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the adverse repercussions of broad-scale deforestation. But in the main, the damage will have been done. For reasons of island biogeography and equilibration, some extinctions in Amazonia will not occur until well into the twenty-second century, or even further into the future. So a major extinction spasm in Amazonia is entirely possible, indeed plausible if not probable.
TROPICAL FOREST AND CLIMATIC CHANGE
Protected areas are not likely to provide a sufficient answer for reasons that reflect climatic factors. In Amazonia, for instance, it is becoming apparent that if as much as half the forest were to be safeguarded in some way or another (e.g., through multiple-use conservation units as well as protected areas), but the other half of the forest were to be developed out of existence, there could soon be at work a hydrological feedback mechanism that would allow a good part of Amazonia’s moisture to be lost to the ecosystem (Salati and Vose, 1984). The remaining forest would likely be subjected to a steady desiccatory process, until the moist forest became more like a dry forest, even a woodland—with all that would mean for the species communities that are adapted to moist forest habitats. Even with a set of forest safeguards of exemplary type and scope, Amazonia’s biotas would be more threatened than ever.
Still more widespread climatic changes with yet more marked impact are likely to occur within the foreseeable future. By the first quarter of the next century, we may well be experiencing the climatic dislocations of a planetary warming, stemming from a buildup of carbon dioxide and other so-called greenhouse gases in the global atmosphere (Bolin and Doos, 1986; DoE, 1985). The consequences for protected areas will be pervasive and profound. The present network of protected areas, grossly inadequate as it is, has been established in accord with present-day needs. Yet its ultimate viability will be severely threatened in the wake of a greenhouse effect as vegetation zones start to migrate away from the equator with all manner of disruptive repercussions for natural environments (Peters and Darling, 1985; Peters, Chapter 51 of this volume).
These, then, are some dimensions of the extinction spasm that we can reasonably assume will overtake the planet’s biotas within the next few decades (unless of course we do a massively better job of conservation). In effect we are conducting an irreversible experiment on a global scale with Earth’s stock of species.
REPERCUSSIONS FOR THE FUTURE OF EVOLUTION
The foreseeable fallout of species, together with their subunits, is far from the entire story. A longer-term and ultimately more serious repercussion could lie in a disruption of the course of evolution, insofar as speciation processes will have to work with a greatly reduced pool of species and their genetic materials. We are probably being optimistic when we call it a disruption; a more likely outcome is that certain evolutionary processes will be suspended or even terminated. In the graphic phrasing of Soulé and Wilcox (1980), “Death is one thing; an end to birth is something else.”