Many hypotheses link tropical forest tree diversity with vegetation dynamics and productivity. Evaluation based on permanent sample plot data face problems of interpretation. I suggest, as examples, three points requiring consideration: 1) Species richness in a plot is the outcome of the detailed history of that particular site and the available species (i.e. the species pool). Diversity cannot be explained as a product of current conditions unless these are stable and the system is at equilibrium: 2) Existing permanent sample plots (PSPs) do not provide unbiased samples of global tropical forests; and 3) Variation in stand parameters may be more appropriate than averaged values when considering the maintenance of diversity, e.g. spatial and temporal variation in mortality and recruitment may be more crucial than mean values. In this note I emphasise how every site has a specific explanation for local species occurrences and that theories which do not include historical components are incomplete. The above points are illustrated by consideration of a paper by Phillips et al. where PSP data have been used to argue a causative relationship between forest productivity and species richness.