Floristic relationships of terra firme forests in the Brazilian Amazon

Multivariate analyses of floristic composition at the genus level were perf ormed on a set of 31 tree inventories from 12 sites in the Brazilian Amazon , one site in the Bolivian Amazon, and one in the northeast Brazilian Atlan tic coastal forest. All plots are terra firme forests on clay or loam soil. Rainfall ranges from 1600 to 2600 mm/year. Floristic dissimilarity between plots was associated with three factors: (1) physiognomic type, with a dis tinct separation between evergreen 'dense' and the more seasonal 'open' for ests; (2) geographic distance and (3) past disturbance. Among the dense for est plots those from central Amazonia are floristically intermediate betwee n western and eastern regions, strengthening the hypothesis that central Am azonia is an area of phytogeographical confluence. Based on this work fores t physiognomy and distance have been suggested to policy-makers as unbiased indicators of Aoristic dissimilarity and these proxies are now being used to define priority conservation areas for the Brazilian Amazon. (C) 2001 El sevier Science B.V. All rights reserved.