In terms of the changes it brings, desertification is viewed as an adverse environmental process. The negative descriptors used in these definitions of desertification include: deterioration of ecosystems, degradation of various forms of vegetation, destruction of biological potential, diminution of biological potential, decay of a productive ecosystem, reduction of productivity, decrease of biological productivity, alteration in the biomass, intensification of desert conditions, and impoverishment of ecosystems. Then, what is changed by desertification? Different definitions focus on changes in soil (e.g. salinization), or vegetation (e.g. reduced density of biomass), or water (e.g. water logging), or solar radiation (e.g. increased albedo). Most of them, regardless of primary emphasis, also describe changes in biological productivity, with comments related to the type, density, and value of vegetation.
Nigeria, which is located between latitudes 4oN and 14oN and longitudes 2o 2' and 14o 30' East has a total land area of 923,773 km2 and the population of Nigeria in 2006 was put at 140,019,952, divided almost equally between females (48.68%) and males (51.32%). Thus, Nigeria today accounts for about a quarter of the total population of the African countries south of the Sahara and its people consist of over 200 ethnic groups, speaking about 395 languages and dialects. By virtue of its spatial extent the country encompasses various climatic regimes and physiographical units that give rise to a wide variety of ecological zones. These zones range from flush forest vegetation in the south to Guinea savanna in the middle belt region, Sudan savanna in the north and Sahelian vegetation in the extreme northern part of the country. Of these ecological zones, the Sudan and Sahelian regimes are most vulnerable to climatic and human pressures.
There is a general consensus that desertification is by far the most pressing environmental problem in the drylands parts of the country. Nigeria loses over 350,000ha annually to advancing desert; the visible sign of this phenomenon is the gradual shift in vegetation from grasses, bushes and occasional trees, to grass and bushes; and in the final stages, expansive areas of desert-like sand. It has been estimated that between 50%-75% of Adamawa, Bauchi, Borno, Gombe, Jigawa, Kano, Katsina, Kebbi, Sokoto, Yobe, and Zamfara States in Nigeria are being affected by desertification and are particularly vulnerable to wind and erosion. These states, with a population of about 50 million people, account for about 43% of the country's total land area. In these areas, population pressure resulting in overgrazing and overexploitation of marginal lands has aggravated desertification and drought. Entire villages and major access roads have been buried under sand dunes in the extreme northern parts of Katsina, Sokoto, Jigawa, Borno, and Yobe States. The pressure of the migrating human and livestock populations from these areas are absorbed by pressure point buffer states such as the Federal Capital Territory, Plateau, Taraba, Niger, Kwara and Kaduna states. It is reported that these buffer states have about 10-15% of their land area threatened by desertification. This action leads to an intensified use of fragile and marginal ecosystems resulting into progressive degradation even in years of normal rainfall. However, desertification is made very severe in the drylands of the country by increasing human attempts to exploit the resources of the ecological zone in the face of persistent drought. It has been reported that over 50,000 farmers in about 100 villages scattered along the desert fringes of the northern states affected by desertification are currently at risk of abandoning this year's farming due to the sand dunes. These dunes are threatening life-supporting oasis and burying water points. Trees planted by government as shelter belts to check the advancing dunes are withering due to lack of attention. Similarly, shelters established by government along the desert fringes of the affected states under the World Bank-assisted afforestation programme have not been very effective as the trees have been felled for firewood, while some have withered due to high temperature, inadequate rainfall and drought. In the same vein, some boreholes dug by government to provide water have dried up due to acute drought aggravated by the effects of desertification in the affected zone. A report by the Federal Ministry of Environment says that Nigeria plunders its forest by more than 30 million tonnes for firewood annually due to pressure on the urban poor who resort to the cheapest means of cooking. The rate of fuel wood consumption far exceeds replenishment rate.
The consequence of human dependence on wood for fuel and construction, according to the report is that about 350,000 hectares of land is under the threat of deforestation annually, while the annual rate of reforestation is estimated at about 30,000 hectares Before now, Nigeria has been tackling the problem of desertification the best way it could, but with little success. It is now obvious that the menace should be addressed in a holistic manner in order to ensure that the drylands of the country continue to support human and natural resources.
The natural causes of desertification in Nigeria include the poor physical conditions of soils, vegetation and topography as well as the inherent extreme climatic variability as evidenced in periodic droughts. Climate variation is perhaps the most important natural cause of desertification and drought in the drylands of Nigeria while the anthropogenic factor is mainly the disruption of the ecological system caused by poor land use and ever-increasing pressure put upon the available resources by the expanding population. According to Medugu (2007), there are four primary causes, notably overexploitation, overgrazing, deforestation and poor irrigation practices; and these are influenced by factors such as changes in population, climate and socio-economic conditions. It is obviously a complex inter-relationship, which includes: poor physical conditions in terms of soils, vegetation, topography and inherent extreme variability of climate as manifested in frequent drought; disruption in ecological balance caused by poor land use and ever increasing demand being made on the available resources by the expanding population and socio-economic systems of the affected areas; and improper land-use practices and poor land management. Thus, desertification is a result of complex inter-relationships between social and natural systems.
Nasiru Idris Medugu is a PhD Researcher, Faculty of Built Environment, University of Technology, Malaysia.