Recent studies have discussed relationships between narrowly defined ecosystems and human activities or human biology.' These have led to interesting developments in the concept of human adaptation to extreme environments. and to a better understanding of the human ecology of small isolated groups, but the results have had limited applicability. Most human groups capitalize on resources from several different zones rather than confining their activities to a single zone, and humans characteristically make major modifications of the microenvironments in which they live. Moreover. the association between human activities and particular ecological zones has become progressively weaker Modern technology has led to increased ability to make extensive or localized environmental modifications, and these modifications have increased with the growing densities of human populations Population movements between ecological zones have become more frequent, and local economic systems have been increasingly affected. modified, or dominated by regional, national, and world wide economic systems. For these reasons it is appropriate for us to consider human activities and resource use within the region of Northern Thailand in terms of interaction between the two major ecological zones or types-the highland and the lowland. Emphasizing the interactions between zones is a break with the tradition of planning for development within a single zone which assumes correspondence with the boundaries of a self-contained system. This has proved to be an unrealistic and ineffective approach, particularly in the highlands.