Research on population growth and land use change has been made more complicated by the use of two conflicting paradigms, one based in natural science (or classical economics) and the other in neoclassical economics. The natural science paradigm places more emphasis on the finiteness of resources than on technological and institutional change and the accumulation of physical and human capital. This paradigm views population growth as a threat to the inherent limits of arable land to provide food, shelter, and sustenance. The neoclassical economics paradigm emphasizes the accumulation of both physical and human capital and the substitution of abundant factors for scarce ones. This paradigm suggests that population growth can be the impetus for technological and other changes that mitigate or even eliminate the effects of natural resource limits on economic well-being. Empirical research is capable of indicating which of these paradigms has more explanatory power, but the research base is thin and has not yet led to a body of knowledge on which public or scientific consensus has developed.
Much of the empirical research done under the natural science paradigm has focused on estimating carrying capacity to identify areas of population pressure. Research has also analyzed the effects of increasing human populations on species loss and ecosystems. A large study, undertaken by the Food and Agriculture Organization (FAO), analyzed the ''population supporting capacities'' of 117 developing countries and concluded that over half of the countries could not achieve food self-sufficiency by the year 2000 with low levels of inputs (mainly labor). Almost a third of the countries could not meet their needs even with an intermediate level of inputs (some fertilizer tools and simple conversation techniques). Nineteen countries could not meet their needs even at very high levels of inputs (advanced technology, complete mechanization, and all necessary conservation measures [Higgins et al., 1983]).
This is the beginning of an important research area, not its culmination. Clearly the workshop papers and discussion raised more questions than they answered. The current population growth rates in some of the developing countries make this research not only important but essential to their ability to accommodate their future populations. Therefore, the questions raised by these workshop papers will be used to direct the subsequent work of the Committee on Population and, we hope, others in this area with the purpose of stimulating new research on the relationship between population growth and land use change in the future.
The problems of scale and time horizon require that further research be focused on carefully designed and coordinated case studies, such as have been included in this volume. Indicators of how to measure and judge land use change need to be developed. Mortimore's case study of northern Nigeria suggests what some of the physical indicators might be; DeWalt's case study utilizes some of the social indicators. Only when there is a much larger number of sophisticated case studies will we be able to generalize about how current and future population growth rates in the world are likely to change land use.
Despite some careful research examining the relationship of population growth and land use change, we are still reviewing the beginning of an applied discipline rather than reviewing a mature body of research. The growing importance of these relationships to many countries is inconsistent with the lack of broad, systematic research attention. This lack of a thorough body of research, however, is due in part to some of the problems mentioned in this introduction. At this stage, methodological suggestions are easier to make than substantive conclusions.
Boserup, E. 1965 The Conditions of Agricultural Growth: The Economics of Agrarian Change Under Population Pressure. Chicago: Aldine Press.
With clear property rights, robust soils, and efficient markets, population growth is less likely to result in land degradation. Under these conditions, rapid population growth, which results in larger markets for agricultural products, gives land owners incentives to protect soil quality, which they are able to do by borrowing in relatively efficient capital markets. At the same time, land ownership provides collateral for the borrowing needed to invest in the protection of soil. Most real situations are somewhere between these two extreme scenarios, and more research is needed on the role of these conditioning factors in different areas.
Because the effects of population growth on land use depend on many factors, case studies that clearly delineate the relative role of these factors are needed. Among these conditioning factors are markets for agricultural and forestry products, land tenure systems, soil quality, climate, and capital markets. The workshop case studies suggest that population growth is most likely to result in land degradation when land is held in common without rules governing its access, when production is mainly for subsistence, and when the soil is fragile and rainfall light. Under these conditions, fast population growth clearly creates potential for producing soil degradation. Parts of Africa may fit this pattern, but the northern Nigeria case study by Michael Mortimore shows that the farmers have adapted quite well to the doubling of their population.
It was noted in conclusion that the workshop focused primarily on changes in the states or faces of the earth—how much deforestation is occurring, how much soil is being lost, etc. What needs more attention are changes in biogeochemical flows in which land use plays a major role. For example, feeding 10 billion people will require increased fertilizer use. If fertilization is intensified, methane production will increase, which may interfere with attempts to sustain the biosphere as we know it. Land use is an important factor, but it is related to many others that change with population growth.
Most of the changes in land use associated with very rapid population growth are likely to be disadvantageous for human beings. The changes that Boserup and others have described show that as populations grow, the technology required to maintain output is more expensive and requires more investment and labor. These are mainly the direct, on-site costs. There are also indirect, off-site costs that may be as great or greater than the on-site costs. They include salinization resulting from irrigation and contamination of common property resources (resources that are commonly owned, but without rules or regulations governing their use) from fertilizer use.
more food, a situation that will affect how land is used for agriculture. The evidence is partly historical, as illustrated in M. Gordon Wolman's paper, which shows that land use patterns over the last 6,000 years are associated with the expansion of the human population. These associations have existed for over three decades in Thailand as documented in Theodore Panayotou's case study. There is also cross-sectional evidence, as illustrated in Richard Bilsborrow and Martha Geores's paper, that notes a correlation between a country's population density and the percentage of its arable land that is used in production. Finally, evidence based on Ester Boserup's model and research shows how population increases induce people to cultivate additional land or to farm their present land more productively, as demonstrated in Robert Evenson's paper.
Lele, U., and S. Stone 1989 Population Pressure, the Environment and Agricultural Intensification: Variations on the Boserup Hypothesis. Madia Discussion Paper 4. Washington, D.C.: World Bank.