SPECIES RICHNESS, TROPICAL FOREST DYNAMICS AND SAMPLING - QUESTIONINGCAUSE AND EFFECT

Many hypotheses link tropical forest tree diversity with vegetation dy namics and productivity. Evaluations based on permanent sample plot da ta face problems of interpretation. I suggest, as examples, three poin ts requiring consideration: 1) Species richness in a plot is the outco me of the detailed history of that particular site and the available s pecies (i.e. the species pool). Diversity cannot be explained as a pro duct of current conditions unless these are stable and the system is a t equilibrium; 2) Existing permanent sample plots (PSPs) do not provid e unbiased samples of global tropical forests; and 3) Variation in sta nd parameters may be more appropriate than averaged values when consid ering the maintenance of diversity, e.g. spatial and temporal variatio n in mortality and recruitment may be more crucial than mean values. I n this note I emphasise how every site has a specific explanation for local species occurrences and that theories which do not include histo rical components are incomplete. The above points are illustrated by c onsideration of a paper by Phillips et al. where PSP data have been us ed to argue a causative relationship between forest productivity and s pecies richness.