other groups, but also more ecologically effective and economically efficient (Liu et al., Chapter 9). Site-based studies have shown that environmental effects are seen most clearly when broad land use and environmental categories, such as the urban-rural distinction, are unpacked into more focused distinctions. For example, the distinction between primary forest and secondary forest is crucial to understanding the role of migration, land use practices, deforestation, and rates of regrowth in the Brazilian Amazon (Moran et al., Chapter 5). Site-based studies have shown that population–land use–environment relationships are scale dependent, that is, that the relationships that are evident at one level of spatial, social, or temporal analysis are not necessarily found when analysis is conducted at another level. Such findings caution against naïve generalization across scales and have opened the question of how interactions occurring at one scale affect or embed interactions at other scales.
Site-based studies have also led to methodological advances, such as in the design of multithematic longitudinal data sets, the development of methods to link population units to land units and land units to environmental effects, and innovative approaches to modeling. They have also led to improved methods of measuring land use variables by remote observation—a necessary building block for research that can compare larger numbers of sites.
The site-based approach has also clarified the key challenges for future research. One is to move from descriptive to causal understanding of population–land use–environment relationships. A major challenge is to improve comparability of data and analyses across sites in order to build generalizable knowledge. There is also the challenge of developing interdisciplinary collaboration across the wide range of sciences relevant to this topic and developing the capacity for this interdisciplinary research in the next generation of scientists.
After consideration of research developments over the past decade and the state of knowledge on population–land use–environment relationships, the panel makes the following recommendations for the continued development of this field.
1. Research should be increasingly coordinated to promote creation of a body of integrated knowledge. Knowledge about the relationships among demographic, land use, and environmental variables has been substantially enriched in recent years by empirical studies using new multithematic, multilevel, longitudinal, and spatially explicit data sets to describe and analyze these relationships at specific sites around the world. Of course, with respect to the development of general knowledge, there are inherent limitations of such site-specific studies, as noted in Chapter 1. Such general knowledge is critical for anticipating possible scale dependencies and cross-