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is settled (i.e., the frontier is closed), various land-saving options are employed. Improved varietal technology (high-yielding varieties) reduces the pressure on resources. The combination of changing economic conditions and new technology brings cropland expansion to a halt in developed countries. Cropland expansion in farms in the United States stopped around 1920, and cropland area has declined in recent years. (Farm production has tripled since 1920.) This is also true for pastureland. The same situation holds in Europe generally.

Large areas of savannah-type land exist in sub-Saharan Africa and in the local Cerrado-Llianos region in Brazil and Colombia (with some in Bolivia and Paraguay). Agricultural research programs in these countries have sought to achieve efficient land use expansion and have been successful in facilitating land expansion in the Cerrado regions in Brazil. This expansion has also been fueled by subsidized credit, which has fueled expansion in the Amazon, where it is sink-reducing. On balance, the agricultural research systems in Brazil and Africa have facilitated expansion on sink-neutral or sink-expanding areas. It is not clear that any policies can materially change some of the land use patterns that will occur in much of Africa over the next few decades. Populations are growing at rapid rates, and few countries have effective family planning. To the extent that improved agricultural technology can be developed, it will alter the ultimate course of expansion of cropped areas. Industrial development and nonfarm employment opportunities for workers will, as well. Much of this expansion will be sink-neutral, however, because savannah lands are not large sinks. The most severe problems will be associated with desertification and the management of shorter fallow systems on savannah soils.

In developed and developing countries alike, however, even if oil prices do not rise appreciably over the next two decades, continued technological improvements are likely to bring some biomass energy options into the competitive range. No major breakthroughs are necessary (although some may be achieved). Continued support for well-established plant breeding and agronomic research programs is required to bring this biomass energy option.

Agricultural Greenhouse Gas Mitigation

General Options

For purposes of assessing the relative impacts of U.S. emission controls and controls in other countries, the range of emission reduction (million tons of carbon) from a 10 percent reduction in rice production or ruminant production in different regions is used in this analysis.1 The United States is a minor contributor of CH4 from rice paddies and contributes virtually