Towards a dynamic list of Amazonian tree species

Abstract

To provide an empirical foundation for estimates of the Amazonian tree diversity, we recently published a checklist of 11,675 tree species recorded to date in the region (ter Steege H, et al . (2016) The discovery of the Amazonian tree flora with an updated checklist of all known tree taxa. Scientific Reports 6:29549). From this total of plant records compiled from public databases and literature, widely used in studies on the Amazonian plant diversity, only 6,727 tree species belong to the first taxonomically-vetted checklist published for the region (Cardoso D, et al . (2017) Amazon plant diversity revealed by a taxonomically verified species list. PNAS 114:10695-10700). The striking difference in these two numbers spurred us to evaluate both lists, in order to release an improved Amazonian tree list; to discuss species inclusion criteria; and to highlight the ecological importance of verifying the occurrence of “non-Amazonian” trees in the region through the localization and identification of specimens. A number of species in the 2016 checklist that are not trees, non-native, synonyms, or misspellings were removed and corresponded to about 23% of the names. Species not included in the taxonomically-vetted checklist but verified by taxonomists to occur in Amazonia as trees were retained. Further, the inclusion of recently recorded/new species (after 2016), and recent taxonomic changes added up to an updated checklist including 10,071 species recorded for the Amazon region and shows the dynamic nature of establishing an authoritative checklist of Amazonian tree species. Completing and improving this list is a long-term, high-value commitment that will require a collaborative approach involving ecologists, taxonomists, and practitioners.

Biased-corrected richness estimates for the Amazonian tree flora

“…Because the most up-to-date dataset already contains 5,027 tree species and considering that the 1,946 plots constitute a very small sample of the complete Amazonian forest (0.00035%), estimates close to that number are clearly an underestimate. Any trustable estimate should at least be more than the ~10,000 tree species already collected in Amazonian forests 8 . The LS, LSE and ABC estimations showed a wide range of richness, so which species estimate is most believable?…”

“…To delineate the surface area for estimation, we created a base map of Amazonia, the borders of which were the same as those in our earlier estimate 1 . Following 8,22 , we gridded this landscape 32 into 0.1-degree grid cells (01DGC) and eliminated all 01DGCs that were more than 50% open water 32 , non-forest vegetation such as open wetlands or savannahs 33,34 , or>500 m elevation 35 . We quantified the area of all individual 1-degree grid cells (1DGCs), which varies with latitude due to distance from the equator (~124 km 2 at the equator, ~106 km 2 at 14° S, and ~120 km 2 at 8° N).…”

“…Analyses of tree species composition were carried out using the 1,946 plots having species composition. Species synonymy was updated following 4,8 , which resulted in a reduction of almost 10% of the species observed in our sample in comparison to the 2013 version of the ATDN database. Species with a "cf. "…”

“…The 10 most common species were: Eschweilera coriacea, Euterpe precatoria, Oenocarpus bataua, Pseudolmedia laevis, Protium altissimum, Iriartea deltoidea, Mauritia flexuosa, Socratea exorrhiza, Astrocaryum murumuru, and Pentaclethra macroloba (species authorities follow ref. 8 ). Six of these species are palms (see Appendix 1 for the population estimates for all species).…”

“…A number that has both been criticized [2][3][4] and accepted as plausible for plot inventories 5 . In the following years there has been considerable progress both in the taxonomy of Amazonian tree species 4,[6][7][8] and the number of forest inventory plots available 9 , which has steadily grown from 1,170 to 1,946. In addition, our previous richness estimate was based on a single estimation method, the linear extension of a hypothetical logseries 10 of the estimated population sizes of the Amazonian tree species present in our plots 1 .…”