concentrations of species with exceptional levels of endemism and that face exceptional threat of depletion, whether quantitative or qualitative. They include the Choco forest of Colombia; the Napo center of diversity in Peruvian Amazonia, plus seven other centers (out of 20-plus centers of diversity in Amazonia) that lie around the fringes of the basin and hence are unusually threatened by settlement programs and various other forms of development; the Tai Forest of Ivory Coast; the montane forests of East Africa; the relict wet forest of Sri Lanka; the monsoon forests of the Himalayan foothills; northwestern Borneo; certain lowland areas of the Philippines; and several islands of the South Pacific (New Caledonia, for instance, is 16,100 square kilometers, almost the size of New Jersey, and contains 3,000 plant species, 80% of them endemic).
These various sectors of the tropical forest biome amount to roughly 1 million square kilometers (2.5 times the size of California), or slightly more than one-tenth of the remaining undisturbed forests. As far as we can best judge from their documented numbers of plant species, and by making substantiated assumptions about the numbers of associated animal species, we can estimate that these areas surely harbor 1 million species (could be many more)—and in many of the areas, there is marked endemism. If present land-use patterns and exploitation trends persist (and they show every sign of accelerating), there will be little left of these forest tracts, except in the form of degraded remnants, by the end of this century or shortly thereafter. Thus forest depletion in these areas alone could well eliminate large numbers of species, surely hundreds of thousands, within the next 25 years at most.
Looking at the situation another way, we can estimate, on the basis of what we know about plant numbers and distribution together with what we can surmise about their associated animal communities, that almost 20% of all species occur in forests of Latin America outside of Amazonia and that another 20% are present in forests of Asia and Africa outside the Zaire basin (Raven, 1987). That is, these forests contain some 1 million species altogether, even if we estimate that the planetary total is only 5 million. All the primary forests in which these species occur may well disappear by the end of this century or early in the next. If only half the species in these forests disappear, this will amount to several hundred thousand species.
What is the prognosis for the longer-term future? Could we eventually lose at least one-quarter, possibly one-third, or conceivably an even larger share of all extant species? Let us take a quick look at Amazonia (Simberloff, 1986). If deforestation continues at present rates until the year 2000, but then comes to a complete halt, we could anticipate an ultimate loss of about 15% of the plant species and a similar percentage of animal species. If Amazonia’s forest cover were to be ultimately reduced to those areas now set aside as parks and reserves, we could anticipate that 66% of the plant species will eventually disappear together with almost 69% of bird species and similar proportions of all other major categories of species.
Of course we may learn how to manipulate habitats to enhance survival prospects. We may learn how to propagate threatened species in captivity. We may be able to apply other emergent conservation techniques, all of which could help to relieve