Relatively little information exists on neotropical secondary rain forests that have progressed beyond the pioneer stages of succession, or on the potential of natural regeneration to restore forest on large areas. We determined the structural and floristic characteristics (10 cm dbh) of a 30‐year‐old secondary forest developing on a 32.5 ha pasture on hilly terrain, abandoned after use of moderate intensity. Ten 0.24 ha sample plots covered the range of site conditions. The forest was dominated by long‐lived pioneer tree species; overall, the majority of species (70%) was vertebrate dispersed but the majority of individuals (52%) was of wind‐dispersed species. Tree species, including the dominants, were a mixture of those present in old‐growth and adventives colonizing from agricultural land. The forest was very heterogeneous. Vochysia ferruginea‐dominated stands characterized slopes with soils of high exchangeable acidity, while the adventive Cordia alliodora dominated sites with gentler topography and soils of lower acidity. Structural differences between the two forest types were slight, but Cordia forest had significantly greater species diversity and absolute and relative abundances of vertebrate‐dispersed tree species than Vochysia forest, which had significantly greater absolute and relative abundances of wind‐dispersed tree species. These latter differences between forest types, as well as the wide structural variation of the forest as a whole, were probably largely due to spatial and temporal variation in seed rains, some of it linked to the characteristics of the dominant species. Rain forest restoration on large pastures may depend greatly on wind dispersal and adventive tree species, and techniques for silvicultural diagnosis must be developed as a basis for the management of heterogeneous successional stands. Studies of early colonization of pastures should be expanded to focus on the causes of heterogeneity in older forests.