level. The Amazon Basin has ≈50,000 described vascular plant species, in round numbers, of which approximately half are woody. Of these, approximately half are trees, reaching reproductive maturity >10 cm DBH. This yields an estimate of ≈12,500 tree species in the entire Amazon Basin. This is undoubtedly conservative because the number of synonymous species is probably much less than the number of undescribed species. The Brazilian Amazon, which constitutes two-thirds (64.7%) of the entire basin, is expected to have ≈11,210 tree species. This number is what would be expected with an Arrhenius species area relationship with a z value of 0.25. We can estimate the biodiversity number θ or Fisher’s α for all Amazon tree species when we know the number of individual trees in the Amazon. The mean number of trees >10 cm DBH in the 752 plots across the Amazon is 600 ha−1, which translates to 60,000 km−2. The area of the Amazon Basin is 7,179,100 km2, which yields 4.3075·1011 trees >10 cm DBH. The area of the Brazilian Amazon is 4,468,400 km2, which gives 2.6810·1011 trees. From the logseries, we have the relationship S=αln(1 + N/α), which yields α = 743 for the entire Amazon and α = 500 for the Brazilian Amazon. These numbers are quite reasonable in light of the estimate of θ for the 50-ha plot in Yasuni National Park in Amazonian Ecuador (θ = 212).
Now that we have estimated the fundamental biodiversity number θ for the Amazon Basin and for that portion of the basin that lies inside Brazil, we can compute the corresponding logseries relative species-abundance distributions. The logseries rank abundance curve for the Brazilian Amazon is shown in Fig. 6.3. The most abundant species has an estimated total abundance of 3.89 billion individuals >10 cm DBH, but despite its abundance, it comprises only 1.393% of all trees. Large numbers of tree