Field studies of land use have provided information of great relevance to global and regional atmosphere-biosphere modeling. For example, coarse-resolution satellite data tend to represent the predominant soil type or vegetation in each grid cell, even if a minor soil or vegetation type is of major economic or ecological significance. Such a representation of the data can seriously misrepresent land use and productivity potential as well as biogeochemical cycles. Another important development is the focus on explaining trends and patterns in land use intensification, in which crop yields are increased through the use of agricultural chemicals and irrigation, resulting in alterations in regional and global biogeochemical cycles and ecosystems.

Progress in the past decade is evident in the rise of an International Human Dimensions Programme/International Geosphere-Biosphere Programme (IHDP/ IGBP) core project on land use/land cover change, with a coordinated, comparative, multilevel strategy for understanding, monitoring, and modeling land use.36 In developing frameworks, case studies, and models of how social forces drive changes in land use and land cover, this type of comparative research program has the potential to explain and predict land use change but also to assist in identifying strategies for managing land use and protecting ecosystems.

Recent important U.S. initiatives include the expansion of the population program at the National Institute of Child Health and Human Development (NICHD) into population and environmental research in 1995, the creation in 1996 of an NSF-funded research center that works on land use— the Center for the Study of Institutions, Population and Environmental Change at Indiana University—and the National Aeronautics and Space Administration's (NASA) Land Use Cover Change request for proposals. In summary, there has been considerable progress in understanding the human causes of land use change, including the following insights:

  • Humans have been altering land cover and use for centuries.

  • Some regions that now appear pristine have been subject to human management since prehistoric times.

  • There is no simple relationship between population and deforestation or between common property rights and resource degradation.

  • The analysis of institutions—in their broadest sense, including political, legal, economic, and traditional institutions—and their interactions with individual decision making is critical in explaining land use.

  • Satellite images can provide important insights for social science, and social science can help guide satellite programs to useful applications.

  • The age and gender structure of landholding households affects how much forest is cut for farming.

  • Tax incentives affect Amazonian deforestation.37

  • Secure land tenure is important to long-term resource conservation. 38

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