It has been argued that overpopulation leads to too many people farming too little land, degrading it in a downward spiral. Surprisingly, though some researchers are finding that increasing populations lead to land rehabilitation if conditions are right.
This viewpoint traces back to Boserup's (1965) stimulating formulation of the 'induced innovation' model. He noted that as populations increase, the demand for food also increases - creating more remunerative opportunities for productive agriculture - and therefore incentives for farmers to invest more in their lands. Tiffen (2002) and Kaboré and Reij (2004) describe cases where this idea seems to be working, in places such as Machakos, Kenya, Gombe, Nigeria and the Central Plateau of Burkina Faso.
Tiffen and Bunch (2002) propose that these observations fit into a larger conceptual model of agricultural development. From the original state of virgin dryland, animal herding is sustainable as long as relatively few people are herding across large areas. But as populations and land pressure increase, too many animals overgraze and destroy the vegetation, starting the downward spiral of desertification. As they add farming without using fertilizers this further impoverishes the soils.
However, from this bottom point, an upward trend sometimes emerges, as has been documented in places like these. Tiffen (2003) further notes that rural population growth is currently leveling off in many parts of Africa while urban growth is accelerating - adding fuel to the fire of this market-driven revolution.
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Boserup, E. 1965. The Conditions of Agricultural Growth: The Economics of Agrarian Change Under Population Pressure. Aldine, Chicago.
Kaboré, D. and Reij, C. 2004. The emergence and spreading of an improved traditional soil and water conservation practice in Burkina Faso. EPTD Discussion Paper No. 114. Washington D.C.: International Food Policy Research Institute.http://www.ifpri.org/divs/eptd/dp/eptdp114.htm
Tiffen, M. 2003. Transition in Sub-Saharan Africa: agriculture, urbanization and income growth. World Development 31:1343-1366.
Tiffen, M. 2002. The evolution of agroecological methods and the influence of markets: case studies from Kenya and Nigeria. Pp. 95-108 in Uphoff, N. (ed.) Agroecological Innovations. London: Earthscan.
Tiffen, M. and Bunch, R. 2002. Can a more agroecological agriculture feed a growing world population? Pp. 71-91 in Uphoff, N. (ed.) Agroecological Innovations. London: Earthscan.