longitudes 21 52 E and 27 54 E and had a population of 2.1 million according to 2003 census. The climate of the state is semi- desert (a typical Sahel). In the Sahel zone three divisions are recognized. The sub-desert (200mm), the typical Sahel( 200-400) mm with a rainy season of 2 to 2.5 months, and the Sahel of Sudanese border (400-600) mm with a growing season of 3 months. The main features of the climate are a short rainy and highly variable season, between July and September with unpredictable droughts and 90% of 4. 30the rainfall falls between July and September. The key features, which adversely affect agriculture, are the low and erratic rainfall. The economy of the state is based on traditional rain-fed farming, animal rearing and petty trading. The elevation of the state is about 600-900 m above sea level and the topography of the region is interspersed with various hills and mountains. Jebel Marra which is located between latitudes 12 25 N and 13N and longitudes 2410 E and 24 12 E, constitutes a volcanic mountain range about 135 km long and 80 km wide with maximum elevation of 3042 m and covering an area of about 8000 km2 .The region is situated in a transitional zone between the northern Sudan savannah and desert vegetation. The vegetation consists of annual grass and scattered bush steppe in the north, gradually merging in the savannah with perennial grasses and scattered trees (White, 1983). The vegetation classes based on structural type are: Woody grassland, with trees more widely spaced up to 15 m, and different species includes many broad-leaved types, which contains species such as Combretum , Terminalia, Baobab, anddifferent species of Acacia. The main types of grasses are Aristida. Ergrostis and Cenchrus. The trees are mostly including Acacia, Zizphus and Commiphora spp., Acacia Senegal is regarded as the characteristic tree in the sandy soils, in areas rainfall between 200 -450 mm, Aristida sieberana is dominated in clay soils, acacia mellifera is common. Semi-desert: on the margins of the desert, consist of Acacia, 5. 39Commiphora, Hymphaene ,Salvadora persica (Harrison and Jackson, 1958).Soil surveys carried out by Hunting Technical Services (HTS, 1976) divided Darfur region into six main soil classes: desert soils, stabilized dune sand, cracking clays, riverine soils, Nagga and alternating non-cracking clay soils. The two main soils in North Darfur State are the sandy soils and the dark clay soils. The sandy soils are mainly stabilized sand dunes known as qoz lands. They are deep and often uniform over vast areas forming the different dunes. Some dunes are quite pronounced, while others are heavily eroded and almost flat and having red, yellow and white. The dunes lie in one main direction, like the recent ergs or they may have a circular form without any specific orientation. They consist of 60% coarse fine sand and less than 10% clay. Soils developed on the recent erg have a coarser texture than those developed on materials deposited later. Plants can satisfactorily grow there but those with shallow root network dry up at the end of rains. Erosion by wind or water is high where the vegetation has been consumed or destroyed by livestock around watering places and nomads encampments. Large quantities of water can infiltrate at the collection points, contributing to growth of trees or feeding reservoirs. The landscape is generally flat and the dune slope between 1-3 % in various directions. These soils have been subjected to inappropriate management, leading to wind and water erosion (Brown and Hall, 1991). This was followed by organic matter and nutrient losses, which in turn affected soil physical, chemical and 6. 31thermal properties. The main causes of land degradation are inappropriate land use, mainly unsustainable agricultural practices such as clearing of agricultural lands, especially mechanized clearing, over-grazing, fuel wood extraction, building of settlements and bush burning. These wide spread effects on both cover and composition of vegetation. The intensification of these events due to human and ruminant's population has led to shortening of fallow periods, thereby limiting the regenerative capacity of soil flora and fauna. Also, the shortening of fallow periods under intensive cropping weakens the natural ability of soil to recover its fertility leading to land degradation, lower crop productivity and reduce income (Clunies- Ross and Hildyard, 1992). The main on-site effect of land degradation is the decline in yield which can amount to more than 50% or an increased need for inputs to maintain yields (Olaitan and Lombin, 1984). Moreover, the addition of fertilizers alone cannot compensate for all the nutrients lost when top soil is eroded (FAO, 1983).Where degradation is serious the plots may either be abandoned temporarily or permanently or converted to grazing land or left to shrubs. Yield reduction due to soil erosion may range from2-40% with a mean loss of 8.2%. If accelerated erosion continues unabated, yield reduction by 2020 may reach 16.7% (lal, 1995). Recent studies indicated that the storms were 34 and 51 incidents for2002 and 2003 in Al-Fashir (Ayoub,1999). Soil particles analysis showed that, soil samples of Khartoum State were medium textured including 20 sandy clay loam and 16 sandy loam, while North Darfur State were coarse textured 7. 35soil including15 sand,10 loamy sand and 6 sandy loam. For the wind erodibility indices, the range for Khartoum State and North Darfur State samples range from 0.0 to 259.3 and from 25 to 695 ton/ha, respectively (Medani, 2004)Farmers practiced cultivations of millet, sorghum, sesame and groundnuts during the rainy season and they keep livestock. The dominant grass species in the range land are panicum furgidum and Aristida hordeocea. The northern parts of the state is poor in forage trees and in the dry season supports only relatively small number of animals. Trees such as Acacia ehrenbergions , Salvadosa persidea and Acacia raddiana are very rare, scattered and they are small in size. Dry season range land: good grazing is found and cover large areas sometimes late until March. The common species are Commiphara Africa, Aristida mutabililis and Aristida funiculate.2- Land Degradation and desertificationDesertification is combinations of drought processes which result in more or less irreversible of the vegetation cover leading to the extension of new desert landscapes to areas which were formally not desert. The increasing destruction has influence through reduction of food production and loss of genetic resources of plants and animals. Desertification can be defined as: "the land degradation in arid and semi- arid and dry sub-humid areas resulting from various factors including human activities and climatically variations (UNCCD, 2001) ". 8. 01Land degradation is the reduction of the current and potential productive capacity of the land. Vegetation degradation is the quantitative and /or qualitative reduction of the vegetation cover resulting from various factors including human induced activities and severe prolonged droughts under poor land resource management Mustafa,2007). Despite adverse and fragile initial conditions of most tropical soils, human activities significantly contribute to land degradation, either directly or indirectly.2-1 Causes of desertificationa--Climatic variationDroughts have frequently happened as a natural disaster and