according to bioclimatic data. There is also general agreement that between 76,000 and 92,000 square kilometers are eliminated outright each year, and that at least a further 100,000 square kilometers are grossly disrupted each year (FAO and UNEP, 1982; Hadley and Lanley, 1983; Melillo et al., 1985; Molofsky et al., 1986; Myers, 1980, 1984). These figures for deforestation rates derive from a data base of the late 1970s; the rates have increased somewhat since then. This means, roughly speaking, that 1% of the biome is being deforested each year and that more than another 1% is being significantly degraded.

The main source of information lies with remote-sensing surveys, which constitute a thoroughly objective and systematic mode of inquiry. By 1980 there were remote-sensing data for approximately 65% of the biome, a figure that has risen today to 82%. In all countries where remote-sensing information has been available in only the past few years—notably Indonesia, Burma, India, Nigeria, Cameroon, Guatemala, Honduras, and Peru—we find there is greater deforestation than had been supposed by government agencies in question.

Tropical deforestation is by no means an even process. Some areas are being affected harder than others; some will survive longer than others. By the end of the century or shortly thereafter, there could be little left of the biome in primary status with a full complement of species, except for two large remnant blocs, one in the Zaire basin and the other in the western half of Brazilian Amazonia, plus two much smaller blocs, in Papua New Guinea and in the Guyana Shield of northern South America. These relict sectors of the biome may well endure for several decades further, but they are little likely to last beyond the middle of next century, if only because of sheer expansion in the numbers of small-scale cultivators.

Rapid population growth among communities of small-scale cultivators occurs mainly through immigration rather than natural increase, i.e., through the phenomenon of the shifted cultivator. As a measure of what ultrarapid growth rates can already impose on tropical forests, consider the situation in Rondonia, a state in the southern sector of Brazilian Amazonia. Between 1975 and 1986, the population grew from 111,000 to well over 1 million, i.e., a 10-times increase in little more than 10 years. In 1975, almost 1,250 square kilometers of forest were cleared. By 1982, this amount had grown to more than 10,000 square kilometers, and by late 1985, to around 17,000 square kilometers (Fearnside, 1986).

It is this broad-scale clearing and degradation of forest habitats that is far and away the main cause of species extinctions. Regrettably, we have no way to know the actual current rate of extinction, nor can we even come close with accurate estimates. But we can make substantive assessments by looking at species numbers before deforestation and then applying the analytic techniques of island biogeography. To help us gain an insight into the scope and scale of present extinctions, let us briefly consider three particular areas: the forested tracts of western Ecuador, Atlantic-coast Brazil, and Madagascar. Each of these areas features, or rather featured, exceptional concentrations of species with high levels of endemism. Western Ecuador is reputed to have once contained between 8,000 and 10,000 plant species with an endemism rate somewhere between 40 and 60% (Gentry, 1986). If we suppose, as we reasonably can by drawing on detailed inventories in sample plots, that there are at least 10 to 30 animal species for every one plant

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