. "6 How Many Tree Species Are There in the Amazon and How Many of Them Will Go Extinct?--STEPHEN P. HUBBELL, FANGLIANG HE, RICHARD CONDIT, LUIS BORDA-DE-ÁGUA, JAMES KELLNER, and HANS TER STEEGE." In the Light of Evolution, Volume II: Biodiversity and Extinction. Washington, DC: The National Academies Press, 2008.
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In the Light of Evolution: Volume II—Biodiversity and Extinction
Extinction scenario 3 showed a significant “rescue effect” relative to scenario 1 for species with population sizes between 103 and 105 (Fig. 6.7b) even though the probability of survival of species in heavy-impact areas was small on a per-cell basis. A total of 3,085 species (27.5%) are expected to go extinct under extinction scenario 3, which is 571 fewer species than under extinction scenario 1, under the pessimistic case. There is also an ≈3% improvement in the mean survival of species with <103 individuals, but the extinction rate of these rare species is still very high, <47%.
One question we cannot answer is how many of these extinctions have already taken place. At the time this chapter was written, we did not have a map of areas already deforested in the Brazilian Amazon. It is quite clear that much of the Atlantic forest in Amazonia is already gone. This fact is reflected by the scant change in heavy-impact areas in the eastern Amazon between the maps for the optimistic and nonoptimistic deforestation scenarios. Thus, our estimates of extinction rates due to future deforestation are likely to be overestimates because they include species that have already gone extinct.
CONCLUSIONS AND CAVEATS
A controversy in recent years has been developing over the future of the Amazon. On the one side are scientists legitimately concerned with the rapid deforestation of the Amazon and the potential consequences for not only species extinction but also for the loss of ecosystem services, such as climate amelioration, soil conservation, and the welfare of wildlife and other species that depend on the trees for their survival (Laurance et al., 2001, 2002, 2004; Brooks et al., 2002). On the other side, however, are scientists who believe that the short-term extinction threat, particularly from human population growth, is greatly exaggerated, and that rates of deforestation are likely to decline in the future (Wright and Muller-Landau, 2006a,b). In retrospect, many of the predictions of tropical deforestation made in the 1970s and 1980s have not come to pass (Myers, 1980). For example, the eminent tropical forest ecologist and biogeographer, T. C. Whitmore (1980) wrote, nearly three decades ago, that “the onslaught [on tropical forests] will continue to accelerate, reducing the forest to scattered fragments by A.D. 2000.” Although he was wrong on his dates, if one takes a longer view, one may worry that Whitmore’s dark vision will prove to be accurate.
The results of the present analysis paint a somewhat more complex and nuanced picture of the future of Amazon forests and its tree species. On the one hand, under all of the scenarios we considered, a large number of very common tree species will almost certainly survive habitat losses, whether one takes an optimistic or nonoptimistic view of deforestation