along rivers and coastlines. Rates of population growth in the humid tropics were generally low, and although ownership and control over prime agricultural land became increasingly concentrated in many areas, small-scale farmers migrated to intact forestlands on a relatively limited basis. Deforestation on the scale that has occurred more recently was technically and economically infeasible.

During the twentieth century, and especially in the past 5 decades, the rate of forest conversion has accelerated in response to economic pressures, population growth, technological developments, and programs and incentives to open lands for development (Hecht and Cockburn, 1989; Repetto and Gillis, 1988). Many of the physical constraints, such as the lack of roads and machinery for timber extraction, that had previously limited the intensity and extent of forest conversion have been overcome. At the same time, global markets for timber and other tropical products have expanded (Kartasubrata, Part Two, this volume; Ngandu and Kolison, Part Two, this volume; Serrão and Homma, Part Two, this volume). These factors have combined to encourage resource-poor countries to clear forests for timber and to convert forestlands to cash crops, plantations, pastures, and other uses of higher but shorter-term economic value (World Bank, 1992).

A classic example of deforestation brought about by population pressures and demand for agricultural land is that of the islands of Java and Bali in Indonesia (Kartasubrata, Part Two, this volume). In Côte d'Ivoire, which has one of the highest population growth rates in the world, population pressures combined with unstable shifting cultivation and logging have been a principal cause of deforestation. Part of the country's agricultural growth has been achieved at the expense of the natural resource base (Ehui, Part Two, this volume).

Forest conversion has followed diverse pathways in the humid tropics, but a general pattern can be discerned. The clearing of forests usually occurred first in areas where the soils and climatic conditions were most favorable for agriculture and for densely populated settlements and where transportation was not a major problem—islands and coastal zones, river basins, lowlands, and the more fertile uplands (Tosi, 1980; Tosi and Voertman, 1964). It then expanded to both wetter and drier life zones, initially affecting easily accessible forestlands. Less accessible lands are now being deforested, including areas unfavorable for human habitation and agriculture, such as steep slopes, mangrove swamps, and flood plains (Green and Sussman, 1990; Harrison, 1991; Kangas, 1990; Sader and Joyce, 1988; Smiet, 1990).