ABSTRACT
Approximately half of all tropical land surfaces can be classified as humid, with rates of annual rainfall equalling or exceeding those of evapotranspiration. The remainder is subhumid or semi-arid (National Research Council 1993). About 60 countries occur entirely or partly within the humid tropics and in 1991 these contained, in aggregate, over 2 billion persons (National Research Council 1993). Per capita GNP for these countries averaged $1, 262 and rates of natural population increase varied from 1.1 to 3.8 per cent per annum. These rates translate into population doubling times of 62 and 18 years, respectively. Thus these countries are not only generally poor, but likely to grow rapidly more so at the present rates of population increase.
