duction. Unless this intensification is addressed by new technologies that are not now in the pipeline, we can expect additional impacts on global climate change from land use conversion and ntensification —for example, use of nitrogen fertilizer may increase by a factor of 6 to 10. This and other increased material inputs into agricultural production will have environmental implications that are not yet well understood, but that are likely to include impacts on global environmental systems. In addition, as agricultural intensity increases, the effects of any environmentally induced changes in the productivity of agricultural lands will increase proportionally; and to the extent that nonagricultural demands on the land also grow, options for responding to those effects will be limited. For these reasons, it is important to understand the linkages of agricultural and other demands on land, land use change, and changes in agricultural and industrial metabolism or ecology.
The role of market forces in land use change for the production of agricultural commodities has long been a subject of substantial research. The issue of land use and supply response was an active field of research in agricultural economics and development economics from the mid-1950s through the 1960s (Krishna, 1967). There is also a literature on the relationships of population change and land use change in the tropics (Grainger, 1992; Jolly and Torrey, 1993).
Efforts to estimate global demand for agricultural land depend on data on market forces and population. But because these data often exist only at the national level and above, it can be difficult to model processes at the subnational (regional and local) levels, where actual land use change is taking place. There, a wide variety of social, political, and cultural institutions mediate the pace and character of land cover conversion for human use, the interaction of market and nonmarket influences, and the influence of national and international policies. In order to understand the driving forces of land use change at the global level, it is essential to know the mechanisms and dynamics by which land use managers at the local level govern land. That includes analysis of land use institutions, assessment of short-term biophysical constraints and feedbacks, and cross-scale macroeconomic and macropolitical influences involving markets and states.
A focused research effort on land use change will support the wider needs of the USGCRP in at least the following ways:
by improving forecasts of the future status of land cover and thus changes in the earth's albedo and other physical parameters affecting climate change;