The main objective of these PhD studies was to obtain insight in physical and biotic aspects of the forest in the middle Caquetá area of Colombian Amazonia. The information presented is mainly the result of a land-ecological survey of the area at a 1:100,000-reconnaissance scale, carried out within the framework of the Tropenbos-Colombia programme. Fieldwork was based on the interpretation of aerial photographs, covering about 700,000 ha. Information on soils (mineral profiles and humus forms) and vegetation was collected in more than 160 plots, situated in most land units recognised in the area. Above-ground litter and litterfall were estimated in five forest plots and the (near) total vascular plant species composition was described and sampled in ten 0.1 ha forest plots. The survey provides information on spatial patterns and interrelations between geomorphology, mineral soils, humus forms, plant diversity and composition of the vegetation, to be used as base-line information for evaluation and planning procedures and for more detailed research on the functioning of tropical rain forests in the area.