Agricultural Land Degradation or Improvement
Land-cover change research also considers changes in the quality of land resources as a result of human uses. The most debatable issue in population-environment interaction concerns the relationship between increasing population density in subsistence agricultural and land degradation or improvement.
This is as a result of widely differing estimates regarding the extent of land degradation, with global estimates ranging from 20 to 51 million km2. On agricultural land degradation, there exist arguments and evidence as marshalled by two major schools of thought, the vicious circle proponents who believe that increasing population density in the context of high poverty almost inevitably leads to land degradation and the Boserupians who suggest that increasing density leads to intensification of agricultural systems such that yields per unit area (and per capita) are increased.
In the vicious circle in its simplest form suggested that, the model describes the following causal connections. Poverty leads to high fertility through mechanisms such as a demand for farm labour.
High fertility contributes to population growth, which further increases demands for food and resources from an essentially static resource, the declining per capita resource base reinforces poverty through soil fertility loss, declining yields, and poor environmental sanitation and poverty, in turn, contributes to land degradation by increasing incentives for short-term exploitation and because poor farmers lack access to costly fertilizers and other technologies.
The implication of these reinforcing linkages is that, absent intervention, the circle will continue and soil fertility will decline until the land is no longer suitable for crops or pasture.
Panayotou (1994), have suggested that children are valued by rural households, in part, because they transform resources (forests, fisheries, and rangeland) into household income.
Household-level responses to resource scarcity can lead to problems at the societal level as each household copes with increased risk and uncertainty by maximizing its number of surviving children.
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The Boserupian or intensification hypothesis has been tested in a number of studies spanning Africa, Asia, and Latin America.
A frequently cited study by Tiffen et al. 1996 examined changes in population density and agricultural productivity in Machakos District, Kenya. From 1930 to 1990, the population of Machakos District grew six fold, from 240,000 to 1.4 million people, with a 1990 population density of 654/km2.
The region is mountainous and semiarid (<500 mm rainfall a year), and in the 1930s, it was suffering already from soil erosion (mass wasting and gullies). The region was also isolated from national markets, and there were colonial restrictions on access to certain lands and crops.
In the 1950s and 1960s, a new form of terracing was propagated by local work groups, agricultural systems shifted from livestock to intensive farming with emphasis on higher-value crops, feeder roads were built to market towns, and market towns developed with agricultural processing facilities and other small industries.
By 1990, the value of agricultural production had doubled on a per capita basis. Many factors led to a positive outcome for this region, including infrastructure development, market growth, private investment, increasing management capacity and skills, self-help groups, food relief during drought, and secure land tenure.
This study confirms the basic Boserupian hypothesis: increased food demand, a denser network of social and market interactions, labour-intensive agriculture and economies of scale helped to avert a Malthusian crisis.
Mortimore (2005), also found similar scenario in three dry land areas of West Africa: Kano State in northern Nigeria, the Diourbel Region of Senegal, and the Maradi Department, Niger.
Outcomes were assessed in improved ecosystem management, land investments, productivity, and personal income. The author researcher found some common ingredients that resulted in improved or stable soil fertility and yields despite rapid population growth and high densities.
These include markets for agricultural produce, physical infrastructure, producer associations, knowledge management, and incentives for investment and income diversification.
He concludes that productivity responds to economic incentives and that the capacity of resource-poor farmers to invest in on-farm improvements should not be under rated.
These case studies bring out clearly that, population is but one among many factors that influence degradation or intensification.
Other variables that are of crucial significance include institutional factors (land tenure system, local governance, accessibility to resources), market linkages (road network, crop prices), social conditions (education, inequality of landholding), and the biophysical environment itself (original soil quality, slopes, climatic conditions).
Hence, it would appear that population growth is neither a necessary nor sufficient condition for either declines or improvements in agricultural productivity to occur.
Population growth can either operate as a negative factor, increasing pressure on limited arable land, or a positive factor, helping to induce intensification through adoption of improved technologies and higher labour.
Where it does which depends on factors in the economic and institutional systems, Mortimore (1994).
Population can be discounted as the only relevant variable; there is little doubt that rapid population growth in poor rural areas with fragile environments can be a complicating factor in the pursuit of sustainable land use, especially because policies and markets are rarely aligned in such a way as to produce the most favorable results.
