Discusses four related ecological topics: (1) the occurrence of tropical blackwater rivers (rich in humic acids and poor in nutrients) in areas with poor white-sand soils; (2) the poverty of animal communities that occur in forests in such areas (3) the evolution of gregarious fruiting in the Dipterocarps of SE Asia; and (4) the persistence of certain lowland tropical tree species in forests of very low species-diversity. In the hypotheses put forward considerable attention is given to the role of \secondary\ or \defensive\ compounds (in general phenolics that are toxic difficult to degrade and hence relatively persistent) in the living vegetation and in plant and litter leachates as a factor in the formation of blackwater rivers and in the defence of plants against attack by animals. The gregarious fruiting of Dipterocarps is seen as a mechanism of escape from seed consumers that is unique to the region concerned because it has reduced animal communities.