Insights into regional patterns of Amazonian forest structure, diversity, and dominance from three large terra-firme forest dynamics plots
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We analyze forest structure, diversity, and dominance in three large-scale Amazonian forest dynamics plots located in Northwestern (Yasuni and Amacayacu) and central (Manaus) Amazonia, to evaluate their consistency with prevailing wisdom regarding geographic variation and the shape of species abundance distributions, and to assess the robustness of among-site patterns to plot area, minimum tree size, and treatment of morphospecies. We utilized data for 441,088 trees (DBH ≥1 cm) in three 25-ha forest dynamics plots. Manaus had significantly higher biomass and mean wood density than Yasuni and Amacayacu. At the 1-ha scale, species richness averaged 649 for trees ≥1 cm DBH, and was lower in Amacayacu than in Manaus or Yasuni; however, at the 25-ha scale the rankings shifted, with Yasuni < Amacayacu < Manaus. Within each site, Fisher’s alpha initially increased with plot area to 1–10 ha, and then showed divergent patterns at larger areas depending on the site and minimum size. Abundance distributions were better fit by lognormal than by logseries distributions. Results were robust to the treatment of morphospecies. Overall, regional patterns in Amazonian tree species diversity vary with the spatial scale of analysis and the minimum tree size. The minimum area to capture local diversity is 2 ha for trees ≥1 cm DBH, or 10 ha for trees ≥10 cm DBH. The underlying species abundance distribution for Amazonian tree communities is lognormal, consistent with the idea that the rarest species have not yet been sampled. Enhanced sampling intensity is needed to fill the still large voids we have in plant diversity in Amazon forests.
KeywordsAboveground biomass Abundance Forest conservation Fisher’s alpha Rarity Species richness
We gratefully acknowledge the contributions of the many people who assisted in collecting the tree census data. In Colombia, this work was made possible by the Parques Nacionales de Colombia, and in particular to Eliana Martínez and staff members of the Amacayacu Natural National Park. The census of Yasuni plot was financed by Pontifical Catholic University of Ecuador (PUCE, research grants of Donaciones del Impuesto a la Renta from the government of Ecuador). The Yasuni plot census was endorsed by the Ministerio de Ambiente del Ecuador through several research permits. We also thank the Center for Tropical Forest Science-Forest Global Earth Observatory (CTFS-ForestGEO) of the Smithsonian Tropical Research Institute for partial support of plot census work. This manuscript was advanced at a working group meeting funded by a grant from the US National Science Foundation (DEB-1046113). Comments from Hans ter Steege and an anonymous reviewer helped to improve the contents of this manuscript.
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