Range lands have become subject to many pressures; socio- economic and environmental. In western economies such as the west USA and Australia range land degradation is due to over stocking and irrigation systems that have caused salinization of the soil. Chemical inputs have also played their part. In developing countries especially in Africa, range lands have become degraded due to a number of interconnected relationships and feedback mechanisms. From governments and arbitrary borders being hostile to nomadic peoples to the imposition of western ideas of ranching and 'carrying capacity' to the influence of the world economy. Population pressure in such areas seems to be worse when a more sedentary agricultural life style is adopted or forced upon nomadic people or people moving in from other areas. Traditionally nomadic people overstock their herds as insurance against hard times, opportunistically exploiting the erratic and the localised nature of rainfall. The key is mobility, (transhumance) which in modern times has been largely eradicated and pastoralists have been forced to operate in increasingly narrower and marginalised areas. Agriculture and protected areas are largely to blame denying pastoralists traditional feeding grounds.
As cash crops and plantations dominate the best land in conjunction with increasing population pressures, people are forced to cultivate more marginal areas not suited to agriculture, with decreasing fallow periods reducing soil fertility. The removal of vegetation for fuel also degrades the land by breaking the nutrient cycle and facilitating erosion and desertification. In other instances a lack of population is the problem as people migrate out leaving fewer people to maintain irrigation channels and fields and forced to collect wood from a narrower range.
Inequitable access to resources has meant that large rich landowners are able to have large herds to supply the beef demand from the west. In Brazil even if herds are inefficient, unprofitable and cause deforestation and degradation of the land, owners are still able to receive large returns through tax write offs and land speculation.
Arid, semi-arid or subhumid zones are characterized by low erratic localised rainfall of up to 700mm per annum, periodic droughts and different associations of vegetative cover and soils. Interannual rainfall varies from 50-100% in the arid zones of the world with averages of up to 350 mm. In the semi-arid zones, interannual rainfall varies from 20-50% with averages of up to 700 mm. Regarding livelihoods systems, in general, light pastoral use is possible in arid areas and rainfed agriculture is usually not possible. In the semi-arid areas agricultural harvests are likely to be irregular, although grazing is satisfactory.
Range lands have highlighted the conflicts of development theory. On the one hand is the western ideal influenced by equilibrium theory and the need to manage nature in well defined systems. The belief that rangelands in arid areas are delicate and can only support a certain 'carrying capacity' determined largely by the level of technology. On the other is the belief that rangelands are resilient, with traditional methods of management responding opportunistically in a chaotic environment.
Deterioration in soil and plant cover have adversely affected nearly 50 percent of the land areas as the result of human mismanagement of cultivated and range lands. North America and Spain have the largest percentage of their arid lands affected. Overgrazing and woodcutting are responsible for most of the desertification of rangelands. About 18 percent of the arid region of Africa is severely desertified.