In 1871 Charles Darwin feared for the future of great apes. “At some future period, not very distant as measured by centuries,” he wrote, “the anthropomorphous apes … will no doubt be exterminated” (Darwin, 1871, p. 891). While Darwin's prognostication might seem gloomy, to those concerned with the conservation of great apes Darwin seems optimistic to have anticipated extinction in centuries rather than decades. The contemporary threats to tropical forests are so numerous and intense that most conservationists would be delighted if they could be assured that orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes), bonobos (Pan paniscus), and gorillas (Gorilla gorilla) would all still survive in the wild in 2100. Unfortunately, however, even such a modest hope may be unrealistic. The three most threatened species, orangutans, bonobos, and gorillas, are widely considered as candidates for global extinction within the next 100 years (Beck et al., 2001; Miles, 2005). If they go, so will large numbers of other animals and plants.

The problem would be bad enough if the scale of the threats to which tropical forests are currently exposed were to continue unchanged in the near future. All indications are, however, that the challenges of maintaining forests are going to grow enormously. This means that, if the tidal wave of forest destruction is ever to be turned back, a critical question is how much will be lost before then. What we do now will substantially affect the answer.