Information available concerning all but the most common timber species in the Guianas is scattered and difficult to obtain, Very little is known of the ecological requirements of these timber species. Over 170 tree species in Guyana, Suriname and French Guiana were found to have useable timber properties. Three-quarters of these are currently harvested in one of the three countries and less than 20% account for greater than 90% of production. Most timber species are mammal-dispersed (51%), followed by bird and wind dispersal (21 and 20%, respectively). The seeds of less than 8% of the species are transported through unassisted modes, though several of these are important timber trees. The largest seeds are associated with mammal dispersed and unassisted species. Most bird and wind dispersed species have seed sizes below the median for all timber species. The seeds of timber species in Guyana were significantly larger than non-timber species, Dispersal is important in maintaining timber tree population structures and avoiding inbreeding depression. Maintaining adequate dispersal of timber species in the Guianas depends largely on the conservation of mammals. Many species can not be dispersed by smaller animals because their seeds are too large. Wind and bird dispersed species are at a relative advantage since their seeds are smaller and can be effectively dispersed by wind and mammals in the absence of their primary agents. Available data suggest that disproportionate harvesting of mammal-dispersed species relative to their contribution to total estimated standing volumes occurs in Guyana, while bird and wind dispersed species are the most disproportionately harvested in Suriname and French Guiana, respectively. Groups of species with the same dispersal mode should be exploited in relative proportion to their availability to avoid altering resources for animals. Maintaining the widest spectrum of resources available to animals will increase the likelihood that they continue to act as effective dispersal agents of valuable timber trees in the Guianas.