Tree communities of white-sand and terra-firme forests of the upper Rio Negro

Stropp et al. Acta Amazonica 41: 521-544. DOI: 10.1590/S0044-59672011000400010

The high tree diversity and vast extent of Amazonian forests challenge our understanding of how tree species abundance and composition varies across this region. Information about these parameters, usually obtained from tree inventories plots, is essential for revealing patterns of tree diversity. Numerous tree inventories plots have been established in Amazonia, yet, tree species composition and diversity of white-sand and terra-firme forests of the upper Rio Negro still remain poorly understood. Here, we present data from eight new one-hectare tree inventories plots established in the upper Rio Negro; four of which were located in white-sand forests and four in terra-firme forests. Overall, we registered 4703 trees ≥ 10 cm of diameter at breast height. These trees belong to 49 families, 215 genera, and 603 species. We found that tree communities of terra-firme and white-sand forests in the upper Rio Negro significantly differ from each other in their species composition. Tree communities of white-sand forests show a higher floristic similarity and lower diversity than those of terra-firme forests. We argue that mechanisms driving differences between tree communities of white-sand and terra-firme forests are related to habitat size,
which ultimately influences large-scale and long-term evolutionary processes.

A model of botanical collector’s behaviour in the field: Never the same species twice

ter Steege, H.et al. American Journal of Botany 98: 31-37. DOI: 10.3732/ajb.1000215

Because of their numbers, specimens in natural-history museums cannot be ignored when trying to answer one of the fundamental questions in science: What determines species diversity? The nonrandom nature of collecting does not allow most statistical tests or extrapolations of species estimates, or comparison of richness between areas (which, however, is still done frequently).

We present a simple simulation model, which starts from the assumption that collectors never collect the same species twice during collecting trips. The model allows the generation of the abundance distribution in a herbarium for any natural species abundance distribution, using a simple set of collecting strategies.

We show that, in essence, the strategy of “ never collect the same species twice ” is enough to generate the relative abundance distribution as found in a herbarium. We illustrate this using real plot and specimen data from two well-collected areas, one in central Guyana and one in Suriname.

Because of the oversampling of rare species, it is perhaps not possible to use museum data to reconstruct the community structure in the fi eld or even estimate a proper diversity number other than the number of species in a region.

ATDN plots were also used in:

Toledo, M. Patterns and determinants of floristic variation across lowland forests of Bolivia. Biotropica 43: 405–413.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith